Arctocyonides arenae

Arctocyonides arenae

Russell, 1964

Common name Arctocyonid mammal
Fossil group Mammals
Order Arctocyonia
Family Arctocyonidae
Genus Arctocyonides
Taxonomic status Accepted
Geological age Thanetian

Summary

Arctocyonides arenae was a medium-sized late Palaeocene placental mammal, with published estimates placing it at roughly 4–5 kg. It belonged to the archaic mammalian radiation traditionally called arctocyonid “condylarths”, and ecological comparisons suggest a semiterrestrial animal rather than a highly specialised climber or runner.

Its very low-crowned, bunodont cheek teeth formed broad crushing surfaces. That dentition is consistent with a dietary generalist eating fruit and other plant foods alongside insects or small animal prey, rather than a specialised meat-slicing predator. The exact diet is inferred from tooth form and related mammals.

Quick Identification

Look for: very low-crowned, broadly squarish bunodont cheek teeth with rounded cusps and a broad crushing surface. In adult upper P4, Arctocyonides arenae differs from A. weigelti in having a markedly larger protocone, a labial cingulum and a comparatively straight postparacrista. Deciduous upper premolars require especially cautious comparison because directly comparable DP4 material is sparse.

Diagnostic Features

  • Cheek teeth are very low-crowned and broadly squarish, with bunodont rather than strongly sectorial cusps.
  • Upper molars bear a developed hypocone that enlarges the crushing surface.
  • Adult upper P4 has a markedly enlarged protocone compared with Arctocyonides weigelti.
  • A labial cingulum is present on adult upper P4, unlike the condition described for Arctocyonides weigelti.
  • The adult upper P4 postparacrista is comparatively straight; deciduous premolars require caution because directly comparable DP4 material is limited.

Fossil Details

Typical size
Estimated body mass approximately 3.9–5.4 kg.
Fossil material
Tooth, Skull / Cranial Bone
Preservation
Most material is dental or cranial. Isolated teeth may be worn, cracked or incomplete, and loss of cingula, crests or cusp tips can remove characters needed for species-level identification. Deciduous premolars are particularly difficult to assign where comparative juvenile material is limited.

Recorded Fossil Sites

References

  • De Bast, E.; Steurbaut, E.; Smith, T. (2013). New mammals from the marine Selandian of Maret, Belgium, and their implications for the age of the Paleocene continental deposits of Walbeck, Germany. Geologica Belgica, 16(4), 236–244 View reference
  • Halliday, T. J. D.; Upchurch, P.; Goswami, A. (2017). Resolving the relationships of Paleocene placental mammals. Biological Reviews, 92(1), 521–550 View reference
  • Hooker, J. J.; Collinson, M. E. (2012). Mammalian faunal turnover across the Paleocene-Eocene boundary in NW Europe: the roles of displacement, community evolution and environment. Austrian Journal of Earth Sciences, 105(1), 17–28 View reference
  • Hooker, J. J.; Millbank, C. (2001). A Cernaysian mammal from the Upnor Formation (Late Palaeocene, Herne Bay, UK) and its implications for correlation. Proceedings of the Geologists' Association, 112(4), 331–338 View reference
  • Orliac, M. J.; Argot, C.; Gilissen, E. (2012). Digital Cranial Endocast of Hyopsodus (Mammalia, “Condylarthra”): A Case of Paleogene Terrestrial Echolocation?. PLoS ONE, 7(2), e30000 View reference
  • Smith, T.; Smith, R. (2003). Terrestrial mammals as biostratigraphic indicators in upper Paleocene–lower Eocene marine deposits of the southern North Sea Basin. Causes and Consequences of Globally Warm Climates in the Early Paleogene, 513–520. Geological Society of America, Boulder, Colorado View reference
Last Reviewed
22 August 2026 Reviewed by Sam Harris