High-tech CT reveals ancient evolutionary adaptation of extinct crocodylomorphs

June 18, 2020

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 Acadamy of Sciences of the USA".

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.
-end-


Forschungsverbund Berlin

Related Whales Articles from Brightsurf:

Blue whales change their tune before migrating
While parsing through years of recorded blue whale songs looking for seasonal patterns, researchers were surprised to observe that during feeding season in the summer, whales sing mainly at night, but as they prepare to migrate to their breeding grounds for the winter, this pattern reverses and the whales sing during the day.

Shhhh, the whales are resting
A Danish-Australian team of researchers recommend new guidelines for noise levels from whale-watching boats after having carried out experiments with humpback whales.

Fishing less could be a win for both lobstermen and endangered whales
A new study by researchers at Woods Hole Oceanographic Institution (WHOI) found that New England's historic lobster fishery may turn a higher profit by operating with less gear in the water and a shorter season.

North Atlantic right whales are in much poorer condition than Southern right whales
New research by an international team of scientists reveals that endangered North Atlantic right whales are in much poorer body condition than their counterparts in the southern hemisphere.

Solar storms could scramble whales' navigational sense
When our sun belches out a hot stream of charged particles in Earth's general direction, it doesn't just mess up communications satellites.

A better pregnancy test for whales
To determine whale pregnancy, researchers have relied on visual cues or hormone tests of blubber collected via darts, but the results were often inconclusive.

Why whales are so big, but not bigger
Whales' large bodies help them consume their prey at high efficiencies, a more than decade-long study of around 300 tagged whales now shows, but their gigantism is limited by prey availability and foraging efficiency.

Whales stop being socialites when boats are about
The noise and presence of boats can harm humpback whales' ability to communicate and socialise, in some cases reducing their communication range by a factor of four.

Endangered whales react to environmental changes
Some 'canaries' are 50 feet long, weigh 70 tons, and are nowhere near a coal mine.

Stranded whales detected from space
A new technique for analysing satellite images may help scientists detect and count stranded whales from space.

Read More: Whales News and Whales Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.