How to get a head. Or, what your skull is saying about you.
By Katherine Aitchison, on 30 November 2011
Can you read a skull? Did you know that the human is actually a fish? Can you tell your synapsids from your diapsids? Well read on to learn all the skull can tell us about life and evolution.
The UCL Grant Museum of Zoology has been a teaching collection for more than two decades, but last night it opened its collection for a public workshop for the first time, and I was one of the lucky souls who bagged a ticket and went along looking forward to getting my hands on some bones.
To begin, we took a seat at tables displaying a range of notably different skulls. We were then asked to take a look at the specimens in front of us and identify a number of key features that would help tell us more about what animal the skull had come from.
This was a real hands-on event, which meant actually picking the skull up and moving it around to have a good look at it which offered a unique chance to handle some incredibly rare specimens.
Some of the features we were asked to look for seemed relatively straightforward such as “where do the eyes go”. It’s not until you stop and think about what that tells you about the animal that you really see the significance.
Primates have eyes at the front of the skull and facing forward which allows binocular vision and is used for depth perception. This is a mark of a predator, as depth perception is needed to judge how far away an animal is before pouncing. In contrast, a skull with eye sockets on the side indicates an animal that is commonly preyed upon, as the side-facing eyes allow for a wide field of vision, giving early warning of an approaching predator.
Other features may not be so easily identifiable, but still give us important information. For example; “how does it breathe?” Looking at the “internal nostrils” where air from the nose enters the oral cavity of the skull can tell you if an animal is warm or cold blooded.
In warm-blooded animals, such as primates, breathing is a constant process as we need a lot of oxygen to generate our body heat. Therefore, air enters the oral cavity right at the back of the throat, which allows us to continue breathing while we are eating. The opposite of this can be seen in a cold-blooded turtle skull, where air goes straight into the mouth as it is not so critical for the animal to be able to continue breathing while feeding.
Next, we were given a crash course in taxonomy and a whistle-stop tour through the evolution of the skull, starting with the jawless fish and going right through to the diverse ‘amniote’ skulls seen among land-dwellers.
This brings me to the point about humans being fish. Taxonomy is a hierarchical classification system, which means that every branch of the family tree remains a member of the group it originally branched from. Vertebrate evolution began in the ocean with fish who developed a brain case and a jaw (gnathastomes), then developed skeletons of bone not cartilage (osteichthyes) and who then went on to develop four limbs and walk on land (tetrapods).
Every new member of the tree is still a member of the previous class, which means tetrapods (including humans) are still classified as osteichthyes and that almost every vertebrate alive today is officially classified as a fish! Bet you didn’t know that now did you?
The term amniote (think amniotic fluid) refers to all creatures apart from fish and amphibians and they are split into three categories based on the number of holes in their skulls. Synapsids (mammals) were the first to develop and they have one hole behind the eye socket (I should point out here that eye sockets, ear holes and the mouth don’t count) although this is hard to identify in primates as we have filled the hole with brain, clever things that we are.
Anapsids (such as turtles) have no holes and diapsids (everything else including snakes, dinosaurs and birds) have an additional hole on the top of the head. And that is the major point to remember in classifying an amniote skull!
One last interesting fact from the evening came while we were examining snake skulls. You may have heard that a snake can dislocate its jaw in order to swallow food whole, but this is actually not the case. In fact, a snake’s skull, instead of being hinged once at the jaw, is hinged in seven different places, which allows it to form a complete circle from its skull without dislocating a thing!
It was a fascinating evening that allowed me to indulge my love of evolution as well as giving me a real insight into the workings of the skull and lots of juicy facts to drop into conversation the next time I want to show off!
For anyone who hasn’t been, I highly recommend a trip to the Grant Museum and taking a close look at the skulls they have on display to see what you can read in them.