Shuotherium

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Shuotherium
Temporal range: Middle-Late JurassicMiddle Jurassic–Late Jurassic
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
(unranked): Yinotheria
Chow & Rich 1982
Order: Shuotheridia
Chow & Rich 1982
Family: Shuotheriidae
Chow & Rich 1982
Genus: Shuotherium
Chow & Rich 1982
Species

Shuotherium is a fossil relative of the monotremes known from Bathonian (Middle Jurassic) layers of the Forest Marble Formation, England, and from Middle-Late Jurassic layers of the Shaximiao Formation of Sichuan, China.[1]

The original holotype is composed of a partial dentary and seven teeth (two which are incomplete). The holotypes for other species of this genus are solely represented by isolated molars. Shuotherium, along with Pseudotribos has been placed in the Order Shuotheridia, Family Shuotheriidae as a sister taxon of the Australosphenida (see, Yinotheria).[1]

Description[edit]

In it lower molars, the talonid is situated in front of the trigonid, such a unique dental form is distinct from the typical tribosphenic pattern. In this "pseudotribosphenic" trait, the mesial cingulid is expanded to form a pseudotalonid, and its distal talonid is underdeveloped. It shares with Australosphenida a thin, slender dentary but differs from the non-monotreme Ausktribosphenida by having more developed postdentary trough. Its dental formula has been reconstructed as: <p4, m3.[1][2]

Kielan-Jaworowska, Cifelli & Luo 2002 had this to say regarding the fossil:[2]

In our view, the most compelling evidence as to the affinities of Shuotherium lies in the structure of the last premolar, which shares striking similarities to that of Australosphenida

Lower molar structure of Shuotherium and Australosphenida is obviously quite different, and for this reason we do not place Shuotherium within this Gondwanan clade. Based on the limited evidence available, however, we suggest that Shuotherium is a viable sister-taxon to Australosphenida.

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