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Acritohippus isonesus
Taxonomy
Hippotherium isonesum was named by Cope (1889) ["Hypotherium"]. Its type specimen is AMNH 8175, a partial skeleton (A nearly complete skull, cervical vertebrre, pelvis and hind limbs), and it is a 3D body fossil.
It was recombined as Hipparion isonesum by Trouessart (1898), Matthew (1899) and Hay (1902); it was recombined as Neohipparion isonesum by Trouessart (1905) and Lull (1907); it was recombined as Merychippus (Merychippus) isonesus by Stirton (1940); it was synonymized subjectively with Merychippus seversus by Downs (1956), Downs (1961), Kelly and Lander (1988) and Fremd (1994); it was recombined as Stylonus isonesus by Kelly and Lander (1988); it was recombined as Acritohippus isonesus by Kelly (1995) and Kelly (1998); it was recombined as Merychippus isonesus by Gidley (1907), Matthew (1909), Osborn (1918), Matthew (1924), Scharf (1935), Wallace (1946), MacFadden and Nelson (1980), Tedford et al. (1987), Hulbert and MacFadden (1991) and MacFadden (1998).
It was recombined as Hipparion isonesum by Trouessart (1898), Matthew (1899) and Hay (1902); it was recombined as Neohipparion isonesum by Trouessart (1905) and Lull (1907); it was recombined as Merychippus (Merychippus) isonesus by Stirton (1940); it was synonymized subjectively with Merychippus seversus by Downs (1956), Downs (1961), Kelly and Lander (1988) and Fremd (1994); it was recombined as Stylonus isonesus by Kelly and Lander (1988); it was recombined as Acritohippus isonesus by Kelly (1995) and Kelly (1998); it was recombined as Merychippus isonesus by Gidley (1907), Matthew (1909), Osborn (1918), Matthew (1924), Scharf (1935), Wallace (1946), MacFadden and Nelson (1980), Tedford et al. (1987), Hulbert and MacFadden (1991) and MacFadden (1998).
Synonyms
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Synonymy list
Year | Name and author |
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1889 | Hippotherium isonesum Cope p. 451 |
1898 | Hipparion isonesum Trouessart |
1899 | Hipparion isonesum Matthew |
1902 | Hipparion isonesum Hay p. 620 |
1905 | Neohipparion isonesum Trouessart |
1907 | Merychippus isonesus Gidley p. 909 |
1907 | Neohipparion isonesum Lull p. 179 |
1909 | Merychippus isonesus Matthew |
1918 | Merychippus isonesus Osborn p. 101 figs. Plates 6.8, 10.4, 13.1,2, 17.3,4, 42.1,2. Text Figs. 75, 77 |
1924 | Merychippus isonesus Matthew |
1933 | Merychippus praecocidens Russell p. 11 figs. 1-6 |
1935 | Merychippus isonesus Scharf |
1940 | Merychippus (Merychippus) isonesus Stirton p. 181 |
1940 | Merychippus (Merychippus) praecocidens Stirton p. 181 |
1946 | Merychippus isonesus Wallace |
1980 | Merychippus isonesus MacFadden and Nelson |
1987 | Merychippus isonesus Tedford et al. |
1988 | Stylonus isonesus Kelly and Lander |
1991 | Merychippus isonesus Hulbert, Jr. and MacFadden |
1995 | Acritohippus isonesus Kelly |
1998 | Acritohippus isonesus Kelly p. 6 |
1998 | Merychippus isonesus MacFadden p. 547 |
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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.
†Acritohippus isonesus Cope 1889
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†Merychippus isonesus quartus Osborn 1918
†Merychippus isonesus tertius Osborn 1918
Invalid names: Merychippus praecocidens Russell 1933 [synonym]
†Merychippus isonesus quintus Osborn 1918
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Diagnosis
Reference | Diagnosis | |
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H. F. Osborn 1918 | (1) Molars comparatively short-crowned, of true Merychippus
type; (2) protocone and hypocone subequal in size, elongate-oval, with internal spurs approaching protoconule and metaconule respectively; (3) hypocone early joining metaconule; (4) protocone separated half way down the crown; (5) median crest of metaconule and crochet region ptychoid; (6) a pli caballin. (7) Facial region relatively short; (8) a single lachrymo-malar fossa, not well separated. | |
T. S. Kelly 1998 | Differs from Acrito- hippus tertius, A. isonesus, and A. quinni by having the following characteristics: (1) larger size (mean UTRL = 134 mm); (2) relative depth of malar fossa greater (ratio of depth to UTRL = 0.06); (3) upper cheek teeth with slightly less complex fossette pli- cations; (4) P2-M 1 protocones connect with proto- lophs in earlier wear stage (before M3 begins to wear); (5) P2-M 2 plis caballin less persistent, usu- ally worn away when M3 in onset of wear (specif- ically, when M3 metaloph and hypocone beginning to wear). Further differs from A. tertius by having the following characteristics: (1) cheek teeth higher crowned; (2) upper cheek teeth with less curvature; and (3) upper molar protocones slightly more an- teroposteriorly elongated. Further differs from A. isonesus and A. quinni by having P2-M 1 hypoconal grooves worn away at earlier wear stage (when M3 in onset of wear). Further differs from A. quinni by having the following characteristics: (1) relative muzzle length longer (UDL = 40-45% of UTRL); and (2) DPOF not pocketed posteriorly. Also see Table 2 for comparison of species. |