New discoveries - Heterodontosaurus

Have a look at the cover of the latest newsletter of the PSSA (Palaeontological Society of South Africa). This is one of two new skulls of Heterodontosaurus that Billy De Klerk has found in the Elliot Formation of South Africa. It seems Billy is O.K. with showing them off to the world before he publishes on them, so I don't think there should be any problem with me posting this picture here. Things to note: the premaxilla fails to contact the lacrimal (a lacrimal-premaxilla contact was one of the proposed characters linking Heterodontosauridae to Ornithopoda)and the angular (ventral edge of the lower jaw) has a Yinlong-like rugose boss. There is a complete postcranium to go with this skull - so we can expect even more information on these rather wierd, early ornithischians in the nearish future.

Another squamate post - Acontias gracilicauda

Photos by Matt Bonnan

No time for an in depth post today, so I'm keeping the squamate theme going with a picture from my archives. This is a legless skink (Acontias gracilicauda)that happened to have made it home directly above an early Jurassic sauropod bone bed. So it had to be relocated. There is a moderate diversity of acontine skinks in southern Africa: they are just one of many lizard lineages, apart from snakes, that have beome completely limbless.

Happiness is a bucket of lizards

One of the aspects of academic life in a small research institute is that you are sometimes called upon to supervise student projects that are outside your normal sphere of research activities. Broadening your experience and knowledge can only be a good thing so I welcome this. It also can provide an outlet of unusual activities that can break the monotony of the usual working week.
I am currently supervising one such project that is proving to be quite entertaining. The project is centred upon the almost entirely neglected herpetofauna that occurs alongside the famous Australopithecus fossils of the Cradle of Humankind World Heritage Area.
I found out, much to my surprise, when this project was started that there are no comparative osteological collections of southern african reptiles available in South Africa. So we have had to set about creating one. Fortunately we have been given permission to prepare the skulls of duplicate specimens from the Transvaal Museum collections. I was very pleasantly surprised at the breadth of the taxonomic scope we were supplied with - two specimens of over 40 species from the eastern half of
South Africa. So it was with some excitment that we took consignment of the above pictured and rather full bucket of lizards (Can anyone name the species visible? I'd be impressed if someone managed five or more).
Of course it is the students job to prepare the skulls, but with so many to get through, I've been mucking in and helping with the defleshing, which is surprising satisfying work, especially when you finish with a nice clean skull.

Early Jurassic side-winder - but is it a snake?

Francois Durand's side-winding trace from the Clarens Formation. From Durand (2005.

Discussion about fossil side-winding traces over at Tet Zoo prompted me to get off my butt and actually put something up on this blog.
Its Francois Durand's apparent side-winding trace from the Clarens Formation of South Africa. Not much has been made of this and the only two references to it that I know of are rather obscure so I'm putting it up here to let people know about it.
It certainly looks like a track left by a modern sidewinding viper.



A modern side-winder

Francois made it fairly clear in his presentation of this fossil to the Geoscience Africa conferance back in 2004 that he thought it was made by an Early Jurassic viperid although he only hints at this in the two publications featuring this fossil that I know of. Such an occurence is strongly at odds with the known fossil record of snakes. Even the most primitive snakes don't show up until the Cretaceous, and advanced snakes like viperids don't start radiating until well in the Cenozoic, thus to have a Jurassic Viperid means that just about all tradtional family level clades of snakes have massive ghost lineages stretching back tens of millions of years. The fossil record can be spotty but it ain't THAT bad.
My take is that sidewinding habit may have evolved sporadically from time to time in all sorts of elongate limb-reduced tetrapods when the conditions warranted it. The whole discussion started over the possible sidewinding traces from a Permian, wet muddy, if not aquatic environment that I had a hand in describing.If correctly interpreted sidewinding need not be restrited to dry loose sand, wet sloppy mud might be just as capable of supporting it.
So what was elongate sidewinding tetrapod of the Clarens? We haven't a clue.

references

Durand, J.F. 2004. The origin of snakes. Geoscience Africa 2004. Abstract Volume, University of the Witwatersrand, Johannesburg, South Africa, pp. 187.

Durand, J.F. 2005. Major African contributions to Palaeozoic and Mesozoic
vertebrate palaeontology. Journal of African Earth Sciences 43: 53-82.

Access Denied! When ignorance stops science

I've been back from my field trip for exactly a week now, but I simply haven't found time to blog at all. The field crew was a large one and juggling the group was logistically difficult - especially in the face of having to make up new plans on the spot, when the old ones fell through. What went wrong? I'll tell you.
The trip was originally planned to continue work began last year by a joint Wits - BSP (Munich) expedition with a small contingent (Richard Butler) from the NHM (London). This trip began exploration and collection in the historically rich Herschel district of what is now the Eastern Cape. As a breif primer it was this district that produced the holotypes of Melanorosaurus readi, Plateosauravus cullingworthi, Heterodontosaurus tucki, Blikanasaurus cromptoni and Stormbergia dangershoeki as well as a some of the best specimens of Massospondylus carinatus and the spectacular complete skeleton of Heterodontosaurus (not the holotype).
Politically the area is a difficult one to work in because historically it was an isolated fragment of the Transkei, a 'homeland' for black south africans - not to dissimilar to Indian reservations in the US. Although integrated with South Africa in 1994, the Herschel district has remained in dire poverty and partly under the old governance of cheifs and big men. The national government has however set up wards and councillors who are supposed to work together with the traditional rulers.
It was some trepidation that our team stepped into this region, with the view of exploring this territory. One of our goals was placing new positively associated and identified dinosaur specimens on accurately measured strat sections to better understand dinosaur distributions through the Elliot. We also just wanted to see what else we could find to flesh out the fauna of the Elliot - many taxa are still known from single specimens and new discoveries are made often enough to indicate that the discovery curve for the Elliot is not yet near a plateau.
We decided that Blikana Mountain - magnificent area of near continuous outcrop would form the basis of our search effort. After contacting the local councillor responsible for Blikana and meeting with her we were granted permission to explore and excavate.
Although the region has a fearsome reputation we found the locals friendly, somewhat bemused by our interest in stones and eager to help. Many knew about fossilised bones and told us about likely sites.
Thus when we returned this year we were hoping this good relationship would continue. Alas it was not so.
Immediately upon arrival we knew something was up. We had to meet with the councillor in town and under no circumstances set foot on Blikana. It turns out that the councillor was not going to grant us access because she claimed some residents of the area thought we were digging up the bones of their forefathers and robbing their graves and she supported their concerns. It seems the problem started when we showed the councillor herself some of the dinosaur bones we were looking for and gave them to the local school for educational purposes (isolated surface bones are generally abundant). This part of South Africa must be one of the very few places on Earth where the general population has never heard of dinosaurs. Sadly the councillor was unwilling to listen to our explanation that these bones predated any human and were certainly not hers or anyone elses ancestors. Reason didn't seem to work when we pointed out that these bones patently couldn't even fit inside a human body. I suspect that there was more to the problem than was being stated, perhaps we were a difficult problem and the councillor simply wished us to go away. Afterall the elections are near, there has been a split in the ruling party and tensions are running high. No politician wishes to stick their neck out at times like these. Another argument levelled at us was that we were giving no benefit to the locals. Here we are fighting an insidious meme that unfortunately has deep roots in South Africa, that is science = colonial imperialism. Sadly we could not convince her that our science uncovered important natural heritage for all South Africans, indeed all people of the world to share.
In anycase the exposures of the Elliot Formation are simply too good to ignore (they are the best in South Africa), it seems we will have to embark on a campaign to raise local awareness of the important natural heritage that lies beneath their feet.

Egg Eating Snake

Moving to a new continent is a simulataneous joy and frustration for those with a naturalist bent. On the plus side there is a whole new fauna and flora to discover. On the downside until you become very familiar with it you often haven't got a clue what you find is. This happened to me on a recent short field trip to Golden Gate Highlands National Park. The trip was a total washout, heavy rains and bad weather made it unpleasant in the field and had caused a rockfall that obscured much of the site we wanted to investigate. However while scrabbling around the rockfall I found this beautifull little snake. I didn't know it at the time but I had found a rhombic egg-eater (Dasypeltis scabra), a member of a fascinating group of snakes I had always wanted to see. Sadly I thought it was a night adder so treated it cautiously I didn't give it a very close look. Night adders are quite venemous whereas egg eaters are virtually toothless and quite harmless (unless you happen to be a small bird egg). Only later when I was back home did I identify what it really was.

A little about Dasypeltis snakes for those who don't know. They are an african genus of colubrids that are adapted to feeding exclusively on bird eggs. They are capable of swallowing eggs up to three times the width of their head. They have highly reduced dentitions and use ventral projections from the vertebrae in the gullet region to pierce the shell. The liquid contents are swallowed and the collapsed shell is regurgitated. I would love to see this in action, but my little guy was just sheltering from the bad weather when I found him.

Worst case of mistaken identity since Aachenosaurus!

OK on with Fish fortnight,
Aachenosaurus is an infamous a case of misidentification where some pieces of petrified wood were mistaken for dinosaur bones, and a name was coined for them in the literature. The small pieces of bone in the photos above were also strikingly misidentified in the BPI catalogue as belonging to a dinosaur (though fortunately never published as such). They actually belong to a fish, a ray-finned fish (actinopterygian) to be a little more precise. As fish they are very interesting because the come from the upper Elliot Formation, and as far as I can tell are the first recognized ray-finned fish from this unit (lungfish are known from the odd small toothplate here and there). The upper Elliot Formation was deposited in arid conditions with most of the streams being small and ephemeral. Nonetheless ray-fins can’t cocoon themselves when their pond dries up the way some lungfish can and their presence indicates that some permanent water bodies, however small, existed on the upper Elliot floodplain. That’s all I can say about this fish right now - the fossil will be subjected to further prep and study.

The littlest sauropodomorph?

The known remains of Thecodontosaurus minor, the scale bar was added by me but the rest is taken directly from Haughton 1924

What better way to kick off the new year but with a post about basal sauropodomorphs from South Africa?
In 1918 Sidney Haughton named a small collection of tiny sauropodomorph bones from the Elliot Formation, near the town of Maclear, Eastern Cape, as Thecodontosaurus minor. There isn’t much to the specimen, just a cervical vertebra, a tibia and a fragmentary ischium. This little guy has remained in almost complete obscurity ever since it was named. All recent treatments that even give it a mention regard it as either a nomen dubium, or as a synonym of Massospondylus carinatus. However there are some odd things about these remains that suggest this taxon deserves a closer look. Firstly it is very small, with the tibia just over 10 cm, a length not much greater than that of Microraptor zhaoianus which is widely cited as the smallest non-avian dinosaur. Usually T. minor is dismissed as a juvenile but this is not necessarily the case because it appears that the neurocentral suture of the cervical vertebra is closed. I freely admit that I’ve only ever given the specimen a cursory look, and that this needs to be checked more closely. If it is closed then it would indicate the individual was approaching maturity. One does have to be careful when using the closure of neurocentral sutures to age a dinosaur but in this case there is abundant evidence that basal sauropodomorphs did not close their neurocentral sutures until close to maturity, or even after adult size had been reached. Indeed the majority of all presacral vertebrae preserved in the basal sauropodomorph record have separated along their neurocentral sutures. Now if T. minor really is a mature, or near mature individual, then it would have the smallest known adult size of any sauropodomorph. Just for fun here is the silhouette of a small sauropodomorph scaled to a tibia length of 10 cm, next to the hand of Brachiosaurus brancai.

So what else is odd about this taxon? Well the ischium is a little odd. Although incomplete there is a short stretch of the ischial shaft preserved behind the proximal obturator region. This shaft is unusually flattened, whereas most basal sauropodomorphs, have an ischial shaft that has equilaterally triangular cross-section. Amongst basal sauropodomorphs I’ve only seen this type of flattened ischial shaft in Thecodontosaurus, Anchisaurus and Mussaurus. By itself this isn’t enough to hang a taxon on but it is enough to reject synonymy with Massospondylus (unless of course there is postmortem crushing at play, or I've misjudged the amount of ischial shaft that is present).
However there is one other aspect of this little fossil that has me kicking myself for not looking more closely at it when I had the chance. It would appear that this little fossil comes from the lower Elliot Formation. This became apparent after I read the original (unillustrated) description, rather than Haughton’s later 1924 illustrated monograph on the fossils of the Stormberg group. Quoting the 1918 paper the horizon in which this specimen was discovered was the “Red beds, just below halfway from base”. As I’ve mentioned before on this blog ‘red beds’ is the old name for the Elliot Formation and this Formation comes has two members, of different age, depositional style and fauna. At the southern end of the outcrop area (where Maclear is located) the lower Elliot makes up about two thirds of the stratigraphic thickness of the Elliot Formation, placing T. minor in the lower Elliot and puts paid to any notion that the specimen is a juvenile Massospondylus. This is remarkable for the sauropodomorph fauna of the lower Elliot consists entirely of large robust forms. Indeed small vertebrate fossils of any sort are exceedingly rare. Indeed there are only two named taxa that would have massed less than 50 kg as adults: the ornithischian Eocursor and the trithelodontid cynodont, Elliotherium, both of which are based on unique specimens. A minute sauropodomorph from the Triassic of South Africa would be an interesting and welcome addition.
So is T. minor a valid taxon? That is a difficult question. The known remains do not present any obvious autapomorphies other than its tiny size. If it can be confirmed either by histological sampling of the tibia, or micro ct scanning of the cervical vertebrae, that these are indeed the remains of a mature individual then, yes I think it would be a valid taxon, though just barely (on the basis that it can be excluded from all other known Triassic sauropodomorphs on the basis of size and the mix of characters it displays). Sadly the known remains are utterly inadequate for narrowing down its phylogenetic placement among basal sauropodomorphs, it could easily fall anywhere between Thecodontosaurus and Melanorosaurus. So there is little justification for keeping it in Thecodontosaurus, a new name will have to be coined for it but I think that that action would be best held off until such time as better remains come to light. I just hope that I might find some on my next field excursion.

References

Haughton, SH (1918) On a new dinosaur from the Stormberg beds of South Africa. Ann. Mag. nat. Hist. 2: 468-469.

Haughton, SH (1924) The fauna and stratigraphy of the Stormberg series. Ann. S. Afr. Mus. 12: 323-497.

Dracovenator by request: the age of the Elliot

Randy and Bill asked an apparently simple question that will require an involved answer. What age is the Elliot Formation? What follows is a detailed account of my thoughts that will probably get to technical for those without a geological bent.
Still here? Great I’ll try to make it worth your while. As I mentioned in the last post the Elliot Formation occurs near the top of the vast sedimentary pile that fills the famous Karoo Basin of South Africa. It underlies the Clarens Formation and overlies the Molteno Formation. Dating the formation is difficult as there is little to constrain it, there are no known ash or lava beds within it that have been radiometrically dated, and the formation lacks any marine microfossils or palynomorphs (spores and pollen) that could be used to date it. The upper constraint on its age comes from the Drakensburg lavas that overlie the Clarens Formation. These represent a rapid pulse of volcanism that is precisely dated to 183 million years ago, which places it at the Pliensbachian-Toarcian boundary of the Early Jurassic in the timescale of Gradstein et al. (2004). Thus the Elliot Formation cannot be any younger the Toarcian-Pliensbachian boundary. At the other end, the constraint on the maximum age of the Elliot Formation is much woollier. The Molteno Formation is said to have palynomorphs of Carnian age, but this is a thick unit and it is not known how much younger the upper parts of the Molteno Formation gets. Furthermore it is now know that terrestrial ‘Carnian’ deposits (e.g. the famous Ischigualasto Formation of South America) actually correlate with the latest Carnian to early Norian stages of the marine sequence. A Carnian/Norian age for the Molteno Formation is also supported by the vertebrate fauna of the Pebbly Arkose Formation of Zimbabwe which is presumed to be a lateral equivalent of the Molteno Formation. This fauna consists of a rhynchosaur and a primitive dinosaur that resembles Saturnalia (which comes from the ‘Ischigualastian’ of Brazil). Thus the Elliot Formation is unlikely to be any older than the Early Norian (about 225 million years old). However this is a huge spread of time, about 42 million years in fact, can we narrow it down any further? Before we examine this question we need to dispel a common model for the deposition of the Elliot Formation which is often portrayed in the literature. This is the model of continuous deposition. This figure (taken from Holzforster 2007) is typical.

In this diagram the Elliot Formation is portrayed as filling the entire block of time between the Molteno and Clarens Formation. However this is not realistic. Deposition in the Karoo Basin was controlled by subsidence in response to tectonic activity in the Cape Fold Belt. Tectonic activity is rarely, if ever, continuously sustained over tens of millions of years. Further the sediments themselves show evidence being deposited in discontinuous pulses. The lower and upper members of the Elliot Formation represent two such pulses. Although no angular unconformity or extensive erosional surface separates these two members there is evidence that there was a non-depositional gap between the deposition of these two units. Firstly we have the wholesale changeover in fauna between the two members. There is no known vertebrate species or genus that occurs in both units. There are also lithological differences that indicate that the style of rivers crossing the floodplain had changed, from sinuous, deep permanent streams to shallow emphemeral braided streams. The latter seems to be coupled with a more arid climate which is also betrayed by other indicators of aridity such as the development of extensive calcareous paleosols, deeply muckcracked overbank horizons, and evidence of floodplain denudation during flash-flood events. Other features such as palaeocurrent indicators suggest that the overall direction of drainage also changed as did the source of the sediment. These features could have suddenly ‘switched’ but a time gap allowing these features to change more gradually seems far more likely.
So if we accept two pulses of deposition what age constraints can we put on them? There is little doubt now that the first pulse was Late Triassic in age. I’m currently preparing a paper describing rauisuchians from the Elliot Formation. They have been reported before but this will be the first time the identification will be based on diagnostic derived characteristics. If we accept that rauisuchians went extinct at the end of the Triassic then these occurrences certainly place the lower Elliot in the Triassic. But where in the Triassic? Geology can help us a little here. According to the model of Catuneanu et al. 1998 and Bordy et al. 2004 the deposition in the part of the Karoo basin where the Elliot Formation crops out occurred during an offloading phase when the Cape Fold mountains were shedding sediment after a mountain building event. During the offloading phase the more distal part of the basin (where the Elliot Formation lies) sags after bulging upward, creating accommodation space for the sediment to collect in.


The reciporical flexural model for basin development, as applied to the deposition of the lower Elliot Formation. Part of a figure from Bordy et al. 2004.

Structural and metamorphic geologists date the end of the mountain building event that is believed to have immediately preceded the deposition of the lower Elliot Formation to 215 million years, give or take 3 million years. This puts the lower Elliot in the mid to late Norian, maybe even extendig into the Rhaetian (depending how long the offloading phase lasted after the mountain building finished) as Randy suggested. Whatever its age I’m willing to bet that the lower Elliot Formation is more or less equivalent to the vertebrate-bearing horizons of the Los Colorados Formation based on similarities of their sauropodomorph faunas. These similarities include Lessemsaurus and Antetonitrus which are very, very similar (though a few telling differences do keep them as separate taxa, e.g. the proportions of metatarsal I). Eucnemesaurus (ex Aliwalia) is also extremely similar to one of the taxa lurking under the label ‘Riojasaurus’.
OK so that’s the lower Elliot, what about the upper Elliot? Here we don’t have ahelping hand from geology. A pulse of mountain building after 215 million years has not been detected (indicating it was a minor event).
Faunally the upper Elliot Formation contains taxa that seem to indicate an Early Jurassic age (e.g. the crocodyliform Protosuchus and a diversity of ornithischians) but this is rather weak reasoning. Nevertheless I think an age younger than the Hettangian one usually assigned to the unit can be supported on the following grounds:
1. The same biozone (the Massospondylus Range Zone)can be found from the beginning of the upper Elliot through to the top of the Clarens. Fossils are extremely rare near the top of the Clarens but Billy De Klerk of the Albany museum has collected a couple of good Massospondylus skeletons, that if I recall correctly, come from near the top of the Clarens. Basically the fauna of the Clarens is a depleted subset of what you find in the upper Elliot (easily explained by the limited sample from the Clarens). The only possible faunal change is that the little trithelodontid cynodont, Pachygenelus, might be replaced by a different trithelodontid, Diarthrognathus, in the Clarens. This suggests to me that we aren't dealing with a large span of time. Dinosaur genera seem to turn over every five million years or so, thus we are probably dealing with a duration in this vicinity for the entire upper Elliot to Clarens sequence.
2. The deposition of the Clarens is terminated by a sudden and precisely dated volcanic event - the eruption of the Drakensburg lavas which is dated to 183 million years.
3. There is no evidence of a time gap between the Clarens Formation and the volcanic eruptions. Indeed there is evidence that one followed the other without a hiatus. For instance in some localities lava flows can be seen to have filled the interdunal spaces in the Clarens dune desert. Clarens deposition seems to have continued after the eruption of the first few flows in some places. A great example can be seen on the road between Barkly East and Rhodes in the Eastern Cape. Lastly there is evidence that the volcanism was begining during the deposition of the Clarens - as is shown by the Clarens filled crater reported by Holzforster (cited in my last post). It would be great to get a date for the pyroclastic flows that form the basal layers of this crater but sadly no-one seems to have done it yet - any young geochronologist looking for a project?
4. So if we accept that the end of the Clarens can be precisely dated to 183 million years AND we only allow a duration of 5 million years or so for the Massospondylus Range Zone then the begining of the upper Elliot Formatio dates to the Early Pliensbachian (about 188 million years). Perhaps we could allow a few million years to have elapsed right at the end of the Clarens, before the volcanic lava flows began spilling out over the basin, and allow a rather long duration for the Massospondylus and its cohabitants but that would still only take us down into the late part of the Sinemurian.

There you have it. My guess is that the lower Elliot is mid-late Norian, there is a hiatus of about 15 million years before the upper Elliot and Clarens which probably span most of the Pliensbachian. How can this be tested? Detrital zircons would be a wonderfull source of data - once again any young geochronologists out there looking for a project?

references

Bordy EM, Hancox PJ and Rubidge BS (2004) Basin development during the deposition of the Elliot Formation (Late Triassic - Early Jurassic), Karoo Supergroup, South Africa. South African Journal of Geology, 107: 395-410.

Catuneanu O, Hancox PJ, Rubidge BS (1998) Reciporical flexural behaviour and contrasting stratigraphies: a new basin development model for the Karoo retroarc foreland system, South Africa. Basin Research 10: 417-439

Holzforster F (2007) Lithology and depositional environments of the Lower Jurassic Clarens Formation in the eastern Cape, South Africa.South African Journal of Geology, 110: 543-560.

Thoughts from the field: Welcome to Lake Drumbo

I want to float some ideas based on some observations I've made in the field this year. So what have I been up to? Well firstly I've been poking my nose further south than I usually do. Most of the sites I've been working over the past half a decade are in the north end of the main Karoo Basin of South Africa. Here the dinosaur bearing Elliot Formation is relatively thin, probably because it lies over the solid Kaapval Craton, a big ancient continental block. This block probably prevented the basin floor from sagging too deeply during mountain building events off to the south (Tectonics is a VERY important factor controlling of deposition in the Karoo Basin). But down south you get off the Craton and the Elliot Formatin becomes thicker...over four times thicker. So with some money from Germany, and a collaborative team from Germany (led by Ollie Rauhut) and Great Britain, we began looking down south (mostly in the Eastern Cape Province). Despite the great thickness of sediment good outcrop is hard to find as the rainfall is quite high and vegetation rather thick.
Another rucurrent problem is figuring out where you are in the stratigraphy, these rocks don't come with labels!
So first a quick primer of the stratigraphy of the dinosaur bearing part of the Karoo.
The top of the sedimentary pile is usually referred to as the 'Stormberg Group' although this is not an officially recognised stratigraphic unit. The Stormberg Group consists of three formations: the Molteno, the Elliot and the Clarens. The Molteno is a series of coarse grained to conglomeratic sandstones, with fine grained siltstones, mudstones and coals in the south. It is rich in plant fossils (and some insects) but has not produced a single piece of bone - although there a some dinosaur tracks reputed to have come from this formation. The Elliot Formation marks the begining of the dinosaur body fossil record in South Africa. It is divided into two units: the upper and lower. At times it can be very difficult to determine in which unit you are in. The Elliot Formation is predominately made of red overbank muds and silts deposited on a humid (lower) to semi-arid (upper) floodplain. It would appear that the Elliot Formation covers quite a time range, with the lower member almost certainly being of Late Triassic age while the fauna of the upper member is very much Early Jurassic in aspect. The Clarens Formation consists of pale cream to white massive cliff-forming sandstones that are aeolian (wind blown) in origin. It records further aridification and the onset of a dune desert. Strangely the fauna doesn't seem to change much, if at all between the upper Elliot and the Clarens. You get pretty much the same taxa in the Clarens, just fewer specimens.
Now here is a parorama of the main valley wall on Upper Drumbo near Barkly East.

We excavated two dinosaur skeletons (Nelly and Charlie) from near the bottom of the Valley. You can see the cap of massive sanstone at the top of the peak in the centre (Castle Rock. This is clearly Clarens Formation. But where is the top of the Elliot Formation and where in the Elliot Formation do our dinosaurs come from?

At first glance the change in slope at the top of the valley seems to mirror the outcrop pattern of the boundary between the lower and upper Elliot Formations.

A colourised diagram of the outcrop of te Elliot and Clarens Formations. Note the change in slope between the two members of the the Elliot Formation. Modified from Bordy et al. 2004.
You can see this even better from a photograph taken from a higher vantage point looking across at Castle Rock, rather than up at it from the valley floor.

In this photo only the thick sandstone bench at the top of the valley can be seen. The smooth ramp-like slope leading up to Castle Rock is obvious. The mountains in the distance are made of the 2km thick pile of basalt that was extruded toward the end of the Liassic. You can read more about them here.
If this was the case then the upper Elliot Formation would form the smoother upper slopes leading to Castle Rock and our dinosaurs would be from the lower Elliot (hence Triassic). BUT one of them is almost certainly a Massospondylus (typical of the upper Elliot) and the sediments that enclose them are also typically upper Elliot in aspect. Perhaps everything from the base of Castle Rock to the valley floor is upper Elliot. Thats a verticle height of 210 m. The upper Elliot reaches thicknesses of 150 m down in the south, but 210m is a bit much. A few observations point me towards what I think is the answer. Firstly you will notice a thin bed of narrowly banded siltstone just below the big sandstones of the valley rim.

I've see a similar bed at the very base of the Clarens Formation in a number of locations (but not all). These are probably a series of playa lake deposits (about the only fossils you will find in them are little mussel shrimps or conchostracans) and they form a pretty good marker for the end of the Elliot.the smooth slope above the valley is not made of red overbank fines like the Elliot Formation. Further evidence that the upper slopes are actually within the Clarens Formation can be found if you actually climb up to them to take a look. The slope isn't made of red fluviatile mudstones, instead you will find thinly laminated pale creamy-grey shales. I've seen this lithology before - in small localised lenses of the Clarens Formation. They are interpreted as small interdune emphemaral pond, or playa lake deposits. However the thickness here (about 80 m) is, as far as I can find out, unprecedented. It seems to me that far from being a dune desert, this part of the world was host to a pretty large long lasting lake. Even more cool is that the same big package of shale can be found in near Blikana and at Rhodes. This may indicate a lake about 100 km across. Strange that I can find no mention of such an obvious feature in the literature. So what lived in or or around it (assuming my interpretation is correct? Bugger all I'm afraid. You won't find even scattered fish bones or scales. My guess is that it was very shallow, hypersaline and prone to frequent drying out. Much like Lake Eyre in the Tirari Desert of South Australia. Indeed given that it is surrounded by a dune desert and the northern section of the Lake is about the same size as the lake I'm suggesting, Lake Eyre makes a pretty good analogue.

Lake Eyre

However there IS a report of a large Lake in the Clarens Formation off to the South West of this deposit. However this lake is an altogether different kind of thing. Holzforster (2007) reports on lacustrine deposits in the Clarens Formation in the Exterem South West end of the outcrop of the Formation. However here the Clarens is incised down into the Elliot Formation, and the lake deposits are underlain be thick pyroclastic deposits. In other words this south-western lake was developed in a volcanic crater. Sadly no fossils have come from here either, - its a pity because a late Early Jurassic Liaoning-style lagerstatte would be sooo cool.

references

Bordy EM, Hancox PJ and Rubidge BS (2004) Basin development during the deposition of the Elliot Formation (Late Triassic - Early Jurassic), Karoo Supergroup, South Africa. South African Journal of Geology, 107: 395-410.

Holzforster F (2007) Lithology and depositional environments of the Lower Jurassic Clarens Formation in the eastern Cape, South Africa.South African Journal of Geology, 110: 543-560.

Field trip photos

I'm currently writing up a report on the lightening quick field trip I took at the end of November for this blog but am getting delayed by all sorts of real-world duties. So for now I'll just show-case some of the pictures.



Matthew Yates assists Charleton Dube and Sifelani Jirah in excavating a dinosaur tail.



The tail of 'Charlie' the sauropodomorph (yes another one!) emerges



Upper Drumbo, type locality of Dracovenator regenti, and site of 'Charlie'. Casle Rock is in the background but where is the contact between the Elliot Formation and the Clarens Formation?.

Two new Fossil Cowries

A small paper has just been published on two new fossil cowries from the Miocene of South Australia (Yates 2008). Although it is unlikely to set the palaeontological world on fire it is a personally satisfying paper as it represents my first published foray into a subject area that has actually been close to me for most of my life. As I have mentioned before growing up in South Australia provided next to nothing in the way of actual dinosaur digs or even museum displays of dinosaur bones. If you wanted to get out and dig for your own fossils then the marine limestones and marls of the River Murray cliffs was about the only game in town. Most of these sediments are rather coarse grained calcarenites that unfortunately offered no protection ravages of groundwater which dissolves shells made from aragonite (the form of calcium carbonate that the majority of molluscs use). As a consequence nearly all mollusc fossils are present only as moulds surrounding the void where the shell once was. There is a gleaming exception: a silty marl unit called the Cadell Formation (formerly the Cadell Marl Lens of the Morgan Limestone).


The Cadell Formation in outcrop (note the house boat on the river channel in the background).



The Cadell Formation in context. The creamy coloured beds (largely grassed over) are the Cadell Formation while the strongly banded orange limestones above it belong to the Bryant Creek Formation.

This formation is packed with aragonitic mollusc shells, sometimes so well preserved they look as if they have freshly come off the beach. The extent of the shelly facies of the Cadell Formation is quite limited, the main exposure stretches for just over 10 km between the towns of Murbko and Morgan, however for most of this length the exposures form sheer cliffs that plunge straight into the river. Only one decent access point exists, at the type locality for the formation, about 6km south of Morgan. This site is well-known and collectors have visited it for over a century. The first thorough documentation of the fossils of the Cadell Formation were published by Ralph Tate, a British born geologist, palaeontologist and botanist who emigrated to South Australia, and became the head of the Department of Geology at the University of Adelaide. Incidentally the Tate medal is still awarded each year to the best honours research project in the department for that year. In 1994, yours truly was the recipient of this award, definitely one of the proudest moments of my life, not least because Tate with his extremely broad knowledge of natural history was a personal hero of mine. I was very surprised to learn, while googling around for details of the man’s life I found that he and I share the same birthday.
Anyway back to the Cadell Formation, one would think that with such a long and venerable history of study and collection, there would be little left to discover. Not so; the mollusc fauna has not received a comprehensive survey since Tate’s pioneering work and the paleoenvironment of the Formation remains an enigma. I first visited this site when I was just 13 years old and fell in love with the site. I visited the site several times a year until I finally left Australia when I was 28. Over the years I’ve amassed a collection that includes more than 200 species of mollusc. Many of these are new records for the formation, and several represent new species. However as my academic career took me into vertebrate paleontology and dinosaur research, I left my interest in these mollusc fossils lie dormant but not forgotten. Late last year I finally got my chance to produce my first publication in this field. I hope many more of greater significance will follow. The paper outlines two new species of cowry from the Cadell Formation that were formerly thought to belong to middle Miocene species from the mollusc-rich basins to the east in Victoria. The first of these is Umbilia caepa, an extraordinarily fragile member of the basal cowire genus Umbilia.


Umbilia caepa

Umbilia was featured on this blog here and here. U. caepa is quite similar to the Victorian contemporary species U. leptorhyncha but consistently differs from it in a number of respects including the weaker apertural dentition, the development of a plate-like posterior columellar callus bordering the posterior canal and broad plate-like flanges on each side of the anterior rostrum. It also has a more strongly developed pyriform shape which resembles the bulb of an onion (hence the name). Of course with palaeontological samples it would have been impossible to demonstrate that U. caepa was a reproductively isolated from the eastern U. leptorhyncha or was simply the western end of a clinally variable species. However much to my surprise that when sorting through the various fragments from the Cadell Formation I found a small thin piece of Umbilia that does indeed have strong apertural dentition and weak lateral ridges on each side of the anterior rostrum (as opposed to broad flanges) amongst other features that indicate it was actually a true U. leptorhyncha. No intermediate specimens could be found indicating that the two species were sympatric in the Murray Basin but only U. leptorhyncha extended east into Victoria.
The next species I described belongs to the endemic southern Australian clade Austrocypraea, which is now regarded as cold-water adapted subgenus of the large tropical Indo West Pacific genus Lyncina (this includes the famous ‘golden cowry’ Lyncina aurantium) based on molecular evidence (Meyer 2003).


Lyncina aurantium image from en.wikipedia.org/wiki/Cypraea_aurantium

The species, which I called L. (A.) cadella, is abundant at the site and many specimens had been found and examined by previous researchers but had not received its own name due to a particularly bad tangle of taxonomic confusion surrounding the species.
Tate had found this species but had regarded as a mere variant of the Victorian species L. (A.) contusa. In a similar case to U. caepa, L. (A.) cadella is close to L. (A.) contusa but consistently differs from it in a number of respects relating to size, dentition and shape of the fossula.

Lyncina (Austrocypraea) cadella

As there are consistent differences between the two populations I think that the South Australian population is deserving of separate species status. Frank Schilder thought so too, when he revised the Australian fossil cowries in 1935. Schilder was a dedicated cowry researcher, and it is a testimony to his deep knowledge of the group that much of his generic classification of these extremely conservative and homoplastic shells was upheld by recent molecular phylogenic work. Sadly his work on Australian fossil cowries was not among his better efforts. The main problem was that he was working from collections held in Europe that were rife with poor locality data, leading to all sorts of confusion. To cut a very long story short Schilder described L. (A.) cadella -twice! – using two different names, neither of which are available. In the first instance he confused his own specimen of L. (A.) cadella with an Eocene species named by Tate – ‘Cypraea’ ovulatella and referred it that species using the combination ‘Austrocypraea ovulatella’. But ‘C’ ovulatella (now Willungia ovulatella) clearly isn’t the same thing as L. (A.) cadella, it isn’t even a cowry! (the confusion was the result of relying only on illustrations and an icorrect locality label). Secondly he described a second sample of L. (A.) cadella that was obtained directly from Tate himself by the French malacologist Alexandre Cossmann as a new species ‘Austrocypraea subcontusa’. So the species from the Cadell Formation should be called L. (A.) subcontusa right? Wrong. In an inexplicable move after describing the Cossmann’s sample Schilder selected an aberrant dwarfed Victorian specimen as the holotype of his new species. After looking at the Victorian specimens I’m convinced that the holotype of Austrocypraea subcontusa is just an extreme variant of true L. (A.) contusa. It still differs from L. (A.) cadella in a number of respects and can be connected to typical L. (A.) contusa by a number of intermediates. The upshot of all this is that the common species of Lyncina (Austrocypraea) from the Cadell Formation has never received a valid scientific name despite being known for well over a century.
So what is the significance of all this arcane taxonomy? The main significance is that these species are more evidence of faunal differentiation between the various Miocene epicontinental basins. This is in contrast to the modern molluscsn faunas of southern Australia where most species have broad ranges stretching across the entire southern Australian seaboard. Although there certainly were many widespread middle Miocene species in southern Australia there does appear to have been higher levels of endemicity, perhaps fueled by the presence of restricted epicontinental basins and the propensity for many southern Australian molluscs to abandon the planktonic dispersal stage of their development.

Adam Yates (2008). Two new cowries (Gastropoda: Cypraeidae) from the middle Miocene of South Australia Alcheringa: An Australasian Journal of Palaeontology, 32 (4), 353-364 DOI: 10.1080/03115510802417927

C.P. Meyer (2003) Molecular systematics of cowries (Gastropoda: Cypraeidae) and diversification patterns in the tropics. Biological Journal of the Linnean Society 79: 401-459.

Picture of the Day: long tailed widow bird

Just a quick post while I'm on leave - I'll be revealing the mystery orifice soon, so keep guessing - one of you is very close. We took a family outing to the rhino and lion park in ‘The cradle of humankind’ a world heritage area that includes the famous Sterkfontein and Swartkrans caves where several australopithecines have been found. While there I managed to get this shot of a breeding male long-tailed widow bird (Euplectes progne), the epitome of an elaborate sexual display that is a major handicap to its owner. Non-breeding males are drab, brownish, sparrow-like birds with tails of normal length.

From the galleries of the BPI: The Cape Giant Zebra

This specimen is a partial set of jaws of Equus capensis, the so called cape giant zebra, from Makapansgat, the most northerly australopithecine site in South Africa. Actually, although robust these equids are not so giant, being about the size of a big modern horse. Fossils of this robust equuid are widespread throughout South Africa, with the type coming from close to Cape Town, way down in the southwest.
It is often said that Africa escaped the megafaunal extinctions of the late Pleistocene but there is a definite set of large African mammal species that clearly did not make it through to the present. These include the giant buffalo Pelorovis, other bovids like Megalotragus, and supposedly Equus capensis. But if Charles Churcher is right reports of E. capensis' demise are greatly exaggerated. It s apparently alive and well in the form of.... Grevy's Zebra.


Image from wikimedia commons

Apparently the teeth (which are what most extinct Equus taxonomy is based on)of E. capensis do not differ in significant ways from those of E. grevyi and a bunch of east and northern african fossil equiids (e.g. E. oldowayensis).
Grevy's zebra is now restricted to East Africa and cannot be found anywhere near Suth Africa. So if it doesn't represent an actual extinction it does represent a drammatic range contraction.

reference

Churcher CS (2006)Distribution and history of the Cape zebra (Equus capensis) in the Quaternary of Africa. Transactions of the Royal Society of South Africa 61:89-95

What was it?

That ugly mystery bone is out now. What a disaster! when lifting it from its jacket, an undetected puddle of glue had soaked through the sepparator and firmly welded the underside to the jacket (lesson for the future - make sure there are several layers of sepparator between the bone and the jacket). The remarkable thing about the bones from this quarry is that although the compact outer bone is well-preserved the interior is like compressed flour. Once a break is started the whole bone tends to crumble to powder, much like the unravelling of a woollen jumper once the stiching comes undone in one place. Consequently the finished product is not one of our lab's proudest moments and I won't be showcasing it here. Nonetheless two things are apparent 1) it is a busted ischial peduncle from an ilium - exposed in medial view in the photo. 2) this part alone is about the same size as a middling Massospondylus, so although Rutger was halfway right he doesn't get full marks. The diagram below indicates which part of the ilium the bone is, and should give the astute clues to where I think its relationships lie (incidentally it is from the same site as the sauropod caudal I described in the South African Journal of Science (2004, vol. 100. 504-506)

End of year blues

Hi guys,

This blog has become far more quiescent than I ever intended it to be. I am currently feeling exhausted and swamped by marking at the end of the year, including honours projects, exam papers and essays - urgh. Of all my duties I hate marking the most. Time is of the essence but I want to be scrupulously fair to all, a desire that used to compell me to read and re-read each essay two or three times before finally settling on a mark. When not marking I am tidying up various other bits of end of year business - and occasionally writing up some of my research for publication. I wish I could tell you guys about it (it is one of the most enjoyable aspects of my job) but sadly this work has to go through the long drawn out process of peer-review and publication first. Maybe I'll be able to say something in 2010!
Anyway I've dragged up a picture of an old field trip from my vaults. You can see that the weather was kind of .... damp. This happened a lot on my field trips (and not always in rainy season either) so much so that one of the dinosaurs we happened to find in between rainstorms received the nickname 'Rainmaker'.
Anyway the load on shoulders should be lifting soon. I'll have a visit from my mum soon and we'll be doing a few trips round Gauteng. Then I'll be off on a short field trip to retrieve a dinosaur we left behind earlier in the year. So by December my batteries will be recharged and blogging will begin with renewed vigour (I hope!)

What is it?

...... The answer is - I don't know. This is one of those weird 'head scratchers' or GOKs (God only knows) that we get from time to time. Celeste is prepping it up right now. Its been sitting down in the lab for over two years and various volunteer preparators have had a go at it and quickly left it for easier more exciting projects. It comes from the upper Elliot Formation in a quarry that has produced more than one type of sauropodomorph as well as a protosuchian crocodile and some honkin' big theropod teeth. Any suggestions?

Lookin' out my back door

Well out my back window actually. We've been watching this industrious little guy for almost three years now. He is a masked weaver (Ploceus velatus), and in order to attract a mate he has to construct a nest of sufficient quality to encourage a female to lay her eggs in it. Sadly he's a bit of a loser. Although several females have checked him out he has never been able to seal the deal. After every rejection he would demolish the nest and start again. Now however it appears he is so riddled with frustration and self-doubt that he just builds and destroys nest after nest without even getting it looked at first. I kind of empathize with him, my early years (15 through to 26) weren't too dissimilar.

The Drakensburg Lavas and the First Great Dinosaur Dying

What you are looking at is a thick pile of basalt, that was extruded onto the Earth’s surface some 183 million years ago, during the latter part of the Pliensbachian stage (or at the Pliensbachian-Toarcian boundary, depending on whose timescale you follow) of the Early Jurassic. They are part of a 2 km thick sheet that is centred on the mountainous nation of Lesotho in Southern Africa. They take their name, the Drakensburg Group, from the Drakensburg Range, a ragged row of peaks said to resemble the back of a dragon that runs along the border of Lesotho and the South African province of Kwazulu-Natal. This large pile of basalt is an erosional remnant of a truly enormous volcanic province. Other parts of what was once a continous sheet of lava extend north to Zimbabwe, Botswana and Zambia, and westward into Namibia. What is even more jaw dropping is that if Gondwana is reassembled, then these southern African lavas (generally called the Karoo flood basalts) are just part of one enormous province that extends into the Southern tip of South America (the Chon Aike Province) and across Antarctica (the Ferrar Province) and into southern Australia. Taken together the total volume of magma that was either extruded onto the surface, or emplaced as intrusions below it, would come to more than two and a half million cubic kilometres (Wignall 2001). This volume actually exceeds the estimated original volume of the famous Deccan Traps of India, which were extruded at the end of the Cretaceous (when most dinosaur lineages famously kicked the bucket). Given that these vast volcanic outpourings seem to be linked with mass extinction events with disturbing regularity it seems odd that the truly enormous Karoo-Ferrar province is not linked to a big extinction event – or is it?
An extinction event amongst marine molluscs (yay! see molluscs have much to teach us!) in the late Pliensbachian has been recognised in Europe and South America and this has been tied to the Karoo-Ferrar eruptions (Hallam 1961, Aberhan and Fürsich 1996). But the general consensus is that this was a weak mass extinction, well below the level of the ‘big five’ mass extinctions.
But how sure can we be? One thing that is clear to dinosaur aficionados is that the early Middle Jurassic has an abysmal record of terrestrial faunas and this may well be masking the effects of a terrestrial mass extinction. Indeed the first stage of the Middle Jurassic Epoch, the Aalenian, is the only Mesozoic stage that does not have its own valid, diagnostic dinosaur taxon (or at least it didn’t a few years ago, maybe there is one now). Another thing that the dinosaur record shows is that prior to the middle Jurassic, dinosaur faunas were rather uniform the world over with a community structure dominated by basal sauropodomorphs (usually a massospondylid) with small coelophysid and larger dilophosaurids representing the theropod contingent and much rarer small basal ornithischians. This type of fauna can be found in Southern Africa (Elliot, Clarens and Forest Sandstone Formations), North America (Kayenta, Navajo and Portland Formations), Antarctica (Hanson Formation) and China (Lower Lufeng Formation). It is interesting that the two dominant components of this faunal association, the basal sauropodomorphs and the coelophysids are basically holdovers from the Triassic. However once the record picks up again higher up in the middle Jurassic things have changed a great deal. Gone are the coelophysoids and basal sauropodomorphs*. In their place we find ceratosaurs and tetanurans filling the large predator niches while eusauropods and eurypods (that is ankylosaurs and stegosaurs) occupy the large herbivore niches. This combination of taxa remained dominant around the world to the end of the Jurassic. So was this turnover a gradual affair? Maybe not, and I have suggested that there was actually a terrestrial mass extinction event that cleared away the coelophysoids and basal sauropodomorphs in my so far unpublished chapter in the upcoming Complete Dinosaur II. If so, it would seem very likely that this event was the same one that killed those poor little clams in the late Pliensbachian. In other words the Drakensburg and associated lavas really were significant for dinosaur evolution. Perhaps without them we may never have got such majestic beasts as Apatosaurus and Brachiosaurus. Quite independently Ronan Allain and Najat Aquesbi came to the same conclusion in their monograph on Tazoudasaurus, which I featured here. Ronan and myself must think alike for this isn’t the first time we’ve come up with the same idea more or less simultaneously. Earlier we both published the connection between the dating of the Karoo-Ferrar volcanics and the age of Vulcanodon at more or less the same time (Allain et al.2004, Yates et al. 2004).
Nevertheless there exists an alternative explanation. A team of French geologists led by Fred Jourdan have suggested that the late Pliensbachian extinction event was really mild because the Karoo-Ferrar basalts were extruded over an extended 8 million year period (Jourdan et al. 2005). Other continental flood basalt provinces show a pattern where 90% or more of their volume is extruded in a brief spell of less than 600 000 years. Jourdan et al. clearly demonstrated that the lavas to the north of South Africa were extruded over a period extending from 182 to 177 million years ago. Does this spell the end of the late Pliensbachian dinosaur extinction hypothesis? Perhaps but I’m not ready to discard this idea just yet. Note that the long duration of eruptions is restricted to regions north of South Africa. The Drakensburg (an erosiaonal remnant of a truly vast area shown by the intrusions that riddle the rest of the Karoo Basin) still yields a tight cluster of dates, while palaeomag indicates the whole pile experienced just one magnetic reversal (Duncan et al. 1997). What we need is a comprehensive sampling of the Antarctic, South American and Australian lavas to see whether they also extruded rapidly at the same time the Drakensburg lavas were extruded.

*There is one recorded Middle Jurassic basal sauropodomorph, Yunnanosaurus youngi, but I would like to see a better stratigraphic control on its age.

references

Aberhan M, Fürsich FT (1997). Diversity analysis of Lower Jurassic bivalves of the Andean Basin and the Pliensbachian-Toarcian mass extinction. Lethaia 29: 181-195

Allain R,Aquesbi N, Dejax J, Meyer CA, Monbaron M, Montenat C, Rechir P, Rochdy M, Russell DA and Taquet P (2004). A basal sauropod dinosaur from the Early Jurassic of Morocco. Comptes Rendus Palevol 3(3):199-208

Duncan RA, Hooper PR, Rehacek J, Marsh JS, Duncan AR (1997) The timing and duration of the Karoo igneous event, southern Gondwana. Journal of Geophysical Research 102 (B8): 18127-18138.

Hallam A (1961). Cyclothems, transgressions and faunal change in the Lias of North West Europe, Transactions of the Edinburgh Geological Society 18: 132–174.

Jourdan F, Féraud G, Bertrand H, Kampunzu AB, Tshoso G, Watkeys MK, Le Gall B (2005). The Karoo Large Igneous Province: brevity, origin and relation with mass extinction questioned by new 40Ar/39Ar age data. Geology 33: 745-748.

Wignall PB (2001) Large Igneous provinces and mass extinctions. Earth Science Reviews 53: 1-33.

Yates AM, Hancox PJ, Rubidge BS (2004). First record of a sauropod dinosaur from the upper Elliot Formation (Early Jurassic) of South Africa. South African Journal of Science 100: 504-506.

What was it?

Wouldn't you know it?, I went to take a photo of the now-prepared mystery skull, and the thing is away on exhibition, arrgh. Nonetheless I do have a snout photo of the skull lurking in my research folder, which should make its identity rather obvious.

Yes, I'm afraid it was nothing so unusual. Just another Massospondylus skull. Nonetheless it was one I collected so I'm quite proud of it. It also came from quite a beautiful site from the Clarens Formation making it one the youngest known specimens.

Beatrix Farm in the Free State, where the skull was found.

Recently I've tallied up the number of Massospondylus skulls known (not including the Kayenta and South American specimens which, although related, are something else). There are 14 more-or-less complete skulls that I know of (if you include the two embryonic skulls, and 1 unprepared skull). Now I'm sure that there are more Psittacosaurus skulls floating around but they are divided between a host of species. Currently all these Massospondylus skulls are classified as one species, M. carinatus. Could this be the most numerous dinosaur species in terms of whole skulls?