[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Did avian and mammalian homeothermy evolve in China?

From: Ben Creisler

NOTE: I am posting this one NOT because I agree but because it's an
alternative theory published in a scientific journal.

Sven Kurbel (2013)
Hypothesis of homeothermy evolution on isolated South China Craton
that moved from equator to cold north latitudes 250 to 200 Myr ago.
Journal of Theoretical Biology (advance online publication)
doi: http://dx.doi.org/10.1016/j.jtbi.2013.09.018

Based on avian and mammalian fossils found in the northeastern Chinese
province of Liaoning and physiological traits linked to homeothermy, a
hypothesis of evolution of homeothermic animals is proposed. It is
based on the importance of muscle function in cold environment, as a
strong selection pressure that favors endothermic metabolism during
periods of cold climates. The presented hypothesis postulates that in
progressively cooling environment, animals will develop thermal
insulation, increased basal metabolism if food is available, and
torpor when food is scarce. Since late Permian, Triassic and
Cretaceous global temperatures were high, an exceptional place that
gradually became cold was needed for the homeothermy evolution.

South China Craton is here proposed as a plausible candidate for that
role since it drifted across the Paleo-Tethys ocean, from equator to
high northern latitudes in a journey that lasted from 250 to 200 Myr
ago. After this small continent collided with North China Craton some
200 Myr ago, the already cold-adapted animals had spread to large,
mostly empty spaces on the North China Craton, due to their
evolutionary advantage of making active living in the cold
environment. The most advantageous early homeothermic animals went
further north to the cold Liaoning to start an oasis that delivered
modern birds during next 50 Myr. Modern mammals possibly evolved
somewhere in the cold vicinity. This made Liaoning and similarly cold
places the cradles of early birds and early mammals since for the
following millions of years these places remained too cold for
poikilotherms to enter and warm enough for homeotherms to dwell, until
the Cretaceous–Paleogene extinction event and subsequent global
cooling that diminished poikilotherms. Homeothermy was probably even
more important as a survival advantage in cooler climates of
Paleogene, when mammals and birds became dominant animals.

This interpretation is probably supported by a recent report that a
small primate Archicebus achilles dated ~55 Myr ago was found in the
more south central China Hubei Province, while Hadrocodium wui,
extinct mammaliaform that lived 195 Myr ago in what is now the Yunnan
province in southwestern China. The final confirmation of the proposed
scenario would be to find somewhere in South China avian fossils older
than those found in Liaoning, or to find the cradle of early mammals
somewhere in Northern China.