Introducing Xenoposeidon

1st October 2007

[Click on any image to view the high-resolution version.]

Xenoposeidon is a new dinosaur, to be named in the November 2007 edition of the British journal Palaeontology. It is a sauropod: an elephant-sized hebivorous dinosaur with a long neck and tail and a small head, looking a bit like Apatosaurus, Diplodocus or Brachiosaurus. It is from the Early Cretaceous, probably about 130 million years old.

We know about it from a single bone -- and even that is only about half complete. Here it is:

It's a dorsal vertebra (part of the backbone), and the preserved portion is about 30 cm (one foot) tall. In this photo, we're looking at it from the left-hand side.

Those bony struts towards the top of the bone give us a good idea where various other parts of the bone must have been when it was complete. The whole thing would have looked something like this:

In life, a sequence of about a dozen vertebrae similar to this open would have been strung together to form the backbone:

The rounded part at the front of each vertebra's lower section fits neatly into a corresponding hollow at the back of the next.

Although in the last picture the successive bones are all shown the same, in reality there is a smooth change between those nearer the shoulders and those near the hips. From features that vary along the column, we can tell that the preserved bone was from near the hips. Here's where it would have been positioned in the live animal, and a rough guess at the size and shape of the whole dinosaur. (The size and shape are just informed guesses and shouldn't be taken too seriously.)

And here is the same image, but with the rest of a sauropod skeleton greyed out. Remember, there is no reason to think that the Xenoposeidon skeleton was particularly similar to this: it's just to give a rough idea.

The name Xenoposeidon means, roughly ``alien sauropod''. We chose that name because the single bone that is known from this animal is so weird it looks like it could have come from another planet. The name is pronounced ZEE-no-puh-SYE-d'n. (Why does "Poseidon" mean "sauropod"? There's some sleight of mind involved here: Xenoposeidon is named with another sauropod in mind, the giant brachiosaur Sauroposeidon from Oklahoma. We think of "-poseidon" as a suffix denoting a sauropod in the same way that "-raptor", which literally means "thief", is understood to mean a smallish, nasty theropod.)

In biology, all organisms (animals, plants, fungi, bacteria) have a two-part name, made up of the genus name and the species name - like Tyrannosaurus rex and Homo sapiens. The full name of the new dinosaur is Xenoposeidon proneneukus: the species name means ``forward sloping'', because the upper part of the bone that the new dinosaur is based on slopes forwards. It's pronounced pro-nen-YOO-koss.

The Xenoposeidon bone was excavated in the early 1890s, in Ecclesbourne Glen near Hastings, by Philip James Rufford. Unfortunately, detailed records weren't kept, so we don't know exactly where it was found and can't go looking for more of the skeleton.

The bone was acquired by the Natural History Museum and briefly reported (along with other bones) by Richard Lydekker in 1893.

But that report pretty much sunk without trace, and the specimen was ignored for the next 113 years.

In January 2006 I was searching the Natural History museum's collection of sauropod material, looking for something completely different, when I stumbled across this specimen, labelled as BMNH R2095. Just in case anyone cares, here's are some photos of me down in the Natural History Museum collections with the Xenoposeidon bone. (And, yes, I do realise that in the second one I appear to be gazing deeply into its eyes.)

I immediately realised the bone that would eventually become Xenoposeidon was something strange: it was unmistakable a dorsal vertebra from a sauropod, but didn't look like any dorsal I'd ever seen before. It seemed likely that it was something new to science, but there's a mound of literature to check and illustrations to compare with before you can come to that conclusion.

A label on the specimen told me that it had been described and figured by Lydekker, and gave the reference for his brief paper, so I got in touch with my colleague Darren Naish, who has a huge collection of old papers about Early Cretaceous English dinosaurs, to ask whether he had Lydekker's paper. Darren's reply was classic Naish: despite never having seen the specimen or even knowing its catalogue number, he already had some text about it lying around for an abandoned review article he'd been working on. So we decided to collaborate on a redescription and reassessment.

We had a big advantage over Lydekker: 113 years of work on sauropod dinosaurs. By the time we went to work on the bone that would become Xenoposeidon, a hundred sauropods had been named, many of them from excellent remains. There were lots of animals we could compare our specimen with, and lots of useful papers describing and discussing them. It was quickly apparent that my first instinct had been right: this bone was a dinosaur previously unknown to science. Not only that, it seems that it's the first known representative of a whole new family of sauropods.

Although scientists disagree on some details, we now have a pretty solid agreement on the sauropod family tree. A technique called cladistics is used to figure out the most likely relationships between the better known sauropods, and those known from less complete remains can then be slotted in where they fit best. Here's a fairly recent family tree from Harris (2006), showing the names of the most important groups of sauropods and the genera that they contain.

When we tried to place Xenoposeidon in this tree, we found that it was securely within the large group called Neosauropoda, but that we couldn't confidently place it in any of the subgroups. We verified that conclusion by running a cladistic analysis of our own, which confirmed our feeling that it could belong in any of the neosauropod groups even though it doesn't closely resemble bones from any of them.

We wrote the paper and sent it to the British journal Palaeontology in June 2006. Later that month, I presented what we knew about the new dinosaur at the Progressive Palaeontology conference (Taylor 2006).

Before a paper like this is published it has to go through a time-consuming peer-review process so that other palaeontologists can either confirm or dispute our findings. In this case, as with most papers, they did a bit of both: so we had to make some changes, including adding the cladistic analysis. Christmas came and went while this process rumbled on: I sent my friends a distinctive Christmas card:

After two rounds of review, Palaeontology is finally set to publish Xenoposeidon on 15 November 2007.


Here are the references to papers and presentations I've mentioned on this page:

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