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E. niobrarensis Hay 1913a, type: USNM 4999, Hay Springs, Nebraska, 300ky?
The type cranium belongs to a young adult mare (Fig.1) and 1bis. I have seen only a cast. On it, the cranial height is unusually large and the basilar proportions cannot be ascertained.
As it is, the information on the cranium is poor: large size, muzzle length and breadth moderate.
The bilobated protocones are modertely long; plis caballin are present on all teeth. The enamel pattern is unlike most other horses but the type teeth of E. pacificus and LACM 9G14-10.5 from Rancho La Brea, both probably caballine (Fig.2).
On the lower cheek teeth ectoflexids are shallow even on the molars.
The enamel pattern is caballine and similar to the Rancho La Brea series and some other Hay Springs specimens (Fig.3).
Cups are present on lower I1 and I2; not perfectly developed on I3 (Fig.4).
E. niobrarensis was probaby living in milder conditions than E. alaskae and E. lambei (longer, but not very long, muzzle) and eating a softer food (smaller protocones).