Paleontologists have revealed a wondrous new reptile from the Middle Triassic called Mirasaura grauvogeli. This small, tree-dwelling reptile lived around 247 million years ago in what is now northeastern France.
It had a stunning crest of long, feather-like appendages running along its back. These appendages formed a continuous surface with tiny ridges. It is possible that they were flexible, and would shimmer in the light.
New analysis confirms that Mirasaura grauvogeli could not fold its crest down, which stood upright at all times. The reptile would have thus delivered a constant visual signal, whether warning predators or attracting mates.
So what was Mirasaura?
Mirasaura was a nimble forest dweller of the Middle Triassic. It had a bird-like, beak-tipped skull, forward-facing eyes, and a prehensile tail. These traits would have made it well-suited to climbing and hunting insects among the canopy. We do not see these features in any modern reptile.
The holotype, preserving the skull, partial postcranial skeleton and crest.
The discovery also proves that advanced skin structures (integumentary structures) appeared much earlier and beyond bird or mammal lines, challenging long-held assumptions about reptile evolution.
The crest was likely for communication
The Scientists write in their paper that the exact function of the crest is uncertain, because we don’t have existing reptiles with similar features. However, a function in gliding flight can be excluded, because the crest is restricted to a single, unpaired row along its back. For the same reason, body insulation can also be excluded.
It is also unlikely that the crest served for mimicry either through camouflage or to deter predators by resembling a potentially harmful organism. This is because the crest of Mirasaura does not resemble the shape of any other known taxon from the region.
Instead, the large size of the crest and its vertical orientation indicate a role in visual communication. The researchers posit that Mirasaura would have had good sight based on its large, front-facing eyes and possible arboreal habits.
Not Feathers, but Feather-like Convergent Evolution
These enigmatic appendages are not true feathers, but they mimic feather form. Each segment is a single, continuous blade without branching barbs, unlike bird feathers. They share another feather trait, melanosomes. These are pigment cells shaped closely like those in modern feathers.
Though its skull also looks superficially bird-like, Mirasaura does not belong with dinosaurs or birds. It falls within the slightly obscure Drepanosauromorpha, a group of tree-climbing Triassic reptiles. Since Mirasaura is not closely related to birds and other feather-having creatures, this supports a case of convergent evolution: complex skin appendages evolved independently in different reptile lineages.
“The integumentary appendages of Mirasaura are distinct from known skin crests, scales, horns and hair of other amniotes in their highly consistent and organized morphology”, wrote lead author Stephan N. F. Spiekman in the paper. “these appendages are remarkably long relative to body size”
The evolution of feathers and hair is considered to have played a crucial role in the evolutionary success of both reptile-ancestors and mammal-ancestors. Paleontologists call this the ‘Triassic arms race’. It facilitated the evolution of warm-bloodedness and bigger brains, by providing body insulation.
Unfortunately, unlike mammal-ancestors and reptile-ancestors, drepanosauromorphs did not survive into the Jurassic. Also unlike them, Mirasaur’s integumentary appendages probably served for visual display rather than insulation. This adds another possible evolutionary driver for the origin of complex integumentary appendages. And finally, the presence of structurally distinct integumentary appendages highlights the importance of the Triassic as a time of evolutionary innovation.
The Fossil has its Own History
Two well-preserved skeletons and 80 specimens were found in northeastern France during the Second World War. Isolated appendages and preserved soft tissues were also found. However, they remained unidentified until further preparation was undertaken in recent years. Initially misidentified as plant or fish parts, the crest was finally recognized in 2019 when the collection reached Stuttgart’s State Museum of Natural History. Only now have paleontologists revealed Mirasaura’s true nature.