Ben Creisler
Some recent papers and abstracts:
Now with a free pdf (posted yesterday):
J. Matthias Starck, James R. Stewart & Daniel G. Blackburn (2021)
Phylogeny and evolutionary history of the amniote egg.ÂÂ
Journal of Morphology (advance online publication)
doi: https://doi.org/10.1002/jmor.21380
https://onlinelibrary.wiley.com/doi/10.1002/jmor.21380
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Darren Naish and Will Tattersdill (2021)
Art, Anatomy, and the Stars: Russell and SÃguinâs Dinosauroid.
Canadian Journal of Earth Sciences (advance online publication)
doi: https://doi.org/10.1139/cjes-2020-0172
https://cdnsciencepub.com/doi/abs/10.1139/cjes-2020-0172
Art, Anatomy, and the Stars: Russell and SÃguinâs Dinosauroid.
Canadian Journal of Earth Sciences (advance online publication)
doi: https://doi.org/10.1139/cjes-2020-0172
https://cdnsciencepub.com/doi/abs/10.1139/cjes-2020-0172
It takes a bold, innovative mind to publish an exercise in speculative evolution pertaining to an alternative timeline. Dale Russellâs studies of the troodontid Stenonychosaurus and of ornithomimid theropods, published in 1969 and 1972, inspired him to consider the possibility that some theropod dinosaur lineages might have given rise to big-brained species had they never died out. By late 1980, Russell had considered the invention of a hypothetical descendant of Stenonychosaurus dubbed the 'dinosauroid'. There is likely no specific inspiration for the dinosauroid given Russellâs overlapping areas of interest, but his correspondence with Carl Sagan and his involvement in the SETI programme were likely of special influence. The early-1980s creation of a life-size Stenonychosaurus model with Ron SÃguin gave Russell the impetus to bring the dinosauroid to life. Authors have disagreed on whether the dinosauroidâs creation was an exercise in scientific extrapolation or one of speculative fiction, and on whether its form reflects bias or an honest experiment: Russell justified his decisions on the basis of the dinosauroidâs anatomy being adaptive and linked to efficiency, but he also stated or implied that the human form may be considered a predictable evolutionary outcome among big-brained organisms, and expressed a preference for directionist views which posit humans as close to the pinnacle of evolution. Both derided and praised at the time of its construction, the dinosauroid is undergoing a resurgence of interest. Given that its aim was to spark discussion and invite alternative solutions, it can only be considered an extraordinary success.
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Exaeretodon and Tawa
Free pdf:
Brenen M. Wynd, Josef C. Uyeda & Sterling J. Nesbitt (2021)
Including distorted specimens in allometric studies: linear mixed models account for deformation.
Integrative Organismal Biology, obab017
doi: https://doi.org/10.1093/iob/obab017
https://academic.oup.com/iob/advance-article/doi/10.1093/iob/obab017/6277730
Allometry--patterns of relative change in body parts--is a staple for examining how clades exhibit scaling patterns representative of evolutionary constraint on phenotype, or quantifying patterns of ontogenetic growth within a species. Reconstructing allometries from ontogenetic series is one of the few methods available to reconstruct growth in fossil specimens. However, many fossil specimens are deformed (twisted, flattened, displaced bones) during fossilization, changing their original morphology in unpredictable and sometimes undecipherable ways. To mitigate against post burial changes, paleontologists typically remove clearly distorted measurements from analyses. However, this can potentially remove evidence of individual variation and limits the number of samples amenable to study, which can negatively impact allometric reconstructions. Ordinary least squares regression (OLS) and major axis regression are common methods for estimating allometry, but they assume constant levels of residual variation across specimens, which is unlikely to be true when including both distorted and undistorted specimens. Alternatively, a generalized linear mixed model (GLMM) can attribute additional variation in a model (e.g., fixed or random effects). We performed a simulation study based on an empirical analysis of the extinct cynodont, Exaeretodon argentinus, to test the efficacy of a GLMM on allometric data. We found that GLMMs estimate the allometry using a full dataset better than simply using only non-distorted data. We apply our approach on two empirical datasets, cranial measurements of actual specimens of E. argentinus (nâ=â16) and femoral measurements of the dinosaur Tawa hallae (nâ=â26). Taken together, our study suggests that a GLMM is better able to reconstruct patterns of allometry over an OLS in datasets comprised of extinct forms and should be standard protocol for anyone using distorted specimens.
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Free pdf:
Stephanie L. Baumgart, Paul C. Sereno & Mark W. Westneat (2021)
Wing shape in waterbirds: morphometric patterns associated with behavior, habitat, migration, and phylogenetic convergence.
Integrative Organismal Biology, obab011
doi: https://doi.org/10.1093/iob/obab011
https://academic.oup.com/iob/advance-article/doi/10.1093/iob/obab011/6276991
Wing shape plays a critical role in flight function in birds and other powered fliers and has been shown to be correlated with flight performance, migratory distance, and the biomechanics of generating lift during flight. Avian wing shape and flight mechanics have also been shown to be associated with general foraging behavior and habitat choice. We aim to determine if wing shape in waterbirds, a functionally and ecologically diverse assemblage united by their coastal and aquatic habitats, is correlated with various functional and ecological traits. We applied geometric morphometric approaches to the spread wings of a selection of waterbirds to search for evolutionary patterns between wing shape and foraging behavior, habitat and migratory patterns. We found strong evidence of convergent evolution of high and low aspect ratio wing shapes in multiple clades. Foraging behavior also consistently exhibits strong evolutionary correlations with wing shape. Habitat, migration and flight style, in contrast, do not exhibit significant correlation with wing shape in waterbirds. Although wing shape is critical to aerial flight function, its relationship to habitat and periodic locomotor demands such as migration is complex.
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Free pdf:
Ning Wang, Edward L Braun, Bin Liang, Joel Cracraft & Stephen A. Smith (2021)
Categorical edge-based analyses of phylogenomic data reveal conflicting signals for difficult relationships in the avian tree.
bioRxiv 2021.05.17.444565 (preprint)
doi: https://doi.org/10.1101/2021.05.17.444565
https://www.biorxiv.org/content/10.1101/2021.05.17.444565v1
Phylogenetic analyses of large-scale datasets sometimes fail to yield a satisfactory resolution of the relationships among taxa for a number of nodes in the tree of life. This has even been true for genome-scale datasets, where the failure to resolve relationships is unlikely to reflect limitations in the amount of data. Gene tree conflicts are particularly notable in studies focused on these contentious nodes in the tree of life, and taxon sampling, different analytical methods, and/or data-type effects are thought to further confound analyses. Observed conflicts among gene trees arise from both biological processes and artefactual sources of noise in analyses. Although many efforts have been made to incorporate biological conflicts, few studies have curated individual genes for their efficiency in phylogenomic studies. Here, we conduct an edge-based analysis of Neoavian evolution, examining the phylogenetic efficacy of two recent phylogenomic bird datasets and three datatypes (ultraconserved elements [UCEs], introns, and coding regions). We assess the potential causes for biases in signal-resolution for three difficult nodes: the earliest divergence of Neoaves, the position of the enigmatic Hoatzin (Opisthocomus hoazin), and the position of owls (Strigidae). We observed extensive conflict among genes for all data types and datasets even after we removed potentially problematic loci. Edge-based analyses increased congruence and examined the impact of data type, GC content variation (GCCV), and outlier genes on analyses. These factors had different impact on each of nodes we examined. First, outlier gene signals appeared to drive different patterns of support for the relationships among the earliest diverging Neoaves. Second, the position of Hoatzin was highly variable, but we found that data type was correlated with the signals that support different placements of the Hoatzin. However, the resolution with the most support in our analyses was Hoatzin + shorebirds. Finally, GCCV, rather than data type (i.e., coding vs non-coding) per se, was correlated with an owl + Accipitriformes signal. Eliminating high GCCV loci increased the signal for an owl + mousebird relationship. Difficult edges (i.e., characterized by deep coalescence and high gene-tree estimation error) are hard to recover with all methods (including concatenation, multispecies coalescent, and edge-based analyses), whereas "easy" edges (e.g., flamingos + grebes) can be recovered without ambiguity. Thus, the nature of the edges, rather than the methods, is the limiting factor. Categorical edge-based analyses can reveal the nature of each edge and provide a way to highlight especially problematic branches that warrant further examination in future phylogenomic studies. We suggest that edge-based analyses provide a tool that can increase our understanding about the parts of the avian tree that remain unclear, even with large-scale data. In fact, our results emphasize that the conflicts associated with edges that remain contentious in the bird tree may be even greater than appreciated based on previous studies.
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Also:
Matthew Owen Moreira, Carlos Fonseca and Danny Rojas (2021)
Parthenogenesis is self-destructive for scaled reptiles.ÂÂ
Biology Letters 17(5): 20210006
doi:Âhttps://doi.org/10.1098/rsbl.2021.0006
Biology Letters 17(5): 20210006
doi:Âhttps://doi.org/10.1098/rsbl.2021.0006
https://royalsocietypublishing.org/doi/10.1098/rsbl.2021.0006
Parthenogenesis is rare in nature. With 39 described true parthenogens, scaled reptiles (Squamata) are the only vertebrates that evolved this reproductive strategy. Parthenogenesis is ecologically advantageous in the short term, but the young age and rarity of parthenogenetic species indicate it is less advantageous in the long term. This suggests parthenogenesis is self-destructive: it arises often but is lost due to increased extinction rates, high rates of reversal or both. However, this role of parthenogenesis as a self-destructive trait remains unknown. We used a phylogeny of Squamata (5388 species), tree metrics, null simulations and macroevolutionary scenarios of trait diversification to address the factors that best explain the rarity of parthenogenetic species. We show that parthenogenesis can be considered as self-destructive, with high extinction rates mainly responsible for its rarity in nature. Since these parthenogenetic species occur, this trait should be ecologically relevant in the short term.
Parthenogenesis is rare in nature. With 39 described true parthenogens, scaled reptiles (Squamata) are the only vertebrates that evolved this reproductive strategy. Parthenogenesis is ecologically advantageous in the short term, but the young age and rarity of parthenogenetic species indicate it is less advantageous in the long term. This suggests parthenogenesis is self-destructive: it arises often but is lost due to increased extinction rates, high rates of reversal or both. However, this role of parthenogenesis as a self-destructive trait remains unknown. We used a phylogeny of Squamata (5388 species), tree metrics, null simulations and macroevolutionary scenarios of trait diversification to address the factors that best explain the rarity of parthenogenetic species. We show that parthenogenesis can be considered as self-destructive, with high extinction rates mainly responsible for its rarity in nature. Since these parthenogenetic species occur, this trait should be ecologically relevant in the short term.
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Free pdf:
Jeremy A. Spool, Matheus Macedo-Lima, Garrett Scarpa, Yuichi Morohashi, Yoko Yazaki-Sugiyama & Luke Remage-Healey Â(2021)
Genetically identified neurons in avian auditory pallium mirror core principles of their mammalian counterparts
Current Biology (advance online publication)
DOI: https://doi.org/10.1016/j.cub.2021.04.039
https://www.cell.com/current-biology/fulltext/S0960-9822(21)00574-1
Highlights
CaMKIIÎ and GAD1 promoters segregate pallial cell types in birds
Physiology and auditory coding roles distinguish these cell types in avian pallium
GAD1 and mDlx neurons drive local network synchrony and gamma oscillations
These distinctions in birds precisely match their mammalian pallial counterparts
Summary
In vertebrates, advanced cognitive abilities are typically associated with the telencephalic pallium. In mammals, the pallium is a layered mixture of excitatory and inhibitory neuronal populations with distinct molecular, physiological, and network phenotypes. This cortical architecture is proposed to support efficient, high-level information processing. Comparative perspectives across vertebrates provide a lens to understand the common features of pallium that are important for advanced cognition. Studies in songbirds have established strikingly parallel features of neuronal types between mammalian and avian pallium. However, lack of genetic access to defined pallial cell types in non-mammalian vertebrates has hindered progress in resolving connections between molecular and physiological phenotypes. A definitive mapping of the physiology of pallial cells onto their molecular identities in birds is critical for understanding how synaptic and computational properties depend on underlying molecular phenotypes. Using viral tools to target excitatory versus inhibitory neurons in the zebra finch auditory association pallium (calmodulin-dependent kinase alpha [CaMKIIÎ] and glutamate decarboxylase 1 [GAD1] promoters, respectively), we systematically tested predictions derived from mammalian pallium. We identified two genetically distinct neuronal populations that exhibit profound physiological and computational similarities with mammalian excitatory and inhibitory pallial cells, definitively aligning putative cell types in avian caudal nidopallium with these molecular identities. Specifically, genetically identified CaMKIIÎ and GAD1 cell types in avian auditory association pallium exhibit distinct intrinsic physiological parameters, distinct auditory coding principles, and inhibitory-dependent pallial synchrony, gamma oscillations, and local suppression. The retention, or convergence, of these molecular and physiological features in both birds and mammals clarifies the characteristics of pallial circuits for advanced cognitive abilities.
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Free pdf:
Lauren Lawson & Njal Rollinson (2021)
A simple model for the evolution of temperature-dependent sex determination explains the temperature sensitivity of embryonic mortality in imperiled reptiles.
Conservation Physiology 9(1): coab020
doi: https://doi.org/10.1093/conphys/coab020
https://academic.oup.com/conphys/article/9/1/coab020/6273340
A common reptile conservation strategy involves artificial incubation of embryos and release of hatchlings or juveniles into wild populations. Temperature-dependent sex determination (TSD) occurs in most chelonians, permitting conservation managers to bias sex ratios towards females by incubating embryos at high temperatures, ultimately allowing the introduction of more egg-bearing individuals into populations. Here, we revisit classic sex allocation theory and hypothesize that TSD evolved in some reptile groups (specifically, chelonians and crocodilians) because male fitness is more sensitive to condition (general health, vigor) than female fitness. It follows that males benefit more than females from incubation environments that confer high-quality phenotypes, and hence high-condition individuals. We predict that female-producing temperatures, which comprise relatively high incubation temperatures in chelonians and crocodilians, are relatively stressful for embryos and subsequent life stages. We synthesize data from 28 studies to investigate how constant temperature incubation affects embryonic mortality in chelonians with TSD. We find several lines of evidence suggesting that warm, female-producing temperatures are more stressful than cool, male-producing temperatures. Further, we find some evidence that pivotal temperatures (TPiv, the temperature that produces a 1:1 sex ratio) may exhibit a correlated evolution with embryonic thermal tolerance. If patterns of temperature-sensitive embryonic mortality are also indicative of chronic thermal stress that occurs post-hatching, then conservation programs may benefit from incubating eggs close to species-specific TPivs, thus avoiding high-temperature incubation. Indeed, our models predict that, on average, a sex ratio of >75% females can generally be achieved by incubating eggs only 1ÂC above TPiv. Of equal importance, we provide insight into the enigmatic evolution of TSD in chelonians, by providing support to the hypothesis that TSD evolution is related to the quality of the phenotype conferred by incubation temperature, with males produced in high-quality incubation environments.
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Abstract only:
Isengops luangwensis gen. et sp. nov.
Christian A. Sidor, Neil J. Tabor and ÂRoger M. Smith (2021)
A new late Permian burnetiamorph from Zambia confirms exceptional levels of endemism in Burnetiamorpha (Therapsida: Biarmosuchia) and an updated paleoenvironmental interpretation of the upper Madumabisa Mudstone Formation.
Frontiers in Ecology and Evolution (abstract only)
doi: 10.3389/fevo.2021.685244
https://www.frontiersin.org/articles/10.3389/fevo.2021.685244/abstract
A new burnetiamorph therapsid, Isengops luangwensis, gen. et sp. nov., is described on the basis of a partial skull from the upper Madumabisa Mudstone Formation of the Luangwa Basin of northeastern Zambia. Isengops is diagnosed by reduced palatal dentition, a ridge-like palatine-pterygoid boss, a palatal exposure of the jugal that extends far anteriorly, a tall trigonal pyramid-shaped supraorbital boss, and a recess along the dorsal margin of the lateral temporal fenestra. The upper Madumabisa Mudstone Formation was deposited in a rift basin with lithofacies characterized by unchannelized flow, periods of subaerial desiccation and non-deposition, and pedogenesis, and can be biostratigraphically tied to the upper Cistecephalus Assemblage Zone of South Africa, suggesting a Wuchiapingian age. Isengops is the second burnetiamorph recognized from Zambia and is part of a tetrapod assemblage remarkably similar to others across southern Pangea during the Wuchiapingian. A revised cladistic analysis of Biarmosuchia yielded over 500 most parsimonious trees that generally reaffirm the results of previous analyses for burnetiamorphs: Lemurosaurus is basal, Lobalopex and Isengops are proximate burnetiid outgroups, and Bullacephalus, Burnetia, Mobaceras, Niuksenitia, and Pachydectes are burnetiines. Furthermore, Russian biarmosuchians are scattered throughout the tree and do not form sister taxon relationships with each other. Burnetiamorphs display a wide disparity of cranial adornments and are relatively speciose (13 species), especially when compared to the number of specimens discovered to date (~16 specimens). As has been suggested in some other tetrapod clades (e.g., ceratopsian dinosaurs), the burnetiamorph fossil record supports an inferred macroevolutionary relationship between cranial adornment and increased speciation rate.
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Also correcting a recent abstract-only post:
Arjan Mann, Thomas W. Dudgeon, Amy C. Henrici, Dave S. Berman and Stephanie E. Pierce (2021)
Digit and ungual morphology suggest adaptations for scansoriality in the late Carboniferous eureptile Anthracodromeus longipes.
Frontiers in Earth Science (abstract only)
doi: 10.3389/feart.2021.675337
https://www.frontiersin.org/articles/10.3389/feart.2021.675337/abstract
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 claws. With these data, we quantitatively evaluate the locomotor ecology of Anthracodromeus using morphometric analyses of the phalangeal proportions, claw curvature, and claw shape. Our findings indicate that the anatomy of Anthracodromeus likely facilitated scansorial clinging to some degree via recurved claws 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.
Digit and ungual morphology suggest adaptations for scansoriality in the late Carboniferous eureptile Anthracodromeus longipes.
Frontiers in Earth Science (abstract only)
doi: 10.3389/feart.2021.675337
https://www.frontiersin.org/articles/10.3389/feart.2021.675337/abstract
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 claws. With these data, we quantitatively evaluate the locomotor ecology of Anthracodromeus using morphometric analyses of the phalangeal proportions, claw curvature, and claw shape. Our findings indicate that the anatomy of Anthracodromeus likely facilitated scansorial clinging to some degree via recurved claws 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.