Mesozoic Reptiles Origin, Evolution, and Demise. Origins n Presumably, Mesozoic reptiles are derived...
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Transcript of Mesozoic Reptiles Origin, Evolution, and Demise. Origins n Presumably, Mesozoic reptiles are derived...
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Mesozoic Reptiles
Origin, Evolution, and Demise
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Origins
Presumably, Mesozoic reptiles are derived from early amniotes.– Oldest amniotes are from Mississipian of
Nova Scotia: Westlothiana lizzae was found in 1991.
– Archaeothyris (Pelycosaur) and Hylonomus (Romeriid) were around before the end of the Permian.
– Generally small: 15cm SVL.
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Origins
Pelycosaurs were the basal stock of synapsids. The synapsids are the mammal-like reptiles (a single temporal fenestra instead of 2).– Synapsids radiated into about 24 genera.– Small (30cm SVL) and lizard-like.– Radiated into both carnivorous and
herbivorous lineages.
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Carnivorous Synapsids
Ophiacodon and Dimetrodon.– Both had elongated neural spines,
presumably for a large sail tham may have been used for thermoregulation.
– Both were over 3m long.– Ophiacodon had a narrow snout and may
have fed on fish.– Dimetrodon was broad jawed and likely a
terrestrail predator.
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Herbivorous Synapsids
Edaphosaurus was sail finned like Dimetrodon and Ophiacodon.
It had peg-like teeth indicating herbivory.
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Synapsids
Pelycosaur lineage disappeared by the end of the Permian.
Disappearance is perhaps a consequence of the therapsid radiation in the late Permian.
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Paleozoic Reptiles
There are 2 anapsid lineages.– Testudines – there is a complete lack of
fossils in the late Paleozoic.– Captorhinids – medium sized, lizard-like
reptiles, with broad heads.• Some level of heterodont dentition.• Limbs are slender and long, suggesting agility.
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Romeriids
These are pre-diapsid, but are not on the anapsid line.
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Diapsid Origins
Essentially, this is a consideration of the Diapsida (Crocodilians, birds, Rhyncocephalians, and squamates).
It is a monophyletic group. Diapsids have 2 temporal openings or
fenestrae, separated by a single bony arch.
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Diapsid origins
The upper arch is formed by the 3-pronged postorbital bone and a 3-pronged squamosal bone. The lower arch is formed by the jugal and quadratojugal.
Both arches have been lost repeatedly in various groups - an important point because this loss permits kinesis.
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Lepidosaur-omorphs: A) Permian petrolacosaurus. B) Sphenodon. E) Crotaphytus. G) Snake, G)
Amphisbaenian.
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Diapsid Origins Derived forms also have a sub-orbital
fenestra. Earliest known diapsid is
Petrolacosaurus from the late Carboniferous of Kansas (60-70cm TL).
Derived diapsids can be split into the Archosauromorpha (Crocs, birds, pterosaurs, and dinosaurs) and Lepidosauromorpha (squamates, sphenodon, and some marine reptiles).
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Araeoscelidia
These are the first true diapsid reptiles.– Lizard-like in body proportions.– Dentition is homodont and suggets
carnivory.– Dissapear in the middle Permian.
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Parareptiles
Difficult to classify.– They contain both primitive and advanced
characters.– They do not fit neatly with either the
Romeriids, the Diapsids, or the Anapsids. Include the following:
– Mesosaurs• Early Permian, miniature (1m TL), marine,
gharial-like.
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Parareptiles
– Millerosaurs– Pareiasaurs– Procolophonoids
All four of these groups appear in the mid-Permian.
Only the Procolophonoids persisted to the end of the Triassic.
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IchthyostegidaeNectridiaMicrosauriaTemnospondylaCaeciliaAnuraUrodelaCrassigyrinusAnthracosauridaeSeymouriamorphaCaptorhinidaeProcolophonidaePareiasauridaeTestudinesDiapsidaDinosauriaSynapsida
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IchthyostegidaeNectridiaMicrosauriaTemnospondylaCaeciliaAnuraUrodelaCrassigyrinusAnthracosauridaeSeymouriamorphaCaptorhinidaeProcolophonidaePareiasauridaeTestudinesDiapsidaDinosauriaSynapsida
1
2
3
4
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Characters
1 = Five digit hand and foot 2 = Pedicellate teeth 3 = Astragalus and Calcaneum in Ankle 4 = Two temporal openings in skull.
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YoungiformesSphenodontidaeSauriaSerpentesCrocodyliaPterosauriaTheropdaAves?SauropodomorphaOrnithopodaCeratopsiaStegosauriaAnkylosauriaIchthyosaursPlesiosaurs
5
6
7
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Characters
5 = Kinetic Skull 6 = Antorbital Fenestra 7 = Simple Hinge-like Ankle.
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Albertosaurus
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Characters for phylogeny:
1) Diapsida: Skull w/ upper and lower temporal fenestrae w/ triradiate postorbitan and squamosal, suborbital fenestra, ossified sternum, complex ankle joint between tibia and astragalus, and 1st metatarsal less than half the length of the 4th metatarsal.
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Characters for phylogeny:
2) Sauria (Neodiapsida): Anterior process of squamosal narrow, squamosal mainly restricted to top of skull, tabular absent, stapes slender, cleithrum absent, 5th metatarsal hooked, trunk ribs mostly single-headed.
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Characters for phylogeny:
3) Archosauromorphia: Cervical ribs w/ 2 heads, concave-convex articulation between astragalus and calcaneum.
4) Archosauria: Presence of antorbital fenestra; triangular shaped orbit; and serrated, laterally compressed teeth.
5) Elongated pubis and ilium, 4th trochanter on femur.
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Characters for phylogeny:
6) Crown group Archosauria: Parietal foramen absent; no palatal teeth on pterygoid, palatine, or vomer.
7) Crurotarsi: Astragalus forms a peg that fits into a socket on the calcaneum.
8) Crocodylomorpha: Secondary palate fromed from at least the maxilla.
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Characters for phylogeny:
9) Ornithodira: Anterior cervical vertebrae longer than mid-dorsals, interclavicals absent, clavicles reduced or absent, tibia longer than femur, clacaneal tuber rudimentary or absent, metatarsals bunched together and 2-4 elongated.
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Characters for phylogeny:
10) Pterosauria: Hand w/. 3 short fingers and elongate 4th finger supporting winglike membrane, pteroid bone in wrist, short trunk, short pelvis w/ prepubic bones.
11) Dinosauria: S-shaped swan-like neck, forelimb less than half the length of hindlimb, hand digit 4 reduced, etc.
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Characters for phylogeny: 12) Lepidosauromorpha: Postfrontal
enters border of upper temporal fenestra, supratemporal absent, teeth absent on lateral pterygoid flanges, etc.
13) Sauropterygia: Elongation of postorbital region of skull, enlargement of upper temporal fenestra, elongate and robust mandibular symphysis, curved humerus, radius and ulna equal length.
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Characters for phylogeny: 14) Lepidosauria: Determinant growth
with epiphyses on articulating surfaces of long bones, postparietal and tabular absent, fused astragalus and calcaneum, etc.
15) Squamata: Loss of lower temporal bar (and quadratojugal), kinetic skull, reduction or loss of squamosal, nasals reduced, etc.
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Petrolaco-saurus and Euparkeria.Note the difference in limb proportions of these early Diapsids.
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Euparkeria
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a) Prolacerta w/ incomplete lower temporal arch.b) Typical Archosaur Carnosaur Ornithosuchus.c) Femur of Thescelosaurus showing 4th trochanter.
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Evolution
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Mesozoic aquatic reptiles. All but (d) are Lepidosauromorphs.a) Ichthyosaur - Upper Jurassicb) Plesiosaur – Upper Jurassicc) Nothosaur - Triassicd) Thallatosaur – Middle Triassice) Placodont – Middle Triassicf) Hupehsuchus – Middle Triassic.
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Pterosaurs: a) Jurrasic Rhamphorhynchus, b) Cretaceous Pteranodon, c) Anuroganthus (insectivore?), d) Eudimorphodon (small verts), e) Dorygnathus (fish), f) Pteradaustro (plankton), g) Dsungaripterus (mollusks – prying teeth as well as molariform for crushing).
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Thecodonts(Teeth implantedin alveoli, rear legslonger than foreLegs).
All laterArchosaurs
Saurischia(Reptile Hips)
Ornithischia(Bird Hips)
Phytosaurs: becomeAquatic & croc-like
Solve breathing problemdifferently than crocs –move nares to top of skull
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Saurischia
Palaeopoda(4-legged gait)
Palaeosaurs(bipedal – predaceous)
Plateosaurs(bipedal, small heads,long necks, long tail)
Die out at end ofTriassic
SauropodaStart in Jurassic.
Good propulsion, but slowGetting leg forward.
Theropoda: good prop & leg forward.
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Sauropoda Most fantastic of all dinosaurs.
– Jurassic to end of Cretaceous.– Lasted 120my– All basically 1) robust bodies, 2) long tail,
3) long neck, 4) pillar like legs.– Length up to 90’
• Ex Brontosaurus 70ft., 30 tons, hind leg 3 claws, foreleg 1 claw.
• Cope and Marsh• Diplodocus 90ft., slender & only 10 tons.• Camarasaurus, 15ft., short neck & tail.• All quadrupeds, but rear legs longer than fore.
Derived from bipeds?
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Sauropoda cont.• Exception to the rule: Brachiosaurus – Fore-
limb is longer than hind-limb. TL = 75ft., shoulder = 20ft., head at 40ft., nostrils on top of head therefore under water it could breath easily. Weight = 78 tons to 100 tons (= giant whale).
• Remember, strength of bone increass in proportion to crossectional area, but weight increases as the cube of the length.
• Therefore, as length doubles, limbs are 4x as strong, but mass increases 8x.
• Implications? Tend to minimize weight or become aquatic.
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Sauropoda cont.
Did they grow rapidly?– Large pituitary body then you can get rapid
growth.– There is a paucity of 3m individuals.– Endothermy? Small heads (and a wealth
of other evidence) does not support the endothermy hypothesis.
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Theropoda
There are 2 lineages:– Coelurosauria
• To end of Cretaceous, small and medium size (to 10ft), bipedal, hollow bones w/ air sacs.
• Split in late Cretaceous: ostrich Dinosaurs, eg. Struthiomimus - toothless jaws, look like ostrich, horny bill as in birds. Feed on eggs?
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Theropoda cont.
– Carnosaurs• Predators of early Jurassic.
– Antrodemus c. 30 ft.– Megalosaurs– Allosaurs
» large head, large jaws. Extreme fenestration. 2 tons.
– Ceratosaurus (horned - 15 ft.)– Spinosaurus (sail)– Deinodonts– Gorgosaurus– Tyrannosaurus 47 ft, 7 tons.
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Ornithichians
These are herbivorous jaws are toothless, at least in front. Probably a horny beak. Tend to be bipedal.
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Ornithopoda– Hypsilophodon (small, high enamel folds in
teeth, late Jurassic to Cretaceous)– Camptosaurus (17ft., 1600 lbs, well
developed cheek teeth, – Iguanodontidae (Iguanodon 25 ft.)– Heterodontosaurus (has tusks, skull only
4”)– Hadrosaurus (duck-billed dinosaurs - 30ft,
3 tons). Some had up to 600 teeth in each jaw half, and therefore up to 2000 teeth. Diet consisted of terrestrial vegetation, based on mummies.
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Ornithopoda cont.
– Stegosaurs (2nd group of ornithichians). They go extinct before Tyranosaurus shows up.
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Ornithichians
Ornithopoda(bipedal)
Ceratopsia(quadrupedal forms)
Stegosaurs(quadrupedal)
Ankylosaurs
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Ornithopods
Ceratopsians
Ankylosaurs
Stegosaurs
Sauropods(Brachiosaurus)Theropods(T. rex, Oviraptors)
There is a general trend for hind legs longer than fore.
Thecodonts
Aves???
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Ornithich-ians
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Stegosaurs & Ankylosaurs
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Sauropods
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Theropods
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Demise
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Deinony-chus
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Archeo-pteryx, Ornitho-lestes, and Aves.
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