I love reading through Charles Darwin’s diaries. Who wouldn’t? Written in his early 20s, Darwin writes detailed accounts of his days on board HMS Beagle. For me, these are accounts of fantastic, real, adventures: travelling where no Englishman had travelled before, discovering new animals and plants, and finding gigantic creatures trapped in the rocks. His own words, scrawled in his cramped cabin, or beneath the clear South American night transports you back with him.

Who doesn’t dream of adventure like that? I am a strong believer in creating your own adventures in life, yet there is something wonderfully romantic about being swept away in somebody else’s.

Darwin was almost never on the Beagle. A young Robert Fitzroy unexpectedly took command of the big ship during it’s first voyage when the captain shot himself. It wasn’t unusual for captains to fall into depression on long voyages away from home. Fitzroy was paranoid and didn’t want to go the same way as his predecessor (or his uncle, who slit his own throat). He wanted a travel companion for the next voyage. News of this potential opportunity reached Darwin in a letter from his old lecturer, John Henslow, at Cambridge University. After a meeting with Captain Fitzroy, and then persuading his father it would be a worthwhile journey, Darwin joined the HMS Beagle on what would almost be a 5 year voyage around the world. A voyage that would change how this man viewed the world he lived in.

As the captain’s companion, Darwin had no official duties on the ship. Captain Fitzroy was making a detailed survey of the South American coastline, so there was ample opportunity for Darwin to explore. And explore he did. He collected, prepared and sent back to England numerous crates of new animals and plants unknown to science. Much to Robert McCormick’s frustration. As the ship’s surgeon, McCormick also wore the title of ship’s naturalist. But he was tied up too much in treating sick sailors he couldn’t compete with the enthusiastic young Darwin who was free to spend days collecting as much as he wanted to. McCormick left the Beagle after only 4 months on board.

The route of the 2nd Voyage of the HMS Beagle. The majority of the voyage was spent surveying the coastline of South America. (Image by WEBMASTER at the German language Wikipedia. from here)

The legacy of Darwin’s Beagle voyage goes beyond the Galapagos finches. A huge number of new animals stored in alcohol, prepared as skins, or delicately pinned, were shipped to England in enormous crates. My personal favourite is the beautifully unusual Rhinoderma darwinii: Darwin’s frog. The males of this bizarre amphibian have an extra large air sac, which they uses to raise their young. Inside their body. Nature never ceases to amaze.

There were also bones in the crates Darwin shipped back to England. Bones of giants.

Exploring rugged rock outcrops, and using the local knowledge, Darwin found troves of fossils from all over South America. Fossilised bones of very large beasts. These were the remains of Pleistocene mega-fauna: creatures no one had seen before.

The majority of these long dead creatures were relatively easily identified by the great comparative anatomist, Richard Owen. There were several species of giant sloth (Mylodon darwinii, Glossotherium sp., and others). Other fossils included remains of a horse, a Glyptodont, and some Stegomastodon bones. There were two other animals Darwin collected that were so strange, they baffled even the great Owen: the weird looking Macrauchenia and the misfit rhinoceros-looking beast Toxodon. 

A herd of wonderfully weird Litopterns. (Art by Tabitha Paterson @TabithaPaterson)

Owen thought the Macrauchenia belonged to the now obsolete group, Pachydermata (which grouped the elephants along with some herbivores). He also placed it as being close to the camels. It was later placed in a new Order of its own, the Litopterna.

The unusual native ungulate of South America, Toxodon platensis. This beast has been moved in and out of different taxonomic groups several times, never really settling in to something which fitted. (Illustration © Peter Schouten)

Toxodon caused similar confusion straight from the beginning. Darwin thought one specimen he purchased was the giant ground sloth Megatherium. Another specimen he suggested belonged to the Rodentia. Owen placed it in that great group that never was, Pachydermata, but he also suggested it shared affinities with Rodentia (mice, rats, etc.), Edentata (sloths) and herbivorous cetaceans (whales). It seems Owen couldn’t really make up his mind about where this creature should sit in life’s grand tree. More recently Toxodon has been reassessed and placed in the Order Notoungulata (which includes Toxodon and Typotheria, another large, extinct rodent-like beast).

Features in the bones of Toxodon and Macrauchenia both have hinted at relationships to several different types of animals, including elephants, rodents and camels. But for over 180 years their true identity has been hotly debated. It’s all been a little chaotic for these two strange animals.

Until now.

A new study by Welker et al. (2015) published in Nature may have sorted out this taxonomic nightmare.

Exploring relationships between organisms can be done by studying DNA. This is the most common way of producing a species tree (or phylogeny). Unfortunately, DNA degrades very quickly and rarely turns up in fossils that are tens of thousands of years old (although it does happen in special cases). Something else in fossils does survive much longer: collagen. This is a pretty tough, resilient protein, which makes up a large part of the muscles, tendons, and organic fraction of bones in our bodies. Collagen can also be a source of evolutionary information, as it is variable. The amino acid sequence that makes up collagen (coded for by genes in the organism’s DNA) differs slightly from species to species, with the closer together the species, the more similar the collagen they share. In an analogous way to DNA phylogenies, the variation in the amino acid sequence from collagen can be used to construct family trees for species.

A large number of Toxodon and Macrauchenia bones were tested, analysed, arranged, and modelled. The team even sequenced a number of other extinct animals with less confused taxonomies – a horse, mammoth and a giant ground sloth, as well as some modern species to check that their methods worked. The results show that these two creatures were more closely related to other mammal groups than previously thought. They both belong to the Order Perissodactyla (the odd-toed ungulates, a group that includes horses, rhinos and tapirs).

An early draft of the tree showing the relationship between the Toxodon and Macrauchenia to other mammals. The chicken at the bottom is there for a reason – it tests that the other results are sound: if they fit into the chicken group, then something is very wrong! At the top right, the close relationship between the rhinos, horses, and tapirs. The protein analysis places Toxodon and Macauchenia related to the Perissodactyla, creating the new Panperissodactyla. (Image reproduced with kind permission from Matthew Collins)

This is huge news! As well as resolving one of the oldest mysteries in palaeontology, the methods discussed in this new paper open the door for a  suite of new studies of strange and enigmatic taxa! Ancient DNA is great, but because it is quite a fragile molecule, there are only a few special sites and conditions that allow it to be preserved. Looking at proteins, which are much sturdier molecules, could give us a whole new window into the past!

Written by Jan Freedman (@JanFreedman) and Ross Barnett (@DeepFriedDNA)

Further reading:

Welker, F, et el. (2015), ‘Ancient proteins resolve the evolutionary history of Darwin’s South American ungulates’, Nature. [Abstract only]

Charles Darwin’s Beagle diary online: here

Fernicola, J. C., Vizcaino, F, and de Iuliis, G. (2009), ‘The Fossil Mammals collected by Charles Darwin in South America during his travels on board the HMS Beagle’, Revista de la Asociatión Geológica Argentina. 64 (1), 147-59. [Full article]