Baby Dinosaurs may have had Different Feathers from their Parents

In a few weeks time those garden birds that have nested and raised a brood successfully will be seeing their youngsters fledge and leave the nest.  A baby Blackbird for example, will moult, losing its downy insulation of feathers and develop feathers that are indistinguishable from its parents.  This youngster, that just a short while ago was an embryo, will look very similar to an adult of its species.  However, in a new paper published in the scientific journal “Nature” it seems that juvenile dinosaurs may have looked strikingly different from their parents.

In a study of two fossils one of an adult, the other of a juvenile dinosaur of the same species; by Chinese scientists, there is evidence to suggest that Theropod dinosaur species at different growth stages may have had dramatically different feathers.  The fossils may indicate that as dinosaurs grew, their feathers changed dramatically.  This is the first time that such evidence has been seen in the fossil record and the interpretation of these two fossils, both recovered from the fossil rich Yixian Formation of western Liaoning (northern China), is being hotly debated by both palaeontologists and ornithologists.

The sedimentary rock formations of Liaoning Province are world famous due to the remarkably well-preserved Cretaceous fossils that they contain.  Much of our knowledge about feathered dinosaurs is due to the myriad of amazing and superbly well-preserved fossils of small Theropod dinosaurs that have been discovered in quarries from this part of China.  The fine-grained, siltstones were formed by volcanic ash from nearby volcanoes that frequently erupted during the early Cretaceous.  Animal and plant remains that had become deposited in lakes in the area were rapidly buried by the ash and this has led to the remarkable state of fossil preservation.  A number of small, feathered Theropod dinosaurs are known from the area, dinosaurs such as Sinosauropteryx and Sinornithosaurus as well as birds, plant remains and even insects.

The dinosaur fossils that have attracted so much interest over how feathers may have changed dramatically as dinosaurs grew and reached maturity; are those of the small, Oviraptorid Similicaudipteryx (Similicaudipteryx yixianensis).  This particular Theropod is known from three specimens and it was formerly named and described in 2008.  Crucially, the local farmers who help the scientists to find fossils, found examples of an adult, whilst the other two fossils represent younger animals.

The Fossils of Similicaudipteryx (Similicaudipteryx yixianensis)

Picture Credit: Zheng Xiaoting

The picture above shows a fossil of a juvenile Similicaudipteryx on the left with the fossilised remains of an adult on the right.  A team of researchers from the Institute of Vertebrate Palaeontology and Palaeoanthropology (IVPP) from Beijing have interpreted the fossils and produced a paper suggesting that unlike modern birds, the plumage and feathers of dinosaurs changed as these animals grew and reached maturity.

Similicaudipteryx was a small, bipedal, feathered dinosaur it was closely related to Caudipteryx (another feathered dinosaur discovered in Liaoning).

An Image of Caudipteryx

Picture Credit: Everything Dinosaur

To view a model of Caudipteryx: Dinosaur Toys for Boys – Dinosaur Models

The fossils indicate that this little Theropod had a maturation pattern not seen in modern birds.

Commenting on the paper, one of the authors, Xing Xu of the IVPP stated:

“This baby dinosaur has bizarre flight feathers, which are strikingly different from those of adults.  These 125-million year old fossils expand our knowledge of feather evolution.”

The wing and tail feathers of the more mature dinosaur resemble quill pens. These ‘pennaceous’ or contour feathers have a central shaft that runs through its entire length. Conversely, the feathers of the younger dinosaur have a flat, ribbon-like stem at one end, but the more familiar pennaceous feather at the tip.  The early juvenile also has smaller wing feathers than tail feathers, but this size difference is less significant in the specimen that represents an older more mature specimen.  Neither adults or juveniles could fly, it is likely primitive feather-like structures first developed to help insulate and keep warm these small active animals.  In mature adults, the feathers may have become more ornate and might have played an important role in communication and display.

Palaeobiologists say that if the Chinese team’s interpretation of the fossils is correct, it would be the first time that juvenile dinosaurs have been shown to have a different type of feather from adults.

Mike Benton from the University of Bristol (UK) added:

“Modern birds don’t make such a transition.  Apart from the downy feathers of newborns, all later stages of modern birds are characterised by the same flight feathers. This paper marks the first step in attempts to disentangle the evolution of developmental sequences among birds and their ancestors.”

However, some ornithologists and developmental biologists have questioned the conclusions made in the Chinese paper.  They query whether the younger fossil shows a ribbon-like feather or is instead from the bird’s moulting phase.

Yale University’s Richard Prum, a leading ornithologist and expert on bird plumage stated:

“Feathers are complicated.”

When modern birds regenerate their feathers, the new ones grow rolled-up in a tube sheath.  Prum has commented that the fossilised feathers of the younger dinosaur could be interpreted as a preserved image of feathers emerging from their sheath; like modern feathers in active moult.

But IVPP scientist Xu maintains that this finding is “not an artefact of preservation or temporary morphology” based on the proportions of the feathers.  If the juvenile feathers were simply in active moult, he would expect the ribbon-like part of the feather to be shorter.  If the Chinese interpretation of the fossil data is correct then this will be the first demonstration that these feathered dinosaurs could undergo changes of plumage as they grew and matured.

An Artist’s Illustration of a Juvenile and Adult Similicaudipteryx

Adult and juvenile feathered dinosaurs

Picture Credit: Xing Lida and Song Qijin

The picture shows an artist’s interpretation of the Similicaudipteryx fossils, the juvenile is in the foreground with the adult just behind.

Using work done by Prum, Chuong and others, Xu and his colleagues at the IVPP suggest that the unusual partially-pennaceous feather might be a result of the delayed expression of genes that are activated earlier in modern birds.

Canadian palaeontologist Phil Currie commented:

“Dinosaurs had been experimenting with feathers and feather-like structures for a period of at least 25 million years before the dinosaurs described here [Similicaudipteryx].  The wonderful thing about this paper is that it provides developmental clues that may force palaeontologists, ornithologists and developmental biologists to recognise a broader spectrum of possibilities rather than looking for some simple answer.”

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