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Juramaia sinensis
Taxonomy
Juramaia sinensis was named by Luo et al. (2011). Its type specimen is BMNH PM1143, a partial skeleton, and it is a 3D fossil preserving soft parts. Its type locality is Daxigou, which is in an Oxfordian terrestrial shale in the Tiaojishan Formation of China. It is the type species of Juramaia.
Synonymy list
| Year | Name and author |
|---|---|
| 2011 | Juramaia sinensis Luo et al. p. 442 figs. 1-2 |
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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.
†Juramaia sinensis Luo et al. 2011
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| Z.-X. Luo et al. 2011 | I5–C1–P5–M3/I4–C1–P5–M3 (Fig. 2), with identical formula as the eutherian Eomaia3 and typical count of five premolars and three molars for Cretaceous eutherians1. Molars tribosphenic, with derived eutherian features of distinctive paraconule, incipient metaconule (M2 only), long preprotocrista past the paracone and long postprotocrista past the metacone. The postmetacrista and the extended postprotocrista of an upper molar form two separate ranks of shearing crests that pass the prevallid crest (paracristid) of the succeeding lower molar (Fig. 3). The preparacrista and the preprotocrista form two ranks of shearing crests that pass the postvallid crest (protocristid) of the preceding lower molar. This kind of stepwise or en-echelon shearing is much better developed in Juramaia than in most metatherians17. Distinct from metatherians in lacking the vertical keel of the paraconid and the hypoconulid shelf18, 19 and in lacking the close approximation of the hypoconulid and the entoconid as in Sinodelphys7 or the twinning of these cusps in other metatherians6. Differs from metatherians (except Sinodelphys) in lacking the inflected mandibular angle and flat ventral surface of the angle. Juramaia sinensis is similar to many eutherians in having the posterior mental foramen of the mandible below the p4–p5 junction, by contrast to metatherians that have the posterior mental foramen below m1. Juramaia sinensis is similar to several Cretaceous eutherians in retaining a deciduous dP3 in the middle of the right premolar series1 but differs from metatherians wherein replacement only occurs at the ultimate premolar position6, 20. Juramaia sinensis differs from all australosphenidans in lacking the continuous mesial cingulid and the wrapping cingulid, and from most australosphenidan and pseudotribosphenidan mammals in lacking the postdentary trough on the mandible14, 21, 22, 23, 24. Among the earliest-known eutherians, Juramaia sinensis differs from Eomaia in having a two-rooted upper canine3, and from Acristatherium in having different numbers of upper and lower incisors, a larger M3 and absence of diastemata between the anterior upper premolars6. It differs from Prokennalestes, Murtoilestes and Acristatherium in having a much lower protocone and longer postprotocrista1, 25, 26, from all known Early Cretaceous eutherians in a deeper ectoflexus on P5–M2, and from Montanalestes in having larger lower premolars 3 and 4. See Supplementary Information for full differential diagnosis and summary of morphological distinction from other Mesozoic mammal groups. |
Measurements
No measurements are available
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| Source: s = species, g = genus, subc = subclass | |||||
| References: Luo et al. 2011, Ji et al. 2002 | |||||