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?

Good News Everyone!

After spending the whole week in hospital (it wasn't just tonsilitis after all) Matthew will probably be coming home tomorrow ..... and one of palaeontology's holy grails - a basal stem turtle has been found and published.

I imagine most of my readers know that pinning down the closest relatives of turtles and the origins of their bizarre morphology has been one of the most recalcitrant problems in tetrapod evolution.
While the lack of holes in the cheek region of the skull suggests that they are an offshoot of the anapsid reptiles, with procolophonoids or pareiasaurs being the main contenders, more than one large scale morphological cladistic analysis has found that turtles are members of the Diapsida (derived reptiles with two pairs of holes in the temporal region of the skull). Molecular work also supports a diapsid origin for turtles but tends to place them close to, or within, the Archosauria (crocodilians, dinosaurs, birds and their kin)whereas the morphological work tends to align them with the Lepidosauromorpha (lizards, snakes and kin).

Sadly the new turtle described by Walter Joyce and colleagues in Proceedings of the Royal Society is too fragmentary to really speak to this vexatious issue. But it does tell us quite a bit about how their most distinctive feature - their shells - evolved and lets us know that the answers are out there (given the recent spate of excellent discoveries in the Chinle and its equivalents I'm sure a more complete proto-turtle won't be be a long time coming).

But first a little of the who, what where and when. The new fossil is called Chinlechelys tenertesta (the thin shelled turtle from the Chinle)and the known remains consist of fragments of shell with attached underlying parts of the vertebrae and ribs and isolated osteoderms found in the Bull Canyon Formation of New Mexico. The name is taken from the Chinle Formation, which is a little odd since most stratigraphers and palaeontologists would not to place the Bull Canyon Formation in the Chinle Formation (or Group according to some), prefering instead to place it in the Dockum Group. The age of this part of the Dockum is probably mid-late Norian of the Late Triassic, somewhere between 210 and 219 million years old.
There are other equally old turtles in Europe, Greenland and South America but none so primitive in shell design as Chinlechelys. For starters its shell is unusually thin but more importantly it still has rather individualised ribs, that although joined to the inside of the shell, are not fully subsumed into it.
The telltale fragment - a piece of shell with an individualised rib beneath it.Modified from Joyce et al. 2008

This is important because it helps falsify the model that the shell is a modified ribcage alone and supports the hypothesis that the shell is a composite structure formed from the agglomeration of trunk vertebrae, ribs and several rows of osteoderms (bony armour in the skin). Intriguingly modern developmental studies have suggested the former hypothesis because it appears that the shell grows as part of the endoskeleton (that is it is made of replacement bones that are preformed in cartilage and derived from scleritomic mesodermal cells. Developmental studies can yeild powerfull evolutionary data but I think the takehome message here is that developmental pathways can and do evolve. Palaeontology definately still has a place at the high table of evolutionary studies!
Hypothetical steps in the evolution of the turtle shell following the osteoderm hypothesis. From Joyce et al. 2008

Bonus musing: If the molecular data are correct it is perhaps no co-incidence that some pseudosuchian, or crurotarsan - whatever you preference, archosaurs have rather turtle-like carapaces. Aetosaurs even have a plastron of plate-like osteoderms.
Paratypothorax, an aetosaur. Compare to hypothetical stage II above. Image from www.dinotime.de

WG Joyce, SG Lucas, TM Scheyer, AB Heckert, AP Hunt (2008). A thin-shelled reptile from the Late Triassic of North America and the origin of the turtle shell Proceedings of the Royal Society B DOI: 10.1098/rspb.2008.1196

Tonsilitis again!

My little guy, Matthew, who is one month shy of his second birthday, has come down with serious tonsilitis for the second time in as many months. It would appear to be a law of nature that kids always fall sick on a weekend, usually a Sunday evening when medical services tend to be a little thin on the ground (especially for those not wishing to sit in a casualty waiting room for hours). At the moment this is my main blog-writing time. So sadly I'm empty handed - once again. I don't feel to bad about this however because I managed to get hours of research writing in, before Matthew got sick.
In lieu of my own work I would like to point folks to Matt Wedel's thorough dissection of the recent Aerosteon paper.

Matthew in better health doing some computer work of his own.