August 25, 2011 | 27
If you’ve been with Tet Zoo since the early days, you’ll have seen this image before – and, even if you haven’t seen it on Tet Zoo you might have seen it anyway, since everyone loves this model and it’s mentioned just about any time that entelodonts are. Yes, it’s an entelodont – a member of a group of fossil artiodactyls that inhabited North America, Eurasia and Africa between the Eocene and Miocene, with the oldest species in the group being those of Middle Eocene Asia.
Entelodonts (properly Entelodontidae) have generally been regarded as suiforms (close kin to pigs and peccaries) but some recent analyses have found the sampled members of the group to be members of the hippo + cetacean clade Cetancodontamorpha (O’Leary & Gatesy 2008, Spaulding et al. 2009) and hence fairly well removed phylogenetically from pigs and peccaries. Andrewsarchus, the famous Eocene giant predator or omnivore so often regarded as a mesonychian (or mesonychid), seems to be a cetancodontamorphan close to entelodonts (see the links below for much more on Andrewsarchus).
Anyway, the awesome life-sized model you see in the photos above depicts the Oligocene-Miocene North American entelodont Daeodon (formerly better known by its synonym Dinohyus) and is on display at the Denver Museum of Nature and Science. It’s a shame there’s no scale in these photos: Daeodon was huge (c. 1.8 m tall at the shoulder). The model is fantastically accurate. It even has snot in its nostrils.
Entelodonts are widely regarded as omnivores that scavenged dead animals and, at least sometimes, caught and ate live ones. Evidence for this omnivorous lifestyle comes from their pointed incisors, recurved, pointed, serrated canines*, serrated premolars and an unusually mobile** jaw joint. Further evidence comes from studies on bite strength (Effinger 1998, Joeckel 1990) and from bite marks left on the bones of other mammals (Hunt 2005). Oh yeah, and there’s the discovery of a pile of bitten-in-half little camels from the Early Oligocene, the marks on their bones matching the tooth anatomy of the entelodont Archaeotherium (Sundell 1999) [the adjacent illustration depicting this scene comes from Kent Sundell’s page here]. Massive bony cheek flanges and bony tubercles on the lower jaw might have been used in intraspecific fights, and some specimens preserve skull injuries apparently inflicted by other entelodonts.
* The canines were serrated in juveniles, but the serrations generally became worn away during ontogeny.
** Unusually mobile for an artiodactyl that is.
The postcranial morphology of entelodonts is remarked upon less often than their skull anatomy. Even giant forms had a surprisingly gracile, slender neck. Large neural spines on the anterior thoracic vertebrae show that very large nuchal ligaments were present: the anterior thoracic neural spines of Daeodon are almost on par with those of bison and other tall-spined ungulates. Entelodonts were strongly cursorial, with elongate and slender limbs where the radius and ulna, and tibia and fibula, are often fused together. Unlike pigs, entelodonts were didactyl. Not only were they nasty and with a frightening dentition, they were also fast!
Here’s another entelodont rendition, this time showing Entelodon from the Late Eocene and Early Oligocene of western Europe, Kazakhstan, China, Mongolia and Japan (it’s probably the most widely distributed entelodont). The image is kindly provided by Jaime Chirinos of zooartistica.com and is used with permission.
Entelodon was closely related to Late Eocene-Oligocene Archaeotherium from North America and was a large entelodont, with good remains of E. deguilhemi from France showing that it reached 1.3 m at the shoulder, and 65 cm in skull length. Archaeotherium and Entelodon had shallower skulls than Daeodon, but they would still have been formidable predators and scavengers. In the illustration here they’re feeding on a dead horse.
And I only decided to recycle all of this stuff because I also just featured that peccary article from a few days ago. While looking at entelodont images online, I found this one by my good friend Luis Rey. If you work on dinosaurs you might be rather offended, but isn’t that why we’re here?
For previous Tet Zoo articles on entelodonts, Andrewsarchus and various of their friends and relatives, see…
Refs – -
Effinger, J. A. 1998. Entelodontidae. In Janis, C. M., Scott, K. M. & Jacobs, L. L. (eds) Evolution of Tertiary Mammals of North America. Volume 1: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals. Cambridge University Press, pp. 375-380.
Hunt, R. M. 2005. An Early Miocene dome-skulled chalicothere from the “Arikaree” conglomerates of Darton: calibrating the ages of High Plains paleovalleys against Rocky Mountain tectonism. American Museum Novitates 3486, 1-4.
Joeckel, R. M. (1990). A functional interpretation of the masticatory system and paleoecology of entelodonts Paleobiology, 16, 459-482
O’Leary, M. A. & Gatesy, J. 2008. Impact of increased character sampling on the phylogeny of Cetartiodactyla (Mammalia): combined analysis including fossils. Cladistics 24, 397-442.
Spaulding, M., O’Leary, M. A. & Gatesy, J. 2009. Relationships of Cetacea (Artiodactyla) among mammals: increased taxon sampling alters interpretations of key fossils and character evolution. PLoS ONE 4(9): e7062. doi: 10.1371/journal.pone.00070672
Sundell, K. A. 1999. Taphonomy of a multiple Poebrotherium kill site – an Archaeotherium meat cache. Journal of Vertebrate Paleontology 19 (Supp. 3), 79A.