The virtual brain endocast of Trogosus (Mammalia, Tillodontia) and its relevance in understanding the extinction of archaic placental mammals
Bertrand, Ornella C. (Institut Català de Paleontologia Miquel Crusafont)
Jiménez Lao, Marina (University of Edinburgh. School of GeoSciences)
Shelley, Sarah L. (University of Edinburgh. School of GeoSciences)
Wible, John (Carnegie Museum of Natural History. Section of Mammals)
Williamson, Thomas E. (New Mexico Museum of Natural History and Science)
Meng, Jin (American Museum of Natural History. Division of Paleontology)
Brusatte, Stephen L. (University of Edinburgh. School of GeoSciences)

Data:	2023
Resum:	After successfully diversifying during the Paleocene, the descendants of the first wave of mammals that survived the end-Cretaceous mass extinction waned throughout the Eocene. Competition with modern crown clades and intense climate fluctuations may have been part of the factors leading to the extinction of these archaic groups. Why these taxa went extinct has rarely been studied from the perspective of the nervous system. Here, we describe the first virtual endocasts for the archaic order Tillodontia. Three species from the middle Eocene of North America were analyzed: Trogosus hillsii, Trogosus grangeri, and Trogosus castoridens. We made morphological comparisons with the plaster endocast of another tillodont, Tillodon fodiens, as well as groups potentially related to Tillodontia: Pantodonta, Arctocyonidae, and Cimolesta. Trogosus shows very little inter-specific variation with the only potential difference being related to the fusion of the optic canal and sphenorbital fissure. Many ancestral features are displayed by Trogosus, including an exposed midbrain, small neocortex, orbitotemporal canal ventral to rhinal fissure, and a broad circular fissure. Potential characteristics that could unite Tillodontia with Pantodonta, and Arctocyonidae are the posterior position of cranial nerve V3 exit in relation to the cerebrum and the low degree of development of the subarcuate fossa. The presence of large olfactory bulbs and a relatively small neocortex are consistent with a terrestrial lifestyle. A relatively small neocortex may have put Trogosus at risk when competing with artiodactyls for potentially similar resources and avoiding predation from archaic carnivorans, both of which are known to have had larger relative brain and neocortex sizes in the Eocene. These factors may have possibly exacerbated the extinction of Tillodontia, which showed highly specialized morphologies despite the increase in climate fluctuations throughout the Eocene, before disappearing during the middle Eocene.
Ajuts:	European Commission 792611 European Commission 756226 Agència de Gestió d'Ajuts Universitaris i de Recerca 2021/BP-00042
Nota:	Altres ajuts: CERCA Programme/Generalitat de Catalunya
Drets:	Tots els drets reservats.
Llengua:	Anglès
Document:	Article ; recerca ; Versió acceptada per publicar
Matèria:	Behavior ; Competition ; Ecology ; Environment ; Eocene ; Neocortex ; Olfactory bulb ; Senses
Publicat a:	Journal of Anatomy, First publication 18th sep. 2023, ISSN 1469-7580

DOI: 10.1111/joa.13951
PMID: 37720992

Disponible a partir de: 2024-12-30 Postprint

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