Fossils tell a colourful tale

Pterosaurs are the first known vertebrate group to have evolved powered flight – preceding birds and bats – over many millions of years. From the size of small birds to small planes, pterosaurs lived alongside dinosaurs and went extinct around the same time. Many things about these creatures remain mysterious, not least their origins – the oldest pterosaur fossils ever found are fully capable of flight, and there are no confirmed transitional fossils to show that they Which reptile group did they come from?

It’s different from, say, birds. Revelations over the past two decades that bird-like feathers were present on dinosaurs – with the ability to live on land and the flight ability of a sack of spanner – have illuminated our understanding of the evolution of birds and their distinctive structures.

The bodies of at least some pterosaurs with a type of fuzz are known (or at least suspected) since the 1830s, but this fluff was the subject of study only after the description of the exceptionally hairy Kazakh pterosaur Sordes pilosus in 1971. became the center. .

Pterosaur fluff, technically known as ‘pycnofiber’, is structurally distinct from mammalian fur or hair. Each pycnofiber is a short, simple filament with a canal running through it, and is much more superficially attached than the deep-rooted hairs of mammals. Pycnofibers have been observed on the heads, limbs, and bodies of many pterosaur fossils.

Ironically, given that they can fly, discussion of feathers and wing-like structures has neglected pterosaurs. Instead it has focused on non-avian dinosaurs, which could not. As a result, the relationship – if any – between pterosaur pycnofiber and dinosaur feathers has been unclear.

not anymore. A paper out this week in Nature Ecology & Evolution suggests that some pycnofibers, far from being simple monofilaments, were branching or brush-like structures – like birds and their closest dinosaur relatives (J. Feathers found. Evolution 3, 24–30; 2019).

Therefore, the study suggests that pycnofibers may share an evolutionary origin with dinosaur and bird feathers. And the common ancestor of birds, dinosaurs and pterosaurs may also have been able to produce such pycnofiber structures.

The study’s evidence comes from fossils of two sparrow-sized pterosaurs from the Jurassic period in China, between 160 million and 165 million years old (the earliest known bird, Archeopteryx, is about 150 million years old).

Pterosaurs have four different types of pycnofiber: regular monofilaments seen in other pterosaurs; a type with a brush at the distal ends; a variety in which brush-like fibers protrude from the middle of the main fibre; and a fourth, in which several fibers emerge from a common root. Structures belonging to all four types of pycnofiber have been found to be associated with various dinosaurs, underscoring the case that pterosaurs are indeed related to dinosaurs.

Importantly, each type of fiber is not randomly distributed over the bodies of the two pterosaurs. The simple monofilament form is found throughout the body; brush-like appearance on special areas of the head, limbs and tail; And the curious form with sprouted fibers is confined to the head. The fourth form, which resembles the underside of a bird’s chick, is found on the wing membranes.

This distinctive distribution indicates that each type had a biological function, and that one type of fiber was not merely a decay product of another.

What were these tasks? The first and second types of pycnofiber provided insulation to reduce aerodynamic drag and streamlined body shape, as do feathers in birds and fur in bats. The sprung type on the head may function similar to the sensory bristles found on the heads of modern birds. The inferior, fourth type of fiber may have helped keep feathers warm, as feathers with this structure are known to be more efficient at trapping warm air than mammalian hairs.

In addition, pycnofibers contain remnants of melanosomes – organelles commonly found in feathers, feather-like structures, and mammalian hair, and which help lend these structures their distinctive colours. When applied to pterosaur fuzz, a technique called Fourier-transform infrared spectroscopy produces the same spectra found in both ancient and modern birds, as well as red (but not black) human hair.

For the first time, we can imagine pterosaurs with a touch of color, as we can fossilize birds, dinosaurs, and even dinosaur eggs. Flying alongside early birds and even some early flying mammals, pterosaurs may have made the skies of the Mesozoic Era a riot of life and color.

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