Stegosaurs of Whitby
Leading a family fossil hunt at Whitby, I walked my group onto East Scar, beneath Whitby Abbey. The rocks in the foreshore and lower part of the cliffs here are Early Jurassic marine shales. The dark grey layers, peppered with hard, pale lumps, belong to the Whitby Mudstone Formation. The hard pale lumps are limestone nodules (concretions) that grew around a dead body (or other organic material) buried in the mud. They are the source of the best three-dimensional fossils, such as ammonites, in the Whitby area. You can also find lovely fool’s gold-coated bivalves, such as Pseudomytiloides dubius.
The upper part of the East Cliff, meanwhile, is made of younger sandstones and siltstones, formed during the early part of the Middle Jurassic. These sediments weren’t deposited in the sea, but on a coastal plain, and belong to what is called the Saltwick Formation. Rather than yielding lumpy limestone nodules with body fossils, the sandstones and siltstones are packed full of trace fossils.
My research interests centre on traces made by burrowing invertebrates, such as worms, molluscs, and crustaceans. The Saltwick Formation has plenty of these. However, it also has plenty of trace fossils made by vertebrate creatures, especially Jurassic vertebrates of the extinct reptilian variety, and as most family fossil-hunters are hoping to find dinosaurs, I’m very happy to try and oblige.
A recent landslip has brought down large quantities of the Saltwick Formation from the top of the East Cliff onto the beach. STAY AWAY FROM THE CLIFFS – THEY ARE VERY DANGEROUS PLACES. Let nature do its thing, and bring the rocks to you.
Picking through the beach-strewn boulders, I was sure we would find some dinosaur footprints. They are present in many of the Middle Jurassic layers, typically where sand filled in prints made in quite firm silty mud. I scoured the blocks for lumpy surfaces, where the footprints have been fossilized as casts.
And, as shown in the video at the top of this post, I found some lovely examples. These are specimens of one of the most distinctive – and reasonably common – dinosaur footprints found in the Saltwick Formation: Deltapodus brodricki. This name was given to quite elongate, three-toed footprints by Martin Whyte and Mike Romano of Sheffield University in the 1990s. You can read some of their research into Yorkshire’s dinosaur footprints here.
The interpretation of Deltapodus brodricki is that it is a trace fossil made by the hindfeet of early stegosaurs. Stegosaurus lived in the late Jurassic of what is now the USA, around 150 million years ago, but its relatives lived from the Middle Jurassic to the Early Cretaceous, including in Britain. Dr Susie Maidment of the Natural History Museum is one of the world experts on these creatures, and gives marvellous talks, such as this one:
We have no body fossils of the stegosaurs themselves. The Saltwick Formation very rarely yields any dinosaur bones. Researchers therefore have to compare the footprints with skeletons of dinosaurs known from elsewhere in the world. This is what led Martin Whyte and Mike Romano to conclude in 2001 – after initially thinking that Deltapodus was made by sauropods – that stegosaurs might have made the footprints. You can read their research here.
Their work highlights both the magic and the mystery of trace fossils. The mystery comes from the fact the tracemaker is almost never fossilized, so we can’t know for sure what it looked like. You have to use your imagination, and your scientific detective skills, to come up with a plausible interpretation.
Trace fossils are magic, though, because they are traces of life, rather than death. They are structures made by a living creature. So you can stroll along the sands and scars of North Yorkshire’s Dinosaur Coast and, if you know what you’re looking for, place your hand – or foot – on the very place where a stegosaur did just the same thing, 170 million years earlier. And though I may not be the world’s biggest dinosaur aficionado, I’m happy to admit this is pretty cool.
(The 2024 Yorkshire Fossil Festival is coming to Redcar over the late May bank holiday weekend: Saturday 25th and Sunday 26th of May, with a Fossil Festival Field Day on Monday May 27th. Follow our Facebook page and website for information on how to get involved.)
