An Early Miocene Land Mammal (Oreodonta) from a Marine Limestone in Northern Florida

An Early Miocene Land Mammal (Oreodonta) from a Marine Limestone in Northern FloridaAuthor(s): Bruce J. MacFaddenSource: Journal of Paleontology, Vol. 54, No. 1 (Jan., 1980), pp. 93-101Published by: SEPM Society for Sedimentary GeologyStable URL: http://www.jstor.org/stable/1304166 .

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JOURNAL OF PALEONTOLOGY, V. 54, NO. 1, P. 93-101, 3 TEXT-FIGS., JANUARY 1980

AN EARLY MIOCENE LAND MAMMAL (OREODONTA) FROM A MARINE LIMESTONE IN NORTHERN FLORIDA

BRUCE J. MACFADDEN Florida State Museum, University of Florida, Gainesville 32611

ABSTRACT-A phenacocoeline oreodont (Mammalia: Artiodactyla) is described from a marine limestone informally referred to as "Unit 9" at the Martin-Anthony Roadcut in Marion County, Florida. This oreodont represents Phenacocoelus luskensis previously known only from the late Arikareean (early Miocene) Harrison Formation of southeastern Wyoming. The invertebrate fauna and lithological characteristics of "Unit 9" are at present very poorly known. "Unit 9" either represents the Tampa Limestone or a basal limestone of the Hawthorne Formation. There also is a small collection of biostratigraphically useful land mammals from the overlying clastic sediments of the Hawthorne Formation. The oreodont and these other land mammals indicate a late Arikareean Land Mammal "Age" and also, based on intercontinental correlations, a late Aquitanian European Stage. Despite the fact that oreodonts were abundant, diverse, and widespread in the Oligocene and Miocene of the midcontinent, they were rare in the Gulf Coastal region. This scarcity probably resulted from a zoogeographic filtering mechanism between these regions.

INTRODUCTION

DURING THE OLIGOCENE and beginning of the Miocene epochs, the herbivorous mammals commonly known as oreodonts were extremely abundant, taxonomically diverse, and geographically widespread throughout much of North America. They were so ubiquitous that early vertebrate paleontologists often referred to appropriate-aged terrestrial sediments, notably around the Big Badlands region of South Dakota, as "Oreodon Beds," and this group has been heavily relied upon for correlations in western North America. De- spite their widespread abundance in western North America, oreodonts are poorly known in the east. For example, only a few specimens have been reported from both the extremely prolific early Miocene Thomas Farm site (Ma- glio, 1966) and the fossiliferous Gulf Coastal Miocene sequence of Texas (Patton, 1969b).

The purpose of this report is to describe an oreodont collected from a marine limestone ("Unit 9") at the Martin-Anthony Roadcut in Marion County, Florida. There is no doubt that this specimen was collected in situ because it is still embedded in the limestone matrix. It is unfortunate that at present there is considerable controversy as to whether "Unit 9" from the Martin-Anthony Roadcut should be considered the Tampa Limestone or a basal limestone unit of the Hawthorne Formation. When this controversy is resolved, the pres- ence of this oreodont that was washed into this

Copyright ? 1980, The Society of Economic Paleontologists and Mineralogists (

"Unit 9" nearshore limestone will provide an important basis for correlations between the North American Land Mammal "Ages" and marine stages. Furthermore, this and other Gulf Coastal oreodont occurrences appear to have an interesting paleozoogeographical significance in contrast to distributional patterns seen in western North America.

The following abbreviations are used in the text: F:AM, Frick American Mammals, The American Museum of Natural History, New York; UF, Vertebrate Paleontology Collec- tion, Florida State Museum, University of Florida, Gainesville; L.F., Local Fauna, a geographically and stratigraphically restricted fossil assemblage (see Tedford, 1970).

SYSTEMATIC PALEONTOLOGY

Class MAMMALIA Linnaeus, 1758 Order ARTIODACTYLA Owen, 1848

Infraorder OREODONTA Osborn, 1910 Family MERYCOIDODONTIDAE

Thorpe, 1929 Subfamily PHENACOCOELINAE Schultz

and Falkenbach, 1950 PHENACOCOELUS LUSKENSIS

(Schultz and Falkenbach), 1950 Text-figs. 1, 2, 3

Holotype.-F:AM 44853A, skull, mandible and probably associated postcranial elements, from Harrison Formation, late Arikareean Land Mammal "Age" (sensu McKenna, 1965; Hunt, 1978; and Tedford et al., pers. comm.;

002 2-3360/80/0054-0093$03.00 93



BRUCE J. MACFADDEN

0S cg

TEXT-FIG. 1-Oreodont localities in Florida (from north to south): Thomas Farm L.F., early Heming- fordian (early Miocene), Gilchrist Co.; Buda L.F., late Arikareean (early Miocene), Alachua Co.; 1-75 L.F., Whitneyan (late Oligocene), Alachua Co.; Martin-Anthony Roadcut, locality of Phenacocoelus luskensis, late Arikareean, Marion Co.; and Brooksville L.F., late Arikareean, Hernando Co.

see discussion below), 4 km SW of Van Tassel, Niobrara County, Wyoming (Schultz and Fal- kenbach, 1950, p. 122).

Previously reported distribution. -Restrict- ed to type locality.

Referred specimen.-UF 24202, fragmentary right palate and anterior portion of zygomatic arch with right C1, pl_p3, broken root of P4, alveoli for M1, M2-M3, fragment of left premaxillary with partial left canine root.

Locality, horizon, and age. -Martin-Antho- ny Roadcut, junction Martin-Anthony Road

and Route 441, NE corner Sec. 12, T14S, R21E (U.S. Geol. Survey Reddick 71/2' Quad.), 11.5 km N of Ocala, Marion County, Florida, elevation about 45 m (Text-fig. 1). Specimen collected by Prof. H. K. Brooks from Unit 9 of measured section (Brooks, 1967), which is either Tampa Limestone or basal limestone unit of Hawthorne Formation (Nicol et al., 1976). Age is late Arikareean based on correlation to the other known oc- currence of this species in eastern Wyoming (see Discussion below).

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EARLY MIOCENE OREODONT

A

/

,

0 1 2cm l I I

TEXT-FIG. 2-Phenacocoelus luskensis, UF 24202, fragmentary right palate with C1, P-_p3, alveoli M1, and M2-M3, from "Unit 9" at the Martin-Anthony Roadcut, Marion Co., Florida, late Arikareean (early Miocene). A, Lateral view. B, Occlusal view. Note: This specimen consists of three pieces still imbedded in the limestone, and some reconstruction was done when preparing this illustration in order to align the tooth row.

Description. -Medium-sized oreodont with mesodont dentition (Table 1). A portion of the left premaxillary is preserved with a fragment of the left canine root. Anterior portion of right zygomatic arch is preserved; it extends ante- riorly to above M1 and is not inflated as is the condition in some other oreodonts.

The canine is robust and extends far below the occlusal surface of the premolar (Text-fig. 2A). The posterior portion of this tooth has a well-developed wear facet for occlusion with the lower caniniform P,. On the internal sur-

face of the canine there is a distinct groove similar to that of F:AM 44853A (other groups of oreodonts, e.g. the merychyines, also have this groove). The relative robustness of the canine and the other characters discussed below are derived phenacocoeline characters that separate this group from other subfamilies of oreodonts. Some merychine oreodonts are of similar size and superficially similar dental morphology; however, this subfamily lacks the robust canine present in the phenacocoelines (also see Stevens, 1977, p. 36).

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TABLE 1-Dental measurements (mm) for Phenacocoelus luskensis from Florida and Nebraska.

C P' P2 p3 P4 M1 M2 M3

Apa Tb AP T AP T AP T AP T AP T AP T AP T

UF 24202 Right 7.7 8.3 7.9 6.0 11.1 8.6c 10.4 10.3 - - - 17.3 19.9 20.6 19.5c

F:AM 44853A Holotype Right 7.3 8.8 9.2 7.6 11.9 10.8 11.2 10.7 9.6 13.3 14.5 15.4 17.9 19.7 21.5 19.6 Left 8.4 9.3 8.8 7.1 11.4 10.4 11.4 11.3 9.9 13.4 14.8 16.0 18.1 18.9 22.4 20.3

a Greatest anteroposterior length. b Greatest transverse width. c Measurement approximate.

Between the canine and P1 of UF 24202 is a diastema that measures 5.4 mm and is similar to that of F:AM 44853A (right = 5.1 mm, left = 4.8 mm). P1 and p2 are oriented obliquely relative to the tooth row, as is the case in advanced oreodonts (Stevens et al., 1969; Woodburne et al., 1974; Stevens, 1977). P1 has an anterior internal (also called inter- mediate) crest, and posteriorly there is a large wear facet. The external cingulum on UF 24202 is very poorly developed on P1, poorly developed on P2, and moderately developed on p3. P2 and P3 have anterior internal crests, primary cusps, and posterior crescents (see Stevens et al., 1969, Fig. 9F, for cusp termi- nology). The anterior transverse widths of p2 and P3 are narrower than the posterior widths. Frailey (1979), in his study of the Buda L.F., stated that one character complex distinguish- ing the Phenacocoelinae from other subfamilies of oreodonts is the anteroposteriorly com- pressed P3 that approaches P4 in outline. In the P3 of UF 24202, the anterior portion is reduced; however, based on examination of F:AM specimens, this is also the case in other subfamilies of oreodonts, for example, the Merychyinae. Therefore, the significance of this character to diagnose the Phenacocoelinae is somewhat doubtful.

The P4 is represented only by a broken root. M1 is broken at the base of the crown so that the alveoli and top of the roots are exposed. The M2 and M3 have well-developed external cingula. There is a poorly developed internal cingulum on M2. The development of external and internal cingula, i.e., progressively more distinct posteriorly, is similar in both UF 24202 and F:AM 44853A. The molars of UF 24202 have the characteristic oreodont pat-

tern. M3 is roughly square in outline and does not have the well-developed posterior projec- tion of the posterior style of the ectoloph characteristic of many oreodonts that results in a roughly triangular outline for this tooth. In side view the cheek teeth form an arcuate grinding surface characteristic of many oreodonts rather than the flat surface seen in many other ungulates (Text-fig. 2A).

P. luskensis from both Nebraska and Flor- ida are of similar size to P. leptoscelos from the late Arikareean or early Hemingfordian of Texas and California; however, these two species differ in that P. luskensis is less hyp- sodont than P. leptoscelos (Stevens et al., 1969; Woodburne et al., 1974; Stevens, 1977).

DISCUSSION

The oreodont specimen from "Unit 9" of the Martin-Anthony Roadcut, Marion County, Florida, compares favorably in size, robust development of the canine, and degree of me- sodonty with the holotype of Phenacocoelus luskensis, F:AM 44853A, from the Harrison Formation of Niobrara County, Wyoming.

Schultz and Falkenbach (1950) originally assigned the species P. luskensis to the genus Hypsiops. Stevens et al. (1969) described the new species leptoscelos from the Castolon L.F. of Big Bend National Park. Based on additional cranial material not available during the original description of the Castolon L.F., Stevens (1977) questionably transferred the species leptoscelos to the genus Phenaco- coelus. Stevens (1977, p. 39) stated: "At the time that ?Phenacocoelus leptoscelos was described, I thought that it was related to the species that Schultz and Falkenbach (1950) had described as 'Hypsiops luskensis,' and be-

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TEXT-FIG. 3-Chart showing lithostratigraphic, time, and time-rock terms used in this report. A, Upper part of Martin-Anthony Roadcut stratigraphic section. "Unit 9" lies on clastics and carbonates and unconformably above the late Eocene Crystal River Formation (Brooks, 1967). B, North American Land Mammal "Ages" with dashed approximate boundaries (Tedford et al., pers. comm.). C, European Stages with dashed approximate boundaries (Berggren and Van Couvering, 1974; Van Couvering and Berggren, 1977; Van Couvering, 1978). D, Cenozoic Epoch (same references as for C). E, Absolute time scale (approximate myBP). Dates used to calibrate this column are from Evernden et al. (1964), Hunt (1978; pers. comm), and Tedford et al. (pers. comm.).

cause of this I referred it to the genus Hyp- siops. ?Phenacocoelus leptoscelos (as well as 'H. luskensis'), however, has no close affinity to the type species of Hypsiops, H. brachy- melis. As demonstrated by its cranial morphology, ?Phenacocoelus leptoscelos is related more closely to Phenacocoelus, based on [the genotypic species] P. typus Peterson (1907), than it is to any other Arikareean oreodont genus."

The conclusions of Stevens (1977) that P. typus, ?P. luskensis, and ?P. leptoscelos are closely related is well substantiated by numerous cranial and dental characters. In short, I believe that these similarities are so close that

the species P. luskensis (and P. leptoscelos) should (not questionably) be included in the genus Phenacocoelus.

The specimen of Phenacocoelus luskensis, UF 24202, was collected from "Unit 9" (Text- fig. 3A) of the stratigraphic section described by Brooks (1967). There is some controversy as to the stratigraphic assignment of "Unit 9." Brooks (1967) stated that this limestone "Unit 9" is Tampan in age. Espenshade and Spencer (1963), in their stratigraphic study of northern Florida, did not recognize the Tampa Lime- stone in Marion County. It appears that they considered "Unit 9" to be a basal member of the Hawthorne Formation. There is volumi-

l

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nous literature on the problems and history of the Florida Miocene time-rock and time terms "Tampa Limestone," "Tampan Stage," "Haw- thorne Formation," and "Hawthorne (or "Alum Bluff') Stage." A comprehensive discussion of this problem is beyond the scope of this report (see Mansfield, 1937; Espenshade and Spencer, 1963; Puri and Vernon, 1964; and Weisbord, 1973). The invertebrate fauna from "Unit 9" at the Martin-Anthony Roadcut is presently not well enough known to be biostratigraphically useful. There should be lithological criteria to distinguish between the Tampa Limestone and the Hawthorne For- mation. Puri and Vernon (1964, p. 118) stated that: "Lithologically, the Tampa consists of sand, silts, marls, subordinate limestone, and fuller's earth downdip." Espenshade and Spencer (1963, p. 17) stated that: "The Haw- thorn[e] Formation in this region [north peninsular Florida], as defined here, consists of a sequence of beds of distinctive lithologies- limestone, dolomite, phosphatic dolomite, clay, phosphatic clayey sand, and phosphorite

. .." Therefore "Unit 9" cannot presently be allocated to either the Tampa Limestone or the Hawthorne Formation based solely on lithological criteria. With the absence of diagnos- tic biostratigraphic or lithological criteria, "Unit 9" at the Martin-Anthony Roadcut is considered here to be either the Tampa Lime- stone or a basal limestone unit of the Haw- thorne Formation. Detailed studies of con- trasting carbonate petrologies or characteristic invertebrate faunal assemblages might resolve this problem in the future.

At the Martin-Anthony Roadcut, "Unit 9" lies unconformably above the late Eocene Crystal River Formation (Upper Ocala Group, Text-fig. 3A, see also Nicol et al., 1976). Clas- tic sediments assigned to the Hawthorne For- mation lie above "Unit 9." In these Hawthorne clastic sediments, there are remains of du- gongs, turtles, and a few biostratigraphically significant specimens of land mammals. These include a large temnocyonine amphicyonid (UF 24203; identification by Hunt, pers. comm.), cf. Menoceras cooki (UF 24204), and a small camelid (UF 24205). The small camelid is significant in that it represents a taxon described in the late Arikareean Buda L.F. (Frailey, 1979). The close similarity of UF 24204 to Menoceras cooki (the latter is

common in the Harrison Formation of northwestern Nebraska and adjacent Wyoming) indicates an Arikareean age. The large temnocyonine amphicyonid indicates a late Arikareean age (Hunt, pers. comm.). Based on the biochronology of the land mammals at the Martin-Anthony Roadcut, there appears not to be a substantial amount of time represented at the unconformity between "Unit 9" and the overlying Hawthorne clastic sediments.

There are several reasons that support a correlation between the later halves of both the Arikareean Land Mammal "Age" and the Aquitanian European Stage. The amphicyonids described from the Arikareean sediments of northwestern Nebraska appear to be contemporaneous with the same taxa known from the medial Aquitanian of Europe (Hunt, 1972; Hunt, pers. comm.). The subsequent appear- ance in North America of numerous Eurasian immigrant carnivore taxa during the early Hemingfordian Land Mammal "Age" indicates an approximate equivalence with the early Burdigalian European Stage (Tedford and Frailey, 1976). In addition, based on faunal criteria, it has been suggested for some time that the Arikareean-Hemingfordian and Aquitanian-Burdigalian boundaries are roughly contemporaneous (e.g. Wood et al., 1941; Wilson, 1960). More recently, precise calibrations of the Neogene time scale in Eu- rope place the Aquitanian-Burdigalian boundary at roughly 19-21 myBP (Berggren and Van Couvering, 1974; Van Couvering and Berggren, 1977; Van Couvering, 1978). In North America, the Arikareean-Hemingfordi- an boundary is approximated by a radiometric (fission-track, bulk glass shards) date from the Upper Harrison Formation of 19.7 ? 4.1 myBP (Hunt, 1978). Present fieldwork by the University of Nebraska in western Nebraska is aimed towards the goal of documenting the biostratigraphic transition from Arikareean to Hemingfordian "Ages" as represented by mammalian faunal evolution (Hunt, pers. comm.). In summary, based on correlations among Florida, mid-continental North America, and Europe, it is suggested that "Unit 9" and the overlying clastic sediments of the Hawthorne Formation at the Martin-Anthony Roadcut are late Arikareean in age and roughly equivalent to the late Aquitanian European Stage.

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Oreodonts were extremely abundant, taxonomically diverse, and geographically widespread in North America during the Oligocene and the beginning of the Miocene epochs, a time interval spanning some 20 million years. However, until recently, oreodonts were vir- tually unknown from the Gulf Coastal region. The conspicuous absence of a group so abundant elsewhere has not been easily explained. Firstly, it could have been a result of the fact that there were only a few well-known appropriate-aged terrestrial vertebrate localities in this region, e.g. the Miocene Texas Gulf Coastal Plain sequence (e.g. Quinn, 1955; Wilson, 1956; Patton, 1969b) and the Thomas Farm site in northern Florida, which is the best-known locality in eastern North America (e.g. Romer, 1948; Olsen, 1962). A second fac- tor contributing to the absence of oreodonts in this region could have been a result of zoogeographic phenomena such as climatic filters. In recent years, as Gulf Coastal medial Tertiary terrestrial vertebrate faunas are becoming bet- ter known, additional data can be added to resolve this problem.

Admittedly, without any early and medial Oligocene sites, we only have knowledge of the latter half of the Gulf Coastal history of oreodonts. In this region, the first oreodonts are recorded in the Whitneyan (late Oligocene) 1-75 L.F. from Alachua County, Florida (Text-fig. 1; Patton, 1969a). Due to the fact that this collection has not yet been described in detail, the phylogenetic affinities of these oreodonts are not yet certain. The next record of oreodonts comes from the late Arikareean of Florida, including the Buda L.F. from Ala- chua County, the Brooksville L.F. of Hernan- do County, and the Phenacocoelus luskensis specimen described in this report from Marion County. These occurrences are all represented by the Phenacocoelinae (Frailey, 1979; this report). During the Hemingfordian, oreodonts are known from the Garvin Gully L.F. of Tex- as (e.g. Quinn, 1955; Patton, 1969b) and the Thomas Farm L.F. of Gilchrist County, Flor- ida (Maglio, 1966). These occurrences, which together are only represented by a few fragmentary specimens, are referred to cf. Meryc- hyus (subfamily Merychyinae). In the post- Hemingfordian sequence of the Texas Gulf Coast, one specimen of Ticholeptus rileyi (subfamily Ticholeptinae) is known from the

Barstovian (medial Miocene) Cold Spring L.F., and one specimen of Ustatochoerus pro-

fectus (subfamily Ticholeptinae) is known from the Clarendonian (early late Miocene) Lapara Creek L.F. There are no oreodonts known from the post-Hemingfordian of Flor- ida; however, it is not clear if this is a result of lack of well-known localities or zoogeographic factors. By late Clarendonian time oreodonts became extinct on the midcontinent (Schultz and Falkenbach, 1969). In the very rich latest Clarendonian Love Bone Bed of Alachua County, Florida (Webb, MacFadden, and Baskin, pers. observ.), and some abundant but presently unpublished Clarendonian Lower Bone Valley sites (Waldrop, pers. comm.), there are no records of late or "relic- tual" oreodonts. This absence probably re- flects the true zoogeography of this group at that time.

Returning to the question of why the Gulf Coastal region does not have oreodonts abun- dantly represented in late Oligocene to late Miocene sediments; this absence is apparently a result of zoogeographic phenomena rather than due to inadequate sampling. When present at abundant localities such as Thomas Farm, oreodonts are only known from a single or a few specimen(s). The Gulf Coastal oreodonts (not considering the presently uniden- tified 1-75 specimens) are restricted to three closely related subfamilies; Phenacocoelinae, Merychyinae, and Ticholeptinae (see Schultz and Falkenbach, 1968, p. 416-24; also Ste- vens, 1977). It is not surprising that in post- Arikareean sediments only merychyine and ticholeptine oredonts are known from the Gulf Coastal region, because these were among the few subfamilies that were extant at that time elsewhere. However, it is interesting that only phenacocoelines are known from the three Arikareean sites in Florida, when at the same time in the midcontinent oreodonts are abun- dantly represented by several subfamilies (including the Phenacocoelinae).

The low diversity of oreodonts in this region might have resulted from zoogeographic phenomena such as a climatic filter. It is true that many groups of early Miocene mammals are found in both of these regions, implying rela- tively easy migration. However, it has been suggested (e.g. Romer, 1948) that some other mammals common to the midcontinent, such

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as rhinoceroses, chalicotheres, and anchithe- rine horses are rare in the Gulf Coastal region, and they were probably affected by zoogeographic filters as were the oreodonts.

ACKNOWLEDGMENTS

Prof. H. K. Brooks collected the oreodont specimen and kindly donated it to the Florida State Museum. I thank Beryl Taylor for per- mission to study relevant F:AM specimens un- der his care and for his help while I studied at the American Museum of Natural History. Henry Galiano, Robert M. Hunt, Jr., Muriel Hunter, Earl Manning, John F. Meeder, An- thony F. Randazzo, Thomas Scott, and John S. Waldrop provided valuable suggestions that improved this research. Jon A. Baskin and S. David Webb critically read the manuscript. Howard Converse skillfully prepared the Florida oreodont from very hard matrix. Nancy Halliday and assistants prepared the Text-figures. S. Sidaway and Rhoda J. Rybak typed the manuscript. This research was sup- ported partially, by National Science Founda- tion Grant DEB 78-10672.

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MANUSCRIPT RECEIVED DECEMBER 11, 1978 REVISED MANUSCRIPT RECEIVED MAY 20, 1979

The University of Florida contributed $500 to- ward publication of this article. University of Flori- da Contribution to Vertebrate Paleontology num- ber 178.

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An Early Miocene Land Mammal (Oreodonta) from a Marine Limestone in Northern Florida

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