Ontogeny of the <i>Massospondylus</i> labyrinth: implications for locomotory shifts in a basal sauropodomorph dinosaur

Neenan, James M.; Chapelle, Kimberley E. J.; Fernández, Vincent; Choiniere, Jonah N.

doi:10.1111/pala.12400

Cited by 27 publications

(28 citation statements)

References 49 publications

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“…For instance, changes in labyrinth geometry associated with the evolution of bipedality within dinosaurs, particularly the elongation of the vertical semicircular canals, have been recorded for dinosaurs 60 . On the other hand, these changes could not be found in an ontogenetic labyrinth series of the dinosaur Massospondylus carinatus 61 , which experiences a change from quadrupedality to bipedality during ontogeny 62 .…”

Section: Vestibular Anatomy As a Guide To Ecological Reconstructions?mentioning

confidence: 81%

Neuroanatomy of the spinosaurid Irritator challengeri (Dinosauria: Theropoda) indicates potential adaptations for piscivory

Schade

Rauhut

Evers

2020

Sci Rep

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Spinosauridae, a theropod group characterized by elongated snouts, conical teeth, enlarged forelimbs, and often elongated neural spines, show evidence for semiaquatic adaptations and piscivory. It is currently debated if these animals represent terrestrial carnivores with adaptations for a piscivorous diet, or if they largely lived and foraged in aquatic habitats. The holotype of Irritator challengeri, a nearly complete skull from the late Early Cretaceous Santana Formation of northeastern Brazil, includes one of the few preserved spinosaurid braincases and can provide insights into neuroanatomical structures that might be expected to reflect ecological affinities. We generated digital models of the neuroanatomical cavities within the braincase, using computer tomography (CT) data. The cranial endocast of Irritator is generally similar to that of other non-maniraptoriform theropods, with weakly developed distinctions of hindbrain and midbrain features, relatively pronounced cranial flexures and relatively long olfactory tracts. The endosseous labyrinth has a long anterior semicircular canal, a posteriorly inclined common crus and a very large floccular recess fills the area between the semicircular canals. These features indicate that Irritator had the ability for fast and well-controlled pitch-down head movements. The skull table and lateral semicircular canal plane are strongly angled to one another, suggesting a downward angling of approximately 45° of the snout, which reduces interference of the snout with the field of vision of Irritator. These neuroanatomical features are consistent with fast, downward snatching movements in the act of predation, such as are needed for piscivory. Spinosauridae is a large-bodied theropod group within Megalosauroidea known from the Cretaceous, although their phylogenetic relationships indicate that the clade must have originated in the Jurassic 1. Spinosaurids are characterized by a long and slender skull, conical teeth, strongly developed forelimbs with exceptionally large thumb claws and elongated neural spines 2-6. Due to superficial similarities in cranial form with piscivorous Crocodilia, such as the gharial, and the wealth of fossil fish within the assemblages they were found in, spinosaurids were repeatedly associated with a semiaquatic lifestyle and piscivory [e.g. 3,7-12 ]. Direct evidence for piscivory comes from acid-etched fish scales in the stomach contents of Baryonyx walkeri 3 , although the same individual also includes terrestrial dinosaur bones of a juvenile ornithopod. Predation on pterosaurs has also been shown for spinosaurids 13. Thus, direct evidence for spinosaurid diets indicates a mix, or opportunistic behaviour with a tendency towards relatively small prey items. Additional evidence to support semiaquatic adaptations beyond dietary preference in spinosaurids comes from: isotope signals acquired from tooth enamel of samples from different geographical contexts, which show that spinosaurids spent a significant amount of their lifetime in water 8,14,15...

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Section: Vestibular Anatomy As a Guide To Ecological Reconstructions?mentioning

confidence: 81%

Neuroanatomy of the spinosaurid Irritator challengeri (Dinosauria: Theropoda) indicates potential adaptations for piscivory

Schade

Rauhut

Evers

2020

Sci Rep

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“…This is consistent with previous observations of functional morphology (Bonnan & Senter ) and with observations of the endosseous labyrinth (Neenan et al . ). We also reject the hypothesis that Maiasaura was bipedal as a juvenile and became quadrupedal as an adult, which was previously suggested based on biomechanical and morphometric analyses (Dilkes ).…”

Section: Discussionmentioning

confidence: 97%

A quantitative method for inferring locomotory shifts in amniotes during ontogeny, its application to dinosaurs and its bearing on the evolution of posture

et al. 2019

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Evolutionary transitions between quadrupedal and bipedal postures are pivotal to the diversification of amniotes on land, including in our own lineage (Hominini). Heterochrony is suggested as a macroevolutionary mechanism for postural transitions but understanding postural evolution in deep time is hindered by a lack of methods for inferring posture in extinct species. Dinosaurs are an excellent natural laboratory for understanding postural transitions because they demonstrate at least four instances of quadrupedality evolving from bipedality, and heterochronic processes have been put forward as an explanatory model for these transitions. We extend a quantitative method for reliably inferring posture in tetrapods to the study of ontogenetic postural transitions using measurements of proportional limb robusticity. We apply this to ontogenetic series of living and extinct amniotes, focusing on dinosaurs. Our method correctly predicts the general pattern of ontogenetic conservation of quadrupedal and bipedal postures in many living amniote species and infers the same pattern in some dinosaurs. Furthermore, it correctly predicts the ontogenetic postural shift from quadrupedal crawling to bipedal walking in humans. We also infer a transition from early ontogenetic quadrupedality to late‐ontogenetic bipedality in the transitional sauropodomorph dinosaur Mussaurus patagonicus and possibly in the early branching ceratopsian Psittacosaurus lujiatunensis but not in the sauropodomorph Massospondylus carinatus. The phylogenetic positions of these ontogenetic shifts suggest that heterochrony may play a role in the macroevolution of posture, at least in dinosaurs. Our method has substantial potential for testing evolutionary transitions between locomotor modes, especially in elucidating the role of evolutionary mechanisms like heterochrony.

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“…() and Neenan et al . () to compare the endosseous labyrinths of extant snakes, extinct sauropterygians and Massospondylus individuals, respectively. However, unlike those mentioned this analysis compares each of the different semicircular canals (anterior semicircular canal, ASC; lateral semicircular canal, LSC; posterior semicircular canal, PSC) separately.…”

Section: Methodsmentioning

confidence: 99%

Endocranial anatomy and life habits of the Early Triassic archosauriformProterosuchus fergusi

et al. 2019

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Proterosuchids are an important group of carnivorous basal archosauriforms characterized by a bizarre and enigmatic downturned premaxilla that overhangs the lower jaw. They are particularly significant because they radiated in the immediate aftermath of the Permian–Triassic mass extinction and represent one of the best known ‘disaster taxa’ following that event. While traditionally considered to be semi‐aquatic, recent histological studies and geological data have suggested that it is more likely that they inhabited terrestrial environments. By using computed tomographic (CT) data, we virtually reconstruct the brain endocast and endosseous labyrinths of two adult specimens of Proterosuchus fergusi from the earliest Triassic of South Africa, in an attempt to understand its life habits within the context of basal archosauriform evolution. Endocasts reveal that the brain cavity is tubular in shape and the endosseous labyrinths are highly pyramidal. The angle of the lateral semicircular canal suggests that P. fergusi naturally held its head upwards ~17°, while the length of the cochlear duct suggests its auditory abilities were specialized towards low‐frequency sounds. Furthermore, beam theory analysis suggests that the rostrum of P. fergusi is highly resistant to both bending and torsion when compared to modern crocodilians, although this resistance is neither enhanced nor reduced by the overhanging premaxilla. Comparative anatomical analyses suggest P. fergusi was probably a semi‐aquatic, generalist apex predator capable of surviving the harsh environmental perturbations of the Early Triassic.

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Ontogeny of the Massospondylus labyrinth: implications for locomotory shifts in a basal sauropodomorph dinosaur

Cited by 27 publications

References 49 publications

Neuroanatomy of the spinosaurid Irritator challengeri (Dinosauria: Theropoda) indicates potential adaptations for piscivory

Neuroanatomy of the spinosaurid Irritator challengeri (Dinosauria: Theropoda) indicates potential adaptations for piscivory

A quantitative method for inferring locomotory shifts in amniotes during ontogeny, its application to dinosaurs and its bearing on the evolution of posture

Endocranial anatomy and life habits of the Early Triassic archosauriformProterosuchus fergusi

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