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Scientists have discovered the oldest known fossil of a tadpole, dating from about 161 million years ago, in the Middle Jurassic.
Scientists have discovered the oldest known fossil of a tadpole, Notobatrachus degiustoi, which is about 161 million years old and dates back to the Middle Jurassic. Details of this “beautifully preserved” 16 centimeter long larva, discovered in the La Matilde Formation in Patagonia, Argentina, were published in the scientific journal Nature. Lead researcher Mariana Chuliver, a biologist and herpetologist at Maimonides University in Argentina, expressed her surprise at the fossil’s exceptional preservation, noting that it contains soft tissues not normally found in fossils, such as nerves and eyes.
“This is not only the oldest known tadpole fossil, but also the ‘best preserved’ among such fossils,” Chuliver said, as reported by Xinhua News Agency. The fossil includes parts of the tadpole’s skull, spine, eyes and nerves, as well as soft organs such as cranial nerves and a cartilaginous branching skeleton. The preservation of these soft tissues provides unique insights into the evolutionary history of anurans, the group to which frogs and toads belong, and clarifies aspects of the evolution of their life cycle.
The tadpole is about 16 inches long, making it well above the size of most living tadpoles. According to The Guardian, it is a younger version of an extinct giant frog species, with its skeleton visible and parts of its soft tissues preserved. The adult frogs of Notobatrachus degiustoi were also considered giants, growing between 9 and 15 centimeters in size and living in shallow ponds that dried out and reformed with the seasons.
The discovery is important because until now scientists had never unearthed tadpole fossils from before the Cretaceous Period, which began about 145 million years ago, according to Newsweek. This new fossil pushes back the known existence of tadpoles by about 20 million years, as no older tadpole fossils have been found. “The timing of when frog metamorphosis first evolved has long been a mystery,” says Ben Kligman, a paleontologist at the Smithsonian National Museum of Natural History, who was not involved in the study. “It starts to narrow the time frame in which a frog becomes a frog,” he added, according to The Guardian.
The fossil shows that today’s tadpoles have not changed significantly from their Jurassic-era ancestors. Tadpole morphology has remained largely unchanged for millions of years, showing minimal changes in tadpole morphology since that time period, according to Reuters. This finding shows that a two-phase life cycle, in which filter-feeding tadpoles live in a short-lived aquatic environment, was already present in the early evolutionary history of anurans and has remained stable for at least 161 million years.
Chuliver explained, “We now know that this filter feed system had been in place since the group’s inception,” according to The New York Times. The fossil even contains remains of a gill scaffold system that modern tadpoles use to sift food particles from water, indicating that specialized filter-feeding anatomy had already evolved in this fossilized tadpole, according to ABC News. Agustín Scanferla, a palaeontologist and researcher who studied the specimen with Chuliver, added: ‘Thanks to the excellent preservation of the tadpole’s hyoid skeleton, we can confirm that it is fed by filtration, capturing food particles from the water, a mechanism which is performed by the continuous action of water. a buccal pump, just like that found in tadpoles of the current species,” says La Nacion.
The fossil also provides evidence that both the juvenile and adult stages of Notobatrachus degiustoi reached large sizes, indicating that tadpole gigantism was present in the ancestors of anurans. “The gigantism of tadpoles was probably related to long development and the absence of predators,” Chuliver explains. “Additionally, the high availability of food sources and the absence of competitors such as fish or other anuran species were also key factors in the tadpoles growing large,” she continued, as reported by Newsweek.
The discovery was made in January 2020 during a joint expedition searching for dinosaur fossils in the La Matilde Formation in Santa Cruz Province, Argentina. Paleontologists found the tadpole’s remains and then took them to the laboratory for further examination, Infobae said. The research team included scientists from Maimonides University, the Argentine Museum of Natural Sciences and the Chinese Academy of Sciences.
Notobatrachus degiustoi thrived in a warm, tropical climate, alternating with seasonal dry and wet phases during the Middle Jurassic. The species lived alongside small mammals, dinosaurs and freshwater shrimp. The fossil was found encased in volcanic ash and silt, preserving its delicate structures in exceptional detail. “The deposition of these sediments promoted excellent preservation of the specimen, which lasted more than 160 million years,” Chuliver said, according to Newsweek.
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This discovery is a major breakthrough in understanding the evolution of frogs and toads, as it provides the first evidence for the presence of a tadpole, followed by a drastic metamorphosis in the life cycle of anurans from the very beginning of their evolutionary history. Australian broadcaster. It helps refine the evolutionary timeline and contributes to the understanding of the origins and endurance of the biphasic life cycle seen in frogs today.
“Until now, no tadpoles were known from such ancient frogs, so some researchers hypothesized that they could have developed directly into adult frogs,” Chuliver said, as reported by La Nacion. “By discovering this new fossil, we proved this wasn’t true,” VICE said. The presence of a tadpole suggests that metamorphosis was present in frogs as we know them today from the beginning.
The researchers hope that this finding will encourage further explorations and discoveries that can shed more light on the early evolution of frogs and their life cycles. “With this information and more specimens, we can learn more about the anatomy and the different stages of development,” Scanferla concluded, as reported by La Nacion.
Sources: Primera Hora, VICE, Aftonbladet, Folha de S.Paulo, EL DEBER, Australian Broadcasting Corporation, New York Post, AP NEWS, The Independent, The Guardian, Reuters, The New York Times, The National Geographic Society, La Nacion, Infobae, Clarin, Asharq News, Newsweek, ABC News, Popular Science
This article was written in collaboration with generative AI company Alchemiq