Primal reptiles heard better than expected

260 million year old reptiles from Russia with first modern ears

The 260-million-year-old reptile Bashkyroleter from the Permians of Russia - the owner of the first modern ear including eardrum (pink area in the reconstruction). The total length of the skull is 6.5 cm. © Humboldt University Berlin
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The earliest known reptile ears have been discovered by scientists in more than 260 million year old fossil remains of the species Bashkyroleter in Russia. Surprisingly, they possess all the attributes of a modern ear and, therefore, unexpectedly move their origins far back into the evolutionary early days of terrestrial vertebrates, according to the researchers in the journal "PLoS One". The find from the Perm, however, also brought first indications of a revolutionary strategy for the time: night activity.

Originally, the earliest land-adapted ancestors of mammals, reptiles, and birds were largely deaf and relied primarily on vision to navigate their environment. However, today's terrestrial vertebrates possess a so-called impedance-transforming hearing device, which bundles sound waves from the air via an eardrum and transmits them via bony connections to the brain for signal processing. Although today's hearing is hugely important for prey acquisition or communication, it has previously been thought that it did not develop until just before the birth of the dinosaurs, just over 200 million years ago.

Now, however, the new fossils from Russia prove that modern hearing must have originated much earlier: in all the fossils studied for the study, the temple was apparently covered by a broad eardrum, and a bone structure comparable to the human ossicles connected that with the inner ear and the Brain.

Night activity as trump card

Johannes Müller and Linda Tsuji of the Museum of Natural History of the Humboldt University Berlin compared the auditory abilities derived from the fossil structures with those of modern vertebrates and came to the conclusion that the fossil reptiles from Russia could hear at least as well as, say, a modern lizard, But what was the reason for the development of these ears? "Of course, this question is not easy to answer, " says Müller, "but if you look at today living animals with excellent hearing, such as cats, owls or geckos, then it is noticeable that these animals are all night or dawn active. Probably that also applies to the fossil reptiles from Russia. "

In fact, all investigated fossils show not only a well-developed organ of hearing but also significantly enlarged eye openings, which is also typical of a nocturnal lifestyle. Such an adaptation in this early evolutionary stage of the terrestrial vertebrates is surprising, as warm-blooded reptiles normally require a lot of sunlight to maintain a healthy body temperature. Therefore, the first step into the nightlife was certainly not easy. display

New insights into evolution

The discovery of a modern grafting device in Permian vertebrates unexpectedly provides new insights into the evolution of early-stage ecosystems, which seem far less primitive than previously thought. The ecological competition between the species living at that time was probably already largely comparable to today's, and evolutionary novelties were necessary to gain an advantage in survival. Ultimately, it was these innovations that paved the way to our environment today.

(idw - Humboldt University Berlin, 14.09.2007 - DLO)