Lucas J. Legendre

Bio: Lucas J. Legendre is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Bone growth & Medicine. The author has an hindex of 9, co-authored 17 publications receiving 244 citations. Previous affiliations of Lucas J. Legendre include Indiana Statewide Testing for Educational Progress-Plus & University of Paris.

Palaeohistological Evidence for Ancestral High Metabolic Rate in Archosaurs

Abstract: Metabolic heat production in archosaurs has played an important role in their evolutionary radiation during the Mesozoic, and their ancestral metabolic condition has long been a matter of debate in systematics and palaeontology. The study of fossil bone histology provides crucial information on bone growth rate, which has been used to indirectly investigate the evolution of thermometabolism in archosaurs. However, no quantitative estimation of metabolic rate has ever been performed on fossils using bone histological features. Moreover, to date, no inference model has included phylogenetic information in the form of predictive variables. Here we performed statistical predictive modeling using the new method of phylogenetic eigenvector maps on a set of bone histological features for a sample of extant and extinct vertebrates, to estimate metabolic rates of fossil archosauromorphs. This modeling procedure serves as a case study for eigenvector-based predictive modeling in a phylogenetic context, as well as an investigation of the poorly known evolutionary patterns of metabolic rate in archosaurs. Our results show that Mesozoic theropod dinosaurs exhibit metabolic rates very close to those found in modern birds, that archosaurs share a higher ancestral metabolic rate than that of extant ectotherms, and that this derived high metabolic rate was acquired at a much more inclusive level of the phylogenetic tree, among non-archosaurian archosauromorphs. These results also highlight the difficulties of assigning a given heat production strategy (i.e., endothermy, ectothermy) to an estimated metabolic rate value, and confirm findings of previous studies that the definition of the endotherm/ectotherm dichotomy may be ambiguous.

The evolution of mechanisms involved in vertebrate endothermy.

Abstract: Endothermy, i.e. the endogenous production of metabolic heat, has evolved multiple times among vertebrates, and several strategies of heat production have been studied extensively by physiologists ...

Evidence for high bone growth rate in Euparkeria obtained using a new paleohistological inference model for the humerus

Abstract: The study of bone growth rate and metabolic rate evolution in archosaurs (crocodiles, dinosaurs including birds, and pterosaurs) and close outgroups has become a subject of major interest among paleontologists in recent years. In this paper, we estimate the bone growth rate of Euparkeria using a new statistical inference model for the humerus. We modified the taxonomic range of extant species used in previous studies, on which we performed quantitative measurements of histological features and bone growth rates. Bone growth rate values estimated for Euparkeria are crucial in understanding the ancestral condition for archosaurs because this taxon is considered the closest relative to the archosaur crown group. We obtained an instantaneous growth rate of 6.12 µm/day, suggesting that Euparkeria shared with other non-archosaurian archosauromorphs (Prolacerta, Proterosuchus, and Erythrosuchus) a condition of high growth rate compatible with endothermy. This derived state may have been inherited by som...

Phylogenetic signal in bone histology of amniotes revisited.

Abstract: There is currently a debate about the presence of a phylogenetic signal in bone histological data, but very few rigorous tests have fuelled the discussions on this topic. Here, we performed new analyses using a larger set of seven histological traits and including 25 taxa (nine extinct and 16 extant taxa), using three methods: the phylogenetic eigenvector regression, the tree length distribution and the regressions on distance matrices. Our results clearly show that the phylogenetic signal in our sample of bone histological characters is strong, even after correcting for multiple testing. Most characters exhibit a significant phylogenetic signal according to at least one of our three tests, with the phylogeny often explaining 20-60% of the variation in the histological characters. Thus, we conclude that the phylogenetic comparative method should be systematically used in interspecific analyses of bone histodiversity to avoid problems of non-independence among observations.

Bone histology, phylogeny, and palaeognathous birds (Aves: Palaeognathae)

Abstract: The presence of a phylogenetic signal in the variation of osteohistological features has been recently debated in the literature. Previous studies have found a significant signal for some features, but these results were obtained on a small amount of characters and a reduced sample. Here we perform a comprehensive study in which we quantify the phylogenetic signal on 62 osteohistological features in an exhaustive sample of palaeognathous birds. We used four different estimators to measure phylogenetic signal – Pagel's λ, Abouheif's Cmean, Blomberg's K, and Diniz-Filho's phylogenetic eigenvector regressions PVR – and four topologies taken from the literature. Bone size and bone vascular density exhibit a strong phylogenetic signal, whereas all but four of the remaining features measured at the histological level – cellular size in caudal and medial transects of femora, and proportion of oblique vascular canals in rostral and caudal transects of tibiotarsi – exhibit a weaker signal. We also found that the impact of the topologies used in the analyses is very low compared with that of sample size. We conclude that the analysis of a comprehensive sample is crucial to obtain reliable quantifications of the phylogenetic signal. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112, 688–700.

Bones Structure And Mechanics

Abstract: Thank you for downloading bones structure and mechanics. As you may know, people have search hundreds times for their favorite books like this bones structure and mechanics, but end up in malicious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they are facing with some malicious virus inside their laptop. bones structure and mechanics is available in our book collection an online access to it is set as public so you can download it instantly. Our book servers saves in multiple countries, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the bones structure and mechanics is universally compatible with any devices to read.

Facts and Fiction

Abstract: • Jess chose a study because it was likely to be scaled up, but she was not very interested or strong at it. She got a VCE study score of 25 for the study, which was scaled up to an ATAR subject score of 29. This was lower than the rest of her VTAC Scaled Study scores, all scaled down to between 32 and 34. Jess would have been better off choosing all her studies based on her interests and strengths. • Morgan on the other hand chose all his studies based on his strengths and interests. Morgan still selected two studies that were scaled down, but got VCE study scores of 38 for one and 40 for the other. These were scaled down to 36 and 39 respectively. These were about the same as the rest of Morgan’s VTAC Scaled Study scores, which were around 38 to 39. Morgan was not disadvantaged by choosing those studies.

Development-based revision of bone tissue classification: the importance of semantics for science

Abstract: Research on the bone histology of extant and extinct animals has a long scientific history and an accurate description of microstructural tissues is the cornerstone of the field. Ideally, terminology needs to convey as much information as possible about the structural, developmental, and functional aspects of bone tissues corresponding to the up-to-date knowledge of the time. However, current terms are not always consistent with new observations and advances in the field of bone biology. We provide a brief overview of some ambiguities and their origins, and suggest a new approach of bone tissue classification and description that is congruent with our current understanding of bone as a living tissue, emphasizing its developmental aspects. This approach requires the introduction of a new term, namely ‘woven-parallel complex’, for describing a broad range of complex bone tissue types, including intramembranous and endochondral bones, and different types of primary as well as secondary bone tissues. We reconsider the classical concept of fibrolamellar complex, which we place within the new developmental approach. Finally, using non-archosaurian archosauromorphs as an example group, we demonstrate how the new approach can be utilized in an evolutionary context. The present study demonstrates the relevance and constant evolution of technical terminology along with the advances of the field of science. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112, 799–816.