Field of Science

Ectothermic Bovids? Is Nothing Sacred?

OK...this is pretty far out from the Triassic, but really interesting so I thought I'd share.

Kohler, M., and S. Moya-Sola. 2009. Physiological and life history strategies of a fossil large mammal in a resource-limited environment. Early online, PNAS. doi: 10.1073/pnas.0813385106

Abstract - Because of their physiological and life history characteristics, mammals exploit adaptive zones unavailable to ectothermic reptiles. Yet, they perform best in energy-rich environments because their high and constant growth rates and their sustained levels of resting metabolism require continuous resource supply. In resource limited ecosystems such as islands, therefore, reptiles frequently displace mammals because their slow and flexible growth rates and low metabolic rates permit them to operate effectively with low energy flow. An apparent contradiction of this general principle is the long-term persistence of certain fossil large mammals on energy-poor Mediterranean islands. The purpose of the present study is to uncover the developmental and physiological strategies that allowed fossil large mammals to cope with the low levels of resource supply that characterize insular ecosystems. Long-bone histology of Myotragus, a Plio-Pleistocene bovid from the Balearic Islands, reveals lamellar-zonal tissue throughout the cortex, a trait exclusive to ectothermic reptiles. The bone microstructure indicates that Myotragus grew unlike any other mammal but similar to crocodiles at slow and flexible rates, ceased growth periodically, and attained somatic maturity extremely late by ~12 years. This developmental pattern denotes that Myotragus, much like extant reptiles, synchronized its metabolic requirements with fluctuating resource levels. Our results suggest that developmental and physiological plasticity was crucial to the survival of this and, perhaps, other large mammals on resource-limited Mediterranean Islands, yet it eventually led to their extinction through a major predator, Homo sapiens.

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  1. There are more than a few juicy bits there.

    First and foremost, a fscking placental ectothermic mammal. o.O

    Second, the dwarfing exhibited obviously breaks all the insular dwarfing "laws" that have been thrown around with respect to Homo florienesis. (aka the Hobbit)

    Third, this increases the likelihood of what I'd heard before you guys all started blogging: that archosaurs might have been basally endothermic and then crocs et al lost it. I had a hard time believing that. However...this would be a second data point in favour.


    Reading the paper between clickety clacks.

  2. "Second, the dwarfing exhibited obviously breaks all the insular dwarfing "laws" that have been thrown around with respect to Homo florienesis. (aka the Hobbit)"

    Er, how?

  3. This is super cool stuff, but I'm not certain it means that the species was ectothermic. Although all extant tetrapods with sustained high growth rates are endothermic, there are endothermic tetrapods that grow slowly. I'm more inclined to interpret this as an example of a very slow growing, but endothermic mammal. Remember that bone histology reflects growth rate - there is an extra step of inference connecting growth rate to endothermy/ectothermy.

  4. Yeah, it's not like this animal suns itself during the day.

    (does it?)

  5. Is the title of your post a pun on sacred cow? If it was a previously unrealized pun, I'm dubbing it one. I will also accept that I'm just slow.


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