Tuesday, 21 May 2013

Fossils are Important ( All of Them )


 
One of the most important things for me in palaeontology as a whole is never to take fossils for granted. It does not matter that some of them are astonishingly abundant and are so well known that they have little scientific importance. We must never lose track that these wonderful artefacts have survived millions of years and give us a vivid picture of life many millions of years ago. It is truly a miracle of nature that anything got fossilised at all when you consider the conditions that are required for fossilisation. Just look at the delicate preservation in the clay of the crustacean Mecochirus pearcei.
Taking such factors into consideration then it comes as no surprise that there are those fossils which are so unusual, so rare and so revealing that their fossilisation appears nigh on impossible. And there are those fossils which, although may actually be quite abundant in some places, bring us closer to the living breathing animal – the very essence of past life.
The most obvious candidates for examples of the latter are trackways of dinosaurs and their contemporaries that wandered over the coastal flood plains and river banks leaving their footprints behind them. These trace fossils can reveal a wealth of information and today’s progressive digital technology widens our knowledge and has opened up a catalogue of data that was unheard of only 25 years ago.
I do not profess to have a great knowledge of trackways and there are many palaeoichnologists out there far better qualified to discuss tracks than I am but I am, never the less, fascinated by them for here is the proof that the bones and skeletons of the animals we find were living, breathing and often fast moving components of a long vanished ecosystem. From trackways we can accumulate detail that helps us determine gait, stance, stride pattern, speed, weight and, most interesting of all, possible behaviour.
Fossilised impressions and remnants of skin also give us tangible evidence of what some dinosaurs may have looked like although there is always an element of caution due to preservational issues. We are all familiar with the mummified hadrosaurs of which Leonardo, a specimen of Brachylophosaurus, is the most well documented of previous times and these fossils have given us considerable insight into the appearance of some dinosaurs. Leonardo, of course, is an exceptional specimen since nearly all of its body is covered in skin revealing various textures and different sized scales and tubercles.
 
A recent specimen of Triceratops is also sending shockwaves throughout the palaeocommunity due to its exceptional skin preservation and we look forward to the publication of the associated paper.  As noted in my previous post we even have skin impressions from Tyrannosaurus and a whole host of other dinosaurs. And, of course, we have the well documented feathered dinosaurs from China that has given us a whole new dimension when it comes to visualising dinosaurs. Even colour is slowly being decrypted from some fossil feathers and this is an area that I expect to see a lot more exciting developments in the future.
It is hard to believe that any soft parts of an animal would fossilise and yet, in exceptional circumstances, this too has happened. The most famous example of this is the little theropod Scipionyx from the Lower Cretaceous of Italy. This wonderful little specimen has the muscles, intestines – even the liver are all preserved and give us many clues to aid in our understanding of dinosaur physiology (Dal Sasso & Maganuco 2011). And we must not forget too, the remarkable work by palaeontologist’s such as Mary Scweitzer et al (2007) who have actually managed to recover blood vessels and other soft structures from the bones of a 68 million year old Tyrannosaurus.
Away from dinosaurs there are other superb fossils that must be noted.  There are occasions when specimens are found that, although flattened, are so well preserved in the fine grained sedimentary rocks that the outline of the whole body is preserved.  The wonderful ichthyosaur specimens from Holzmaden enabled scientists to reconstruct these marine reptiles accurately for the first time due to these outlines in the shale.  Initially reconstructed without a dorsal fin or the crescent shaped tail we are all now very familiar with the dolphin-esque shape of the ichthyosaur.
Similarly, the lithographic limestones of Solnhofen have opened a window into the past of the Upper Jurassic landscape of Bavaria. Rightly famous for the fossils of Archaeopteryx, there are also wonderfully preserved examples of the animals that shared Archaeopteryx’s environment and, of particular note, are the exquisitely preserved specimens of fish, marine reptiles and even pterosaurs with clearly preserved outlines of the wings.
Amber fossils are amongst the most beautiful examples of ancient life that are preserved to an almost unparalled degree. We are all familiar with the notion of insects captured in amber, most famously eulogised in Jurassic Park, and these are the most common animals preserved but, occasionally, even vertebrates are trapped and these are the rarest amber fossils of all and have included examples of frogs and lizards.
 
Stomach contents are yet another source of data. Although not commonplace they do occur on occasion – Baryonyx, most famously, had the remains of both fish and an iguanodontid preserved. The aforementioned Leonardo’s last meal was also exquisitely preserved and consisted of ferns, magnolias and conifers and further examination of pollen grains in the gut reveal at least forty different species of plant. Specimens of Sinocalliopteryx preserved both dromaeosaurid and bird remains (Xing et al 2012) whilst various marine reptile remains reveal diets that comprise, not only of their reptilian contemporaries, but also ammonites, belemnites and, in one case, the osteoderms from a thyreophoran dinosaur although this cannot be categorically confirmed due to possible taphonomic distortion.
Naturally enough, what goes in must come out and coprolites are another of those extremely common fossils that are greatly underrated. Many are simple phosphatic nodules that may be identified by their peculiar structural patterns and are often outwardly rather plain looking. But some show clear inclusions and these are very much more interesting. They reveal a great deal about an animal’s diet and although it is nigh on impossible to identify which animal may have produced these mineralised faeces we can still take some educated guesses. The most famous coprolite in recent years is the specimen that almost certainly came from a T.rex and was found to contain a mass of pulverised bone (Chin et al 1998).
There are other examples of evidence which also indicate possible behaviour. For identifying predator/prey relationships it is obviously fossils that display signs of predation that you need. These include puncture marks and drag marks that sometimes even display the marks of the jagged edges of serrated teeth. Although these bones are not that common, I suspect that there are many more in collections than are actually realised and that the marks have either been missed, misinterpreted or disregarded as preservational phenomena.
Of course, tooth and claw marks on bone do not actually confirm that the feeding animal had actually killed the prey item – only that it fed on the remains. Much more interesting are bones that show signs of predation but have healed up because then they obviously survived being attacked which is indeed evidence of attempted predation. These are much rarer specimens but both hadrosaur and ceratopsian dinosaur bones are known displaying such pathologies (eg Carpenter 1998, Happ 2008).
So it can be seen that we have this great wealth of information that enables us to interpret how animals lived and died in the past, what they may have looked like, how they moved and what the environment was like that they lived in. And yet there is still so much that we don’t know and we are still scratching the surface of certain aspects of palaeontology and desperately need more fossils and so much more data.
I, and so many others, are constantly referring to sampling and preservational issues with good reason – there are still so many gaps in the fossil record and without more specimens in numbers to fill those gaps then there will always have to be elements of conjecture and speculation – amply supported by the available science of course.
This is why fossils are so important and is why we must never ever take them for granted – they are, after all, a finite source. I never have forgotten this and I am still inspired every time I see a fossil that has seen the light of day for the first time in perhaps millions of years. So next time you are casually throwing aside the odd brachiopod as you look for more “significant” remains just remember how lucky we all are that they are even there in the first place.
References
Carpenter, K. 1998. Evidence of predatory behavior by theropod dinosaurs. Gaia 15: 135 - 144.
Chin, K., Tokaryk, T.T., Erickson, G.M. and Calk, L.C. 1998. A king-sized theropod coprolite. Nature 393: 680 - 682. 

Dal Sasso, C. & Maganuco, S. 2011. Scipionyx samniticus (Theropoda: Compsognathidae) from the Lower Cretaceous of Italy: Osteology, ontogenetic assignment, phylogeny, soft tissue anatomy, taphonomy, and plaeobiology. Memorie della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano. XXXVII (1) 1 - 281pp.
Happ, J. (2008). "An analysis of predator-prey behavior in a head-to-head encounter between Tyrannosaurus rex and Triceratops". In Larson, P.; and Carpenter, K. (editors). Tyrannosaurus rex, the Tyrant King (Life of the Past). Bloomington: Indiana University Press. pp. 355–368.
Schweitzer, M.H., Suo, Z., Avci, R, Asara, J.M., Allen, M.A., Teran Arce, F. & Horner, J.R. 2007. Analyses of soft tissue from Tyrannosaurus rex suggest the presence of protein. Science 316: 277 - 280.
Xing L, Bell PR, Persons WS IV, Ji S, Miyashita T, et al. (2012) Abdominal Contents from Two Large Early Cretaceous Compsognathids (Dinosauria: Theropoda) Demonstrate Feeding on Confuciusornithids and Dromaeosaurids. PLoS ONE 7(8): e44012.

A fossil track of the future?

 

1 comments:

emailmark said...

Yes I agree - what I find especially engaging with trackways is that they preserve a moment in time. In a very real sense the footprints of, say, a theropod is no less remote than the photo you showed in the article Mark - something left it in the mud (it's just that the mud has either stayed wet, hardened or consolidated into rock.

Fossilised skin - actually impressions of mummified skin that has first dessicated and then left an impression in sediment which has become rock are amazing artefacts too and incredible that any should have survived through geological time.

I hope that someday, somewhere, a dinosaur will be found preserved in the equivalent of a mesozoic tar pit....dream on!

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