Thursday, 29 March 2012

A Test of Time


In today’s fast moving world of palaeontology, modern techniques are constantly being refined taking our science to new levels of data collection and analysis. We near enough take for granted that we can extrapolate maximum data from fossils and we marvel at the wonderful three dimensional restorations of skulls, such as those frequently shared by the Witmer Lab, that enable us to get inside the very head of a dinosaur.
Dating techniques of today, particularly radiometric dating, have enabled us almost unparalleled accuracy in our estimation of the ages of the various rocks and formations throughout the world, getting within around 500,000 years of their true age. No doubt this will be yet further refined and I sincerely believe that completely accurate dating will be achievable within the next ten years or so.
But this has not always been the case and it is always good to reflect how dating and correlation techniques developed in the past and why they are still of great importance and are still very much in use today.   
If we were to go through a photo album that displayed various images of different time periods in our recent past, say the last 200 years, we would automatically try and work out when we believe the photo was taken. We look at the clothes that people wear, the streets, forms of transport and maybe landmarks to make a guess at the time and because of this change we can estimate the period as being the 1850’s, 1880’s and the 1900’s and so on.
Fossils do very much the same thing and enable us to help date the rocks. Evolution dictates that there is a constant turnover of life forms throughout the ages and as older taxa become extinct there is always a new one that replaces it. What this means is that each rock unit within any given formation will contain its own distinguishing set of fossils.

William Smith 1769 - 1839

The man who recognised this sequence in the rocks and was primarily responsible for bringing it to the scientific world’s attention was William Smith. Smith was a surveyor who, in 1793, was working on the construction of the Kennett and Avon Canal and, as the course of the canal was being cut into the terrain, keenly noticed the different types  of strata that were layered on top of each other. Fascinated by what he observed, in 1794, he toured England to examine other canals which provided him with further insights.
Smith worked out that each layer of rock represented a specific moment in time and took a very long time to form and deposit layer upon layer. But, now that he had looked at the different formations throughout the country, he couldn’t work out why the same strata could be found in different sequences and thicknesses in different places. He methodically classified the strata according to its makeup and was able to build up a fine collection of fossils at the same time.
Smith made copious note of the strata that the fossils were found in and, because the fossils were so numerous, he was able to quickly work out that certain fossils were to be found in certain rocks. However, when he tried to make sense of sequencing the strata in various parts of the country he found that he could not match, what he considered to be, the matching rock types. The strata were found to be in different thicknesses and, even more apparent, were in a different order.
But then Smith realised that it was not the type of rock that mattered – rather it was the fossils they contained that were the common denominator. He observed that the same fossils could be found in different locations, in different rocks and at different depths – but they were always in the same sequence. Smith realised that this would enable him to use fossils for dating the rocks just by simply correlating the different strata by the fossils they contained and he also realised that the difference in thickness of the rocks was of no consequence since different sediments accumulated at different rates. Once he worked this out Smith was able to produce the first recognisable geological maps ever produced in the UK and, for me, was amongst the most influential and important geologists ever.
Over the years, as techniques became more refined, it became apparent that some fossils were more important for dating than others and these are known as zone fossils. These are taxa that may have only existed for a relatively short period of time but, of course, this may still cover a time period extending upwards of 10 million years or more.
The best known of the zone fossils are, of course, the ammonites and they have proved to be of considerable importance to palaeontologists worldwide. To demonstrate how zone fossils help us to date rocks, it is best to look at the diagram below.

Fossil “A” was a long lasting taxon found in all five rock units. Obviously this fossil would only allow for very basic date estimates covering a long period of time.
On the other hand, fossil “B” is only found in rock unit four and is therefore a good zone fossil. It has a limited temporal range, is only found in this rock unit and can be constrained to that time period.
You can see that fossils “C” and “D” are both reasonable zone fossils - both being fairly short lived taxa. But you can also see that they are both found in rock unit 3 and this enables to us mark that particular point in time since it is the only period where the two taxa overlap. The same can be seen for fossils “C” and “E” – this time contemporary only in rock unit 2.
Of course, zone fossils are also extremely important for correlating data for different rock formations on a world wide scale. Correlation is the term used to describe what connections exist between these variously located and different forms of strata and this is the technique that William Smith first pioneered all those years ago. Because the same zone fossils are found in rocks that were deposited in completely different environments, in different locations we know that they must have been formed during the same geological time period.
As mentioned earlier, ammonites are the most important of the zone fossils and it is easy to see why. They had a global distribution and were free-swimming organisms that, when they died, sank onto the sea bed and became fossilised in a multitude of ways in different marine environments. They were incredibly numerous and successful animals that diversified into thousands of genera and this combination of factors has enabled correlation of a wide range of sedimentary rocks. Formations, like the Oxford Clay, are separated into these zones and are often informally referred to, for example, as the Jason Zone or the Coranatum Zone – both species of ammonite.
So despite today’s advancement in modern dating techniques it is worth remembering that this very early technique is as sound now as it ever was. It may lack certain panache in the current state-of-the-art digital age but it represents a basic solid technique that is still widely referred to today.




Thursday, 22 March 2012

Dinosaurs, Plants & Coevolution



In my previous post about Laramidia, and in attempting to explain how the plants and trees were able to provide enough fodder for the large numbers of herbivorous dinosaurs that grazed there, I looked at how a combination of climate, physical and meteorological barriers, and the food value of the plants themselves, could have sustained such a voracious herbivorous assault.
And yet, there was another driving force behind the ability of the plants to, not only survive, but to flourish and quickly recover from sustained grazing – and that was the dinosaurs themselves.  Animal partnerships, relationships and animal/plant relationships were almost certainly as evident in the past as they are today and the term used to describe the change affected on one species that interacts with another is coevolution.
The concept of coevolution was first raised by Charles Darwin in Origin of Species and has been gradually refined through the years but the theory still comes under intense scrutiny as scientists try and decide whether the evidence presented for each individual example is truly coevolution.  In other words, any form of interaction or symbiosis that produces evolutionary change can only be classed as coevolution when substantiated by thorough research and the appropriate phylogenetic analysis.
Having said that, however, there is ample evidence that implied coevolutionary interaction is extremely likely and there are numerous examples around today – bumblebees and flowers are an appropriate example. The effect of one species on another cannot be denied and in its simplest form is very apparent. Entire species have become extinct or virtually extinct because a foreign species was introduced by accident or even on purpose. Examples are legion: grey squirrels driving out the reds in England, possums in New Zealand devastating flightless bird populations and, in Mauritius, even Man eradicated the dodo.
Indirect extinctions are yet another form of interaction that is also far removed from coevolution.   The eradication of a species without any thought can have a massive effect, from the smallest invertebrate through to the biggest apex predator – a domino effect if you will. This form of extinction is most likely to affect different species that are extremely dependent on each other or those taxa that are the cornerstone of many niches thus affecting multiple species.
A couple of very simple examples of this include six species of mite that became extinct when the Carolina parakeet disappeared and a vine plant in Singapore that, when it disappeared, took with it one particular species of butterfly that was dependent on it. To demonstrate a possible future scenario, off the coast of California, there is a delicate ecosystem involving kelp, sea urchins and sea otters. These three species are so totally dependent on each other that the fragility of such ecosystems becomes evident.
Image by Katie Hale

The sea otters keep the sea urchin population under control which, if left unchecked, would completely devour the kelp forests. Without the kelp, a multitude of different organisms would disappear and yet, without a sufficient population of urchins, the sea otter population would quickly crash and decline. This clearly demonstrates the fragility of such ecosystems and dramatically highlights how the extinction of one species can affect so many others.

Partnerships, or mutualism to give it its correct term, are another form of interaction. The most oft cited example of this is the relationship between ants and acacia trees. The ants depend on the acacia for nesting and food whereby  the plant provides specialised thorns that provide shelter, special nectar buds that provide food for the ants and leaf tips that are also of a high food value – especially to the larvae. The ants, in return, remove fungal spores from the tree that may invade the acacia host and provide aggressive defence against any herbivore foolish enough to attempt to feed on the tree. This particular example has often been cited as coevolution so amply demonstrates how hard it can be to classify.
All of the examples highlighted above demonstrate how different species affect one another through various examples of interaction. Despite these all being contemporary examples, it does demonstrate that such relationships have existed, almost certainly, from the earliest forms of life right through to the present day. So how does this all relate to dinosaurs?
Bob Bakker, in his book the Dinosaur Heresies, featured a chapter titled Mesozoic Arms Race in which he postulates how both herbivore and carnivore spurred on the mutual evolution of the two groups – in other words, true coevolution. As theropods got bigger to cope with larger prey, the herbivores got bigger still. If it wasn’t size, it was armour, horns, teeth, claws, agility, and social interaction – a plethora of derived traits continually evolving to keep the different genera ahead of the game and ensure survival. Those that did not evolve became extinct. This is the classic example of survival of the fittest – natural selection. Evolve or die.
I suspect that trees and plants were also part of this life or death struggle and that their ability to be able to sustain large populations of giant herbivorous dinosaurs was a direct response to intense grazing pressure from dinosaurs. As herbivorous dinosaurs got bigger and their ability to crop the plants, masticate and digest plant material became more sophisticated, the plants and trees had to adapt or become extinct. They had to find new ways to be able to withstand the stress of being constantly cropped, be able to reproduce quickly, and grow at inflated rates.
The fact that there are so many different shaped and sized herbivorous dinosaurs is highly indicative that they were successful. Small ornithopods would graze at low levels, mid-sized animals could take advantage of both whilst animals such as brachiosaurs and titanosaurs could feed at higher levels. Whilst appreciating this is a very simplified way of looking at things, the point is well made. Herbivorous dinosaurs evolved into many different and complex varieties to cope with the continually evolving plants.
In the Cretaceous, things moved on to another level with the evolution of much more complex herbivorous dinosaurs.  The well-publicised iguanodont and hadrosaurian dental batteries, which enabled a much more efficient form of food processing, along with ceratopsians, ankylosaurs, sauropods and other ornithopods, pushed plants and trees to new heights of production.
But this time the plants and trees had even more help with an increase in the amount of CO2 in the atmosphere, increased warmth and moisture and this combination enabled the flora to grow at inflated rates. And there was yet one more innovation by the plants to come which aided reproduction, fertilisation and increased diversity and sustainability.
It has been often noted that the dinosaurs may have been responsible for the appearance of flowers during the Cretaceous (eg again see Bakker 1986). Although there is no foundation or scientific evidence to back this assertion, it does appear likely that intense dinosaurian herbivory may have contributed to the evolution of flowering plants (Barrett et al 2001 but see also Lloyd et al 2008).
The truth is almost certainly something in between. The dinosaurs probably prompted rapid development in plants to avoid eradication and extinction. During the Cretaceous conditions were so good for growth that the plants simply took advantage of the situation and evolved extremely rapidly - with flowers simply another tool which allowed further diversity and distribution. This enabled the dinosaurs to feed on an almost never ending supply of fodder and is possibly the chief reason why Laramidia was able to sustain such large populations of big dinosaurs.     

References

Bakker, R. 1986. The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and Their Extinction. William Morrow and Company, New York.
Barrett P.M, Willis K.J. Did dinosaurs invent flowers? Dinosaur-angiosperm coevolution revisited. Biol. Rev. 2001;76:411–447. doi:10.1017/S1464793101005735[PubMed]
Lloyd, G.T., Davis, K.E., Pisani, D., Tarver, J.E., Ruta, M., Sakamoto, M., Hone, D.W.E., Jennings, R., and Benton, M.J. 2008. Dinosaurs and the Cretaceous Terrestrial Revolution. Proceedings of the Royal Society, Series B 275, 2483-2490 (doi:10.1098/rspb.2008.0715).

  

Friday, 16 March 2012

The Amazing Complexity of Laramidia


The March issue of Scientific American contains an article by Scott Sampson in which he describes the latest theories about the dinosaurs of Laramidia. In it, he describes his continuing research in the Grand Staircase-Escalante National Monument in Utah – primarily in the Kaiparowits Formation. Of course, to many of us in the palaeocommunity, and readers of blogs like this and many others, the mysteries of Laramidia are well documented.




To begin with, Laramidia itself is remarkably small compared to the total land mass of the United States today and the most interesting debate centres on how so many different dinosaur taxa managed to survive and proliferate with what would appear to be limited resources.

In addition to that, as more fossils are recovered from the south to compliment the already substantial record from the north, the intrigue increases since the faunas are quite distinct from each other which is highly indicative of faunal endemism. These differences in species range across the board, from the smallest troodontids to the largest hadrosaurs, ceratopsians and tyrannosaurs.  

The notion of a barrier(s) separating the different dinosaur provinces have been hard to prove. For instance, it has been suggested that climatic conditions alone may have been enough to segregate the communities or, as seems more likely, a geological barrier may have perhaps prevented faunal exchange. Initially thought to be a mountain range, Sampson points out that geologists are now suggesting a number of large rivers, flowing in series, may have been enough to have kept the communities apart.

From Sampson et al 2010

Of course, this is assuming that there were only two communities from the north and south but it is likely there may have been more. Add to this that other most mysterious of problems to solve – how on earth was there enough fodder available to provide food for so many mega herbivores on such a relatively small piece of land?

Firstly, there is, without doubt, sufficient evidence to support the hypothesis of faunal provincialism within dinosaurs. At first glance the faunas from both the northern and southern provinces are remarkably similar and yet sufficient morphological differences exist that confirm that the taxa are indeed different although Sampson points out that a specimen of Gryposaurus appears very similar to G. notabilis from Alberta and is still under scrutiny.

To back this up, radiometric dating of various Larimidian formations, suggests that the Kaiparowits Formation was temporally coeval with the Dinosaur Park Formation of Alberta suggesting an age between 76.5 and 75.5 million years old and this adds further evidence for different species evolving in different provinces but at the same time.

So we have at  least two different dinosaur faunas, both very similar, both containing many multi tonned animals, being able to survive on what was already a small  land mass which was further reduced in size because of various barriers which may have included, mountains, rivers and lakes. These dinosaurs survived in extraordinarily large numbers in unique conditions which, when compared with extant terrestrial communities of today, does not make sense. It appears impossible and yet it happened. What IS clear is that these dinosaurs flourished and proliferated in a way that exceeds any mammalian equivalent of today.

So this brings us nicely to that old chestnut – dinosaur physiology and metabolic rates. Sampson is very much a champion of the "Goldilocks" theory – that is that dinosaurs possessed a metabolic rate somewhere in between cold blooded ectotherms and warm blooded endotherms.   A fully endothermic dinosaur would need a greatly increased food intake whilst a fully ectothermic dinosaur could get by on considerably less. As we have noted only recently, dinosaur bone histology clearly indicates they were very active, fast growing animals and the indications are highly suggestive of endothermian dinosaurs.

But the "Goldilocks" theory hypothesises that dinosaurs with a middle-of-the-road metabolism could have got by on considerably less food than fully endothermic animals. This theory enables the Laramidian environment to sustain a much greater biomass of large dinosaurs which has been hypothesised to be up to five times greater than present day levels in Africa.

The problem, for me, is that this is all very convenient and does, on the face of it, present a rational theory to describe how so many animals flourished in so small a land area – and it is quite possible that this proposal is correct. But this simply dismisses all the evidence to the contrary, that dinosaurs were likely fully endothermic animals living at fully endothermic rates. For me, there is something else going on here and it appears to be a combination of things.

The Cretaceous is known to have been a time of extremes. The temperature was hot, there was high humidity and significant rainfall. CO2 levels were at a high – 1000 parts per million as opposed to today’s levels of 393 parts per million. It was truly like living in a greenhouse.  And, as in a greenhouse, plant growth was extreme, lush and grew at an astonishing rate with some estimates suggesting the conditions enabled a doubling of global forest productivity throughout the Cretaceous (Peralta-Medina & Falcon-Lang 2012). The proliferation of angiosperms and the increase in rapid pollination and fertilization also contributed to this explosion in the biomass.


The plants themselves were also likely to be highly nutritious and the oft mentioned work of Carole Gee (2011) looking at the food values of the Morrison Formation flora indicates that the plants were very capable of promoting rapid growth in sauropods and by that inference alone, since many of the plants and trees from the Jurassic were also prominent in the Cretaceous, suggests that rapid growth and sustainability in dinosaurs would have been maintained or even surpassed.

It may be that Laramidia was not simply a landmass containing dinosaurs in the north and south and I suggest that it is possible that there were multiple provinces each containing communities of dinosaurs that may be either  identical, have subtle or maybe even more marked morphological differences. Even the plants and trees were likely to have displayed different trends in different provinces.

How is this possible? The combination of different barriers such as mountains, rivers, forests and even the Western Interior Seaway itself could have created multiple enclaves each with its own distinct microclimate, generated by the hothouse Cretaceous climate, and, depending on the type of barriers, would have almost certainly have seen the evolution of flora and fauna with subtle but distinct differences. It’s just possible that such conditions would have sustained large populations of fully endothermic dinosaurs. But this is just my personal opinion so certainly don’t take it as fact.

The answer will almost certainly lie in yet more detailed sampling throughout the Laramidian formations and, as Sampson postulates, the unique provincialism of Laramidia will provide many more new species of dinosaur to help our understanding of this lost land.

References

Gee, C. 2011. Sauropod Herbivory During Late Jurassic Times: New Evidence for Conifer-Dominated Vegetation in the Morrison Formation in the Western Interior of North America. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2011, pp115. 

Peralta-Medina, E and Howard J. Falcon-Lang (2012). Cretaceous forest composition and productivity inferred from a global fossil wood database. Geology 40(3) doi: 10.1130/G32733.1

Sampson SD, Loewen MA, Farke AA, Roberts EM, Forster CA, et al. (2010) New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism. PLoS ONE 5(9): e12292. doi:10.1371/journal.pone.0012292 

Sampson, S.C. (2012). Dinosaurs of the lost continent. Scientific American Vol.306(3) pp34-41



  Note


All of these landscape images are from the south island of New Zealand. I was lucky enough to stumble into this wonderful Gondwanan-like valley and the surrounding mountains and escarpments are how I imagine Laramidia may have been partitioned up back in the Late Cretaceous. 



Thursday, 8 March 2012

Allosaurus in Lisbon

A brief post this week because I was in Portugal for a few days earlier in the week spending most of my time in Lisbon. While I was there, I took the opportunity to visit the Musêu Nacional de História Natural which is currently featuring a special exhibition called Allosaurus: One Dinosaur, Two Continents that focusses on the remarkable discovery of Allosaurus sp remains from Upper Jurassic sediments in Portugal.
The main exhibition takes you through the entire palaeontological process of one particular Allosaurus specimen from discovery to preparation. The exhibition is nicely set out with some interactive displays in place and the Allosaurus story is backed up with many other exhibits, some of which I’ve featured below.
What stood out to me, when looking at the original Allosaurus fossils, is how identical they are to those from the Morrison Formation – absolutely incredible. Even the preservation is similar, right down to that very familiar jet black colour that is prevalent amongst Allosaurus specimens from the USA.
There was lots of interesting goodies to see there and there will be more images and posts referring to this exhibition in the future. If you get the opportunity to visit, the exhibition is there until the end of this year so make sure you check it out. Recommended.

The skull of Giganotosaurus



Herrerasaurus

No prizes for guessing whose muzzle this is!



A Stegosaurus dermal plate

A Stegosaurus thagomizer

"Three horned face"


I liked this particular display. It's not very often you get the chance to compare Velociraptor, Dromaeosaurus and Deinonychus all at the same time.

Friday, 2 March 2012

Bone histology suggests Hadrosaurs endured a polar winter


Fossil bones provide us with a wealth of information, which is just as well, since bone constitutes the overwhelming majority of the material that vertebrate palaeontologists are able utilise in their pursuit of trying to describe the animals of the past. Skeletal remains provide us with the basic body plan of the animal, and vertebrate evolution has provided us with a remarkably stable blueprint to follow from fish right through to Homo sapiens.


Mechanically the skeleton provides the support and scaffolding for the body and, of course, provides vital protection for the organs. Increasingly though, the actual make up of fossil bone is continually providing new data and on-going histological study appears to be maintaining this steady flow of new information.  Histological studies of fossil bones from dinosaurs first came to the fore in the 1970’s, with Armand de Riqlès leading the way, and his work was very much part of the Dinosaur Renaissance. 
Dinosaur bone is heavily vascularised and, since it is remarkably similar to extant mammalian bone in histological make up, it is fair to assume that bone received anything between ten and twenty per cent of the total blood supply pumped around the body by the cardiac system. Bone can also sometimes reveal whether the bone is from a juvenile or adult. Woven bone is a primary bone tissue that is temporary and coverts throughout ontogeny to lamellar and/or fibrolamellar bone and is indicative of maturity. This kind of data has been used extensively recently and particularly within the continuing ceratopsian ontogeny debates.
Bone is also remarkable in that, although you may think that it has stopped growing once maturity has been reached, it continues to develop in various ways and this is a process known as remodelling. Throughout adulthood remodelling is a continuous process as any damaged bone is repaired and can also be reinforced to cope with any additional stresses put upon the animal. The result of this remodelling is the pathologies that are frequently found on dinosaur bones and this is another area of intense interest in dinosaur palaeontology.
Darren Tanke, of the Royal Tyrrell Museum in Alberta,   is currently compiling masses of data on hadrosaur pathologies and some of the images of remodelling that have taken place have to be seen to be believed. In mammals, a remodelling episode may complete in around six months and it is likely that dinosaurian bone took around the same amount of time but, of course, this is purely conjecture.
Fibrolamellar bone is indicative of an animal whose bones need to grow fast and expand in diameter rapidly to cope with the stress of a large body. Large extant mammals of today also have fibrolamellar bone for the same reasons, for it can be laid down extremely rapidly by a complex process that utilises interwoven layers of both woven and lamellar bone.
However, fibrolamellar bone is not always consistent in its development and, in some cases, there are definite interruptions and these are known as lines of arrested growth (LAGS).  These LAGS are layers of bone that are indicative of what can be described as a slowing up of rapid development and are interpreted as a result of some form of environmental stress. Drought, environmental change, food shortage and migratory pressure have all been proposed as possible agents of growth arrest.
This brings us nicely to a recently published paper by Anusuya Chinsamy et al (2012)describing the bone histology of Edmontosaurus  bones from the Prince Creek Formation in northern Alaska and the Horseshoe Canyon Formation in Alberta. Both formations are Late Cretaceous and were temporally very close and were certainly contemporaneous for at least two million years.
The bones of the northern hadrosaur clearly display interrupted fibrolamellar growth whilst those of the southern type do not. However, in the northern type, these interruptions are not LAGS but rather a slowing down of bone deposition whilst the southern type displays no such interruption. This, therefore, poses a rather intriguing scenario.


Northern Edmontosaurus (left) displaying numerous growth interuptions whilst the southern type (right) does not.
From Chinsamy et al 2012.
 The authors pose the possibilities that the differences between the two hadrosaurs may be the result that both types were migratory, that Edmontosaurus may have included both migratory and non-migratory populations and, finally, that the northern type was, in fact, resident all year round. The first suggestion is unlikely since the southern type displays no interrupted fibrolamellar growth.
The second suggestion is a possibility since the northern type does indeed display histological differences that can be associated with migration. The third option is the authors preferred hypothesis since an overwintering scenario would demonstrate a histological sequence exactly as found in northern Edmontosaurus. They suggest that the darkness of a polar winter and a reduction in the quality of fodder that resulted would manifest themselves in differing bone textures.
Southern Edmontosaurus may display the odd signal in bone textures which are symptomatic of occasional stress, perhaps a food shortage, whereas the northern type displays a record of consistent, probably annual, events. The authors stress that histological evidence alone cannot substantiate the overwintering scenario but additional data does appear to support it. For example, a lot of the edmontosaur remains from the Alaskan North Slope are from juvenile animals that were almost certainly too small to migrate.
They also appear to have perished in floodwater events as result of the winter melt which is highly indicative that these animals had overwintered in the North. Further comparison with the polar dinosaur fauna of New Zealand also lends support to the overwintering scenario – for they too endured a polar darkness lasting for perhaps six months.  
Although this paper is short (barely 5 pages), it contains some nice data and adds more substance to the  growing belief that dinosaurs were well equipped to deal with the rigours of the cold and darkness that only a polar winter could throw at them and, again, is highly suggestive of endothermian dinosaurs as I have discussed here previously.
Incidentally, this obviously does not mean that all dinosaurs did not migrate – far from it. It does suggest, however, that not all dinosaurs did either. Besides, there were large numbers of herbivores, including hadrosaurs and ceratopsians, ploughing through enormous amounts of fodder each day and it is almost certain they would have to keep on the move to find new pasture on a pretty regular basis.
Finally, there is yet another histology paper that has just been published (Cerda & Chinsamy 2012) looking at the bone microstructure of the basal ornithopod  Gasparinisaura cincosaltensis , from the Late Cretaceous of Patagonia, which again may be indicative of either sexual dimorphism, suspension of plant growth or localised stressed conditions. Bone histology continues to provide significant information regarding dinosaurian physiology and the environments they frequented and looks like doing so for a long time to come.

References

Ignacio A. Cerda & Anusuya Chinsamy (2012) Biological implications of the bone microstructure of the Late Cretaceous Ornithopod Dinosaur Gasparinisaura cincosaltensis. Journal of Vertebrate Paleontology 32(2): 355-368 DOI:10.1080/02724634.2012.646804
Chinsamy, A., Thomas, D. B., Tumarkin-Deratzian, A. R. and Fiorillo, A. R. (2012) Hadrosaurs Were Perennial Polar Residents. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology (advance online publication) doi: 10.1002/ar.22428