{"id":547992,"date":"2025-06-10T10:22:55","date_gmt":"2025-06-10T13:22:55","guid":{"rendered":"https:\/\/revistapesquisa.fapesp.br\/?p=547992"},"modified":"2025-06-10T10:22:55","modified_gmt":"2025-06-10T13:22:55","slug":"the-eardrum-may-have-saved-reptiles-from-mass-extinction","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/the-eardrum-may-have-saved-reptiles-from-mass-extinction\/","title":{"rendered":"The eardrum may have saved reptiles from mass extinction"},"content":{"rendered":"
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Julia D\u2019Oliveira<\/span>Over 250 million years ago, an ancestral reptile would have heard the buzz of insectsJulia D\u2019Oliveira<\/span><\/p><\/div>\n

For a lizard to survive in a dark, smoky environment with a scarcity of food, as was Earth between around 250 million and 200 million years ago\u2014a period marked by two mass extinction events\u2014a good ear was essential. With it, the reptile could hear prey and predators better or even practice vocal communication with members of the same species.<\/p>\n

The tympanic membrane, a film that moves when it comes into contact with sound waves, was an evolutionary addition that increased the sound spectrum detected by reptiles. This small part of the auditory system in birds, alligators, crocodiles, snakes, lizards, and turtles was fundamental for these animals to survive and proliferate throughout evolutionary history, according to an article published in October in the journal Current Biology<\/em>. The study includes birds because, evolutionarily, they share the same common ancestor as reptiles.<\/p>\n

The research has implications in an important dilemma in evolutionary biology. \u201cThere is a great debate about the evolution of hearing in reptiles: if it emerged independently in various groups or from a single ancestor,\u201d says paleontologist Mario Bronzati, a Brazilian researcher doing a postdoctoral fellowship at the University of T\u00fcbingen, in Germany, and the lead author of the article.<\/p>\n

The debate between hypotheses was intensified by the size of the group of reptiles, which today has more than 20,000 species, and by the lack of studies focused on the evolution of hearing in this group. \u201cMany studies have focused on model animals, such as chickens and mice,\u201d says Bronzati. With this differential, the results outlined in the recent article suggest that hearing arose from a single event and was inherited by the descendants.<\/p>\n

The researchers came to these conclusions by means of the study of reptile fossils and embryos, in a combination of two fields of knowledge: paleontology and evolutionary developmental biology, which studies embryology from an evolutionary perspective and is referred to as evo-devo by researchers.<\/p>\n

\u201cWe would not have been able to answer all the questions we did without this combination,\u201d explains biologist Tiana Kohlsdorf, from the University of S\u00e3o Paulo’s Ribeir\u00e3o Preto School of Philosophy, Sciences, and Languages and Literature (FFCLRP-USP) and coordinator of the study. \u201cThrough fossils, we can infer an older timescale that includes the common ancestor, and the development over a period of life, from embryos, allows us to see how the membrane develops in living reptiles.\u201d<\/p>\n

The analysis of the embryos is also important because the tympanic membrane is a soft tissue, which is not preserved in fossils. Even the bony characteristics associated with hearing are variable and do not always serve as a clue, as seen with a small shell-like structure on the skull of lizards that does not exist in alligators.<\/p>\n

\u201cThe authors approach the question from an innovative angle,\u201d says Brazilian paleontologist Gabriela Sobral, of Stuttgart Museum in Germany, who did not participate in the study. In 2019, she published an article in the journal PeerJ<\/em> about the identification of the eardrum in the ancestral lineage that would have given rise to crocodilians and birds. \u201cThe article shows how the main characteristics used to identify tympanic hearing in fossils, the shell-like structure, is a condition specific to snakes and lizards.\u201d<\/p>\n

\u201cPaleontology and evo-devo complement each other: one field provides the other concrete examples of what is factually possible within an almost infinite universe of possibilities,\u201d adds Sobral. \u201cThe article shows how paleontology is a fundamental part of understanding the evolution of life on Earth.\u201d<\/p>\n<\/div>

\n \n \n \n <\/picture>Alexandre Affonso\/Pesquisa FAPESP on image by Mario Bronzati<\/span><\/div>
\n

One part of the research was to compare embryos of lizards (Tropidurus<\/em>) and alligators (Caiman<\/em>). The researchers collected the eggs from an urban environment in the city of S\u00e3o Sim\u00e3o, in the countryside of the state of S\u00e3o Paulo, in the case of the lizards, and from the Caimasul alligator farm in Corumb\u00e1, Mato Grosso do Sul. \u201cIt was a real challenge, we were still in the period of the pandemic,\u201d recalls Bronzati.<\/p>\n

In the laboratory, the team carefully opened the thin shells of the eggs to examine the baby alligators and lizards, still immersed in the aqueous solution that forms the amniotic fluid. Using microscopes, tomography devices, and traditional tissue examination techniques, the researchers found that the process of tympanic ear formation was very similar in both animals. The same would be the case for bird embryos.<\/p>\n

\u201cIn all of these animals, the tympanic cavity forms from the extension of the pharyngeal cavity, which is connected to the throat,\u201d explains Bronzati. \u201cAnd the tympanic membrane arises in a region called the second pharyngeal arch.\u201d According to Kohlsdorf, another important point is that \u201calthough we see this similarity between birds, alligators, and lizards, the development is different in mammal embryos, with the formation of the tympanic membrane arising from the first pharyngeal arch.\u201d<\/p>\n

\u201cThis all becomes even more intriguing when we note that several extinct relatives of reptiles did not have tympanic hearing,\u201d adds Bronzati. \u201cWe believe that the evolution of this trait favored the survival of the group, especially considering the mass extinction events.\u201d<\/p>\n

Two of these extinction events marked the crucial period for the emergence of tympanic hearing. The first, 250 million years ago, occurred during the Permian period and wiped out over 95% of marine species and 70% of terrestrial species. It is unknown what exactly caused the extinction, but the possibility involves a combination of climatic changes and volcanic eruptions. Similar factors led to a new catastrophe 50 million years later, between the Triassic and Jurassic periods, with the extinction of 80% of the planet’s species.<\/p>\n

In Sobral’s opinion, further investigation is needed into the origin and development of the middle ear cavity and the related structures. \u201cThese issues have only recently been analyzed in mammals, but they are still unknown in reptiles.\u201d<\/p>\n

Other answers reside in genetics. \u201cWe don’t know whether the genes that form the tympanic membrane in chickens and other animals are the same,\u201d says Bronzati. There is still the need to investigate the loss of parts of the auditory system in some reptiles, such as serpents, which lost the tympanic membrane, and some lizards. \u201cIt is an article that opens doors to new areas of research,\u201d concludes Sobral.<\/p>\n

The story above was published with the title “Warning sound to escape extinction<\/strong>” in issue 345 of November\/2024.<\/p>\n

Projects
\n1. <\/strong>Ecology, evolution, and development (eco-evo-devo) in Brazilian herpetofauna (n\u00b0 15\/07650-6<\/a>); Grant Mechanism<\/strong> Thematic Project; Principal Investigator<\/strong> Tiana Kohlsdorf (USP); Investment<\/strong> R$1,261,130.44.
\n2.<\/strong> Evo-devo in dynamic environments: Implications of climate change on biodiversity (n\u00b0 20\/14780-1<\/a>); Grant Mechanism<\/strong> Thematic Project; Biota Program; Principal Investigator<\/strong> Tiana Kohlsdorf (USP); Investment<\/strong> R$3,229,900.69.
\n3.<\/strong> Filling gaps in our understanding of Crocodylomorpha macroevolution using comparative methods (n\u00b0 22\/05697-9<\/a>); Grant Mechanism<\/strong>: Postdoctoral Fellowship; Supervisor<\/strong> Max Cardoso Langer (USP); Beneficiary<\/strong> Pedro Lorena Godoy; Investment<\/strong> R$88,743.56.<\/p>\n

Scientific articles
\n<\/strong>BRONZATI, M. et al<\/em>. Deep-time origin of tympanic hearing in crown reptiles<\/a>. Current Biology<\/strong>. Vol. 34, pp. 1\u20137. Oct. 2024.
\nSOBRAL, G. et al<\/em>. The braincase of <\/a>Mesosuchus browni<\/em><\/a> (Reptilia, Archosauromorpha) with information on the inner ear and description of a pneumatic sinus<\/a>. PeerJ.<\/strong> Vol. 7. May 2019.<\/p>\n","protected":false},"excerpt":{"rendered":"The tympanic membrane in the inner ear emerged in a common ancestor of lizards, crocodiles, alligators, snakes, turtles, and birds 250 million years ago","protected":false},"author":753,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[159],"tags":[224,231,255,266],"coauthors":[4945],"class_list":["post-547992","post","type-post","status-publish","format-standard","hentry","category-science","tag-ecology","tag-evolution","tag-paleontology","tag-zoology"],"acf":[],"_links":{"self":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/547992","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/users\/753"}],"replies":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/comments?post=547992"}],"version-history":[{"count":1,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/547992\/revisions"}],"predecessor-version":[{"id":548010,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/547992\/revisions\/548010"}],"wp:attachment":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media?parent=547992"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/categories?post=547992"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/tags?post=547992"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/coauthors?post=547992"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}