The first known mammal is identified using fossil tooth records

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The oldest known extinct mammal has been identified using fossil dental records

The small animal existed at the same time as some of the oldest dinosaurs and sheds light on the evolution of modern mammals

Scientists from the Natural History Museum and King’s College London contributed to this international collaboration led by the Federal University of Rio Grande do Sul (UFRGS) in Porto Alegre

New research has identified the fossil dental record of the oldest known mammal – Quadrangular Brasilodon – a small shrew-like animal that was about 20 cm long and had two pairs of teeth.

Mammalian glands, which produce milk and nourish the young of mammals today, have not been preserved in any fossils found to date. Therefore, scientists have had to rely on “hard tissue,” mineralized bones and teeth that fossilize, to find alternative clues.

dental records date to 225 million years ago (Upper Triassic/Norian), 25 million years after the Permian-Triassic mass extinction event that led to the extinction of around 70% families of terrestrial vertebrates. Morganucodon is generally considered the first mammal but its oldest fossils, represented only by isolated teeth, date from around 205 million years ago.

Dr Martha Richter, science associate at the museum and lead author of the paper, says: ‘Comparative studies with recent mammalian dentitions and patterns of tooth replacement suggest this was a placental lifelong animal. relatively short. Dated to 225.42 million years old, it is the oldest known mammal in the fossil record contributing to our understanding of the ecological landscape of this period and the evolution of modern mammals.

Brasilodon is the oldest extinct vertebrate with two successive sets of teeth that includes only one set of replacements, also known as diphyodontia. The first set begins to develop at the embryonic stage and a second and final set of teeth develops once the animal is born. The tooth replacement pattern occurs with the same temporal and morphological pattern that is a key characteristic of mammals. This differs from that of reptiles which regenerate new teeth many times over their lifetime, the “many-for-one” replacement also known as polyphyodonty.

Diphyodontia is a complex and unique phenomenon which, together with the replacement of teeth, involves profound and time-controlled changes in the anatomy of the skull, for example the closure of the secondary palate (the roof of the mouth) which allows young to suckle, while breathing at the same time. It has also been shown to be linked to endothermy and even placentation (live birth) and fur.

Brasilodon existed at the same time as the oldest known dinosaurs and probably lived in burrows like shrews do today.

This new research pushes back the origin of diphyodontia in Brasilodon and mammals with related biological traits within 20 million years and illuminates the debate about the rise of mammals in deep time.

Professor Moya Meredith Smith, Contributing Author and Emeritus Professor of the Evolution and Development of Dentoskeletal Anatomy at King’s College London, says: “Evidence of how the dentition was constructed during development is crucial and definitive. to show that Brasilodons were mammals. Our article raises the level of the debate over what defines a mammal and shows that this was a much earlier time of origin in the fossil record than previously known.

Dr. Martha Richter concludes: “This research is a collaboration between Brazilian and British scientists, who have brought together their expertise in skull development, dental anatomy, physiology and histology to interpret juvenile and adult fossils of extinct species Brasilodon quadragularis.’

The paper Replacement of the diphyodont tooth of Brasilodon – a late Triassic eucynodont that 2 defies the age of origin of mammals is published in the Journal of Anatomy.

Notes to Editors

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How to cite this article:

Cabreira, SF, Schultz, CL, da Silva, LR, Lora, LHP, Pakulski, C. & do Rêgo, RCB et al. (2022) Replacement of the diphyodont tooth of Brasilodon – A late Triassic eucynodont that challenges the time of origin of mammals. Anatomy Journal, 00, 1–17. Available at: https://doi.org/10.1111/joa.13756


Co-authors:

Sergio F. Cabreiraa, Cesar L. Schultzb, Lúcio R. da Silvaa, Luiz Henrique Puricelli Lorac, Cristiane Pakulskid, Rodrigo CB do Rêgoe, Marina B. Soaresb,f, Moya Meredith Smithg,m and Martha Richterg*

Associação Sul Brasileira de Paleontologia. A V. Vicente Pigatto, 305, Faxinal do Soturno, RS, Brazil.

Universidade Federal do Rio Grande do Sul, Instituto de Geociências, Campus do Vale Av. Bento Gonçalves, 9500 – Porto Alegre – RS – Brazil.
Porto Alegre, Brazil.

Avenida Irmão José Otão, 170/801, 90.035-060, Porto Alegre, RS, Brazil.

Rua Engenheiro João Luderitz, 204, 91130-050, Porto Alegre, RS, Brazil.

Unilasalle University, Av. Vitor Barreto, 2288, Canoas, RS, Brazil.

Universidade Federal do Rio de Janeiro, Departamento de Geologia e Paleontologia, RJ, Brazil.

Department of Earth Sciences, Natural History Museum, SW7 5BD London, UK.

Center for Craniofacial and Regenerative Biology, King’s College London, UK.

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