High-tech CT reveals ancient evolutionary adaptation of extinct crocodylomorphs
They transitioned from land to water during the Mesozoic era

Date:
June 18, 2020
Source:
Forschungsverbund Berlin
Summary:
New insights into the anatomy of the inner ear of prehistoric
reptiles, the thalattosuchians, revealed details about the
evolutionary adaption during the transition into the ocean after
a long semiaquatic phase.

These new findings were made possible by the use of a Canon
high-tech computed tomography (CT) scanner.



FULL STORY ==========================================================================
The tree of life is rich in examples of species that changed from living
in water to a land-based existence. Occasionally, some species took the opposite direction. New insights into the anatomy of the inner ear of prehistoric reptiles, the thalattosuchians, revealed details about one
of these evolutionary turning points. During the Mesozoic era, these
now extinct crocodile relatives ventured into the ocean after a long semiaquatic phase.

During this process, the skeleton of the thalattosuchians gradually
adapted to the new pelagic habitat. In particular, the changes to the
inner ear vestibular system of these reptiles enhanced their ability
to swim. Compared to whales, which adapted quickly to life in water
without a prolonged semiaquatic stage, this is a strikingly different evolutionary path for the same transition. These new findings of an international research team were made possible by the use of a Canon
high-tech computed tomography (CT) scanner from the Leibniz Institute for
Zoo and Wildlife Research (Leibniz-IZW). The results have been published
in the Proceedings of the National Academy of Sciences.


========================================================================== Thalattosuchians lived during the Mesozoic about 182 to 125 million
years ago and evolved from their land-living relatives to become
fast-swimming marine predators. An international research team led
by scientists from the School of Geosciences at the University of
Edinburgh studied the evolutionary changes which these crocodylomorphs
went through during their transition from land to the ocean. The team
focused on one of the most important vertebrate sensory systems -- the
inner ear. Using high-resolution computed tomography (CT), the skulls of
18 thalattosuchians from the late Triassic to the Early Cretaceous were
scanned to span much of the evolutionary history of crocodylomorphs. The
CT scans were compared with the scans of modern crocodiles. Some of the
scans were performed at the Leibniz-IZW in Berlin. The x-ray scans reveal detailed changes in the vestibular system of the inner ear, particularly
in the bony labyrinth, which plays a crucial role in sensing balance
and spatial orientation. "As they transitioned from land to water, thalattosuchians developed a strikingly compact, reduced and thickened
bony labyrinth reminiscent of the reduced labyrinths of other marine
reptiles and whales," explains Guido Fritsch, scientist and CT expert
at the Leibniz-IZW. "Extinct land crocodiles, on the other hand, had a
taller and narrower bony labyrinth.

The labyrinths of semiaquatic crocodiles, which also include modern
crocodiles, are longer and more compact than those of their land-living relatives." These results illustrate that the inner ear morphology of
an animal is strongly linked to its habitat.

Interestingly, thalattosuchians developed the reduction of their inner
ear labyrinth only after a long semiaquatic phase that lasted tens of
millions of years. First, their skeleton changed during this phase --
limbs became flippers, the body became streamlined, which allowed them to
move efficiently in the water and improved their ability to swim. Only
then did the changes in the inner ear develop, possibly as a response
to changing sensory requirements, when the thalattosuchians moved into
deeper, more open waters. This adaptation process distinguishes them
from whales, whose inner ear labyrinth was miniaturised soon after
their transition from land to water, without a prolonged semiaquatic
phase. Thus, thalattosuchians and whales took different evolutionary
routes for the same type of transition.

Future studies will examine the advantages of a reduced inner
ear labyrinth for water-living animals, investigate how quickly thalattosuchians developed the adaptations in their inner ear as they
entered the water, and how other sensory organs changed during this
transition.


========================================================================== Story Source: Materials provided by Forschungsverbund_Berlin. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Julia A. Schwab, Mark T. Young, James M. Neenan, Stig A. Walsh,
Lawrence
M. Witmer, Yanina Herrera, Ronan Allain, Christopher A. Brochu,
Jonah N.

Choiniere, James M. Clark, Kathleen N. Dollman, Steve Etches, Guido
Fritsch, Paul M. Gignac, Alexander Ruebenstahl, Sven Sachs, Alan H.

Turner, Patrick Vignaud, Eric W. Wilberg, Xing Xu, Lindsay E. Zanno,
Stephen L. Brusatte. Inner ear sensory system changes as extinct
crocodylomorphs transitioned from land to water. Proceedings
of the National Academy of Sciences, 2020; 117 (19): 10422 DOI:
10.1073/ pnas.2002146117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200618120155.htm

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