Monday, 21 April 2014

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. 

1 comment:

  1. Which troodontidan synapomorphies support Yaverlandia's updated classification?

    It'd be nice comparing Yaverlandia to Byronosaurus, Albertavenator, Jinfengopteryx and Mei skull roof bones to establish its status as a troodontid and go a bit deeper on its possible position in the troodontids phylo-tree

    Danny C