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

Squamate heart structure and function



From: Ben Creisler
bcreisler@gmail.com


A new non-dino paper that may be of interest:

Bjarke Jensen, Antoon F. M. Moorman & Tobias Wang (2013)
Structure and function of the hearts of lizards and snakes.
Biological Reviews (advance online publication)
DOI: 10.1111/brv.12056
http://onlinelibrary.wiley.com/doi/10.1111/brv.12056/abstract


With approximately 7000 species, snakes and lizards, collectively
known as squamates, are by far the most species-rich group of
reptiles. It was from reptile-like ancestors that mammals and birds
evolved and squamates can be viewed as phylogenetically positioned
between them and fishes. Hence, their hearts have been studied for
more than a century yielding insights into the group itself and into
the independent evolution of the fully divided four-chambered hearts
of mammals and birds. Structurally the heart is complex and debates
persist on rudimentary issues such as identifying structures critical
to understanding ventricle function. In seeking to resolve these
controversies we have generated three-dimensional (3D) models in
portable digital format (pdf) of the anaconda and anole lizard hearts
(‘typical’ squamate hearts) and the uniquely specialized python heart
with comprehensive annotations of structures and cavities. We review
the anatomy and physiology of squamate hearts in general and emphasize
the unique features of pythonid and varanid lizard hearts that endow
them with mammal-like blood pressures. Excluding pythons and varanid
lizards it is concluded that the squamate heart has a highly
consistent design including a disproportionately large right side
(systemic venous) probably due to prevailing pulmonary bypass
(intraventricular shunting). Unfortunately, investigations on
rudimentary features are sparse. We therefore point out gaps in our
knowledge, such as the size and functional importance of the coronary
vasculature and of the first cardiac chamber, the sinus venosus, and
highlight areas with implications for vertebrate cardiac evolution.