Dinosaur DNA Linked to Birds

Would You Call T. rex Chicken?

New research using ancient fossilised proteins retrieved from the 68 million year old femur (thigh bone) of a Tyrannosaurus rex has confirmed the long held theory that birds are the closest living relatives of dinosaurs. This new study, conducted by researchers at Harvard University in association with the Harvard Medical School, also adds extra impetus to the now widely accepted theory that birds are the direct descendants of a particular group of dinosaurs – the Theropods.

Molecular Evidence of Dinosauria/Birds Link

These findings are the first molecular evidence indicating that Aves (the birds) are the closest living relatives to Dinosauria, controversial earlier studies from Russian scientists also linked dinosaurs to birds. In the earlier research, the Russian team studied fossil Triceratops bones at the molecular level and concluded that their work indicated that these ancient horned dinosaurs were closely related to ostriches. Although much of this previous work was refuted by the scientific community, this new study seems to indicate that the Russians were on the right track.

The American team’s findings are to be published in an edition of the academic journal “Science”.

Examining Fossil Skeletons

A close examination of the skeletons of Theropod dinosaurs and birds reveal a number of similar anatomical features. In fact you do not have to be a scientist to find evidence of this close anatomical relationship between these two types of animal, a brief study of a roast chicken cooked for Sunday lunch will provide quite a lot of evidence – if you know what to look for.

Breakthrough in Theropod Taxonomy

The new research follows a breakthrough study in 2007, scientists reported the recovery and partial molecular sequencing of fossilised Tyrannosaurus rex and Mastodon (a type of elephant) proteins. Both animal fossil studies (the Tyrannosaurus and the Mastodon) involved collecting and examining samples of collagen, the main protein component of bone.

In fact collagen is the main protein found in connective tissue of animals and the most common protein found in mammals including ourselves- making up around 25% of all the proteins in our bodies.

As well as providing further evidence to support the close evolutionary relationship between Theropod dinosaurs and birds, the study into the Mastodon proteins helps provide information on the evolution of the elephant family and helps identify the ancestry of extant elephants today.

The Tyrannosaurus rex proteins were extracted from fossilised soft tissues preserved inside a Late Maastrichtian faunal stage fossil femur (thigh bone), estimated to be around 68 million years old. The discovery of potential protein information inside the femur was reported in 2005.

The Mastodon remains were much younger, dating from the Pleistocene epoch and believed to be between 160,000 and 600,000 years old.

Using a variety of techniques the research team compared the T. rex and Mastodon protein chains with those of 21 extant animals including ostriches, chickens and alligators.

Comparing Protein Chains

Such comparisons are commonly used by biologists to construct evolutionary “family trees,” since similar protein structure is an indicator of shared genetic makeup.

Until very recently, however, protein sequences have not been available for ancient organisms such as dinosaurs, since most fossils do not yield proteins or DNA. The problem with genetic analysis is that molecules such as proteins and DNA tend to break down rapidly after death. The preservation of such delicate material is extremely rare and controversial, despite the claims highlighted by Michael Crichton, the author of the story “Jurassic Park” in which Dinosaurs and Pterosaurs were brought to life by combining amphibian DNA with fossilised DNA extracted from the remains of blood sucking insects preserved in amber.

Proving that DNA could Survive for Millions of Years

It was thought (and indeed some scientists still hold this view), that DNA could not survive more than 10,000 years unless the tissue was preserved in some unusual manner such as being rapidly frozen, for example, in the case of the Siberian Mammoths.

Many attempts have been made to extract DNA from insects that had been trapped in amber, recreating the storyline from Mr Crichton’s novel and scenes from the film “Jurassic Park”. There have been claims for success, but all attempts to replicate the experiments have proved inconclusive; indeed many scientists claim that the experiments may have been contaminated by modern DNA and therefore the results are invalid.

Studying Species Alive Today

Molecular analysis of extant species (animals living today) have revealed some surprising evolutionary relationships. For many years, the edentate mammals such as the armadillo had been regarded as the most primitive placentals, but analysis of new molecular data suggests that insectivores such as the hedgehog may be the most primitive. Fossil evidence for both types of mammal have been uncovered in the Eocene deposits of Messel in Germany. It is the molecular data from living representatives of these groups that indicates that the insectivores are the more ancient lineage.

Rabbits Closely Related to Primates

Another remarkable mammalian discovery using molecular analysis may be that the lagomorphs (such as rabbits and hares) may be closely related to the primates. Previously, using just anatomical comparisons this group of mammals had been classified with the rodents (mice, rats, squirrels and such like).

If molecular data become more widely available for dinosaurs, researchers will be able to fill in gaps and overcome possible errors in the existing classification based on physical features.

Extracting DNA from Fossil Remains

It remains to be seen whether even small sequences can be extracted from ancient fossils with any regularity, experts say.

The doubters still voice their concerns. Peggy Ostrom is a biologist at Michigan State University in East Lansing and an expert on fossil proteins, she is one of many palaeontologist that remain extremely sceptical about the Tyrannosaurus rex protein findings.

Many have remained sceptical about the T. rex protein findings, she is believed to have commented, because of the small size of the sequences isolated so far.

If other fossilised bones are found to contain proteins then further evidence could be gathered. It has also been noted that many recent findings, including the Mastodon remains dated to nearly half a million years ago, have greatly pushed back previously accepted time limits for protein molecule preservation.

Jurassic Park Dinosauria

In truth, the evolutionary relationships amongst certain elements of Dinosauria are still largely unclear. If biological information could be gathered at the molecular level then this would lead to a more robust Dinosaur family tree, helping to fill in the missing branches and links due to the paucity of the Dinosaur fossil record.

Whatever, the outcomes of further research, scientists are still a long way off recreating the Jurassic Park scenarios as depicted in the Hollywood films.



Source by Mike Walley

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