Tuesday, March 6, 2012

[Paleontology • 2005] Heishanlestes changi • A new spalacotheriid symmetrodont from the Early Cretaceous of Northeastern China

Right dentary and cheek teeth of Heishanlestes changi (IVPP V 7480, holotype)

Symmetrodonts are Mesozoic mammals having lower molars with nearly symmetrical trigonids but lacking talonids. They appear to be stem members of the mammalian clade that led to extant tribosphenic mammals, but the fossil record of symmetrodonts is poor. Here we report a new genus and species of an acute-angled spalacotheriid symmetrodont, Heishanlestes changi, n.gen. and n.sp., represented by well-preserved lower jaws with teeth from the Early Cretaceous of northeastern China. The new mammal has four tightly spaced premolars and three morphological groups of lower molars, in which the first molar has an obtuse trigonid angle and the last two molars have a large neomorphic cusp in the center of the trigonid, a feature not seen in other mammals. Heishanlestes appears to be a specialized member of the spalacotheriid subfamily, Spalacolestinae, which is otherwise only known from North America. The animal probably used the premolars to crush its prey before shearing it with the molars.



SYSTEMATIC PALEONTOLOGY
CLASS MAMMALIA LINNAEUS, 1758
ORDER SYMMETRODONTA SIMPSON, 1925
FAMILY SPALACOTHERIIDAE MARSH, 1887
SUBFAMILY SPALACOLESTINAE CIFELLI AND MADSEN, 1999
Heishanlestes, new genus
TYPE SPECIES: Heishanlestes changi, n.sp.
DIAGNOSIS: As for the type and only species.
ETYMOLOGY: ‘‘Heishan’’ is the name of the county in northeastern China in which the materials of the type species were collected.
DISTRIBUTION AND AGE: As for the type and only species.

Heishanlestes changi, new species
HOLOTYPE: IVPP V 7480, a nearly complete right dentary containing p1–4, m1–6 (figs. 1, 3, 4, 5).
REFERRED SPECIMENS: IVPP V 7481, anterior part of a left dentary containing an erupting canine, p1–4, m1 (figs. 2, 3); IVPP V 7482, anterior part of a left dentary containing p4, m1, and alveolus for p3 (fig. 2).
ETYMOLOGY: ‘‘changi’’ is for Professor Zhenglu Chang, from Liaoning Technical University, for his important contribution to the study of Mesozoic stratigraphy and paleontology of northeastern China during the past 50 years.

Y. -M. Hu, R. C. Fox, Y. Wang and C. Li. 2005. A new spalacotheriid symmetrodont from the Early Cretaceous of Northeastern China. American Museum Novitates 3475:1-20 DOI: 10.1206/0003-0082(2005)475[0001:ANSSFT]2.0.CO;2

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