Thursday, 26 April 2012

Feathered Tyrannosaurids: In Defence of Scaly Dinosaurs

If Gideon Mantell was alive today and able to visit various museums throughout the world, then he would be amazed at how much the appearance of his beloved dinosaurs has changed over the years.  As he passed the various skeletons and reconstructions, he would wonder how on earth the appearance of creatures such as Iguanodon and Megalosaurus could have changed so much and probably the biggest shock to him would be the reconstructions of dinosaurs with feathers – feathers! 
Think about it. How difficult would that be? To Mantell, dinosaurs were simply overgrown cold blooded lizards and, with the knowledge that was available at the time, this was a pretty reasonable assumption. They were seen as great ponderous reptiles, covered in scales, plodding around in the primordial swamps that routinely fought for their lives with tooth and claw. Feathers would never have crossed his mind.
We now know, of course, that Mantell, and all the other early workers, were a long way from the truth although we must also recognise that Richard Owen pointed out that dinosaurs were remarkably bird-like at a very early point in his initial studies. Even after the discovery of Archaeopteryx, feathered dinosaurs were a long way away even though various palaeontologists over the years highlighted the possible relationships between birds and dinosaurs. Without significant evidence of feathered dinosaurs, the majority of palaeontologists, and certainly the general public, recognised the dinosaurs as giant scaly reptilian superstars of the Mesozoic.
However, our perception of dinosaurs has changed. We used to think of sauropods as huge swamp dwellers, theropods as relatively slow moving cold blooded killers, stegosaurs with the brain the size of a walnut and a multitude of other stereotypical analogies. We were all pretty comfortable with this image throughout the twentieth century and dinosaurs remained this way in our minds for a very long time.
But the Renaissance changed all that.  Sauropods became fully fledged terrestrial animals, theropods became swift and agile hunters while stegosaurs were suddenly able to turn on a sixpence and keep their flailing tail spikes in the face of their aggressors. Suddenly, other dinosaurs too became active energetic animals and the possibility that they were warm blooded really gathered momentum. The bird/dinosaur link was again brought to the fore and Bob Bakker reconstructed Deinonychus with integument suggesting that they had probably already developed feathers and that we should expect to find fossils of dinosaurs with such a covering. How prophetic that was!
During the nineties, the superb fossil localities in China burst onto the scene and we were (and continue to be) thrilled by each and every new specimen that is announced to the world.  These specimens are truly remarkable and confirmed, once and for all, that birds are indeed living dinosaurs and, despite the various protestations of creationists and a few fringe scientists who continue to deny the truth, there can be no doubt as to the bird’s dinosaurian origins.
So far, so good but there has been a casualty in this race to the truth and that is the humble dinosaur with traditional reptilian scales. It appears that nearly every dinosaur is now being looked at for traces of feathers. For example we now have basal ornithischians and basal ceratopsians sporting fuzz, quills and bristles.  Every fossilized skin impression is being screened for any signs of a covering that might be considered of feathered origin. This is not a bad thing, of course, but there is now a trend to cover every dinosaur in feathers even if there is only inferred phylogenetic evidence and no physical trace.
Now I am not a “feather denier” – far from it – but I have to admit to a certain sadness as the scaly dinosaurs that I grew up with have slowly been eroded down to almost being of no consequence and of no interest. Brian Switek, amongst others, suggested (tongue-in-cheek I hasten to add) that people such as myself should quit whining and get on with it but they misjudge us.  
Those of us who like our dinosaurs scaly appear to be frowned upon – as if we don’t know what we are talking about and that we really ought to “get with it” and rejoice that the dinosaurs are covered in fuzz and feathers. Well that isn’t going to happen – certainly not by me and, I am sure, not for many others.
Again I reiterate that I am just as fascinated with feathered dinosaurs as any of you but I do feel a tinge of sadness every time another scaly lineage is consigned to the palaeo- rubbish bin. And now we have the impressive Yutyrannus and this one is just another step closer to assaulting that bastion of awesomeness – Tyrannosauridae.

I’ll be blogging properly about Yutyrannus at some point in the future but for now let us consider the one important factor about this interesting tyrannosauroid – its size. One of the considerations that many of us have been hanging on to with regards to tyrannosaurids not sporting feathers was size. It seemed likely that big tyrannosaurids may sport integument when they were young to add a protective insulation to their smaller bodies. After a while they would gradually lose this covering as they became adult animals to become fully loaded scaly tyrannosaurs. This was a get out clause for us whilst, at the same time, also accepting that feathers may have been involved at some point during ontogeny.


Yutyrannus has changed all this, and at nine metres long and approaching 1.5 tonnes in weight , is certainly not small and the fact now is that some big tyrannosauroids did indeed display a feathery /fuzzy covering and that the larger, more derived tyrannosaurids are now coming into range. My heart sinks at the thought.
Of course, Yutyrannus is still a basal tyrannosauroid and still possessed fairly large forelimbs with three large clawed digits as opposed to the more derived and reduced sized two digits of tyrannosaurids. It is also Barremian in age (Early Cretaceous – 125 million years old) and was alive at least 40 million years before the appearance of Tyrannosauridae proper. Despite this, and in a phylogenetic context, there is a real chance that proper tyrannosaurids may have at least been partially covered by integument of some form.
We scaly supporters will hang on the fact that Tyrannosauridae is still free of feathers – as far as we know of course. This may very well be a sampling bias since the Liaoning deposits represent a lacustrine environment with very fine sediments that aided superb preservation whilst the traditional tyrannosaurid beds of North America are not.  Still, Tyrannosauridae remains an untouched bastion of scalyness - but the walls are certainly crumbling.
Perhaps I can best put it this way.  The T.rex in Dinosaur Revolution was awesome. But anybody who saw the dancing Gigantoraptor sequence in Dinosaur Revolution can be left in no doubt – is this the kind of thing you want to see a T. rex perform? Do you really want the ultimate theropods, the megastars of the dinosaurian world - the tyrannosaurs - displaying colourful yet gaudy feathers and dancing like a demented turkey cock?
I think not. Like I said – I know the feathered phylogenetic tooth fairy is rattling the front door of Tyrannosauridae but at least let us enjoy the time that is left for our magnificent fully scaled heroes. And if not, there will always be the ankylosaurs…….

Thursday, 19 April 2012

New Field Season Begins


When the days grow longer, the temperatures start to rise and you start getting restless, then you know that the new field season is just around the corner and the first trip has just taken place at the Bluff. Those of you who have frequented this blog for any amount of time will know that I have posted about this quarry on a regular basis but, if you are new here, simply type in “Bluff” into the search bar for multiple posts to look at.  
The weather for this particular trip appeared to be spot on – a bright sunny day was forecast, a stiff breeze coming in from the north and it would be cold. There had been some significant rainfall in the week leading up to the trip and, again, this seemed to be perfect. There was enough moisture to get the clays and sandstones wet but there had been around 72 hours of dry weather to ensure it was reasonably firm underfoot.
However, the fact remained that this quarry had not been excavated since 2008 when the brickworks was put into mothballs just as the worldwide recession had well and truly taken hold.   Every year since then, prospecting has got increasingly more difficult and now it is ultra-tough. The problem with the clay, as I have mentioned before, is that successive years of snow, ice and rain have combined to form a hard crust on the surface of the clay and very little now crops out. Without scraping every year, the problem only gets worse.
Having said all that, you have to keep the faith and keep trying. I’ve said it before and I’ll say it again – this quarry will almost certainly throw up significant dinosaur material in the future. The Bluff is a beguiling place once you get to know it and it is still an important site and certainly one of the last quarries in the country which is still accessible and one of less than a handful that crops out the remains of dinosaurs.
Arriving at the quarry, the first thing that struck me was the depth of the water in the bottom of the quarry and I was sure it had not been higher. The other thing of note was that the north east banks were displaying a green hue to them as mosses, weeds and other plants have started to get a foothold – another consequence of quarry inactivity. A good number of fellow workers had arrived and soon everyone was diligently prospecting.
One large group worked on the north east bank, excavating near the top of the quarry whilst a couple of smaller groups worked on the south eastern bank at the same level. Others ranged far and wide in an effort to find anything that may be exposed on the surface. Suffice to say it was yet another day of frustration for the majority of those concerned and I especially felt sorry for those who had put in a not insignificant amount of work into the excavations.  
Strangely, for all those efforts, only a nice sacral vertebra was recovered and this was found quite early on and was weathering out on the surface. Subsequent excavation around the vertebra revealed nothing. A scrappy piece of rib was also recovered but there was nothing else of consequence found. And, perhaps for the first time in all my years visiting the site, not a single tooth was found.
Other material recovered included some fish scales, vertebrae and a small (20mm) jet black but beautifully marked and as yet unidentified bone that is incredibly thin. The general consensus was that it most likely came from a fish. Towards the end of the day some insect remains were uncovered from the same level where some dinosaur footprints were removed a few years ago. The traces of insect wings are well preserved and are exceptionally beautiful.
In summary, the trip was well attended but conditions were poor. We all hope that sooner, rather than later, the brick works reopens and the quarry will be excavated again and that the many fine specimens that are undoubtedly there will one day be recovered.

Footnote

It is very obvious to many people that gaining access to quarries is getting incredibly difficult now. Not only have so many quarries been closed over the last four years but those that remain have so many health and safety pressures placed on them that it is far easier for the quarry owners to deny access to both palaeontologists and geologists than deal with the aggravation that accompanies letting the public into their sites.
Having said that, there are still a number of quarries that permit entry and these are well worth searching out. Of course if, like me, you are primarily interested in Mesozoic vertebrate fossils, then you opportunities are extremely limited and you tend to be restricted to the coastal locations both on the mainland and the Isle of Wight but these are so heavily scoured these days that you would be incredibly lucky to find anything of note.
Some glacial quarries appear to be the best option these days and these quite often give the chance of finding some decent Pleistocene mammal material and, on occasion, some derived Jurassic and Cretaceous fossils. And, depending on the location of such a quarry, they sometimes break through to much older strata below the sands and gravels giving you a chance of something different. However, it continues to get even harder to gain any access at all these days and I fear it will only get worse.

Monday, 16 April 2012

Rancho La Brea - In Widescreen


Marc Vincent, over at Love in the Time of Chasmosaurs, has just blogged about the book Purnell's Book of Dinosaurs and Prehistoric Animals. Mark commented about the above image as "....gorgeous" and I have to agree.


This version comes from the book Prehistoric Animals by Ellis Owen - published by Octopus, and features many of the same models and dioramas. I figured Mark might like to see this particular edit - a widescreen version - since it features a herd of mammoths(?) in the background and displays a slightly different aspect from his version. Pretty cool.

Friday, 13 April 2012

Papers in Review


A look at a few recently published papers now. Just lately I appear to have been quite lucky with my choice of posts since, on a couple of occasions, no sooner have I published or am about to publish than, lo and behold, another subject related paper is released. Sometimes this appears to vindicate or agree with what you believe and sometimes it makes you completely re-evaluate and reassess your line of thinking. Either way, it is another indication of how fast things move in today’s palaeoworld and it is always, but always interesting.

Not too long ago, I looked at how dinosaurs may have slept. This post surprised me in as much that it has been one of my most read of late and a recent, but brief, paper by Frederico Agnolin and Augustin G. Martinelli describes a specimen of Guaibasaurus candelariensis that is again suggestive of an avian-like resting posture in dinosaurs.
Guaibasaurus was a basal saurischian from the Late Triassic and the referred specimen was found in the Caturrita Formation in an abandoned quarry in the Linha Sao Luis locality in Brazil. The specimen is essentially complete but it is unfortunately missing the skull, neck and some forelimb elements. The authors report that the specimen is preserved tightly articulated and the elements display no evidence of post depositional transport or erosion. Indeed, the only erosion evident is recent as the fossil became exposed on the surface.
This specimen of Guaibasaurus is preserved with flexed forelimbs, the hind limbs are flexed below the body and the base of the neck appears to be curved around to the side – exactly what you would expect in Aves. This is significant since other dinosaur specimens recovered in the supposed avian resting position ie Mei and Saurornithoides are derived coelurosaurian theropods and Guaibasaurus suggests that this posture evolved at the stem level of basal Theropoda and maybe even earlier.
Back in November last year I highlighted research by Michael D’Emic et al that reported on remains of Acrocanthosaurus atokensis recovered from the Lower Cretaceous Cloverly Formation for the first time. The paper was published on line during March and makes for interesting reading. The referred specimen in the paper was successfully identified as Acrocanthosaurus atokensis and is significant since it is a juvenile and also the first representative of the taxon in the north.

It is intriguing that, throughout the Lower Cretaceous of North America, only Acrocanthosaurus is representative of large bodied Theropoda  and, despite fragmentary remains of large theropods from other formations such as the Patuxent and Cedar Mountain, nothing could be labelled as satisfactorily diagnostic to erect further large theropod  taxa throughout the Aptian/Albian time period.
Although there isn’t a great volume of collected material, there are enough characteristics displayed, especially the femoral head, which supports the referral of the material to Acrocanthosaurus. This specimen, again, suggests that, despite many vertebrate fossil localities from the Lower Cretaceous of North America, there is still currently only one large theropod species represented   throughout a large geographic range and the authors highlight the similarities, therein, with the Late Cretaceous Maastrichtian fauna which also has the one large theropod – Tyrannosaurus rex.
Acrocanthosaurus femora from D'Emic et al 2012

The authors also performed bone histology analysis which confirmed the specimen as a juvenile and revealed that the specimen grew at fast avian-like rates – comparable with tyrannosaurids. The specimen, and other elements examined, suggests a span approaching 20 to 25 years for an Acrocanthosaurus to reach adult size.  This again highlights comparison with Tyrannosaurus in as much that both taxa were large, displayed rapid growth and ranged across a large area.
Miriam Reichel, of the University of Alberta, has published more about her continual research into tyrannosaurid teeth and this latest paper is a hi-tech treat which is fully indicative of today’s use of digital technology in palaeontology. This time, focussing on how carinal variation, both anterior and posterior, display different angles that may be used for functional and/or taxonomic analysis.
Carinal angle has always been difficult to measure but, by using a Microscribe® Digitizer, Reichel was able to successfully interpret the angles between carinae by using the tip of the tooth as a “centroid” - a central point between the carinae - which, in turn, highlighted variation in the teeth. Five tyrannosaurid taxa were analyzed and only teeth in situ – that is teeth still in the jaw - were measured accordingly.  This preliminary analysis provided some interesting data.
Perhaps the most obvious result is that there is a significant amount of carinal angle variation in tyrannosaurid teeth – and this was expected.  This was also the case when comparing teeth from different parts of the jaw although there is variation in the acuteness of angles depending on the location of the tooth set.
This also highlights the previously held notion by some workers that different teeth perform different functions. This may be obvious when comparing teeth from the premaxillary with the others in the jaws but are maybe not so obvious between the other teeth. Tyrannosaurid teeth vary in size, shape and placement and this all contributes to the variation in carinal angles but, despite this, the angles do display expected tendencies in accordance with their function and appear to confirm the earlier hypotheses.
This methodology has great promise and the author admits that a greater sampling of in situ specimens in the future will add strongly to the dataset. The study also adds to the continuing fascination with tyrannosaur tooth morphology and perhaps, more significantly, confirms the presence of heterodonty in Tyrannosauridae.
I have only skimmed the depth of this paper and have simplified a few of the conclusions but you have to be very impressed with the depth and quality of Reichel’s work. She has featured on this blog before with her work on Albertosaurus sarcophagus and I look forward to more of her work with tyrannosaurids in the future.
References
Federico Agnolin & Agustín G. Martinelli (2012): Guaibasaurus candelariensis (Dinosauria,Saurischia) and the early origin of avian-like resting posture, Alcheringa: An Australasian Journal of Palaeontology, DOI:10.1080/03115518.2012.634203 

D'Emic, Michael D., Melstrom, Keegan M., Eddy, Drew R., Paleobiology and geographic range of the large-bodied Cretaceous theropod dinosaur Acrocanthosaurus atokensis, Palaeogeography, Palaeoclimatology, Palaeoecology (2012), doi:10.1016/j.palaeo.2012.03.003.

Reichel, M. 2012. The variation of angles between anterior and posterior carinae of tyrannosaurid teeth.Canadian Journal of Earth Sciences, 2012, 49(3):477-491, 10.1139/e11-068. 


Friday, 6 April 2012

The Weird World of Theropod Scapulae


One of the most striking observations of the skeletal anatomy of tyrannosaurids and abelisaurids is the proportionate size of the scapulocoracoid in relation to the rest of the forelimb. It looks almost absurd and, for me, the fact that there is virtually no contact between the scapula itself and any other articulating bone is always of interest. Indeed the scapula appears to be almost suspended in mid-body virtually independent of the skeletal structure except for its union with the coracoid which, in turn, is an essential component of the pectoral girdle.

Scapula orientation in theropod dinosaurs is quite interesting and it is worth looking, to begin with, at what orientation is displayed in primitive reptiles. The scapula is generally held at an angle of 90 degrees to the horizontal line held by the backbone – in other words it was held in a perpendicular fashion.  At the other extreme, extant birds rotated the scapula so that it lies parallel to backbone – a position also evolved by the pterosaurs.
Theropods, and non-avian dinosaurs in general (but not bird-like theropods), evolved a condition that can be described as something in between – an intermediate position if you will. The scapula is held in an oblique position laterally to the ribcage but actually determining the exact position is somewhat problematic. There are not that many fully articulated specimens that can be referred to and there is always the spectre of both taxanomic and taphonomic variation to throw yet another spanner into the works.
This variation shows itself in as much that more derived theropods, such as dromaeosaurids, display the scapula in a much more horizontal position than, by way of example, coelophysoids.  This evolutionary trend of rotating the scapula is almost certainly due to different taxa utilising their forelimbs for different functions which in turn dictated how the attached levator, subscapularis and serratus muscles held the blade in place.
The scapula itself is usually, in non-avian theropods, described as strap-like and is generally, but not always so apparent in some taxa, anteroventrally expanded to form the contact with the coracoid whilst the posterodorsal terminus tends to be narrower. The scapula increases in thickness as it expands to form part of the glenoid cavity and also strengthens the union with the coracoid. The upright stance of theropods meant that the pectoral girdle itself was narrow and was positioned anteriorly of the ribs. The girdle was held fast by the furcula and this acted as reinforcement for the scapula blades.
Just why the scapula remained so large in theropods such as tyrannosaurids and abelisaurids is unclear. The bone itself can actually be described as mobile because of its virtual isolation from the rest of the appendicular skeleton although it is the anchor point for many muscle attachments including those that held it in place attaching from the upper extremity as well as those that provided the “motion” for the forelimbs.
It appears that the scapulas main function was protection for the thoracic cage as well as increasing stability and, of course, providing the attachment for the coracoid, clavicle and formation of the shoulder joint.  Still have to say though – it does look weird.
From Burch & Carrano 2012

Reference

Sara H. Burch & Matthew T. Carrano (2012): An articulated pectoral girdle and forelimb of the abelisaurid theropod Majungasaurus crenatissimus from the Late Cretaceous of Madagascar, Journal of Vertebrate Paleontology, 32:1


Tuesday, 3 April 2012

Aquatic Dinosaurs - Fact

Well no actually and that’s got your attention which is what this very well publicised radio interview has done in the palaeoworld today. It has also featured in this newspaper article and between them has drawn almost universal condemnation on the social networks, mailing lists and blogs.

This is the biggest furore of its kind since the infamous kraken paper was announced at the Geological Society of America meeting during October last year and is, therefore, worthy of the same denouncement as a result. There is some debate whether this is actually some kind of April fool’s joke that’s got out of control or whether, indeed, this is actually some form of extremely misinformed speculation. The latest suggestion is that Brian Ford is actually a pseudonym of creationist Bryan J. Fischer with the aim of causing the palaeoworld mass embarrassment.
Of course it is almost certainly a publicity stunt but the damage is done and, as usual, it’s down to everyone in the palaeoworld to put things right and I’m pleased to say that most of us are rallying to the call. It’s regrettable that, yet again, the blame for this doesn’t lie with the perpetrator of this drivel, but with the media. What the BBC and the Today programme were thinking of is unclear – don’t these guys do any investigation before transmitting or, as in the case of the newspapers, publishing? 
Well we all know the answer there and this is one of those things that I have perpetually moaned about since I’ve written this blog. The media have to realise that this form of reporting is irresponsible and, ultimately, unacceptable presenting the “facts” as they do without any substantiation or quantification.
For more, look everywhere!