Origins of Feathers More Complex Than Previously Thought

Over the last week or so, team members at Everything Dinosaur have reported upon new research into whether dinosaurs were warm-blooded or not.  In addition, in response to requests from readers, we discussed the lack of feathers in dinosaurs such as the fearsome Velociraptors that are featured in the forthcoming movie “Jurassic World”.

Feathered Dinosaurs

This morning, we turn once again to the “were dinosaurs feathered” debate as a new study published in the journal “Biology Letters” suggests that the common ancestor of the Dinosauria was not covered in feathers and indeed, most dinosaurs probably were scaly.

Analysis undertaken by scientists from the Natural History Museum (London), Uppsala University (Sweden) and the Royal Ontario Museum (Toronto, Canada) suggest that feathered dinosaurs were probably the exception amongst the Order Dinosauria.  A comprehensive review of known dinosaur skin fossils coupled with an in-depth study of the dinosaur family tree was used to assess the probability of feathers appearing in different types of dinosaur.

The team conclude that the majority of non-avian dinosaurs were more likely to have had scales like a crocodile or lizard rather than exhibiting signs of feathers or “feather-like” structures.

Once Again Palaeontologists Debate the Extent of Feathers in the Dinosauria

Adult and juvenile feathered dinosaurs

Adult and juvenile feathered dinosaurs.

Picture credit: Xing Lida and Song Qijin

Why do Scientists Get into a Flap over Feathers?

If the majority of dinosaurs had feathers then this has huge implications for dinosaur biology and behaviour.  Insulating feathers infer that the animal that possesses them must be warm-blooded (endothermic), so this argument links directly into the cold-blooded versus warm-blooded dinosaur debate.

To read the article on the research from Stony Brook University that challenges 2014 data on mesothermic dinosaurs and argues that dinosaurs were indeed warm-blooded: Dinosaur Warm-blooded Debate Hots Up.

Thanks to the astonishing fossils from Liaoning Province (China) scientists have been able to identify feathers in a number of different types of theropod dinosaur.  It is widely accepted that many different types of meat-eating dinosaur were feathered or at least partially feathered.

Those dinosaurs which are believed to be closely related to birds provide the greatest number of candidates for feathers rather than scales.  Dinosaurs such as Caudipteryx (Oviraptoridae), Beipiaosaurus (Therizinosauridae), Microraptor (Dromaeosauridae) and Deinocheirus (Ornithomimosauria) were all very probably feathered.  All these dinosaurs are classified as coelurosaurian theropods, the clade of dinosaurs that taxonomically are placed close to the evolutionary line leading to the Aves (birds) fossil evidence supports this hypothesis.

Beautifully Feathered Dinosaur Fossil from Liaoning Province (Microraptor)

Feathers found preserved in many dinosaur fossils from China.

Feathers found preserved in many dinosaur fossils from China.

Scored for the Presence of Absence of Feathers

The researchers included thirty-four ornithischian dinosaurs, six sauropods and forty theropods (which included some Mesozoic birds).  These taxa along with a number of others were scored for the presence of feathers or proto-feathers in the fossil record.  Where on the body feathers had been found was also taken into account along with the type of depositional environments that allowed the preservation of filamentous feathers or scaly skin.

Pterosaurs as a group related to the Dinosauria and also archosaurs were included in the study.  Although the fossil record is extremely poor, the team were able to conclude that, based on the probability analysis and the consensus tree that was constructed, it was likely that the ancestor of the dinosaurs was not feathered.  In addition, the research suggests that although the majority of coelurosaurian theropods were indeed feathered to some degree, the majority of other dinosaurs were very probably not feathered.

Commenting on the research, one of the authors of the paper, Nicolás E. Campione (Uppsala University) stated:

“As palaeontologists we are at the mercy of available data, which given the interest in the field are ever changing.  Our study shows that dinosaurs experimented extensively with their “outer look” and potentially independently along separate evolutionary lineages.  That is what the data allows us to say at present.”

The Way Flying Reptiles (Pterosaurs) Were Assessed Affected the Results

Intriguingly, the single biggest influence on the feather versus scales debate in this analysis was the way in which the Pterosauria (flying reptiles) were treated.  Pterosaurs are not dinosaurs, but a related group belonging to the archosaurs just like the Dinosauria.  How closely related the pterosaurs are to the dinosaurs remains an area of controversy.  This research showed that if the ancestor of the Pterosauria was assumed to be scaly then different feather probabilities in the Dinosauria resulted when compared with the study with a fuzzy Pterosaur ancestor included in the database.

Professor Paul Barrett, (Natural History Museum), one of the co-authors of this report summarised the team’s findings:

“Using a comprehensive database of dinosaur skin impressions, we attempted to reconstruct and interpret the evolutionary history of dinosaur scales and feathers.  Most of our analyses provide no support for the appearance of feathers in the majority of non-avian dinosaurs and although many meat-eating dinosaurs were feathered, the majority of other dinosaurs, including the ancestor of all dinosaurs, were probably scaly.”

Feathered Dinosaurs

The biology of the dinosaurs is going to remain a hotly debated topic.  Work such as this new study helps to move the debate forward by reflecting evidence put forward by new fossil discoveries.  However, the fossil record is far from complete and conclusions such as the ones made in this research need to be tested in the light of further fossil finds that help to fill in important and significant gaps in our knowledge of the epidermal coverings of dinosaurs and their close relatives.

To read an article about a fossil find that suggests a Jurassic Ornithischian dinosaur was feathered: Kulindadromeus – Did All Dinosaurs Have Feathers?

A consequence of the inference that most coelurosaurian theropods were probably feathered is that the most famous dinosaur of all Tyrannosaurus rex may also have been covered in a coat of feathers.  Perhaps a young T. rex had a shaggy coat of feathers to help keep it warm.  As the animal grew and became more massive, the need to insulate its body (surface area to volume ratio), became less important.  An adult Tyrannosaurus rex, however, may indeed have been feathered, at least in part.

As fossils of filaments and feathers are associated with low energy depositional environments and finely grained substrates (not a description readily given to much of the Hell Creek Formation), then palaeontologists may never find a feathered T. rex fossil.

CollectA Will Introduce a Feathered T. rex Model in the Summer of 2015

1:40 scale model of a feathered T. rex.

1:40 scale model of a feathered T. rex.

To view the CollectA scale model range and the feathered T. rex (from late summer 2015): CollectA Prehistoric Life Models.