Amazingly revealing: Fossil inner ears can reveal secrets about the abilities and behavior of extinct animals, according to a study. Since it also includes the organ of equilibrium in addition to the hearing system, features of the inner ear allow conclusions to be drawn about the flight abilities and even the brood care behavior of reptiles, dinosaurs or early representatives of birds, the paleontologists report.
Armed with a shovel, brush and tape measure, paleontologists have long been concerned primarily with the more superficial features of fossils: They described shape, size and anatomical features such as wings or fins, which enabled fundamental conclusions to be drawn about the way of life of extinct animals. However, these fossil findings were often unable to provide details on how they once moved and behaved. Opportunities for well-founded insights into these questions are therefore very popular in paleontology. In this context, the researchers led by Bhart-Anjan Bhullar from Yale University in New Haven are now focusing on the inner ear as a particularly informative source of information.
“Apparatus” with two functions
The tiny structure sits in the skull of vertebrates and includes two systems of perception: the inner ear consists of the cochlea and the organ of equilibrium (vestibular organ). “Of all the structures that can be reconstructed from fossils, the inner ear is probably the closest thing to a technical device,” says Bhullar. The characteristics of the cochlea are linked to the auditory abilities of a living being, and the properties of the organ of equilibrium reflect the way in which it moved, the scientists explain. “If you are able to reconstruct its shape, you can draw conclusions about certain characteristics and behaviors of extinct animals in an almost unprecedented way,” says the paleontologist.
Paleontologists have previously used features of the inner ear as clues – but Bhullar and his colleagues are now systematically showing the potential of this procedure. Techniques that are currently revolutionizing palaeontology form the basis: With micro and nano computed tomography it is possible to look inside fossils and to show hidden fine structures in detail. In this way, the inner ears in fossil skulls can now also be examined in detail.
As part of their study, the scientists have now collated, analyzed and categorized the inner ear data of numerous current and extinct animal species. In today’s species, the characteristics can be combined with the known behaviors and abilities of the respective species. Characteristic signatures emerged in the structures that could be compared with the fossil inner ears of extinct species.
Characteristic similarities
As the researchers report, their data analyzes led to groups of species with similar inner ear characteristics. The members of a cluster show a clear similarity in how they move through the world and perceive it. Three clusters are characterized by certain structural features of the so-called vestibular system of the organ of equilibrium. “This three-dimensional structure provides information about an animal’s maneuverability. The shape of the vestibular system thus represents a window for understanding bodies in motion, ”says the paleontologist.
A vestibular cluster includes animals that move on four legs. Other characteristic features of the organ of equilibrium are typical for two-legged species and the less agile fliers. These include, for example, the modern chickens and gliders such as some seabird and vulture species. The third cluster then form the pronounced aerial acrobats, such as today’s birds of prey and many species of songbirds. In the case of the inner ear characteristics of many of the primeval wing carriers, the data evaluations now make it clear: Pterosaurs or the famous “primeval bird” Archeopteryx belonged to the category of less agile fliers, the paleontologists report.
Notes on brood care behavior
As for the characteristics of the cochlea, the researchers were able to identify a characteristic feature in the representatives of the archosaurs, which is associated with hearing certain frequencies. Archosaurs not only include extinct animal groups such as dinosaurs and pterosaurs – they also include today’s crocodiles and birds. As the researchers explain, a typical characteristic of these animals is that they make sounds. In the crocodiles, too, the young communicate with the mother, for example by means of sounds.
The results of the paleontologists now suggest that the transformation of the cochlear shape in the ancestors of the archosaurs was related to the development of high-pitched breeding calls in the young animals. “We discovered a transitional form of the cochlea in the Euparkeria”. These were primeval forms of the archosaurs from the Lower and Middle Triassic. “This suggests that the ancestors of the archosaurs began to make sounds as they evolved into little predators,” said the paleontologist.
As a summary of the study, Yale University writes: “It is becoming apparent that studies of the inner ear will in future be able to provide interesting information on how agile an animal could move on the ground, in the air or in the water. In some cases, comparisons could also shed light on whether a species was brood-tending by listening to the high-pitched cries of its babies ”.
Source: Yale University, Article: Science, doi: 10.1126 / science.abb4305