Thursday, 31 January 2013

Dinosaur Diversity Knew No Limits


 
Following on from my feathered tyrannosaurs post, it seems reasonable to consider how the incredible diversity of the dinosaurs may have led to many different ecological niches being filled. It would be churlish to think of dinosaurs as a group of animals that were only simplistic herbivorous or carnivorous animals and, because of today’s rapid improvements in research techniques and the ever increasing amounts of new dinosaur species announced each year, we really are starting to gain further insight into what was a truly remarkable and successful group of animals.
Of course, many dinosaurs were indeed humble herbivores being preyed upon by equally humble carnivores and yet these are not the taxa we are particularly interested in on this occasion. What specialist dinosaurs were there and how diverse were they? What ecological niches could some of them have filled?
One thing that many of the supposed specialist dinosaurs have in common is that they are all a little odd looking. Take the alvarezsaurid Mononykus for example – here is an animal only about a metre long which is best known for its ridiculous little forelimbs armed with only a single claw. The whole forelimb only amounted to about 75mm in total length and it has been speculated that this specialist forelimb may have been useful in breaking into termite mounds.
 
Mononykus by Thomas Cowart
 
I am not so sure about this. Surely it would have been more advantageous to have a longer and stronger forelimb to perform such actions? Check out the forelimbs of anteaters if you want to see proper equipment for dismantling ant hills and the like. I am not suggesting that the forelimbs of Mononykus did not have a specialist use but I am not convinced of their mound busting ability. More fossils will perhaps help to solve the riddle.
Mononykus is also described as having large eyes which have led some palaeontologist’s to suggest that they were nocturnal.  Troodontids and Leaellynasaura are also considered animals of the night due their enlarged eye sockets. This makes a lot of sense anyway and no ecosystem today is comprised of strictly day or night active creatures (cave dwellers not withstanding). Lions today feed almost exclusively at night contrary to their regular appearance on television documentaries as animals that feed during the day although, of course, they are not restricted and do indeed feed during the day.
A study published in 2011 (Schmitz & Motani 2011) looked at the eyes of extant birds and crocodiles and specifically concentrated on whether the sclerotic ring was a good indication of pupil size. Results were encouraging and indicated that, after careful examination of 33 dinosaur specimens, that dinosaurs were active throughout the 24 hour cycle including nocturnal, diurnal and both. For me this is completely what I expected from this successful and adaptable group of animals.
 In the study small theropods were largely nocturnal or day and night active whilst large herbivores were active 24/7 which again makes sense since they needed copious amounts of vegetation to fill their large guts. I suspect that many dinosaurs were active at night including some larger theropods which would clearly have taken the advantage of the dark to ambush unsuspecting prey. This is also indirect confirmation that dinosaurs were certainly more endothermic than ectothermic being able to keep active during the night as it were.
The recently published heterodontosaurid Pegomastax africanus is another bizarre dinosaur that may or may not have led a strange life. Paul Sereno described the animal as “…..a bird, a vampire and a porcupine.” I wish he had not mentioned the word  ”vampire” since the media, of course, latched onto this and we were deluged with headlines about the “vampire dinosaur”.
Pegomastax was recovered from the Lower Jurassic Elliot Formation in Cape Province, South Africa many years ago and remained hidden from view until Sereno rediscovered the remains in 1983. Pegomastax was another small dinosaur that was characterised by an unusual parrot-like predentary combined with two large caniniform teeth at the anterior of the dentaries which, in turn, combined with other tall teeth that cut through vegetation.
Pegomastax africanus
There is debate whether this peculiar arrangement may have also been an adaption for catching insects or eating meat but this would appear unlikely since the teeth of Pegomastax clearly show wear from grinding vegetation although it has often been suggested that heterodontosaurs, as a group, may have been omnivorous. It is also conceivable that the fangs may have also been used for intraspecific conflict and defence.
This extreme jaw development is  more likely to be a specialist feeding adaption and I suspect that all heterodontosaurids were variants based upon a similar evolutionary trait that were highly dependent on specific plants and foliage for their nourishment.  This is exactly what I see when I look at Pegomastax – it really does look like a niche species with a highly derived feeding technique.
Stomach contents can reveal a lot about an animal’s behaviour and ecology. A PLoS One paper last year highlighted two specimens of Sinocalliopteryx with preserved stomach contents which indicate that they fed on primitive birds and other feathered dinosaurs.
Sinocalliopteryx gigas was a compsognathid around the two metre length mark which was relatively large for one of these small theropods. Named in 2007, its remains were recovered from the Lower Cretaceous Jianshangou Beds of the Yixian Formation in Liaoning Province, China. According to Xing et al (2012), one specimen contains the remains of a dromaeosaurid (attributed to Sinornithosaurus) whilst the other specimen contains the multiple remnants of the primitive avialan Confuciusornis.
The authors, quite reasonably, suggest that two separate specimens of Sinocalliopteryx both containing similar prey may be indicative that these dinosaurs actively preyed on other feathered dinosaurs as well as flying primitive birds. This should not be a surprise really since a large proportion of animals in this biota were small and feathered and it figures that they would be actively hunting each other.
Of course, evidence of feeding is not necessarily evidence of hunting as other palaeontologists’ have already pointed out but this will always be the same counter argument whenever stomach contents of this nature are discovered and, indeed, holds true for bones that display marks of predation. I suggest that, since all available physical and physiological evidence leads to this conclusion, it is probably likely that Sinocalliopteryx was an agile and active hunter.
From Xing et al 2012
The authors also speculate that this could be the case and hypothesise that Sinocalliopteryx could have been an ambush predator, perhaps concealed in the underbrush waiting for its unsuspecting prey to fly unwittingly past before rapidly striking out and grasping the now doomed prey animal. And, of course, this leads to conjecture just what other niches were being filled by all these fascinating feathered dinosaurs.  
Other dinosaurs of note that were likely to be specialist animals include the therizinosaurs and the enigmatic Deinocheirus. Contrary to the previous animals we have been looking at, these dinosaurs were much larger taxa but both had similar adaptions in their forelimbs since they were large robust appendages armed with not insignificant claws.
Therizinosaurs were certainly unusual theropods by anyone’s standard. Their forelimbs, however, are enormous and were obviously of some significance to the animal. The most common theory to describe what these forelimbs were used for is tied in with the fact that therizinosaurs were herbivorous animals and that they used these large limbs to gather in vast tracts of foliage rather like a rake. This is quantified by their possession of a large “pot-belly” which would have  been a large fermenting vat to help digest the tough fibrous plant tissue.
This is interesting in a number of ways. Certainly I subscribe to the theory that therizinosaurs were essentially herbivorous but I am more inclined to think that they were actually more omnivorous than that. Those arms were very capable of tearing down termite mounds (as I alluded to earlier when mentioning anteaters) so I feel certain that insects perhaps may have figured on their diet on occasion. Equally those arms could have easily ripped into a rotting carcass so meat may have also figured on their menu. All this and they could have been used for defence as well – therizinosaurs were certainly specialist animals.
Deinocheirus mirificus is actually very well known in the palaeoworld mainly due to the fact that its remains consist of an enormous pair of forearms which measure around eight feet long. Just what kind of animal Deinocheirus was is still under scrutiny although latest phylogenetic analysis and hypotheses suggest that it is a rather primitive ornithomimosaur albeit extremely large.
 
If it is an ornithomimosaur then we perhaps find an example of parallel evolution with therizinosaurs. It appears generally accepted that ornithomimosaurs were also omnivorous and, that being the case, may have also evolved large forelimbs in Deinocheirus to gather in the various foodstuffs that were available. With the recent announcement of feathered ornithomimosaurs it seems likely that both genera were also feathered.
If this is the case then it would be no surprise that a largely herbivorous omnivore (that’s a new one) may have demanded large body size to sustain such a lifestyle. Within Saurischia, sauropods grew large very early in dinosaurian evolution and developed huge guts to cope with the vast amounts of fodder required to sustain their enormous bodies. Therizinosaurs and ornithomimosaurs are Cretaceous animals, and their origins are a little blurry, but it is interesting that these too evolved to be massive animals.
Deinocheirus really is a fascinating beast and you would love to think that it was a massive super-theropod of some sort if it was built to standard theropod proportions. If this were the case then it would be a theropod to defy the imagination. There has been more material recovered a few years ago but nothing has been published yet but do keep an eye out in Spring of this year when there will likely be news on Deinocheirus that will cause quite a stir!
There must be many dinosaurian taxa yet to be found and it is fascinating to wonder just how many of those will be found with some form of bizarre evolutionary trait and trying to figure out what on earth it was used for.
References
Schmitz & Motani. 2011. Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology. Science http://dx.doi.org/10.1126/science.1200043
Sereno P (2012) Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs. ZooKeys 226 : 1–225, doi: 10.3897/zookeys.223.2840.
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. doi:10.1371/journal.pone.0044012

Thursday, 24 January 2013

Project Daspletosaurus 2013


Yes I know that I am extremely bias when it comes to Daspletosaurus but I have been saying for some time now that this tyrannosaurid is becoming more and more important in our understanding of Tyrannosauridae as a whole. Certainly, what with Thomas Carr's upcoming monograph of the genus and this new research by uber blogger Dave Hone in the pipeline, it is very apparent that now is the time of Daspletosaurus.

Be that as it may check out this post by Dave over at his Guardian blog for some detail and have a look at the video below. You may want to consider making a contribution and, if you do, all the detail is there. And yes I will be making a contribution, not just because it is Daspletosaurus, but because it is also a very cool and, ultimately, a very important piece of science. All this and free access at the end of it - way to go Dave!



Thursday, 17 January 2013

The Feathered Elite



A recent post from the guys over at Love in the Time of Chasmosaurs brought to our attention the palaeoimagery of Alexander Lovegrove whose many fine works can be seen over at deviantART. Alex is obviously a big fan of tyrannosaurs and he depicts many taxa in various artistic situations. In the LITC post one image, in particular, caught my attention and that was the one above and featuring my beloved Daspletosaurus attacking a herd of chasmosaurs. Please note that the image is used with the artist’s permission.

The daspletosaur is depicted with a light covering of fuzz along the upper portion of the body running from the lacrimal horns to the tip of the tail. What makes this image stand out are the naked legs which Alex points out were influenced by an article by Andrea Cau who suggested that it was possible that large theropod dinosaurs that were fully covered in integument would probably be able to avoid substantial overheating issues.

Ostriches display bare legs such as these and, when the wing feathers are raised exposing the thigh, help with dissipating excess heat. Whether or not you want to subscribe to a hypothesis like this for dinosaurs, I liked the idea of Alex’s “chicken drum-stick” legs and this got me thinking about feathers and fuzz and what they would mean to theropods and particularly to tyrannosaurids proper as opposed to tyrannosauroids in general.   
  
So if we avoid the many heated discussions regarding feathers in theropods such as maniraptorans and whether they flew or climbed and, indeed, the origin of flight completely – then we have quite an interesting topic ahead of us. The fact that Yutyrannus has finally condemned the notion that big theropods could not have a feathery covering of some description makes for interesting speculation.

So how would big theropods have utilised a fuzzy or feathery covering? Well we can eradicate one notion straight away and that is that these animals flew – remember we are only dealing with large theropods here. When you think about it, even the smallest of theropods would have struggled to fly since they were not that advanced aerodynamically anyway.

Using fuzz or feathers as form of temperature control is another matter completely and there is enough information out there to fill an entire database. It would seem unlikely that whatever shape or form the integument took that it would not have been used in this way in some form or another. We are all aware of dinosaurs that lived in the Polar Regions and it would seem a reasonable assumption that even large theropods would have benefitted from a covering of feathers or similar to help them keep warm.

Downy feathers today help birds incubate their eggs and we all know that some smaller dinosaurs certainly incubated their eggs so it is possible that animals such as oviraptorosaurs and perhaps dromaeosaurids also had a downy insulation for this purpose. Perhaps it may have been a seasonal development – growing only for the nesting season before being moulted shortly afterwards. It would also seem reasonable to assume that feathers and fuzz would have been utilised as nesting material as well to help line a nest. Pure speculation on my part, of course, but it does seem a reasonable hypothesis. Of course, when you get to large theropods, then incubating eggs becomes somewhat difficult, probably impossible – especially when you weigh upwards of a couple of tons.

The biggest single use of feathers and fuzz in, not only theropods, but dinosaurs as a whole would be for intraspecific communication and signalling. This is undoubtedly the most important function for feathers within today’s extant bird populations and, by implication, must have been just as important to non- avian dinosaurs. Species recognition, courtship and intimidation are just a few of the distinct uses that large theropods would have utilised if they had displayed a feathery covering.



It seems likely that colour would have played a part as well since most dinosaurs likely had good colour vision. It’s interesting to think that some theropods may have become distinctly brightly coloured during courtship and rutting periods (did dinosaurs “rut”?) and the lacrimal horns of theropods are often portrayed as brilliantly coloured in restorations and, in tandem with a distinct plumage, could have made for a wondrous display.

Not that I am in favour of many of these gaudy technicoloured restorations that we see today – far from it. Of course, it is possible that many species may have been brightly coloured but I am just not buying it – it makes no sense. If I was a big 30 foot theropod on the lookout for prey then the last thing I would want to do is advertise my presence by strutting around in a gaudy multi-coloured plumage. No – I believe that that colours utilised would have been used much more subtly - only being brightened up during the aforementioned breeding season.

This brings us nicely to another possible use for integument – camouflage. For me this makes much more sense and the adaptability of feathers and fuzz to take on the colours of their surroundings would make for a stealthy and very effective predator. Herbivorous dinosaurs could have been as equally adapted. I am a big proponent of this anyway since fully scaled dinosaurs could have easily utilised the same technology lest we forget that both fuzz and feathers are derived scales. 
    
One use of feathers that is not often appreciated in extant birds is their ability to produce sound. Scientists are only now really coming to grips with this aspect of a bird’s communication and there are not that many documented cases. Birds such as Wilson’s`snipe, grouse, peacock and manakins all make sound with specialist feathers and one, the club-winged manakin, actually rubs feathers together almost like a violin to produce sounds to entice a mate. However, I do not believe that feathered theropods would have had feathers derived enough to make such sounds or, indeed, the dexterity to perform such an act – but it is an interesting concept.

Keeping with sound – is it possible that any theropods used facial fuzz or feathers to channel sound into their ears? The most obvious example of this today is the owl which surrounds its huge eyes with two almost circular depressions constructed by feathers which function like satellite dishes to collect sound and this enables the owl to hunt with astounding accuracy even in the blackest of nights. Whilst I do not believe that any large theropod evolved similar evolutionary traits I suggest that we do not completely dismiss this notion.

Certainly the small theropod Troodon formosus had large eye sockets which lead some palaeontologists to suggest it was nocturnal. It may have also displayed specialist feathers to help channel sound at night. Similarly the small ornithopod Leaellynasaura also had large eyes and endured long periods of perpetual dark in the Polar winter. It would seem very reasonable to consider that any feathered nocturnal dinosaur would evolve their feathers in whatever way was necessary to survive.  

Of course, something I have mentioned in previous posts is that if large theropods had a fuzzy or feathery covering then it would need to be kept in pretty good condition through regular maintenance and grooming otherwise it would soon be of little use. Birds do this today by preening and having both dust and water baths and it is an interesting scenario imagining a big tyrannosaurid trying to preen or rolling around on the ground for a dust bath. This is one of the things that has always caused me to doubt whether big tyrannosaurs were feathered – could an adult T.rex weighing anything from 5 to 7 tons have the dexterity to preen? Would it really have rolled on the ground for a dust bath? In my mind the answer is no but I am not daft enough to deny that it was possible. Only time will tell on this one.

Black Heron - image courtesy of Wikipedia


One final use of feathers as a hunting aid may seem a bit fanciful but, again, perhaps we should not completely dismiss the notion. The black heron uses a technique known as canopy feeding whereby it uses its wings to form an umbrella which in turn attracts fish under the canopy enabling the heron to strike at the fish. Can you imagine the giant fish eating theropod Spinosaurus fishing this way? What a sight that would have been!

So how would I perceive what a feathered tyrannosaurid may have looked like? I think most interpretations of the head have been reasonable and are very similar to Alex’s Daspletosaurus although I believe that even this might be slightly overdone. A big tyrannosaur with a fresh kill would likely go for the tasty innards first and opening up the torso of a big hadrosaur or ceratopsian would enable the predator to bury his head into the body cavity to remove the offal.

Vultures do this today and their entire head and neck are virtually feather free. This makes a lot of sense to me since congealed blood and other body fluids would soon make a mess of feathers and fuzz. So I would expect a tyrannosaurid to have a pretty bare head although I do not discount a few token feathers developing during courtship.

The small arms of tyrannosaurids continue to spark debate about whether they had some use or, indeed, were vestigial.  I believe that they did have a use and I currently hypothesise that they may have been used for courtship and/or the act of mating. It is entirely possible that these forelimbs may have been feathered and used for display or to send courtship signals. This may take a leap of faith in some circles but extant large animals often display surprising delicacy when it comes to mating and since tyrannosaurs were probably sexually dimorphic then it makes sense to have some form of technique, when approaching a larger prospective mate, that your intentions are honourable!

I would also tend to agree that the legs in tyrannosaurids would remain unfeathered although this is much harder to quantify. Certainly, at lower levels, it would make sense to keep the legs free of integument and then they would not catch on bushes and plants or impede the carnivores’ progress during a hunt.
As for the rest of the body and tail I like Alex’s interpretation of Daspletosaurus which displays a half-and-half coverage. This would seem to have a lot going for it in as much that there is enough bare skin to help control the body temperature should the animal get too hot whilst the upper coverage affords protection from the elements as well as help retaining body heat.

So all in all it would appear that there are significant advantages for a tyrannosaurid having some form of integument whether it is feathers, fuzz or a combination of both. But as is my way I remind you that Tyrannosauridae is still feather free for now but I now find myself actually looking forward to the day that a tyrannosaurid is found with feather impressions and if not – well that just means my scaly clade remains just as awesome as it ever did. Long live the Kings!

This has been doing the rounds on the social networks - made me laugh anyway!


Thursday, 10 January 2013

Shark Teeth Lift the Christmas Blues


The period following the over indulgence and excesses of Christmas and the New Year is often a period of relative inactivity in the palaeontological world. Everything is quiet with just the blogs, websites and social media posting about the year that has just passed and looking forward to the new. We sometimes need to shake ourselves out of the malaise and get ourselves back into the groove so to speak.
The best way to do this, for me, is a visit to the east coast of England and the search for shark’s teeth. This is one of those pursuits best reserved for the winter time and a trip soon after the holidays is a great way to unwind and get some air in those lungs. There are many sites to choose from and I tend to pick one that is a little off the beaten track and not over exposed. I will not be revealing where this site is since it is relatively little known, does not suffer from over hunting and, as a result, usually provides a few teeth. So many exposures these days are virtually exhausted until a rock fall or a spring tide comes in to scour the beds.
All of the east coast beds are Eocene age – around 50 million years old and are representative of a rich marine life. All of these various sites are part of the London Clay Formation of which the most famous, the Isle of Sheppey, has yielded the most extensive fauna of all. The large and varied invertebrate fauna that is found consists mainly of animals that lived on the sea floor or attached themselves to rocks in the surf. Marine turtles have been found as well as a large fauna of fish. The rarest fossils are those of land animals such as crocodile, hippo, birds such as Prophaethon and that most iconic of fossils – the dawn horse Hyracotherium (Eohippus).
The sea during this time was a warm, highly oxygenated low energy shelf environment and the London Clay was deposited over a period of five transgression events. During this period, which covered around 4 million years, the fish were masters of the seas and chief amongst those were the sharks and their teeth can be locally abundant at some localities. Just why are sharks teeth so abundant as fossils anyway?
Well it is, of course due to the amount of sharks that were present during this time and the amount of teeth that were constantly being shed throughout their lifetime. We have to realise that there were no vast fishing fleets depleting the seas of fish and sharks and, just as any ocean throughout prehistory, a sea teeming with life must have been a sight to behold.
 

Sharks have a living conveyor of teeth which constantly replace those that are lost. It is a remarkable mechanism which most people do not appreciate and the fact that the teeth are set in the gums of the shark in layered rows, as opposed to being fixed in the jaw, often catches people out by surprise. But despite the abundance of teeth lost, not all are fossilised and there is still an element of luck required to ensure fossilisation.
When teeth are shed or lost, just like any other fossil, they have to be buried quickly to stand any chance of fossilisation. Have you ever wondered why there are hardly any modern day shark teeth found on the beaches of the world? Because shark teeth are essentially made up of calcium phosphate and, without a quick burial, would disintegrate over a period of time.
Burial prevents decomposition of the tooth by oxygen and bacteria and the slow process of fossilisation takes place. Gradually mineralisation occurs and the teeth absorb these minerals from the sediments they are buried in.
Those of you who are familiar with fossil sharks teeth will be familiar with their beautiful colours. Some are blue, some are green, a few on occasion are red and others can be ivory but the most common colour, by far, is black. How do these teeth end up in these colours when, at time of deposition, they are all white? Well the minerals that are absorbed are instrumental in influencing the colour of the tooth simply because the chemical composition dictates the colour as it replaces the calcium. This is the same with all kinds of fossil teeth all over the world – including dinosaur teeth.


Finding sharks teeth is not as simple as you may think. Sure there are occasions when a nice specimen will be sitting on some sand and you can just walk up and pick it up and you think “hell this is easy”. The truth is that you often have to really work for your teeth but if you are patient and get your eye in then the rewards are there. 
My last trip was on the back end of a gale and I arrived an hour or so after high tide so that I could search on a falling tide. The sea was crashing in to the shore with some ferocity and I was excited at the prospect of finding some nice specimens. However, despite the fact that the tide had turned, the rough sea ensured that there was still no way onto the shore and I had to be patient and wait. Unfortunately, this was the only day that I could get here with the tide in my favour and even then I only had a few hours prospecting before dark.
Eventually the tide relented and I was able to start looking. The majority of sharks teeth at this particular site are black in colour and the shore is particularly “noisy” when you are trying to differentiate teeth from everything else. “Noisy” is my way of describing a bed where there is a lot of collateral material such as seaweed, algae, sand, shingle, a selection of man-made bits and copious amounts of shell debris. The Oxford Clay is also “noisy” in some beds due to the amount of fossil debris that accumulates and finding material of consequence can be difficult.


The best way to search, unquestionably, is to get on your hands and knees and get intimate with the beds. This is best done with some form of knee protection of which the best things to use are knee pads and these are readily available at any hardware store. Do not neglect your back though since bending over for long periods can have consequences if you are not use to such exertion or if you have had back issues in the past.
Other than that, you just have to get your eye in and once you have found a couple of teeth then they can turn up at regular intervals. Light levels can be important too and sometimes morning light is often preferable to other periods of the day as the sun is lower and tends to bounce off the enamel of the teeth betraying their presence although, in truth, you can find them at any time of the day. Indeed, on this trip, I found two in quick succession when it was virtually dark and the sun had disappeared – there was just enough reflection for me to spot them.
Despite what I thought were good conditions, larger teeth were largely absent although I managed to find 18 smaller teeth of which a few examples are quite delightful. Fossil sharks teeth are stunning and are often beautiful to look at and are a proper Nature’s gem which I believe are often taken for granted. Please don’t since it is still a form of miracle that they fossilise in the first place and, in the case of these teeth, are over 50 million years old. Wonderful.

Just look at this stunning preservation 
So this is how I beat the Christmas blues and have done so for a few years now. It does not compare with digging for marine reptiles or excavating dinosaur remains in the south but it still fascinates and I love doing it as much now as I did the first time I searched for sharks teeth. Searching for sharks teeth is not just for Christmas and I do a few trips every year but if you want dust off the cobwebs and fill those lungs with ozone after the festivities, then I can think of nothing better.