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Arenahippus pernix

Mammalia - Perissodactyla - Equidae

Taxonomy
Eohippus pernix was named by Marsh (1876). Its type specimen is YPM 11304 (lectotype), a set of limb elements (left astragalus and associated distal tibia), and it is a 3D body fossil. Its type locality is Bitter Creek, which is in a Wasatchian terrestrial horizon in the Wasatch Formation of Wyoming.

It was synonymized subjectively with Hyracotherium index by Wortman (1896), Trouessart (1898) and Matthew (1899); it was synonymized subjectively with Hyracotherium vasacciense by Kitts (1956); it was recombined as Hyracotherium pernix by Gingerich (1991) and MacFadden (1998); it was considered a nomen dubium by Granger (1908); it was recombined as Arenahippus pernix by Froehlich (2002).

Synonymy list
YearName and author
1876Eohippus pernix Marsh p. 402
1902Eohippus pernix Hay
1909Eohippus pernix Matthew
1930Eohippus pernix Hay
1991Hyracotherium pernix Gingerich
1998Hyracotherium pernix MacFadden p. 542
2002Arenahippus pernix Froehlich p. 171

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RankNameAuthor
kingdomAnimalia()
Triploblastica
Nephrozoa
Deuterostomia
phylumChordataHaeckel 1847
subphylumVertebrata
superclassGnathostomata
Osteichthyes()
Sarcopterygii
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
Tetrapoda()
Reptiliomorpha
Anthracosauria
Batrachosauria()
Cotylosauria()
Amniota
Synapsida()
Therapsida()
RankNameAuthor
infraorderCynodontia()
Epicynodontia
infraorderEucynodontia
Probainognathia
Mammaliamorpha
Mammaliaformes
classMammalia
subclassTribosphenida()
infraclassEutheria()
Placentalia
orderPerissodactyla()
suborderLophodontomorpha
infraorderEuperissodactyla
Hippomorpha
superfamilyEquoidea
familyEquidae
genusArenahippus
speciespernix()

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

Diagnosis
ReferenceDiagnosis
D. J. Froehlich 2002This taxon lacks any unambiguous autapomorphies but the clade composed of Arenahippus pernix and all more-derived equids is uniquely diagnosed by the presence of P3 paraconule somewhat anterior (Character 24, 0 to 1), lower molar metaconid twinned and equal in size (Character 83, 1 to 2), and lower molar metaconid separation large (Character 84, 0 to 1) but lacks the crenulated M3 heel (Character 103, 0 to 1), the synapomorphy of the next more-derived equid clade.