Darwinopterus – A Transitional Pterosaur Fossil

Pterosaurs may have quickly evolved forms to take advantage of a new food source – flying theropods like Microraptor.

One hundred and sixty million years ago the skies of north eastern China were filled with primitive feathered dinosaurs that flapped awkwardly from tree to tree.  These early aviators, descendants of small, meat-eating, bipedal dinosaurs had perhaps evolved flight feathers to escape from larger ground based predators or to exploit an environmental, arboreal niche.

Pterosaurs

However, pterosaurs, those aerial masters of the skies, whose ancestors had taken to the wing some seventy million years earlier, may have quickly evolved forms to take advantage of this new food source of flying theropods.  At least that is what can be speculated from the research and published papers of a joint Chinese and British team of scientists as they published their work on Darwinopterus. Darwinopterus may be a transitional fossil between the long-tailed rhamphorhynchoids and the later, short-tailed pterodactyloids.

An Artist’s Impression of Darwinopterus

Picture credit: Mark Witton University of Portsmouth.

Darwinopterus

The illustration depicts Darwinopterus attacking a small bird-like creature, an ancestor of modern birds, a flexible neck combined with the curved, sharp teeth in the jaws of this raven-sized pterosaur seem ideally suited to grabbing hold of small prey.  Whether this animal hunted on the wing is speculation.

The joint Chinese and British based team of palaeontologists have published their work on this 160 million-year-old Pterosaur in the scientific publication the “British Journal Proceedings of the Royal Society B”, the “B” stands for Biology.  In total, more than 20 individual fossil specimens of this pterosaur have been found.  This new type of flying reptile has been named Darwinopterus modularis, to honour the 200th anniversary of the birth of Charles Darwin and the 150th anniversary of his ground-breaking work on the theory of evolution – “The Origin of Species by means of Natural Selection or The Preservation of Favoured Races in the Struggle for Life”.

Darwinopterus modularis

The species name modularis meaning “composed of interchangeable units”.  This alludes to the fact that this pterosaur has traits of both primitive long-tailed rhamphorhynchoids and parts of its anatomy more closely associated with the more advanced, later pterodactyloids.  These specimens could be termed transitional fossils, capturing an example in the fossil record of one type of flying reptile, evolving into a different form.  It is as if a sculptor has created a whole creature, a sort of prehistoric, flying chimera from various parts of other genera.  One has to be careful about this, as there are several instances of composite fossils originating from China, perhaps most famously Archaeoraptor.

Archaeoraptor turned out to be an elaborate fake.  Instead of proving to be a transitional fossil form between theropod dinosaurs and the first birds, it was simply pieces of at least two different fossils stuck together – it fooled the National Geographic Society.

A Close up of the Skull and Jaws of Darwinopterus

Fossil material (pterosaur).

Picture credit: Lü Junchang (PA)

Darwin’s Theory

Interestingly, one of the arguments put forward by scientists in support of the idea that all species were fixed and immutable, before the publication of Darwin’s theory, and indeed an argument that was used long after Darwin had written and published his 1859 work, was that the fossil record did not show many transitional species.

The fossil record, as Darwin admitted himself was very incomplete.  The beautiful argument put forward by the likes of a number of eminent American palaeontologists later in the 19th century, for the evolution of the horse was not available to Darwin at the time of his writing of his book on natural selection.  In the famous volume – “The Principles of Geology” written by the English geologist Sir Charles Lyell , a tremendous influence on Darwin himself, it was written:

“There is no foundation in geological facts for the popular theory of successive development of the animal and vegetable world, from the simplest to the most perfect forms”.

Commenting on this new discovery, Dr David Unwin of the University of Leicester stated:

“Darwinopterus came as quite a shock to us.  We had always expected a gap-filler with typically intermediate features such as a moderately elongated tail — neither long nor short — but the strange thing about  is that it has a head and neck just like that of advanced pterosaurs, while the rest of the skeleton, including a very long tail, is identical to that of primitive forms.”

Bursts of Evolution

The long tail can be seen at the bottom of the slab on some of the fossil image.  The investigators, led by Junchang Lu of the Institute of Geology in Beijing, believe that pterosaurs went through bursts of evolution characterised by swift changes to groups of features.  They have postulated that the head and neck evolved first, followed later by the body, tail, wings and legs.

A sort of sequence of rapid evolutionary jumps.  It can be speculated as the competition between predator and prey escalated in the air, the prey animals; the flying theropods were under a great deal of evolutionary pressure to adapt quickly and evolve into more efficient flying forms.  This competition may have speeded up the evolutionary flight path (excuse the pun), of modern birds.

For replicas of pterosaurs and feathered theropods, take a look at the Safari Ltd model range: Wild Safari Prehistoric World.

Archaeopteryx – New Study casts doubt on Avian Lineage

A new study carried out by American scientists with support from other teams of palaeontologists in China and Germany has cast doubt over just how closely Archaeopteryx may have been to the true origin of birds.  This new research published in the on line scientific journal PloS One (Public Library of Science), suggests that the metabolism and subsequent growth rate of this Jurassic creature was perhaps more reminiscent of the growth rate expected of a dinosaur than to a modern bird.

In a microscopic study of several Archaeopteryx fossils and other extinct creatures such as some of the ancient birds from the Liaoning Formation of China, images taken of the ancient cells and blood vessels inside the bones of Archaeopteryx show slow growth.  This Jurassic animal may have taken years to mature and reach adult size.  This pattern of ontogeny (growth) is similar to what dinosaurs had.  In contrast, modern birds grow rapidly and mature in a matter of weeks.

Think of the birds in your garden or neighbourhood, you may have seen blackbirds, sparrows, and thrushes all nesting in the Spring and by late Summer the offspring are not much smaller than their parents.  Modern birds (Neornithes), grow and mature very quickly.  Most reptiles grow much slower, from this study it seems that evidence from the fossilised bones of Archaeopteryx indicate that this feathered creature, claimed to be the first bird and ancestral to all birds, grew at the same speed expected of a dinosaur, not at the same rate as your garden sparrow.

An Illustration of Archaeopteryx

Archaeopteryx lithographica by Everything Dinosaur.

Picture credit: Everything Dinosaur

Importantly, this research indicates that rapid bone growth, a trait common to all living birds was absent from the first birds.  Rapid growth and maturation was not necessary for avian dinosaur flight.

This new paper follows the recent of announcement of the discovery of several feathered dinosaurs that pre-date the 150 million-year-old Archaeopteryx, providing evidence that creatures like Archaeopteryx may have evolved from feathered dinosaurs.

To view an article about feathered dinosaurs: Older than Archaeopteryx – Supporting Evidence of Birds evolving from Feathered Dinosaurs.

The paper co-authored by a number of palaeontologists including Gregory Erickson, an Associate Professor at Florida State’s Department of Biological Science supported by scientists at the Institute of Vertebrate Palaeontology and Palaeoanthropology (IVPP) in Beijing, compares the microscopic analysis of the long bones in various Archaeopteryx fossils with extant birds as well as theropod dinosaurs and birds such as the primitive Confuciusornis from the Cretaceous of China.

Dr Erickson stated that there was already evidence to support the theory that birds are in fact dinosaurs, but this paper attempted to answer the question: – “Just how dinosaur-like, or even bird-like was the first bird? [Archaeopteryx]“.

A Cast of an Archaeopteryx Fossil on Display

Archaeopteryx fossil cast. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

There has been considerable debate over how well this crow-sized creature could fly.  Some scientists have even speculated that this early bird may not actually have been capable of powered flight, perhaps gliding from tree to tree.  However, studies carried out by scientists at the Natural History Museum in London, seemed to indicate that Archaeopteryx possessed and excellent sense of balance and had the faculties required to produce and control powered flight.  In addition, research has indicated that the structure of the inner ear of Archaeopteryx was more bird-like than reptilian.

To read an article on the London research: Let’s hear it for Archaeopteryx.

Commenting on the ontogeny of birds, Dr Erickson stated:

“Living birds mature very quickly.  That’s why we rarely see baby birds among flocks of invariably identical-size pigeons.  Slow-growing animals such as Archaeopteryx would look foreign to contemporary bird-watchers”.

Similar microscopic bone studies were carried out on the 130 million-year-old fossils of Confuciusornis.  This phase of the project was supervised by scientists from the IVPP.  It was concluded that the confuciusornithids were the first known birds to show a transition to the rapid growth rates associated with modern bird species.  Not only was the jay-sized flyer Confuciusornis more advanced anatomically than Archaeopteryx (the development of a pygostyle rather than a long, cumbersome tail is evidence of this), but it seems that the growth rate of these two creatures was also very different.  More advanced bird fossils from approximately 100 million years ago, show bones well supplied with blood vessels and were probably faster growing than the confuciusornithids.

It seems that the bird cladogram and the evolutionary path taken by our feathered friends is turning out to be every bit as complex as first thought when Huxley back in the 19th century put forward the theory of a link between Dinosauria and Aves.

Visit Everything Dinosaur’s award-winning website: Everything Dinosaur.