Tuesday, November 7, 2017

[PaleoMammalogy • 2017] Durlstodon ensomi & Durlstotherium newmani • Highly Derived Eutherian Mammals from the earliest Cretaceous of southern Britain


the Purbeck lagoon at dusk with Durlstodon gen. nov. (left foreground), Durlstotherium gen. nov. (right and center foreground) and the theropod Nuthetes holding a captured Durlstotherium (centre middle distance). 

A. Durlstotherium newmani gen. et sp. nov., NHMUK PV M 99991.
B. Durlstodon ensomi gen. et sp. nov.
, NHMUK PV M 99992.

Artwork by Mark Witton. @MarkWitton 

Eutherian mammals (Placentalia and all mammals phylogenetically closer to placentals than to marsupials) comprise the vast majority of extant Mammalia. Among these there is a phenomenal range of forms and sizes, but the origins of crown group placentals are obscure. They lie within the generally tiny mammals of the Mesozoic, represented for the most part by isolated teeth and jaws, and there is strongly conflicting evidence from phenomic and molecular data as to the date of origin of both Eutheria and Placentalia. The oldest purported eutherians are Juramaia from the Upper Jurassic of China, and Eomaia and Acristatherium from the Lower Cretaceous, also of China. Based on dental characters and analyses of other morphological and molecular data, doubt has recently been cast on the eutherian affinities of the Chinese taxa and consequently on the date of emergence of Eutheria. Until now, the only tribosphenic mammal recorded from the earliest Cretaceous (Berriasian) Purbeck Group of Britain was the stem tribosphenidan Tribactonodon. Here we document two new tribosphenic mammals from the Purbeck Group, Durlstotherium gen. nov. and Durlstodon gen. nov., showing highly derived eutherian molar characters that support the early emergence of this clade, prior to the Cretaceous.

Key words: Mammalia, Eutheria, dentition, Early Cretaceous, Purbeck Group, Britain.


Fig. 5. Normal light photographs of studied specimens of eutherian mammal teeth from the Berriasian Purbeck Group of Dorset, southern England; in mesial (A1, B1), distal (A2, B2), lingual (A3, B3), and labial (A4, B4) views.
 A. Durlstotherium newmani gen. et sp. nov., NHMUK PV M 99991. B. Durlstodon ensomi gen. et sp. nov., NHMUK PV M 99992.

Systematic palaeontology
Class Mammalia Linnaeus, 1758
Subclass Tribosphenida McKenna, 1975
Infraclass Eutheria Gill, 1872
Order and Family incertae sedis

Genus Durlstotherium nov.

Type species: Durlstotherium newmani sp. nov., monotypic, see below.

Etymology: In reference to Durlston Bay, Dorset, UK, the locality from where the holotype and only specimen was obtained; and from Greek, therion, beast; a commonly used suffix in the names of mammals.; In honour of Charlie Newman, recognising his intimate local knowledge, willingly shared, and his help in the field.


Genus Durlstodon nov. 
Type species: Durlstodon ensomi sp. nov., monotypic, see below.

Etymology: In reference to Durlston Bay, Dorset, UK, the locality from where the holotype and only specimen was obtained; and from Greek, odontos, tooth.; In honour of Paul Ensom, recognising his major contribution to Purbeck palaeontology.

Fig. 7. Artist’s impression of the Purbeck lagoon at dusk with Durlstodon gen. nov. (left foreground), Durlstotherium gen. nov. (right and center foreground) and the theropod Nuthetes holding a captured Durlstotherium (centre middle distance).

Artwork by Mark Witton. @MarkWitton

Steven C. Sweetman, Grant Smith and David M. Martill. 2017. Highly Derived Eutherian Mammals from the earliest Cretaceous of southern Britain. Acta Palaeontologica Polonica. in press. DOI: 10.4202/app.00408.2017


No comments:

Post a Comment