The mystery of a missing bone: revealing the orbitosphenoid in basal Epicynodontia (Cynodontia, Therapsida) through computed tomography

Benoît, Julien; Jasinoski, Sandra C.; Fernández, Vincent; Abdala, Fernando

doi:10.1007/s00114-017-1487-z

Cited by 17 publications

(39 citation statements)

References 30 publications

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“…10 b). Given their basal position in Therapsida phylogeny [Rubidge and Sidor, 2001], it can be reasonably hypothesised that this represents the plesiomorphic condition for this clade and that the ventral border of the braincase/brain was likely similar to this in most other NMT and bordered by cartilaginous or membranous tissue [Benoit et al, 2017a]. Also, the hypophyseal fossa is completely ossified and is protruding anteriorly in Herpetoskylax , Lemurosaurus (NMQR1702), and the indet.…”

Section: Endocast Shape and Size In Early Therapsidamentioning

confidence: 87%

“…Five additional taxa displaying reasonable (yet not complete) ossification of the braincase (i.e., Tritylodon , Massetognathus , Microgomphodon , and 2 gorgonospsians [Benoit et al, 2017a]) were also scanned and their endocasts segmented to expand the comparative sample. Since the membranous brain leaves few or no direct imprints on the braincase in most NMT, it is reasonable to think that their endocranial volume does not exactly reflect the corresponding brain volume, which was likely smaller in NMT [Jerison, 1973;Quiroga, 1980Quiroga, , 1984Laass and Kaestner, 2017].…”

Section: List Of Materials Scanned and Detailsmentioning

confidence: 99%

“…This appears unlikely considering that enlargement of the olfactory bulbs in NMT characterises only Brasilitherium and Mammaliaformes [Rowe et al, 2011;Rodrigues et al, 2014]. Apart from Kawingasaurus [Laass and Kaestner, 2017], the ethmoidal fossae for the olfactory bulbs and tracts are never completely ossified in NMT, despite different levels of extension of the sphenethmoidal complex [Benoit et al, 2017a]. In biarmosuchians, only the proximal ventral part of the olfactory tract is preserved ( Fig.…”

Section: Shape Of the Endocastmentioning

confidence: 99%

“…1 ) [Jerison, 1973;Hopson, 1979;Rubidge and Sidor 2001;Kielan-Jaworowska et al, 2004;Kemp, 2005]. Unfortunately, the vast majority of the nonmammalian Cynodontia display little to no osseous enclosing of the braincase [Jerison, 1973;Hopson, 1979;Gow, 1986;Benoit et al, 2017a;Crompton et al, 2017a], which makes them a problematic NMT group to undertake endocast studies. Hence, to get a better idea of the morphology of the endocast and bony labyrinth at the root of the mammalian clade, attention should be given to NMT that have ossified braincases, rather than the cynodonts.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, to get a better idea of the morphology of the endocast and bony labyrinth at the root of the mammalian clade, attention should be given to NMT that have ossified braincases, rather than the cynodonts. Therocephalia, Gorgonopsia, Dicynodontia, and some of the most derived Cynodontia are characterised by the presence of an anteroposteriorly elongated and hemicylindrical sphenethmoidal complex (mostly made by the orbitosphenoid) that only partially encloses the braincase [Kemp, 1969;Sigogneau, 1970;Hopson, 1979;Laass, 2015a;Benoit et al, 2017a;Crompton et al, 2017a].…”

Section: Introductionmentioning

confidence: 99%

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Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals

Benoît

Fernández²,

Manger³

et al. 2017

Brain Behav Evol

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The origin and evolution of the mammalian brain has long been the focus of scientific enquiry. Conversely, little research has focused on the palaeoneurology of the stem group of Mammaliaformes, the Permian and Triassic non-mammaliaform Therapsida (NMT). This is because the majority of the NMT have a non-ossified braincase, making the study of their endocranial cast (sometimes called the “fossil brain”) problematic. Thus, descriptions of the morphology and size of NMT endocranial casts have been based largely on approximations rather than reliable determination. Accordingly, here we use micro-CT scans of the skulls of 1 Dinocephalia and 3 Biarmosuchia, which are NMT with a fully ossified braincase and thus a complete endocast. For the first time, our work enables the accurate determination of endocranial shape and size in NMT. This study suggests that NMT brain size falls in the upper range of the reptilian and amphibian variation. Brain size in the dicynodont Kawingasaurus is equivalent to that of early Mammaliaformes, whereas the Dinocephalia show evidence of a secondary reduction of brain size. In addition, unlike other NMT in which the endocast has a tubular shape and its parts are arranged in a linear manner, the biarmosuchian endocast is strongly flexed at the level of the midbrain, creating a near right angle between the fore- and hindbrain. These data highlight an unexpected diversity of endocranial size and morphology in NMT, features that are usually considered conservative in this group.

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Section: Endocast Shape and Size In Early Therapsidamentioning

confidence: 87%

Section: List Of Materials Scanned and Detailsmentioning

confidence: 99%

Section: Shape Of the Endocastmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals

Benoît

Fernández²,

Manger³

et al. 2017

Brain Behav Evol

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Craniogenetic studies in Sus scrofa: With emphasis on the ‘orbitosphenoid’ problem

Maier

Lächele

Ruf

2023

The Anatomical Record

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The orbitosphenoid is a skeletal element of the endocranium of extant mammals. However, it has also been described in many of their fossil ancestors. Craniogenetic studies show that it is composed of two types of bone: first, the cartilaginous ala orbitalis and parts of the trabecular plate are transformed by endochondral ossification; second, so‐called ‘appositional bone’ (‘Zuwachsknochen’) arises directly from the perichondrium of the two optic pilae and spreads in all directions and overlays the remaining cartilage and the endochondral ossifications. For some time, both bone types can be distinguished microscopically, but later in craniogenesis they fuse completely to become the presphenoid sensu lato of the osteocranium. We interpret the ‘appositional bone’ as neomorphic mode to reinforce the endocranial bone structures, which are the ossification of the delicate cartilaginous template of the chondrocranium. We studied the ossifications of the presphenoidal skull region in a series of ontogenetic stages of the pig Sus scrofa. We applied conventional histology as well as stained and unstained μCT scans. We can show the above‐mentioned modes of ossification, and we can demonstrate the contribution of ‘appositional bone’ well into neonatal and infantile stages. The ossifications of the presphenoid (including the orbitosphenoid) are very slender in therapsids and early mammaliaforms as previously described by other authors. In mammaliaforms, they tend to become thicker and closely connected with the frontal bone, which may be due to the contribution of neomorphic appositional bone. We assume that thereby the presphenoid sensu lato becomes an enforcement of the orbital pillars.

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Skull anatomy and paleoneurology of a new traversodontid from the Middle‐Late Triassic of Brazil

Kerber,

Roese‐Miron,

Medina

et al. 2024

The Anatomical Record

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Traversodontidae, a clade of gomphodont cynodonts, thrived during the Middle and Late Triassic, displaying a wide geographical distribution. During fieldwork in 2009, a new specimen was discovered in Ladinian/early Carnian stratigraphic layers in southern Brazil. Here, we describe this specimen and propose a new taxon closely related to Traversodon stahleckeri (Traversodontinae) but displaying a unique combination of traits (e.g., presence of a poorly developed suborbital process, mesiodistal length of the paracanine fossa similar to the length of the canine, short diastema between the fourth incisor and the upper canine, and coronoid process not entirely covering the distalmost lower postcanine). Furthermore, the endocranial anatomy of the new taxon was examined. The reconstruction of the cranial endocast revealed paleoneurological features consistent with non‐Gomphodontosuchinae traversodontids. These features include the presence of a pineal body (but the absence of an open parietal foramen). These recent findings contribute significantly to our understanding of the evolutionary history and cranial anatomy of Middle‐Late Triassic traversodontids, shedding light on the diversity and adaptations of non‐mammaliaform cynodonts.

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The mystery of a missing bone: revealing the orbitosphenoid in basal Epicynodontia (Cynodontia, Therapsida) through computed tomography

Cited by 17 publications

References 30 publications

Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals

Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals

Craniogenetic studies in Sus scrofa: With emphasis on the ‘orbitosphenoid’ problem

Skull anatomy and paleoneurology of a new traversodontid from the Middle‐Late Triassic of Brazil

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