It was John Howe who studied the equids of Natural Trap but his manuscript was never published.
Instead, part of his work was included in "Eisenmann V., Howe J., Pichardo M. 2008 (published in 2011) : Old World Hemiones and New World slender species (Mammalia, Equidae). Palaeovertebrata 36(1-4) : 159-233, 73 fig., 4 append. fig., 8 tabl.".
This web article is based on the data he kindly communicated to me.
The details of the data and their elaboration may be found in the Appendix Natural Trap, Appendix.
The doubtful measurements are printed in red and highlighted in yellow ; if "corrected" they appear in blue and are highlighted in blue.
In many cases the referral to a particular species is difficult or impossible, partly because of the material itself, partly because of the measurements chosen by John Howe and his students.
The size range is very large. Although the equid fossils are extremely numerous, all size groups are not equally represented. I believe that are present :
– a large Amerhippus : cranium,teeeth, bones Natural Trap, Large Amerhippus
– an Amerhippus conversidens : cranium, mandibles, bones Natural Trap Amerhippus conversidens
– an Amerhippus cf. pseudaltidens : mandible, teeeth, bones Natural Trap Amerhippus cf pseudaltidens
– an Equus caballus : mandibles, teeth, bones Natural Trap, Caballine