Doctor Who and the key to deep time

Originally published at Lost Worlds Revisited for the Guardian Science Blog Network on 12 July 2017:

https://www.theguardian.com/science/2017/jul/12/doctor-who-and-the-key-to-deep-time

Time-travel would be a useful tool for palaeontologists, but Doctor Who has already explained some of the fossil record for us

 

Every palaeontologist wants a time machine. The tantalising, scrappy bits of biology that survive in the fossil record are a tiny fraction of what I could find out from a quick field trip to the Cretaceous. I’ve got my list prepared of the first four or five trips I’ll make when such technology becomes widely available. And being forty-something and British, there’s one time machine that’s been a constant in my life: the Tardis.

Doctor Who has explored ideas in evolution and the fossil record many times. Old school fans will be happy to explain how the origins of life of Earth are not in hydrothermal vents in the deep oceans four billion years ago, but were actually triggered by Scaroth, last of the Jagaroth, taking off in his faulty spaceship which promptly exploded, causing a cascade of new organic molecules to form.

The end-Cretaceous mass extinction, which wiped out three quarters of all species on Earth, including the non-avian dinosaurs, is marked in the rock record by a thin, worldwide layer of sediments which tell us that the Earth was hit by an extra-terrestrial body. We have even found the impact crater in the Gulf of Mexico. But as all classic Doctor Who fans will tell you, it wasn’t a meteorite that struck the Earth and caused the global iridium spike, but a space freighter hijacked by Cybermen which fell through a time warp to 66 million years ago while the Doctor’s doomed companion Adric struggled to stop it. Poor Adric.

Then there’s the Silurians. The Silurians are intelligent, bipedal humanoids who have evolved on Earth, but from a reptilian, rather than mammalian, ancestor. The first thing to deal with is their dodgy name. The fossil record from the Silurian Period, around 420-440 million years ago shows us abundant life in the ocean, but only the first faltering steps towards life on land. No tetrapods strolling around, and definitely no smart, bipedal dinosaurs. When the third Doctor meets the closely allied Sea Devils, he tells us that the Eocenes would be a better name, but since the Eocene Epoch was 56 to 34 million years ago, ten million years after dinosaurs became extinct, this doesn’t really work either. Especially since we now know that the Silurians sent out space arks from Earth, replete with dinosaurs, to escape the end-Cretaceous impact. Frankly, I’m not sure how to reconcile this with the Cyberman explanation above.

Silurian rock: What life in the Silurian actually looked like Photograph: Susannah Lydon

The Silurians have a third commonly-used name: Homo reptilia. There’s a whole lecture in this one, about how we classify organisms, to explain why this is a rubbish name. Living things are classified in nested groups together according to how closely related they are. Our species, Homo sapiens, is a member of the genus Homo, which also contains other (extinct) species of humans, such as Homo habilis and Homo erectus. They all share a common ancestor. The Silurians, with their separate evolutionary history, could never be crowbarred into the genus Homo. You’d have to go several levels up the classification hierarchy, to somewhere in the Amniota clade, find their last common ancestor, which would have lived about 300 million years ago (were this not all, of course, fictional).

Of course, palaeontologists had already come up with the idea of sleek, bipedal reptilians evolving on Earth long before the Silurians got their makeover in new Doctor Who. Back in 1982 Dale Russell, at the National Museum of Canada in Ottawa, indulged in a thought experiment: what would have happened if theropod dinosaurs such as Troodon hadn’t been wiped out by the end-Cretaceous event? How would they have continued to evolve? This process resulted in a striking sculpture, called the Dinosauroid. Russell predicted an increase in brain size, large, forward-facing eyes, an upright stance, ‘fingers’ for manipulation of tools –no external genitals (it’s still a ‘reptile’). Which leads to interesting questions about what consenting Silurians get up to in private.

An interpretation of Dale Russell’s dinosauroid sculpture, from the Dinosaur Museum, Dorchester, Dorset. Photograph: Jim Linwood

Some palaeontologists were dismissive of this somewhat fanciful approach – but in terms of engaging the imagination of non-scientists, speculative fiction has a powerful reach. I, for one, welcome more overlaps between my favourite real, and imaginary, evolutionary histories.