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Wednesday, 3 June 2015

New takes on the Wealden Supergroup palaeobiota, part 2: Baryonyx, freshwater plesiosaurs, ornithomimosaurs and others

Last week we took a look at some new art of animals from the Wealden Supergroup, the intensively studied, historically important Lower Cretaceous rocks of Southern Britain. We all know the Wealden for celebrity dinosaurs like Iguanodon and Baryonyx, but there's a heap of other interesting animals in there which get relatively little publicity. It's mostly these we're focusing on here, in the second (and final) part of these 'picture of the day'-style posts. 

As before, if you like anything here, remember that you can buy prints of them all from my shop (the Wealden section might be relevant) and its new Facebook outlet. Indeed, if you like my work and are on Facebook, why not 'like' the new Mark Witton Palaeoart page? It's the best place to see when new prints and finished pictures are available.

Baryonyx walkeri: king of the fishers, redux

Baryonyx walkeri, off for a stroll among the crocodyliforms and pterosaurs.
Let's break this post in with a familiar animal: spinosaurid Baryonyx. It's hard to appreciate now how weird this animal seemed back in the 1980s and 1990s. At this point, other spinosaur material was only very poorly known, and laymen and scientists alike found this weird, superficially-crocodile like animal fascinating. Ironically, it's recently turned out that we first collected Wealden spinosaur material centuries ago, but struggled to recognise its significance until more complete remains were unearthed in the 1980s. We now know that Baryonyx can be found throughout a good chunk of upper Wealden stratigraphy and teeth referable to it - or another spinosaurid - are fairly common, at least as Wealden dinosaur fossils go. Baryonyx provided the basic template we'd recognise for all spinosaurid anatomy until last year when, famously, some spinosaurs were proposed to be rather different. It's clear that, whatever is going on with Spinosaurus, Baryonyx retains more conventional hindlimb and pelvic proportions, and may not have been so aquatically adapted as true spinosaurines. In this updated image, B. walkeri is splashing into a body of water while goniopholidid crocodyliforms and gnathosaurine pterosaurs go about their business around it. Note how much larger Baryonyx is compared to the crocs: Baryonyx is the largest theropod in the Wealden Supergroup, by a good margin.

Button-toothed crocs, redux

Bernissartid Koumpiodontosuchus aprosdokiti foraging for molluscs. It's eating a mud snail, Viviparus cariniferus, while tiny (6 mm long) physid gastropods Prophysa crawl over pond scum in the lower left of the image. Dragonflies provide scale, and unnamed tetanurans prowl around the background.
Last year I was lucky enough to provide the first restoration of Kompiodontosuchus aprosdokiti, a small neosuchian crocodyliform common to the Wessex Formation, and perhaps other parts of the Wealden sequence. Koumpiodontosuchus is a bernissartid, a group of small-bodied crocodyliforms with robust, shell-cracking teeth at the back of their jaws. As you'll know if you read my write up last year, these were likely employed in smashing molluscs and insects. The tetanuran theropods in this image are unnamed, but are not thought to be referable to any existing Wealden taxa. We probably need more material of them to consider them nameable, however: recognising that they are different from other Wealden theropods is only half the battle. Modern students of Wealden fossils famously do their best to preserve historic names based on fragmentary bones, but there seems to be an effort to 'future proof' Wealden taxonomy against confusion by only naming well-represented, characteristic animals. I guess I could have chosen one of the better known theropods to play the 'This was the Age of Dinosaurs' card for this PR image, but I think it's good to show that not all large theropods in the Wessex palaeobiota were Neovenator, Baryonyx or Eotyrannus

Welcoming the new Wealden ornithomimosaurs

A flock of Wessex Formation ornithomimosaurs forage in a marshland, while istiodactylid pterosaurs skulk about behind them.
Those keeping their ears to the ground will know that the newest arrivals to the Wealden dinosaur palaeobiota are ornithomimosaurs, commonly known as ostrich dinosaurs. Two specimens show that these animals were present in both the Weald and Wessex basins of the broader Wealden succession, and one of these fossils represents a historic taxon named in 1889: Valdoraptor oweni. Key to identifying ostrich dinosaurs in the Wealden was the discovery of abundant ornithomimosaur remains in France, many of which are so reminiscent of Valdoraptor and other Wealden theropod material that they may represent the same taxon. If you want to know more about these and their relationship to the complex story of Wealden theropods, check out Darren Naish's post on this at Tetrapod Zoology.

The above new painting shows a group of (nameless) Wessex Formation ornithomimosaurs in a well-vegetated marshland, in the rainy season, while istiodactylid pterosaurs mosey about in the background. The abundance of ostrich dinosaurs and juveniles in the middle-right are nods to the frequent recovery of abundant specimens of different levels of maturity at many ostrich dinosaur sites, including the new, French 'Angeac ornithomimosaur'. Note that the wings of the running foreround animal are somewhat swept back: I don't think the more common way of reconstructing ornithomimosaurs with 'dangly arms' looks right. They look like they should be holding shopping bags or something.

Valdosaurus in the forest, redux

Two Wealden dryosaurids Valdosaurus canaliculatus, and a stubborn avialan.
Ornithomimosaurs weren't the only fast runners in Wealden landscapes. Dryosaurids, like Valdosaurus canaliculatus were also fleet-footed animals with powerful, well-muscled hindlimbs, and tiny bodies attached to the front. In this reworked image, two of these 3-4 m long animals are taking it slow through a Wealden woodland. Although Wealden climates were quite warm and arid, leaving much of the landscape looking quite chaparral-like, some relatively upland parts seem to have been more vegetated: it's here that this picture is set. In my mind, these animals always walked with the stooping posture of the foreground animal - as noted last time, I like the idea that prehistoric animals had characteristic postures varying slightly from those we consistently restore in skeletal restorations. Note the avialan on the left of the image, which is a nod to the recovery of bird teeth from Wealden deposits. Anyone who's ever been forced to walk around a stubborn reclined mallard will recognise the situation now facing the Valdosaurus.

Barilium dawsomi in leathers, redux

Barilium dawsoni, a large and very robust iguanodont from Sussex. A flock of 'Ashdown maniraptorans' add scale.
Last time we featured Iguanodon bernissartensis: now it's the turn of the 'other' big Wealden iguanodont, the stratigraphically older, and osteologically chunkier Barilium dawsoni. In this redone painting, I've tried to make the Barilium skin more interesting than just plain old scales, covering the back in small, horny ossicles and creasing the flanks as if the skin is particularly thick, leathery and folded. I think we should be rendering more interesting skin regularly in scaly dinosaur palaeoart, as it seems most extensive dinosaur skin remains show unexpected features - strangle scales, wattles, folds and that sort of thing - which small skin patches mostly cannot record adequately. It's interesting to contrast these skin impressions with homogeneous restorations of scaly dinosaur appearance presented by some, where every species is covered in smooth hide following perfect contours of the underlying tissues: I'm not sure that's what fossils are telling us. As before, the 'Ashdown maniraptoran' provides scale to the bulk of Barilium. For the uninitiated, the Ashdown maniraptoran is seriously small for a Mesozoic dinosaur - maybe about 30-50 cm long. If you find big iguanodonts exciting, be sure to check out this previous post.

Polacanthus redux, again

A Wealden tree vies for attention with Polacanthus foxii, and some tiny birds.
OK, I'm cheating a bit with this one. This redone version of a much older painting has been posted fairly recently, but it seemed a bit remiss to skip this ankylosaur in this run down of recently produced Wealden palaeoart. Polacanthus foxii is, of course, the Wealden's sacral-shield-bearing nodosaurid, shown here strolling around a Cretaceous hillock with some birds for company. Having scratched the completist itch, let's move on, because we've seen this all before.

Accidentally sinister Leptocleidus, redux 

Mother and calf Leptocleidus superstes, a freshwater leptocleidid plesiosaur, explore a river inlet in Lower Cretaceous Sussex. 
Our final stop is in Wealden rivers and estuaries, where Leptocleidus superstes and other species of freshwater leptocleidid plesiosaurs roamed. The new version of this image has added a lot of detail on top of the original, which has inadvertently made the mother and calf Leptocleidus look more sinister than intended - hey, it's not my fault their teeth stick out like that. Back in the original post on these animals I mentioned that pliosaurs may also have been present in Wealden lakes and rivers, but note that this is no longer certain: the Hastanectes valdensis remains once provisionally considered pliosauroid have been placed in Leptocleididae in more recent analyses. That does make for a neater story - it means that leptocleidids retain their dominant role as 'near-shore-or-freshwater' animals, but perhaps a slightly less interesting one.

And that's all for now - I hope you've enjoyed this jaunt back to the ancient Wealden and these revised artworks. I'm sure we'll visit the Wealden again in time. Coming next, probably: walking with non-pterodactyloid pterosaurs.

2 comments:

  1. Excellent. Very nice paintings.

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  2. Lovely paintings. I'm especially fond of the Polacanthus entry; you've managed to capture its bizarre proportions--something a great many ankylosaur/nodosaur pictures fail to do.

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