Amerhippus fraternus and related species, Introduction
This article is not intended to make clear the extremely confused and confusing taxonomy of "Equus fraternus" and of actually or allegedly related equids. It intends only to bring together data and photographs collected in the bibliography or by myself as well as tentative reconstructions of fossils and biometrical and morphological comparisons. Although resemblances do not guarantee conspecificity, I believe they must be pointed.
E. fraternus, Leidy, Proc. Acad. Nat. Sci., 1858, Niobrara, 11, no figure nor type but it is the smaller of the two Niobrara species and that which resembles most a modern horse.
1. Leidy, 1860, 99-122, Pl XV et XVI.
E. fraternus and E. complicatus “appear to have held the same relation to each other as E. primigenius and E. plicidens in Europe.”
In the vicinity of Charleston, hard in texture, stained brown or black, sometimes water-worn.
E. fraternus : teeth neither larger nor more plicated than in the modern horse. Ashley river, John’s Island, S. Carolina, N. Carolina, Natchez Islands, Brunswick Canal (Georgia).
E. complicatus : more plicated and larger.
2. Cope 1892 : Tomolabis because no infundibula.
3. According to Hay (1913), the type was AMNH 9202 an upper worn M1 without protocone.
But Cope has chosen as ‘type’ AMNH 9200, an upper small or middle-sized P2 with grooved mesostyle.
3. Savage 1951, Nomen vanum.
4. Quinn 1957 : Onager altidens, new species. Powers ranch, Gulf Coastal Plain, Texas, Sangamon (75-125 ka ?). Renamed E. pseudaltidens by Hulbert 1995.
5. Azzaroli 1995 and 1998.
Azzaroli referred quite a number of specimens from Irvingtonian and Rancholabrean to E. fraternus. For many of them (Pool Branch FSM 1143 ; Venice UCNP V-4504 ; Hay Springs FAM 116141 broken female ; Texas : Ironbridge AMNH 113791 cast ; Alberta : Medicine Hat) I have no data.
The three remaining specimens
Florida : Cedar Meadow Spring, FAM 116143, Rancholabrean ;
Florida : Pool Branch, casts of cranium and mandible AMNH 95558, Irvingtonian, 460-490 BP ? ;
Nebraska : Hay Springs UNSM 1349 (female with mandible, 6 years), Irvingtonian, 300 BP ?, will be discussed below.
According to Azzaroli the characteristics of E. fratenus are : no infundibula ; strongly flexed skull like in South-American species ; narrow muzzle, small upper cheek teeth exceedingly plicated with long protocones ; lower cheek teeth with shallow vestibular valleys and diverse enamel patterns ; short and slender limb bones.
6. At Leisey Shell Pit 1A (1.07-1.55 My) were found numerous fossils of Equus. Hulbert (1995) referred the Pool Branch skull to Equus sp. A, the most abundant of the three species he recognized at Leisey Shell Pit A.
7. According to Pichardo (2000) E. fraternus is posssibly restricted to the South-East of North America.