Sunday, 30 October 2011

SVP 2011 is Here!

It’s that time of year again and all roads lead to Las Vegas for this year’s 71st SVP meeting -  and what an event it promises to be. The meeting is quite possibly the biggest one of its kind and I cannot remember seeing so many talks and posters at the one conference – especially the posters and Heinrich Mallison alludes to this over at dinosaurpalaeo.

There is so much of interest this year and so much to discuss but, of course, any discussion about content of the meeting is embargoed until the posters and talks actually begin. That’s fair enough and we should all be use to that by now but I will be highlighting some of those talks and posters that are really interesting over the next few weeks and,  I promise you, these will only scrape the surface of the amount of data being presented at this year’s SVP.


I’m quite sure that many of you are already en route and that many will be leaving imminently. To all my friends and colleagues attending this year’s meeting – I hope that the event lives up to your expectations and hope you all have a great time!

Thursday, 27 October 2011

Humerus Preparation Finished

Sticking with all things Oxford Clay and I’m pleased to reveal the fully prepared humerus of our mystery plesiosaur – and what a fine example it is. Although the bone was in pretty good condition when it was recovered, it was in two pieces and slightly scraped at both the dorsoproximal and distal ends. This was a clean fresh break that was almost certainly caused by an excavator as it passed overhead and this was almost certainly the same machine that uncovered the specimen in the first place – a double edged sword so to speak.


To be able to look at the finer detail of the bone it was obviously necessary to remove the matrix that was adhering to the specimen. It was also a requirement that the two pieces be stuck together and, since the specimen was densely mineralised and heavy, the join would have to be of considerable strength.

Because of the nature of the matrix and its “stickability”, a variety of different tools were used on the preparation and the form of the matrix dictated what tool was to be used. The amount of matrix removed mechanically was very small and primarily revolved around the proximal end and distal flange whilst the bulk matrix on the shaft and flange were removed with various hand held tools. This was necessary because some sediment tends to blend in with the bone and the external patina is easily damaged if you are not extremely careful.

One problem that I’ve not encountered with material from the clay is knowing where matrix ends and bone begins - unlike some other material I’ve been preparing. It is easy to differentiate unless you make the mistake of going too deep in the first place – then you can have a problem but, if you are careful, then mistakes should be rare. Some Triassic skull material I’ve been working with, on the other hand, is almost identical to the surrounding matrix and is slow going.

Although the bone was tough, it still needed support throughout the preparation process and I used small sand bags in combination with mutil-layered bubble wrap to provide it. The humerus has needed very little in the way of consolidation although it has been given a gentle protective coat of Paraloid B-72 and this has also been used to glue the two parts of the bone back together at a 50/50 solvent to consolidant ratio. This has made for an extremely tough bond and appears very robust.


The shaft of the humerus was stood in a container of sand which effectively held it in place and upright and, once the glue had been applied, the flange was very quickly joined on and held in place by various bits of ethafoam, which not only held the bone in place but also allowed for adjustment. The join was so perfect that I used the weight of the flange to create the pressure required and then left it for 48 hours to really harden.

The join appears to be excellent and is likely to be strong enough but if it is found to be wanting then I can always redo it and will probably add glass beads which would form an even stronger bond but I really don’t think it will be necessary in this case.

Next up is the ulna (below) and then the radius, which shouldn’t take too long to prepare and then we will be into the proximal carpals – the ulnare, intermedium? and radiale and, after that, the distal carpals.

Thursday, 20 October 2011

The Other Oxford Clay Fauna

The Oxford Clay Formation in England has yielded a diverse community of marine reptiles and fish for well over 150 years now and has featured in this blog many times, as regular readers will know. What does not get mentioned so often is the fact that there is also a significant invertebrate fauna, trace fossils and, as I have mentioned previously, plant fossils.

The bed that we study most intensely is known as Bed 10 which is Middle Callovian in the Lower Oxford Clay – more familiarly known as the Jason Zone. Bed 10 is at the very base of the clay quarries that have been dug out over recent years and is as far as excavations take place. This is primarily due to the fact that the bed is full of concretions that would easily damage very valuable machinery and interrupt the brick making process.

The other issue would be the fact that further penetration would break into the underlying Kellaways Formation that has no commercial value although this formation has produced some excellent vertebrate fossils where it has been exposed on occasion. The only other excavations into Bed 10 are to dig drainage ditches which help control the water level in the quarries although these are not as common as they once were. This is unfortunate since many excellent finds have been made in and around these ditches over the years.


The most abundant fossils in the clay, that are readily apparent to the naked eye, are the ammonites and these are dominated by the Kosmoceratidae – specifically Kosmoceras jason, from which the zone epithet is derived, but there are others represented such as K. medea and other species such as Sigaloceras. Preservation of ammonites, in these quarries, is often spectacular to look at in the clays and shales but are impossible to collect since they are nearly always crushed flat and are wafer thin. They can occasionally be found in three dimensions in nodules but, again, are almost impossible to extract.

Belemnites are also abundant and, on occasion, are spectacularly preserved. These, in contrast to the ammonites, are easily collected since the rostra fossilise well. Belemnite rostra, like the nodules, also cause problems for the brick makers and will often explode in the curing process so they are always removed where possible.

The most common species are Cylindroteuthis puzosiana and if you are fortunate to visit a quarry after fresh clay extraction, then you can find many undamaged rostra in superb condition. Some are giants, approaching 25cm long, but are more likely to be 15 – 20cm long although you can find some that are as small as 25mm as well. Fragments suggest even bigger specimens exist but these are very elusive and it is apparent that their size and length make them vulnerable to extreme damage.


Cylindroteuthis (left) & Belemnopsis (right). 

Phragmacones are fairly common and, every now and then, you can observe the badly preserved outline of the soft parts at the head of the animal, including the tentacles, in the clay. Hooklets are occasionally found but I personally have yet to see one. The other locally common species, Belemnopsis bessina, is much smaller with the rostra probably reaching a maximum of 75 to 80mm and these are sometimes mistaken for fish bone.

Crustaceans are present in the shales and are meant to be locally abundant, especially at the top of the Jason zone, but I have never seen one until this year when a specimen of Mecocheirus pearcei was recovered. However, just because I have not seen them does not mean they are not there since I am looking for vertebrate remains more often than not.

In my eyes, some of the most remarkable and delicate fossils are those of Genicularia vertebralis, an annelid worm of the class Polychaetia. The “fossils” are actually the casts of the burrows these worms created and are represented by calcified shells. Some are wonderfully preserved, albeit somewhat fragile and the preservation of the ornamentation never fails to delight.

Genicularia

Bivalves are well represented in the quarries and are dominated by Gryphaea dilobotes and these, although generally abundant throughout, can often be found in large dense encrustations. Some can get really big, with some recovered pieces suggesting shells over 100mm long but they are exceptional and most are around half that size with every other size and morphology in between. They are quite fragile as well and need gentle handling when a good specimen is found.

Gryphaea

Other bivalves include Pinna mitis which are often only found as imprints in newly uncovered clay. These are often mistaken for the imprints of fish fins or tails by those who are unfamiliar with them and it is easy to see why. Pinna are elongate fan-like bivalves with multiple, densely packed ribbing and, when crushed, really do look like fish fins. Another bivalve I’ve seen is Trigonia Sp. But this is likely to have been derived from the Middle Oxford Clay.

Plant fossils are not so well known from the clay and yet there is evidence for them throughout the quarries. They are all land plants that have drifted out to sea, most likely carried by rivers in flood that have eventually sunk to the sea floor. Large chunks of wood that have become carbonised can be found all over the place although once exposed to air they quickly crumble and often turn to dust. Some of us have attempted to save a few of the better preserved pieces but it takes vast amounts of consolidant to stabilise them and they need constant review otherwise they are prone to deterioration at a rapid rate.

Whole logs are sometimes uncovered but they are seldom removed, as you may remember from an earlier post. But every now and then, an odd branch or frond may fossilise well and these are extremely rare. My very first visit to Quarry 4, some years ago, revealed a freshly exposed piece of tree bark - the only example I have ever seen. It has taken a lot of maintenance to keep it intact but it is a wonderful piece and displays superb ripple-like marks in the bark.

Tree Bark

There is one other fossil worth a mention and that is that there is an abundance of fish coprolites in the clay. These are often ignored by some who do not recognise them as such and there are those who ignore them anyway but they are missing out in my opinion. The vast majority are small, only 5 to 10mm on average, pretty nondescript and are a dirty white in colour. They tend to be like this because they are largely composed of phosphate derived from digested fish bone.

However, some have quite distinct forms and the bigger ones are much more interesting since closer inspection reveals the remnants of what had been digested and passed through the gut such as small fish bones and remains of crustaceans. Rarest of all are coprolites of the marine reptiles but, every now and then, one is found and the inclusions in these are much larger and, although almost impossible to identify, are suggestive of bone and ammonite pieces, and are quite intriguing.

Coprolites displaying inclusions


Thursday, 13 October 2011

Alamosaurus and the Naashoibito

In the latest edition of the Journal of Vertebrate Paleontology, there was an interesting paper by Michael D’emic et al describing a titanosaurid pes from the Naashoibito member of the Kirtland Formation in New Mexico. The specimen (NMMNH P-49967) displays synapomorphies referable to a titanosauriform neosauropod and is almost certainly referable to Alamosaurus sanjuanensis, although additional remains would be needed to confirm validity.

The specimen, however, is from a very large sauropod indeed and, when limb proportions are compared and scaled up, is comparable to both Brachiosaurus altithorax and Paralititan stromeri. Alamosaurus is the only recognised Late Cretaceous titanosaur from North America but its taxanomic status has always been subject to review (eg Sullivan & Lucas 2000) but this paper reaffirms its belief that the Alamosaurus holotype is diagnostic and should be considered a valid genus.

The interesting thing for me in the paper is the referral, yet again, to the geological position of the Naashoibito Member and whether it belongs to the Ojo Alamo Formation or not. There is a consensus these days, however, regarding the age of the Naashoibito and it is now generally accepted to be Maastrichtian. The type specimen of Alamosaurus was recovered from the Ojo Alamo Sandstone which, during 1980, had been considered part of the Naashoibito Member of the Kirtland Shale (Kues et al 1980).

However, the Ojo Alamo is amongst the stratigraphically highest horizons for dinosaur remains, so high in fact that there has been occasion to suspect that a few dinosaurs survived into the Palaeocene but this has been hotly contested (Fasset et al 2002, Lucas & Sullivan 2000) and is generally not considered these days but, as these things do, rumours persist. Today, the Ojo Alamo appears to be distinct from the Naashoibito and is a particularly interesting formation in its own right because it does indeed straddle the Maastrichtian/Danian contact.

From Williamson & Weil 2008
  • The general consensus (it appears to me) is that the Naashoibito is part of the underlying Kirtland Formation demonstrating a Lancian fauna or, as is generally known, the "Alamosaurus fauna". It has been recognised for some time now that there have been distinct Maastrichtian faunas and this provincialism is perhaps better recognised from earlier Campanian times but it is a fact that faunal provincialism continued right through to the end of the Cretaceous.
The paleoenvironment of the Alamosaurus fauna was characterised by valleys that were situated between mountain ranges and were frequented, not only by titanosaurs, but by hadrosaurs, ceratopsians and theropods. The Hell Creek Formation, by contrast, represents a coastal plain environment that was warm, humid and wet and was dominated by ceratopsians, hadrosaurs and tyrannosaurids – but no sauropods. The Scollard and Willow Creek formations demonstrate a third environment described as a semiarid, alluvial plain and contains remains of ceratopsians, hadrosaurs, ankylosaurs and tyrannosaurs but, again, no sauropods.

It is this provincialism that has kept apart Alamosaurus and Tyrannosaurus, thus preventing a possible (and very popular) clash of these titanic animals – but maybe not for much longer. Tyrannosaurus appears to have been able to exist in a range of paleoenvironments and a specimen recovered from the North Horn Formation of Utah (Sampson 2005) was the first example of the giant carnivore apparently co-existing with Alamosaurus.

Just when Alamosaurus appeared in the Late Cretaceous is still subject to debate but it seems that titanosaurs appeared during the Campanian around 73 million years ago although their exact point of origin remains undetermined. Suggestions include a possible migration from South America to the north due to the appearance of a land bridge between the continents. This may have been due to climate change since the Western Interior Seaway was also receding at this time and this may have created the ideal conditions for the migration and establishment of a relatively localised population of sauropods. Another possible titanosauriform doorway into North America may have been via Asia but this appears to lack any substantial fossil evidence at this moment in time.

It is obvious that there are vast gaps in our knowledge regarding this fascinating stage in dinosaurian history including unanswered questions that include, amongst others, sauropod phylogeny, paleoecological implications and, of course, the geology and stratigraphy of the San Juan Basin as a whole. It is apparent that the best is still to be revealed by both the Ojo Alamo and Naashoibito and one can’t help but be intrigued by these fascinating formations

Footnote

There will be yet more detail revealed regarding the taxanomic status and paleobiogeography of Alamosaurus at this years SVP conference in November and I will report on this after the conference has finished and embargo lifted.

From Russel 1992
The above image is a poor quality scan but demonstrates the San Juan Basin quite well. This is Ojo Alamo Spring revealing the yellowish sandstonesof the Naashoibito. The Ojo Alamo Formation is exposed on the horizon in this shot.

References

D’emic, M.D., Jeffrey A. Wilson & Thomas E. Williamson (2011): A sauropod dinosaur pes from the latest Cretaceous of North America and the validity of Alamosaurus sanjuanensis (Sauropoda, Titanosauria), Journal of Vertebrate Paleontology, 31:5, 1072-1079

Fassett, J. E., R. A. Zielinski, and J. R. Budahn. 2002. Dinosaurs that did not die: evidence for Palaeocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico; pp. 307–336 in C. Koeberl and K. G. MacLeod (eds), Catastrophic Events and Mass Extinctions. Geological Society of America Special Paper 356.

Kues, B. S., T. Lehman, and J. K. Rigby Jr. 1980. The teeth of Alamosaurus sanjuanensis, a Late Cretaceous sauropod. Journal of Paleontology 54:864–868.

Lucas, S. G., and R. M. Sullivan. 2000. The sauropod dinosaur Alamosaurus from the Upper Cretaceous of the San Juan Basin, New Mexico. New Mexico Museum of Natural History and Science Bulletin 17:147–156.

Russel, D.A. 1992. The “Modern” Cretaceous in An Odyssey in Time: The Dinosaurs of North America. University of Toronto Press in association with the National Museum of Natural Sciences. ISBN 0-08020-7718-8.

Sampson, S. D., and M. A. Loewen. 2005. Tyrannosaurus rex from the Upper Cretaceous (Maastrichtian) North Horn Formation of Utah: biogeographic and paleoecologic implications. Journal of Vertebrate Paleontology 25:469–472.

Sullivan, R. M., and S. G. Lucas. 2000. Alamosaurus (Dinosauria: Sauropoda) from the late Campanian of New Mexico and its significance. Journal of Vertebrate Paleontology 20:400–403.

Wednesday, 12 October 2011

Amazingly Preserved New Theropod Announced


Meet the new guy on the block. This has broken out all over the paleoworld tonight and is causing quite a stir – and rightly so. Oliver Rauhut and his fellow workers from the Bavarian State Museum for Palaeontology and Geology made the announcement earlier today.
Found in Upper Jurassic sediments, around 150 million years old, the skeleton is incredibly 98% complete representing a juvenile theropod and is 72cm long. This small animal represents the most complete theropod ever found in Europe and one of the most complete in the world. The animal will be officially announced on October 27th in Munich and as yet has no official name or description but as you can see from this image, it is a spectacular specimen.

Fellow blogger Andrea Cau has initially described it as possibly a “compsognathid-grade tetanuran”  (with a proviso!) and very Juravenator-like whilst Tom Holtz has already mentioned that the animal has “.....some pretty big implications.” Expect the wires to be ablaze for days to come regarding this little guy!

Thursday, 6 October 2011

Pterosaur Sneak Preview


Just a brief post this week because of work commitments and features a sneak preview of one of the most wonderfully preserved pterosaur fossils I’ve ever seen. I’ll be featuring more of this spectacular specimen in the near future - it really does have to be seen to be believed. I will be back to normal posting next week.