Number 16 of this series of bad casts is another shocker. All the casts are actually really bad (possibly apart from that pretty darn good bad cast, but this is a cast of a model, not a real fossil). It is amazing how truly bad these casts are and nobody seems to have ever questioned them!
This week’s specimen fails to excite, as you would expect by now.
The ‘rock’ for this cast is fairly good for a change. Normally, the ‘rock’ (the block the fossil sits on) is just splattered with one colour where you can see the enormously clumsy brush strokes. This one has a little shading, and even a couple of ‘cracks’ thrown in. Nice touch.
The ‘rock’ looks pretty real. This (momentarily) takes your eyes away from what you are supposed to be looking at; the tennis racket in the middle of the slab.
The tennis racket is, of course, the cast of the fossil crocodile head. There are a few other bones included; two vertebrae and a leg bone. Presumably these were on the original fossil.
‘Presumably’, ‘probably’, ‘may have’, are words that often come up in this series of posts, because there is very little information with the specimens. With this cast there is a faded number but no information.
We can make educated guesses about what it is and why the museum possibly has it.
Looking at the snout, I know it is a crocodile skull. Alligators have wider snouts, whereas crocodiles have long thin snouts. It is quite a small specimen, but why have one?
I have a tingly feeling that all of these bad casts may have once been used to illustrate life through time. The collection of casts includes some trilobites, some ancient fish and even a dinosaur tooth. There are some mammals as well (which will come in the next few weeks). This crocodile ‘fossil’ may well have been used to show the people of Plymouth in 1910 a selection of different creatures that lived millions of years ago. Although the fossil is pretty bad, the choice of animal pretty good.
True crocodiles evolved around 200 million years ago. Before these, the ancestors lived on land and looked a little different. In the skull you can see four holes;
The front two holes are for the eye sockets. The two holes at the back are shared with many other animals, including, birds, snakes, lizards, dinosaurs, rhynchosaurs and others. These two holes (found in diapsids) would have attached muscles to the head. Because they are present in all these animals (including some other extinct ones), it shows that they are all closely related. But crocodiles and birds are even more closely related.
Crocodiles, dinosaurs and birds all belong to the group called archosaurs. This group is defined by the animals within it having two extra openings in the front of the skull (below the eye sockets). Sharing a similar feature like this means that the animals in this group all shared a common ancestor which split apart and evolved into some incredible forms!
Around 250 million years ago, during the Triassic Period, the dinosaurs were becoming the dominant land animals. The ancestors of crocodiles (known as crocodylomorphs) had evolved to take advantage of a number of food sources, including insects, meat, plants and fish. These land loving ancestors felt the pressure of the successful dinosaurs, and around 50 million years later, during the Jurassic Period, crocodiles were living solely in the water.
It was at this time, around 200 million years ago, that crocodiles began to look like crocodiles. Before then they were strange reptiles, some with nostrils on the tops of their heads (rather than at the end of their snouts), and others walks on two legs. They waited patiently in the rivers while large dinosaurs were taking sips of water, and some grew to enormous sizes to tackle this larger prey. The enormous Sarcosuchus was almost as long as a basketball court (around 20m), and would have enjoyed a dinosaur for dinner.
There is more information behind a bad cast than would first appear. A lot of information can be told around this bad cast and we can work out why the museum purchased it.
I may be trying to make this bad cast look extremely good with all the exciting information. Our educated guesses may actually be nothing more than an old Christmas present to a previous curator who left it in the office by mistake. I will never know.