Fleshing-out a dinosaur-eating snake

Tyler Keillor (USA)

In the March 2010 issue of the open-access journal, PLoS Biology, palaeontologist Jeff Wilson and colleagues give an account of a truly unique and amazing fossil discovery. In their article entitled Predation upon Hatchling Dinosaurs by a New Snake from the Late Cretaceous of India, the snake Sanajeh indicus is described, based upon multiple specimens. In particular, one snake fossil was found in a nest of sauropod eggs, looped around a crushed egg, with hatchling sauropod bones next to the broken egg. The very moment of predation seems to have been preserved in rock, as a sudden plug of sand from a flash flood smothered the animals, preserving them for millions of years.

Jeff contacted me about creating a reconstruction of this fossilised scene ‘in the flesh’ as a display. I had previously collaborated with him while he and Paul Sereno were studying the bizarre African sauropod, Nigersaurus taqueti, at the University of Chicago’s Fossil Laboratory. For that project, I created a restored skull model of the dinosaur for its unveiling, as well as a life-sized flesh model of the head and neck.

These models are an extremely effective, visual means of conveying new discoveries to the public. The value of a model is underscored when a fossil isn’t very photogenic or might otherwise not make much of an impact with a lay audience on its own. This was true of the Sanajeh fossil – remarkable scientifically, yet hard to decipher at a glance for the general public. Jeff saw the value of a life-sized model to illustrate the dramatic scene and make the unveiling that much more exciting.

From my suburban Chicago workshop, I drove to visit Jeff’s laboratory at the University of Michigan to see the specimen and discuss the project. I measured the fossils and Jeff loaned me casts of the discovery to take back with me. Back at my workshop, I used the details we had discussed to sketch the scene as Jeff envisioned it – a partial nest, with whole eggs, the snake wrapped around a crushed egg and the hatchling sauropod. From that sketch, I created a clay maquette of the scene, so we could visualise the display in 3D at a smaller scale.

It was very important that the pose and position of all of the elements from the discovery were transferred into the life reconstruction, making it a true, full-scale representation of the fossil. Of course, as is the case with many vertebrate fossils, there were damaged, missing and weathered parts. Therefore, a certain amount of speculation was necessary to fill in the missing bits, and we realised that careful decisions would have to be made around every element in the display to bring it to life.

I built a few more prototypes to work out details of the sauropod eggshell texture, the overall size of the display and nest thickness, full snake length, hatchling size and so on. I made another trip to Jeff’s lab for a review of these samples and to discuss the latest interpretations that he had made with the fossil. After this preliminary groundwork, I had enough information to begin working on the full-sized sculpture.

I started with the nest. I used sheets of Styrofoam to build a structure about four feet (1.2m) in diameter and one foot (30cm) thick. This represents a portion of the sauropod nest, with one edge exposed in cross section to reveal the true size of the partially buried eggs. Jeff and colleagues determined from the fossil matrix that the nest wasn’t built from a mound of vegetation like a crocodile nest. Instead, it was more akin to a turtle nest built in a depression in the sand. A shallow hollow, with a non-distinct rim was carved into the foam, with places to set each of the eggs, as well as a shallow track from the snake, as it slithered into the nest. I coated the Styrofoam surface with polyurethane resin to harden it and to prepare the surface for the final step much later in the process, when I applied a layer of real sand.

The size of the eggs was based upon an estimate of their diameter when they were ‘fresh’. Onto a spherical form of appropriate size, I stuck a layer of micro glass beads to recreate the characteristic texture of the fossil sauropod eggshells. I completed one master egg model, which I moulded and reproduced in multiples to fill the nest. From this same whole-egg mould, I could cast a thin-walled shell to crack and crush for the hatchling’s broken egg. I had to ensure that the cross-sectional thickness of the eggshell was appropriate, based upon the fossil.

The hatchling was sourced from a small number of bones in the nest, which Jeff used to create a skeletal drawing of the hatchling’s expected dimensions. I made a wire armature at that same scale and bent it into an evocative pose – the hatchling struggles to get to its feet, as it looks back towards the egg it has just emerged from, only to see the snake about to strike. I drew on references from the extensive sauropod nest remains that have been found in Argentina, particularly with regard to recreating the dinosaur’s skin.

Patches of exquisite fossilised embryonic sauropod skin have been found in some of these fossil eggs, and the rounded scales gave me a good idea of what the hide of my sculpture should look like. I used a small brass tube to individually stamp a scale pattern into my clay model. I also sculpted creases and folds into the neck, tail and body, to suggest the tight fit of the baby when it was curled up within the egg, just moments earlier before hatching.

The snake had to be convincingly created, because most people have a pretty good idea of what a snake ‘should’ look like. Observation and measurements of living snakes, as well as comparative observations of CT scanned snakes on the Digimorph website, provided extant references. The snake was modelled to follow the layout that the fossil vertebral column traced. From the size of the vertebrae, the length of the snake was estimated. The scales weren’t preserved, but an average pattern of scales from boid snakes was chosen, and a custom diamond shaped stamp-tool was used to press each scale into the clay sculpture. The skull helped flesh-out the details of the head. The snake is gaping slightly, about to strike, and the shape and size of the teeth are subtly visible, embedded in the soft tissues of the gums.

The entire sculpted scene was moulded with silicone rubber and a lightweight cast was made with polyurethane resin. Glass eyes were inserted into the hatchling and the snake, and the elements of the scene were decorated with acrylic paint. Clear epoxy resin created a wet-look for the hatchling and the layer of slime between it and the crushed egg. Sand was adhered onto the surface of the nest to create a realistic finish. Black velvet was applied to the sides of the display, with the exception of the cross-section, which was detailed to show the strata of the nest with one full-size egg exposed. A custom crate was constructed for the display, which was shipped to the Geological Survey of India in Mumbai, to become a permanent exhibit there. The reconstructed scene is now installed and the fossils have also been returned to India under the terms of the loan agreement that permitted the research and preparation to take place.

This amazing story of life and death, which the fossil and the display so vividly depict, has finally been unveiled for the world to see. Casts of the fossil have been created and are available to researchers who can’t make the trip to India to study the original. The life reconstruction of the discovery, as a museum exhibit, can also be re-cast for installation at other institutions around the world. I hope that this dramatic fossil, brought back to life with my sculpture, will inspire in kids of all ages (and also adults) a sense of wonder and curiosity for science and the natural world.