For years palaeontologists have been trying to convince the public that Brontosaurus doesn’t, and never, existed but now a new study has been published that returns this name to the ranks of the dinosaurs. So why the sudden turn around?



Such a change is in fact a very normal part of the constant updates and revisions that come with the process of taxonomy (identifying and naming new species) though in this case it comes as part of a quite exceptionally detailed study. Taxonomy may sound like a relatively easy job, species are either new or not, but things are perhaps inevitably rather more complex than that. Evolution doesn’t proceed in big leaps and with discrete boundaries between different groups, but instead one thing grades into another over time as changes and differences accumulate. Eventually populations are different enough to be recognised as separate entities and given a name. However, such smearing of boundaries causes enough problems in sorting out living organisms, but with fossils where there is never a whole organism, (and even half a skeleton is a good find), this can be a more tricky area.

In the case of Brontosaurus, it was named mistakenly - the evidence at the time, and indeed for many decades afterwards, was insufficient to separate it from the already described Apatosaurus. That meant that under the rules of taxonomy (yes, there are rules) that name-wise, Apatosaurus should stay and Brontosaurus should go. This issue was actually recognised quite soon after the creation of the name Brontosaurus and so actually the persistence of the ‘thunder lizard’ is down to a commendable staying power in the public consciousness, despite its rejection by palaeontologists.

The return of Brontosaurus then while something of a surprise, is not a great rejection of previous work. Names undergo constant revision and as with any branch of science, new information means that current orthodoxy can change. Despite the jibes, taxonomists don’t routinely name new species after fragments of bones (though in some cases, new species can be identified from very little remains) but this has happened in the past and some names and descriptions do need to be tidied up and corrected. I’ve been privileged to help name a number of new dinosaurs and other fossil reptiles, and also been responsible for sinking a couple of others and it requires careful consideration of the details of the specimens at hand and the existing traits that define the various species.

Reconstruction of Brontosaurus - after a century this name has been returned to the pantheon of dinosaurs. Photograph: Davide Bonadonna

New information can come about a number of ways. New and better specimens can show what the rest of an animal was like and provide information that would help split it from an existing species, or show that an apparently unique feature was common, removing a diagnostic trait. We have recently gained a much better understanding of the growth of dinosaurs for example, that has helped show that some previously named animals were in fact juveniles of other, already known, species. In the case of Brontosaurus though, it’s mostly down to a detailed and thorough analysis of huge numbers of specimens of the giant sauropod dinosaurs.

The new paper took the approach of looking at every single available specimen as far as possible and then sorting out their anatomical similarities and differences. With this kind of data, it is possible to reconstruct a family tree of who is closest to whom and how they relate to one another. This kind of work is routine for looking at evolutionary pathways, but it can also sort out details of taxonomy, showing that species that have been identified as new in fact lie within all other specimens of another kind (and thus are not different) or alternatively that those thought to be ‘just another’ member of a species are actually separate and different.

Such an undertaking is not trivial: a huge amount of work has gone into the data and analysis for a project this big, with hundreds of measurements and characters assessed for each of dozens of specimens. From a practical point of view it’s far from simple either - plenty of the bones involved are colossal in size and weight and cannot be easily moved if at all (they are big, but also fragile) so collecting the data can be a painful process.

In this case, a number of specimens all previously identified as Brontosaurus in the past do actually come out together as close relatives of one another, and, although still close to Apatosaurus, are separate from this genus and show several distinct features that suggest they are different. Since the name Brontosaurus already exists for these animals, a new name doesn’t need to be created and instead the ‘thunder lizard’ (surely this wonderfully evocative translation is a large part of its popularity) is resurrected for them and thus returns to the ranks of the dinosaurs.

This is certainly a welcome return of one of one the most famous names in palaeontology and this time it might last a little longer. The strength of this new analysis suggests that Brontosaurus is back for the long haul, and while many people might not have realised it ever went away, a good number of palaeontologists and educators are going to be delighted that it’s no longer a sore point.

Tschopp et al. (2015), A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 3:e857; DOI 10.7717/peerj.857