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1. Body size evolution in crocodylians and their extinct relatives

   https://doi.org/10.1002/9780470015902.a0029089  

   Godoy PL, Turner AH (October 2020, Els)

   null (Ed.)

   Crocodylians are currently facing evolutionary decline. This is evinced by the rich fossil record of their extinct relatives, crocodylomorphs, which show not only significantly higher levels of biodiversity in the past but also remarkable morphological disparity and higher ecological diversity. In terms of body size, crocodylians are mostly large animals (>2m), especially when com-pared to other extant reptiles. In contrast, extinct crocodylomorphs exhibited a 10-fold range in body sizes, with early terrestrial forms often quite small.Recent research has shed new light on the tempo and mode of crocodylomorph body size evolution,demonstrating a close relationship with ecology, in which physiological constraints contribute to the larger sizes of marine species. Abiotic environmental factors can also play an important role with in individual subgroups. Crocodylians, for instance,have been experiencing an average size increase during Cenozoic, which seems to be related to along-term process of global cooling. 

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2. Reevaluation of the cranial osteology and phylogenetic position of the early crocodyliform Eopneumatosuchus colberti , with an emphasis on its endocranial anatomy

   https://doi.org/10.1002/ar.24777  

   Melstrom, Keegan_M; Turner, Alan_H; Irmis, Randall_B (October 2021, The Anatomical Record)

   Abstract Eopneumatosuchus colbertiCrompton and Smith, 1980, known from a single partial skull, is an enigmatic crocodylomorph from the Lower Jurassic Kayenta Formation. In spite of its unique morphology, an exceptionally pneumatic braincase, and presence during a critical time period of crocodylomorph evolution, relatively little is known about this taxon. Here, we redescribe the external cranial morphology ofE.colberti, present novel information on its endocranial anatomy, evaluate its phylogenetic position among early crocodylomorphs, and seek to better characterize its ecology. Our examination clarifies key aspects of cranial suture paths and braincase anatomy. Comparisons with related taxa (e.g.,Protosuchus haughtoni) demonstrate that extreme pneumaticity of the braincase may be more widespread in protosuchids than previously appreciated. Computed tomography scans reveal an endocranial morphology that resembles that of other early crocodylomorphs, in particular the noncrocodyliform crocodylomorphAlmadasuchus figarii. There are, however, key differences in olfactory bulb and cerebral hemisphere morphology, which demonstrate the endocranium of crocodylomorphs is not as conserved as previously hypothesized. Our phylogenetic analysis recoversE.colbertias a close relative ofProtosuchus richardsoniandEdentosuchus tienshanensis, contrasting with previous hypotheses of a sister group relationship with Thalattosuchia. Previous work suggested the inner ear has some similarities to semi‐aquatic crocodyliforms, but the phylogenetic placement ofE.colbertiamong protosuchids with a terrestrial postcranial skeletal morphology complicates paleoecological interpretation. 

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3. Evolutionary structure and timing of major habitat shifts in Crocodylomorpha

   https://doi.org/10.1038/s41598-018-36795-1  

   Wilberg, Eric W.; Turner, Alan H.; Brochu, Christopher A. (January 2019, Scientific Reports)

   Abstract Extant crocodylomorphs are semiaquatic ambush predators largely restricted to freshwater or estuarine environments, but the group is ancestrally terrestrial and inhabited a variety of ecosystems in the past. Despite its rich ecological history, little effort has focused on elucidating the historical pattern of ecological transitions in the group. Traditional views suggested a single shift from terrestrial to aquatic in the Early Jurassic. However, new fossil discoveries and phylogenetic analyses tend to imply a multiple-shift model. Here we estimate ancestral habitats across a comprehensive phylogeny and show at least three independent shifts from terrestrial to aquatic and numerous other habitat transitions. Neosuchians first invade freshwater habitats in the Jurassic, with up to four subsequent shifts into the marine realm. Thalattosuchians first appear in marine habitats in the Early Jurassic. Freshwater semiaquatic mahajangasuchids are derived from otherwise terrestrial notosuchians. Within nearly all marine groups, some species return to freshwater environments. Only twice have crocodylomorphs reverted from aquatic to terrestrial habitats, both within the crown group. All living non-alligatorid crocodylians have a keratinised tongue with salt-excreting glands, but the lack of osteological correlates for these adaptations complicates pinpointing their evolutionary origin or loss. Based on the pattern of transitions to the marine realm, our analysis suggests at least four independent origins of saltwater tolerance in Crocodylomorpha. 

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4. Rostral neurovasculature indicates sensory trade‐offs in Mesozoic pelagic crocodylomorphs

   https://doi.org/10.1002/ar.24733  

   Bowman, Charlotte_I_W; Young, Mark_T; Schwab, Julia_A; Walsh, Stig; Witmer, Lawrence_M; Herrera, Yanina; Choiniere, Jonah; Dollman, Kathleen_N; Brusatte, Stephen_L (August 2021, The Anatomical Record)

   ABSTRACT Metriorhynchoid thalattosuchians were a marine clade of Mesozoic crocodylomorphs that evolved from semi‐aquatic, “gharial”‐like species into the obligately pelagic subclade Metriorhynchidae. To explore whether the sensory and physiological demands of underwater life necessitates a shift in rostral anatomy, both in neurology and vasculature, we investigate the trigeminal innervation and potential somatosensory abilities of metriorhynchoids by digitally segmenting the rostral neurovascular canals in CT scans of 10 extant and extinct crocodyliforms. The dataset includes the terrestrial, basal crocodyliformProtosuchus haughtoni, two semi‐aquatic basal metriorhynchoids, four pelagic metriorhynchids and three extant, semi‐aquatic crocodylians. In the crocodylian and basal metriorhynchoid taxa, we find three main neurovascular channels running parallel to one another posteroanteriorly down the length of the snout, whereas in metriorhynchids there are two, and inP. haughtonionly one. Crocodylians appear to be unique in their extensive trigeminal innervation, which is used to supply the integumentary sensory organs (ISOs) involved with their facial somatosensory abilities. Crocodylians have a far higher number of foramina on the maxillary bones than either metriorhynchoids orP. haughtoni, suggesting that the fossil taxa lacked the somatosensory abilities seen in extant species. We posit that the lack of ISO osteological correlates in metriorhynchoids is due to their basal position in Crocodyliformes, rather than a pelagic adaptation. This is reinforced by the hypothesis that extant crocodyliforms, and possibly some neosuchian clades, underwent a long “nocturnal bottleneck”—hinting that their complex network of ISOs evolved in Neosuchia, as a sensory trade‐off to compensate for poorer eyesight. 

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5. Neuroanatomy of the crocodylian Tomistoma dowsoni from the Miocene of North Africa provides insights into the evolutionary history of gavialoids

   https://doi.org/10.1111/joa.13846  

   Burke, Paul_M J; Mannion, Philip D (July 2023, Journal of Anatomy)

   Abstract The interrelationships of the extant crocodyliansGavialis gangeticusandTomistoma schlegeliihave been historically disputed. Whereas molecular analyses indicate a sister taxon relationship between these two gavialoid species, morphological datasets typically placeGavialisas the outgroup to all other extant crocodylians. Recent morphological‐based phylogenetic analyses have begun to resolve this discrepancy, recoveringGavialisas the closest living relative ofTomistoma; however, several stratigraphically early fossil taxa are recovered as closer toGavialisthanTomistoma, resulting in anomalously early divergence timings. As such, additional morphological data might be required to resolve these remaining discrepancies. ‘Tomistoma’dowsoniis an extinct species of gavialoid from the Miocene of North Africa. Utilising CT scans of a near‐complete, referred skull, we reconstruct the neuroanatomy and neurosensory apparatus of ‘Tomistoma’dowsoni. Based on qualitative and quantitative morphometric comparisons with other crocodyliforms, the neuroanatomy of ‘Tomistoma’dowsoniis characterised by an intermediate morphology between the two extant gavialoids, more closely resemblingGavialis. This mirrors the results of recent studies based on the external anatomy of these three species and other fossil gavialoids. Several neuroanatomical features of these species appear to reflect ecological and/or phylogenetic signals. For example, the ‘simple’ morphology of their neurosensory apparatus is broadly similar to that of other long and narrow‐snouted (longirostrine), aquatic crocodyliforms. A dorsoventrally short, anteroposteriorly long endosseous labyrinth is also associated with longirostry. These features indicate that snout and skull morphology, which are themselves partly constrained by ecology, exert an influence on neuroanatomical morphology, as has also been recognised in birds and turtles. Conversely, the presence of a pterygoid bulla inGavialisand several extinct gavialoids, and its absence inTomistoma schlegelii, could be interpreted as a phylogenetic signal of crocodylians more closely related toGavialis than toTomistoma. Evaluation of additional fossil gavialoids will be needed to further test whether these and other neuroanatomical features primarily reflect a phylogenetic or ecological signal. By incorporating such previously inaccessible information of extinct and extant gavialoids into phylogenetic and macroecological studies, we can potentially further constrain the clade's interrelationships, as well as evaluate the timing and ecological association of the evolution of these neuroanatomical features. Finally, our study supports recent phylogenetic analyses that place ‘Tomistoma’dowsonias being phylogenetically closer toGavialis gangeticusthan toTomistoma schlegelii, indicating the necessity of a taxonomic revision of this fossil species. 

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