(mammalia, creodonta) from the bridgerian (middle ...

Journal of Vertebrate Paleontology 25(1):251–255, March 2005 © 2005 by the Society of Vertebrate Paleontology

NOTE

NEW SPECIES OF LIMNOCYON (MAMMALIA, CREODONTA) FROM THE BRIDGERIAN (MIDDLE EOCENE) MICHAEL MORLO1 and GREGG F. GUNNELL2, 1Forschungsinstitut Senckenberg, Abt. Messelforschung, Senckenberganlage 25, 60325 Frankfurt am Main, Germany, [email protected]; 2Museum of Paleontology, University of Michigan, Ann Arbor, MI 48109–1079; [email protected]

Creodonts are an order of carnivorous mammals that first appeared in the Paleocene and then flourished from the Eocene through Miocene across the northern continents and Africa. Limnocyoninae are a subfamily of hyaenodontid creodonts characterized by having only two molars in the upper and lower dentition (e.g., Matthew, 1909; Gunnell, 1998a; Morlo and Gunnell, 2003). In North America, Limnocyoninae first appear in the early Eocene (Wasatchian NALMA), represented by Prolimnocyon (Matthew, 1915). In the earliest Bridgerian NALMA (Bridgerian Biochrons Br0 and Br1, late early Eocene, see Gunnell, 1998b, for a biochronological subdivision of the Bridgerian), limnocyonines are rare (Matthew, 1909). Morlo and Gunnell (2003) noted the presence of Prolimnocyon Matthew, 1915 (previously known from the Wasatchian only), and Iridodon Morlo and Gunnell, 2003, from Br1a sediments at South Pass, Wyoming, each only represented by a single specimen. In the middle and late Bridgerian (Br2 through Br3, early middle Eocene), limnocyonines are represented by the relatively abundant genera Thinocyon Marsh, 1872 and Limnocyon Marsh, 1872. The relationships of Limnocyoninae to other hyaenodontids are controversial. Polly (1996) performed a phylogenetic analysis in which the limnocyonines Prolimnocyon and Thinocyon were recognized as the sister group of a clade consisting of Arfia Van Valen, 1965 + Hyainailourinae Pilgrim, 1932 (⳱ Pterodontinae Polly, 1996). Gunnell (1998a) set limnocyonines apart from other hyaenodontids in their own family, while Morlo and Gunnell (2003) suggested a closer relationship to those proviverrine genera similar to Prototomus Cope, 1874 (sensu Gingerich and Deutsch, 1989). In this paper we describe a second Br2 species of Limnocyon, a genus previously represented in the Bridgerian by L. verus only. We also briefly outline the temporal distribution of North American Bridgerian limnocyonines and discuss the intrasubfamilial phylogenetic relationships (Fig. 1). Abbreviations—AMNH, American Museum of Natural History, New York; NALMA, North American Land Mammal Age; SMF, Forschungsinstitut Senckenberg; UM, University of Michigan Museum of Paleontology, Ann Arbor; YPM, Yale Peabody Museum, New Haven. SYSTEMATIC PALEONTOLOGY Order CREODONTA Cope, 1875 Family HYAENODONTIDAE Leidy, 1869 Subfamily LIMNOCYONINAE Wortman, 1902 LIMNOCYON Marsh, 1872 LIMNOCYON CUSPIDENS, sp. nov. Fig. 2A–C Holotype—AMNH 140004, left premaxilla and maxilla with alveoli for I1–C1, and complete P1 to M2. Only known specimen, found July 15, 1999 by M. Turnow. Type Locality—American Museum of Natural History Ice Castle Locality, Grizzly Buttes Area, Uinta County, Green River Basin, Wyoming (Alexander and Burger, 2001). Age and Horizon—Middle Eocene, Bridgerian Biochron Br2, Blacksforkian Member, Bridger Formation. Etymology—“cuspidens,” Latin and Greek for “cusped tooth” for the presence of a protocone on P3. Diagnosis—Limnocyon cuspidens is characterized by the combination of the following characters: size similar to L. verus; I1 alveolus half

breadth of I3 alveolus; P2 paracone very high with strong enamel striations, P3 protocone moderate, P3–4 parastyle and posterior heel relatively long; P4–M1 protocone strong; P4–M2 protocone cingula not continuous lingually; M2 metacone small and placed directly posterior to paracone; M3 absent. Differential Diagnosis—L. cuspidens additionally differs from L. verus (Figs. 3A–B) in: P1–2 much narrower and less blunt; P3 protocone present (absent in L. verus); P3–M1 with larger parastyles; P4 with larger metastyle and more anteriorly oriented protocone; M1 labial cingulum more V-shaped; M1–2 lacking cingulum at lingual tip of protocone; and M2 slightly more reduced. L. cuspidens additionally differs from L. potens (Fig. 3C) in: being smaller; having much less blunt teeth; presence of I1; P3 protocone stronger and not posteriorly shifted; P3–4 parastyles longer; P4–M1 protocones less broad; and M1 labial cingulum more Vshaped. L. cuspidens additionally differs from Oxyaenodon (Fig. 3D; see Gunnell, 1998a, for the last review of this genus) in: maxilla relatively longer; P2 well developed; P3 as lowest premolar; P3 with parastyle and protocone; P4 labial cingulum weak; P4–M1 protocones less cusp-like; M1–2 with developed metacone; and M2 talon larger. Limnocyon cuspidens additionally differs from Thinocyon (see Morlo and Gunnell, 2003, for the last review of this genus) in: being larger; having premolars relatively more blunt; P1 much better developed; P3 protocone present; M1 metastyle relatively shorter; P4–M1 protocones stronger; and M2 talon relatively broader. L. cuspidens additionally differs from Iridodon in: being much larger; and having much more blunt teeth. It differs from Prolimnocyon in lacking M3. Description—AMNH 140004 is the only known specimen of L. cuspidens, preserving the left premaxilla and maxilla with P1 to M2. Sutures between the maxilla, premaxilla, lacrimal, and jugal are not ossified, indicating that this specimen represents a young adult. The maxillary foramen is placed directly above the anterior root of P3. The premaxilla is long and narrow with its anterior-most portion being narrower than in L. verus. Consequently, there is less transverse space for the three upper incisors of L. cuspidens. The upper incisors are narrower in the new species relative to those of L. verus, as is verified by the alveoli of I1–2 and the broken root of I1. The alveolus for I1 is much narrower than that of I2, which is about 1.5 times as broad. Both I1 and I2 are about equal in antero-posterior length. The alveolus of I3 is larger still, about twice as large as that of I1. The round I3 alveolus is placed at the antero-labialmost corner of the premaxilla. As is typical for limnocyonines, the upper canine is large relative to the cheek teeth. The labial border of the canine alveolus is broken, obscuring the actual breadth of the tooth root. P1 is separated from C1 and P2 by small diastemata. P1 is well developed, double-rooted, has a high paracone with enamel striations on its labial side, and possesses a posterior heel with a cusp. P2 is a high and short tooth with a small antero-lingual cuspule representing the end of the preparacrista, which runs slightly lingually. The paracone is high, posteriorly angled, and has strong enamel striations. A short posterior heel, which bears a small basal cuspule, is developed. Cingula are lacking on both P1 and P2. P3 is lower than P2 with a paracone that is slightly angled posteriorly. The parastyle extends anteriorly, and bears a relatively large basal cuspule. The paracone has small enamel striations on its lingual side. A well-developed protocone is present and placed directly lingual to the paracone. Consequently, P3 has three roots. At the lingual-most point of the protocone, a small cuspule is developed. Posteriorly, a small meta-

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FIGURE 1. Top, stratigraphic distribution of Bridgerian and Uintan Limnocyoninae. Note that Prolimnocyon antiquus is not yet known from Br0. Bottom, 50% majority-rule consensus tree resulting from a phylogenetic analysis of 11 taxa and 29 morphological characters performed with PAUP. A branch and bound analysis resulted in four most-parsimonious trees of 61 steps with consistency index 0.69 and retention index 0.60. All characters were unweighted and all except character 20 (see Table 1) were unordered. Multistate characters were treated as variable. Notice the exact match of stratigraphic distribution and position in the tree of all Bridgerian and Uintan taxa except P. antiquus, which is too poorly known to be included into the analysis.

style is present with a low metacone and a small cingular cuspule. The tooth has well-developed cingula, which are strongest labial to the metastyle and lingual to the parastyle. P4 is a blunt, compact tooth with a well-developed, cusped parastyle. The paracone is angled posteriorly and has small enamel striations at its labial base. The relatively large and high protocone is placed directly lingual to the anterior margin of the paracone. There is a short, blunt metastyle. With the exception of the anterior and lingual parts of the protocone, the whole tooth is surrounded by strong cingula. M1 has a labio-anteriorly extended parastyle, creating a broadly Vshaped labial cingulum. The paracone and metacone are fused at their bases and appear to be nearly equal in height, although the metacone is

slightly broken. A small paraconule and metaconule are present with the former being better developed. The protocone is very similar to that of P4 but the talon is more basined. The metastyle is well developed, low, and relatively broad. Cingula are present except at the lingual tip of the protocone. M2 is very similar to that of L. verus. It has a labially extended parastyle, a strong paracone, and a smaller metacone placed directly posterior to the paracone. Para- and metaconules are well developed with the latter forming a short, relatively high crest. The talon is relatively deep and there is a distinct protocone. The tooth is relatively shorter than in L. verus, which is why the labial cingulum extends at a lower angle relative to the parastyle. As in M1, cingula are present except at the lingual tip of the protocone.

NOTES

FIGURE 2. AMNH 140004, holotype of Limnocyon cuspidens sp. nov. A, left maxilla in labial view; note high P2 with strong enamel striations, strong parastyles on P3–4. B, left maxilla in occlusal view; note relative size of incisors, presence of a P3 protocone, V-shaped labial border of M1, and M2 metacone directly posteriorly to paracone. C, left maxilla in lingual view. All figures × 0.6.

DISCUSSION AMNH 140004 clearly belongs to the Limnocyoninae based on its upper dental formula of 3.1.4.2 and the morphology of the upper molars (e.g., Matthew, 1909; Morlo and Gunnell, 2003). Of all known limnocyonines it mostly resembles L. verus. The less blunt teeth and the anterior and posterior enlargements of the premolars suggest a different dietary adaptation towards increased carnivory compared to L. verus. However, using the ecomorphological classes of Morlo (1999), both species fall into the same ecomorphospace (Fig. 4). Due to the overall morphological similarity of the postcranium among all Bridgerian limnocyonines (e.g., Matthew 1909; Morlo and Gunnell, 2003), we suppose L. cuspidens to be semifossorial. Limnocyoninae, thus, represent the only semifossorial taxa among carnivorous mammals in Br2, but diversify into small to very small hypercarnivores (Thinocyon) and middle-sized omnivores (Limnocyon). The fact that P3 has a protocone and that the protocone of P4 has well-developed wear striations suggests that lower premolars may have had relatively well-developed posterior heels. This character would be unique among middle Eocene Limnocyoninae, but is present in Wasatchian Prolimnocyon atavus (Matthew, 1915), possibly indicating that the origin of L. cuspidens as well as of Limnocyon generally is rooted in

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FIGURE 3. Upper dentitions of Bridgerian and Uintan Limnocyoninae. A, AMNH 12155, Limnocyon verus, left maxilla with C1–P1, P4–M2 in occlusal view; note P3 lacking protocone, P3–4 with short parastyles, M1 with less V-shaped labial cingulum, M2 with lingual cingulum surrounding protocone, and high angle of labial cingulum relative to parastyle. B, AMNH 19199, Limnocyon verus, left maxilla with P3–M2 in occlusal view; note absence of P3 protocone. C, AMNH 13138, Limnocyon potens, right maxilla with I2–M2 in occlusal view; note blunt teeth, absence of I1, vestigial P3 protocone, large P4–M1 protocones, and nearly straight labial cingulum on M1. D, AMNH 2515, holotype of Oxyaenodon dysclerus Wortman, 1902 (⳱Oxyaenodon dysodus), left maxilla with P1–M2 in occlusal view; note shortened palate, low P1, P3 without protocone, completely fused M1 metacone and paracone, and absence of M2 metacone. All figures × 0.6.

P. atavus, or in a common ancestor. We performed a phylogenetic analysis using PAUP 4.0 (Fig. 1; Tables 1–2) for all Bridgerian and Uintan limnocyonine species (Fig. 1, Table 2) except Prolimnocyon antiquus, which is too poorly known to be included. The best-represented Prolimnocyon species, P. atavus and P. haematus, both from the Wasatchian, as well as the Wasatchian proviverrines Galecyon mordax and Prototomus phobos, were used as outgroup taxa. This analysis supports the placement of L. cuspidens as the sister taxon to L. verus. However, the new taxon provides no additional information to assess the relationships between Oxyaenodon, an Uintan hypercarnivorous limnocyonine that was extremely specialized, and Limnocyon. Of the known Limnocyon species, L. potens appears to be the sister taxon of Oxyaenodon. Morlo and Gunnell (2003) recently published a detailed study of Thinocyon, the most abundant Bridgerian limnocyonine taxon, and argued that only two, highly variable, species were present. Some differences

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exist between L. verus and L. cuspidens (e.g., variably larger protostyles, more or less V-shaped labial cingula on M1, variable cingular development, and metastyle length on M1) that can also be found intraspecifically within T. velox. There are, however, other characters that justify the recognition of the new species L. cuspidens, because they extend the morphological variability of limnocyonine species beyond that demonstrated by specimens of Thinocyon. These include the relative size of the incisors, the presence of a protocone on P3, and the more anteriorly oriented protocone on M1. Further analysis of dental variability in Limnocyon cuspidens awaits discovery of lower dentitions and more upper dentitions. Acknowledgments—We especially thank Miss Anika Hebs (SMF) for producing Figure 1, Jin Meng (AMNH) for lending the type specimen and comparative material, and Jon Bloch (UM) for comments on the phylogenetic analysis. P. David Polly and an anonymous reviewer enhanced the quality of the manuscript by several suggestions.

Morlo, M., and G. F. Gunnell. 2003. Small Limnocyoninae (Hyaenodontidae, Mammalia) from the Bridgerian, middle Eocene of Wyoming: Thinocyon, Iridodon n. gen., and Prolimnocyon. Contributions from the University of Michigan, Museum of Paleontology 31:43–78. Pilgrim, G. E. 1932. The fossil Carnivora of India. Palaeontologica Indica, new series 18:1–232. Polly, P. D. 1996. The skeleton of Gazinocyon vulpeculus gen. et comb. nov. and the cladistic relationships of Hyaenodontidae (Eutheria, Mammalia). Journal of Vertebrate Paleontology 16:303–319. Van Valen, L. 1965. Some European Proviverrini (Mammalia, Deltatheridia). Palaeontology 8:638–665. Wortman, J. L. 1902. Studies of Eocene Mammalia in the Marsh Collection, Peabody Museum. Part I. Carnivora. Paper 7. American Journal of Science (4) 13:197–206. Submitted 16 February 2004; accepted 19 May 2004.

LITERATURE CITED Alexander, J. P., and B. J. Burger. 2001. Stratigraphy and taphonomy of Grizzly Buttes, Bridger Formation, and the middle Eocene of Wyoming; pp. 165–196 in G. F. Gunnell (ed.), Eocene Biodiversity, Unusual Occurrences and Rarely Sampled Habitats. Kluwer Academic/Plenum Publishers, New York. Cope, E. D. 1874. Report upon vertebrate fossils discovered in New Mexico, with descriptions of new species: Chief of Engineers Annual Report, U.S. Government Printing Office, Washington, Appendix FF:589–606. Cope, E. D. 1875. On the supposed Carnivora of the Eocene of the Rocky Mountains. Paleontological Bulletin 20:1–4. Gingerich, P. D., and H. A. Deutsch. 1989. Systematics and evolution of early Eocene Hyaenodontidae (Mammalia, Creodonta) in the Clarks Fork Basin, Wyoming. Contributions from the Museum of Paleontology, University of Michigan 27:327–391. Gunnell, G. F. 1998a. Creodonta; pp. 91–109 in C. M. Janis, K. M. Scott, and L. L. Jacobs (eds.), Evolution of Tertiary Mammals of North America. Volume 1: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals. Cambridge University Press, New York. Gunnell, G. F. 1998b. Mammalian fauna from the lower Bridger Formation (Bridger A, early middle Eocene) southern Green River Basin, Wyoming. Contributions from the Museum of Paleontology, University of Michigan 30:83–130. Leidy, J. 1869. The extinct mammalian fauna of Dakota and Nebraska including an account of some allied forms from other localities, together with a synopsis of the mammalian remains of North America. Journal of the Academy of Natural Sciences of Philadelphia (2) 7:8–472. Marsh, O. C. 1872. Preliminary description of new Tertiary mammals. American Journal of Science and Art (3) 4: Part I:122–128, Part II–IV:202–224. Matthew, W. D. 1909. The Carnivora and Insectivora of the Bridger Basin, middle Eocene. Memoires of the American Museum of Natural History 9:289–567. Matthew, W. D. 1915. A revision of the lower Eocene Wasatch and Wind River faunas, Part I: Order Ferae (Carnivora), suborder Creodonta. Bulletin of the American Museum of Natural History 34:4–103. Morlo, M. 1999. Niche structure and evolution in creodont (Mammalia) faunas of the European and North American Eocene. Géobios 32(2):297–305.

TABLE 1. Characters (bold indicates ordered character) used in phylogenetic analyses 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

p2 posteriorly short (0) or elongate (1) p3 with posterior heel absent (0) or present (1) p3 with posterior cingulum cusp absent (0) or present (1) p3 as high as or higher than p2 (0) or p3 not as high as p2 (1) p4 preprotocristid bowed posteriorly (0) or protoconid straighter (1) m1 with tricuspid talonid (0) or entoconid/hypoconulid merged into talonid edge (1) m1 metaconid higher (0), equal (1), smaller (2) than paraconid or fused (3) m1 hypoconulid highest talonid cusp (0) or hypoconid highest (1) m1 shorter than m2 (0) or longer (1) m1 cristid obliqua angled labially at greater than 30° (0) or less and more posteriorly (1) m2 cristid obliqua angled labially at greater than 30° (0) or less and more posteriorly (1) m2 metaconid higher (0), equal (1), or smaller (2) than paraconid m2 hypoconulid highest talonid cusp (0) or hypoconid (1) m2 larger than m3 (0), much larger (1), or m3 absent (2) P3 with posterior accessory cusp absent (0) or present (1) P3 with protocone large (0), vestigial (1), or absent (2) P3 as high as or higher than P2 (0) or P3 lower than P2 (1) P4 lacking (0), with small (1), or with strong (2) parastyle P4 paracone sloped posteriorly (0) or not sloped posteriorly (1) P4 with protocone weak (0), strong (1), or enlarged (2) M1 metacone as high as paracone (0) or lower (1) M1 metacone fused with paracone higher than half height (0) or completely fused (1) M1 with metaconule present (0) or absent (1) M1 with cingula at protocone strong (0), weak (1), or lacking (2) M2 metacone posterior to paracone (0), lingual (1), or fused (2) M2 with metaconule present (0) or vestigial to absent (1) M2 with cingula at protocone strong (0), expanded (1), or weak or lacking (2) M2 less than two times as broad as long (0) or more than two times (1) M3 present (0), reduced (1), or lacking (2)

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FIGURE 4. Guild analysis of carnivorous mammals in Br2, showing Limnocyoninae as only semifossorial taxa. Included taxa are: Pantolestidae: 1, Pantolestes elegans, 2, Pantolestes longicaudus; Oxyaeninae: 3, Patriofelis ulta; Limnocyoninae: 4, Limnocyon verus, 26, Limnocyon cuspidens sp. nov., 5, Thinocyon velox; Proviverrinae: 6, Sinopa rapax, 7, Sinopa grangeri, 8, Sinopa minor, 9, Sinopa major, 10, Tritemnodon agilis; Machaeroidinae, 11, Machaeroides eothen; Viverravidae, 12, Viverravus gracilis, 13, Viverravus minutus; Miacidae, 14, Miacis parvivorus, 15, Vulpavus palustris, 16, Vulpavus profectus, 17, Vulpavus ovatus, 18, Palaearctonyx meadi, 19, Oodectes herpestoides, 20, Oodectes proximus, 21, Uintacyon edax, 22, Uintacyon vorax, 23, Uintacyon major; Mesonychida: 24, Mesonyx obtusidens, 25, Harpagolestes macrocephalus.

TABLE 2.

Character-taxon matrix used for phylogenetic analysis

Taxon

1

2

3

Thinocyon velox Thinocyon medius Iridodon datzae Limnocyon verus Limnocyon cuspidens n. sp. Limnocyon potens Prolimnocyon atavus Prolimnocyon haematus Oxyaenodon dysodus Galecyon mordax Prototomus phobos

1 1 1 1 ? 0 0 1 0 1 0

1 1 1 0 ? 0 0 0 0 1 0

1 1 1 1 1 1 1 ? 0 1 0/1 1 ? ? ? 1 1 1 1 1 1 1 ? 0 0 0 1 ? 0 0 1 0 0

4

5

6

7

8

1 1/2 0 1 1 0 1 0 0 1 0 0 ? ? ? 1 0 0 1 0 0 0 0 0 1 3 1 0 ? 0 0 1 1

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 0 0 1 0 ? 0 0 0 0 0 0

1 1 0 1 ? 1 1 1 1 0 0

1 1 0 1 ? ? 1 0 1 0 0

2 2 1 2 ? ? 1 1 2 ? 1

0 0 0 0 ? ? 1 1 0 1 1

2 2 2 2 2 2 1 1 2 1 0

0 0 ? 1 1 1 ? 0 0 ? 1

1 2 ? 2 0 2 ? ? 2 ? 1

1 1 ? 1 1 1 ? 0 0 ? 0

0/1 2 ? 1 1 2 1 1 2 ? 1

0 0 ? 0 0 0 0 0 1 ? 0

1 2 ? 2 2 2 0 0 2 ? 0

0 0/1 ? ? 1 ? 1 1 1 ? 1

0 0 ? 0 0 0 0 0 1 ? 0

0 0/1 ? 1 0 1 0 0 0 ? 0

1 1 ? 1 1 0 1 1 2 ? 0

0 1 ? 0 0 1 0 0 2 ? 0

0 1 ? 0 0 1 1 1 1 ? 1

0/1 1 ? 0 0 0 0 0 2 ? 0

1 1 1 1 1 1 1 1 1 ? 0

2 2 2 2 2 2 1 1 2 ? 0