Near-stasis in the long-term diversification of Mesozoic tetrapods

How did evolution generate the extraordinary diversity of vertebrates on land? Zero species are known prior to ~380 million years ago, and more than 30,000 are present today. An expansionist model suggests this was achieved by large and unbounded increases, leading to substantially greater diversity in the present than at any time in the geological past. This model contrasts starkly with empirical support for constrained diversification in marine animals, suggesting different macroevolutionary processes on land and in the sea. We quantify patterns of vertebrate standing diversity on land during the Mesozoic–early Paleogene interval, applying sample-standardization to a global fossil dataset containing 27,260 occurrences of 4,898 non-marine tetrapod species. Our results show a highly stable pattern of Mesozoic tetrapod diversity at regional and local levels, underpinned by a weakly positive, but near-zero, long-term net diversification rate over 190 million years. Species diversity of non-flying terrestrial tetrapods less than doubled over this interval, despite the origins of exceptionally diverse extant groups within mammals, squamates, amphibians, and dinosaurs. Therefore, although speciose groups of modern tetrapods have Mesozoic origins, rates of Mesozoic diversification inferred from the fossil record are slow compared to those inferred from molecular phylogenies. If high speciation rates did occur in the Mesozoic, then they seem to have been balanced by extinctions among older clades. An apparent 4-fold expansion of species richness after the Cretaceous/Paleogene (K/Pg) boundary deserves further examination in light of potential taxonomic biases, but is consistent with the hypothesis that global environmental disturbances such as mass extinction events can rapidly adjust limits to diversity by restructuring ecosystems, and suggests that the gradualistic evolutionary diversification of tetrapods was punctuated by brief but dramatic episodes of radiation.27 page(s

Climate constrains the evolutionary history and biodiversity of crocodylians

The fossil record of crocodylians and their relatives (pseudosuchians) reveals a rich evolutionary history, prompting questions about causes of long-term decline to their present-day low biodiversity. We analyse climatic drivers of subsampled pseudosuchian biodiversity over their 250 million year history, using a comprehensive new data set. Biodiversity and environmental changes correlate strongly, with long-term decline of terrestrial taxa driven by decreasing temperatures in northern temperate regions, and biodiversity decreases at lower latitudes matching patterns of increasing aridification. However, there is no relationship between temperature and biodiversity for marine pseudosuchians, with sea-level change and post-extinction opportunism demonstrated to be more important drivers. A ‘modern-type' latitudinal biodiversity gradient might have existed throughout pseudosuchian history, and range expansion towards the poles occurred during warm intervals. Although their fossil record suggests that current global warming might promote long-term increases in crocodylian biodiversity and geographic range, the 'balancing forces' of anthropogenic environmental degradation complicate future predictions

New information on the Jurassic lepidosauromorph Marmoretta oxoniensis

The earliest known crown-group lepidosaurs are known from the Middle Triassic; however, their stem group is poorly sampled, with only a few representative fossils found. This is partly due to the small size and delicate bones of early stem-lepidosaurs (= non-lepidosaurian lepidosauromorphs), which make both preservation in the fossil record and subsequent discovery less likely. The Middle Jurassic lepidosauromorph Marmoretta oxoniensis is re-examined using high-resolution micro-computed tomography to reveal parts of the skull anatomy that were previously unknown. These include a squamosal, postorbital, more complete parietal, pterygoids, and an articulated posterior section of the mandible. Some differences between this and other Marmoretta specimens were identified as a result, such as the arrangement of palatal teeth and the shape of the parabasisphenoid. The status of Marmoretta as a stem-lepidosaur or stem-squamate has been debated. To evaluate this, we tested the phylogenetic position of Marmoretta by including our new data in an adapted phylogenetic character matrix. We recover Marmoretta as a stem-lepidosaur and sister to Fraxinisaura rozynekae. Our findings support the hypothesis that both taxa belonged to a clade of non-lepidosaurian lepidosauromorphs that co-existed with lepidosaurs into the Middle Jurassic

Total-evidence framework reveals complex morphological evolution in nightbirds (Strisores)

Strisores is a clade of neoavian birds that include diurnal aerial specialists such as swifts and hummingbirds, as well as several predominantly nocturnal lineages such as nightjars and potoos. Despite the use of genome-scale molecular datasets, the phylogenetic interrelationships among major strisorean groups remain controversial. Given the availability of next-generation sequence data for Strisores and the clade’s rich fossil record, we reassessed the phylogeny of Strisores by incorporating a large-scale sequence dataset with anatomical data from living and fossil strisoreans within a Bayesian total-evidence framework. Combined analyses of molecular and morphological data resulted in a phylogenetic topology for Strisores that is congruent with the findings of two recent molecular phylogenomic studies, supporting nightjars (Caprimulgidae) as the extant sister group of the remainder of Strisores. This total-evidence framework allowed us to identify morphological synapomorphies for strisorean clades previously recovered using molecular-only datasets. However, a combined analysis of molecular and morphological data highlighted strong signal conflict between sequence and anatomical data in Strisores. Furthermore, simultaneous analysis of molecular and morphological data recovered differing placements for some fossil taxa compared with analyses of morphological data under a molecular scaffold, highlighting the importance of analytical decisions when conducting morphological phylogenetic analyses of taxa with molecular phylogenetic data. We suggest that multiple strisorean lineages have experienced convergent evolution across the skeleton, obfuscating the phylogenetic position of certain fossils, and that many distinctive specializations of strisorean subclades were acquired early in their evolutionary history. Despite this apparent complexity in the evolutionary history of Strisores, our results provide fossil support for aerial foraging as the ancestral ecological strategy of Strisores, as implied by recent phylogenetic topologies derived from molecular data.Parts of this project were supported by Systematics Research Fund awards to A.C. and D.J.F. by the Linnean Society of London and the Systematics Association. D.J.F. also acknowledges support from the Isaac Newton Trust early career support scheme. Parts of this project were also funded by the European Union’s Horizon 2020 research and innovation program 2014–2018 under grant agreement 677774 (European Research Council [ERC] Starting Grant: TEMPO) to R.B.J.B. N.D.W. and M.J.B. received Smithsonian Institution support through the Predoctoral Fellowship Program (N.D.W.), the Frontiers in Phylogenetics Program, the Scholarly Studies Program, and the Consortium for Understanding and Sustaining a Biodiverse Planet

A reassessment of the enigmatic diapsid Paliguana whitei and the early history of Lepidosauromorpha

Lepidosaurs include lizards, snakes, amphisbaenians and the tuatara, comprising a highly speciose evolutionary radiation with widely varying anatomical traits. Their stem-lineage originated by the late middle Permian 259 million years ago, but its early fossil record is poorly documented, obscuring the origins of key anatomical and functional traits of the group. Paliguana whitei, from the Early Triassic of South Africa, is an enigmatic fossil species with the potential to provide information on this. However, its anatomy and phylogenetic affinities remain highly uncertain, and have been debated since its discovery more than 100 years ago. We present microtomographic three-dimensional imaging of the cranial anatomy of P. whitei that clarifies these uncertainties, providing strong evidence for lepidosauromorph affinities based on the structure of the temporal region and the implantation of marginal dentition. Phylogenetic analysis including these new data recovers Paliguana as the earliest known stem-lepidosaur, within a long-lived group of early diverging lepidosauromorphs that persisted to at least the Middle Jurassic. Our results provide insights into cranial evolution on the lepidosaur stem-lineage, confirming that characteristics of pleurodont dental implantation evolved early on the lepidosaur stem-lineage. By contrast, key functional traits related to hearing (quadrate conch) and feeding (streptostyly) evolved later in the lepidosaur crown-group

Evolutionary versatility of the avian neck

Bird necks display unparalleled levels of morphological diversity compared to other vertebrates, yet it is unclear what factors have structured this variation. Using three-dimensional geometric morphometrics and multivariate statistics, we show that the avian cervical column is a hierarchical morpho-functional appendage, with varying magnitudes of ecologically driven osteological variation at different scales of organization. Contrary to expectations given the widely varying ecological functions of necks in different species, we find that regional modularity of the avian neck is highly conserved, with an overall structural blueprint that is significantly altered only by the most mechanically demanding ecological functions. Nevertheless, the morphologies of vertebrae within subregions of the neck show more prominent signals of adaptation to ecological pressures. We also find that both neck length allometry and the nature of neck elongation in birds are different from other vertebrates. In contrast with mammals, neck length scales isometrically with head mass and, contrary to previous work, we show that neck elongation in birds is achieved predominantly by increasing vertebral lengths rather than counts. Birds therefore possess a cervical spine that may be unique in its versatility among extant vertebrates, one that, since the origin of flight, has adapted to function as a surrogate forelimb in varied ecological niches

Geographic range did not confer resilience to extinction in terrestrial vertebrates at the end-Triassic crisis

Rates of extinction vary greatly through geological time, with losses particularly concentrated in mass extinctions. Species duration at other times varies greatly, but the reasons for this are unclear. Geographical range correlates with lineage duration amongst marine invertebrates, but it is less clear how far this generality extends to other groups in other habitats. It is also unclear whether a wide geographical distribution makes groups more likely to survive mass extinctions. Here we test for extinction selectivity amongst terrestrial vertebrates across the end-Triassic event. We demonstrate that terrestrial vertebrate clades with larger geographical ranges were more resilient to extinction than those with smaller ranges throughout the Triassic and Jurassic. However, this relationship weakened with increasing proximity to the end-Triassic mass extinction, breaking down altogether across the event itself. We demonstrate that these findings are not a function of sampling biases; a perennial issue in studies of this kind

Climate-mediated diversification of turtles in the Cretaceous

The file attached is the published version of the article

The first definitive carcharodontosaurid (Dinosauria:Theropoda) from Asia and the delayed ascent of tyrannosaurids

Little is known about the evolution of large-bodied theropod dinosaurs during the Early to mid Cretaceous in Asia. Prior to this time, Asia was home to an endemic fauna of basal tetanurans, whereas terminal Cretaceous ecosystems were dominated by tyrannosaurids, but the intervening 60 million years left a sparse fossil record. Here, we redescribe the enigmatic large-bodied Chilantaisaurus maortuensis from the Turonian of Inner Mongolia, China. We refer this species to a new genus, Shaochilong, and analyze its systematic affinities. Although Shaochilong has previously been allied with several disparate theropod groups (Megalosauridae, Allosauridae, Tyrannosauroidea, Maniraptora), we find strong support for a derived carcharodontosaurid placement. As such, Shaochilong is the first unequivocal Asian member of Carcharodontosauridae, which was once thought to be restricted to Gondwana. The discovery of an Asian carcharodontosaurid indicates that this clade was cosmopolitan in the Early to mid Cretaceous and that Asian large-bodied theropod faunas were no longer endemic at this time. It may also suggest that the ascent of tyrannosaurids into the large-bodied dinosaurian predator niche was a late event that occurred towards the end of the Cretaceous,between the Turonian and the Campanian

New Forearm Elements Discovered of Holotype Specimen Australovenator wintonensis from Winton, Queensland, Australia

New skeletal elements are reported of the holotype specimen Australovenator wintonensis, from the type locality, near Winton, central western Queensland. New elements include left and right humeri, right radius, right radiale, right distal carpal 1, near complete right metacarpal I, left manual phalanx II-1, left manual phalanx II-2, near complete left manual phalanx II-3 and a left manual phalanx III-3. These new elements combined with those previously described are compared against other neovenatorids