Friday, 31 May 2013

My Family And Other Animals

The 150 million year old fossil of Archaeopteryx
, the first bird on the planet, from the
Solnhofen Limestones the Bavaria Region of Germany.
150 million years ago above the limey, predator infested waters of a lagoon which would become Bavaria, lived Archaeopteryx lithographica, the first ever bird on our planet.

Archaeopteryx, for many palaeontologists has always occupied a spot of certainty. What has always been less clear is its evolutionary run up  and how this connects to its descendants.

Diagrams of relationships have been drawn up over the years, but each new fossil discovery throws up problems with the existing schemes of classification. Now, a new fossil discovery from China provides a new link. 

Archaeopteryx and its descendants are all part of the family aves. In turn, these are part of a larger group known as the avialans, a tight knit group consisting of all birds and three immediate dinosaur ancestors/relatives, including Anchiornis which in 2010 became the first prehistoric creature to have its complete colours reconstructed.

The very name 'avialan' means 'bird wing.' Indeed, even the non-avian members of this very select group are often referred to as proto-birds, as the boundaries separating the true avians from the rest are blurry. As a result, while the origins of birds with Archaeopteryx was clear, the origins of avialans was less defined, until now.

Unearthed from 160 million year old rocks of the Tiaojishan Formation in the world famous Liaoning Province, this new specimen was purchased from a local fossil dealer and examined by a team led by Pascal Godefroit from the Royal Belgian Institute of Natural Sciences. Without knowledge of the the locality from which the fossil came, it would have been impossible to date the fossil accurately. A study of the sediment which made up the fossil's matrix showed it to be linked with the Tiaojishan fossil beds. The fossil itself was well preserved, with all the bones present and delicate feather impressions marking out the creature's original dimensions. In life, it would have been around 50 centimetres in length with a toothy beak, long tail, clawed hands and feathers covering the entire body.
The 160 million year old fossil of Aurornis xui, the first avialan on the
planet, from the Tiaojishan Formation in the Liaoning Province of China.
From the outset, it was clear that it was not a true avian on the basis of its short forelimbs, which could not have been used for gliding let alone flying. Yet it was very similar to other, ancestral avialans. This placed it within that group. What was interesting was its forelimbs which were shorter than the most primitive members of the group to date.

Other features common to avialans were poorly defined in this creature yet similar to other relatives, such as troodontid dinosaurs. It was clear that the dinosaur, now named Aurornis xui (dawn bird) was very close to the base of its group's evolutionary family tree. "Previous phylogenetic investigations were based on maybe only 200 morphological characteristics. Here, we recognise almost 1,500 characteristics,' explained Dr Godefroit. 'The new creature we describe is also a basal bird; and in fact it is even more primitive than Archaeopteryx.'
A reconstruction of Aurornis xui which clearly
shows its bird-like characteristics
The researchers placed Aurornis at the very beginning of avialan evolutionary history. So while Archaeopteryx represents the first bird on the planet. Aurornis represents the beginning of the lineage. The ten million years separating the two was the time in which the more advanced avialans developed the muscles, bone structure and the physiology required for flight. 

It is rare for a discovery to be marked out as the first of its group. Most of the time, a fossilized creature will be another group member or lie close to its group's evolutionary origin. Yet just occasionally a specimen hits the mark.