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Did dinosaurs originate in Scotland? Probably not.

by on 2017/05/03

Written by Young Academy of Scotland member Steve Brusatte

Last month, a Guardian headline proclaimed: ‘Radical shakeup of dinosaur family tree points to unexpected Scottish origins’.

The article referred to a sensational new study of dinosaur genealogy by Cambridge University PhD student Matthew Baron and his colleagues, which was published as the cover article in the March 22, 2017 issue of Nature. The crux of that peer-reviewed study was a new family tree of dinosaurs, which broke with 130 years of consensus among palaeontologists by placing the meat-eating theropods (T. rex and kin) in a group with the beaked, plant-eating ornithischians (Triceratops and its cousins), rather than with the long-necked sauropods (the Brontosaurus group).

The new genealogy has sparked intense debate among dinosaur researchers, and generated news coverage across the globe. Some of these headlines were more hyperbolic than others, but most referenced the main conclusion of the study: that the dinosaur family tree may need to be redrawn.

The Guardian article, however, took a different approach. Much of its focus was on the idea that the new family tree may imply a Scottish origin for dinosaurs. Many other news outlets picked up on the Guardian story, including an Esquire piece that wove together the ‘Scottish origins’ narrative with that week’s big political story, the failure of the Republican health care bill in the USA.

The Guardian piece stated that, in the new study, scientists ‘(proposed) an unlikely origin for (dinosaurs): an obscure cat-sized creature found in Scotland.’ This creature—a slender and fast-moving reptile that lived about 230 million years ago, called Saltopus—was said to be ‘the closest thing in the fossil record to what the hypothetical common ancestor (of dinosaurs) might look like.’

In actuality, neither of these things were discussed, or even implied, in the peer-reviewed Nature study. What the study did find, however, was that Saltopus was most likely a close dinosaur relative, and along with the placement of some other northern hemisphere species close to the base of dinosaur genealogy, it might imply that dinosaurs originated in the northern part of the ancient supercontinent Pangea, not the southern part as scientists have long argued.

There are several issues with using Saltopus to determine the ancestral home of dinosaurs:

1) There is only a single fossil that has ever been found, and it is extremely fragmentary and highly damaged. It is encased in hard sandstones from the Lossiemouth area of Morayshire, and the poor preservation of the bones makes it very difficult to describe its anatomical features and compare it to dinosaurs and other fossil reptiles.

2) The new genealogical study of Baron et al. does not find Saltopus to be a dinosaur. It places the Scottish reptile as a close cousin of dinosaurs, tangled up with several other close dinosaur relatives in a thicket of branches near the base of the family tree. These cannot currently be resolved with the data at hand and the computer algorithms used by the authors. The main issue is that the scrappy single fossil of Saltopus preserves so few anatomical features that it is represented mostly by question marks (designating uncertainty) in the dataset. In fact, it is so incomplete that the authors exclude it in a secondary sensitivity analysis that allows them to recover a much better resolved tree.

3) Baron et al.’s study does not use any quantitative, statistical approach to predict the ancestral geographical area for dinosaurs. They simply note that the presence of some northern hemisphere species near the base of the tree may support a northern origin, but this hypothesis is not rigorously tested. There are also several southern hemisphere species still occupying branches near the root of the tree, so it is unclear if a northern or southern origin is a better fit to the data. Even if a northern hemisphere origin was favoured by a statistical analysis, that is a far cry from demonstrating that dinosaurs originated specifically in Scotland.

4) Although new dinosaur discoveries regularly make the headlines, the fossil record is hugely incomplete and heavily biased. Only a tiny fraction of everything that once lived will ever be preserved as fossils, to be discovered and studied by scientists. Therefore, there is always a danger of using a single fossil (in this case, a single fragmentary Scottish specimen) to make a grand hypothesis about the origin of a major group like dinosaurs. Even if Saltopus was statistically supported as the very closest relative of dinosaurs in the Baron et al. dataset, who’s to say that tomorrow somebody won’t find an even closer dinosaur relative in Uzbekistan or Romania, or any number of other places?

The authors of the Nature paper were aware of these issues. Matthew Baron was quoted in the Guardian piece as saying ‘It may just be that dinosaurs originated in Scotland’. We would be wise to heed the uncertainty permeating that statement.

 

 

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