Thursday, 31 March 2011

A Doorway into the Weald


It’s the eve of another field season and first up this year, as always, is Misty Bluff. Although there have been many blog entries regarding the Bluff, I thought it may be of interest to describe the quarry in some detail and put some meat on the bones as it were.

The quarry is situated in the south of England and is one of several that were once located around the area although the Bluff is now one of only two surviving brickworks and regular readers of this blog are aware that the Bluff is currently mothballed and no work is currently taking place although there is a small maintenance crew on site.

Exposures in the quarry are from the Weald Clay Group which, along with the Hastings Group, collectively forms the Wealden Supergroup. The clays and sandstones were deposited by rivers and lakes in a largely freshwater or brackish floodplain environment. These sediments in the Bluff are Early Cretaceous in age, Barremian and belong to the Upper Weald Clay Formation. The sediments exposed demonstrate a gradual shallowing from a lake or lagoon-like environment to a fluvial mud plain.

The Bluff has provided an extensive and diverse fossil record over the years and is an important mainland site. Although I primarily search for vertebrate fossils, the Bluff is renowned for its varied insect and plant faunas.

The insects are normally found in sideritic and mudstone lenses that crop out in various exposures. These include examples of termites, wasps, flies, beetles and lacewings. Other invertebrates found in these lenses include, ostracods, isopods and conchostracans, which are locally abundant in the light grey mottled silty clays, and the much rarer bivalve Filosina.

Filosina
Plant remains are relatively common at the Bluff. Marsh dwelling plants and ferns are those mostly recovered and are often found associated with insects in the aforementioned sideritic lenses as well as cropping out in other clay layers. Bevhalstia pebja is one of the earliest recorded flowering plants and is well known here. Other plants found include horsetails, club mosses and both conifer twigs and cones.

But for me, of course, it is the vertebrate fauna that is of the most interest. There have been some quite significant finds over the years – more than most people realise. By far the most commonly recovered remains are isolated elements and teeth. A lot of these can be quite scrappy and water worn but others are spectacularly well preserved. The bone can be either jet black or brown but is usually well mineralised and I haven’t seen a piece of bone yet that could be described as soft or flaky.

The earliest records of bone being excavated from the Bluff are from the 40’s and 50’s. Over a hundred bones belonging to multiple individuals of Iguanodon bernissartensis, Mantellisaurus atherfieldensis and also a titanosaurid sauropod were recovered. There were also many gastroliths found and all of these remains came from the sandstone exposures at the top of the Bluff and these are still producing today. The bones were often encrusted with pyrite and demonstrated both scuff marks and rounding off at the ends thus indicating probable fluvial transportation.

There have been at least three partial iguanodont skeletons excavated during the last 25 years. Two were recovered from the top of the northeast face and a third came from the southeast face and this specimen, which is a juvenile, has proven to be the most complete Mantellisaurus ever found in the UK.

The most famous discovery at the Bluff is, of course, that of Baryonyx walkeri in 1983. The story of its discovery has been well documented and continues to fascinate. To my knowledge there have been no further significant remains of Baryonyx found since then but teeth occasionally turn up and a few teeth were found in association with the Mantellisaurus skeleton mentioned above, which some workers have interpreted as evidence of scavenging. Baryonyx was also found on the southeast face and, indeed, the same horizon as Mantellisaurus. I am unaware of any other theropod remains but I imagine the chances are good of something showing up in the future.

Crocodile remains have turned up regularly over the years mainly attributable to Goniopholis sp. These are mainly teeth and osteoderms although there is also various postcrania found, including vertebrae, limb bones and ribs. Pterosaur remains are rarely found but they crop out every now and then and a phalanx bone was recovered last year.

Croc verts & osteoderm
Most dinosaurian and other reptilian remains are located in the clay and sandstone beds although Baryonyx was found in sideritic siltstone nodules. These nodules have also produced footprints and several have been found and excavated during the last few years in the southeast face but these appear to be isolated examples and a track way does not seem likely although there may be more to be found in the future.

Fish remains can be locally abundant and the most common fossils are those of Lepidotes mantelli and include scales, head plates, fin bones and teeth. Freshly exposed scales are beautiful and display a wonderful dark blue lustre. Occasional hybodont shark spines are found as well as Teleost fish and, back in 2005, an articulated pycnodont fish was found, the first ever recorded from the Wealden.

So it can be seen that the Bluff has been an important source of early Cretaceous Wealden fossils for many years now and will continue to be so as long as the quarry is worked. Before the site was mothballed we were informed that the next significant excavations were to be in the southeast face thus exposing more dinosaur bearing strata. Obviously, when this will take place is unclear but with an estimated supply of over 100 years of clay remaining, I think we can be fairly optimistic that new discoveries will continue throughout the 21st century.

Iguanodon caudal vertebra

A small croc tooth weathering out of the clay

Lepidotes scales

Monday, 28 March 2011

More Nanotyrannus

Funny how these things happen but bearing in mind my previous post the following is purely coincidental. In case you haven't looked at the blog list side bar, go and check out Michael Ryan's blog here. Yet more data from Witmer and Ridgely after CT scanning the Cleveland skull.

Of particular interest is the referral to "......new, as yet unpublished specimens." The fact that there may be other specimens of Nanotyrannus intrigues me, especially since any information regarding new specimens found attributable to this taxon would inevitably leak out. Perhaps it is yet more tyrannosaurid skull material of indeterminate nature. As I said previously, we'll have to wait for the paper.

More importantly, analysis reveals structures attributable to respiratory turbinates and this is incredibly interesting since this has significant implications regarding metabolic physiology. Really fascinating and I look forward to further revelations in the near future.

Thursday, 24 March 2011

At Last...........Nanotyrannus?

The Cleveland Skull
I recently became engaged in a lively discussion regarding the validity or not of Nanotyrannus lancensis. Everybody has an opinion of some sort. Mine at first was that it was indeed a valid taxon since the skull seemed to be totally fused, a sure sign of maturity and the original paper (Bakker 1988) stated as much.

Nanotyrannus never bothered me that much and as the years progressed it seemed more and more likely that it was going to end up being a juvenile Tyrannosaurus and more and more palaeontologists were convinced that this was so, although I was still unsure since nobody could explain the fused sutures in the skull.

Jane (BMRP 2002.4.1) was found by the Burpee Museum in 2001 as the first more or less complete Nanotyrannus ever found. Here, at last, was the specimen that would apparently confirm the taxon’s existence but even then, I thought, since we already had a complete skull and still couldn’t confirm its validity, the chances of validation were slim. Jane was ultimately described as a juvenile Tyrannosaurus – no surprises there then.

Larry Witmer’s recent paper (2009) which looked at the braincase region of tyrannosaurs was excellent. The “type” skull (CMNH 7541) of Nanotyrannus appears a conundrum. The skull demonstrates basal characteristics found in albertosaurines but also shared characteristics with Tyrannosaurus. Indeed, Witmer emphasises the fact that this skull is uniquely different from all other tyrannosaurs and not just T.rex.

As to why the skull is so divergent remains unclear. The skull has suffered a little minor distortion and displacement but not that much. Pathology also appears unlikely since there are no obvious signs of disease or tumours. Ontogeneric change appears to be the natural choice but even here there are dichotomies. The amount of difference in the skull cannot be put down to ontogeny alone. The skull does indeed display signs of maturity and yet fundamental differences remain and it is strange that the braincase of a Gorgosaurus juvenile (ROM 1247) is actually closer to Tyrannosaurus than the Cleveland skull is.

Some fascinating insights by the Witmer Lab and yet even here, the Nanotyrannus issue came out unresolved. In Witmer’s own words:

“Our data on CMNH 7541 may be taken as evidence for the validity of N. lancensis on the grounds that it is ‘‘too different’’ from T. rex. However, we are hesitant to argue that the debate over its status is settled for the simple reason of sample size. CMNH 7541 presents one specimen—one highly divergent specimen. Although we see no clear signs of distortion or pathology in the braincase, its divergent nature concerns us, and we maintain that the possibility remains that future discoveries will show CMNH 7541 to be aberrant. For that reason, we urge caution and continue to regard the specimen’s status as open.”

This brings us to a couple of weeks ago when the Nanotyrannus question raised its head yet again. For me the biggest single problem with the taxon is that there is only the one specimen – the Cleveland skull. Jane has been more or less defined as a juvenile Tyrannosaurus and this in itself is exceptional since juveniles of the species are unheard of. Even if Nanotyrannus was valid then where were the fossils? Granted that some tyrannosaurid post-crania could easily be misinterpreted as Tyrannosaurus even if it were Nanotyrannus, but the fact remains there is no other skull material.

And although Nanotyrannus is a “pygmy tyrant”, at maybe 16 to 20 feet in length, it is still a pretty big animal and you would have thought that more material related to the taxon would have been uncovered. And when you consider the rich diversity of fossils in the Hell Creek Formation (HCF) and the fact that Hell Creek is certainly the most sampled formation in the world, it is surprising that nothing else of note has ever turned up or been recovered.


“Nano” teeth are, however, fairly commonplace and are often labelled as simply tyrannosaurid teeth of uncertain affinities although they are markedly different from what I would consider conventional tyrannosaur teeth. But they are just teeth. It is possible, of course, that there was a form of niche partitioning during the late Maastrichtian and that Nanotyrannus avoided the territory of T.rex, thus avoiding the deltas and river channels and greatly reducing chances of fossilisation.. Maybe.

So I was a little amazed to hear that a lower jaw had turned up that would settle the debate once and for all! The dentary was recovered in 2006 from the HCF in South Dakota and I have to admit is a pretty impressive jaw except that it isn’t from Nanotyrannus. No – it appears to be clearly from a juvenile Tyrannosaurus. I would love to share a couple of images of this jaw but have been requested not to do so just yet and that’s fair enough as far as I am concerned.

The dentary is about 0.4 metres in length and has all of its teeth of which some are huge. The bone is very robust and strong and the big Tyrannosaurus-like teeth are up to about 60mm in length. I believe that the jaw has been prepared at the Field Museum of Natural History in Chicago but feel free to correct me if you know different. The jaw is currently being described by Pete Larson of the Black Hills Institute who, I am led to believe, regards it, and I quote, as the “smoking gun” which will confirm that Nanotyrannus is a valid taxon.

On the face of it, I can see why this would seem to be the case. This dentary is markedly different from both the Cleveland skull and Jane and is very Tyrannosaurus-like. Very powerful with very big conical robust teeth. So if this is a juvenile Tyrannosaurus (and it really does look like it is) then it appears that Jane actually is the most complete Nanotyrannus ever found. Right? Well maybe.

The problem I have with tyrannosaurid phylogeny is that they are extremely similar morphologically. I don’t like keep going over old ground but there are obvious problems defining taxa. As I keep alluding to, the debate over ceratopsian lumping and splitting goes on and the same problems exist in defining tyrannosaurids. The fact that Jane has been declared a Tyrannosaurus suggests that, if it indeed exists, Nanotyrannus is so similar to Tyrannosaurus as to make no difference. And I’m still not convinced because of the lack of detailed fossils.

So for me, the debate goes on and that, for now, I remain to be convinced about the validity of Nanotyrannus. The old adage “wait for the paper” was never better realised than in this particular case. Not only the Larson paper but whatever happened to the new Bakker, Currie and Larson research as well? We will see.

In any event, as I commented earlier, I’m not too bothered either way. If Nanotyrannus exists – fine, if not then Tyrannosaurus remains as the last its kind but it will be a great day when the Nanotyrannus saga is finally put to bed forever. Until the next one that is!

References

Bakker, R. T., M. Williams, and P. J. Currie. 1988. Nanotyrannus, a new genus of pygmy tyrannosaur, from the latest Cretaceous of Montana. Hunteria 1:1-30.

Witmer, L.M. and Ridgely, R. C. 2009. New insights into the brain, braincase, and ear region of tyrannosaurs (Dinosauria, Theropoda), with implications for sensory organization and behavior. The Anatomical Record 292:1266-1296.



Thursday, 17 March 2011

Quarry 4 - The Last Field Trip


We all returned to Quarry 4 in mid-December and this was the first time in ages that we had all managed to meet up since early Spring. How fitting this would prove to be since, although we did not know at the time, this was to be our last ever trip to the quarry.

We all knew, however, that it was indeed likely to be the last visit for some time because Winter had well and truly set in and when the clay gets sodden and the water builds up, conditions become impossible. So it was good to meet up with everyone and catch up on all things palaeo.

Again we were lucky with our choice of day. The weather had been poor the weekend previous and the following weekend, after this trip, was even worse. Temperatures were reasonable and the clay underfoot was just about walkable so it appeared conditions were tolerable.

As we made our way down into the quarry it was obvious that there was a lot more water build up than first appeared. It seeped through every footprint we made and clay that was firm underfoot was at a premium. We walked to the back of the quarry and saw that the breech in the corner was still pouring plenty of water into the quarry.

We all made for the same spot where Cliff had found his Liopleurodon tooth previously. Carl and I both had an idea that the tip of that tooth may be hidden in the clay somewhere where the rest of the tooth had been found and this was only a few yards away from where I had also found a Peloneustes tooth. In fact this small area had produced quite a few teeth throughout the year.

But now it was much wetter and muddier. The water breech in the quarry wall was also bringing other clay and silt into the area and it was increasingly harder to walk and locate any fossils. However, it had only been five minutes (again!) when Cliff, who was only a few yards form Carl and myself, promptly found yet another Liopleurodon tooth!

We could hardly believe it – a second tooth from the giant pliosaur and found within a couple of yards of where the first one was found. This was really unusual and for the first time we all began to think that there may more than just teeth from this animal. If not that, then maybe there may have been some sort of natural eddy or current that had washed these teeth to this spot – a sort of tidal collection point if you like.

After admiring the tooth and commenting on the colour of a certain part of Cliff’s anatomy, we all returned to the search determined to see if we could find more. Unbelievably, just as we turned our backs and returned to our spots, Cliff, in his matter-of-fact way, said “Here’s another one.” A third Liopleurodon tooth! Now this was unheard of and we quickly reassembled to discuss the matter.

Three teeth and we wondered if they could be from the same animal. Indeed Cliff had brought the previous tooth with him and we were able to compare. Strikingly, they did indeed look like that they may be from the same animal – indeed maybe even from the same dentary. We were starting to believe that there just might be some important Liopleurodon material not far from being unearthed.


At this point I mentioned the big pliosaur vertebra that I found previously and it was apparent that this had been found only about 50 yards away from where these teeth were coming to light. We were all a little excited and started to believe that there may be more to find of this animal for sure.

We searched the area as if our lives depended on it but no other fossils were forthcoming. Conditions were made worse by the fact that there were four of us searching the same small area and we were churning up the clay simply by walking around. Eventually we all moved on.

The rest of the session was simply prospecting as best we could, walking through the clay mire, hoping to glean some surface finds. But apart from Cliff locating some more scrappy Leedsichthys bone, there was not a lot forthcoming although there were several small fish coprolites recovered, a couple of which seemed to have inclusions present.

As time moved on it was obvious to all of us that were would not be too much more to be found. I decided to return to the Liopleurodon zone for a final look – just in case. I spent another twenty minutes or so scouring as best I could but to no avail. Little did I know that I was to be the last person ever to search that particular spot.

Soon after, we all returned to the cars to discuss the day’s events. We realised that it was quite likely that there were more Liopleurodon remains to be found and were hopeful of returning to Quarry 4 early in 2011. However fate was to take a hand and we found out only a few weeks later that the quarry had been closed.

As we entered 2011, it was apparent that things were changing and any future work would be done in the same formation but in Quarry 5 and, at last, we received the news that we had gained access during the Spring. This was a huge relief but was tempered by the fact that control of entry would be much tougher, although this would be good for fossil collecting since this quarry was very secure - almost inaccessible.

So began a period of waiting – waiting for new disclaimer forms, new permits and, most of all, for news of when we could visit the quarry for the first time. We were in a period of transition and this period of not knowing made all of us a little restless.

Wednesday, 9 March 2011

More on Ceratopsians


I thought it was time for some more selected snippets from last years SVP meeting, this time focussing on ceratopsians. I’ve been doing a few of these retrospective posts on last years meeting simply because not everyone has access to these details and new information is always appreciated about work going on in the world of vertebrate palaeontology.

To the detail then and yet more data that may throw more light on the Triceratops/Torosaurus dichotomy. Penkalski and Skulan displayed an interesting poster about remains from two partial chasmosaurs from a quarry in Carter County, Montana (Hell Creek Formation). This is interesting since the authors interpret the remains as showing characteristics from both Triceratops and Torosaurus.

Examination of various elements such as the parietal, squamosal, dorsal vertebrae and humerus all display morphological differences, some subtle, others more so, that appear to indicate the presence of both taxa in the quarry. The authors suggest that the remains may indicate the presence of a new taxon (unlikely in my opinion), or that these are sexual diamorphs of Triceratops or that these are, indeed, specimens of both Triceratops and Torosaurus that were simply fossilised together after deposition.

Bearing in mind the continual discussion regarding the synonymy of both taxa, I do tend to favour that these specimens are both Triceratops but it will be interesting to see if there will be a detailed taphonomic study of this quarry.

This brings me nicely to Clayton et al’s poster demonstrating a revised look at the epiparietal homology of chasmosaurs. The “et al” in this instance is the not to be sniffed at trio of Mark Loewen, Andy Farke and Scott Sampson, so the data here is clearly not to be ignored.

They have come up with a new method of classifying chasmosaurine epiossifications which, in conjunction with both newly discovered centrosaurs and chasmosaurs from the Kaiparowits Formation, may help in the continual discussions regarding what are and what are not valid taxa. They reach a number of conclusions but, of course, the most interesting outcome is that Torosaurus is indeed recovered as a valid taxon, distinct from Triceratops. The authors also list other reasons for this such as the existence of morphs of both taxa that are of similar size, the apparent existence of sub-adult torosaurs, and the fact there are formations where fossils of Torosaurus are found but not Triceratops. Thus this debate looks likely to rumble on for some time.

Denver Fowler’s presentation, on the other hand, demonstrates how a combination of stratigraphy and ontogeny influence morphology in chasmosaurines. Using this framework reveals that southern chasmosaurs are likely to be earlier Maastrichtian variants of a Triceratops clade. Adult morphological traits of these earlier forms occur earlier in ontogeny than they do in Triceratops thus supporting earlier trends already highlighted within the clade.

Additionally, it appears that these same trends occur in the late Campanian and two new chasmosaurs from the Kirtland Formation in New Mexico come out as intermediate taxa between Pentaceratops and Anchiceratops, thus consolidating earlier work showing Pentaceratops and Anchiceratops as sister taxa.. Because of this combination of morphological traits that are clearly separated stratigraphically, the author interprets this data as good evidence of anagenesis within Chasmosaurinae. The paper, when published, which demonstrates the new framework and the methodology used, will be compelling reading. Incidentally, Fowler was also co-author of a poster with Liz Freedman, utilising similar techniques describing anagenesis in Hadrosaurs.

Finally, Pachyrhinosaurus lakustai is a ceratopsian known from a monodominant bone bed in Alberta, Canada. The various sized recovered elements were classified as adult, sub-adult and juvenile and, to demonstrate whether this hypothesised ontogenetic growth stage actually had a factual base, Joseph Fredrickson from the University of Wisconsin, ran a detailed cladistic analysis using 67 hypothetical growth characters from 42 specimens.

Fascinatingly, instead of the expected three stage growth series, the analysis reveals a continual ontogenetic growth which appears to split at maturity and may be indicative of sexual dimorphism. Although both morphs have seven identical traits at maturity, one clearly displays another seven defining characteristics including a rostral comb and a tall nasal boss. The other morph is also characterised by six unique traits including a long nasal boss (as opposed to tall) and straight caudal parietal horns. Thus, this analysis has revealed that original diagnostic characters for the taxon are, in fact, only present in one of the adult skulls (probably male) and not in the other skulls – so these are almost certainly female



References

Clayton, K, M. Loewen, A. Farke, and S.D. Sampson 2010 A re-evaluation of epiparietal homology within chasmosaurine ceratopsids (ornithischian) based on newly discovered taxa. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2010, 73A.

Fowler, D.,2010 Anagenesis and long term morphologic trends in Chasmosaurinae (Dinosauria: Ceratopsidae) revealed by a new high resolution chronostratigraphic framework, ontogenetic analysis and description of two new taxa. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2010, 91A.

Frederickson, J., 2010 Craniofacial ontogeny in Pachyrhinosaurus lakustai: evidence for sexual dimorphism in an ornithischian dinosaur. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2010, 92A.

Freedman, E and D. Fowler.2010 Stratigraphic correlation of Judith River Formation (Campanian, Upper Cretaceous) exposures in Kennedy Coulee (north central Montana) to the Foremost Formation (Alberta): implications for anagenesis in hadrosaurid dinosaurs. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2010, 92A.

Penkalski, P and J. Skulan.2010 An unusual ceratopsid quarry from the Hell Creek Formation of Montana. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2010, 145A.

Thursday, 3 March 2011

Still Producing

The following post is one of the final two entries regarding field trips to Quarry 4 before its eventual closure.

During November, it was obvious that Autumn was fading away and that the full effect of winter was on its troublesome path. The amount of rain was increasing and the temperature was dropping rapidly. It had been hard to visit Quarry 4 for some time because we all had other commitments but we all knew that trips would become extremely limited this winter.

Firstly, now that the quarry was no longer being worked, water build up would be considerable since there were no new trenches and there were no pumps to keep the water level under control. Secondly, it was now that the quarry was due to be flooded anyway. Although the date was not cast in stone, it was always a possibility that this could happen. So we planned a trip for early November.

The weather in the immediate couple of weeks leading up to the trip was a bit of a mixture. Although there had been quite heavy rain, this was interspersed with some dry days and I figured that conditions would not be too bad. Mark couldn’t make the trip because of a back problem so it would be Cliff, Carl and myself.

The weather was forecast to be kind to us on the day and sure enough it was a bright sunny morning as I pulled up to the quarry. Cliff was already there and it was only 5 minutes more when Carl joined us. We quickly kitted ourselves up and made our way into the quarry. Initially the quarry looked fairly water free but looks can be deceiving.

As we dropped into the quarry it became obvious that the quarry was extremely wet and cloggy underfoot but still there was no surface water. We headed to the area that was the most productive throughout the year as I wanted to look for more teeth and this area had produced several teeth during the last few trips.

However there had been a natural breech in one corner of the quarry wall and a fair torrent of water was gushing in. It brought down with it some of the surrounding clay and discarded bricks that lined the edge of the quarry. The main tooth bearing area was flooded and the fish bearing strata was also under water. Not much but enough to be a pain and the water was interspersed with little islands of clay that could be searched.


Undeterred we started to prospect. Cliff had already picked up a delightful little digit bone from a plesiosaur when he spotted a piece of rib sticking out from one of those little dry spots, only a few yards away from where the water was pouring in. As he cleaned it off, Carl pointed out that he actually had a massive Liopleurodon tooth.

We could hardly believe it! Although the tip was missing the tooth was truly massive, as big as some tyrannosaur teeth. Although it wasn’t as pristine as Carl’s tooth (see here), what it lacked it completeness it made up for in attitude. A truly wonderful example. We all busily returned to the hunt.

Cliff really started to produce the goods finding a super Hypsocormus jaw with a few in situ teeth and yet another nice vertebra from the ichthyosaur bed. There is obviously a disarticulated specimen somewhere in the area but finding it is impossible although the odd bone keeps popping out and further recovery seems unlikely if the quarry is flooded.

He also found yet more scrappy Leedsichthys bone and another superb belemnite. While he was doing this Carl and I were struggling although Carl slowly started to get his eye in and found a small plesiosaur tooth and metriorhynchid tooth. I, on the other hand, was finding it hard but that’s how it is sometimes.

As the day wore on we slowly covered a large area of the quarry although nothing of significance could be found. We returned to the Lepidotes bed and sure enough recovered yet more scales although it was apparent that this area was becoming exhausted.

We called it quits later in the afternoon and made arrangements to meet again. We hoped to get down during December for one last trip before Christmas – flood waters permitting. Every trip to Quarry 4 may be the last one now so we intended to make the most of it.

But admittance to Quarry 5 really was edging closer now and we all hoped to move onto pastures new in the new year.