THE SYSTEMATIC POSITION OF THE SABER-TOOTHED AND HORNED GIANTS OF THE EOCENE:

THE UINTATHERES (ORDER DINOCERATA) BURGER, Benjamin J., Utah State University Uintah Basin Campus, Vernal, UT, 84078

United States of America

Abstract

Ever since their discovery in the American West in 1871, the saber-toothed horned uintatheres,

belonging to the order Dinocerata have defied placement on the mammalian tree. Previous

researchers have suggested a wide range of relationships to insectivores, rodents, condylarths,

proboscideans, pantodonts, and South American xenungulates.

Utilizing a large dataset of characters downloaded from Morphobank, the two best known

Middle Eocene uintatheres species Uintatherium anceps and Eobasileus cornutus were added

to a large character matrix of 4,541 morphological characters sampled across 86 other

mammalian taxa. Parsimony analysis was performed using nearest-neighbor interchange in

Mesquite, as well as search algorithms using TNT to find the most parsimonious placement of

Dinocerata among other mammals. Uintatheres were found to be most closely related to the

xenungulate Carodnia vieirai (together as Uintatheriamorpha).

If the molecular supported Afrotheria clade is held together, Uintatheriamorpha is positioned

within Laurasiatheria (Liptyphla, Pholidota, Carnivora, Perissodactyla and Cetartiodactyla)

excluding Chiroptera. The most parsimonious tree using TNT search algorithms split the

Afrotheria clade across Mammalia, and resulted in the placement of rodents, proboscideans,

hyraxes and sirenians among a polyphyletic ungulate clade including uintatheres. In light of

molecular data for living mammals, uintatheres were found within a monophyletic ungulate

clade and not closely related to Afrotheria. The early Paleocene North American

Protungulatum donnae is considered the most primitive member of a monophyletic clade that

includes Condylarthra, Meridiungulata, Dinocerata + Xenungulata, Perissodactyla, and

Cetartiodactyla. Morphological similarities between proboscideans, sirenians and uintatheres

are likely convergent adaptations.

Uintatheres group within other mesoaxial-grade ungulates, including perissodactyls,

phenacodont condylarths, and South American ungulates, suggesting an interchange

between North and South America during the early Paleocene, and isolation of Africa.

Uintatheres share the following synapomorphies with other mesoaxial ungulates:

1) presence of hooved distal phalanges, 2) weight bore principally by third metacarpal as

central axis of the fore and hind foot, 3) loss of the centrale bone (with no indication of fusion

with scaphoid), 4) lack of a deep cotylar fossa on the astragulus.

The nearest living relatives of uintatheres are rhinos, horses and tapirs.

Methods

To investigate the systematic relationship of uintatheres

with other mammals both living and extinct I utilized the

O’Leary et al. (2013) MorphoBank character matrix which

contains 4,541 morphological characters coded for 86

mammalian species.

Using publications and fossil specimens housed at the

Field House Museum in Vernal, Utah, two of the most

well known uintatheres were added to the character

matrix: Eobasileus cornutus known from the Uintan

North American Land Mammal Age in the Uinta

Formation of Utah and Washakie Formation of Wyoming

and Uintatherium anceps known from the Bridgerian

North American Land Mammal Age of the Bridger

Formation of Wyoming. The resulting character matrix

was analyzed with the computer program TNT to retrieve

the most parsimonious tree (Goloboff et al 2000). As well

as using the computer program Mesquite (Maddison &

Maddison, 2011) to analyze resulting trees and map

morphological characters across various clades.

The Elephant in the Tree (effect of Afrotheria) The Accepted Phylogenetic Tree

References and Acknowledgements

Eobasileus cornutus

The South America Connection

The Importance of Ungulate Feet

Uintatherium anceps

Early Uintatheres from North America

A single most parsimonious tree was

found using a traditional search

algorithm in TNT the results show a

close relationship of uintatheres

with the African Elephant

Loxodonta africana. Such a

relationship harks back to early

notions of Cope (1872), that

uintatheres were an extinct member

of the proboscideans (Wheeler,

1960). However, recent molecular

phylogenies strongly support the

Afrotheria clade, which was not

resolved using morphological

evidence, and members are widely

distributed in the tree. The close

relationship between uintatheres and

proboscideans is likely due to

homoplastic characters associated

with large graviportal adaptions

found in both elephants and

uintatheres. Using molecular

support, the Afrotheria clade was

held as a true monophyletic

grouping, and a new search

algorithm was performed on

morphological characters.

Watch a video

presentation of this

research on

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The xenungulate Carodnia from the Paleocene of South America was found to be the

nearest extinct relative of uintatheres. Carodnia lacks the characteristic horns and

long saber-like canines, but postcranial features in the limbs support this relationship.

This also suggests a biotic interaction between North and South America during the

early Paleocene followed by isolation during the late Paleocene and Eocene.

A clade composed of Xenungulata and

Dinocerata (Uintatheriamorpha) is supported

by a number of synapomorphies, including

traits of the nasal bone, maxilla-frontal

contact, zygomatic arch, and a number of

characters of the posterior premolars, as well

as a number of postcranial features in the feet.

This relationship has been supported by

various authors (Wheeler, 1961; McKenna,

1980; Gingerich, 1985; Schoch and Lucas,

1985; Lucas, 1993) as well as criticized (Rose,

2006). Fossil pantodonts, once thought close

relatives to uintatheres (Osborn, 1898) have

long been argued unrelated based on major

differences in the dentition (Simpson, 1929).

By including more early fossil ungulate

mammals, such as pantodonts in future

studies, the strength of a monophyletic

Uintatheriamorpha clade can be further tested.

FHPR 1151 Eobasileus cornutus from the Washakie Formation of Wyoming

Uintatherium

Uintatherium

Eohippus

Eohippus

Pachyaena

Pachyaena Sus

Hippopotamus Metamynodon

Metamynodon

Hin

d

Fee

t F

ore

Fee

t

The position of the central axis in the feet is an important character that divides the major groups of early ungulate mammals. Uintatheres

exhibit a mesoaxial condition similar to phenacodont condylaths, South American ungulates, and perissodactyls.

Mesoaxial

Feet

Paraxial

Feet

Skull and reconstruction of Eobasileus cornutus based on Field

Museum of Chicago Specimen P 12710 collected from the Uinta

Formation of Northeastern Utah.

Skull and reconstruction of Uintatherium anceps based on American

Museum of Natural History specimen 1694 from the Bridger

Formation of Southwestern Wyoming.

Bathyopsis fissidens

Probathyopsis newbilli

Earlier and smaller forms of uintatheres are known from the early

Eocene and late Paleocene of North America, but were not

included in the analysis because they are known from less

complete skeletons.

I decided to rerun the analysis, but hold the

living taxa belonging to Afrotheria as a true

monophyletic group, and using branch and

bound search algorithm I reanalyzed the

character matrix. The resulting single tree is

less parsimonious, with a tree length of 28,836

meaning that an additional 518 state changes

occurred. This is the most parsimonious tree

that still retains living members of the

Afrotheria within a monophyletic grouping.

The consistency index is 0.189 and retention

index is 0.434. Both trees show a close

relationship of Eobasileus and Uintatherium

with Carodnia, supporting a clade referred as

the Uintatheriamorpha. In the second tree,

Uintatheres were not found to be close to

elephants, and instead placed within the

Laurasiatheria clade, which includes

Euliptyphla (shrews and hedgehogs), Pholidota

(pangolins), Carnivora (cats and dogs),

Perissodactyla (horses and rhinos) and

Cetartiodactyla (cows, hippos, and whales). In

particular uintatheres group within other

mesoaxial-grade ungulates, including

perissodactyls, phenacodont condylarths, and

South American ungulates.

Uintatheres share the following

synapomorphies with other mesoaxial

ungulates: 1) presence of hooved distal

phalanges, 2) weight bore principally by third

metacarpal as central axis of the fore and hind

foot, 3) loss of the centrale bone (with no

indication of fusion with scaphoid), 4) lack of a

deep cotylar fossa on the astragulus.

Cope, E.D. 1872. Notice of proboscideans from the Eocene of southern Wyoming. American Philosophical

Society, Proceedings, 12:580.

Gingerich, P.D. 1985. South American mammals in the Paleocene of North America; pp. 123-137 in F.G. Stehli

and S.D. Webbs (eds.), The Great American Biotic Interchange. Plenum Press, New York.

Goloboff, P., Farris, J., & Nixon, K. 2008. TNT: a free program for phylogenetic analysis. Cladistics 24: 774-

786

Lucas, S. 1993. Pantodonts, tillodonts, uintatheres, and pyrotheres are not ungulates; pp. 182-194 in F.S. Szalay,

M.J. Novacek, and M.C. McKenna (eds.), Mammal Phylogeny: Placentals. Springer-Verlag, New York.

Maddison, W. P. and D.R. Maddison. 2015. Mesquite: a modular system for evolutionary analysis. Version 3.04

http://mesquiteproject.org

Marsh, O.C. 1884. Dinocerata, a monograph of an extinct order of gigantic mammals. United States Geological

Survey Monograph, 10:1-237.

O’Leary, M. A., Bloch JI, Flynn, J.J., Gaudin, T.J., Giallombardo, A., Giannini, N.P., Goldber, S.L, Kraatz,

B.P., Luo, Z-X, Jin Meng, Xijun Ni, Novacek, M.J., Perini, F.A., Randall, Z.S., Rougier, G.W., Sargis, E.J.,

Silcox, M.T., Simmons, N.B., Spaulding, M. Velazco, P.M., Weksler, M., Wible, J.R. Cirranello, A.L. 2013.

The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals. Science 339:6120:662-667.

Data downloaded from http://www.morphobank.org/

Osborn, H.F. 1898. Evolution of the Amblypoda. Part I. Taligrada and Pantodonta. Bulletin of the American

Museum of Natural History 10:169-218.

Rose, K.D. 1996. The beginning of the age of mammals. John Hopkins University Press, Baltimore p. 428.

Wheeler, W.H. 1960. The uintatheres and the Cope-Marsh war. Science, 131: 1171-1176.

Wheeler, W.H. 1961. Revision of the Uintatheres. Peabody Museum of Natural History Bulletin, 14.

Schoch, R. and Lucas, S. 1985. The phylogeny and classification of the Dinocerata (Mammalia, Eutheria).

Bulletin of Geological Institutions, University of Uppsala 11:31-50.

Simpson, G.G. 1929. A new Paleocene Uintathere and molar evolution in the Amblypoda. American Museum

Novitates 387:1-9.

Turnbull, W.D. 2002. The mammalian faunas of the Washakie Formation, Eocene Age, of Southern Wyoming.

Part IV. The Uintatheres. Fieldiana Geology 47:1-189.

Silhouettes used in cladogram downloaded from http://www.phylopic.org Morganucodon by

FunkMonk (Michael B. H.) Ornithorhynchus by Sarah Werning Eomaia by Nobu Tamura Macropus

by Cathy Rattus by Maija Karala and Equus Mercedes Yrayzoz. Help support T. Michael Keesey’s

work at: https://www.patreon.com/tmkeesey

Special thanks to Steve Stroka, and Dale Gray at the Field House Museum in Vernal, Utah for

allowing me to work in their collections and play with their Uintatheres.