Palaeoartworks, the case studies, part 3: Ammonites and... extinct snails?

For the the final set of Palaeoart Case Studies produced for my Lyme Regis palaeoart gallery (running up until May 4th - catch it now before it's too late! Details here.), we're going to focus on molluscs. Yeah, that's right: palaeoart of squidy things, snails, clams and allies. Given that most palaeoart focuses on charismatic reptiles and mammals, this might be a hard sell. Let's see how the blog hits go with this one...

The general rarity of molluscan palaeoart occurs in spite of this group having a much better fossil record than virtually any vertebrate, as well as being fossils with uses beyond keeping socially awkward vertebrate palaeontologists off the streets. Molluscs do occur in palaeoart of course, but mostly as secondary or background animals, adding flavour to scenes dominated by larger, more charismatic species. This is a shame because molluscs are extremely interesting creatures in their own right, and especially so when we look at the bizarre forms that existed before our Recent molluscan fauna. Conchology is fun in the modern day, but becomes downright mind-bending when multiplied with deep time.

How confident can we be about the life appearance of these ancient shellfish? Because many molluscs have a fossil record quality which is basically opposite that of many palaeoart favourites (i.e. mountains of complete specimens), you might expect that we know a lot about their soft-tissues and life appearance. Do we? Read on to find out.

Erymnoceras: Ammonites - common fossils, artistic enigmas

Are there any more creatures more frustrating to palaeoartists than ammonites? These ancient cephalopods (the group of molluscs that comprising the shelled Nautilus, and the coeloids - squid, octopuses and cuttlefish) are superabundant in many Mesozoic marine deposits and, given this, we would expect at least a few extremely well-preserved specimens which reveal details of their soft-part anatomy and life appearance. This has certainly happened for fossil squid and belemnites, which are known from specimens showing their tentacle counts, ink sacs, body shapes and - sometimes - even the sizes of their eyes. Ammonite fossils are nearly as common as belemnites and certainly far more abundant than fossil squid, so there must be some fossils which inform palaeontologists and palaeoartists about their life appearance... right?

Male and female (respectively) Jurassic ammonites, Erymnoceras coronatum. The size difference between these genders is well constrained by fossil data, but the appearance of the actual animals is not.

Amazingly, no. The basic details of ammonite life appearance are far from clear, and exceptional preservation in the group is almost unheard of. Even the mineralised components of their radulae (rasping organs bearing numerous ‘teeth’, common to most molluscs) are incredibly rare, and good soft-tissue outlines of their bodies are unknown. While we can be certain that a squid-like organism lived in the last chamber of their shells (the ‘body chamber’) and was anchored in by muscles which left distinctive scars on the internal body chamber wall, little else can be said with certainty about their appearance. For instance, how many tentacles did they have? They very likely had some because they represent a grade of cephalopod evolution between Nautilus and coeloids, both of which bear tentacles. However, Nautilus has 90 small tentacles, and most coeloids have 10 large ones (octopuses, of course, have only eight). So how many did ammonites have? 10? 90? Another number entirely? And what of their eyes? Coeloids have large eyes and excellent vision on par with that of vertebrates, while Nautilus eyes are little more than organic pin-hole cameras. Which sorts, if either, did ammonites have?

And these are only immediate, cosmetic quandaries: much remains to be learned about ammonite floating postures, swimming abilities, and lifestyles. Given how elaborate some of their shell shapes are, and the unusual proportions of their body chambers, some ammonites must have had very unexpected appearances and floating mechanics indeed.

Despite being creatures which occur so commonly as fossils that it seems like we should know everything about them, ammonites are creatures fraught with uncertainty for artists and palaeontologists alike. Until new data comes to light, all life reconstructions of ammonites should be taken as extremely tentative, almost speculative renditions of their actual appearance.

Viviparus: a modern glimpse of the past

At first consideration, it may seem that accurately restoring ancient snails may be as hopeless as precisely restoring an ammonite. Like ammonites, their soft-parts are virtually unknown in the fossil record, the slug-like organisms inhabiting their coiled shells only represented by muscle scars left inside the shell.

The Creaceous Wealden mud snail, Viviparus cariniferus; probably the most accurately reconstructed extinct animal on this blog.

This is only sometimes the case, however. Unlike ammonites, snails - known formally as gastropods - are still alive in the modern day, and some types have extraordinarily long evolutionary histories. In some cases, members of modern genera evolved hundreds of millions of years ago, and remain largely unchanged in the present. This is so for members of the gastropod genus Viviparus, which first appear in the Middle Jurassic (c. 168 million years ago) and are still around today. For palaeoartists, these modern animals provide direct insights into the probable life appearance of their older cousins. For instance, modern Viviparus often have variably developed brown and ochre colour banding swirling around shells, so we may infer that their extinct relatives had the same patterning. The head and muscular foot (the name of the creeping gastropod propulsive organ) of modern Viviparus are also rather short and relatively broad, with two long tentacles emerging from the head and prominent eyes situated at their bases. We can’t know for certain that this is exactly what ancient Viviparus looked like, but it’s more parsimonious to assume that they resembled their modern counterparts than looking drastically different. The Early Cretaceous species shown here, Viviparus cariniferus, has been reconstructed with this logic in mind.

Modelling extinct animals on modern variants of the same species does not only apply to gastropods. The closer a fossil assemblage is to the present, the more likely it is to contain animals which have extremely close modern relatives, if not the exact same species. These instances provide palaeoartists with many models to essentially copy and paste into extinct scenes. If the biology of the modern variants is also well understood, they can also lend some compositional input to a palaeoartwork. A painting with Viviparus, for instance, would be most sensibly set around a relatively still or slowly moving water body, as this is where species of these gastropods occur in the modern day. Likewise, the salinity tolerances of modern Viviparus are low, so they only occur in freshwater: a reconstruction of these animals in this domain would therefore be logical. As with lots of palaeoartistic tricks, this technique is directly adapted from palaeontological science, where the biology of modern animals with fossil counterparts is frequently used to shed light on the depositional conditions and palaeoenvironmental settings of the rocks they occur in.

Palaeoartworks, the case studies, part 2: Feathered dinosaurs and tiny Crocodyliformes

It's time for part 2 of our 'Palaeoart Case Studies' series, this time featuring two subjects: the tiny Cretaceous crocodyliform Koumpiodontosuchus and the probable Lower Cretaceous troodontid Yaverlandia bitholus. Unlike our last subject in this series, giant pterosaurs, neither of these animals is huge. Koumpiodontosuchus is particularly diminutive with an estimated adult length of 600 mm long. Presenting the scale of an animal accurate is important for good palaeoart, as it's not only an important factor in the animal's biology and ecology, but also an integral part of it's character. Small animals present palaeoartists with a particular challenge because many folks hold the preconception that all extinct animals were large. For diagrammatic images, simply adding a person, modern animal or familiar object next to our creature shows its size, but this cannot work when rendering scenes that took place millions before familiar entities appeared. How do palaeoartists get around this? Read on to find out.

Yaverlandia represents the result of a recent palaeoart success story. After many years of trying, it seems palaeoartists have finally got the hang of recreating convincing-looking feathered dinosaurs. How did they do this? In short, by abandoning the need to show all dinosaurs as scaly reptiles and embracing the birdiness inherent to many species (or, to flip this around, realising that many traits unique to modern birds were common to many of their dinosaur ancestors). But what does this mean for the way we reconstruct troodontids and other feathered dinosaurs? Again, the answers are below.

This series of case studies is in aid of my art gallery in Lyme Regis, running until May 4th, at the Town Mill. Full details here.

Koumpiodontosuchus: a tiny, button-toothed crocodyliform

Reconstruction of the tiny Wealden bernissartid Koumpiodontosuchus aprosdokitii. Hopefully, you can see that it's not a large animal without having to think about it too much, but why is that? Prints of this image are available here.

The size of extinct animals a favourite topic of palaeontology aficionados, and presenting it accurately is an important goal for palaoartists. Although we often think of extinct species as very large animals, most were not giants. The skull of the tiny Cretaceous crocodyliform Koumpiodontosuchus show below, for instance, belonged to an adult individual that, in life, was about 600 mm long. But how can palaeoartists express a sense of animal size - big or small - without the use of modern objects, animals or people for reference?

Some general trends of animal appearance can be useful in conveying size in extinct species. These probably aren’t features that most of us think about when observing animals, but they provide palaoartistists with some tricks to give a sense of scale to their subject matter without using other objects or animals for scale. Generally speaking, facial features - particularly the eyes - of larger creatures are relatively smaller than those of more diminutive animals. The limb bones of larger animals are more robust and, as they approach the extremities, are proportionally shorter. Smaller animals often have less conspicuous muscle contours than larger animals, particularly if they have a fluffy covering and, in being lighter, smaller creatures are frequently more sprightly and ‘weightless’ than larger ones.

Animal proportions only give a very general sense of scale, however. To give a more precise measure, palaeoartists often juxtapose relatively familiar species alongside their subjects. The use of ‘background’ animals, or different varieties of plants, are useful in this respect. Even if the audience is not very familiar with these background entities, their proportions in relation to the subject gives an impression of scale. This can work in inverse, too: bigger animals or plants, shown in low contrast at a distance, can help reinforce the size of smaller subjects. Crafty consideration of point of view can also help: does the subject need a very low, tight point of view to be seen, or does a wider frame capture it more adequately? Again, these are not necessarily factors that we consider when viewing animals or artwork of them, but they are essential considerations for palaeoartists attempting to reconstruct not only the anatomy and lifestyle of their subject, but also their size and physical presence.

Yaverlandia: Britain's most bird-like dinosaur

Two Yaverlandia investigate a termite-riddent tree stump in Lower Cretaceous Britain. As with many other dinosaurs, their depiction here as very bird-like creatures is the result of palaeoartists having to completely overhaul the way feathered dinosaurs are rendered. 

Known only from skull caps, Yaverlandia bitholus is one of Britain’s lesser known dinosaurs. Found in Lower Cretaceous Wessex Formation cliffs close to its namesake, the Isle of Wight coastal village of Yaverland, it was thought for a long time to represent a member of the bone-headed dinosaur group Pachycephalosauridae. Recently, it has been reinterpreted as Britain’s first troodontid, an omnivorous theropod dinosaur closely related to birds and familiar carnivores like Troodon, Velociraptor and Deinonychus. Troodontids were big brained, nimble animals and most were rather small. Yaverlandia was no exception, with a tentative length estimate of about 2 m. 

Any restoration of Yaverlandia and its kin has to incorporate data on dinosaur feathering, details of which have only been available in earnest for the last 20 years or so. The uptake of feathered dinosaurs among palaeoartists has been variable. Some restrict them to specific regions of the body, while others provide smatterings of feathers across primarily scaly skin. Increasing numbers of artists restore these animals as very bird-like however, with feathers across their entire bodies including their heads, tails and legs. Fossil evidence is clearly in line with this latter approach. Bird-like dinosaurs, including troodontids, have been discovered with extensive feathering that covers their not only their torsos necks, heads and tails, but even sometimes their legs and toes. 

These discoveries have given palaeoartists a lot to think about when restoring the appearance of bird-like dinosaur species. Feathers are complex, three-dimensional structures which alter the body profile of their owners. They plump the appearance of the body and smooth contours of the animal’s profile. Thus, if a dinosaur has complex feathers, we can no longer simply restore their musculoskeletal system and wrap skin over it, as often done in the past. What’s more, palaeoartists have to think carefully about the way feathered dinosaur arms and hands are rendered, because their feather configuration is similarly complex modern bird wings: feathers erupt from the tip of the second finger to the elbow, with feathers of the shoulders covering the ‘gap’ between forelimb and body feathering. 

These ‘new look’ dinosaurs are more bird-like than ever, and evidence is mounting that feathers appeared much earlier in dinosaur evolution than classically realised. It is even quite probable that Tyrannosaurus was feathered. This is disheartening to some who ‘prefer’ the appearance of scaly dinosaurs, and many still erroneously render troodontids and their kin with scaly hides. Wholly feathered restorations of such dinosaurs are without doubt factually accurate renditions however, and entirely uncontroversial among scientists. 

Palaeoartworks, the case studies, part 1: Giant pterosaurs

If you're heading to Lyme Regis this weekend, or indeed at any point until May 4th, you should stop by the Town Mill: a dedicated gallery of palaeoart lies within. It contains more than just a bunch of pictures however, as it also endeavours to explain how palaeoart is done. A good palaeoartist restores long vanished skeletomuscular systems; knows how to fill anatomical gaps; gives a sense of size to alien-looking creatures, and constantly adapts to changing science to render their subjects more accurately. If they do their job well, viewers won't see how much (often considerable!) paper palaeoartists pull across the patchy, cracked fossil record. But how, specifically, are these illusions pulled off? And can we really be that confident about the results?

Some of the answers lie at my Lyme Regis gallery. Along with the paintings you'll find 'Palaeoart Case Studies', short explanations outlining the path from fossil to reconstruction. In each case, relevant fossil material is also provided to demonstrate how much - or little - artists have to work with. There's six of these in total, and I'll be sharing most or all of them here over the next few weeks. First up are the crowd-pleasing giant azhdarchid pterosaurs, animals which are so commonly reconstructed that we must know buttloads about their anatomy and proportions. Or do we? Read on to find out how confident, or not, pterosaur palaeoartists really are about reconstructions of giants like Arambourgiania philadelphiae, below.

Giant azhdarchid pterosaurs: iconic, famous, mysterious

Reconstruction of the giraffe-sized monster pterosaur Arambourgiania philadelphiae. The dirty secret is that 95% of what you see here is extrapolated from other animals.

Restorations of giant azhdarchid pterosaurs like Arambourgiania, Quetzalcoatlus and Hatzegopteryx are understandably common. What captures the imagination more than a giraffe-sized animal with wings spanning 10 m and a 2 m long head? All pterosaurs have an unusual air about them, but giant azhdarchids also have a majesty which is hard for artists to resist. Despite the common nature of their reconstructions however, giant azhdarchid fossils are not only very rare but also extremely fragmentary. No complete, or even near complete, fossils of giant azhdarchid skeletons are known, and a standard family kitchen table could hold the entire inventory of giant azhdarchid bones from around the world. Arambourgiania, for instance, is known from little else than the giant, tubular neck vertebra shown below. It stands to reason that these reconstructions are based largely on inference and educated guesswork, but are they simply products of imagination, or is there more to it?

Arambourgiania philadelphiae holotype vertebra, UJA VF1. From Martill et al. 1998. Scale bar represents 100 mm.

When attempting to restore the appearance of a poorly known fossil species, the first port of call is the anatomy of more completely known, close relatives - the closer the better. The best known azhdarchid species have 3 and 5 m wingspans, so were only a fraction of the size of their bigger cousins. With such a size difference, it is not sensible to assume that the larger animals were perfectly scaled-up versions of these smaller ones. Organisms rarely evolve different sizes without changing proportion somewhere. Bones of larger animals are often more robustly built than those of smaller ones, for instance, because bigger animals have greater masses to support. This is certainly true for giant azhdarchids, as is an disproportionate increase their neck lengths which correlates with size. Paying attention to seemingly trivial scaling details like this can make a tremendous difference to the accuracy of a reconstruction, especially when a lot of extrapolation is involved.

However, this is only half of the story about restoring giant azhdarchids, because deciding which animals are closely related among this group can be difficult. Not all azhdarchids were alike, and the interrelationships between them is unclear. In these muddy taxonomic waters, palaeoartists have to make some educated guesses. Whereas palaeontologists can admit that their data has limitations or that the relevant studies have not been done, palaeoartists have to stretch current data to finish their work. Artists restoring animals with poorly determined taxonomy like giant azhdarchids have to decide which other animals serve as the best models for their reconstructions, and this often involves some degree of intuition and opinion. Such palaeoartworks are especially vulnerable to being proved inaccurate when new data becomes available. Until then, the best reconstructions of these animals are simply those which use the most careful extrapolations and guesswork, and this should be borne in mind when looking at any reconstruction of a giant azhdarchid or other, poorly known fossil species.

Come back soon for the next case study!

Reference

• Martill, D. M., Frey, E., Sadaqah, R. M., & Khoury, H. N. (1998). Discovery of the holotype of the giant pterosaur Titanopteryx philadelphiae ARAMBOURG 1959, and the status of Arambourgiania and Quetzalcoatlas. Neues Jahrbuch fur Geologie und Palaontologie Abhandlungen, 207, 57-76.