Although isolated Champsosaurus remains are common in Upper cretaceous sediments of north America, the braincase of these animals is enigmatic due to the fragility of their skulls. Here, two wellpreserved specimens of Champsosaurus (CMN 8920 and CMN 8919) are CT scanned to describe their neurosensory structures and infer sensory capability. the anterior portion of the braincase was poorly ossified and thus does not permit visualization of a complete endocast; however, impressions of the olfactory stalks indicate that they were elongate and likely facilitated good olfaction. the posterior portion of the braincase is ossified and morphologically similar to that of other extinct diapsids. The absence of an otic notch and an expansion of the pars inferior of the inner ear suggests Champsosaurus was limited to detecting low frequency sounds. comparison of the shapes of semicircular canals with lepidosaurs and archosauromorphs demonstrates that the semicircular canals of Champsosaurus are most similar to those of aquatic reptiles, suggesting that Champsosaurus was well adapted for sensing movement in an aquatic environment. this analysis also demonstrates that birds, non-avian archosauromorphs, and lepidosaurs possess significantly different canal morphologies, and represents the first morphometric analysis of semicircular canals across Diapsida.Palaeoneurology, the study of the brain in the fossil record and how it has changed through time 1 , provides some of the best evidence for how extinct animals behaved and interacted with their environment. The behaviour and sensory abilities of extinct taxa are inferred based on the morphology of regions of the brain that are directly responsible for processing sensory information and forming behaviour. Other neural structures are often included in palaeoneurological studies, such as the cranial nerves and membranous labyrinth, which transmit sensory and motor information to and from the brain, and facilitate the sensation of movement and orientation, respectively. Estimations of sensory ability and behaviour based on the morphology of the brain are made possible by the principle of proper mass, which states that the size of a brain region dedicated to a specific function is directly correlated with the amount of processing power required to complete that function 2 . Therefore, regions of the brain that require more processing power tend to be larger to accommodate a greater number of neurons.This correlation allows hypotheses to be made about the sensory ability of extinct animals based on the morphology of the brain; 3,4 however, the brain endocast is not a perfect reflection of the brain in life, as it also represents other soft-tissue structures housed within the endocranial cavity that did not fossilize, such as the dura matter and vascular tissue 5 . Despite this, a description of the endocranial cavity of an extinct animal provides data that can be used to infer its neurosensory capabilities by comparison to closely related extant taxa, which allows for the formation o...

Rare occurrences of dinosaurian embryos are punctuated by even rarer preservation of their development. Here we report on dental development in multiple embryos of the Early Jurassic Lufengosaurus from China, and compare these to patterns in a hatchling and adults. Histology and CT data show that dental formation and development occurred early in ontogeny, with several cycles of tooth development without root resorption occurring within a common crypt prior to hatching. This differs from the condition in hatchling and adult teeth of Lufengosaurus, and is reminiscent of the complex dentitions of some adult sauropods, suggesting that their derived dental systems likely evolved through paedomorphosis. Ontogenetic changes in successive generations of embryonic teeth of Lufengosaurus suggest that the pencil-like teeth in many sauropods also evolved via paedomorphosis, providing a mechanism for the convergent evolution of small, structurally simple teeth in giant diplodocoids and titanosaurids. Therefore, such developmental perturbations, more commonly associated with small vertebrates, were likely also essential events in sauropod evolution.

Choristoderes are extinct neodiapsid reptiles that are well known for their unusual cranial anatomy, possessing an elongated snout and expanded temporal arches. Although choristodere skulls are well described externally, their internal anatomy remains unknown. An internal description was needed to shed light on peculiarities of the choristodere skull, such as paired gaps on the ventral surface of the skull that may pertain to the fenestra ovalis, and a putative neomorphic ossification in the lateral wall of the braincase. Our goals were: (i) to describe the cranial elements of Champsosaurus lindoei in three dimensions; (ii) to describe paired gaps on the ventral surface of the skull to determine if these are indeed the fenestrae ovales; (iii) to illustrate the morphology of the putative neomorphic bone; and (iv) to consider the possible developmental and functional origins of the neomorph. We examined the cranial anatomy of the choristodere Champsosaurus lindoei (CMN 8920) using high‐resolution micro‐computed tomography scanning. We found that the paired gaps on the ventral surface of the skull do pertain to the fenestrae ovales, an unusual arrangement that may be convergent with some plesiosaurs, some aistopods, and some urodeles. The implications of this morphology in Champsosaurus are unknown and will be the subject of future work. We found that the neomorphic bone is a distinct ossification, but is not part of the wall of the brain cavity or the auditory capsule. Variation in the developmental pathways of cranial bones in living amniotes was surveyed to determine how the neomorphic bone may have developed. We found that the chondrocranium and splanchnocranium show little to no variation across amniotes, and the neomorphic bone is therefore most likely to have developed from the dermatocranium; however, the stapes is a pre‐existing cranial element that is undescribed in choristoderes and may be homologous with the neomorphic bone. If the neomorphic bone is not homologous with the stapes, the neomorph likely developed from the dermatocranium through incomplete fusion of ossification centres from a pre‐existing bone, most likely the parietal. Based on the apparent morphology of the neomorph in Coeruleodraco, the neomorph was probably too small to play a significant structural role in the skull of early choristoderes and it may have arisen through non‐adaptive means. In neochoristoderes, such as Champsosaurus, the neomorph was likely recruited to support the expanded temporal arches.

For sheer complexity, braincases are generally considered anatomically conservative. However, recent research on the braincases of tyrannosaurids have revealed extensive morphological variations. This line of inquiry has its root in Dale Russell’s review of tyrannosaurids in which he established Daspletosaurus torosus — a large tyrannosaurine from the Campanian of southern Alberta. In the wake of systematic revisions to tyrannosaurines previously assigned to Daspletosaurus, one potentially distinct species remains undescribed. This paper describes and compares a braincase referable to this species with that of the holotype for Daspletosaurus torosus using computerized-tomography-based reconstructions. The two braincases have numerous differences externally and internally. The specimen of Daspletosaurus sp. has a bottlenecked olfactory tract, short and vertical lagena, and a developed ascending column of the anterior tympanic recess. The holotype of Daspletosaurus torosus has many unusual traits, including an anteriorly positioned trochlear root, elongate common carotid canal, distinct chamber of the basisphenoid recess, asymmetry in the internal basipterygoid aperture, and laterally reduced but medially expanded subcondylar recess. This comparison also identified characters that potentially unite the two species of Daspletosaurus, including deep midbrain flexures in the endocasts. However, many character variations in the braincases are known in other tyrannosaurids to correlate with body size and maturity, or represent individual variations. Therefore, taxonomic and phylogenetic signals can be isolated from background variations in a more comprehensive approach by using additional specimens. New information on the two braincases of Daspletosaurus is consistent with the emerging view of tyrannosaurid braincases as highly variable, ontogenetically dynamic character complexes.

A new skeleton of the exceedingly rare, late Carboniferous eureptile Anthracodromeus longipes (Carroll and Baird, 1972), reveals the presence of a reduced phalangeal count in the manus and pedes and uniquely recurved unguals. With these data, we quantitatively evaluate the locomotor ecology of Anthracodromeus using morphometric analyses of the phalangeal proportions, ungual curvature, and ungual shape. Our findings indicate that the anatomy of Anthracodromeus likely facilitated scansorial clinging to some degree via distally recurved unguals and increased surface area of the large manus and pes. This suggests that Anthracodromeus was among the earliest amniotes to show climbing abilities, pushing back the origins of scansoriality by at least 17 million years. It further suggests that scansoriality arose soon after the origin of amniotes, allowing them to exploit a wide range of novel terrestrial niches.