THE DIGITAL PLATEOSAURUS I: BODY MASS, MASS ...Mallison, Heinrich, 2010. The Digital Plateosaurus I:...

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PE Article Number: 13.2.8ACopyright: Palaeontological AssSubmission: 14 April 2009. Acc

Mallison, Heinrich, 2010. The DDigitally Mounted Complete Skehttp://palaeo-electronica.org/20

THE DIGITAL PLAND POSTURE

Plateosaurdinosaurs. Destons, its postuassessments oincapable of maalternatives havfrom a detailedassessment of obligate biped. the basic modeels allow a starequirements ofer from locomorange in the for

Heinrich Mallison, Glamb

KEY WORDS: Plateosau

INTROD

The prosauropod Meyer, 1837 from the Europe is well known fromnumber of locations, sevefect articulation. Among ethe best-known genera.heated debate about the the animal. Huene (1907for digitigrade bipedality function to the manus. H

eontologia Electronica alaeo-electronica.org

ATEOSAURUS I: BODY MASS, MASS DISTRIBUTION ASSESSED USING CAD AND CAE ON A DIGITALLY MOUNTED COMPLETE SKELETON

Heinrich Mallison

ABSTRACT

us from the late Triassic of Central Europe is one of the best knownpite the large number of finds, including complete and articulated skele-re and locomotion capabilities are still being debated. While recentf the range of motion of the forelimb indicate that Plateosaurus wasnus pronation, and thus an obligate biped, practically all other possiblee been suggested in the literature. Here, I present evidence, derived

mounting of a 3D digital skeleton and a computer-aided engineeringa digital 3D model of the living animal, that Plateosaurus was indeed anThe position of the center of mass is assessed in several variations ofl to account for differing interpretations of soft tissue amounts. All mod-ble bipedal pose with a subhorizontal back that is consistent with thef both slow and rapid locomotion. Quadrupedal models, in contrast, suf-tion restrictions due to highly uneven limb lengths and a limited motionelimb, and result in a smaller feeding envelope.

ecker Weg 6, 13467 Berlin, Germany. [email protected]

rus, locomotion, virtual skeleton

ociation July 2010eptance: 9 April 2010

igital Plateosaurus I: Body Mass, Mass Distribution and Posture Assessed Using CAD and CAE on a leton. Palaeontologia Electronica Vol. 13, Issue 2; 8A: 26p;

10_2/198/index.html

UCTION

Plateosaurus engelhardtiLate Triassic of Central many specimens from aral of them in nearly per-arly dinosaurs, it is one of The finds have causedlocomotory adaptations of-08, 1926, 1928) arguedand attributed a graspinge was convinced that Pla-

teosaurus was an obligate biped, much as the sim-ilar Anchisaurus that had been described asexclusively bipedal and digitigrade by Marsh(1893a, 1893b). A good indicator for this is thehighly divergent length of fore- and hindlimbs.Huene had the mounts of GPIT1 and GPIT2 (Fig-ure 1.1) set up in Tübingen in bipedal postures andadamantly stuck to this interpretation of the mate-rial, despite criticism from many sources.

Other researchers have suggested practicallyany possible stance: obligate quadrupedality andplantigrady ‘like lizards’ was proposed by Jaekel

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RE 1. GPIT1 Plateosaurus engelhardti. 1: Skeletal mount at IFGT. Photograph by the author. 2: Lateral view of

0), who later changed his mind and concludedmsy, kangaroo-like hopping as the only possi-

mode of locomotion (Jaekel 1911, 1913-14).s (1912, 1913) referred to the (dorsoventrallypressed by sediment compaction) position ofskeletal finds in the field, arguing for a sprawl-bligatorily quadrupedal gait. He had the skele-

SMNS 13200 mounted in this position in thetgart museum. Later, researchers began to agree with Huene

the issue of digitigrady, although plantigradye a comeback in Sullivan et al. (2003).shampel and Westphal (1986) depicted Plateo-

saurus running digitigrade and bipedally, but theyargued for facultative quadrupedality. Interestingly,the metacarpals were shown widely spread, inmarked contrast to the interpretation by Huene(1926, but contra the reconstruction drawing in thatpublication), a position that does not seem to fit anactive role of the manus in locomotion. Paul (1997)also argued for bipedality, but his outlined skeletaldrawing seemed to imply permanent quadrupedal-ity, not bipedality. Facultative bipedality was alsoproposed by Van Heerden (1997).

Among others, Galton (1971a, 1976, 1990,2000) advocated facultative bipedality in prosauro-

al mount (virtual skeleton) in bipedal pose. Skull from SMNS13200, various other elements from GPIT2. Lengthft femur is 595 mm.

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s. He based his opinion on the hindlimb to trunk, which was also invoked by Bonaparte (1971).lnhofer (1994) also depicted Plateosaurus in adrupedal stance, based on characteristics oftail of material from Ellingen now in the BSP,h he figured with a strong downward curveing a bipedal stance impossible.In the first functional morphology approach on

eosaurus locomotion, Christian et al. (1996)ied the vertebral column’s resistance to bend-in various vertebrates in order to determiner locomotory modes. Since Plateosaurusws an intermediate pattern between obligateds and obligate quadrupeds, exhibiting aium peak of resistance to bending over the

ulders instead of either the small peak ofds or the large peak of quadrupeds, Christianl. (1996) argued that the animal was probablyltatively bipedal at high speeds only. Christian Preuschoft (1996) investigated the shape ofacetabulum and agreed with Huene 1926 on ar-vertical position of the femur in anterior viewead of a more sprawled configuration.

The latest extensive publication on the osteol- of Plateosaurus, Moser (2003), claimed thateosaurus would only have been capable of tinyffling steps when walking bipedally. Moser alsocribed the remounting of the skeletal mountiously exhibited in the BSP for the Naturhisto-

he Gesellschaft in Nuremberg. The animal wased into what Moser called the track of a qua-edal prosauropod (Moser did not specify which

k exactly; probably he referred to the trackicted in Moser (2003: fig. 28, Tetrasauropusuiferus, from Ellenberger [1972]), despite the that the track exhibits medially curving andted short toes and fingers, while almost allulated finds of Plateosaurus and the morphol-

sauropod track: a bipedal track with two manusimprints on which the fingers point outward at aright angle to the direction of movement. Theimprints fit the shape of the Plateosaurus manusand pes in a semi-plantigrade position. The pes ofPlateosaurus has been claimed also to fit the pesprint of, suggested as another possible quadrupe-dal prosauropod track by Lockley and Meyer(2000). Porchetti and Nicosia (2007) concludedthat a Plateosaurus-like prosauropod is a possiblecreator of Pseudotetrasauropus, again requiring amore or less plantigrade position.

The latest development in the controversyabout the locomotory abilities of Plateosaurus is anassessment of the range of motion of the forelimbof Plateosaurus and the close relative Massospon-dylus by Bonnan and Senter (2007), which indi-cated that manus pronation was impossible.Therefore, Bonnan and Senter (2007) concludedthat Plateosaurus was an obligate biped.

Recent research (Fechner 2006; Remes2006, 2008) suggests that the paradigm of obliga-torily bipedal ancestral dinosaurs may be wrong,and that the first dinosaurs were at most faculta-tively bipedal, holding their hind limbs in stronglyflexed poses during quadrupedal locomotion. Sucha posture allows subequal functional limb and thusstride lengths despite significantly different totallimb lengths, and is similar to the posture of manysmall mammals. If this model of early dinosaurianlocomotion is correct, then the obligate quadrupe-dal posture of sauropods is a primitive character,most small ornithischians with highly different limblengths may have been facultatively quadrupedalas well, and bipedal posture would have evolvedde novo and potentially separately in several dino-saurian lineages, such as theropods, some ‘pro-sauropods’, and some ornithopods.

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of the phalangal articular surfaces indicate noitudinal rotation of the toes or fingers. Also, the of Plateosaurus are long and slender. Moser3) suggested that this discrepancy may indi- an early sauropod instead of a prosauropodhe trackmaker. Galton (1971a, b) already sug-ted medial curving of the fingers in Plateosau- on the basis of GPIT1, and proposed a walkingfiguration of the manus that kept the laterallyrging first digit’s claw off the ground. Baird0) concluded that the track of Navahopus falci-

ex from the Navaho Sandstone of Arizona wase by a quadrupedally walking plateosauridsaur. The ichnofossil Otozoum, originallycribed by Hitchcock (1847) and redescribed byforth (2003), is another candidate for a pro-

The best approach to assess the locomotioncapabilities of an extinct animal is to create anexact 3D digital mount of it, based on a well-pre-served complete individual, and test all potentiallypossible postures for osteological and for kinematicprobability. For the latter, it is necessary to createan accurate 3D model to determine the position ofthe center of mass (COM). Impossible posturescan thus be eliminated. Here, I test the hypothesisthat Plateosaurus was a facultative bipedal, usingfour-legged gaits for slow speed, while runningbipedally. I used two possible basic postures ofPlateosaurus engelhardti in various variations andassessed the position of the center of mass (COM)for a spread of mass distributions for each posture.If only the first posture, a quadrupedal stance,

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lts in a stable and probable posture, it is safessume that Plateosaurus was an obligate

druped. The second posture, bipedal, wouldate an obligate biped if it is the sole feasibleure. If both postures are possible, at similar orrent walking speeds, it is probable that Plateo-us may indeed have been capable of bothmotory modes. E: Different researchers have articulated the

osteologically feasible, others are impossible butwere tested because they, or gaits based on them,were explicitly suggested in the literature. To deter-mine whether a posture is stable, a CAD model ofPlateosaurus was created on the basis of the vir-tual skeleton. For several variations of this model,accounting for different distributions of soft tissueson the skeleton, the position of the center of mass(COM) was determined in a CAE program.

EO 1. Virtual skeleton of GPIT1 Plateosaurus engelhardti in bipedal posture (see website for full video).

es of Plateosaurus differently, both in museumnts and in reconstruction drawings. Thosenstructions that have a bearing on the investi-ns described here will be discussed below

the details of the articulation of the digital skel- of Plateosaurus.

MATERIAL AND METHODS

The basic postures were tested for feasibilityreating a digital mount (a virtual skeleton) ofT 1 (Figure 1.2, Video 1), a complete skeleton Trossingen (GER), and posing it accordingly.eral versions were created that take differentpretations of shoulder girdle articulation, limb

ion ranges, and foot position into account (seeison in press). Some of these variations are

Institutional abbreviations

AMNH American Museum of Natural History, NewYork, USA

BSP Bayrische Staatssammlung für Paläontolo-gie und Geologie, München, Germany (for-merly Bayrische Staatssammlung fürPaläontologie und historische Geologie)

GPIT see IFGTIFGT Institute for Geosciences, Eberhard-Karls-

Universität Tübingen, Tübingen, Germany(also IFG or UT in the literature)Formerly Geologisch-PaläontologischesInstitut Tübingen (abbreviated GPIT)

MB.R. see MFN

MFN

MNMSF

perf3.11skeusinNURerospolysionInc.MSCby S

LudhardSomwasmmwerslicepolyThisfacewasneigIntethe inaldle sav

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Museum für Naturkunde – Leibniz-Institutfür Evolutions- und Biodiversitätsforschungan der Humboldt-Universität zu BerlinFormerly Museum für Naturkunde derHumboldt-Universität zu BerlinAlso abbreviated MNHB. Collection num-bers are MB.R.####.

HB see MFNSauriermuseum Frick, Frick, Switzerland

Computer programs

Extraction of the bone surface shapes wasormed in a time-limited trial version of AMIRA® by AMIRA Corp. CAD tasks (mounting the

leton, CAD model creation) were conductedg McNeel Associates Inc. ‘Rhinoceros® 3.0BS modeling for Windows®’ and ‘Rhinoc-® 4.0 NURBS modeling for Windows®’. Forgon mesh editing I used a time-limited trial ver- of ‘Geomagic Qualify 8.0®’ from Geomagic CAE models were created and assessed in

.visualNastran 4D® by MSC Corp. and NX5®iemens PLM Software.

3D FILE EXTRACTION

The bones of GPIT1 were CT-scanned by B.escher at the University Hospital of the Eber--Karls-University Tübingen on a SiemensTM

atom Sensation© scanner. Slice thickness 0.5 mm, with a 0.5 mm increment and a 0.25 overlap. The surface shapes of the bonese extracted from the resulting DICOM-format graphics using AMIRA® 3.11 and saved asgon meshes in stereolithography format (*.stl). created artifacts (massive wrinkling of the sur-s), and a reduced set of every second slice

[ONP], see Stevens and Parrish 1999) three sepa-rate times, with several weeks pause between thedigital mountings, in order to avoid one mountinginfluencing decisions in the next mounting. In eachcase, the vertebrae were articulated with eachother in pairs, so that only the last added vertebraand the one currently being placed were visible, toavoid errors in placement caused by apparent cur-vatures of the entire column. Two instances werecreated by proceeding along the vertebral columnvertebra by vertebra, once from the front and oncefrom the tail tip. The third mount was created inpieces, with the cervicals, dorsals, and caudalsarticulated separately and then combined in a finalstep. This redundancy in mounting was intended toremove bias caused by preconceived notions asfar as possible. Neutral pose was determined byplacing the anterior and posterior surfaces of thecentra as parallel as possible while guaranteeingmaximal overlap of the zygapophyses. Becausenearly all dorsals in GPIT1 are distorted, with thetransverse processes and zygapophyses rotateddorsally on the right and ventrally on the left side,and some show signs of slight antero-posteriorcompaction, neutral pose had to be approximatedas a best guess in some of the articulations. How-ever, comparison with other Plateosaurus material(SMNS 13200, GPIT2, SMNS F33) indicates thatthe induced errors are probably smaller than differ-ences caused by intraspecific variation. All threedigital mounts show highly similar curvatures andtotal lengths of the assembled spine, so only onewas used in all further analyses. All differenceswere significantly smaller than even extremely con-servative assessments of the range of motion inthe intervertebral joints, and did not influence theoverall trends in the spine. The limbs were alsomounted repeatedly.

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instead used. This removed overlap betweenhboring slices and eliminated the artifacts.rnal surfaces and artifacts were removed, andfiles were reduced in size to about 25% of orig- size using Geomagic Qualify 8.0®. Large (gir-and limb) bones were further reduced in size, toe computing time.

Mounting the virtual skeleton

The bones were mounted in Rhinoceros® 3.0 4.0. The limbs were articulated separately the vertebral column and girdle elements, andpartial assemblages later combined to createtwo basic postures (bipedal and quadrupedal) their variations.The vertebral column was placed into near-

tral articulation (ostgeologically neutral pose

The bipedal and quadrupedal postures werecreated based solely on the osteology and posessuggested in the literature, even if the latterdemanded impossible joint articulations. Theexpected position of the COM was not taken intoaccount to avoid bias. The bipedal and quadrupe-dal poses resembled published reconstructions(Galton 1990, 2000; Paul 1987, 1997; Wellnhofer1994; Weishampel and Westphal 1986), withoutregard for joint limits, center of mass, or other con-siderations.

3D model creation

Rhinoceros® 3.0 and 4.0 were used to createNURBS bodies for a 3D model for the living animal(Figure 2). Initially it consisted of ellipsoid bodies

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were deformed to approximate the 3D shapeed by the extents of the skeleton. Then, the

bodies were further enlarged to incorporate for soft tissues. This method differs from the

ses-based method of Henderson (1999), allow-on-elliptical cross sections. The amount of softe is conservative, except for the hips and

er hindlimbs. Here, relatively ample amounts ofcles were assumed, because dinosaurs pro- most of the posteriorly directed force required

apid locomotion not by limb extension, but by retraction (see Gatesy 1990), in contrast tomals. Therefore, the iliofemoral, ischiofemo-

and especially caudofemoral musculature must been relatively stronger than in mammals.

recent discovery of a hadrosaur mummy inh Dakota (US) confirms that at least hadro-

neck, body, and tail were sectioned vertically intoslices. Each part was thus turned into a separateentity, so that it could be given an individual densityvalue. Theoretically, it would have been possible tosubtract the bones from these volumes and givethe remaining 3D bodies the average density ofsoft tissues. However, the gain in accuracy wouldhave been minimal, especially given the uncer-tainty considering the amount of soft tissues, andthe calculation demands for the computer pro-grams would have increased massively.

CAE assessment of mass distribution

The center of mass (COM) was determined ina computer-aided engineering (CAE) softwareusing NASTRAN. NASTRAN is a finite elementanalysis solver originally developed by NASA and

URE 2. Four views of the CAD model of Plateosaurus engelhardti and the virtual skeleton of GPIT 1 on which theel was based. Model is displayed in translucent mode to make segmentation and skeleton visible. Note that somees stick out of the CAD model, mainly because the bones are deformed and were therefore ignored during modeltion.

s possessed much more musculature in theer hindlimbs and tail than most previous recon-ctions assumed (National Geographic Society7, Dec. 12). Since the musculoskeletal systeme all non-avian dinosaurs is relatively uniform, Ithat a robust soft tissue reconstruction of thelimb and basal tail of Plateosaurus is reason-. Additional evidence comes from extant croco-ns. Persons (2009) found that all of the manynt taxa used for his study had a far largerunt of tail musculature than is usually assumede present in dinosaurs. Specifically, the muscles sections protrude far beyond the tips of themal arches and transverse processes (Persons9).The model’s limbs were sectioned into func-l units (manus, antebrachium, etc.), while the

today available in several versions able to handlekinetic/dynamic modeling of rigid body systems.Problems are time-discretized in NASTRAN, whichsolves them using the simple Euler integration, orthe more complex and thus computer calculationtime intensive Kutta-Merson integration. The latterallows a variable number of repeated integrationsper (pre-defined) time step, and attempts to esti-mate the integration error. Thus, it delivers signifi-cantly more accurate results for highly unequalmass or speed combinations in the model (see Fox1962 for details on the integration methods). Forquasi-static analysis as presented here (i.e., stand-ing models of Plateosaurus used to determine theposition of the COM), Euler integration is sufficient.Tests using both methods on the same file failed to

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RESULTS

Virtual skeletal mount of Plateosaurus

tebral column. Plateosaurus has 10 cervicalss a rudimentary proatlas), 15 dorsal and threeral vertebrae. The tail is composed of 45 verte- in GPIT1. Figure 3.1 shows a lateral view ofcervical, dorsal, and caudal series of GPIT1 inologically neutral position.The cervical column articulates in a nearly

ight line, parallel to the long axis of the cervical

slight downward angle, and the ‘stepping up’ of thecervical is required to bring the head to aboveshoulder level in ONP. This position is similar tothat of SMNS 13200 as figured in Huene (1926).The slightly different curvature of SMNS 13200 canbe explained by the damaged dorsal 6 and theslight disarticulation between dorsals 4 and 5(Huene 1926: plate II).

In the anterior tail, the neutral pose placing thecentra faces parallel (ONP) cannot be created.Nearly all vertebra show slight keystoning. Asnoted by Moser (2003), this keystoning is intrinsicto the osteology, but its degree varies. In GPIT1 thevariance is lower than in the material from Ellingen

URE 3. GPIT1 Plateosaurus engelhardti 1: vertebral column with skull of SMNS13200 in neutral articulation, lat- view. Color code: cervicals in light blue, dorsals in red, sacrum in dark green, tail in dark blue. Total length of ver-al column is 5.17 m. 2: ribcage in anterior and 3: dorsal view. Total length 1.35 m. Note deformation of ribs andebrae that result in seemingly incorrect articulations.

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tra. However, this line is not perpendicular toanterior and posterior faces of the vertebrae,ascends anteriorly. Therefore, ONP displaceshead dorsally, resulting in a skull position at orve shoulder height, depending on the angle ofanterior face of the first dorsal relative to therior.The anterior dorsals arch dorsally (dorsals 1

ugh 4), while the middle part curves markedlytrally (dorsals 5 through 10). Further posteriorlydorsal column is nearly straight. In all, thenward curve results in a ventral rotation of the axis of dorsal 5 by 22°, while the anteriorard curve angles the base of the neck up bycompared to dorsal 5, and 15° down comparedorsal 15. Therefore, if the sacrum is placed withong axis horizontal, the neck is attached at a

(Germany) described in detail by Moser (2003),which may be caused by a lower degree of tapho-nomic deformation. If the centra are placed at anangle to bring their anterior and posterior faces intoa parallel position, the haemal arches can not befitted to their articulation surfaces on the vertebrae.Neutral pose is supposed to provide the maximumcontact of articular surfaces. Omitting the haemalarches, or moving them out of close articulation,would violate that principle. To accommodate thezygapophyses in articulation dorsally and the hae-mal arches in close articulation ventrally, the inter-vertebral disks were reconstructed as havingslightly greater thickness ventrally than dorsally,i.e., slightly wedge-shaped. Adjustment for thehaemal arches results in a straight tail, with varyingintervertebral disc thickness and shape.

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age. The articulations between ribs and dorsalebrae show that the anterior body was narrow side to side (Figure 3.2). As in all dinosaurs,ribs of Plateosaurus have two heads (Huene6), the dorsal capitulum that articulates with theophysis on the transverse process of the verte- and the ventral tuberculum, which contacts thepophysis. The ribs move by rotating aroundaxis connecting the two articulations (Mallisonress). Whether the rib motion enlarges the rib- volume, e.g., for breathing in as in humans,hether the rib motion has no influence on the

y volume depends on the orientation of the. In Plateosaurus, the first five dorsal ribs movero-posteriorly, while all later body ribs swingards, increasing the volume of the body cavity

llison in press). For the analysis presented, an intermediate position of the ribs was cho- In- or exhalation does not significantly changeposition of the COM, because there is practi- no antero-posterior motion of large tissue vol-s.

toral girdle and forelimb. The pectoral girdle the functionally associated axial elements arempletely preserved in GPIT1. Only the co-ossi-scapula and coracoid are preserved on each, while the left clavicle and sternals are miss-The right clavicle is partially preserved and

ched to the coracoid by sediment. It is a thin as described by Huene (1926). The scapulac-oids follow the usual prosauropod pattern in general morphology, but show a number ofliarities (Remes 2008), some of which have a

ound impact on the interpretation of possiblemotion poses. Most importantly, the glenoid is

ple trough, restricted to the caudal margin ofscapulocoracoid. It does not extend to the lat-

tion, would tend to rotate the scapula anterodor-sally. A placement of the scapula steeper than 65°is unreasonable, as it would lead to a nearly hori-zontal orientation of the coracoids, and direct theglenoid exclusively posteriorly.

Angles of the scapula between 45° and 65°appear reasonable, as they do not push the cora-coids too far forward, but also place the tip of thescapular blade at the level of the fourth dorsal (Fig-ure 4.1). Such a position, with tightly spaced cora-coids, is biomechanically advantageous, as thegirdle then can form a strong brace, both for pro-jecting large forces through the arms, and as asupport structure when the animal is lying on theground. Remes (2008) also suggested thisarrangement based on an analysis of the myologyin basal sauropodomorphs. In Massospondylus, aclose relative of Plateosaurus, Yates and Vascon-celos (2005) found articulated clavicles that werearranged in a furcula-like manner, touching at themidline. This further confirms the narrow arrange-ment of the shoulder girdle. For Plateosaurus, thiscondition of touching but not co-ossified coracoidsand clavicles was already explicitly mentioned byHuene (1926) in several skeletons. The scapulaecannot be separated laterally and shifted dorsopo-steriorlys on the side of the ribcage as suggestedby the mounts in the SMNS. It is important to notethat dorsolaterally shifting the scapulocoracoidsforces a quadrupedal Plateosaurus into a sprawledforelimb posture, with an extremely reduced func-tional forelimb length.

The width of the shoulder girdle has been dif-ferently reconstructed with the ‘old’ museummounts in the SMNS separating the coracoids bymore than the length of a coracoid and placing thescapula blade almost parallel to the dorsal series.However, these mounts show a grossly exagger-

surface of scapula or coracoid, and only theromedial rotation of the entire scapulacora-s leads to a caudoventrolateral orientation ofglenoid. If the scapula is placed at an angle shallower 45° in reference to the sacrum–1st dorsal line,r the pectoral girdle projects forward beyond

second to last cervical, a position contrary to allulated finds, or the scapular blade overlapsnd the fifth dorsal. Due to the lateral expan-

of the ribcage during breathing, this would to lateral displacement of the dorsal end of theula, and thus require a hinge-joint motioneen the coracoids. The forelimbs would there-

move laterally with each breath. Additionally,force pressing dorsally on the glenoid, e.g.,pressive forces in the forelimb during locomo-

ated width of the ribcage. GPIT1 and GPIT2 weremounted with a narrower arrangement by Huene,as was AMNH 6810, another excellently preservedskeleton from Trossingen. As shown by Mallison(2007, in press), the ribcage is high-oval in theshoulder area, and only widens further posteriorly.Also, the anterior ribs sweep caudally slightly,allowing for a narrow girdle architecture, withsteeply inclined scapula blades and mediallyalmost contacting coracoids. Motion is restricted toantero-posterior sweeps (Mallison in press) only inthe first five dorsal ribs, while further posteriorlythere is a significant lateral expansion. Huene(1926) already mentioned that in SMNS 13200these five ribs are significantly thicker and sturdierthan those of more posterior dorsals (see Figure

4.1)flattthe indiribsfirstthroal. (prescag

dorsrotaseeJen200of th~80axisthe zonvertbe leadforcwouheaanycanresumed

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. They also have a flattened cross-section. Thisening is not caused by the ribs’ attachment tosternum, as the rough thickened distal ends

cating attachment are found on the first eight. The most plausible explanation is that only the five ribs had to absorb large forces transmittedugh the pectoral girdle. Recently, Fujiwara et2009) indeed found that more robust ribs areent where the M. serratus attaches to the rib-

e in quadrupeds.The proximal end of the humerus is broad ando-ventrally compressed. This indicates that ation of the humerus head in the glenoid, as isn in animals with sprawling gaits (Goslow and

humerus displaces the elbow laterally. A purelyparasagittal motion of the humerus seems not pos-sible. The cranioventral torsion of the distal end ofthe humerus relative to the proximal end is usually45° in prosauropods (Remes 2008), but only 30° inPlateosaurus.

Radius and ulna can only be articulated withthe distal end of the humerus if they are placed intoclose proximity with each other (Mallison in press,fig. 5). The imperfect preservation of the distalhumeral condyles allows separating radius andulna by a few millimeters or up to about 2 cm. Atight arrangement seems more realistic, especiallysince the lateral side of the triangular distal end of

URE 4. Pectoral girdle and forelimb of the virtual skeleton of GPIT1 Plateosaurus engelhardti. 1: lateral view of pectoral girdle. Thick, flattened ribs indicated by arrows. 2: oblique view of the left scapula with two instances of left humerus showing maximum rostrocaudal motion range in the glenoid.

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kins 1983; Landsmeer 1983, 1984; Meers3), was not possible. Due to the simple shapee glenoid, protraction-extension is limited to an° angle, from 55° to 135° in relation to the long of the scapular blade (Figure 4.2). Therefore, ifscapula is placed at a 35° angle from the hori-tal, the humerus can not be protracted beyondical. The possible amount of abduction can notascertained, but any angle greater than 30°s to an instable position, in which only limitedes can be placed on the joint. Large forcesld lead to a medial shifting of the humerald, as the glenoid does not contain it laterally in way. These findings, more details on which be found in Mallison (in press), confirm thelts of Bonnan and Senter (2007). Due to theial rotation of the glenoid axis, retraction of the

the ulna forms an articular surface conforming tothe shape of the proximal radius. Distally, bothbones do not form contact surfaces, and arespaced slightly apart in all articulated finds (Figure5). In GPIT2, the left radius and ulna each show asmall deformation where they were pressed intoeach other during fossilization. This relatively tightplacement allows only minimal motion betweenradius and ulna, making full pronation by rotation ofthe radius impossible. Several other factors alsoindicate that Plateosaurus was not capable of sig-nificantly pronating the hand this way: the proximalend of the radius is oval in circumference, with aratio between the longest and shortest axes of1.8:1 (Mallison in press, fig. 5). Rotating the radiushead requires a circular circumference as seen inhumans and cats. Only a sliding motion, which is

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not reminvean founpronskelgentrapstucpedout singpronthe und23 flexedireHueGPIshowthe (righ

FIGU1. Sante


seen in any extant animal capable of pronation,ains possible. Bonnan and Senter (2007)stigated the ability to pronate the manus usingextant phylogenetic bracket approach andd none of the extant outgroup taxa capable ofation. Additional evidence comes from theetons that were found in articulation in Trossin-

wedged between the coracoids, etc.) indicates thatthe skeleton was significantly displaced in a semi-macerated state, so that the position of the manusas found is not indicative of the potential motionrange in vivo.

The carpus is not well preserved in GPIT1 andGPIT2, but MNHB Skelett XXV from Halberstadt

RE 5. Articulated forelimbs of Plateosaurus from Trossingen and Frick, drawn from photographs by the authorMNS F33 left antebrachium and manus 2. SMNS F33 right antebrachium and manus. 3. MSF unknown numberbrachium and manus. 4. MSF 23 left antebrachium and manus.

(GER) and Frick (CH). The animals wereped in mud (Sander 1992), their hindlimbsk while the forelimbs were still free. A quadru- should in such a situation attempt to push itselfof the mud with its forelimbs. However, not ale one of the skeletons shows a forelimb with aated manus close to the body midline. Rather,arms are widely spread (SMNS F33), placeder the belly with the palm facing dorsally (MSFright arm), or widely abducted with stronglyd elbow, wrist, and fingers and medially

cted palm in full supination (MSF 23 left arm).ne (1928: plate X) figured a quarry map ofT1, the only find in which one arm potentially

s manus pronation (left forelimb). However,overlap pattern of the girdle and limb bonest scapula overlaps right humerus, left humerus

has five carpals. The proximal row consists of twolarge elements that are shallow triangular in plantarview. The radiale has contact with the radius, meta-carpal I, and the ulnare, as well as a small articula-tion with a distal carpal. The ulnare is situatedbetween the ulna and the distal carpals. It isunclear whether it had any contact to the radius.The distal carpal row is formed by a flat, box-shaped bone closely corresponding to the form ofand in close contact with the proximal end of meta-carpal II, and two small rounded elements situatedbetween the ulna and metacarpals III and IV.These do not block metacarpal V from contact withthe ulna. The range of motion in the carpus is diffi-cult to determine. Bonnan and Senter (2007) con-cluded that rotational or twisting motions are madeimpossible by the block-like structure of the carpus.

Extea si

theisplasurfMetandang

uneing (198quarotazonof tclosto oicanmetmetthe sizebeinof thout simphawith

FIGflex


nsion and strong flexion, however, possibly tomilar degree as in humans, appear possible.

Metacarpals I through III articulate tightly withr proximal ends. Distally, they show minimalying. Metacarpal IV also has an articulationace for metacarpal III, but angles laterally 20°.acarpal V has two distinct articulation surfaces, contacts both metacarpal IV and the ulna. Itles laterally about 50° from metacarpal III. The manus digits of Plateosaurus are highly

qual, with digit I developed as a strong grasp-claw, and digit IV and V much reduced. Paul7, 1997, 2000) depicted Plateosaurus in a

unremarkable, with strong claws. However, it isimportant to note that hyperextension is less pro-nounced than in the toes, even though there aredistinct but shallow hyperextension pits. In contrastto the first three, digits IV and V do not show well-developed trochleae, resulting in greater freedomof motion but a reduced ability to withstand forces.The entire hand (Figure 6, Video 2) appears to beadapted to strong grasping, with some ability tooppose digits IV and V. Pelvic girdle and hindlimb. The hindlimb of Plate-osaurus (Figure 7) shows a number of adaptationsto cursoriality compared to basal archosaur taxa.

URE 6. Left manus of the digital mount of GPIT2 Plateosaurus engelhardti, palmar view. 1: straight digits, 2:ed digits. Length of metacarpal is 3 is 97 mm.

11

drupedal pose, with the first digit mediallyted by almost 90°, so that the claw is in a hori-tal position at mid-stance. Digital manipulationhe scans of GPIT1 shows that this angle ise to 27° during hyperextension and decreasesnly 13° at maximum flexion, because the signif-t size difference in the articular condyles ofacarpal I are partially countered by an asym-rically shaped proximal articulation surface onfirst phalanx of digit I. The significance of the difference lies with the larger medial condyleg subjected to higher forces, not with a cantinge main axis of the digit. Additionally, as pointedby Galton (1976), in Anchisaurus, which has ailarly shaped hand, during flexion the unguallanx rotates laterally, and thus nearly lines up the second and third digits. The latter are

The femur is long, and its head is medially offset,indicating a parasagittal limb posture, as alreadyconcluded by Huene (1926, 1928). The distal fem-oral condyles in Plateosaurus face slightly cau-dally, which indicates that the knee could not befully straightened. Combined with the longitudinalcurvature of the femur shaft and its sub-circularcross-section this means that Plateosaurus had apermanently flexed limb posture, and that thefemur was not held vertically during standing or atmid-stance.

In anterior view, the probable rotation axis ofthe knee joint is canted against the shaft of thefemur by approximately 70° (Figure 7.1). The axisof the proximal end is hard to determine, butappears to be roughly parallel to that of the knee. If

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the axisinclikneeIn Fmorthe undbipeped

saurin caatingM. ccasethat

VIDengweb


tion. A limit on protraction is imposed by the pubesat low abduction angles. Retraction is not hinderedby the ischia, so a maximum angle must be esti-mated based on the path of the M. caudofemoralislongus and its maximum contraction. This at best iseducated guesswork, but it seems reasonable,given the position of the tail in relation to the pelvis,to assume that during locomotion retraction waslimited to a position in which the femur shaft is par-allel to the ischia, as at this point all ischiofemoralmusculature has no retraction function left at all. Ifthis is correct, then the angle that the femur cancover without significant abduction is 65°. Figure7.2 depicts the hindlimbs and pelvic girdle in lateralview, with a suggested stride length of 1 m for anormal walk. This correlates roughly to a walkingspeed of 3.7 km/h, using an average of Alexan-der’s (1976) and Thulborn’s (1990) formulas. Forthis stride length, the femora need only cover a 50°angle. For angles larger than 65°, abduction isrequired so that the femur passes the pubis later-ally, or retraction to beyond the level of the ischia.Compared to the neutral position chosen here (dis-tal end of femur directly ventral from acetabulum inanterior view), the former requires 20° abduction. Itappears therefore doubtful whether significantlylarger protractions than to the level of the pubiswere possible. Not only is all pubofemoral muscu-lature ineffective for protraction when the femur isclose to the pubis and has a purely adductingeffect. Also, there is no greatly enlarged proacetab-ular process on the ilium of Plateosaurus. There-fore, the iliofemoral muscles that still have aprotracting component are weak. Passive protrac-tion, e.g. by transfer of rotational inertia from theshank to the thigh, is possible, but only effective atvery high limb swing speeds (running gaits). Onemust assume that femur motion during normal

EO 2. Virtual skeleton of GPIT1 Plateosauruselhardti: left manus in full flexion. For full video, seesite.

femur is placed in the acetabulum so that the of the knee joint is horizontal, the shaft isned medially and the approximate center of the is placed directly ventrally from the hip joint.

igure 7.1, the femur is shown adducted slightlye, so that the first pedal digit is placed underbody midline. Such a position under or nearlyer the COM is necessary for walking gaits inds, and today seen in practically all quadru-s.Gatesy (1990) showed that non-avian dino-s use femur retraction as the major componentudally directed foot displacement, thus gener- most of the required force in the

audofemoralis. As this was certainly also the in Plateosaurus, it is reasonable to assume

the femur covered a large arch during locomo-

locomotion was limited to the mentioned 65° atmedium speeds, while slower speeds probablyused less retraction. The center of mass waslocated in front of the acetabulum, and mid-stanceposition as reconstructed here was at slight pro-traction (20° from vertical, Figure 7.2).

The tibia shaft is straight, and the tibiaexpands slightly proximally, but there is no distinctcnemial crest projecting anteriorly in lateral view.Knee extension therefore did not form a major partof locomotory limb motions, excluding the possibil-ity of a hopping gait as suggested by Jaekel (1913-14), and probably also a bounding gallop as sug-gested by Paul (2000). In the tibia and fibula thereis no canting between the long axis of the shaft andthe apparent joint axes. Distally, the tibia articulates

tighpalsservthrethostaphandnounouarouily thmalcalca hithe covposing simtakeof thso tcal toe (butfron

FIGblacrang


tly with the massive astragalus. Four more car-, a calcaneum and three distal tarsals, are pre-ed in GPIT1. On the left foot of MB.R.4404,e distal tarsals with very similar shapes toe of GPIT1 are preserved, so the likeliness ofonomic deformation is low. The ankle is wide flattened, with no bony structure forming a pro-nced heel, and no indication of a large cartilagi-s projection. Therefore, extension momentsnd the ankle were either low or created primar-

The metatarsals articulate tightly (Figure 8.1),with clearly demarcated, large articulation facetson their lateral sides. These, however, do not rundown the shafts to a great extent, since the proxi-mal articular ends are much wider than the shafts.Some previous reconstructions (e.g., the ‘old’SMNS mounts) have therefore been created withsplayed metatarsals. However, such a placementis not supported by the skeletons found in Trossin-gen, Halberstadt, and Frick, where all feet found in

URE 7. Left hindlimb of the virtual mount of GPIT1 Plateosaurus engelhardti. 1: anterior, 2: lateral view. In 1,k lines mark probable joint axes. 3: as 2, with additional instances of the right hindlimb showing possible extremee for a normal walking cycle. Length of left femur is 595 mm.

13

rough high muscular forces. In contrast, mam-s use a large lever arm in their ankles, the tuberanei (Romer 1949). The ankle of GPIT1 formsnge joint, the axis of which is almost parallel toknee (Figure 7.1). The range of motion is large,ering at least 170°. This would allow any limbe from straight to completely folded, as in rest-birds. Astragali of other individuals show a veryilar morphology, if taphonomic deformation isn into account. As a result of the arrangemente joint axes, placing the femur canted inwards

hat the knee axis is horizontal results in a verti-position of the lower limb, and places the thirdventrally below acetabulum in anterior view not in lateral view, because the COM lies int of the acetabulum).

articulation show the metatarsals closely touchingproximally and almost touching distally (Figure 8.2-4). There is no splaying in these finds, which wouldalso be biomechanically unsound. Splayed meta-tarsals result in a larger, thus heavier foot, whichdecreases the swing frequency of the limb. Addi-tionally, splaying causes lateral bending momentsin the lateral and medial metatarsals. These couldresult in adaptation of the shape of the metatarsalsand toes, e.g., unequal condyles on the interpha-langeal joints and asymmetrical metatarsal shaftcross sections, as well as laterally curved metatar-sal shafts, which are not present in Plateosaurus. Abroader foot would offer more lateral stability, but inextant cursors feet are reduced in size, becausethe above mentioned factors outweigh the advan-

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tagelarlyandtivelrelathe smaate

FIG3 issca


of slightly greater stability. Only animals regu- walking on instable substrates such as snow sand (e.g., arctic foxes and camels, respec-y) show slightly larger support areas than theirtively moving on stable ground. Even in themsize increase in the foot is proportionally muchller than splaying of the metatarsals would cre-in Plateosaurus.

All toes of GPIT1 are almost straight, in con-trast to Skelett XXV (MB.R.4404) from Halberstadt,in which the fourth toe curves laterally. Similarly, inGPIT1 toes 1 through 3 are canted slightly mediallycompared to the long axis of the metatarsus,though beveled distal condyles of the metatarsals.The fourth metatarsal, however, is canted laterally.In contrast, in Skelett XXV, toes 1 through 3 are

URE 8. Pes of Plateosaurus engelhardti in dorsal view. 1: left pes of virtual mount of GPIT1. Length of metatarsal 234 mm. 2: left pes of SMNS F50 3: left metatarsus of SMNS F65 4: right pes MSF unnumbered. 2 – 4 not tole.

cantoe susby iindi

largindistangreapareforedorstarsin thben

posimp

Biptureaccderitionangandalso

FIGanteleng


ted strongly medially, and the base of the fourthis perpendicular to the long axis of the metatar-. It is unclear whether this difference is causedntraspecific variation, or indicates that the twoviduals belong to separate species.

The hindlimb digits of GPIT1 allow somewhater hyperextension angles than in the forelimb,cative of a highly digitigrade to unguligradece just before toe lift-off. This adds to theter effective limb length in the hindlimb com-d to the lower hyperextension angles in thelimb. Further indicators for digitigrady are the

tical or, more probably, sub-vertical position at mid-stance (Figures 1.2, 9.1, 9.2, Video 1).

Any bipedal posture is only feasible if theCOM is supported by the hindfeet. If the COM restsclose to the hips, the exact orientation of the verte-bral column does not matter. If it is placed furtherforward, so that the hindlimb does not support itwhen the back is in a subhorizontal position, thesimplest way to change the anteroposterior posi-tion of the COM is to tilt the vertebral column. Thesteeper it is placed, the further back the COMmoves. Huene 1928 suggested a fairly steep posi-

URE 9. Virtual skeleton of GPIT1 in bipedal posture in 1: subhorizontal back, lateral view, 2: subhorizontal back,rior view. 3: back angled 30° in comparison to reconstruction drawing redrawn from Huene 1928. Left femurth is 595 mm.

15

oventrally flattened cross-sections of the meta-al shafts and the lack of proximal-distal archinge metatarsus, both indicating low craniocaudalding moments.

Poses of the entire skeleton

In the following, both bipedal and quadrupedales are described, and their biomechanicallications are addressed.

edal poses. For a bipedal, theropod-like pos-, the hindlimb of Plateosaurus can be placed inordance with the evidence on bone loadingved from longbone curvature and cross sec-s. The femur is inclined forward at a protractionle around 20°. The knee is flexed, and the tibia fibula inclined slightly posteriorly. The ankle is slightly flexed, placing the metatarsus in a ver-

tion for rapid locomotion (Figure 9.3), similar to thethen prevailing view of Iguanodon (Dollo 1893) andother bipedal dinosaurs. Later, a paradigm shiftlead to almost universal agreement that most dino-saurs had subhorizontal backs when walkingbipedally (e.g., Norman 1980; Bakker 1986; Paul1987). The main reason for the latter posture is thefar greater femur retraction range that it allowscompared to a more upright posture. Plateosauruscan be placed bipedally in either position (Figures1.2, 9.1-3), but the more upright posture limits loco-motion speed significantly. An upwards angle of atleast 45° is required for the long axis of the sacrumto create a significant backwards shift of the COM.However, already at 30° (Figure 9.3), the femurmust be retracted to the level of the ischia, so thatonly very small steps are possible. Also, if the

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COMupwarouthe reasmigh(Figure

the heaTheneckordedrinmodthe flexicontmotgestinhibthe of torqthe ulatior uing scripthatprosmeddowQuaforecantpossgrounot forewardby 1semplanprotheasacrmanventfor ftive glenstan


lies so far posteriorly that this pose (30°ards rotation) is balanced, rotating the bodynd the hips requires very little energy, due tosmall moment arm. Therefore, it seems moreonable to assume that a bipedal Plateosaurust feed with a steeply inclined vertebral column

ure 9.3), but use a subhorizontal posture (Fig-1.2) for locomotion. In a bipedal pose with a subhorizontal back,

neutral pose of the vertebral column leads to ad position above the highest point of the back. animal can thus cover a 360° arc by a small motion alone, i.e., there is no blind area. Inr to bring the snout to the ground, e.g. for

king, a slight increase in hindlimb flexion anderate ventriflexion of the anterior two thirds ofthoracic vertebral column and maximum ventri-on of the neck is sufficient (Mallison in press,ra Huene 1928), but even a slight seesawion that rotates the anterior body down (as sug-ed to be necessary by Huene [1928]) does notit rapid flight. In contrast, to bring the hands to

ground for grasping requires significant flexionthe hindlimbs, with greatly increases jointues required to sustain the pose. Essentially,animal must kneel or squat down when manip-ng objects at ground level for a prolonged time,se a front limb for support. Dual-handed grasp-is then impossible. Rainforth’s (2003) rede-tion of the ichnofossil Otozoum pointed out

one track shows a bipedal animal, potentially aauropod, using both hands, palms facingially, to support itself, probably while squattingn.drupedal poses. In a quadrupedal pose thelimbs must be able to take strides of a signifi- length. If a stride length of only 0.4 m is to be

the semi-plantigrade, and 0.59 for the plantigrademodel. In all these positions the motion of thehindlimb is significantly limited compared to abipedal posture. In the digitigrade model, the femurcan be protracted roughly 20° less than in abipedal pose, reducing stride length. In the semi-and plantigrade models, limb protraction requiresextreme flexion of the ankle while the free limbpasses the supporting limb, due to the great lengthof the pes compared to the tibia. In such a posefemur retraction cannot be the main component ofprotraction unless the animal uses a sprawlingposture, in direct contradiction to the osteologicalevidence (see Gatesy 1990).

Subequal fore and hind limb lengths cannotbe created, even with a pronated manus andparasagittal forelimbs, as it requires femur protrac-tion to beyond the pubes at midstance, and to sub-horizontal for limb protraction (Figure 10.5, Video3). Note that in this position the height of the gle-noid was artificially increased to 0.7 m by using astanding instead of a walking pose in the forelimb.This position does not allow proper walking at all,as it limits stride length to 0.2 m.

However, all these poses were created with apronated manus. If the forelimb is placed in correctarticulation with regards to the wrist and elbow,strong humerus abduction is required to turn topalm ventrally. This would essentially create asprawling pose. However, it is not possible to rotatethe humerus around its long axis to create a sub-vertical antebrachium, so that the animal wouldtouch the ground with its ribcage. If the hindlimbsare placed in a sprawling position (following Fraas1912; contra Huene 1926, 1928; Gatesy 1990;Christian and Preuschoft 1996; Christian et al.1996), the femora must be disarticulated from thepelvis, and the tibia and fibula must be disarticu-
ible, the height of the glenoid above the
nd when placing the manus on the ground canbe more than 0.6 m. Due to this extremely shortlimb length, the vertebral column slope down-s so that the 1stdorsal – 2ndsacral line slopes9° for a digitigrade Figure 10.1), and 9° for ai-plantigrade model (Figure 10.2). In a fullytigrade (FVP) model, whether with a stronglyracted or nearly vertical femur position, thed is at or slightly above the same height as theum (Figure 10.3-4). These postures bring theus on the ground without introducing strongriflexion in the dorsal series, and retain roomemur excursions during locomotion. The effec-forelimb/hindlimb length ratios (i.e., height ofoid divided by height of acetabulum in mid-ce pose) are 0.45 for the digitigrade, 0.54 for

lated from the distal femoral condyles. Alternativelyto a sprawling pose, Plateosarus might havewalked on non-pronated hands, but Bonnan andSenter (2007) show clearly that the required adap-tations are missing.

A potentially negative effect of the only qua-drupedal poses in which the hindlimbs can bemoved in a realistic gait cycle (hindlimbs digiti-grade, Figure 10.1) is the forwardly inclined verte-bral column combined with the low shoulder height.At neutral articulation of the neck, the view the ani-mal can see is quite limited. A blind angle extendsposteriorly, and lateral excursions of the neck to‘check six’ result in a large blind area on the con-tralateral side. Extreme dorsiflexion of the neck isrequired to bring the head to a sufficient height so


17

FIGURE 10. Virtual skeleton of GPIT1 in quadrupedal poses in lateral view. 1: Digitigrade, 2: semi-plantigrade, 3:plantigrade hindlimb. 4: as 3, but with vertically positioned femur at midstance. 5: equal limb length posture. Length ofleft femur is 595 mm.

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thatble necklatioslighserionecklocotiallyningneabelomissgrou

mumfeedthirdpareanimandsaurgateslowto fepedif thenot with

VIDEhind


a 360° view is possible. While possibly feasi-when feeding, during rapid locomotion such a position carries a high risk, because all articu-

ns are at their bony stops. Therefore, event impulses, e.g., from stumbling, can lead tous injury. Extant animals appear to carry theirs close to neutral articulation during rapid

motion (Christian and Dzemski 2007), poten- because of this risk. For Plateosaurus, run- in a quadrupedal posture carrying the neckr neutral articulation leads to a head heightw hip height, close enough to the ground that atep in the forelimbs leads to an impact on the

rearing elephant. However, as shown above, thereare no bipedal poses that do not allow locomotion.

Body mass

The CAD model of Plateosaurus based onGPIT1 has a total volume of 740 l. There are noindications of air sacs invading bone to form post-cervical pneumatic cavities in Plateosaurus orother prosauropods (Wedel 2007), but the dorsalvertebrae show shallow troughs on the centra. Incombination with the ability to breathe through ribmotion, this indicates that prosauropods probablypossessed pulmonary air sacs. An extant phyloge-

O 3. Virtual skeleton of GPIT1 Plateosaurus engelhardti in quadrupedal posture with equal effective fore andlimb lengths. For full video, see website.

nd. A further potential disadvantage is the maxi- possible head height, and thus size of theing envelope. The base of the neck is at twos the height of a bipedal pose (0.99 m com-d to 1.49 m). Additionally, in a bipedal pose theal can tilt the body up to increase shoulder

thus feeding height (Figure 9.3). While Plateo-us could theoretically be envisaged as an obli- quadruped that uses quadrupedal gaits for locomotion, then gets up into a bipedal poseed, and then back down again into a quadru-

al stance for locomotion, this makes sense onlyre are bipedal stances suitable for feeding but

for locomotion. These could only be postures a steeply inclined vertebral column, akin to a

netic bracket (EPB) approach (Witmer 1995) con-firms this: both theropods and sauropods had (andhave) bird-like lungs (Perry and Reuter 1999;Wedel 2005, 2007; O'Connor and Claessens2005), as indicated by the extensive pneumaticityof their skeletons. Birds have densities as low as0.73 kg/l (Hazlehurst and Rayner 1992), and sau-ropod density is therefore probably best assumedto be about 0.8 kg/l or even lower (Wedel 2005).Crocodiles have lungs that, albeit simpler in struc-ture than those of birds, are interpreted as a pread-aptation for the formation of true air sacs and aunidirectional lung (Perry 1998; Farmer and Sand-ers 2010). Therefore, it is most parsimonious toassume the existence of small pulmonary air sacsin Plateosaurus, even though they did not invade

bonservwassaubralsam(basHirabe epresthe ity) beeeledcontiou1.0

entiingldanthemass1.1 are modtotamodamoresu1.13placmovreduandtrunthe thisandmaskg. knoSanmod430

fronbipeat m(TabBipthe


es and thus left no clear marks on the pre-ed parts of the animals. Rib motion probably the main mode of lung ventilation in Plateo-rus, because the architecture of the costoverte- articulations (dual headed hinge joints) is thee as is generally the case in saurischiansal Saurischia: Langer 2004;Tyrannosaurus:sawa 2009), and the air exchange volume canstimated at a value typical for birds (Mallison ins). The air sacs may have been large, but inabsence of solid evidence (skeletal pneumatic-for a large size they must be assumed to haven so small that the overall density can be mod- on that of extant terrestrial vertebrates. As asequence, the average density should cau-sly be assumed at a value between 0.9 kg/l andkg/l.Additionally, density is not uniform across the

re animal, and various body parts were accord-y given values that reflect the relative abun-ce of bone, flesh, intestines, and air volumes in

. Skull, tail, limbs, and the pelvic region areumed to be heavier than water (d = 1.05 kg/l tokg/l), while the neck and anterior trunk regionsignificantly lighter (d = 0.7 kg/l). This basicel has an average density of 0.94 kg/l and a

l weight of 693 kg. Variations of the density ofel parts to account for different soft tissueunts, details of which are given in Table 1,lt in average densities between 0.89 kg/l and kg/l. The basic model has a very posteriorlyed COM, so most variations were designed toe the COM forward. This was achieved bycing the mass of the tail and posterior trunk,

/or increasing the mass of neck and anteriork. However, one variant was produced in whichlimbs were given higher density, too, although partly cancels the effect that a heavier neck

but one the COM rests comfortably above the sup-port area (Figure 11.1). This is true in both the digi-tigrade and the semi-plantigrade pose, andrequires only modest femur protraction (maximumvalue 20° from vertical, in combination with a fullydigitigrade stance and a metatarsus inclination of65° from horizontal). For the most front-heavymass variation at full digitigrady the COM plots justin front of the longest digit. Femur protraction to25° (+5° compared to the basic model) brings thesupport area under the COM in this model.

Quadrupedal poses. In all models with an inclinedfemur the COM plots in the support area of the hindfoot or at its anterior edge, unless the lowerhindlimb is placed at an unrealistic strong posteriorinclination (as in Figure 10.4). If the hind limb isposed as deemed anatomically correct here, with aprotracted femur, limited knee and ankle flexionand fully digitigrade, the ratio of effective limblengths is 0.45, and the hindlimb carries between90% and all of the weight. Unrealistically flexing theknee so that the tibia is strongly inclined leads to amaximum of 35% of the weight supported on theforelimbs, albeit with a low effective limb lengthratio of 0.52. Increased limb flexion, which resultsin less massively unequal limb lengths, moves thesupport area forward, due to increases in femurprotraction and ankle flexion. In fact, even absurdlylight-tailed versions of the model with a significantlyinflated pectoral region and neck have a COM plot-ting solidly within the area of the hindfoot in mid-stance at effective limb length ratios between 0.7and 1. Subequal fore and hind limb lengths in asprawling position place up to 40% of the weight onthe forelimbs but are osteologically impossible.

Models with a vertical femur position placemore weight on the forelimbs, by shifting the sup-

19

anterior body have on shifting the center ofs. Total mass varies between 600 kg and 838Scaled to the size of the largest and smallestwn individuals (total length 10 m and 4.8 m,der and Klein 2005) of Plateosaurus, the basicel gives a weight range from 476 kg to roughly

0 kg for an average density of 0.89 kg/l.

Position of the center of mass (COM)

In the basic model, the COM rests 0.23 m int of and 0.16 m below the acetabulum in adal standing pose. The mass variations resultost in an anterior shift by 0.06 m to 0.29 mle 1). The dorsoventral shift is negligible.

edal poses. In the bipedal poses created onbasis of a best fit of the skeletal elements, in all

port point of the hind limbs posteriorly. However,they either require a strongly inclined position ofthe lower hindlimb, which creates large bendingmoments because of the long moment arm of theCOM and high torques in the knee and ankle joints,or cause an extreme difference in limb length. Inextant animals with parasagittal limbs, the hindfootis almost always placed under the hip joint, orclose to such a position. The Plateosaurus modelswith a vertical femur and strong limb flexion, how-ever, result in a foot position far behind the acetab-ulum. Such a posture causes extreme flexingmoments in the knee and ankle, and can thus bedismissed as unrealistic, especially considering theshort moment arms of the extensor muscles of theankle and knee. The alternative pose, with asteeply placed lower hindlimb (low limb flexion),

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TABLmassthe CPosit

PARNAM

hea

neck

neck

neck

neck

neck

neck

neck

trun

trun

trun

trun

trun

trun

tail

tail

tail

tail

tail

tail

tail

tail

thig

sha

foo

toe

armcomp

total a

totahindl

LISON: DIGITAL PLATEO I

E 1. Mass variations of CAD model of Plateosaurus engelhardti. For each model version, the densities andes for all model parts are given, along with the resulting average density of the model and the shift in position ofOM in craniocaudal (d pos COM y) and dorsoventral (d pos COM z) direction relative to model 1 (basic model).ive numbers indicate caudal/dorsal shift, negative numbers indicate cranial/ventral shift.

Model No. 1 1 2 2 3 3 4 4 5 5

basic model

basic model

T E VOLUME DENSITY MASS DENSITY MASS DENSITY MASS DENSITY MASS DENSITY MASS

kg/l kg kg/l kg kg/l kg kg/l kg kg/l kg

d 5.88 1.10 6.46 1.10 6.46 1.10 6.46 1.10 6.46 1.10 6.46

1 1.50 0.70 1.05 0.70 1.05 0.80 1.20 0.80 1.20 0.80 1.20

2 1.17 0.70 0.82 0.70 0.82 0.80 0.94 0.80 0.94 0.80 0.94

3 1.48 0.70 1.03 0.70 1.03 0.80 1.18 0.80 1.18 0.80 1.18

4 1.88 0.70 1.32 0.70 1.32 0.80 1.50 0.80 1.50 0.80 1.50

5 2.17 0.70 1.52 0.70 1.52 0.80 1.73 0.80 1.73 0.80 1.73

6 2.32 0.70 1.63 0.70 1.63 0.80 1.86 0.80 1.86 0.80 1.86

7 6.20 0.70 4.34 0.70 4.34 0.80 4.96 0.80 4.96 0.80 4.96

k 1 41.03 0.70 28.72 0.70 28.72 0.80 32.82 0.80 32.82 1.20 49.23

k 2 75.47 0.70 52.83 0.70 52.83 0.80 60.37 0.80 60.37 1.20 90.56

k 3 103.91 0.70 72.74 0.70 72.74 0.80 83.13 0.80 83.13 1.20 124.69

k 4 84.77 0.90 76.29 0.90 76.29 1.00 84.77 1.00 84.77 1.00 84.77

k 5 52.90 1.00 52.90 1.00 52.90 1.00 52.90 1.00 52.90 1.00 52.90

k 6 68.91 1.00 68.91 1.05 72.35 1.25 86.14 1.25 86.14 1.25 86.14

1 31.92 1.00 31.92 1.10 35.11 1.25 39.90 1.00 31.92 1.00 31.92

2 23.65 1.00 23.65 1.10 26.01 1.25 29.56 1.00 23.65 1.00 23.65

3 25.77 1.00 25.77 1.10 28.35 1.25 32.21 1.00 25.77 1.00 25.77

4 23.46 1.00 23.46 1.10 25.80 1.25 29.32 1.00 23.46 1.00 23.46

5 11.47 1.00 11.47 1.10 12.61 1.25 14.33 1.00 11.47 1.00 11.47

6 8.72 1.00 8.72 1.10 9.59 1.25 10.90 1.00 8.72 1.00 8.72

7 3.84 1.00 3.84 1.10 4.22 1.25 4.80 1.00 3.84 1.00 3.84

8 2.07 1.00 2.07 1.10 2.28 1.25 2.59 1.00 2.07 1.00 2.07

h 51.26 1.00 51.26 1.10 56.39 1.25 64.08 1.25 64.08 1.25 64.08

nk 12.74 1.00 12.74 1.10 14.02 1.25 15.93 1.25 15.93 1.25 15.93

t 4.72 1.00 4.72 1.10 5.20 1.25 5.90 1.25 5.90 1.25 5.90

s 3.29 1.00 3.29 1.10 3.62 1.25 4.11 1.25 4.11 1.25 4.11

lete

7.38 1.00 7.38 1.10 8.12 1.25 9.23 1.25 9.23 1.25 9.23

xial 580.46 0.86 501.44 0.89 517.97 1.01 583.58 0.95 550.85 1.10 639.01

l imb

72.02 1.00 72.01 1.10 79.22 1.25 90.02 1.25 90.02 1.25 90.02

causes smodels whind limbdistributiokg/l), the weight (F0.45. Notthe acetapoint of snently sub

In alpectoral gribcage, the COM lies significantly higher than theglenoid (e.g., at 1.5 times the height in the modelshown in Figure 11.2). This means that the stabilityof the anterior body part when supported by onlyone forelimb is reduced compared to the patternseen in nearly all extant quadrupeds, in which thelimb articulation with the trunk rests higher than orroughly at the level of the COM.Stability of slow gaits. The extremely posteriorposition of the COM has consequences for the sta-bility of even slow gaits. Slow locomotion meansthat the body, due to its low moment of inertia, hasample time to react to small lateral imbalances.Unless one is balanced well, much energy isexpended correcting the balance instead of movingforward. When walking slowly and bipedally, thebody must sway laterally or the feet must be placed

port area compareminor factor, is obvquadruped, but thwider track in the fing a wide supporlifted.

In Plateosauosteologically posassuming manus ptest of the balancea hindfoot is liftedusing the most fstanding pose witboth limbs, the anally, because the angle formed by hindfoot. The s

total forelimb

total complete

av. density

d pos COM y

(m)

d pos COM z

(m)

PART NAME V

Table 1 (co


her, on the track midline, so thatexactly over the support area.

ns, or any combination of them,b adduction to bring the foot more longitudinal support area,ade instead of a digitigrade foot,tead of bipedal gaits, reduce the well as the need to adduct theider track is possible, creating a

ngle (Henderson 2006). To bedrupedal posture should thuswidth and the length of the sup-

1.25 9.23 1.25 9.23

1.01 749.34 1.13 837.50

1.01 1.1328

-0.06 -0.062

-0.004 0.003

4 4 5 5

DENSITY MASS DENSITY MASSkg/l kg kg/l kg

imilarly low limb length ratios as thoseith an inclined femur and a slightly flexed. At most, using the unreasonable massn of the most front-heavy model (d = 1.13forelimbs carry about 41% of the bodyigure 11.2), with a limb length ratio ofe, however, that for this hindlimb posturebulum is not above, but far in front of theupport, and the hind limb thus perma-jected to large bending moments.

l quadrupedal poses that do not shift theirdle to an absurdly low position on the

in front of each otthe COM passes These two solutiorequire strong limunder the COM. Asuch as a plantigror quadrupedal insrisk of toppling ashindlimbs fully. A wwide support triaeffective, the quaincrease both the

7.38 1.00 7.38 1.10 8.12 1.25 9.23

739.26 0.89 660.24 0.94 692.64 1.06 782.07

0.8931 0.9369 1.0578

0 0.023 0.026

0 -0.003 -0.005

Model No. 1 1 2 2 3 3

basic model

basic model

OLUME DENSITY MASS DENSITY MASS DENSITY MASSkg/l kg kg/l kg kg/l kg

ntinued).

21

d to a bipedal pose. The latter, aiously the case in practically anye former relies on allowing a

orelimbs and hindlimbs for creat-t triangle when any one limb is

rus this is not the case in anysible quadrupedal pose, evenronation, as is best shown by a in a three-point support pose. If off the ground in a CAE model,ront-heavy mass variant, in ah only 10° femoral abduction inimal tends to topple caudolater-COM lies behind the support tri-the forefeet and the remainingupporting hindlimb must be

MALL

22

addavoioffebecahinddetarus Potebe pmal dal TetrNavby aplacdii (H(199scalTetrthis

Platprev107sam

FIGpos


ucted to nearly the same angle as in a biped tod this. Therefore, a quadrupedal pose does notr a significant advantage with regard to stability,use an accidental imbalance in the supporting

limb is as dangerous as in a bipedal stance. Ailed discussion of walking cycles in Plateosau-is beyond the scope of this paper.ntial trackways. The virtual skeleton cannotlaced in a quadrupedal pose that allows nor-locomotion. Therefore, none of the quadrupe-

structed two CAD models based on a high resolu-tion laser scan of the mount of GPIT1. One of themodels has significant volumetric errors (Mallisonin press) and results in a weigh estimate of 912 kg.The other model follows the contours of the mountclosely and results in a 630 kg estimate. Sanderand Klein (2005) estimate the largest individuals ofPlateosaurus to have reached 4000 kg at an over-all length of 10 m, which is nearly identical to theresults presented here. Henderson (2006) deriveda total mass of only 279 kg for Plateosaurus by 3D

URE 11. CAD 3D model of GPIT1 in lateral view. 1: bipedal pose. 2: quadrupedal pose with most anterior COMition. Green dots indicate position of the COM for all (1) and most front-heavy (2) model variations.

trackways assigned to prosauropods, such asasauropus unguiferus (Ellenberger 1972) orahopus falcipollex (Baird 1980) were created plateosaurid. In contrast, the skeleton can beed to conform to the ichnofossil Otozoum moo-itchcock 1847, Rainforth 2003), contra Farlow

2). Porchetti and Nicosia (2007) fitted theed-down pes of Plateosaurus into the track ofasauropus in a plantigrade stance. As shown,posture is highly unlikely for Plateosaurus.

DISCUSSION

The total body volume and mass obtained foreosaurus engelhardti falls within the range ofious estimates. Seebacher (2001) calculated

3 kg for AMNH 6810, an animal roughly thee size as GPIT1. Gunga et al. (2007) con-

mathematical slicing. However, it seems that thescale of the drawing cited by Henderson (2006: p.919) as source data (Paul 1987) has been uninten-tionally altered. The animal is roughly two thirds aslong as GPIT1, much smaller than the smallestknown individual of Plateosaurus (4.8 m totallength, Sander and Klein 2005). Scaling the modelused here down to equal size as Henderson’s 2006model results in a mass of 418 kg (d = 0.6 kg/lneck, 0.9 kg/l remaining body parts as in Hender-son 2006). The main reason for the discrepancy intotal mass appears to be the more slender belly ofthe model used by Henderson 2006, which isunusual for a herbivore. Also, the drawing themodel is based on has a relatively slender tail andhindlimbs.

resusuponevertBipespestridwiderequforeto sHowsauis nlengout in pfor t(192probrapia sua 65in pappboneveIt altionulat

anybecTo tslowhightesttracwithbipeeithweigcomthe morpedis libipe

shoadvsevan u


Posing the virtual skeleton of GPIT1 digitallylted in a bipedal pose in which the COM is well

ported by the support area formed by either adducted foot, or both feet with the limbs heldically in anterior view (Figures 1.2, 9.1-2).dal locomotion appears easily possible at any

ed, because the feet can be adducted at mid-e sufficiently to support the COM. Due to the pubes, very rapid locomotion with long stridesires significant abduction of the femora. There-, at a run Plateosaurus had to sway from sideide, or rotate the pelvis around the vertical axis.ever, the claim by Moser (2003) that Plateo-

rus could only take tiny steps in a bipedal poseot supported by the virtual mount. A strideth of 1.34 m is easily possible for GPIT1, with-requiring any abduction of the femora (Mallisonress). Rather, the stride length limitation is truehe extremely upright pose suggested by Huene6, see Figure 9.3). While rapid running gaitsably require massive abduction of the femora,

d walking can easily be achieved bipedally withbhorizontal back, as the femur can easily cover° angle without significant abduction (Mallisonress). Additionally, a bipedal, digitigrade poseears to create bending moments in the limbes that conform to the observed shapes; how-r, a detailed biomechanical analysis is required.so frees the manus for other uses than locomo-, e.g., inter- and intraspecific combat or manip-ion of food.None of the tested quadrupedal poses offers

locomotory advantage over a bipedal pose,ause neither mobility nor stability is increased.he contrary, locomotion is limited to extremely speeds, and energetically ineffective due to flexion angles in the hind limb joints in most

ed postures. The problem of limited femur pro-

at least one ornithischian adopted a very clumsyquadrupedal gait (Wilson et al. 2009), and for suchcircumstances or for climbing steep inclines Plate-osaurus may have similarly used a crawl on allfours. However, the pedal morphology of Plateo-saurus is more similar to the theropod discussedby Wilson et al. (2009) that did not use a wide-gauge, crawling quadrupedal gait on the samesubstrate, so that even this possibility seemsunlikely. For normal locomotion, it appears unrea-sonable for Plateosaurus to have adopted a qua-drupedal posture, even if one assumes that manuspronation was somehow possible without stronghumeral abduction.

ACKNOWLEDGMENTS

My doctoral advisor, H.-U. Pfretzschner of theIFGT, granted me the utmost liberty to pursue myresearch as I saw fit, and supported me at everystep throughout the research presented here, earn-ing my utmost gratitude. The late W.-E. Reif (IFGT)stepped in as main advisor at a critical time and didmuch to improve my project. B. Ludescher of theUniversity Hospital Tübingen spent many long eve-nings CT scanning GPIT1, for which I will alwaysbe grateful. R. Schoch at the SMNS, W.-D. Hein-rich, S. Scheffel. and L. Berner at the MFN earnedmy thanks by readily granting access to and help-ing in the handling of specimens in their care,sometimes at extremely short notice. Others toonumerous to list aided my work with extensive dis-cussions and helpful comments. K. Stevens (Uni-versity of Oregon) and A. Christian (University ofFlensburg) wrote helpful reviews, which improvedthe manuscript significantly, for which I am verygrateful.

This is contribution number 79 to the

23

tion at low abduction angles due to a collision the pubes is aggravated compared to adal pose. Additionally, a quadrupedal pose

er does not place a significant part of theht on the forelimbs, or exposes them to highpressive loads while inhibiting the step cycle inhindlimbs through extreme flexion. Further-

e, the potential feeding envelope in a quadru-al stance is smaller, and circumferential visionmited to an extreme neck posture, while adal stance offers easy 360° sight. It seems counterintuitive that Plateosaurus

uld have used a posture and gaits that offer noantage, while suffering from several potentiallyere restrictions. For very slow locomotion overnusual substrate, a slippery, muddy river bank,

Research Group 533 ‘Sauropod Biology’ of theGerman Science Foundation.

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