Back in time: Exhibit charts history of vertebrates

A fascinating exhibition by the University of Cambridge’s Museum of Zoology has just opened to the public. It’s called Growing a backbone: Rise of the vertebrates and our very own Will Tingle went along for a spine-tingling preview…

Will - My gym teacher always told me to grow a spine, so today I'm taking his advice and heading down to Cambridge University's Museum of Zoology to meet the man who can tell me all about the virtues of growing a backbone.

Jason - I am Jason Head. I am the curator of vertebrate palaeontology in the University Museum of Zoology at the University of Cambridge, and I'm the professor of vertebrate evolution and ecology in the Department Zoology at Cambridge.

Will - Do we know roughly when the first vertebrate may have come about and what it might have looked like?

Jason - So the oldest fossil vertebrates tell us that the group originates at least by what we would call the early to middle Cambrian. This is going to be somewhere around 520, 530 million years ago.

Will - Why a backbone, though? What about it is so beneficial to those that have one that has allowed such a wide variety of species to evolve?

Jason - The backbone, or the spine, or the vertebral column is a really important structure in vertebrate evolution. When we evolve this multi segmented series of bones that connect together and can bend and twist, we evolve massive body sizes. We can climb, we can swim, we can crawl, we can support ribs, we can support our organs with them. So the vertebral column, the spine, is what we like to call the central axis of the vertebrate body, but it's also the central axis of vertebrate evolution.

Will - As we are looking out here across all these organisms across a great span of time, one thing that strikes me is the fact that you've had to study vertebrates by purely looking at fossil records and the fossil record would imply, if I looked at it, that the spine was just a series of bones. How do you make such assumptions based on just the fossil records that you have?

Jason - The nice thing about bones is that their shapes, their anatomies, their features give us clues about the soft tissues that they're integrated with, that they connect to. So we can know things about the spinal cord by looking at the passages in the bone that the spinal cord passes through, we can tell about the muscles that connect the various bones of the backbone by the attachment sites on the various vertebrae. We do use the fossil record, it's invaluable and it's a necessary component to understanding vertebrae evolution, but we can also look at how the embryological development in living vertebrates occurs and we can see how everything from the genetics that control how vertebrae are patterned to the various ways in which the animals grow and the rate and the speed and how many vertebrae they develop. All of this integrates with the fossil record and then the morphology or the anatomy of living vertebrates to give us a complete picture of how we became this dominant group in terms of ecology, diversity and body size today.

Will - Are there any particular highlights, any favourites that you'd love to walk me through?

Jason - Sure. We can start over here if you want. This is the skeleton of about a three and a half metre long Burmese python. It's one of the largest snake species in the world. What we've done is we've laid the specimen out so that it's in a straight line and we have the spine running straight behind the skull and then the ribs are laid out on either side of this specimen. What we wanted to do is show how the spine changes along the body of a snake and how the ribs change, but also to really accentuate how many individual bones make up the spine of a snake, which is hundreds. That's a really interesting feature of these animals, and we know that evolutionary changes in how they develop as embryos are what led to this increase in the number of bones in the spine. Many snakes do actually keep hind legs. They actually have a femur, a thigh bone and, based on work by one of our postgraduate students here in the museum, we've discovered that some snakes actually have the shin bones, the tibia, and the fibula, still. The interesting thing about the hind legs in snakes is that those snakes that retain them actually use them in mating. A male snake will crawl up next to a female snake and the thigh bone still sticks out of the body, it has a little keratinous covering (keratin being the stuff that our fingernails are made out of) and these little legs are really powerful, and so they can vibrate them really quickly against the side of the female's body. That indicates that the male is ready to mate

Will - And they say romance is dead. This final one, I think I recognise this, but I'm going to be very embarrassed if I get this wrong. This looks awfully like a skull of my own.

Jason - Yeah. This is a human skull and we have it in a case with the skull of a crocodile, and we have it with some birds and sheep and a snake. These skulls are actually built and arranged on a particular type of armature where the skulls are what we call exploded. All the bones are close to each other and in position, but they're all on separate rods so you can see how they fit together. This was actually a Victorian teaching tool, and what we've done is we've used these specimens to illustrate a point about the evolution of special features of vertebrates, specifically how vertebrates evolve a face. If you grab the top of your head with one hand and grab your face with the other hand, you're going to be holding two different types of tissue, two different types of bone, that actually don't have exactly the same evolutionary history.

Jason - Our face is composed of bone that is derived from a special cell type called neural crest. Neural crest is a unique feature of vertebrates. It forms parts of the connective tissues of our sensory systems that could link them to the brain, but it also forms the bones of our face and the bones of our collar bones. The senses in your face and their supports in the bones of the skull are all derived from this unique feature called neural crest. What we've done is, by having these exploded skulls, we've not only been able to use a Victorian teaching tool, we've been able to use it to show a new discovery and development that is really a mid 20th century innovation.

Will - Thank you so much for showing me around. This is absolutely fascinating. I feel like we only touched the surface of what's available at this exhibit. We've talked about backbones and we've talked about jaws, but what else is there for people to enjoy if they come along?

Jason - One of the exhibits we also have is an exhibit that talks about the origin of vertebrates moving from water to land. This was pioneering work done by my predecessor in the museum, Professor Jenny Clack. Anyone who wants to come to the museum and discover how we went from fish in the water to tetrapods on land, and how we went from fins to limbs, can come on up and see those specimens and you can hear about that research.

Will - I'll be there, day one, first in the queue.