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Cormohipparion johnsoni
Taxonomy
Cormohipparion johnsoni was named by Woodburne (2007). Its type specimen is F:AM. 71891, a partial skull, and it is a 3D body fossil. Its type locality is Burge Quarry, which is in a Barstovian/Clarendonian terrestrial horizon in the Valentine Formation of Nebraska.
Synonymy list
| Year | Name and author |
|---|---|
| 2007 | Cormohipparion johnsoni Woodburne p. 57 figs. 16-18 |
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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.
†Cormohipparion johnsoni Woodburne 2007
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| M. O. Woodburne 2007 | Based on the type and re- ferred material, Cormohipparion johnsoni is distinguished from all other species of the subgenus Cormohipparion in having an unworn mesostyle crown height of 40–50 mm (table 3B). In addition, figure 18 in compar- ison with figure 13 indicates that C. johnsoni differs from C. occidentale and the other species in having a much shorter muzzle (no.1) and narrower muzzle at the I3 (no. 15). C. johnsoni differs from the XMas- Kat sample of C. occidentale, but from not the Machaerodus and Hans Johnson sam- ples, in the shortness (no. 2) and lesser palatal breadth (no. 13) and in having shorter premolars (nos. 7, 9). It differs from all samples of C. occidentale in the dimin- ished breadth of the frontals (no. 18) and transglenoid region (no. 19) and from all other species in these parameters, as well (except for no. 19 in C. matthewi). C. johnsoni
also has smaller orbit (nos. 28–29) than in any other species of the group, as perhaps befits its plesiomorphic status (see below). The POB is shorter in C. johnsoni and C. merriami, n.sp., than in the other species. The DPOF (no. 33) is sharply shorter in C. johnsoni (and C. matthewi) and ranges to a comparably small size in C. merriami, n.sp., and C. fricki, n.sp. The separation of the IOF relative to the rear of the DPOF (no. 34) is much less in C. johnsoni as compared with C. occidentale or the other species, except C. matthewi, and the lacrimal nearly reaches the rear of the DPOF (no. 39) and extends across about 80% of the POB (table 3A), in contrast to any other species. Especially as regards parameters 2 and 39, the very large range for the standard de- viation is influenced by the small number of specimens, and the overall smaller dimen- sions can be related to the overall smaller size of the skull of C. johnsoni compared with C. occidentale. Still, the very diminished size of parameters 14 (narrow diastema) and 39 (tip to rear of DPOF; table 11) is noteworthy, as is the fact that other parameters are near or contained within the range of those in C. occidentale (fig. 18): no. 7, premolar row length; no. 8, molar row length; no. 12, choanal width; no. 31, facial length; no. 35, height of DPOF relative to the facial crest; no. 36, relative position of the facial crest and DPOF; no. 37, relative height of the IOF from the alveolar row; no. 38, height of rear of DPOF relative to alveolar row; and no. 40, medial depth of DPOF. Cormohipparion johnsoni (fig. 18) differs from C. matthewi (fig. 15) in having a much shorter snout and palate (nos. 1–3) in con- trast to comparably sized premolar and molar rows (nos. 7–9). C. johnsoni also has a narrower palate (no. 13); a greatly nar- rower diastemal region (no. 14) and muzzle (no. 15); a much narrower frontal width (no. 18); and a narrower transglenoid width (no. 19). In contrast to an equally high snout (no. 25) and equally incised nasal notch (no. 30) relative to C. matthewi, C. johnsoni has a smaller orbit (nos. 28–29), a shorter facial region (no. 31), a relatively shorter POB (no. 32), and a somewhat shorter DPOF (no. 33). However, the IOF location relative to the DPOF is similar (no. 34) in C. johnsoni and C. matthewi, but C. johnsoni has a taller DPOF (no. 35), a diminished separa- tion of the facial crest from the DPOF (no. 36), a decreased separation between the IOF and alveolar border (no. 37), a greater separation between the DPOF and alveolar border (no. 38), a lacrimal that is very close to the rear of the DPOF (no. 39; table 11), and a medially deeper DPOF (no. 40). In comparison with C. merriami, n.sp. (fig. 20), C. johnsoni (fig. 18) has a much shorter snout and palate (nos. 1–2); a much shorter premolar and molar row (nos. 7–9); a much narrower palate (no. 13), diastemal region (no. 14), muzzle (no. 15), frontal re- gion (no. 18) and transglenoid region (no. 19); a much smaller snout (no. 25); a smaller orbit (no. 29); a shallower nasal notch (no. 30); and a much shorter facial region (no. 31). Whereas the POB is comparable (no. 32) in the two species, C. johnsoni has a much shorter DPOF (no. 33); a decreased separa- tion between the IOF and rear of the DPOF (no. 34); a much reduced DPOF height (no. 35); a somewhat diminished separation of the facial crest and DPOF (no. 36); and of the IOF relative to the alveolar border (no. 37), a more normative (cf. C. occidentale) separation of the alveolar border and rear of DPOF (no. 38); a lacrimal anterior tip very close to the rear of the DPOF (no. 39, table 11); and a comparable DPOF medial depth. In addition to overall size and crown height, as well as dental complexity, C. johnsoni differs from C. quinni in the more anterior position of the DPOF, reflected in the fact that the lacrimal barely reaches, but does not penetrate, the DPOF. C. johnsoni is the most plesiomorphic member of the C. occidentale group. |
Measurements
No measurements are available
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| Source: g = genus, subf = subfamily, subc = subclass, c = class, subp = subphylum | |||||
| References: Ji et al. 2002, Carroll 1988, Hendy et al. 2009, MacFadden 1998, MacFadden and Cerling 1996, Lillegraven 1979 | |||||
Age range: base of the Barstovian to the top of the Clarendonian or 16.30000 to 9.40000 Ma
Collections: one only
| Time interval | Ma | Country or state | Original ID and collection number |
|---|---|---|---|
| Barstovian - Clarendonian | USA (Nebraska) | Cormohipparion johnsoni (type locality: 18077) |