Dr Trevor Watts (UK)
I recall reading a sentence in a book some time ago that went something like, ‘Occasionally a dinosaur footprint may be found along the coast.’ In fact, dinosaur footprints are superabundant along the Yorkshire Coast. On a day’s visit to any of 15 or 20 beaches, we (my wife, Chris, and I) would consider finding less than a dozen footprints to be a little disappointing, unless they were especially clear, part of a track or an unusual type. More commonly, we would expect to find two dozen or so recognisable prints.
This article is intended to give an impression of how common they are, what to look for, what might have made them and where exactly they can easily be found. It is not meant to be a technical, profoundly scientific paper: it’s a discussion. I hope it will provide an idea of what they might look like when you’re out on a beach (that is, the sort of things to be looking for on the rock surfaces, so you can recognise a footprint – they aren’t always clear at first sight). It is largely a case of seeing the ridges and bumps – the curves and angles, and the grooves and depressions on a rock surface – for what they are. This is a matter of ‘getting your eye in’.
The article is spread over four parts. This first part looks at the mid-Jurassic environments and how the footprints were created in a variety of ways and shapes. As a minor by-product, it demonstrates the wide range of other fossils that can be discovered here by anyone who cares to look. Later parts will: consider which dinosaurs could have made the footprints; discuss six basic forms of footprints; and finally examine the four locations on the outskirts of Whitby, where dinosaur footprints are very commonly found. Throughout this article, unless otherwise stated, all the photographs of footprints, other fossils and beach scenery were taken by me within one kilometre of Whitby harbour.
Why Whitby? Because it is very easily accessible and, if you can find footprints in such a well-trodden place, then you can surely find them practically anywhere along this coast.
Whitby is an extremely popular coastal town in the northeast of England, famed for being the setting for part of Bram Stoker’s ‘Dracula’, Goth festivals, folk and other music festivals, fishing and (formerly) whaling, holidaymakers, Captain James Cook, a ruined Benedictine abbey and an ancient church, alum mining, jet jewellery and fossils – especially ammonites.
Previously a ship-building port, it is still frequently visited by sailing ships, as well as a host of modern leisure and working vessels. Its written history goes back to the year 656 and the earliest known English poet, Cædmon. However, it ought to be famous for its dinosaur footprints, too. Even at sites as easily reached and much visited as the beaches, cliffs and piers, a stone’s throw from the centre of Whitby Town, dinosaur footprints are plentiful.
The basic geology
The dinosaur footprints along the Yorkshire coast are found in the rock beds that were formed in only one geological period – the middle part of the Jurassic System. The dinosaurs were not even present for the whole of this time.
During the Jurassic, the great landmass of Pangaea was splitting apart. The portion that ultimately became England was in the greenhouse-like climate of the subtropics. It was much closer to the equator than it is now and was becoming part of the new continent of Laurasia. In turn, this was dividing into Eurasia and North America, with the birth of the Atlantic Ocean between them.
The newly-divided lands had much more coastline than previously and the climate was thus much more humid. Eurasia, with the UK on board, drifted south into even warmer climes for a time, closing the Tethys Ocean. It eventually drifted north again, leaving the Mediterranean Sea as a remnant of Tethys. The area around Whitby is now part of England’s ‘green and pleasant land’, but, in Middle Jurassic times, it was the site of warm, dense and lush forests, languid beaches, steaming estuaries, warm lagoons and deep tropical seas. They alternated with bewildering irregularity.
Before the dinosaurs came to Whitby – the black Alum Shales of the rock platform
The Early Jurassic was principally a time of deep seas, so, as dinosaurs were a type of land-living reptile, there were none here. The great swimming reptiles, such as ichthyosaurs and the flying reptiles like pteranodons, weren’t dinosaurs. This oceanic environment continued into the Middle Jurassic, producing thick layers of muds and silts. In the Whitby area, these are the Alum Shale Beds, formerly the Whitby Shales. They form the lower part of East Cliff Beach and the rock platform immediately east of Whitby harbour.
The seas were home to vast numbers of swimming and crawling creatures, such as ammonites, belemnites and Gryphaea; their fossils abound on the beach and rock platform. The ammonites are what most visitors are looking for, but the sea floor was also often riddled with burrowing animals like crayfish, crabs or small lobsters. The fossilised burrows, especially the common one called Rhizocorallium, are found in the layers of rocks, sometimes in complex tangles of filled-in tubes. There are also rock surfaces with traces of crawling creatures’ feet or claws, and wriggle-and-slither marks.
During the dinosaurs’ time here – the Saltwick Formation
The Middle Jurassic lasted from approximately 175mya to 161mya (estimates and calculations may vary by up to four million years either way). During this relatively brief period, the land rose and sank repeatedly in an irregular dance of deep seas, shallow flooding seas, marshy river lands and drier lands. The rocks that were left behind reflect this variety. Most environments saw no dinosaurs, but there were episodes when muddy flatlands provided the perfect conditions for dinosaurs to leave good impressions of their footsteps.
These times only occurred relatively briefly between flooding periods, or perhaps between drier times when the land was probably being worn away. Such periods of footprint-friendly rock creation occurred on five main occasions during the Mid Jurassic, perhaps averaging one million years each. Fortunately, all five of these rock formations are found somewhere along more than 60km of the coast from Port Mulgrave in the north to Gristhorpe in the south. One or more of these beds may be found in almost every headland and bay in this area. The earliest (and therefore lowest) sequence of beds is known as the Saltwick Formation, which is the main one at Whitby. It was previously called the Lower Deltaic or Lower Estuarine Beds. Its rocks form about half the height of the cliff face above the Alum Shales.
At the time of their formation, the lands were mostly low-lying with extensive tropical or sub-tropical forests supporting dense vegetation of conifers, ginkgoes, ferns and cycads, and a great assemblage of small animal and large insect life. True mammals were evolving, along with new types of dinosaurs, such as the huge predator Megalosaurus, together with cetiosaurs, brachiosaurs and the smaller hypsilophodonts. There were other areas of araucarias (monkey puzzles), horsetails (some still grow along this coast more than two metres high), liverworts and mosses.
The land areas were prone to being flooded by rivers, which generally came from the north and east. These formed very extensive deltas, such as are seen now at the mouth of the Mekong, the Nile and the Mississippi rivers, with innumerable criss-crossing channels There were wide mudflats, low river banks, swampy tidal areas, shallow lakes and marshes, and broad estuaries, similar to the Humber, Avon, the Fowey in Cornwall, the Swale in Kent, or Great Bay in New Hampshire, USA today. They might be flooded twice a day with the tides, or occasionally as flash floods washed over them; or seasonally as the rains or monsoons came.
These were periods of deposition – when mud, silt and sand were being laid down, deposited here when the speed of the rivers slowed as they reached the flatter lands of the deltas and marshes. This great matrix of drifting rivers, lagoons, marshes, coastal mudflats and estuaries was in a state of constant flux. The channels shifted and changed. They meandered across the low-lying countryside, depositing more mud and sand in some areas, wearing it away in other places.
The main classification of the dinosaurs themselves has primarily been by the shape and arrangement of their hip bones, which determined how they walked. They are the lizard-hipped saurischians and the bird-hipped ornithischia. Each of these is basically split into two suborders:
- The saurischians comprised the theropods (hunting carnivores such as the raptors and tyrannosaurs}; and the long-necked sauropods (Diplodocus, Apatosaurus and so on).
- The ornithischia were primarily divided between the cerapoda (ornithopods, iguanodons, ceratops, hadrosaurs and so on); and the thyreophora (around here, these are mainly stegosaurs).
As an aside, it seems ironic that the bird-hipped ornithopods (the name even means bird-footed) did not evolve into modern birds. For the ancestors of birds, we must look to two branches of the theropods that later evolved a similar hip-bone structure completely independently of each other – the therizinosauria and the dromaeosauridae. For details, go to: https://en.wikipedia.org/wiki/Ornithischia.
For simplicity and ease of recognition, it is also possible to group most of the dinosaur footprints in this area into the same four broad types – theropods and sauropods; and ornithopods and stegosaurs. Additionally, there are two other forms of footprints, which are determined purely by how the print was made – ‘scratch’ prints and ‘through’ prints. These could have been created by a creature in any of the four principal groups.
The photographs show the main divisions of footprint shapes. The specific dinosaur names mentioned here are purely to give an idea of the type of creature, not the specific species that may have roamed this particular area 170mya.
As well as the actual footprints, there is a lot of fossilised evidence of the environments in which the footprints were formed, within the cliffs and on the beaches around Whitby. These include the mud-cracks, weed beds, rootlets of marsh plants, leaves and fern fragments, the burrows of the mud-dwellers, washed-up starfish, shells of snails, and the footprints of the dinosaurs that walked there.
A particular bed or facies might be only a few dozen yards across – one side of a river bank, or a small tidal marsh, or a temporary channel through the mudflats, for instance. Each bed is a mixture of environments that differed in detail, each with a different selection and quantity of fossils and footprints, as well as the coarseness of the materials that that they are formed of – pebbly, coarse sand, fine sand, silt or clay. The mudstones, sandstones and shales may be mixed together or separated into distinct beds. Some of them have a reddish tone – evidence of iron-staining or heavier amounts of iron bonded into the rocks.
Dinosaurs roamed these ever-changing environments, but, even within each ‘footprint bed’, the footprints are not equally spread over each layer of rock. They tend to be concentrated in certain small areas, where the dinosaurs congregated, perhaps where they fed, nested, drank fresh water, crossed streams at shallow points, walked along river banks and, in some cases, may have waded or swum across lakes and rivers.
Looking at the cliffs now, it is often possible to see where these environments used to be. Cross sections of broad, shallow river channels can be seen in the cliffs here, with gently sloping banks and flat muddy areas surrounding them (Fig. 16).
Dinosaur footprints aren’t the only fossils to be found from this period: the broad and constantly changing range of environments gave birth to rocks with many other indications of the environments with which the dinosaurs would have been familiar. There are enough fossils hereabouts to provide a wonderfully rich picture of the dinosaurs’ world.
Figs. 17, 18 and 19 show a selection of marine fossils commonly found on East Cliff Beach, dating from before the dinosaurs were here.
Very common are fossilised beds of ripples, both linear and crossed. Linear ripples are mainly parallel ridges and are formed where water has flowed consistently across loose sand or mud. These are often astoundingly fresh-looking. Cross-laminae ripples or bi-directional ripples are less definite, formed where water has come from two or more directions, perhaps washing back and forth. This action produces a pattern of low mounds and dimples that often collect plant debris, shell fragments and starfish. It is not unknown to find a slab of rock maybe two metres across with ripples all over it, and there in the centre, a footprint or several footprints.
Equally amazing is the preservation of mud cracks, such as are presently seen as any lake or estuary begins to dry out in the sun. Occasional beds can be found where there was a shower of rain while the mud was still soft – the surface has the marks of individual raindrops that fell about 170mya. And they are still there, almost as fresh as when they were created. I once found a slab of fine sandstone, which had several pebbles embedded in the surface; around these are the unmistakable swirl marks where a final wave on the Jurassic beach sluiced past them and drained away. It is an incredible preservation of an instant in time, just as you could see on any beach today. These are the muddy, sandy and richly forested landscapes in which dinosaurs wandered, ran, hunted, bred and migrated.
After the dinosaurs – the Eller Beck marine rocks and later footprint layers
The dinosaur days of the Saltwick Formation ended abruptly with another major oceanic incursion, which left calcareous, arenaceous and argillaceous deposits (limestone, sandstone and mudstone beds) known as the Eller Beck Formation. The evidence is in the new variety of fossils found in the cliff rocks and scattered over the beaches. Leaves, ferns and footprints gave way to muddy burrows, clear-water limestone corals, bivalve shells and crinoids.
Even so, there were four other periods when dinosaurs roamed the forests and wetlands, and their footprints are now found in many places along this coast. The four later footprint episodes include the Gristhorpe and Sycarham Beds, which are part of the Cloughton Formation, some of which is visible in the high part of East Cliff, Whitby. The others are the Moor Grit and the Long Nab Members, belonging to the Scalby Formation.
How the footprints were formed
Innumerable dinosaurs left tracks in the softer grounds. To form the footprint impressions, the land must have been fairly soft to take the impression of the foot; and hot enough to dry and harden the mud or sandstone before the next flood or tide came over the area. In estuaries and mudflat areas, rising tides tend to come in gradually and very gently, not disturbing the surface markings greatly.
This would enable a tiny proportion of the sun-baked prints to resist being washed away, and eventually to be filled in and buried by new deposits brought in by the flooding waters. With tides covering many estuarine mud flats twice every day, there is a lot of potential for building up a considerable depth of material, filling the depressions, amassing layer after layer, and burying them deeply. This continued for millions of years, building up great depths of hundreds and thousands of thin layers.
Several factors determined the shape and other characteristics of the fossil footprints:
(1) The structure of a dinosaur’s foot
Obviously enough, the biggest factor in deciding the shape of a footprint is the shape of the foot that made it. In turn, this is dependent on which type of dinosaur it was. As land-living vertebrates, dinosaur bone structures have much in common with modern creatures that walk on land.
Comparisons with birds are interesting for tracing direct evolutionary developments. But comparisons with other creatures are more interesting for understanding how dinosaurs walked. Humans tread on the heel of the foot, and take off from the ball and toes – if we run, we only use the ball and toes. This is how dinosaurs walked – on the ball of the foot. And, if they ran, it was often just on the toes, as a dog might (and as a horse always does). In fact, a dinosaur foot is structurally halfway between a human foot and a horse’s. They are raised onto the ball of the foot, and horses onto their middle toe – or hoof. The equivalent for a person would be on tip-toe, or wearing high stiletto heels. The human equivalent for how horses walk would be a ballet dancer on his/her points – or one point.
This means that a dinosaur footprint usually doesn’t include the heel: it is the toes and the ball of the foot. Occasionally, the heel may be pressed down, but only when at rest, and the result is a much extended footprint. It’s just convenient to refer to dinosaur footprints having a heel – but it’s a ‘false heel’ and to say a footprint was the toes and ball just doesn’t sound right. Figs. 30, 31 and 32 illustrate how much of the foot touched the ground, and the kind of footprint it would leave.
(2) How the foot landed and what on
A second major factor in determining the shape of the footprint is the way the foot landed, and what on or in. A single dinosaur could produce footprints that were entirely different from each other, within a few paces. There is evidence of this in the trackways along this coast, notably at Cayton Bay, near Filey. Simply walking sedately would produce a ‘normal’ impression. Poised on tip-toe, while stalking or eating from a high branch, for instance, would give a completely different footprint shape, perhaps only the toes. Running away from danger or towards prey would produce different prints entirely, as would a beast that was making a rapid turn, or one that was at rest, shuffling on the spot and so on. Looking at the modern paw-prints of dogs running on beaches gives exactly the right impression of how things must have been for dinosaurs – prints created by the same animal vary enormously, depending on what it is doing.
On hard ground, the foot might have left only the toe prints or claw prints – the parts which would have had the firmest pressure on the ground. In soft mud, the foot would have sunk deeply and the mud could well have slumped at least partly back into the footprint hole. Examples of mud dribbling or oozing into footprint impressions are common. Again, if the dinosaur wasn’t being especially careful where it put its feet, there could be mud splattered all around. Examples of a ‘splurge halo’ also abound.
(3) How time preserved them
Millions and millions of dinosaurs must have lived in the Jurassic age. Perhaps one in a million left its trace in the form of its footprints on one fleeting occasion that became fossilised. But, with so many dinosaurs, their preserved traces are plentiful in a few time-hallowed places. This is one of them, Whitby. They are a marvel – we know where one specific living creature was at one particular moment 165mya – and we might even have some idea of what it was doing.
It may have been wandering along a river bank looking for food or a crossing, meandering along in a herd or stalking its prey alone. It is only by sheer luck that some few prints were preserved – that they survived the next few minutes when the rest of the herd might have been trampling behind, or a rain storm coming, or the tide rising – all easily distorting or destroying the foot marks.
Fig. 36 illustrates how a lucky few footprints did survive – a slow enveloping and burying by silt, as a tide or river-overflow gently brought a protective covering to them. Repeated over the eons, the footprints were buried. Much, much later, the process was reversed and the overlying layers were eroded away, eventually re-exposing the treasures of the past.
The depression in the surface layer is the actual contact footprint. However, the lower layers may have felt the impact and pressure of the foot and become deformed to some extent, forming ‘transmitted’ prints of diminishing resemblance to the original one.
It is the top one that is the most detailed and faithful reproduction of the underside of the foot. If any durable material filled it in later, it can form a natural cast. Such natural casts occur frequently. In succeeding aeons, the rock may weather down or split apart, or the infill can pop out. These form a solid cast of the underside of the foot and can sometimes be remarkable in the amount of detail they have preserved.
Succeeding layers may reveal ‘transmitted’ prints, becoming less like the original with depth until there is merely a faint depression. Or, if the split-apart rock is turned over, the footprint is raised. A great many of the beach-boulder footprints are of this nature – raised, and originating below the true level where the foot landed.
In Part 2 of this article, I will look at the problems that are encountered in trying to match the footprints to particular dinosaur species; and at the idea of ichno-species. And, finally, I will discuss at a simple suggested compromise in classifying the footprints.
Dinosaurs of the British Isles, by Dean R Lomax and Nobumichi Tamura, Siri Scientific Press, Manchester (2014), 414 pages (softback), ISBN: 978-0-9574530-5-0.