Ben Creisler
Some recent papers:
Free pdf:
Savannah Elizabeth Cobb & William I. Sellers (2019)
Inferring lifestyle for Aves and Theropoda: a model based on curvatures of extant avian ungual bones.
bioRxiv (advance online publication)
Free pdf:
Claws are involved in a number of behaviours including locomotion and prey capture, and as a result animals evolve claw morphologies that enable these functions. Past authors have found geometry of the keratinous sheath of the claw to correlate with mode of life for extant birds and squamates; this relationship has frequently been cited to infer lifestyles for Mesozoic theropods including Archaeopteryx. However, claw sheaths rarely fossilize and are prone to deformation; past inferences are thus compromised. As the ungual phalanx within the claw is relatively resistant to deformation and more commonly preserved in the fossil record, geometry of this bone would provide a more useful metric for paleontological analysis. In this study, ungual bones of 108 birds and 5 squamates were imaged using X-ray techniques and a relationship was found between curvatures of the ungual bone within the claw of pedal digit III and four modes of life; ground-dwelling, perching, predatory, and scansorial; using linear discriminant analysis with Kappa equal to 0.69. Our model predicts arboreal lifestyles for certain key taxa Archaeopteryx and Microraptor and a predatory ecology for Confuciusornis. These findings demonstrate the utility of our model in answering questions of palaeoecology, the theropod-bird transition, and the evolution of avian flight.
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Tetsuro Yoshikawa, Kazuto Kawakami & Takashi Masaki (2019)
Allometric scaling of seed retention time in seed dispersers and its application to estimation of seed dispersal potentials of theropod dinosaurs.
OIKOS (advance online publication)
Seed retention time (SRT), the time interval between seed ingestion and defaecation, is a critical parameter that determines the spatial pattern of seed dispersal created by an animal, and is therefore, an essential component of traitâbased modelling of seed dispersal functions. However, no simple predictive model of SRT for any given animal exists.
We explored the linkage between animal traits and SRT. We collected previously published data on mean SRT for 112 species of birds, mammals, reptiles and fishes and investigated the general allometric scaling of mean SRT with body mass for each taxon. Moreover, we analysed the effects of food habit and digestive strategy on mean SRT for birds and mammals.
In general, mean SRT increased with body mass in all four taxa, whereas the pattern of allometric scaling varied greatly among the taxa. Birds had a smaller intercept and larger slope than those of mammals, whereas reptiles had a much larger intercept and smaller slope than those of either birds or mammals. For birds, food habit was also detected as an important factor affecting SRT. We applied the allometric scaling that was obtained for birds to estimate mean SRT of extinct Mesozoic dinosaurs (Theropoda) -- few of which are assumed to have acted as seed dispersers. SRT for large carnivorous theropods was estimated to be 4--5 days, when considering only body mass.
The present study provides allometric scaling parameters of mean SRT for a variety of seedâdispersing animals, and highlights large variations in scaling among taxa. The allometric scaling obtained could be a critical component of further traitâbased modelling of seed dispersal functions. Further, the potential and limitations of the scaling of animal SRT with body mass and a future pathway to the development of traitâbased modelling are discussed.
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Karin Brigit Holthaus, Leopold Eckhart, Luisa Dalla Valle & Lorenzo Alibardi (2019)
Review: Evolution and diversification of corneous betaâproteins, the characteristic epidermal proteins of reptiles and birds.
Journal of Experimental Zoology Part B: Molecular and Developmental Evolution (advance online publication)
In all amniotes specialized intermediate filament keratins (IFâkeratins), in addition to keratinâassociated and corneous proteins form the outermost cornified layer of the epidermis. Only in reptiles and birds (sauropsids) the epidermis of scales, claws, beaks, and feathers, largely comprises small proteins formerly indicated as "betaâkeratins" but here identified as corneous betaâproteins (CBPs) to avoid confusion with true keratins. Genes coding for CBPs have evolved within the epidermal differentiation complex (EDC), a locus with no relationship with those of IFâkeratins. CBP genes have the same exonâintron structure as EDC genes encoding other corneous proteins of sauropsids and mammals, but they are unique by encoding a peculiar internal amino acid sequence motif betaâsheet region that allows formation of CBP filaments in the epidermis and epidermal appendages of reptiles and birds. In contrast, skin appendages of mammals, like hairs, claws, horns and nails, contain keratinâassociated proteins that, like IFâkeratin genes, are encoded by genes in loci different from the EDC. Phylogenetic analysis shows that lepidosaurian (lizards and snakes) and nonlepidosaurian (crocodilians, birds, and turtles) CBPs form two separate clades that likely originated after the divergence of these groups of sauropsids in the Permian Period. Cladeâspecific CBPs evolved to make most of the corneous material of feathers in birds and of the shell in turtles. Based on the recent identification of the complete sets of CBPs in all major phylogenetic clades of sauropsids, this review provides a comprehensive overview of the molecular evolution of CBPs.
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UPDATE:
These free open access papers (posted earlier in advance form) are now out in final form with new links:
WANG Min, Jingmai O'CONNOR & ZHOU Zhong-He (2019)
A taxonomical revision of the Confuciusornithiformes (Aves: Pygostylia).
Vertebrata PalAsiatica 57 (1): 1-37Â Â ÂÂ
DOI: 10.19615/j.cnki.1000-3118.180530
Free pdf:
Supplementary information:
The Confuciusornithiformes is a basal clade of Early Cretaceous birds that includes the oldest and most basal birds with a toothless beak and an abbreviated bony tail. Over the last two decades, thousands of specimens have been collected, more than for any other group of Mesozoic birds or non-avian dinosaurs. Ten species separated into four genera have been erected with limited taxonomic phylogenetic scrutiny. Here, we perform a comparative study of these ten species, and demonstrate that most of these taxa were originally diagnosed by characters that prove to be either preservational artifacts, intraspecific variations, subject to ontogenetic variation, or widely distributed among the Confuciusornithiformes or a more phylogenetically inclusive group. Our results suggest that 'Confuciusornis suniae', 'C. feducciai', 'Jinzhouornis yixianensis', 'J. zhangjiyingia', and 'C. jianchangensis' are all junior synonyms of C. sanctus. 'C. chuonzhous' lacks autapomorphies of C. sanctus and is referred to Confuciusornithiformes incertae sedis. Our taxonomic reappraisal of published materials indicates that the Confuciusornithiformes consists of one family, three genera, and four species: C. sanctus, C. dui, Changchengornis hengdaoziensis, and Eoconfuciusornis zhengi, for which we provide revised diagnoses.Â
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ZHOU Ya-Chun, Corwin SULLIVAN & ZHANG Fu-Cheng (2019)
Negligible effect of tooth reduction on body mass in Mesozoic birds.
Vertebrata PalAsiatica 57 (1): 38-50
DOI: 10.19615/j.cnki.1000-3118.180307
Free pdf:
ÂTooth reduction and loss was an important evolutionary process in Mesozoic birds. Analysis of evolutionary trends in the total mass of the dentition, a function of tooth size and tooth number, has the potential to shed light on the evolutionary pattern of tooth reduction and loss, and on the causes of this pattern. Because modern birds lack teeth, however, they cannot provide the basis for a model that would allow estimation of tooth masses in their Mesozoic counterparts. We selected the teeth of crocodilians as analogues of those in Mesozoic birds because the former are the closest living relatives of the latter, and the two groups are similar in tooth morphology, tooth implantation, and tooth replacement pattern. To estimate tooth masses in Mesozoic birds, we formulated four regression equations relating tooth mass to various linear dimensions, which were measured in 31 intact isolated teeth from eight individual crocodiles (Crocodylus siamensis). The results for Mesozoic birds show that dental mass as a proportion of body mass was negligible, at least from the perspective of flight performance, suggesting that selection pressure favoring body mass reduction was probably not the primary driver of tooth reduction or loss. Variations in dental mass among Mesozoic birds may reflect the different foods they ate, and the different types of feeding behavior they displayed.Â