''Eozostrodon'' is an extinct morganucodont

mammaliaform Mammaliaformes ("mammalian forms") is a clade of synapsid tetrapods that includes the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts during the Late Triassic. It is defined a ...

. It lived during the Rhaetian stage of the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

. ''Eozostrodon'' is known from disarticulated teeth from

South West England South West England, or the South West of England, is one of the nine official regions of England, regions of England in the United Kingdom. Additionally, it is one of four regions that altogether make up Southern England. South West England con ...

and estimated to have been less than in head-body length, slightly smaller than the similar-proportioned ''

Megazostrodon ''Megazostrodon'' is an extinct genus of basal mammaliaforms belonging to the order Morganucodonta. It is approximately 200 million years old.

''. ''Eozostrodon'' was described on the basis of two teeth discovered in a quarry near

Frome Frome ( ) is a town and civil parish in Somerset, England, on uneven high ground at the eastern end of the Mendip Hills and on the River Frome, south of Bath. The population of the parish was 28,559 in 2021. Frome was one of the largest tow ...

Somerset, England Somerset ( , ), archaically Somersetshire ( , , ) is a ceremonial county in South West England. It is bordered by the Bristol Channel, Gloucestershire, and Bristol to the north, Wiltshire to the east, Dorset to the south-east, and Devon to ...

, each originally assigned to separate species ''E. parvus'' and ''E. problematicus''. The latter was synonymized in 1971. The identity of and status of ''Eozostrodon'' is controversial. Kühne considered ''Eozostrodon'' to be "one and the same" with ''

Morganucodon ''Morganucodon'' ("Glamorgan tooth") is an early mammaliaform genus that lived from the Late Triassic to the Middle Jurassic. It first appeared about 205 million years ago. Unlike many other early mammaliaforms, ''Morganucodon'' is well represent ...

'' which he described from thousands of fossils he collected in Wales, albeit after the published description of ''Eozostrodon'', claiming "...for a number of good reasons ''Morganucodon'' ought to be used, the name of ''Eozostrodon'' being used for sentimental reasons only or because of ignorance." Jenkins and Crompton in 1979 argued ''Morganucodon'' was a subjective synonym of ''Eozostrodon'', yet Clemens (1979) argued for the distinction. A more recent publication again distinguished the two, noting that ''Eozostrodon'' differs from ''M. watsoni'' in relative size and shape of

premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...

structures.Z. Kielan-Jaworowska, R. L. Cifelli, and Z.-X. Luo. 2004. ''Mammals from the age of dinosaurs: Origins, evolution, and structure.'' Columbia University Press, New York 1-630. Its teeth were typical for an early mammaliaform, being differentiated into premolars and molars with triangular cusps.

References

External links

Restoration of ''Eozostrodon''
Morganucodonta Rhaetian life Late Triassic synapsids of Europe Triassic England Fossils of England Fossil taxa described in 1941 Taxa named by Francis Rex Parrington {{paleo-cynodont-stub