Ben Creisler
NOTE:
Royal Society Open Access Week October 22 through October 28.
All content is open access.
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Some recent non-dino papers:
Ashley M. Heers, Jeffery W. Rankin and John R. Hutchinson (2018)
Building a Bird: Musculoskeletal Modeling and Simulation of Wing-Assisted Incline Running During Avian Ontogeny.
Frontiers in Bioengineering and Biotechnology 6:140
Flapping flight is the most power-demanding mode of locomotion, associated with a suite of anatomical specializations in extant adult birds. In contrast, many developing birds use their forelimbs to negotiate environments long before acquiring âflight adaptations,â recruiting their developing wings to continuously enhance leg performance and, in some cases, fly. How does anatomical development influence these locomotor behaviors? Isolating morphological contributions to wing performance is extremely challenging using purely empirical approaches. However, musculoskeletal modeling and simulation techniques can incorporate empirical data to explicitly examine the functional consequences of changing morphology by manipulating anatomical parameters individually and estimating their effects on locomotion. To assess how ontogenetic changes in anatomy affect locomotor capacity, we combined existing empirical data on muscle morphology, skeletal kinematics, and aerodynamic force production with advanced biomechanical modeling and simulation techniques to analyze the ontogeny of pectoral limb function in a precocial ground bird (Alectoris chukar). Simulations of wing-assisted incline running (WAIR) using these newly developed musculoskeletal models collectively suggest that immature birds have excess muscle capacity and are limited more by feather morphology, possibly because feathers grow more quickly and have a different style of growth than bones and muscles. These results provide critical information about the ontogeny and evolution of avian locomotion by (i) establishing how muscular and aerodynamic forces interface with the skeletal system to generate movement in morphing juvenile birds, and (ii) providing a benchmark to inform biomechanical modeling and simulation of other locomotor behaviors, both across extant species and among extinct theropod dinosaurs.
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Matthew H. Shirley, Amanda N. Carr, Jennifer H. Nestler, Kent A. Vliet & Christopher A. Brochu (2018)
Systematic revision of the living African Slender-snouted Crocodiles (Mecistops Gray, 1844).
Zootaxa 4504(2)Â
Molecular and morphological evidence has shown that the African slender-snouted, or sharp-nosed, crocodile Mecistops cataphractus (Cuvier, 1824) is comprised of two superficially cryptic species: one endemic to West Africa and the other endemic to Central Africa. Our ability to characterize the two species is compromised by the complicated taxonomic history of the lineage and overlapping ranges of variation in distinguishing morphological features. The name M. cataphractus was evidently originally based on West African material, but the holotype is now lost. Although types exist for other names based on the West African form, the name M. cataphractus is sufficiently entrenched in the literature, and other names sufficiently obscure, to justify retypification. Here, we designate a neotype for M. cataphractus and restrict it to West Africa. We resurrect M. leptorhynchus as a valid species from Central Africa and identify exemplary referred specimens that, collectively, overcome the obscurity and diagnostic limits of the extant holotype. We additionally indicate suitable neotype material in the event the holotype is lost, destroyed, or otherwise needing replacement, and we rectify the previously erroneous type locality designation. We provide a revised diagnosis for crown Mecistops, and revise and update previous descriptions of the two living species, including providing both more complete descriptions and discussion of diagnostic characters. Finally, we provide considerable discussion of the current state of knowledge of these speciesâ ecology, natural history, and distribution.
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Celeste M. PÃrez-Ben & RaÃl O. GÃmez (2018)
Morphological integration and evolution of the skull roof in temnospondyl amphibians
Journal of Iberian Geology (advance online publication)
Morphological integration refers to the phenotypic interdependence of two or more traits and is estimated by the degree of covariation or correlation among traits at different levels, such as at the intraspecific and evolutionary scales. Intraspecific integration of morphological traits results from the interaction among traits at the genetic, developmental, and functional levels and it has been proposed that it channels morphological evolution by modulating variability. In this work, we test whether the intraspecific integration might have channeled the morphological evolution of the skull roof in a major tetrapod radiation, that of extinct temnospondyl amphibians. To do this, we quantified the patterns of intraspecific integration of different species and explored their relationships with the evolutionary patterns of integration and disparity of three clades of temnospondyls using geometric morphometrics. We recovered that, at the intraspecific level, the integration patterns of the total shape of the skull roof are conserved across the clade and over geological time, but that the integration among individual bones varies in every species considered. We did not find a correlation between the patterns of integration among individual bones at the intraspecific and evolutionary levels, nor between the strength of intraspecific integration of each bone and their respective disparity. These results suggest that the intraspecific integration might have not affected significantly the morphological evolution of the skull roof in temnospondyls over geological time. Thus, it seems that the morphological evolution of this skeletal part might have been driven more by selective pressures than by shared developmental constraints inherited from the temnospondyl ancestor.
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Free pdf:Â
MarÃa Torres-SÃnchez, Christopher J. Creevey, Etienne Kornobis, David J. Gower, Mark Wilkinson & Diego San Mauro (2018)
Multi-tissue transcriptomes of caecilian amphibians highlight incomplete knowledge of vertebrate gene families.Â
DNA Research, dsy034
RNA sequencing (RNA-seq) has become one of the most powerful tools to unravel the genomic basis of biological adaptation and diversity. Although challenging, RNA-seq is particularly promising for research on non-model, secretive species that cannot be observed in nature easily and therefore remain comparatively understudied. Among such animals, the caecilians (order Gymnophiona) likely constitute the least known group of vertebrates, despite being an old and remarkably distinct lineage of amphibians. Here, we characterize multi-tissue transcriptomes for five species of caecilians that represent a broad level of diversity across the order. We identified vertebrate homologous elements of caecilian functional genes of varying tissue specificity that reveal a great number of unclassified gene families, especially for the skin. We annotated several protein domains for those unknown candidate gene families to investigate their function. We also conducted supertree analyses of a phylogenomic dataset of 1,955 candidate orthologous genes among five caecilian species and other major lineages of vertebrates, with the inferred tree being in agreement with current views of vertebrate evolution and systematics. Our study provides insights into the evolution of vertebrate protein-coding genes, and a basis for future research on the molecular elements underlying the particular biology and adaptations of caecilian amphibians.
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Free pdf:
Alexander M. Dunhill, William J. Foster, Sandro Azaele, James Sciberras & Richard J. Twitchett (2018)
Modelling determinants of extinction across two Mesozoic hyperthermal events.
Proceedings of the Royal Society BÂ 285: 20180404Â
DOI: 10.1098/rspb.2018.0404
The Late Triassic and Early Toarcian extinction events are both associated with greenhouse warming events triggered by massive volcanism. These Mesozoic hyperthermals were responsible for the mass extinction of marine organisms and resulted in significant ecological upheaval. It has, however, been suggested that these events merely involved intensification of background extinction rates rather than significant shifts in the macroevolutionary regime and extinction selectivity. Here, we apply a multivariate modelling approach to a vast global database of marine organisms to test whether extinction selectivity varied through the Late Triassic and Early Jurassic. We show that these hyperthermals do represent shifts in the macroevolutionary regime and record different extinction selectivity compared to background intervals of the Late Triassic and Early Jurassic. The Late Triassic mass extinction represents a more profound change in selectivity than the Early Toarcian extinction but both events show a common pattern of selecting against pelagic predators and benthic photosymbiotic and suspension-feeding organisms, suggesting that these groups of organisms may be particularly vulnerable during episodes of global warming. In particular, the Late Triassic extinction represents a macroevolutionary regime change that is characterized by (i) the change in extinction selectivity between Triassic background intervals and the extinction event itself; and (ii) the differences in extinction selectivity between the Late Triassic and Early Jurassic as a whole.