Ecomorphological specialisation and mammalian diversification
Whether specialisation impedes subsequent diversification is a topic of interest across biology, relevant to gene pleiotropy, functional and ecological trade-offs as well as macroevolution. It is generally expected that evolution proceeds from the generalised to the specialised, an observation first made by ED Cope while studying the fossil record of mammals. Cope's 'Doctrine of the unspecialised' specifically discusses his idea in the context of trophic generalists (omnivores) and specialists (herbivores and carnivores).
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This project, was a collaboration between myself and Sam Hopkins (a mammalian palaeobiologist at the University of Oregon), focuses on delimiting the evolutionary impact of dietary specialisation on mammalian phenotypic and lineage diversification using fossil and living mammals. It is based on our finding within extant mammals that different macroevolutionary processes generate trophic specialist and generalist diversity (Price et al., 2012 PNAS). Specialists have the highest rates of net diversification, most extant herbivore and carnivore diversity stems from speciation within those specialist lineages. In contrast, generalists have low rates of net diversification and their extant diversity is generated by specialists transitioning into omnivory. This result suggests that omnivory acts as an evolutionary sink rather than a source, which would be expected if evolution proceeds from the generalised to the specialised.
NSF DEB-1256894 Price, S. A, Hopkins, S. S. B. Smith, K. K & Roth, V. L. (2012) Tempo of trophic evolution and its impact on mammalian diversification. Proceedings of the National Academy of Sciences 109(18), 7008-7012.
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Are morphological proxies for diet within Carnivora phylogenetically biased?
Over the years various measurements of the jaws and teeth of carnivoran mammals have been proposed as proxies for diet in the fossil record of these groups. Although there is a strong statistical relationship between these measures and diet across extant carnivorans, how well they predict diet and the influence phylogeny may play has not been investigated. We used 10 common measurements on the upper and lower teeth and jaws and used discriminant function analysis to see how well we could predict diet when phylogeny was taken into account. We found that there was about 20% misclassification when phylogeny was ignored but up to 50% when it was included. This suggests that the phylogenetic signal within morphology and diet, specifically the strong differences between the cat-like and dog-like sub-orders, improves the predictive nature of the proxies. Therefore, caution should be used when applying these measures to distantly related fossil groups, including stem-carnivorans as phylogeny plays a role in their success.
Over the years various measurements of the jaws and teeth of carnivoran mammals have been proposed as proxies for diet in the fossil record of these groups. Although there is a strong statistical relationship between these measures and diet across extant carnivorans, how well they predict diet and the influence phylogeny may play has not been investigated. We used 10 common measurements on the upper and lower teeth and jaws and used discriminant function analysis to see how well we could predict diet when phylogeny was taken into account. We found that there was about 20% misclassification when phylogeny was ignored but up to 50% when it was included. This suggests that the phylogenetic signal within morphology and diet, specifically the strong differences between the cat-like and dog-like sub-orders, improves the predictive nature of the proxies. Therefore, caution should be used when applying these measures to distantly related fossil groups, including stem-carnivorans as phylogeny plays a role in their success.
Hopkins, S.S.B., Chiono, A. J., & Price, S.A. (2021) Influence of phylogeny on the estimation of diet from dental morphology in the Carnivora Paleobiology.
Price, S.A. & Hopkins, S.S.B. The macroevolutionary relationship between diet and body mass across mammals. Biological Journal of the Linnean Society 15(1), 173-184
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Does trophic strategy influence body size consistently across mammals?
The potential physiological and ecological processes linking size and diet have been the subject of extensive research. A strong relationship between diet and size has been assumed for years, its existence has never been fully tested in a phylogenetic framework across mammals with a wide variety of diets. Using generalized Ornstein–Uhlenbeck models and data on over 1350 species of mammal, I found that evolutionary changes in body mass are consistently associated with dietary changes across mammals. In general, herbivores are larger than omnivores and carnivores and, although omnivores are intermediate, their mass is far more similar to that estimated for carnivores. This pattern is reversed in clades that include marine taxa (Carnivora and Cetartiodactyla): carnivores are substantially heavier than herbivores and omnivores. Such consistent findings at a broad scale may reflect the existence of a universal mechanism linking diet and mass and, with the main differences identified between marine and the terrestrial biomes, there is a hint that it may be ecological in nature. |