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Macroevolutionary Impact of Selective Brain Cooling on the Mammalian Order Artiodactyla

O'Brien, Haley D.,
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470865971

Abstract Details

2016, Doctor of Philosophy (PhD), Ohio University, Biological Sciences (Arts and Sciences).
Artiodactyls are the most speciose large-bodied, terrestrial vertebrates alive today, and processes driving their diversification have long been of interest. The prevailing view is that foregut fermentation digestive physiology (rumination) is a key innovation responsible for artiodactyl evolutionary success. This hypothesis may be incomplete, however, as other specialized physiologies of modern artiodactyls, such as carotid-rete-mediated selective brain cooling, may also be influencing diversification. Selective brain cooling effectively decouples brain and body temperature, prolonging exercise duration and increasing water economy by delaying hydrologically-costly panting and sweating. I trace SBC evolution across Cenozoic climate shifts to test the hypothesis that brain cooling is an artiodactyl key innovation using a combination of anatomical and evolutionary modeling approaches. In artiodactyls, an advanced degree of brain cooling is mediated by the carotid rete, an arterial meshwork that anatomically and functionally replaces the internal carotid artery. A soft tissue survey of nearly all terrestrial artiodactyl families and sub-families was conducted using radiopaque latex vascular injection, CT imaging, and 3-dimensional model building using Avizo. This survey revealed unique basicranial osteology among artiodactyls with a carotid rete, which in turn allowed identification of selective brain cooling distribution in recent and fossil skulls from all extant and 16 extinct artiodactyl families. Digestive physiology was scored from literature for the same taxa. Distributions of brain cooling and rumination were compared using phylogenetic comparative methods, such as binary and multi-state speciation and extinction rate calculations, as well as occurrence-based paleobiological modeling approaches. Extant artiodactyls show significant overlap in brain cooling and rumination (87%); however, surveys of fossil specimens reveal higher disparity among extinct species. Occurrence-based turnover rate models revealed that artiodactyls with a carotid rete arise earlier, speciate faster, and are more insulated from extinction. Neogene trait overlap suggests that brain cooling may be a prerequisite for ruminant digestion, protecting the brain from the high core temperatures needed to support fermentation. Rather than considering each trait independently, a more inclusive diversification paradigm may be that of correlated progression: in the Eocene, the carotid rete and rumination do not evolve in a correlated manner; however, once brain cooling is established, thermally intensive foregut fermentation can be accomplished without damaging the brain. By the Miocene, brain cooling and foregut fermentation are functionally and evolutionarily linked, responding to selective pressures as a unit. Thus, the key innovation for Artiodactyla may be a physiological character complex—wherein brain cooling and rumination are both required to facilitate the group’s expansive evolutionary success.
Nancy Stevens, PhD (Advisor)
Donald Miles, PhD (Committee Member)
Alycia Stigall, PhD (Committee Member)
Susan Williams, PhD (Committee Member)
Lawrence Witmer, PhD (Committee Member)
356 p.
Anatomy and Physiology; Biology; Evolution and Development; Paleontology
Artiodactyla; Carotid Rete; Ruminantiamorpha; Pecora; Tylopoda; Suinamorpha; Selective Brain Cooling; Mammalian Macroevolution

Recommended Citations

Citations

  • O'Brien, , H. D. (2016). Macroevolutionary Impact of Selective Brain Cooling on the Mammalian Order Artiodactyla [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470865971

    APA Style (7th edition)

  • O'Brien, , Haley. Macroevolutionary Impact of Selective Brain Cooling on the Mammalian Order Artiodactyla. 2016. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470865971.

    MLA Style (8th edition)

  • O'Brien, , Haley. "Macroevolutionary Impact of Selective Brain Cooling on the Mammalian Order Artiodactyla." Doctoral dissertation, Ohio University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470865971

    Chicago Manual of Style (17th edition)

ohiou1470865971
108
© 2016, all rights reserved.
This open access ETD is published by Ohio University and OhioLINK.