Oh boy am I excited for this one! Not only will we look into the fascinating science of trace fossils, but ahead you'll be able to read more on an exciting study I have conducted on the South coast of England!
First, let's provide a bit of context as to what this type of fossil is. Dinosaur footprints are imprints left on sediment and are therefore classed as trace fossils or, more formally, ichnites. Ichnites are anything left behind by an organism that isn't its physical body, so that can be anything from footprints, to feeding/burrowing traces to even coprolites (fossilised poop). Ichnites are more commonly referred to as trace fossils.
Dinosaur footprints are the most famous of trace fossils, having been found all around the world from almost every type of dinosaur you can name. Of course, I mean every type and not every species. Dinosaur footprints are notoriously ambiguous, given that they don't preserve many details that can be aligned perfectly with specific species, only a group. This is why trace fossils are categorised as their own genera and species (named ichno-genera and ichno-species). For example, one ichno-genera (specifically the three-toed footprints seen in the picture above) is called Iguanadontipus sp., which refers to any footprint with specific characteristics attributed to all Iguanodontids. On the picture above, there are also sauropod footprints (top left and bottom right), so this particular exposure is a rich one!
This is from a site on the south coast of England, near a town called Hastings. Hastings is an area most famous for a battle that occurred in 1066 when Harold Godwinson attempted to defend against a Norman invasion. What isn't discussed quite as much is how rich the area is in fossils! Since the 19th century, the beaches of Hastings has been combed up and down for fossils, with scientists finding marine fossils, fossilised plant matter, various reptiles and mammals (including a few dinosaurs, such as Iguanodon bernissartensis) and, of course, ichnites! The rock unit found here was deposited during the Berrisian and Aptian stages of the early Cretaceous. Hastings is a perfect example of the turnover rate of fossils on beaches, since new fossils are constantly turning up (and disappearing) due to erosion, but I'll go into Hastings properly in a later post.
In the meantime, back to dinosaur footprints!
Like I said before, dinosaur footprints are found all over the world from all groups of dinosaurs. They can be found on their own or (ideally) as part of a trackway. They are always one of two types: pes or manus. A pes footprint is one made by the hind foot of the dinosaur and a manus is a footprint made by the front foot of the dinosaur (obviously only seen on dinosaurs who were quadrapedal).
Once the footprint has been heavily studied for overall shape and size, paleontologists can inspect smaller details to narrow down what kind of dinosaur made the footprints. Of course, this depends on how much detail has been captured and preserved, so a footprint that has been heavily eroded or wasn't created on a very pliable surface will give very little information. In an ideal scenario, however, incredible details can be captured such as skin impressions!
You'll often see many footprints (such as the ones above) are actually convex (that is, they are raised and coming towards you) and this happens when a dinosaur leaves behind a footprint before sediment is laid down on top of the footprint, creating a mould.
Some amazing sights around the world include the aforementioned Hastings (where yours truly has just finished a paper on), as well as the sauropod footprints in the Isle of Skye, Scotland:
Dinosaur Valley State Park, Texas:
La Rioja, Spain:
And on Cal Orcko, Bolivia, where (due to tectonic uplift) the tracks are on an almost vertical wall of rock!:
But, other than being really cool to look at, why do dinosaur footprints matter? Well, skeletal remains of a dinosaur shows us... well... a dead dinosaur. We can see its body plan, its size and make estimations on what the animal may have looked like. But, trace fossils such as dinosaur footprints show what the animal lived like!
From ichnites such as these, we can learn what dinosaurs ate, how they might have interacted, even how they probably walked!
For example, did you know that iguanodontids walked with a slight instep (that is to say, their toes pointed slightly inwards)? I didn't, until I saw it with my own eyes from the Hastings footprints.
What you see here is one of several 3D models of dinosaur footprints I built up using photogrammetry. The difficulty came when I saw that a few of the footprints were isolated, so there was no track to use to figure out if it was the dinosaur's left foot or right foot. However, the outer toe of a dinosaur is actually made up of more bones than the others, meaning that is more flexible. If weight is put on the foot in a walking motion, it would push this toe further away from the other two toes, meaning you can measure the angle between those toes to find out which side is the outer part of the foot. This was confirmed when I saw a correlation between this and the fact that there was a deeper depression on this side of each print (as seen on the areas in the darkest blue in the above image). This is seen on all of the prints, meaning it was walking with its weight more on the outside of the foot!
All this found from a foot shaped lump on a rock!
On top of this, I also pondered on the idea that these ornithopod footprints could have been made at the same time as the sauropod footprints seen. Of course, there is nothing to confirm this, but it does raise the question of interspecies herding. This is seen in modern times, where zebras have actually learned how to read the body language of giraffes when alerted to a predator (given that giraffes can see much further).
Interspecies herding with dinosaurs is something we see in films all the time, but, believe it or not, we have no evidence of that ever occurring with dinosaurs! That doesn't mean they didn't though. Surely giraffes and zebras herding together isn't the first time occurrence of interspecies herding ever. Well, trace fossils could just be the answer to this burning question (well, burning for me anyway).
Now, this is just a few of the possibilities and conclusions that can be inferred from some dinosaur footprints on a little ol' beach in sunny ol' England. Think of all the possibilities that we could see from future finds!