Paleoneurology of Artiodactyla, an Overview of the Evolution of the Artiodactyl Brain

Orliac, Maëva J.; Maugoust, Jacob; Balcarcel, Ana; Gilissen, Emmanuel

doi:10.1007/978-3-031-13983-3_13

Cited by 4 publications

(2 citation statements)

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“…The absence of sulci on the surface of the neocortex may also represent an ancestral feature related to the limited expansion of the neocortex in Trogosus as in Hyopsodus , which also displays a lissencephalic brain. Sulci might be present in some archaic taxa (e.g., some plesiadapiforms), but they become more common in crown clades such as Rodentia, Euprimates, and Artiodactyla (Bertrand et al, 2019a; Harrington et al, 2016; Orliac et al, 2023). Also related to the development of the neocortex, the more ventral position of the orbitotemporal canal in relation to the rhinal fissure represents an ancestral feature displayed by Trogosus , Pantodonta, and Arctocyonidae.…”

Section: Discussionmentioning

confidence: 99%

Section: Endocranial Anatomy and Phylogenetic Relationshipsmentioning

confidence: 99%

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The virtual brain endocast of Trogosus (Mammalia, Tillodontia) and its relevance in understanding the extinction of archaic placental mammals

Bertrand,

Jiménez Lao,

Shelley

et al. 2023

Journal of Anatomy

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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.

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Section: Discussionmentioning

confidence: 99%

Section: Endocranial Anatomy and Phylogenetic Relationshipsmentioning

confidence: 99%

The virtual brain endocast of Trogosus (Mammalia, Tillodontia) and its relevance in understanding the extinction of archaic placental mammals

Bertrand,

Jiménez Lao,

Shelley

et al. 2023

Journal of Anatomy

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Paleoneurology of Artiodactyla, an Overview of the Evolution of the Artiodactyl Brain

Orliac

Maugoust

Balcarcel

et al. 2022

Paleoneurology of Amniotes

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This chapter presents a detailed review of works published on Artiodactyla endocasts and provides a comprehensive examination of artiodactyl brain evolutionary history, including Cetacea, from the early Eocene (c.a. 45 Ma) onwards. Artiodactyl endocasts have been actively studied from the second half of the 19 th century to the 1970's. These works on natural or artificial endocasts widely took place outside the frame of phylogenetic concerns. We compile here the data available, including recent works using µCT-scan imagery techniques, and place them in a phylogenetic framework. We also provide new additional data regarding paleogene representatives of North American extinct clades (Homacodon, Helohyus, Leptauchenia, Agriochoerus), endemic European clade (Mouillacitherium, Dichobune), and Suoidea (Palaeochoerus) to complete the picture. The brain of modern artiodactyls is remarkable by the expansion and by the folding of the neopallium. We highlight the diversity of neopallium patterns at the Artiodactyla scale and their convergent nature on the last 45 millions years and show that encephalization increases with time, but with different modes between terrestrial and fully aquatic taxa (i.e. Cetacea). Each clade shows a mosaic pattern of derived and plesiomorphic features that now has to be put in perspective with both the history and the ecology of taxa.

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Endocranial Casts of Camelops hesternus and Palaeolama sp.: New Insights into the Recent History of the Camelid Brain

2022

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Endocranial casts are capable of capturing the general brain form in extinct mammals due to the high fidelity of the endocranial cavity and the brain in this clade. Camelids, the clade including extant camels, llamas, and alpacas, today display high levels of gyrification and brain complexity. The evolutionary history of the camelid brain has been described as involving unique neocortical growth dynamics which may have led to its current state. However, these inferences are based on their fossil endocast record from approximately ~40 Mya (Eocene) to ~11 Mya (Miocene), with a gap in this record for the last ~10 million years. Here, we present the first descriptions of two camelid endocrania that document the recent history of the camelid brain: a new specimen of Palaeolama sp. from ~1.2 Mya, and the plaster endocast of Camelops hesternus, a giant camelid from ~44-11 Kya which possessed the largest brain (~990g) of all known camelids. We find that neocortical complexity evolved significantly between the Miocene and Pleistocene Epochs. Already ~1.2 Mya the camelid brain presented morphologies previously known only in extant taxa, especially in the frontal and parietal regions, which may also be phylogenetic informative. The new fossil data indicate that during the Pleistocene, camelid brain dynamics experienced neocortical invagination into the sagittal sinus rather than evagination out of it, as observed in Eocene to Miocene taxa.

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Paleoneurology of Artiodactyla, an Overview of the Evolution of the Artiodactyl Brain

Cited by 4 publications

References 159 publications

The virtual brain endocast of Trogosus (Mammalia, Tillodontia) and its relevance in understanding the extinction of archaic placental mammals

The virtual brain endocast of Trogosus (Mammalia, Tillodontia) and its relevance in understanding the extinction of archaic placental mammals

Paleoneurology of Artiodactyla, an Overview of the Evolution of the Artiodactyl Brain

Endocranial Casts of Camelops hesternus and Palaeolama sp.: New Insights into the Recent History of the Camelid Brain

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