{"id":387010,"date":"2021-03-17T15:48:24","date_gmt":"2021-03-17T18:48:24","guid":{"rendered":"https:\/\/revistapesquisa.fapesp.br\/?p=387010"},"modified":"2021-03-17T17:42:48","modified_gmt":"2021-03-17T20:42:48","slug":"pterosaur-precursors","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/pterosaur-precursors\/","title":{"rendered":"Pterosaur precursors"},"content":{"rendered":"

It has never been easy to classify pterosaurs, the first winged vertebrates to conquer the skies at a time when dinosaurs prowled on land between 230 and 66 million years ago. Controversies over classification remain more than two and a half centuries since the first pterosaur fossil was described, a species now known as Pterodactylus<\/em> antiquus<\/em> that lived during the late Jurassic period, about 150 million years ago. In 1784, Cosimo Alessandro Collini (1727\u20131806) described a strange creature whose fossil skeleton had been unearthed at least two decades earlier at a limestone quarry in Eichst\u00e4tt, a town in Bavaria, Germany. Especially curious among the bone remains was the fossil\u2019s long, sharp-toothed beak and a mysterious, elongated fourth finger. Collini, then curator of the natural history cabinet in the German city of Mannheim, thought it was a sea creature with fins, an impression suggested by his having found the material in a collection of articles of apparent marine origin.<\/p>\n

A few years later, naturalist Jean Hermann (1738\u20131800) of Strasbourg, France, concluded that the animal was instead a mammal with wings formed by a membrane anchored on the large fourth finger, a mechanism bearing some resemblance, but not identical, to the wing structures that would later evolve on bats. In the 1810s, his colleague Georges Cuvier (1769\u20131832), at the Museum of Natural History in Paris, who had received sketches and written descriptions from Hermann, classified the intriguing creature as a flying reptile. He also gave it an unflattering description, calling it \u201cthe product of a sick imagination rather than the ordinary forces of nature.\u201d His description is explained by the peculiar nature of pterosaurs, which became extinct along with dinosaurs and left behind no living descendants: they were unlike like any life forms that preceded them, and apparently emerged with an anatomy purpose-built for flight whose origin remains a mystery.<\/p>\n

A recent study by an international team of paleontologists led by Max Langer, at the Ribeir\u00e3o Preto campus of the University of S\u00e3o Paulo (USP), took an important step toward a better understanding of pterosaur origins. According to the paper\u2014which is featured on the cover of the December 17 edition of Nature<\/em>\u2014lagerpetids, a little-known group of small ground-dwelling bipeds, which are relatively sparse in the fossil record, were precursors to pterosaurs. Until recently, the prevailing view among paleontologists was that lagerpetids were instead precursors to dinosaurs, likely emerging on the ancient southern supercontinent of Gondwana just under 240 million years ago.<\/p>\n

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Tommy\u2009\/\u2009Wikimedia Commons <\/span><\/a> Fossil remains of the pterosaur Eudimorphodon<\/em>, found in the Italian AlpsTommy\u2009\/\u2009Wikimedia Commons <\/span><\/p><\/div>\n

Lagerpetids, which largely fed on insects and perhaps smaller animals, couldn\u2019t fly and had no structures resembling wings, but their forelimbs were elongated. \u201cThe anatomy of their claws suggests they used their forelimbs for purposes other than for moving on the ground, such as for climbing, scratching or capturing prey,\u201d says Langer. That is why in the artistic rendition on the cover of Nature<\/em>, Ixalerpeton polesiensis\u2014<\/em>the lagerpetid species discussed in Langer\u2019s paper, found in the region of Santa Maria, in Rio Grande do Sul\u2014is shown leaping from a tree.<\/p>\n

The article does not suggest that pterosaurs were direct descendants of lagerpetids, whose oldest known fossil predates the oldest remains of winged reptiles found to date by 18 million years. \u201cWe\u2019re saying they are sister groups. They bear the same evolutionary relationship that humans do to chimpanzees. One is not descended from the other. What links them together is that their lineages originated from a common ancestor,\u201d explains Langer. All of these ancient vertebrates\u2014dinosaurs, pterosaurs, and lagerpetids\u2014have some degree of kinship with one another and are lineages that make up an even larger and more ancient group of reptiles\u2014archosaurs. Today, birds (which are representatives of the dinosaur group) and crocodilians are the only living representatives of archosaurs.<\/p>\n

To date, fossils of only six species of lagerpetids, which lived between 237 and 210 million years ago, have been discovered in four countries (Brazil, Argentina, the US, and Madagascar). These species belong to a group of extinct reptiles that have been known to science for only about 50 years. All known forms of these animals are of modest size, measuring between 10 cm and 1 meter (m) in length and weighing no more than 5 kilos. Initially, fossils were found only of the hip bones and hind legs. In the last 10 years, bone remains have been found of other parts of these reptiles, such as the braincase, spine, and forelimbs. This has provided a better understanding of the anatomy of lagerpetids and how it compares to that of early pterosaurs.<\/p>\n

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Laborat\u00f3rio de Paleontologia da USP de Ribeir\u00e3o Preto<\/span><\/a> A fossil of the lagerpetid Ixalerpeton polesiensis<\/em>, discovered in S\u00e3o Jo\u00e3o do Pol\u00easine, southern BrazilLaborat\u00f3rio de Paleontologia da USP de Ribeir\u00e3o Preto<\/span><\/p><\/div>\n

Pterosaurs have been known for two and a half centuries, as the story in the introduction to this article illustrates. About 100 species have been described to date, from specimens the size of a hen (usually the oldest) to animals the size of a four-passenger airplane. All known pterosaurs have characteristic elongated fourth fingers on their forelimbs. \u201cNo pterosaur fossils without this flight mechanism have ever been found,\u201d says Argentine paleontologist Mart\u00edn Ezcurra of the Museo Argentino de Ciencias Naturales Bernardino Rivadavia, in Buenos Aires, the lead author of the Nature article along with colleagues in the US and Europe.<\/p>\n

This is precisely what intrigues paleontologists. In the fossil record, even the oldest species of this group of reptiles, dating back around 220 million years\u2014such as Caelestiventus hanseni<\/em>\u2014already exhibited an anatomy fully adapted for flight. There are no known intermediate forms, or \u201cevolutionary sketches\u201d of what would become the pterosaur. All fossils of these enigmatic animals appear to have emerged ready for flight, which makes it difficult to establish which lineage of reptiles they evolved from.<\/p>\n

In the article in Nature, paleontologists analyzed and reconstructed the anatomical features of these half-dozen species of lagerpetids, using techniques such as microcomputed tomography. They then constructed phylogenetic trees that placed them as the group most closely related to pterosaurs. Although they were wingless and therefore flightless, lagerpetids shared some common anatomical features\u2014such as the jaw, teeth, braincase, and inner ear\u2014with pterosaurs. \u201cOur work on the origin of pterosaurs will open a new line of research that will attempt to understand how these animals became the first vertebrates to acquire the ability for active flight and not just gliding,\u201d says Ezcurra.<\/p>\n

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Steven U. Vidovic, David M. Martill, Matthew Martyniuk\u2009\/\u2009Plos One<\/span><\/a> A fossil of Pterodactylus antiquus<\/em>, the first pterosaur species described in the scientific literature, approximately 250 years agoSteven U. Vidovic, David M. Martill, Matthew Martyniuk\u2009\/\u2009Plos One<\/span><\/p><\/div>\n

Currently, two competing hypotheses attempt to account for the evolutionary process that led to the emergence and radiation of pterosaurs. One suggests they may have arisen more than 250 million years ago, long before their fossil record commences. According to this hypothesis, known as the Iceberg model, pterosaurs had a long evolutionary history before their first appearance in the geological record, spreading gradually across the continents like slow-moving icebergs. The other hypothesis, called the Big Bang model, suggests their appearance was more explosive and occurred in a short space of time. In this model, pterosaurs appeared relatively abruptly in evolutionary history, around 220 million years ago, the age of their oldest known fossils.<\/p>\n

\u201cEvolutionary proximity to lagerpetids [whose oldest fossils are not more than 240 million years old] supports the Big Bang model,\u201d says Italian paleontologist Fabio Marco Dalla Vecchia, from the Museo Friulano di Storia Naturale at Udine, who coauthored the new study. Dalla Vecchia is one of the world\u2019s leading specialists in pterosaurs. Many of their earliest fossils were found near the border between northern Italy and southern Austria.<\/p>\n