Free pdf:
Matthew Aleksander Wysocki (2019)
Fossil evidence of evolutionary convergence in juvenile dental morphology and upper canine replacement in sabertooth carnivores
Ecology and Evolution (advance online publication)
doi: Â
https://doi.org/10.1002/ece3.5732https://onlinelibrary.wiley.com/doi/10.1002/ece3.5732Free pdf:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/ece3.5732The convergent suite of morphological traits characterizing the mammalian sabertooth ecomorphology is well documented, including modifications of the dental and osteological portions of the masticatory apparatus from a lessâspecialized carnivore condition. Equally important is how those specialized adult morphologies developed through ontogeny because previous studies have shown that growing such specialized craniodental traits may require evolutionary modification of growth patterns and tooth replacement mechanisms. Despite the understanding of convergent morphological specialization in adult sabertooth carnivores, the possibility of a convergent ontogenetic trajectory toward those adult morphologies has not been rigorously examined. The present study examines numerous previously undescribed juvenile nimravid specimens. The results provide insights about nimravid ontogeny and show, for the first time, that the nimravid sabertooth lineage included species in which the permanent upper canine erupted within a lingual concavity of the deciduous upper canine until it reached comparable crown height beyond the alveolar border. Furthermore, this investigation assesses the juvenile morphology and upper canine replacement of felid and barbourofelid sabertooth taxa. The results provide evidence of convergence in deciduous upper canine morphology of three sabertooth carnivore lineages (i.e., nimravid, felid, and barbourofelid), as well as preliminary evidence of convergence in the upper canine replacement process. It might be beneficial for studies of extreme morphological specialization to simultaneously consider convergence in adult morphologies and how morphologies change through ontogeny.
========
Also, paywalled:
Meg L. Martin, ÂKenny J. Travouillon, ÂEmma Sherrat,t ÂPatricia A. Fleming Â& Natalie M. Warburton (2019)
Covariation between forelimb muscle anatomy and bone shape in an Australian scratchâdigging marsupial: Comparison of morphometric methods.
Journal of Morphology (advance online publication)
doi:
https://doi.org/10.1002/jmor.21074https://onlinelibrary.wiley.com/doi/10.1002/jmor.21074 Â Â
The close association between muscle and bone is broadly intuitive; however, details of the covariation between the two has not been comprehensively studied. Without quantitative understanding of how muscle anatomy influences bone shape, it is difficult to draw conclusions of the significance of many morphological traits of the skeleton. In this study, we investigated these relationships in the Quenda (Isoodon fusciventer), a scratchâdigging marsupial. We quantified the relationships between forelimb muscle anatomy and bone shape for animals representing a range of body masses (124â1,952âg) using twoâblock partial least square analyses. Muscle anatomy was quantified as muscle mass and physiological crossâsectional area (PCSA), and we used two morphometric methods to characterize bone shape: seven indices of linear bone proportions, and landmarks analysis. Bone shape was significantly correlated with body mass, reflecting allometric bone growth. Of the seven bone indices, only shoulder moment index (SMI) and ulna robustness index (URI) showed a significant covariation with muscle anatomy. Stronger relationships between muscle anatomy and forelimb bone shape were found using the landmark coordinates: muscle mass and PCSA were correlated with the geometric shape of the scapula, humerus, and third metacarpal, but to a lesser extent with shape of the ulna. Overall, our data show that landmark coordinates are more sensitive than bone indices to capturing shape changes evident throughout ontogeny, and is therefore a more appropriate method to investigate covariation with forelimb muscle anatomy. Singleâspecies studies investigating ontogeny require refined methods to accurately develop understanding of the important relationships between muscle force generation and bone shape remodeling. Landmark analyses provide such a method.
====
Although mammalian tail length relative to body length is considered indicative of locomotor mode, this association has been difficult to quantify. This could be because the counterweight function of the tail might associate it more with body weight than body length. Alternatively, relative tail length might not be evolutionarily flexible owing to its integration with the remaining skeleton, particularly the spine. Using comparative analyses of morphological means and ranges in Australian marsupials, including the first co-assessment with body weight, our study supports the second hypothesis, i.e. tail length ranges within species, and tail lengths among species are explained better by body length than by body weight. However, all three variables do not differ in phylogenetic signal or rates of evolution. Associations of tail lengths with locomotion are limited, but suggest that scaling slopes, rather than intercepts, are responsible for limited divergence between relative tail lengths at different locomotor modes. This complicates (palaeo-)ecological interpretations of tail length further. We conclude that relative tail length is not a strong predictor of locomotor mode, probably owing to strong integration of tail and body length. The many well-documented bony and soft-tissue adaptations of tails are likely to be better suited to interpretations of locomotor adaptations.