The internal cranial anatomy of Champsosaurus (Choristodera: Champsosauridae): Implications for neurosensory function

Dudgeon, Thomas W.; Maddin, Hillary C.; Evans, David C.; Mallon, Jordan C.

doi:10.1038/s41598-020-63956-y

Cited by 7 publications

(29 citation statements)

References 85 publications

(117 reference statements)

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“…6,49 We find no evidence for changes in labyrinth shape associated with transitions to aquatic or semi-aquatic habits, either across archosauromorphs, in non-avemetatarsalian archosauromorphs, or in Pseudosuchia (Data S1C and S1D). This contrasts with previous studies that reported both dorsoventrally low aspect ratios in the SCCs of aquatic taxa 32,50,51 and an increase in endosseous canal diameters during the early stages of aquatic adaptation 51 but did not include phylogenetically informed statistical tests of those hypotheses. Instead, we show an association between labyrinth shape and the height/width aspect ratio of the postrostral part of the skull in pseudosuchians and in nonavemetatarsalian archosaurs more broadly (Data S1C and S1D).…”

Section: Discussioncontrasting

confidence: 99%

“…The small SCC sizes of these stem-archosaurs argues against the possibility that their avemetatarsalian-like SCC shapes evolved to optimize vestibular sensitivity. Based on these observations, we urge strongly against the practice of interpreting specific, detailed aspects of locomotion or foraging styles of extinct taxa from SCC geometry (as done by, e.g., Stocker et al, 41 Dudgeon et al, 50 and Schade et al 53 ).…”

Section: Discussionmentioning

confidence: 99%

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Deep evolutionary diversification of semicircular canals in archosaurs

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Section: Discussioncontrasting

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Deep evolutionary diversification of semicircular canals in archosaurs

et al. 2021

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“…10 ], it is quite possible that ancestral constraints on the theropodan bauplan dominate the shape of the spinosaurid labyrinth [e.g. 58 ]. Therefore, semiaquatic adaptations are not necessarily expected to be overly obvious, or present at all, and their absence cannot be taken as strong evidence against semiaquatic lifestyles.…”

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

confidence: 99%

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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“…Choristoderes have been notoriously difficult to place on the phylogenetic tree of diapsids. They have a peculiar suite of anatomical features, including the presence of a neomorphic bone in the braincase [ 15 , 27 , 30 ], a complete set of palatal tooth plates [ 57 ], an elongated, flattened postorbital skull with expanded temporal fenestrae (e.g., [ 15 , 19 , 56 ]), and oval fenestrae on the ventral surface of the skull alongside the parasphenoid [ 15 , 70 ]. Choristoderes are morphologically diverse, and include large, longirostrine forms exceeding 2 m in length [ 19 ], diminutive species with ornamented posterior skull roofs and generalized body plans [ 61 ], and long-necked, short-snouted species [ 25 , 32 ].…”

Section: Introductionmentioning

confidence: 99%

“…The Paleocene of North America appears to have been a hotspot of choristodere diversity. At least four valid species of Champsosaurus and one species assigned to Simoedosaurus ( S. dakotensis ) are known from the Paleocene of the continent [ 15 , 19 , 20 ]. All of these species are among the largest choristoderes known and greatly exceed nearly all Mesozoic forms in size (e.g., [ 19 , 20 , 56 ]).…”

Section: Introductionmentioning

confidence: 99%

High morphological disparity in a bizarre Paleocene fauna of predatory freshwater reptiles

Brownstein

2022

BMC Ecol EvoHas correction 2022-4-15 Has erratum 2022-4-15

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Background The consequences of the K-Pg mass extinction are reflected across present biodiversity, but many faunas that appeared immediately after the extinction event were very different from current ones. Choristodera is a clade of reptiles of uncertain phylogenetic placement that have an extremely poor fossil record throughout their 150-million-year history. Yet, choristoderes survived the K-Pg event and persisted until the Miocene. Results I describe the skulls and skeletons of two new choristoderes from a single Paleocene ecosystem in western North America that reveal the hidden Cenozoic diversity of this reptile clade. Despite their similar size, the new species deviate dramatically in morphology. Kosmodraco magnicornis gen. et sp. nov. possesses an extremely short snout and extensive cranial ornamentation. The sacrum of K. magnicornis bears enlarged muscle attachment sites and other modifications reminiscent of some giant crocodylians. In contrast, Champsosaurus norelli sp. nov. is a longirostrine species with an uninflated and ventrally divergent postorbital skull. Together with a North American choristodere previously classified in the European genus Simoedosaurus, K. magnicornis substantiates a new clade of giant, short-snouted taxa endemic to the Americas. C. norelli is found to be an early-diverging member of the genus Champsosaurus from the Cretaceous-Paleogene of the northern hemisphere. This suggests the presence of several ghost lineages of champsosaurid that crossed the K-Pg boundary. Conclusions The new taxa greatly increase Cenozoic choristodere richness and strengthen the evidence for the existence of distinctive freshwater faunas in Paleogene Eurasia and North America, where this clade diversified to exploit newly available macropredatory niches in the aftermath of the asteroid impact. The new choristoderes also reveal the distinct ecological context in which extant freshwater predators of the Americas like alligatoroids and gars have their origins: Paleocene fluviolacustrine ecosystems in North America displayed high large predator diversity and morphological disparity relative to modern ones.

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The internal cranial anatomy of Champsosaurus (Choristodera: Champsosauridae): Implications for neurosensory function

Cited by 7 publications

References 85 publications

Deep evolutionary diversification of semicircular canals in archosaurs

Deep evolutionary diversification of semicircular canals in archosaurs

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

High morphological disparity in a bizarre Paleocene fauna of predatory freshwater reptiles

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