The oldest known amynodontid (Perissodactyla ...

PALEONTOLOGIEIPALEONTOLOGY (PALEONTOLOGIE DES VERTEBRES/ VERTEBRATE PALEONTOLOGY)

The oldest known amynodontid (Perissodactyla, Ceratomorpha), from the early Eocene of Kyrgyzstan

C.R. Acad. Sci. Paris, t. 323, serie II a, p. 1059 a 1065,

Alexander Averianov and Olga Potapova

Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, 199034 St. Petersburg, Russia.

Abstract

1996

New material of Lushiamynodon (?) kirghisiensis Beliajeva, 1971 from the early Eocene (late Ypresian) locality Andarak II in Kyrgyzstan shows that this species does not belong in the genus

Lushiamynodon. According to the relatively anterior position of the infraorbital foramen and of the zygomatic arch it belongs to the tribe Metamynodontyni, whereas Lushiamynodon is a Cadurcodontini. The new genus Andarakodon is erected here for this species. This oldest known member of the Amynodontidae is advanced for two characters mentioned above, which implies an early Eocene differentiation of amynodontine tribes. Keywords: Perissodactyla, Amynodontidae, Andarakodon, Early Eocene, Kyrgyzstan.

Resume

Le plus ancien Amynodontide {Perissodactyle, Ceratomorphe), de I'Eocene inferieur du Kyrgyzstan Du nouveau materiel de« Lushiamynodon » (?) kirghisiensis Beliajeva, 1971 de Ia localite Eocene inferieur (Ypresien superieur) d' Andarak II montre que cette espece n'appartient pas au genre Lushiamy-

nodon. D'apres Ia position relativement anterieure de son foramen infraorbitaire et de son arcade zygomatique, elle appartient

a Ia tribu des Metaminodontini, alors que Lushiamynodon est un Cadur-

codontini. Le nouveau genre Andarakodon est cree pour cette espece, qui devient le plus ancien Amynodontide connu. Ce genre presente deux caracteres evolues, ce qui implique Ia differenciation des tribus d'Amynodontinae des I'Eocene inferieur. Mots-cles: Perissodactyles, Amynodontidae, Andarakodon, Eocene lnferieur, Kirghizstan.

Version Fram;aise abregee

ES Amynodontidae sont l'une des families les plus anciennes des rhinocerotoides. Ses representants les plus typiques ont un crane raccourci dans sa partie faciale, de grandes canines biseautees, des premolaires petites et pas de P1/1, et enfin des M3/subcarrees, dont l'ectolophe a une partie posterieure bien developpee et dejetee labialement (fig. 2). La famille n' etait connue jusqu'ici que de !'Eocene moyen au Miocene inferieur. Or, !'age des localites Andarak I et II, situees dans Ia Formation Alay inferieure (Kirhizstan)' a ete revise comme etant de l'Ypresien superieur, dans !'Eocene inferieur (Averianov et Udovichenko, 1993). De ce fait,

L

l'espece "Lushiamynodon » (?) kirghisiensis de cette localite (Beliajeva, 1971) devient le plus ancien Amynodontidae connu. Du nouveau materiel de cette espece, recolte par les auteurs aAndarak II (fig. 1, 2), permet de reviser Ia position systematique de cette derniere et conduit a decrire le nouveau genre Andarakodon. Ce genre a pour caracteres diagnostiques : sa petite taille, des dents a couronnes basses, des molaires superieures a cingulum lingual marque et presque complet, et le foramen infraorbitaire au-dessus de P4/. D'apres Wall (1980, 1982, 1989) et Wallet Manning (1986), Ia famille des Amynodontidae est divisee en deux sous-familles. Chez les 1250-8050/96/03231059 • $2.00 © Academie des Sciences

Note

presentee par Yves Coppens.

remise /e 20 novembre 1995, acceptee apres revision le 25 juillet 1996.

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A. Averianoy and G. Potapova

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Oldest,amynodontid from Kyrgyzstan

Rostriamynodontinae et dans les deux tribus des Arnynodontinae (Arnynodontini et Cadurcodontini), Ia position relativement posterieure du foramen infraorbitaire et de Ia racine anterieure de !'arcade zygomatique est conservee. Dans Ia tribu des Metamynodontini, Ia reduction de Ia partie preorbitaire du crane est accompagnee par un deplacement de !'arcade zygomatique et du foramen infraorbitaire vers !'avant, jusqu'au niveau de M1/ ou P4/. On observe, chez Andarakodon, une position assez anterieure du foramen infraorbitaire (au-dessus P4/) et de !'arcade zygomatique (au-dessus M1/, fig. 1), ce qui indique sa parente avec les Metamynodontini. Les Lushiamynodon sont, au contraire, des Cadurcodontini primitifs (Wall, 1989). La forme d'Andarak differe des genres conn us de Metamynodontini par des dimensions plus petites (tableau), des cingulums linguaux plus marques sur M1-2/, par des dents jugales a couronnes moins hautes et par une position plus anterieure du foramen infraorbitaire. Du genre Caenolophus (= Euryodon), de !'Eocene moyen et superieur, il differe principalement par des dimensions plus grandes et par une morphologie plus evoluee des M3/. Celles-ci ont un metastyle tres decale labialement et

The Arnynodontidae is a peculiar group of mostly Palaeogene rhinocerotoids previously known from the middle Eocene to the early Miocene of Asia, Europe and North America (Wall, 1989). Amynodontids are usually called aquatic rhinoceroses due to their presumed amphibious habits. However, only some of them were in fact adapted to an amphibious way of life, whereas others lived in terrestrial environments and had cursorial adaptations. All typical amynodontids possess a shortened skull, especially in the facial region, enlarged chisel-like canines, small premolars and no Pl/1, quadratic M3/ with a well developed and labially deflected posterior part of the ectoloph (postmetacrista), and the other molars of relatively simple morphology (fig. 2). Most of these derived features are not shared with other rhinocerotoids, implying an early separation of amyno-

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une grande post-fossette (fig. 2). Le nouveau genre Andarakodon est ainsi justifie. Parmi les Metamynodontini, Andarakodon semble apparente a Zaisanamynodon de !'Oligocene inferieur du Kazakhstan, avec lequel il partage Ia position tres anterieure du foramen infraorbitaire (au-dessus de P4/). D'autre part, l'un des caracteres cites par Wall (1989) comme apomorphe chez les Metamynodontini, le contact frontal-maxillaire, pourrait bien etre primitif, car 1) un contact frontal-maxillaire etroit est typique des condylarthres, des artiodactyles, et meme des perissodactyles primitifs selon Novacek (1986) ; 2) Ia perte de ce contact est due au lacrymal chez les rhinocerotoldes evolues autres que les Arnynodontidae, et a une expansion du nasal chez les Arnynodontidae, ce qui montre !'acquisition independante de ce caractere. Andarakodon etant ancien, nous suspections qu'il ne possedait pas tous les autres caracteres derives des Metamynodontini, fosse preorbitaire reduite, mandibule et arcades zygomatiques epaissies, et orbite haute sur le crane. Seul un materiel plus complet permettra de le verifier. De toutes fa.;;ons, ce genre met en evidence une diversification des tribus d'Arnynodontidae en Asie, plus precoce qu'elle n'etait reconnue jusqu'ici.

dontids from other families. However, deciphering their origins appears difficult because the earliest record of Ceratomorpha and other Perissodactyla is poor. This record recently improved through the discovery in Asia of the early Eocene Orientolophus (Ting, 1993) and the late Palaeocene perissodactyllike Radinskya (McKenna et al., 1989). This new evidence about the early radiation of the ceratomorphs shows the importance of the study of the Palaeocene-early Eocene faunas of Asia for understanding the origin and early evolution of Perissodactyla. It also demonstrates the importance of extending palaeontological explorations beyond the relatively well studied regions, such as China, Mongolia, Pakistan, and India. One of the oldest members of the Amynodontidae is Lushiamynodon (?) kirghisiensis Beliajeva, 1971 from the vertebrate-bearing

Oldest amynodontid from Kyrgyzstan

locality Andarak I in Kyrgyzstan, the age of which was considered to be middle Eocene (Beliajeva, 1971; Russell and Zhai, 1987). Recently, the study of the abundant and diverse chondrichthyan fauna led to a revision of the age of the Andarak vertebrates as late Ypresian ( Cuisian equivalent), i.e. as early Eocene (Averianov and Udovichenko, 1993). Consequently, the Andarak amynodontid has become the oldest known member of the family.

Lushiamynodon (?) kirghisiensis was based on a partial upper dentition. The generic attribution of the species was not questioned byReshetov (Russell and Zhai, 1987, p. 185). However, the species of Lushiamynodon Chow et Xu are larger (Table). They also have the

A. Averianov and G. Potapova

anterior root of the zygomatic arch originating over M2/ , as in cadurcodontins and primitive amynodontids, whereas the Andarak species has its anterior zygomatic root originating over Ml/. According to Wall (1989), Lushiamynodon is a primitive cadurcodontin, possibly a junior synonym of Sharamynodon Kretzoi, 1942. The new material from Andarak, collected by the authors at Andarak II, i.e. in the same beds as Andarak I, allows us to revise the systematic position of this species and to erect a new genus for it, redescribed here.

Abfffeviations: PIN, Palaeontological Institute, Russian Academy of Sciences, Moscow; ZIN, Zoological Institute, Russian Academy of Sciences, St. Petersburg. Fig. 1 Upper tooth rows of Andarakodon kirghisiensis from Andarak II, Kyrguzstan. A-C, fragmentary left and right maxillae with P4/-M3/ (ZIN 34313); D. lingual part of a left P3/ (ZIN 34021 ). A is a labial view, B to D are occlusal views. Scale bar is 1 em: if is infraorbital foramen. Rangees dentaires superieures d'Andarakodon kirghisiensis d'Andarak II, Kirgizstan. A-C. maxillaires droit et gauche fragmentaires portant P4/-M3/ (Zin 34313). D, partie linguale d'une ?31 gauche (ZIN 34021 ). A est une vue labiale. B aD sont des vues occlusales. La barre d'Achelle est de 1 em; if est le foramen infraorbitaire.

I D

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Fig. 2 Reconstruction of the right upper cheek teeth in occlusal view of Andarakodon kirghisiensis (a), based on teeth from both left and right sides, and of Zaisanamynodon borisovi (b), modified from Beliajeva (1971). Scale bar is 1 em.

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· Reconstitution de Ia rangee jugale superieure droite en vue occlusale d'Andarakodon kirghisiensis (a), a partir de dents des cotes gauche et droit, et de Zaisanamynodon borisovi (b), modifiee d'apres Beliajeva (1971). La barre d'echelle est de 1 em.

SYSTEMATIC PALAEONTOLOGY Class: Mammalia. Order: Perissodactyla. Suborder: Ceratomorpha. Superfamily: Rhinocerotoidea. Family: Amynodontidae Scott and Osborn, 1883. Tribe: Metamynodontini Kretzoi, 1942 (sensu Wall, 1982) Andarakodon gen. nov. Type and only known species: Andarakodon kirghisiensis (Beliajeva, 1971). Diagnosis: small amynodontid with relatively low-crowned cheek teeth. Upper molars with nearly complete and well marked lingual cingulum. Infraorbital foramen placed over P4/. Etymology: from the locality of Andarak and Greek odus, meaning tooth. Andarakodon kirghisiensis (Beliajeva, 1971) Comb. nov. Synonyms: Lushiamynodon (?) kirghisisensis sp. nov. in Beliajeva, 1971, p. 40. Lushiamynodon (?) kirghisensis in Dmitryeva and Nesmeyanov, 1982, p. 90.

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Lushiamynodon (?) kirghisiensis in Russell and Zhai, 1987, p. 185. Holotype: PIN 1996/2, fragment of right maxilla with M2-3/, isolated left M1/ and M2/, lingual half of left P3/, and isolated right P4/, all presumably from the same individual (Beliajeva, 1971, fig. 1). Locality: Andarak I. Referred material from Andarak II: ZIN 34021, lingual half of an isolated left P3/ (fig. 1 D); ZIN 34313, both maxillae with M1-3/ and fragmented P4/ from the same individual (fig. 1 A-C). Distribution and age: both localities Andarak I and II are in the lower Alay Formation, Kyrgyzstan, dated late Ypresian (early Eocene) . Description: P3/ is known only from its lingual parts (fig. 2). The metaloph is short, less than one half the length of the protoloph. The lingual cingulum is high and complete. The posterior valley is large and deep. P4/ is short. Its crown is 1.5 times wider than long. The metaloph is significantly shorter than the protoloph, and both ridges are nearly parallel. The ectoloph bears an incipient crista close to the metaloph. M1-3/ are subquadrate in outline. M2/ is slightly longer than M1/. The parastyle and the anterior rib are robust ridges. The ectoloph is til-


Table


Measurements of the upper cheek-teeth in some Amynodontidae (L), length; W, width). Dimensions des dents superieures des quelques Amynodontidae (L), longueur : W, largeur).

M1/

P4/

Andarakodon kirghisiensis: PIN 1996/2 . ZIN 34021 . .. Lushiamynodon menchiapuensis. Rostriamynodon grangeri Metamynodon sp. Paramynodon birmanicus Zasanamynodon borisovi.

M3/

M3/

L

w

L

w

L

w

L

w

16.0 16.1 18.6 20.0 26.0

24.0 19.1 27.4 34.0 46.0

28.0 25.0 32.0 26.0 37.0 41.0 32.0 61.0

28.0 23.7 30.0 38.0 60.0 47.0 43.0 66.0

36.0 30.6 40.0 44.0 58.0 52.0 44.0 79.0

32.0 26.0 33.5 46.0 63.0 55.0 51.0 77.0

29.0

30.0* 26.0 31.0** 52.0*** 61.0***

33.0

54.0

33.0 47.0 58.0 60.0 45.0 65.0

-

****

46.0**** 74.0*

* after Beliajeva, 1971. * * after Chow and Xu, 1965. ***after Wall and Manning, 1986. ****after Colbert, 1938.

ted lingually, especially on the M2/. There is a weak antecrochet on M1-2/. M3/ has a large postmetacrista which is greatly deflected labially and has a large post-fossette. Measurements, maximal length and maximal width, in millimetres. ZIN 34021, P3/, L = 11.1; ZIN 34313 (best preserved teeth), P4/, L = 16.1; M1/, L = 25.0, W = 23.7; M3/, L = 30.6, W = 26.0; M3/, W= 26.0.

DISCUSSION Amynodontid systematics were recently revised by Wall (1982, 1989), and Wall and Manning (1986). The family was divided into two subfamilies. The Rostriamynodontinae include one genus, Rostriamynodon Wall and Manning, 1986, from the middle Eocene (Lutetian) of China. The Amynodontinae include the remaining genera, from the middle Eocene to the early Miocene of Asia, from the middle Eocene to the late Oligocene of North America, and from the Oligocene of Europe. Rostriamynodon retains a long snout, a feature which is considered to be a primitive ceratomorph condition (Wall and Manning, 1986). Characteristically linked with this condition is the posterior position of the infraorbital foramen and of the ante-

rior root of the zygomatic arch. These are placed above M2/ in Rostriamynodon. In Amynodon Marsh, 1877 (Amynodontinae, only member of the tribe Amynodontini) the snout is slightly shortened, but the position of the anterior root of the zygomatic arch is retained (above M2/) and only the infraorbital foramen is shifted more anteriorly, above the anterior root ofM1/. In the remaining tribes of the amynodontids, the Cadurcodontini and the Metamynodontini, the snout is greatly reduced, in different ways. In the evolution of the Cadurcodontini, a tapir-like proboscis was progressively developed (Wall, 1980), which is reflected in skull morphology by the reduction of the nasals and by the expansion of the nasal incision. This was accompanied by a shortening of the snout, but the infraorbital foramen and the anterior root of the zygomatic arch retained their primitive position above M2/ in Eocene forms (shifting above M1/ in some Oligocene forms). In the evolution of the Metamynodontini, reduction of the preorbital portion of the skull was accompanied by an anterior shift of the infraorbital foramen and the anterior root of the zygomatic arch. In Metamynodontini the anterior root of the zygomatic arch usually originates above M1/ and the infraorbital

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foramen is shifted to the level of the anterior root of M1/ in Metamynodon Scott and Osborn, 1929 and Paramynodon Matthew, 1929, and even above the posterior root of P4/ in Zaisanamynodon Beliajeva, 1971. The Andarak amynodontid has an anterior position of the infraorbital foramen (above the posterior root of P4/) and of the anterior root of the zygomatic arch (above M1/), i.e. the features which are characteristic of the Metamynodontini. These derived features are considered here to be synapomorphies of the metamynodontins, and we therefore place Andarak species in this tribe. On the preserved part of the frontal process of the maxilla of the specimen ZIN 34313 there is no trace of the sutural surface for the nasal medial to the sutural surface for the lacrimal. This may indicate the absence of a lacrymo-nasal contact in the Andarak amynodontid, another feature considered as apomorphic for the Metamynodontini (Wall, 1989). The Andarak amynodontid differs from the other known genera of the Metamynodontini by smaller dimensions (table), lowercrowned cheek teeth, the relatively anterior location of the infraorbital foramen above P4/, and a better defined lingual cingulum on M1, 2/. It also differs from Cadurcotherium Gervais, 1873 by the absence of reduction of the parastylar lobe on the upper molars, and of the postmetacrista on M3/. From the middle to late Eocene Caenolophus Matthew and Granger, 1925 (= Euryodon Xu et al., 1979), which is known only by its dentition and which is placed in Amynodontidae incertae sedis by Wall (1989), the Andarak amynodontid differs by 1) its larger size, 2) relatively higher-crowned cheek teeth, 3) complete lingual cingulum on the upper cheek teeth, 4) relatively longer M3/, 5) much more labially deflected and more enlarged M3/ postmetacrista, 6) more developed post-fossette on M3/. Features 1, 2, 4-6 indicate derived conditions for the Andarak species. All the differences from previously known genera listed above justifY the definition of the new genus Andarakodon.

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Within metamynodontines, Andarakodon seems to be more closely related to the early Oligocene Zaisanamynodon from eastern Kazakhstan, according to the derived position of the infraorbital foramen above P4/ in both taxa. Until recently, the Metamynodontini, like the Cadurcodontini, were considered as representing a late middle Eocene (Bartonian) to Oligocene radiation of the Amynodontidae, whereas in the early middle Eocene (Lutetian) the family was represented by more primitive Rostriamynodon (Rostriamynodontinae), Amynodon (Amynodontini) and Caenolophus (Amynodontidae incertae sedis). The previously oldest known metamynodontin, Paramynodon, comes from the Burmese Pondaung fauna, which is now considered late middle Eocene (Holroyd and Ciochon, 1994). The discovery in Kyrgyzstan of Andarakodon, which appears to be a member of Metamynodontini, shows that this tribe originated earlier than was realized before. Could this raise the possibility that primitive metamynodontins might be ancestral to the cadurcodontins? The presence of a frontal-maxilla contact, which was cited as metamynodontin apomorphy by Wall ( 1989), may well be a primitive feature because 1) the narrow frontal-maxilla contact, confined by nasal and lacrimal, is the typical condition for all primitive ungulates (Condylarthra) and for artiodactyls, and apparently was characteristic of early perissodactyls (Novacek, 1986), and 2) in derived non-amynodontid rhinocerotoids the maxilla is excluded from this contact by large lacrimal, whereas in derived amynodontids it is excluded by a process of the nasal, which suggests the independent development of this feature. The primitiveness of the frontal-maxilla contact weakens the list of the derived characters of the Metamynodontini, but does not invalidate the others; reduced preorbital fossa, thickened lower jaw and zygomatic arch, orbit high on the skull. We suspect that Andarakodon, being older than the other metamynodontins, probably lacked some or all of these characters. However, only more complete specimens will provide a test of this hypothesis.


In any case, Andarakodon suggests an early Eocene differentiation of the two amynodontid subfamilies and of at least two of the


three amynodontine tribes. Such radiation of the rhinocerotoid family Amynodontidae in Asia has not been recognized until now.

Acknowledgments: We are grateful to Dr. M. Godinot, Dr. J.J. Hooker and an anonymous reviewer for criticism and editorial help. We thank Mr. G.A. Apanovich for the photographs.

AVERIANOV, A. 0. and UDOVICHENKO, N. 1., 1993. Age of Vertebrates from the Andarak Locality (Southern Fergana), Stratigraphy, Geological correlation, I, pp. 365-367.

NOVACEK, M. J., 1986. The skull ofleptictid insectivorans and the higher-level classification of eutherian mammals, Bull. Amer. Mus. Nat. Hist., 183, pp. 1-112.

BELIAJEVA, E. 1., 1971. New data on Amynodonts of the USSR, Trans. Paleontol. Inst., 130, pp. 39-61 (in Russian).

RUSSELL, D. E. and ZHAI, R.:J., 1987. The Paleogene of Asia: mammals and stratigraphy, Mem. Mus. Nat. Hist. Nat., 52, pp. 1-488.

CHOW MINCHEN and XU YU-XUAN, 1965. Amynodonts from the upper Eocene of Honan and Shansi, Vertebrata Palasiatica, 9, pp. 190-203, (in Chinese with English summary). COLBERT, E. H., 1938. Fossil Mammals from Burma in the American Museum of Natural History, Bull. Amer. Mus. Nat. Hist., 74, pp. 255-434. DMITRYEVA, E. L. and NESMEYANOV, S. A., 1982. Mammals and Stratigraphy of the continental Tertiary deposits of the South-Eastern Middle Asia, Trans. Paleontol. Inst., 193, pp. 1138 (in Russian) .

REFERENCES

TING, S. Y., 1993. A preliminary report on an Early Eocene mammalian fauna from Hendong, Hunan Province, China, Kaupia, 3, pp. 201-207. WALL, W. P., 1980. Cranial evidence for a proboscis in Cadurcodon and a review of snout structure in the family Amynodontidae (Perissodactyla, Rhinocerotoidea),]. Paleontol., 54, pp. 968-977. WALL, W. P., 1982. The genus Amynodon and its relationship to other members of the Amynodontidae (Perissodactyla, Rhinocerotoidea) ,J Paleontol., 56, pp. 434-443.

HOLROYD, P. A. and CIOCHON, R. L., 1994. Relative ages of Eocene primate-bearing deposits of Asia, in : Anthropoid 01igins, FLEAGLE, J.G. and KAY, R.F., Eds., Plenum Press, New York, pp. 123-141.

WALL, W. P., 1989. The phylogenetic history and adaptive radiation of the Amynodontidae, In: The Evolution of Perissodactyls, PROTHERO, D.R. and SCHOCH, R.M., Eds., Oxford Univ. Press, New York, pp. 341-354.

McKENNA, M. C., CHOW, C. M., TING, S. Y. and LUO, Z. X., 1989. Radinskya yupingae, a perissodactyl-like mammal from the late Paleocene of southern China, In : The Evolution of Perissodactyls, PROTHERO, D. R. and SCHOCH, R. M., Eds., Oxford Univ. Press, New York, pp. 79-101.

WALL, W. P. and MANNING, E., 1986. Rostriamynodon grangeri, n. geu., n. sp. of amynodontid (Perissodactyla, Rhinocerotoidea) with comments on the phylogenetic history of Eocene Amynodontidae,J Paleontol., 60, pp. 911919.

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