Dataset Information

Quantitatively assessing mekosuchine crocodile locomotion by geometric morphometric and finite element analysis of the forelimb.

ABSTRACT: Morphological shifts observed in the fossil record of a lineage potentially indicate concomitant shifts in ecology of that lineage. Mekosuchine crocodiles of Cenozoic Australia display departures from the typical eusuchian body-plan both in the cranium and postcranium. Previous qualitative studies have suggested that these crocodiles had a more terrestrial habitus than extant crocodylians, yet the capacity of mekosuchine locomotion remains to be tested. Limb bone shape, such as diaphyseal cross-section and curvature, has been related to habitual use and locomotory function across a wide variety of taxa. Available specimens of mekosuchine limbs, primarily humeri, are distinctly columnar compared with those of extant crocodylians. Here we apply a quantitative approach to biomechanics in mekosuchine taxa using both geomorphic morphometric and finite element methods to measure bone shape and estimate locomotory stresses in a comparative context. Our results show mekosuchines appear to diverge from extant semi-aquatic saltwater and freshwater crocodiles in cross-sectional geometry of the diaphysis and generate different structural stresses between models that simulate sprawling and high-walk gaits. The extant crocodylians display generally rounded cross-sectional diaphyseal outlines, which may provide preliminary indication of resistance to torsional loads that predominate during sprawling gait, whereas mekosuchine humeri appear to vary between a series of elliptical outlines. Mekosuchine structural stresses are comparatively lower than those of the extant crocodylians and reduce under high-walk gait in some instances. This appears to be a function of bending moments induced by differing configurations of diaphyseal curvature. Additionally, the neutral axis of structural stresses is differently oriented in mekosuchines. This suggests a shift in the focus of biomechanical optimisation, from torsional to axial loadings. Our results lend quantitative support to the terrestrial habitus hypothesis in so far as they suggest that mekosuchine humeri occupied a different morphospace than that associated with the semi-aquatic habit. The exact adaptational trajectory of mekosuchines, however, remains to be fully quantified. Novel forms appear to emerge among mekosuchines during the late Cenozoic. Their adaptational function is considered here; possible applications include navigation of uneven terrain and burrowing.

SUBMITTER: Stein MD

PROVIDER: S-EPMC7301899 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Quantitatively assessing mekosuchine crocodile locomotion by geometric morphometric and finite element analysis of the forelimb.

Stein Michael D MD Hand Suzanne J SJ Archer Michael M Wroe Stephen S Wilson Laura A B LAB

PeerJ 20200615

Morphological shifts observed in the fossil record of a lineage potentially indicate concomitant shifts in ecology of that lineage. Mekosuchine crocodiles of Cenozoic Australia display departures from the typical eusuchian body-plan both in the cranium and postcranium. Previous qualitative studies have suggested that these crocodiles had a more terrestrial habitus than extant crocodylians, yet the capacity of mekosuchine locomotion remains to be tested. Limb bone shape, such as diaphyseal cross- ...[more]

PMID: 32587803

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Project description:BackgroundFor centuries, morphology has been the most commonly selected trait in horses. A 3D video recording enabled us to obtain the coordinates of 43 anatomical landmarks of 2089 jumping horses. Generalized Procrustes analysis provided centered and scaled coordinates that were independent of volume, i.e., centroid size. Genetic analysis of these coordinates (mixed model; 17,994 horses in the pedigree) allowed us to estimate a variance-covariance matrix. New phenotypes were then defined: the "summarized shapes". They were obtained by linear combinations of Procrustes coordinates with, as coefficients, the eigenvectors of the genetic variance-covariance matrix. These new phenotypes were used in genome-wide association analyses (GWAS) and multitrait genetic analysis that included judges' scores and competition results of the horses.ResultsWe defined ten shapes that represented 86% of the variance, with heritabilities ranging from 0.14 to 0.42. Only one of the shapes was found to be genetically correlated with competition success (rg = - 0.12, standard error = 0.07). Positive and negative genetic correlations between judges' scores and shapes were found. This means that the breeding objective defined by judges involves improvement of anatomical parts of the body that are negatively correlated with each other. Known single nucleotide polymorphisms (SNPs) on chromosomes 1 and 3 for height at withers were significant for centroid size but not for any of the shapes. As these SNPs were not associated with the shape that distinguished rectangular horses from square horses (with height at withers greater than body length), we hypothesize that these SNPs play a role in the overall development of horses, i.e. in height, width, and length but not in height at withers when standardized to unit centroid size. Several other SNPs were found significant for other shapes.ConclusionsThe main application of 3D morphometric analysis is the ability to define the estimated breeding value (EBV) of a sire based on the shape of its potential progeny, which is easier for breeders to visualize in a single synthetic image than a full description based on linear profiling. However, the acceptance of these new phenotypes by breeders and the complex nature of summarized shapes may be challenging. Due to the low genetic correlations of the summarized shapes with jumping performance, the methodology did not allow indirect performance selection criteria to be defined.

Dataset Information

Quantitatively assessing mekosuchine crocodile locomotion by geometric morphometric and finite element analysis of the forelimb.

Publications

Quantitatively assessing mekosuchine crocodile locomotion by geometric morphometric and finite element analysis of the forelimb.

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