Tag Archives: Feathered dinosaur

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.

A cuddly tyrannosaur

Feathered Dinosaurs 1

Feathered dinosaur Deinonychus (Photo credit: Aaron Gustafson)

Feathered and fluffy dinosaurs in the families that may have led to birds have become almost commonplace, thanks to wonderful preservation in some Chinese Mesozoic sedimentary rocks (see https://earth-pages.co.uk/2003/03/01/flying-feathers/)  and what has become a cottage industry for local people, under professional direction. Most have been small theropods in the Coelurosauria taxonomic branch that span the Jurassic and Cretaceous Periods. The famous Lower Cretaceous Liaoning lagerstätte in NE China recently yielded something truly awesome: three well-preserved specimens of a feathered dinosaur almost as large as the giant tyrannosaurs of the Late Cretaceous (i.e. > 1 tonne in life) (Xu, X. et al.2012. A gigantic feathered dinosaur from the Lower Cretaceous of China. Nature, v. 484. P. 92-95). In fact Yutyrannus huali (‘beautiful feathered tyrant)is a member of the same subgroup as the Upper Cretaceous T. rex and was clearly a top predator in its day. Equally fortuitous is that the three specimens  comprise one with a living body weight of about 1.4 t, the other two being between 500 and 600 kg. Various differences between the largest and the two smaller individuals suggest that thee find represents two generations, the largest perhaps 8 years older than the two smaller ones. All three preserve densely packed filaments suggesting that they were fluffy rather than truly feathered. So why the difference from its probably scaly relative tyrannosaurs from about 50 Ma later?

Around 125 Ma global climate was considerably cooler than the Late Cretaceous greenhouse world, Liaoning probably having mean annual air temperatures around 10°C compared with 18°C late in the Period. Yutyrannus huali and some of its contemporary theropods probably evolved high TOG insulation to ensure all-season sprightliness. It is also possible that a display function was also involved, as seems to have been the case for other dinosaurs.

Feathers will fly: Archaeopteryx relegated

Archaeopteryx

A not unimaginative reconstruction of Archaeopteryx. Image via Wikipedia

This year, 2011, is the 150th anniversary of the first Archaeopteryx specimen being unearthed from the famous Solnhofen  limestone lagerstätte. With its feathered, lizard-like tail; two-clawed, stubby wings; a bill-shaped muzzle with teeth but no keratin coating; feet capable of perching and unlike those of small dinosaurs; a ‘wishbone’ and lightweight bones, Archaeopteryx was just the half-and-half missing link in the fossil record so desperately needed to support Darwin’s Origin of Species, published two years beforehand.  It has remained controversial ever since, even having been claimed to be a forgery by such luminaries as cosmologist Fred Hoyle in 1985, despite its superbly preserved intricacies and the existence at the time of 6 slightly different specimens from the same source some discovered long after Hoyle’s supposed master craftsman must have died. Creationists soon after the first discovery claimed it was simply a bird created on a Friday together with fish (Genesis 1:20) and must have predated dinosaurs by a day, as they were created on the 6th Day along with all the ‘cattle and creeping thing and beast of the earth’ (Genesis 1:24-31). That scurrilous sect will certainly leap gleefully on the new discovery of a feathered dinosaur from the ever productive Late Jurassic Tiaojishan Formation in NE China (Xu, X. et al.2011. An Archaeopteryx-like theropod from China and the origin of the Avialae. Nature, v. 475, p. 465-470) because ironically, by itself, it could be said to be a missing link too.

Archaeopteryx lithographica, specimen displaye...

Cast of the first-described Archaeopteryx fossil. Image via Wikipedia

In fact, Xiaotingia zhengi possesses features very like those displayed by Archaeopteryx but convincingly close affinities to deinonychosaurian dinosaurs. The shared features show that neither is a bird (Avialae) and nor are they part of the clade that evolved to birds: they are part of the growing group of feathered dinosaurs that may well have glided or even flown. As Lawrence Witmer of Ohio University has observed (Witmer, L.M. 201. An icon knocked off its perch. Nature, v. 475, p. 458-459), ‘This finding is likely to be met with considerable controversy (if not outright horror)…’. However, Witmer still considers Archaeopteryx to have iconic status, indeed yet more, for its taxonomy and that of its related feathery dinosaurs provides compelling evidence that the origin and evolution of life was a ‘rather messy affair’. Undoubtedly, more feathered creatures hundreds of million years old will be unearthed; it is even possible that further finds will push the beast of Solnhofen back onto its avian perch. Let the celebrations begin!

Added 12 August 2011: Ironically, yesterday the German mint issued a €10 silver coin commemorating the 150th anniversary of the first discovery of Archaeopteryx, artwork of the skeleton with fully fledged arms on the reverse side of the coin compared with the stylised German eagle on the front. This event coincides with the greatest crisis facing the eurozone in its short history, though Germany still retains its ‘triple A’ financial status unlike France and the US. See: http://witmerlab.wordpress.com/2011/01/31/evolution-icon-archaeopteryx-turns-150-this-year-how-are-we-celebrating/