Thursday, 25 November 2010


Tomorrow, in much of North America, we dine on avian theropod...that's bird to most folks. The feathery descendants of the dinosaurs, birds, provide us with much insight to their toothy ancestors. Many use birds to provide information on the biology, physiology and even behaviour of dinosaurs...often bracketing the said dinosaurs between crocodiles and an extant (living) bracket to help further constrain the possible characters of the extinct dinosaurs.
In the UK, we tend to eat our turkey on Christmas Day, hence why I used to give a lecture at the Manchester Museum each December, called 'Stuffing the dinosaur at Christmas'...this was a fun take on dissecting (and often eating) a roast turkey, but showing the audience the vast number of features (characters) that birds still possess that place them so close to dinosaurs in evolutionary terms (in my mind, they are still dinosaurs). The old saying that something is, 'As rare as hens teeth', is testament to how close birds are to dinosaurs; as occasionally an ancestral gene is inadvertently 'switched-on' yielding a toothy-hen. We too possess 'fossil' or recessive genes in our DNA that surface in our own species, if the right genetic switch is flicked.

The use of living species to help infer or constrain specific characters in an extinct species is not a new thing, but Professor Larry Witmer gave this a name in 1995...the Extant Phylogenetic Bracket or EPB for short. Larry gave a name to something we already used, and in doing so penned a paper that will continue to receive citations (references within other published works) that will help it rocket into inter-steller levels of fame. Its hard to pick up a book or read a paper on dinosaurs without seeing EPB (Witmer, 1995) being quoted...even Larry agrees this is a rather useful paper in his career.

Basic family tree of the dinosaurs and birds....often subject to change!

In many cases we find additional evidence, such as the scars of muscle attachment on fossil dinosaur bones, that show that the EPB data appear to be appropriate (or not as the case may be). Combining such evidence and EPB with a liberal application of comparative anatomy (back to my dissection fun at Penn!), we can build a theoretical understanding of the complete prehistoric animal, as it was with its soft tissues intact. While evidence supports certain aspects of such extrapolation, in other respects this work is necessarily speculative...something palaeontology is often accused of with wagging fingers (and quite rightly so sometimes). About many points concerning soft tissues, we are completely in the dark. The best known dinosaur enigma is their colour, which is a particularly ephemeral aspect of an animal due to the nature of biological pigmentation and the tendency for such pigments to be lost in the fossilization process...but the Manchester team is hot on the trail of this particular conundrum (more on this later I hope!).

Amber can often trap beasties, providing excellent preservation
environments...sadly not big enough for dinosaurs!
Fossilization is a rare phenomenon that occurs to only a tiny fraction of a community’s population of any given place and period, and to none at all in many cases....we are dealing with disjointed sentences of once vast volumes. Nonetheless, if we consider the fossilization of skeletal elements as the standard, then the fossilization of soft-tissue structures is much rarer still. When these unique discoveries are made, this type of fossilization literally “fleshes out” our understanding of the fossil record in many crucial ways. Even a single example of soft-tissue preservation can be of tremendous value in the interpretation of fossil animal types. In each case, special circumstances prevented the ordinary loss of soft tissues. The explanations for certain of these situations have been reconstructed with a high degree of confidence, while the reasons for other localities’ exceptional preservation remain a mystery.

Dissection of crocs and birds can often tell us much 
about their relatives, the dinosaurs.

If your into the preservation of soft tissue, you might want to track down a paper that the Manchester team published last year (Manning et al 2009) in the Proceedings of the Royal Society, Series B. This is the direction of much of our research watch-out for future papers chasing bio-molecules in the fossil record...with a smattering of EPB!

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