Tag Archives: Feathers

Pterosaurs had feathers and fur

Pterosaurs, which include the pterodactyls and pteranodons, were the first vertebrates to achieve proper, flapping flight. In the popular imagination they are regarded as ‘flying dinosaurs’, whereas the anatomy of the two groups is significantly different. The first of them appeared in the Upper Triassic around 235 Ma ago, at roughly the same time as the earliest known dinosaurs. The anatomical differences make it difficult to decide on a common ancestry for the two. But detailed analysis of pterosaur anatomy suggests that they share enough features with dinosaurs, crocodiles and birds for all four groups to have descended from ancestral archosaurs that were living in the early Triassic, and they survived the mass extinction at the end of that Period. Birds, on the other hand, first appear in the fossil record during the Upper Jurassic 70 Ma later than pterosaurs. They are now widely regarded as descendants of early theropod dinosaurs, which are known commonly to have had fur and feathers.

Pterosaurs leapt into the public imagination in the final chapter of Sir Arthur Conan Doyle’s Lost World with a clatter of ‘dry, leathery wings’ as Professor George Challenger’s captive pterodactyl from northern Brazil’s isolated Roraima tepui plateau made its successful bid for escape from a Zoological Institute meeting in Queens Hall. Yet, far from being leathery, pterosaurs turned out, in the late 1990’s, to have carried filamentous pycnofibres akin to mammalian hair. Widespread reports in the world press during the week before Christmas in 2018 hailed a further development that may have rescued pterosaurs from Conan Doyle’s 1912 description before it sprang from its perch:

It was malicious, horrible, with two small red eyes as bright as points of burning coal. Its long, savage mouth, which it held half-open, was full of a double row of sharp-like teeth. Its shoulders were humped, and round them was draped what appeared to be a faded grey shawl. It was the devil of our childhood in person.

Two specimens from the Middle to Upper Jurassic Yanliiao lagerstätte in China show far more (Yang, Z. and 8 others 2018. Pterosaur integumentary structures with complex feather-like branching. Nature Ecology & Evolution, v. 3, p. 24-30; DOI: 10.1038/s41559-018-0728-7). Their pycnofibres show branching tufts, similar to those found in some theropods dinosaurs, including tyrannosaurs. They also resemble mammalian underfur fibres, whose air-trapping properties provide efficient thermal insulation. Both body and wings of these pterosaurs are furry, which the authors suggest may also have helped reduce drag during flight, while those around the mouth may have had a sensory function similar to those carried by some living birds. Moreover, some of the filaments contain black and red pigments.

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Artist’s impression of a Jurassic anurognathid pterosaur from China (Credit: Yang et al 2018; Fig. 4)

Pterosaurs may have independently developed fur and feathers; a case of parallel evolution in response to similar evolutionary pressures facing dinosaurs, birds and mammals. Alternatively, they may have had a deep evolutionary origin in the common ancestors of all these animal groups as far back as the Upper Carboniferous and Lower Permian.

Related articles: Nature Editorial 2018. Fur and fossils. Nature, v. 564, p. 301-302; DOI: 10.1038/d41586-018-07800-4; King, A. 2018. Pterosaurs sported feathers, claim scientists (The Scientist); Conniff, R. 2018. Pterosaurs just keep getting weirder (Scientific American); New discovery pushes origin of feathers back by 70 million years (Science Daily)

Read more on Palaeobiology

Dinosaurs in the flesh and feathers

Until only a few decades ago artistic portrayals of dinosaurs had them as leathery and scaled like lizards or crocodiles, as indeed rare examples of their fossilized skin seemed to suggest. The animatronic and CGI dinosaurs of the first Jurassic Park film were scary, but brownish grey. Later films in the franchise had them mottled and sometimes in colour, but still as mainly scaled leathery monsters. Reality soon overtook imagination as more and more exquisitely preserved fossils of small species were turned up, mainly in China, that were distinctly furry, fuzzy or feathered as shown below in a Microraptor gui fossil. It is now well-established that birds arose in the Jurassic from saurischian  dinosaurs, the order that also included all of the large carnivorous dinosaurs as well as the many more nimble and diminutive ones whose feathers sometimes conferred an ability to glide or fly. Even the other main order, the ornithischia noted for hugeness and herbivory, has yielded fossil skin that suggest furry or feathered pelts. Once fur and feathers had been found, the next big issue became whether or not dinosaurs may have been as gaudy as many modern birds.

 

Fossil of a feathered dinosaur Microraptor gui from the early Cretaceous Jiufotang Formation in China (source: Wikipedia)

Fossil of a feathered dinosaur Microraptor gui from the early Cretaceous Jiufotang Formation in China (source: Wikipedia)

One of the first palaeobiologists to become immersed in the search for colourful dinosaurs was Jakob Vinther, now of Britain’s Bristol University. In The March 2017 issue of Scientific American he summarises the progress that he and his colleagues have made (Vinther, J. 2017. The true colors of dinosaurs. Scientific American, v. 316(3), p. 42-49). On his account, the major breakthrough was Vinther’s discovery of tiny spherules in fossilised octopus ink that were identical to the granules of the pigment melanin that give the famous cephalopod ‘smoke screen’ its brownie-black colour. Melanin, or more precisely the melanosomes in which it is enclosed, is a key to coloration throughout much of the animal kingdom, especially in fur and feathers. There are two basic kinds, one conferring blackness and the other that imparts a rusty red hue, which combined with paleness due to lack of melanin together produce a gamut of greys, reds, browns oranges and yellows.  Elongated melanosomes when lined up produce the phenomenon of interference fringes that yield iridescence, responsible for the bright colours of starlings, hummingbirds and some ducks when in bright light. There are other pigments, such as carotenoids (bright reds and yellows) and porphyrins (green, red and blue) that add to the gamut possible in animals, but it was melanosomes that captured Vinther’s attention because of their importance in living feather colours.

Melanosomes occur in distinctively grouped assemblages, according to actual colour, and very similar microscopic structures turned up in the first fossil bird feathers that he studied. Others had assumed that they were bacterial colonies, which had grown during decay. The breakthrough was finding a fossil bird feather in which different structures were arranged in stripes; clear signs of patterning. Vinther’s concept bears fruit in a range of furry and feathered dinosaurs. One (Anchiornis) with a black and white body and limb speckles had a bright red crest and another (Sinosauropterix) was ginger over its back with a tiger striped tail and a white underside; an example of countershaded camouflage. His team has even been able to assign different kinds of patterning to a variety of possible habitats. Given superbly preserved specimens it seems likely that dinosaur and bird coloration may be traceable back more than 200 Ma.

English: Illustration of the small theropod di...

Artist’s impression of the small theropod dinosaur Microraptor showing colours predicted by analysis of melanosomes on its feathers.(credit: Wikipedia)

Another aspect of the filmic licence of Jurassic Park was its hinging on preservation of genetic material from the Mesozoic, specifically in a parasite preserved in amber, so that the creatures could be resurrected by bio-engineering. The only relevant find is a 46 Ma old mosquito whose abdomen was blood-engorged when it was fossilised. But all that remains are high iron concentrations the organic molecule porphyrin; break-down products of haemoglobin. Given that fossil DNA can only be reassembled from millions of fragmentary strands found in fossils in digital form that corresponds to the order of AGCT nucleobases that is barely likely to be possible – the oldest full genome yet analysed is that of a 700 ka horse. However, another biological material that varies hugely among living animals, protein, has proved to be tractable, albeit in a very limited way. Frozen mammoth meat, somewhat bloody, is sometimes unearthed from Siberian permafrost, but according to one Russian mammoth expert even the best preserved is inedible.

Beyond the Pleistocene the search for fossilised proteins has been hesitant and deeply controversial, particularly in the case of that from dinosaurs, for the obvious reason of publicity suspicions. But again, it is a story of persistence and patience. Mary Schweitzer of North Carolina State University claimed in 2007 that she had found some, but was howled down by other palaeontologists on the issues of its unlikely survivability and contamination. But other researchers had pushed back the age limits. By repeating their earlier analyses with the greatest possible care Schweitzer’s team confirmed their earlier results with several strands of the protein collagen about 15 amino acids in length from an 80 Ma old duck-billed dinosaur. Moreover they were able to show a closer affinity of the partial proteins to those of modern birds than to other reptiles, tallying with tangible fossil evidence (Schroeter, E.R  and 8 others 2017. Expansion for the Brachylophosaurus canadensis Collagen I Sequence and Additional Evidence of the Preservation of Cretaceous Protein. Journal of Proteome Research, v. 16, p. 920-932). The work continues for other dinosaurs and early fossil birds, with better reason for confidence and a chance of tying-down genetic relatedness. Another approach shows that collagen may still be preserved in a Jurassic (195 Ma) sauropod dinosaur’s rib (Lee, Y-C. and 9 others 2017. Evidence of preserved collagen in an Early Jurassic sauropodomorph dinosaur revealed by synchrotron FTIR microspectroscopy. Nature Communications, v. 8 doi:10.1038/ncomms14220).

See also: Service, R.F. 2017. Researchers close in on ancient dinosaur remains. Science (News in depth), v. 355, p. 441- 442.