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Publications

Peer Reviewed Publications

Gearty, W., McClain, C.R., and Payne, J.L. 2018. Energetic tradeoffs control the size distribution of aquatic mammals. Proceedings of the National Academy of Sciences. doi: 10.1073/pnas.1712629115.


Four extant lineages of mammals have invaded and diversified in the water: Sirenia, Cetacea, Pinnipedia, and Lutrinae. Most of these aquatic clades are larger bodied, on average, than their closest land-dwelling relatives, but the extent to which potential ecological, biomechanical, and physiological controls contributed to this pattern remains untested quantitatively. Here, we use previously published data on the body masses of 3,859 living and 2,999 fossil mammal species to examine the evolutionary trajectories of body size in aquatic mammals through both comparative phylogenetic analysis and examination of the fossil record. Both methods indicate that the evolution of an aquatic lifestyle is driving three of the four extant aquatic mammal clades toward a size attractor at ∼500 kg. The existence of this body size attractor and the relatively rapid selection toward, and limited deviation from, this attractor rule out most hypothesized drivers of size increase. These three independent body size increases and a shared aquatic optimum size are consistent with control by differences in the scaling of energetic intake and cost functions with body size between the terrestrial and aquatic realms. Under this energetic model, thermoregulatory costs constrain minimum size, whereas limitations on feeding efficiency constrain maximum size. The optimum size occurs at an intermediate value where thermoregulatory costs are low but feeding efficiency remains high. Rather than being released from size pressures, water-dwelling mammals are driven and confined to larger body sizes by the strict energetic demands of the aquatic medium.




Racicot, R.A., Gearty, W., Kohno, N. and Flynn, J.J. 2016. Comparative anatomy of the bony labyrinth of extant and extinct porpoises (Cetacea: Phocoenidae). Biological Journal of the Linnean Society, 119(4), pp.831-846. doi: 10.1111/bij.12857.


The inner ear anatomy of cetaceans, now more readily accessible by means of nondestructive high‐resolution X‐ray computed tomographic (CT) scanning, provides a window into their acoustic abilities and ecological preferences. Inner ear labyrinths also may be a source for additional morphological characters for phylogenetic analyses. In this study, we explore digital endocasts of the inner ear labyrinths of representative species of extinct and extant porpoises (Mammalia: Cetacea: Phocoenidae), a clade of some of the smallest odontocete cetaceans, which produce some of the highest‐frequency clicks for biosonar and communication. Metrics used to infer hearing ranges based on cochlear morphology indicate that all taxa considered could hear high‐frequency sounds, thus the group had already acquired high‐frequency hearing capabilities by the Miocene (9–11 Mya) at the latest. Vestibular morphology indicates that extant species with pelagic preferences have similarly low semicircular canal deviations from 90°, values indicating more sensitivity to head rotations. Species with near‐shore preferences have higher canal deviation values, indicating less sensitivity to head rotations. Extending these analyses to the extinct species, we demonstrate a good match between those predicted to have coastal (such as Semirostrum cerutti) preferences and high canal deviation values. We establish new body length relationships based on correlations with inner ear labyrinth volume, which can be further explored among other aquatic mammals to infer body size of specimens consisting of fragmentary material.




Pages

Conference Presentations

Gearty, W., D’Alba, L., Vinther, J., Shawkey, M., Field, D. Melanin concentration gradients in modern and fossil feathers. Journal of Vertebrate Paleontology, Program and Abstracts, 2013, 132.
[SVP Oral Presentation]

In birds and feathered non-avian dinosaurs, within-feather pigmentation patterns range from discrete spots and stripes to more subtle patterns, but the latter remain largely unstudied. Here, we establish a method of quantifying melanosome concentration in fossil and modern feathers, and demonstrate that the darkness of melanin-based feather colors is directly related to the concentration of melanosomes within feathers. By quantitatively demonstrating a link between feather melanosome concentration and feather color, we help substantiate the common assumption that darker plumage can be caused by the deposition of larger amounts of melanin. These data are needed to validate discussion of, for example, the potential physiological costs of producing darker plumage, and the inference of color gradients from darkness gradients in fossil feathers. Our data show that melanosome density predicts brightness of some melanin-based colors, suggesting that it can be used to help determine if feathers were originally dark or pale. These data may help improve the resolution of fossil color reconstructions, enabling more precise functional inferences, and the quantification of intraspecific variation. Because sexual dimorphism and age may influence melanin-based colors of some species, this latter ability may potentially enable detection of sexual dichromatism and individual maturation in the fossil record. Although experimental taphonomic studies have indicated that melanosome size may be diagenetically altered, our inference of relative pigmentation within individual feathers should be robust in most taphonomic settings.


Gearty, W. and Payne, J., 2012, Assessing the completeness of the fossil record using brachiopod Lazarus taxa, Abstract B11A-0387 presented at 2012 Fall Meeting, AGU San Francisco, Calif., 3-7 Dec.
[AGU Poster Presentation]

Lazarus taxa, organisms that disappear from the fossil record only to reappear later, provide a unique opportunity to assess the completeness of the fossil record. In this study, we apply logistic regression to quantify the associations of body size, geographic extent, and species diversity with the probability of being a Lazarus genus using the Phanerozoic fossil record of brachiopods. We find that both the geographic range and species diversity of a genus are inversely associated with the probability of being a Lazarus taxon in the preceding or succeeding stage. In contrast, body size exhibits little association with the probability of becoming a Lazarus taxon. A model including species diversity and geographic extent as predictors performs best among all combinations examined, whereas a model including only shell size as a predictor performs the worst - even worse than a model that assumes Lazarus taxa are randomly drawn from all available genera. These findings suggest that geographic range and species richness data can be used to improve estimates of extensions on the observed fossil ranges of genera and, thereby, better correct for sampling effects in estimates of taxonomic diversity change through the Phanerozoic.


Pages

Other Published Writing

Gearty, W., 2014, "The Good, the Bad, and the Ugly: The Potential Drawbacks of Manually Controlling Our Climate", Yale Scientific Magazine
Gearty, W., 2014, "Fossils Reveal that Many Marine Reptiles Separately Joined the Dark Side", Yale Scientific Magazine
Gearty, W., 2013, “Fly Guts Reveal Rainforest Biodiversity”, Yale Scientific Magazine
Gearty, W., 2013, “125-Million-Year-Old Biplanes: New Evidence Suggests the Earliest Bird Species had Feathers on their Hind Limbs”, Yale Scientific Magazine
Gearty, W., 2013, “Google Maps meets Biodiversity: A New Interactive Map of Life Aims to Integrate Biodiversity Distribution Knowledge”, Yale Scientific Magazine
Gearty, W., 2013, “Volcanoes Implicated in Murder of Dinosaurs: New Evidence Points to Volcanism as the Main Cause of Dinosaur Extinctions”, Yale Scientific Magazine
Gearty, W., 2012, “Fate of Australian megafauna Discovered through Prehistoric Dung”, Yale Scientific Magazine