Study of a digital cranial endocast of the non-mammaliaform cynodont Brasilitherium riograndensis (Later Triassic, Brazil) and its relevance to the evolution of the mammalian brain

Rodrigues, Pablo Gusmão; Ruf, Irina; Schultz, César Leandro

doi:10.1007/s12542-013-0200-6

Cited by 49 publications

(153 citation statements)

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“…Endocast volume excludes the bony labyrinth. Since the ethmoidal fossae housing the olfactory bulbs are not ossified in any of our samples nor in most other therapsids, the endocast volume was measured excluding the olfactory bulbs and tracts, as was commonly done in earlier studies [Jerison, 1973;Quiroga, 1980Quiroga, , 1984Rodrigues et al, 2014]. Previously published accounts on endocranial volume in therapsids included the pineal tube as part of the endocast [Jerison, 1973;Hopson, 1979;Quiroga, 1980Quiroga, , 1984Kielan-Jaworowska et al, 2004;Rowe et al, 2011;Rodrigues et al, 2014;Laass, 2015a].…”

Section: Scanningmentioning

confidence: 99%

“…1 ), the brain was often encapsulated by soft tissues rather than bone, making the borders of the braincase difficult to determine as they are not ossified [Case, 1907;Olson, 1944;Cluver, 1971;Jerison, 1973;Hopson, 1979;Quiroga, 1980Quiroga, , 1984Kielan-Jaworowska et al, 2004;Castanhinha et al, 2013;Rodrigues et al, 2014;Laass, 2015a;mammaliaform Therapsida (NMT) is fused to the bony labyrinth and usually preserves anatomical details only caudal to the pituitary fossa [Case, 1907;Olson, 1944;Kemp, 1969Kemp, , 1979Kemp, , 2009Jerison, 1973;Hopson, 1979;Quiroga, 1980Quiroga, , 1984Kielan-Jaworowska et al, 2004;Rodrigues et al, 2014;Laass, 2015a]. Accordingly, previous attempts to measure brain size and determine brain shape in therapsids resulted more in approximations than true estimations as there was a reliance on a variety of indirect approaches, ranging from geometric simplifications to conjectural visual approximations of brain morphology [Cluver, 1971;Kemp, 1969Kemp, , 1979Kemp, , 2009Jerison, 1973;Hopson, 1979;Quiroga, 1980Quiroga, , 1984Rowe et al, 2011;Rodrigues et al, 2014;Laass, 2015a]. Even the most recent CT scan-based surveys have encountered difficulties in obtaining a reliable picture of the therapsid braincase [Kemp, 2009;Rowe et al, 2011;Castanhinha et al, 2013;<...>…”

Section: Introductionmentioning

confidence: 99%

“…Accordingly, previous attempts to measure brain size and determine brain shape in therapsids resulted more in approximations than true estimations as there was a reliance on a variety of indirect approaches, ranging from geometric simplifications to conjectural visual approximations of brain morphology [Cluver, 1971;Kemp, 1969Kemp, , 1979Kemp, , 2009Jerison, 1973;Hopson, 1979;Quiroga, 1980Quiroga, , 1984Rowe et al, 2011;Rodrigues et al, 2014;Laass, 2015a]. Even the most recent CT scan-based surveys have encountered difficulties in obtaining a reliable picture of the therapsid braincase [Kemp, 2009;Rowe et al, 2011;Castanhinha et al, 2013;Rodrigues et al, 2014;Laass, 2015a;Araújo et al, 2017]. Accordingly, most endocranial volumes have been calculated on indirect evidence [Jerison, 1973;Hopson, 1979;Quiroga, 1980Quiroga, , 1984Kielan-Jaworowska et al, 2004;Rowe et al, 2011;Rodrigues et al, 2014;Laass, 2015a; but see Laass and Kaestner, 2017], and resulting estimations of the encephalisation quotient (EQ, a measure of brain volume relative to body mass [Jerison, 1973]) are controversial [see Kemp, 2009].…”

Section: Introductionmentioning

confidence: 99%

“…Even the most recent CT scan-based surveys have encountered difficulties in obtaining a reliable picture of the therapsid braincase [Kemp, 2009;Rowe et al, 2011;Castanhinha et al, 2013;Rodrigues et al, 2014;Laass, 2015a;Araújo et al, 2017]. Accordingly, most endocranial volumes have been calculated on indirect evidence [Jerison, 1973;Hopson, 1979;Quiroga, 1980Quiroga, , 1984Kielan-Jaworowska et al, 2004;Rowe et al, 2011;Rodrigues et al, 2014;Laass, 2015a; but see Laass and Kaestner, 2017], and resulting estimations of the encephalisation quotient (EQ, a measure of brain volume relative to body mass [Jerison, 1973]) are controversial [see Kemp, 2009]. In addition, the scarcity (and in some cases, the absence) of direct imprints of brain tissues on the braincase in NMT suggests that the braincase walls were separated from the membranous brain by conjunctive tissue, as in modern reptiles, which makes estimation of the actual brain size from endocranial casts even more difficult [Jerison, 1973;Quiroga, 1980Quiroga, , 1984.…”

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: Scanningmentioning

confidence: 99%

Section: Introductionmentioning

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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“…Transitional stages of jaw joint morphology are depicted schematically on the right. Phylogeny simplified after Ruta et al (2013) and Rodrigues et al (2014), jaw joint schematics modified after Luo (2007). Digital skull models not to scale.…”

Section: (A) Thrinaxodon Liorhinusmentioning

confidence: 99%

Morphological evolution of the mammalian jaw adductor complex

et al. 2016

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The evolution of the mammalian jaw during the transition from non-mammalian synapsids to crown mammals is a key event in vertebrate history and characterised by the gradual reduction of its individual bones into a single element and the concomitant transformation of the jaw joint and its incorporation into the middle ear complex. This osteological transformation is accompanied by a rearrangement and modification of the jaw adductor musculature, which is thought to have allowed the evolution of a more-efficient masticatory system in comparison to the plesiomorphic synapsid condition. While osteological characters relating to this transition are well documented in the fossil record, the exact arrangement and modifications of the individual adductor muscles during the cynodont-mammaliaform transition have been debated for nearly a century.We review the existing knowledge about the musculoskeletal evolution of the mammalian jaw adductor complex and evaluate previous hypotheses in the light of recently documented fossils that represent new specimens of existing species, which are of central importance to the mammalian origins debate. By employing computed tomography (CT) and digital reconstruction techniques to create three-dimensional models of the jaw adductor musculature in a number of representative non-mammalian cynodonts and mammaliaforms, we provide an updated perspective on mammalian jaw muscle evolution.As an emerging consensus, current evidence suggests that the mammal-like division of the jaw adductor musculature (into deep and superficial components of the m. masseter, the m. temporalis and the m. pterygoideus) was completed in Eucynodontia. The arrangement of the jaw adductor musculature in a mammalian fashion, with the m. pterygoideus group inserting on the dentary was completed in basal Mammaliaformes as suggested by the muscle reconstruction of Morganucodon oehleri. Consequently, transformation of the jaw adductor musculature from the ancestral ('reptilian') to the mammalian condition must have preceded the emergence of Mammalia and the full formation of the mammalian jaw joint. This suggests that the modification of the jaw adductor system played a pivotal role in the functional morphology and biomechanical stability of the jaw joint.

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Nasal Anatomy of the Non‐mammaliaform Cynodont Brasilitherium riograndensis (Eucynodontia, Therapsida) Reveals New Insight into Mammalian Evolution

Ruf

Maier

Rodrigues

et al. 2014

The Anatomical Record

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The mammalian nasal cavity is characterized by a unique anatomy with complex internal features. The evolution of turbinals was correlated with endothermic and macrosmatic adaptations in therapsids and in early mammals, which is still apparent in their twofold function (warming and moistening of air, olfaction). Fossil evidence for the transformation from the nonmammalian to the mammalian nasal cavity pattern has been poor and inadequate. Ossification of the cartilaginous nasal capsule and turbinals seems to be a feature that occurred only very late in synapsid evolution but delicate ethmoidal bones are rarely preserved. Here we provide the first mCT investigation of the nasal cavity of the advanced non-mammaliaform cynodont Brasilitherium riograndensis from the Late Triassic of Southern Brazil, a member of the sister-group of mammaliaforms, in order to elucidate a critical anatomical transition in early mammalian evolution. Brasilitherium riograndensis already had at least partially ossified turbinals as remnants of the nasoturbinal and the first ethmoturbinal are preserved. The posterior nasal septum is partly ossified and contributes to a mesethmoid. The nasal cavity is posteriorly expanded and forms a distinctive pars posterior (ethmoidal recess) that is ventrally separated from the nasopharyngeal duct by a distinct lamina terminalis. Thus, our observations clearly demonstrate that principal features of the This article includes AR WOW Videos, which can be viewed at

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Study of a digital cranial endocast of the non-mammaliaform cynodont Brasilitherium riograndensis (Later Triassic, Brazil) and its relevance to the evolution of the mammalian brain

Cited by 49 publications

References 52 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

Morphological evolution of the mammalian jaw adductor complex

Nasal Anatomy of the Non‐mammaliaform Cynodont Brasilitherium riograndensis (Eucynodontia, Therapsida) Reveals New Insight into Mammalian Evolution

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