A new Cretaceous Metatherian mammal from Henan, China.

Shundong Bi,Shuo Li,Xingsheng Jin,Tianming Du

doi:10.7717/peerj.896

Abstract

We report a new deltatheroidan mammal from the Upper Cretaceous of Henna, China. The new taxon, Lotheridium mengi, is based on a nearly complete skull and associated lower jaws with full adult dentition. Deltatheroidans are known mostly from fragmentary specimens from Asia and North America. Previous views on deltatheroidan relationships were diverse, but recent studies favored their metatherian affinity. The new specimen represents the most complete skull known for deltatheroidans and provides additional evidence that deltatheroidans already had the distinctive metatherian dental formula and replacement pattern and several other derived metatherian features, supporting the metatherian status for this clade. The new species also indicates that deltatheroidan mammals were more diverse and had broader geographical distributions than previously thought.

Highlights

Deltatheroida is a clade of small basal metatherian mammals known from the Cretaceous of Asia and North America that have significant implications on the origin of therians and the timing of the eutherian-metatherian diversification
Lotheridium mengi is deeply nested within deltatheroidans and shares with other deltatheroidans the following derived features: the metastylar area on penultimate upper molar reduced, the parastyle small or indistinct, the absence of the metasyle, the metacone and paracone bases confluent, salient postmetacrista strongly developed, last upper molar reduced
It has been proposed that the distinctive marsupial tooth-replacement pattern, in which only the deciduous P3/p3 are replaced and the deciduous P1-2/p1-2 are retained throughout life, was present in Deltatheridium (Rougier, Wible & Novacek, 1998)

Summary

Introduction

Deltatheroida is a clade of small basal metatherian mammals known from the Cretaceous of Asia and North America that have significant implications on the origin of therians and the timing of the eutherian-metatherian diversification. Closely resembles Deltatheridium in having a premaxilla contributing to the alveolus of the canine, a distinctive shelf-like, medially inflected angle, the absence of palatal vacuities, M2 being largest among upper molars, an asymmetrical, relatively smaller M3, a less mesiodistally expanded protocone, small p1, and m4 with double cusped trigonid and vestigial talonid.

Results

Conclusion