Better data on Ocepeia: a basal mesonychid from 60 mya

And, in keeping with several recent posts…
Ocepeia is also a baleen whale (mysticete) ancestor (with legs) appearing shortly after the big asteroid impact.

Earlier we looked at a cat-sized herbivore, Ocepeia daouiensis (Gheerbrant et al 2001, 2014; Paleocene, 60 mya; 9 cm skull length; Fig. 1) as a hippo ancestor. And given the data then available (Fig. 1, left) it did look like a hippo ancestor. But, there was less resolution at that node. So, a search for better data recovered a set of CT scans (Fig. 1, right) which cast a new light on Ocepeia, which now nests basal to mesonychids, derived from a sister to Phenacodus. At that node, Ocepeia continues to be a sister to a coeval but unknown hippo ancestor.

Figure 1. Ocepeia: before and after. The original reconstruction is here compared to a tracing of CT scan, duplicated left to right.

Figure 1. Ocepeia: before and after. The original reconstruction is here compared to a tracing of CT scan, duplicated left to right. Ocepeia now nests at the base of the Mesonychidae, close to the origin of hippos, desmostylians and baleen whales.

The pneumatized skull
contains many air spaces. The larger skulls have larger canines and so are considered male. The jugal deepens below the orbit, hiding the posterior molars in lateral view. The premaxilla is transverse. The upper canine rubs against the lower large incsior creating a facet, as in hippos and Harpagolestes.

Ocepeia was found with aquatic taxa
and was probably amphibious. Mesonychids became land hippos. Hippos gave rise to anthracobunids, desmostylians, thick-tailed desmostylians and finally baleen whales.

The name Ocepeia derives from
the initials of Office Chérifien des Phosphates (O.C.P.), the national Moroccan phosphate mining company. In a similar fashion, the name of the basal reptile Eledeceeon, comes from the Livingston Development Corporation.

Gheerbrant E, Sudre J, Iarochene M, Moumni A 2001. First ascertained African “Condylarth” mammals (primitive ungulates: cf. Bulbulodentata and cf. Phenacodonta) from the earliest Ypresian of the Ouled Abdoun Basin, Morocco. Journal of Vertebrate Paleontology. 21 (1): 107–118.
Gheerbrant E, Amaghzaz M, Bouya B and Goussard F and Letenneur C 2014. Ocepeia (Middle Paleocene of Morocco): The Oldest Skull of an Afrotherian Mammal. PLoS ONE. 9 (2): e89739. doi:10.1371/journal.pone.0089739.


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