CONDYLARTH SKULL      Condylarths make up over 70% of the early Paleocene fauna of placental mammals.  Some early species were mouse sized.  Protoungulatum was known from the Late Cretaceous and its teeth had cusps for grinding plant matter.  Although some tooth characteristics link it to the ungulates (cattle, deer, giraffes, horses, rhinos, hyraxes, elephants, whales, sea cows, and extinct groups), it still had the primitive number of teeth and lacked the gap between teeth seen in the ungulates.  It also lacked the postorbital bar and auditory bulla of its descendants.  The first condylarths show links to primitive “zhelestid” mammals known from North America, Asia, and Europe as early as 85 million years ago (Archibald, 1996).  Paleocene animals Pantolambda and Barylambda were sheep- and pony-sized, respectively.  Coryphodon still bore sharp canines.

primitive artiodactyl

BARYLAMBDA coryphodon
     Arctocyon had some jaw characteristics that are more similar to carnivores than herbivores.  Ectoconus had a skull that resembled Arctocyon in its primitive characteristics and was ancestral to later artiodactyls.  It had 5 digits and both bones of the forearm and lower leg that were robust and separate.  It had all the wrist and ankle bones of primitive placentals.

--after Colbert, 1991

      The earliest artiodactyl (a group of “even toed” ungulates including cattle, deer, camels, giraffes, pigs, etc.) was the rabbit sized Lower Eocene Diacodexis, which is similar to condylarths such as Chriacus.  Diacodexis and 4 other early artiodactyls are grouped as Dichiobunid artiodactyls, which are more similar to Oligocene artiodactyls than any living forms.  The ankle of Diacodexis shows characteristics unique to artiodactyls.  Its fibula was reduced and its hind limbs longer than forelimbs.  It still retained the clavicle that later groups would lose and its anklebones were not yet fused.  Its skull and teeth were primitive and its molars lacked a cusp called a hypocone found in later artiodactyls.  The next illustration shows the loss of lateral digits of the legs of early artiodactyls; both possess an ankle bone made of two fused ancestral bones found in some artiodactyl groups (Rose, 1985; Rose, 1996).

diacodesis feet
MESONYCHIANS andrewsarchus
     Because there were no large mammalian predators of the Early Paleocene (creodonts appear in the Late Paleocene and carnivores appear later), a group of condylarths evolved into predators in the Early Paleocene.  Although condylarths were to evolve into many groups of herbivores, the earliest forms lacked many of the later specializations so that this change in lifestyle did not require as many modifications as might be thought. The mesonychians evolved from the condylarths but were carnivorous, not herbivorous like all of the other condylarth descendants.  Some mesonychids had hooves. (Prothero, from Szalay, 1993)
mesyonx harpagolectes
andrewsarchus skull