Tuesday, 16 June 2009

Tyrannosaurids (By the Numbers)


In his excellent article "Oh no, not another Wealden theropod!", Darren Naish briefly describes the remains of MIWG 6350 as belonging to a basal tetanuran theropod. Although fragmentary and non-diagnostic at the taxa level, they are certainly good enough to confirm the presence of yet another big theropod from the Wessex Formation.

Quite rightly he points out that there are several examples of late Jurassic and early Cretaceous palaeo-faunas that have at least three big theropods. Generally, they are from different clades as well and, when you first take that into account, it appears that there was obviously some form of resource partitioning - but does it? And also, as Darren states, why was the late Maastrichtian apparently dominated by only the one big theropod?

Sometime it takes an article such as this to slap you around the face and you ask yourself "What on earth have you been thinking about?". For some time now, I've been looking at the tyrannosaurid fauna of the Dinosaur Park formation (DPF) and particularly the fact there were two big contemporary tyrannosaurids in the form of Gorgosaurus and Daspletosaurus. It appeared to be nice and simple at first. Gorgosaurus appears to be a quick, agile, lightly built albertosaur ideal for tackling hadrosaurs. Daspletosaurus, a much more robust and powerful tyrannosaur, was obviously designed to take on the much tougher ceratopsians. Resource partitioning at its best, right? Maybe not.

Suddenly it appeared that there could be multiple species of tyrannosaurids resident in the DPF alone. Certainly there appears to be another species of Daspletosaurus which (hopefully) will eventually be described by Currie et al. There may be another tyrannosaur in the form of Aublysodon, known from D-shaped non-serrated teeth and (possibly) very fragmentary skeletal remains, but this seems unlikely now since Currie (2005) attributes these teeth to being juvenile premaxillary teeth from the previously mentioned Daspletosaurus Sp.


So, Aublysodon aside, we appear to have, again, three big theropods in the DPF. The only marked difference is the fact that these animals all belong to the one clade, the Tyrannosauridae. So where am I all leading with this? Bear with me and I'll explain my thoughts.

There is no doubt that tyrannosaurids suffer from being over-split at the generic level. However, when you look into tyrannosaurid remains throughout the Campanian and into the Maastrichtian, there is, for me, pretty good fossil evidence (albeit sometimes scrappy), that there are multiple tyrannosaurs present throughout the Upper Cretaceous (for the sake of argument I will use the term "multiple" to describe formations where there are at least two big tyrannosaurids present).

And yet, or so it appears, the Hell Creek formation (HCF) has only the one big predator in the form of Tyrannosaurus. And yet this animal may have a greater stratigraphic range than was initially realised for there is certainly circumstantial evidence that this may be the case and, if not, the evidence again proves the existance of multiple tyrannosaurids right through the Cretaceous until the uppermost Maastrichtian.

By way of examples then. There are elements of a big tyrannosaur from the De-na-zin member of the Kirtland formation as well as the underlying Fruitland formation. Urban and Lamanna (2007) reported on the possible existance of a rex-sized tyrannosaurid in the latest Campanian of the Judith River formation in Montana based on an isolated lacrimal. Although, at the time, it was tentatively referred to Tyrannosaurus, further comparative studies have now rendered this specimen as indeterminate. But what it does show is that the Judith River fauna also had multiple big tyrannosaurs.

There are also large tyrannosaurs known from the Naashoibito member of the Ojo Alamo formation in New Mexico, known mainly from teeth and postcranial skeletal elements. Also from New Mexico, there is material from the McCrae formation. And the same again - large tyrannosaurids are known from both the Javelina and North Horn formations. Interestingly now, the Javelina is dated at being around 69 million years old so this is right on the verge of the "official" T.rex timeline.

This being the case then, why does it appear that there is only the one large theropod in the Maastrichtian of the HCF? Well there are a few theories about this and, to be fair, each of them have a little merit. Firstly the non -predatory fauna of the HCF includes hadrosaurs, pachycephalosaurs, ankylosaurs and ceratopsians and this is a lot prey animals for one single species of tyrannosaur to "control", especially considering all the previously mentioned formations where multiple large theropods are present.

This may suggest an age specific partitioning of Tyrannosaurus to enable an efficient hunting strategy. Alternatively there may be other large theropods which are as yet unknown but this seems unlikely since Hell Creek is one of the most sampled formations in the world and it appears that the collected biomass is close to the actual biomass.

There were other predators present. Theropods such as dromaeosaurs, troodontids, ornithomimosaurs and oviraptorosaurs have all been found in the HCF but these are small animals and could hardly be classed as even mid-sized theropods. Even if the dromaeosaurs and troodontids hunted in packs, and could bring down fair sized prey, there would still be a vast amount of prey animals for adult tyrannosaurs and their juvenile forms to predate on.

This brings us nicely to Nanotyrannus. Currently, it would appear that the general concensus regarding the taxanomic status of this animal is that it is a juvenile Tyrannosaurus. But this is not really an issue since, as mentioned earlier, the probable over-splitting of tyrannosaurids means that these theropods are so closely related to one another as to make no difference. Of course this may mean that sampling is still an issue or, on the other hand, may confirm that resource partitioning by age is relevant.

Maybe it wasn't necessary to have two or three big theropods in the HCF. Perhaps juvenile and half grown Tyrannosaurus were the mid-sized theropods of this time. Of course others may point out that, if this was the case, why was it necessary to have multiple tyrannosaurids in the Campanian? And also, and this particularly frustrates, why are the remains of juvenile tyrannosaurids/Nanotyrannus so rare in relation to adults? Even a half grown rex could be twenty feet long and you would think that there would more found of them than there ever has been.

So where does that leave us? Darrens' question at the beginning remains valid and there appears no definitive answer. Despite my earlier protestation that Hell Creek is extremely well sampled, it is obvious that more sampling will need to be done and, maybe then, a combination of this and a review of tyrannosaurid systematics will provide an answer. Until then, this particular issue will rumble on and on. Don't you just love palaeontology?


References

Currie, P.J. 2005. Theropods, including birds; pp. 384-388 in P.J. Currie and E.B. Koppelhus (eds), Dinosaur Provincial Park, a Spectacular Ancient Ecosystem Revealed. Indiana University Press, Bloomington, Indiana.

Urban, M.A., and Lamanna, M.C. 2007. Evidence of a giant tyrannosaurid (Dinosauria: Theropoda) from the Upper Cretaceous (?Campanian) of Montana. Annals of the Carnegie Museum 75(4):231-235.

Saturday, 13 June 2009

What I Last Caught.....1

Those of you who know me will be aware that I am, and always have been, a keen angler. At one time, it is all I would do. In my younger days (cough) every spare day, every spare hour, every spare moment would be spent fishing. Indeed, I would think nothing of spending an entire week fishing whenever vacation time was available.

Eventually, of course, life moves on, priorities change and all of a sudden fishing became less important but never the less has remained an essential part of my life. It's important because it brings you closer to nature and you see things that you would not otherwise see. It gives you time to think - many a master plan has been hatched on the banks of some lake or a river. Indeed, you often hear fishing described as "simply being there" and I believe that is just about what sums it up.

Catching fish is important too, not as much as it once was but, believe me, you still want to catch. As I've got older, though, I've reached a state of mind where I find myself knowing that, if the fish are feeding, then I will catch them. My rigs are efficient, I use a good bait and, provided I am in the right place, then the fish will do the rest.

Anyway, here's the last fish I caught and what an impressive beast it is - all 22lb 8oz of it. By carp standards it actually isn't that big but what a fight it put up. It was such a dogged slogging match that, if I had lost this fish, then I would have imagined it to have been much bigger than it actually was.

I caught this fish ( a common carp if you didn't know) just before first light this morning. After safely retaining the fish in deep water, I sat back and made myself a cup of tea and waited for the sun to come up so that I could take this picture. Early Summer mornings, by a lake in England with the birds singing to meet the rising sun - it just doesn't get any better than that (although first light in Alberta near Red Deer runs it close).

After the photographs she was safely returned to fight another day and I was grateful to her for sharing the dawn with me.

Wednesday, 10 June 2009

University of Wyoming Geological Museum - Cut!

I appreciate that this story is doing the rounds big time in the palaeoblog world just now, but I feel that all of us who can contribute and help in any way have a duty to do so. For those of you who may be unaware of the situation, a short recap may help.

The University of Wyoming has included the Geological Museum in a group of budget cuts as a result of a decrease in funding by the state. 45 people across the University lost their jobs, including the Director of the Geological Museum Brent Breithaupt and the part-time museum secretary.

This could be the thin end of the wedge and detrimental for palaeontology as a whole and should not be allowed to happen. Many of us in the palaeoworld are spreading the word and you can help by getting as many people as possible (family, friends etc) by signing the petition below:

http://www.ipetitions.com/petition/geomuseum/

The cuts are due on July 1st 2009, so hurry up, sign up and spread the word!

And don't think that this situation is not being observed elsewhere. Remember that the recession is world wide and if we can make a difference now then maybe we can stop other institutions being targeted, both in the USA and elsewhere across the globe.

Finally, a big thank you goes to ReBecca of Dinochick fame who has done a brilliant job in championing the cause and spreading the word. You can find further details here:

http://paleochick.blogspot.com/2009/06/more-information-to-help-save.html

Monday, 8 June 2009

Who is Saurian?

Call me.....Saurian.

Well that's my name as far as you are concerned. Those of you who know me or recognise me will know me by another alias, and I'm sure that others have their own name for me, not necessarily complimentary! So then, who is Saurian?

Saurian was born in 1962 in Lower Clapton, London. I am married with an adult step-son and I am a Production Manager in the manufacturing industry. I drive an estate car with four-wheel drive which is of obvious use out in the field. I enjoy fishing, travel, both home and abroad, and have a passion for food. That's my normal side…..

Saurian came about because of my interest in the prehistoric world, and, more specifically, those wonderful and extraordinary creatures - the dinosaurs. Like so many of you, I grew up with the dinosaurs. When I was at school I spent every spare moment reading or writing about them or drawing them when I should have been concentrating on school work (sorry Mum!) but you know how it is!

Most people tend to lose the bug as they get older, at least temporarily. Those of us who don't share this never-ending thirst for knowledge. We are always scanning the latest news hoping to find that some new animal has been discovered that may solve so many unanswered questions. In reality all a new discovery usually does is to pose more, but that is what makes dinosaurs and the science of palaeontology so enthralling.

Eventually I reached a point where I needed to get involved - just reading wasn't enough. I started to attend lectures to broaden my horizons, and from there I was lucky enough to meet several palaeontologists and geologists. I started to correspond with them and learnt some more. Then I discovered field trips that it was possible to attend - my mind started to race!

That first field trip where dinosaur fossils were involved was simply one of the most incredible, and for me, emotional moments of my life. I wasn't too sure where to look but that didn't seem to matter (I remember this so well!), but without doubt that first time you find a dinosaur bone or tooth is a moment of absolute magic.

On subsequent trips you learn more. It becomes easier to differentiate bone from wood and you start to recognise the bone bearing strata, you become more and more familiar with certain sedimentary rock and the overall stratigraphy of the quarry. You learn more - but all the while you never lose that magical feeling, the feeling that you may be just one hammer blow away from something amazing…………

After a period of time, if you move in the right circles, you may meet some very well known palaeontologists - the ones who appear on certain television programmes and you may have copies of their books or published scientific papers. Those I have met have been fantastic - they are only too pleased to talk to you and share their knowledge of their chosen career, the prehistoric world.

Eventually you may broaden your horizons. Fossils of all sorts are fascinating and the more you vary your collecting the more you learn. You may have the opportunity to join a local club or society and enjoy sharing your experiences with others. I am now at the point where I am being asked to make presentations regarding fossil bone and preparation in the field. I don't have any formal qualifications in this field - just limited experience - but it is great to be able to help people from all walks of life to learn about the subject.

One final piece of advice. If you do go on a dinosaur dig and find yourself in the field, please show these wonderful extinct animals the respect they deserve. I always feel that I am with them spiritually. I know they are there - you can sense them - and as a result the surrounding territory feels …….almost consecrated. It's difficult to put into words, but you'll know what I mean.
Welcome to Saurian's Field Diaries!