A ‘wonder’ fossil changes our understanding of reptile evolution

(Press-News.org) Body coverings such as hair and feathers have played a central role in evolution. They enabled warm-bloodedness by insulating the body, and were used for courtship, display, deterrence of enemies and, in the case of feathers, flight. Their structure is characterised by longer and more complex skin outgrowths that differ significantly from the simple and flat scales of reptiles. Complex skin outgrowths have previously only been observed in mammals in the form of hair and in birds and their closest fossil relatives, dinosaurs and pterosaurs, in the form of feathers. An international team led by palaeontologists Dr Stephan Spiekman and Prof Dr Rainer Schoch from the State Museum of Natural History Stuttgart, Germany, describes a previously unknown tree-dwelling reptile from the early Middle Triassic in a recent study published in the prestigious journal Nature. The 247-million-year-old reptile 'Mirasaura grauvogeli', whose name means 'Grauvogel's Wonder Reptile', had a dorsal crest with previously unknown, structurally complex appendages growing from its skin with some similarities to feathers. The crest was probably used for display to other members of the same species. The find shows that complex skin structures are not only found in birds and their closest relatives but may predate modern reptiles. This important discovery forces us to reconsider our understanding of reptile evolution.

Unique skin structures in early reptiles
The crest of the rather small Mirasaura consists of individual, densely overlapping appendages that each possess a feather-like contour with a narrow central ridge. While real feathers consist of many delicate branched structures called barbs, there is no evidence of such branching in the appendages of Mirasaura. Because of this, the team believes that the structure of the complex, unique skin appendages of Mirasaura evolved largely independently of those of birds.

'The fact that we have discovered such complex skin appendages in such an ancient group of reptiles sheds a new light on their evolution. Mirasaura is even older than the dinosaurs and not closely related to them. Developmental biology studies show that the genetic basis for the growth of complex skin appendages such as feathers probably originated in the Carboniferous period more than 300 million years ago. Mirasaura provides the first direct evidence that such structures actually did form early on in reptile evolution, in groups not closely related to birds and extinct dinosaurs,' says Dr Stephan Spiekman, lead author of the paper and scientist at the State Museum of Natural History in Stuttgart.

Dinosaurs and the origin of feathers
The study marks a turning point in a nearly 30-year trend in palaeontological research that began with the discovery of feathered dinosaurs in China in the late 1990s. Before this time, it was thought that reptiles, including dinosaurs that gave rise to birds, were covered with scales and that only true birds had feathers. As a result, dinosaurs were often depicted as sluggish, scaly animals. This image changed when research started to show that many dinosaurs were much more bird-like than previously thought. The discovery of feathered, non-avian dinosaurs in China caused a wave of new studies that began to blur the lines between scaly, 'cold-blooded' reptiles on the one hand and feathered, 'warm-blooded' birds on the other. Now, it is clear that the story is even more complex.

'Mirasaura grauvogeli shows us how surprising evolution can be and what potential it holds. It repeatedly produces similar structures that are completely independent of each other but also structures that are so different that they can be distinguished. Mirasaura developed an alternative to feathers very early in Earth's history, long before the dinosaurs, which we did not expect and which will stimulate discussion and research,' says Prof. Dr. Rainer Schoch, reptile expert and head of the Palaeontology Department at the State Museum of Natural History in Stuttgart.

Bizarre tree-climbers with bird-like skulls and claws
The latest technologies have been used to study Mirasaura, including synchrotron imaging carried out at the European Synchrotron (ESRF) to reconstruct the skull. This revealed a bird-like shape with a narrow, mostly toothless snout, large forward-facing eye sockets and a large, domed skull. The snout was probably used to extract insects from narrow tree holes. The drepanosauromorphs, to which Mirasaura belongs, are known to palaeontologists as extremely bizarre creatures of the Triassic period. They had grasping forelimbs, sometimes with a huge claw resembling that of a Velociraptor. They had long, barrel-shaped bodies, a long, prehensile tail, and hands that allowed them to grab onto branches like monkeys. Some species even had a hook-shaped claw at the tip of their tail for hanging from branches.

‘Drepanosaurs have many ecological adaptations and have only been known to science for a few decades. Mirasaura lived in trees in one of the first forests that emerged after the great mass extinction at the Permian-Triassic boundary. The dorsal crest with a novel skin structure in Mirasaura adds to the range of remarkable adaptations that make this group of reptiles so unique,’ says palaeontologist Prof Dr Hans Sues from the National Museum of Natural History, Washington DC, USA who participated in the new research.

Melanosomes and skin structures
A thin, brown film was partially preserved on the crest of Mirasaura. Analyses confirmed the presence of melanosomes, tiny organelles that contain melanin pigments. They are found in most animals, including humans. The researchers compared the shape of the Mirasaura melanosomes with those found in the skin of living reptiles, hair and feathers. ‘We know that in modern animals, melanosomes have specific morphologies linked to the tissue where they are found’ says Dr Valentina Rossi, a co-author of the study from University College Cork, Ireland, and an expert on fossil melanosome research. ‘the melanosomes found in Mirasaura soft tissues are more similar in shape to those found in extant and fossil feathers than melanosomes found in mammalian hair and reptilian skin.’

Grauvogel's ‘Wonder Reptile’
Fossil collector Louis Grauvogel began excavating fossils from the Middle Triassic period in Alsace in the 1930s. Among his finds were fossils of Mirasaura. Over the years, he amassed an extensive collection, which remained in the Grauvogel family for many years. In 2019, the collection was transferred to the State Museum of Natural History in Stuttgart, where Mirasaura was discovered during further preparation. The fossils are in the palaeontological collection of the State Museum of Natural History Stuttgart.

Background:

Mirasaura grauvogeli - Discovery story:
Local fossil collector Louis Grauvogel began excavating in Alsace, France, in the late 1930s. The fossils he found dated back to the Middle Triassic period, around 247 million years ago, and consisted mainly of plants, insects and other invertebrates. Unknown to Grauvogel at the time, the finds included the remains of Mirasaura. The collection, which was highly regarded by researchers, remained largely in the family's possession. Dr Léa Grauvogel-Stamm, a palaeobotanist and daughter of Louis Grauvogel, dedicated herself to researching and maintaining the collection. Dr. Grauvogel-Stamm is also involved in the study as a co-author. In 2019, the State Museum of Natural History Stuttgart, Germany, agreed with Dr Lea Grauvogel-Stamm to transfer the extensive collection to Stuttgart. There it will be available for research purposes and will also be on display to the public in future exhibitions. During the preparation of fossils from the Grauvogel Collection in Stuttgart, an unusual small reptile with a crest was discovered and further researched. In honour of its discoverer, Louis Grauvogel, the animal was named Mirasaura grauvogeli - 'Grauvogel's Wonder Reptile'. The fossil is now in the palaeontological collection of the State Museum of Natural History Stuttgart. An interdisciplinary team of palaeontologists wants to further investigate the site where Mirasaura grauvogeli was found to clarify why the skin outgrowths are so well preserved here. Future research will also focus on the ecology, biology and environment of Mirasaura, as well as its interactions with other animals.

State Museum of Natural History Stuttgart:
The State Museum of Natural History Stuttgart is a forward-looking research and communication institute. Its research collections, the archives of diversity, contain over 12 million objects. The museum researches the evolution of life and analyzes the biodiversity of different ecosystems and communicates research findings to the general public.
www.naturkundemuseum-bw.de

Funding:
The research was funded by the DFG - Deutsche Forschungsgemeinschaft (German Research Foundation) and the European Research Council - Consolidator Grant. The State Museum of Natural History Stuttgart was able to acquire the Grauvogel collection several years ago with financial support from the Gesellschaft zur Förderung des Naturkundemuseums Stuttgart e.V., the Cultural Foundation of the German Federal States (Kulturstiftung der Länder) and the Ministry of Science, Research and the Arts Baden-Württemberg.

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