Speculative Palaeoart: Pterosaur Embryos

This micro-project was born out of one of those Facebook art challenges which I tried (and failed) to ignore, and for which I was nominated by Bob Art Models's Bob Follen (remember him from this post?) and Palaeoplushies's Rebecca Groom. The 'rules' of this particular Facebook challenge were pretty simple: produce three pieces of art for five days. That was it. It didn't specify whether they were to be new pieces, or whether they had to be posted over five consecutive days.

It started well enough as I paved the way to its inevitable non-completion with the usual good intentions. In fact, it's not abandoned, just hard to complete, what with everything else I've got going on. Given that I've got a fairly sizeable pterosaur project in the works, I figured it would make sense to stay close to this subject, and I was inspired to try my hand at portraying pterosaur embryos as close as possible to how extant animal embryos are.

It started with a quick mooch around Google, looking at photos of embryos of familiar animals, to get an idea of general bauplans. Most people are used to the proportions of young animals, with their disproportionately large eyes and heads, and comparatively short bodies and small limbs, but embryonic animals, depending upon their stage of development, can look altogether different to how they will appear at the time of their birth. Indeed, in the early stages, many disparate lineages' embryos may look broadly similar to one another. The diagram below shows representatives of the major vertebrate groups.

A selection of early-stage embryos, representing the major vertebrate groups. (Copyright © 2015 Gareth Monger)

You'll no doubt have seen versions of this line-up. I've opted to cut out most of the internal detailing so common to this style of diagram since I'm only dealing with external features in the pterosaur embryos I'm illustrating. It's easy to appreciate the broad similarities in this selection. The embryos, although perhaps not quite the same age, are at a very similar developmental stage, which shows how vertebrates follow a similar pattern of development in their earliest stages before they begin to specialise. As you can probably appreciate, there's not much point in producing a speculative, days-old pterosaur embryo to add into the above line-up as it won't look significantly different enough to add anything to the subject. The extant maniraptor in that diagram doesn't exactly scream 'DINOSAUR!', or at least not to this non-embryologist.

Today, the only flying vertebrates are birds and bats, and since only bats and pterosaurs share a membranous wing, I chose to look at bat embryos. Of course, bats and pterosaurs are not particularly closely related, having both developed flight apparatus independently, separated by an enormous chunk of time. (View this illustrated lineage at Phylopic to see just how distantly-related they are.) The framework on which they support their wing membranes is different, too, with pterosaurs using an enormously-elongated fourth finger and an internal network of aktinofibrils to stiffen the wing, while bats support a comparatively loose membrane on an enormous, five-fingered hand. Presumably this is the trade-off: pterosaurs have a skeletal scaffold reduced to a single spar, but there's more going on in the membrane and the skeletal mechanism by which they fold the wing away may not be as effective as that of at least some bats.

Embryos of the black mastiff bat (Molossus rufus), showing various stages of forelimb development. Compare 1's short manual digits with those of 2 and 3. (Copyright: Dorit Hockman. Used with permission)

This photo of three black mastiff bat embryos, courtesy of award-winning Dorit Hockman, a junior research fellow at Oxford, shows clearly the embryo pups' 'hands' and dactylopatagia (interdigital wing membranes) which are relatively small compared to those of newborn pups. Roll back several days in these animals' development, and at some point the animals' limbs will appear somewhat unspecialised, without any suggestion of the flighted animal to come. It was this intermediacy which I wanted to explore in my pterosaur embryo illustrations.

There's probably not too much that bat embryology tells us about pterosaurs; after all, bats are altricial and, although relatively well-developed at birth, are unable to fly until they are several weeks old, so there is a period of development and growth during this period. Some exceptionally well-preserved pterosaur fossils suggest that they are precocial, to the point that they can probably even fly within a very short time of hatching. It's reasonable to expect this to be reflected in the anatomy of their embryos and that their embryos go through a stage of rapid development before hatching, at which point they are essentially miniature adults. Unfortunately, early-stage embryo skeletons comprise a lot of cartilage which doesn't often fossilise well anyway, hence the speculative nature of illustrating pterosaur embryos.

A relatively-quick digital 'sketch' of a pterodactyloid embryo, with large head, closed eyes and stubby wings. 10a scalpel blade for scale. (Copyright © 2015 Gareth Monger)

It's difficult to make any scientific claims as to the accuracy of these illustrations, given the lack of direct evidence, which is why I tend towards filing these under 'speculative palaeoillustration'. That's also why I don't feel comfortable tying these down to too specific a taxon, leaving it as loose as 'pterodactyloid'. Other than full-term pterosaur foetuses illustrated to support fossil finds, there doesn't appear to be much in the way of palaeoart for prenatal pterosaurs. It's probable that, owing to the lack of any physical evidence, and the fact that the embryonic/foetal stage is comparatively brief, it's simply not important enough to necessitate producing illustrations of an animal at a point in its development where nothing would see it anyway, particularly when the adult reconstructions are being reviewed and refreshed as frequently as they are.

Another generalised pterodactyloid pterosaur embryo, with wing-digit and brachiopatagium beginning to develop. (Copyright © 2015 Gareth Monger)

So, in short, I don't think this is necessarily a critical aspect of palaeoart, but as science and scientific art, including photography, creeps further and further into our lives, whether that be online or through television or in print, the previously-hidden lives of vertebrates become more familiar to us. It makes some sense for palaeoartists to let themselves be influenced by this.

Biggest of thanks go to Dorit Hockman for letting me use her photograph of the bat embryos, which greatly influenced the final look of my pterosaur embryos. View her professional profile here.

Mesozoic Marine Menu: Bone

A little over two years ago, I was contacted by science blogger, Gavin Hubbard, who, knowing I liked to illustrate palaeontological organisms, was interested to see if I had any marine reptile illustrations available to use in a planned article he was in the process of completing. Now, this wasn't an example of how well-known I had become, nor how targeted networking can result in commissioned work. Gavin and I were classmates at an East Anglian primary school from 1984 to '87 and he had remembered my enthusiasm for dinosaurs from then. Now, save for the briefest of encounters in a Wisbech pub circa 1999, I hadn't actually seen Gavin since 1987, when we were both seven years old, so it was touching that he'd remembered me for all the right reasons when he was writing this particular article.

Gavin's blog, aptly named 'ScienceHubb', offers commentary on subjects as disparate as they are interesting, from immunisation to the defensive strategies of moths, and he delivers it in an engaging and humorous way. As a box-ticking exercise, that's pretty much all I want in a blog, and I get to learn something as well. Back in March 2013, Gavin was dealing with a little-known organism going by the name of Osedax, which is a genus of polychaete which invades the bones of 'whalefall', that is, dead whales which die and come to rest on the seabed. Many of us are familiar with deep-sea footage of dead cetaceans being scavenged by crabs, hagfish and sleeper sharks, but often these programmes stop short of documenting what happens after the whale has been reduced to a seemingly-clean skeleton, and the last of the hagfish have swum off to choke some sharks to death.

Don't eat the yellow ones: from lion of the sea to fertiliser for bone-eating snot-flowers. The route by which a Mesozoic marine reptile might find its way to its permanent place on the seabed. (Copyright © 2015 Gareth Monger)

Osedax is the genus name, but these things also answer to 'boneworm', 'zombie worm' and, in case you've not met your word-count, 'bone-eating snot-flower worm'. So, what do these worms want with a whale skeleton? (I'll keep it short since Gavin's already said it perfectly well.) After the removal of all the obvious soft tissues, whalebone is still rammed full of nutritional amazingness, if you're equipped to get to it. Osedax secrete an acid which dissolves the bone mineral, allowing them to 'take root' in its surface. They then utilise their symbiotic chums, a type (or types) of bacteria, to digest the lipids and proteins within the bone; they have to do this since they possess neither stomachs nor mouths. It's not certain if they are specialised cetacean scavengers, or if they will colonise other skeletons and that whales just happen to be longer-lasting on the seabed, easier to find and, therefore, study. Towards the end of Gavin's article at ScienceHubb, he speculated as to whether Osedax's ancestors may have colonised the skeleton's of the Mesozoic's array of large, marine reptiles.

Main illustration: a pliosaur skeleton, representing 'plesiosaurfall'. Inset: an Osedax individual, established on a pliosaur vertebra. (Copyright © 2013 Gareth Monger)

So, in order to illustrate his point, he wanted an existing image of a pliosaur. As it happened, it was my day off, so I had some time to throw something together, rather than reuse an illustration. 'Thrown together' is probably about right. The inset image was easy-enough to sort out, as there was plenty of reference. The main illustration started out as an A3 print of an old illustration of 'Rhomaleosaurus' (now Meyerasaurus), which I photographed at a jaunty angle, reprinted, sketched out, and painted in gouache. (Richard Forrest, at Plesiosaur.com, later pointed out that this particular skeleton was found correctly oriented, but erosion had damaged some of the dorsal features, and the preparators had flipped the specimen onto its back in order to display its better-preserved ventral side!)

Roll on a couple of years, and researchers Silvia Danise and Nicholas Higgs have published a study showing how some Mesozoic marine reptile bones display the telltale signs of Osedax activity, down to the signature cavities produced by their chemical bone-boring. The study demonstrates that Osedax (or at least Osedax's ancestors - I guess we cannot be sure it's the same genus) did not initially co-evolve with cetaceans, but already existed in the Mesozoic, survived the KPg extinction event, and exploited other organisms' skeletons immediately after the Mesozoic reptiles went extinct. They also speculate that snot-worm activity may be responsible for the destruction of skeletons before fossilisation can take place so, presumably, they won't find their way onto the Palaeontology's Favourite Pets list any time soon. It's good to see Gavin Hubbard's speculation justified by a solid scientific study and, personally, it's nice to have provided an illustration for it.

References:

• Higgs, N and Danise, S (2015) Bone-eating osedax worms lived on Mesozoic marine reptile deadfalls. The Royal Society, volume 11, issue 4.
• Hubbard, G (2013) Osedax: Ancient Bone Eaters. http://sciencehubb.co.uk/osedax-ancient-bone-eaters/

LATE EDITION:

A Pteroformer article gets the majority of its hits in its first day, so I've not got long to add in this snippet of maximum importance.

Love In The Time Of Chasmosaurs's blogger, David Orr, and his wife, Jennie, have written 'Mammoth Is Mopey', a children's alphabet book which utilises illustrations of extinct taxa which are rendered as accurate caricatures. That is, they're caricatures, but they're not wrong. Pronunciations are explained, background info is supplied, and the illustrations are fun and engaging. And, let's face it, it'll appeal to the adults who look back at their own childhoods with a hint of sadness at having not had a book like this.

Here's the really important bit: this is a crowd-funded project. And it's all or nothing. Jennie and David are sixty-five percent of the way to their goal of $10K, needed in order to get this thing to press. There's a fortnight left. Two weeks to get the remaining three-and-a-half thousand dollars OR IT DOESN'T HAPPEN. So, if you've not looked at their page at Indiegogo, take a look now. If you've looked but not contributed, please consider contributing. Not your thing? Share the link - it'd help! But seriously, take a look at all the lovely, lovely incentives they offer! Fifteen dollars (what's that in pounds? A tenner?) gets you a book! That's a niece's or nephew's birthday gift sorted! So click the link ->> this one <<- and have a gander. Thanks.

In From The Cold: The Return Of Brontosaurus

I daren't let this story rumble on by without throwing in some of my own observations. Indeed, Brontosaurus was an important dinosaur during my early flirtations with dinosaurology when, perhaps, the palaeontologists of the early '80s would rather it hadn't been - or at least not by the that name. This is such a big story right now, that it's barely worth summarising it yet again, but for the benefit of someone finding this article out of the context of the media 'frenzy', we're talking about the the issue of the genus erected for a fossil sauropod discovered by Othniel Charles Marsh in 1879. In 1903 Brontosaurus was reclassified as a species of Apatosaurus, but despite this, the name Brontosaurus stuck fast. Whatever the actual reason, or reasons, it's not hard to see the appeal of Brontosaurus. It's the 'Thunder Lizard', a veritable superhero of the Mesozoic world, splitting the rocky ground upon which it walked and announcing its approach long in advance of its arrival. Apatosaurus, well, it just sounds kinda vague. Less thunder and more rain: A-pitter-patter-saurus. Apatosaurus is Betamax.

Exactly how it happened. (Copyright © 2015 Gareth Monger)

Back then, and compared with Brontosaurus, Apatosaurus lacked airtime. The authors of the kids' books I owned didn't really imbue it with any personality - if they mentioned it at all. Also discovered by Marsh, and only a couple of years earlier, Apatosaurus ajax shares the same overall 'layout' as Brontosaurus excelsus, being a heavy-set quadruped with an enormously long neck and tail. It's slightly stockier than Diplodocus and holds itself more-or-less horizontally, especially when compared with that other famous sauropod, Brachiosaurus. Certainly in the popular children's books of the '70s and '80s, Brontosaurus was depicted as Diplodocus's squatter cousin, and much of the scientific laziness can probably be attributed to their authors simply taking their lead from existing books they were hoping to emulate and, if only in terms of style, update. The reasoning behind the pair rarely receiving the same attention in the same book probably boils down to the simple reason that since both animals share very similar bauplans, why include both? After all, dinosaur-overview books tend to focus on the most famous and the most disparate forms.

Old and new (and old again). Interesting news but, unfortunately, it won't create much new work in the palaeoart community. (Copyright © 2015 Gareth Monger)

So what does this mean for Brontosaurus's future, as far as its ranking as a kids' favourite? Based on my horribly vague recollections of my friends' dinosaur knowledge in the mid-'80s, if I'd taken a poll and asked my five-year-old friends to name five dinosaurs, you'd almost certainly hear Tyrannosaurus (never "T. rex" back then), Brontosaurus, Triceratops, Stegosaurus and perhaps Diplodocus - and probably not much else. Of course, if you asked the same demographic now, there'd be a whole host of new names, minus Brontosaurus. To be fair, it's to be expected, and for all the obvious reasons: new discoveries, better restorations, better reach, and everything in between - and several years of authors honouring Brontosaurus's 1903 reclassification. But for today's younger dinosaur enthusiasts, they may only have come across Brontosaurus whilst reading about Apatosaurus. For them, Brontosaurus is just an interesting little quirk of the scientific process recorded in the footnotes of an Apatosaurus profile. Whether it recovers its position as a firm favourite with the next generation of dinosaur fans remains to be seen. Can Brontosaurus bounce back from its second extinction?

Read the paper by Tschopp, Mateus and Benson here. It's got all the science bits I ignored in it.