Wednesday 8 April 2015

Bring Back Bronto?

Hitting the science news pages this week is the proposal, by Emanuel Tschopp of Lisbon University and his team, that Brontosaurus be reconsidered as a valid taxon, independent of Apatosaurus.

The story of Brontosaurus, and how it no longer technically exists, is one of the most well-known palaeontological tales. Back in the late 19th century, the so-called Bone Wars raged between rival scientists hoping to make names for themselves in the developing field of palaeontology, particularly with regards to the Dinosauria. As part of this, numerous genera were discovered, but many were in fact duplicates - multiple specimens of the same genera, granted several names. In taxonomy, with some very rare exceptions, the names of taxons are given seniority by publication order. The great bone pioneer Othniel Charles Marsh discovered Apatosaurus ajax in 1877, only for him to rediscover it two years later from a slightly different fossil, which he named Brontosaurus excelsus. Neither specimen was complete, although the second fossil was quite substantial, and both lacked a head. Over time, analysis of the two specimens concluded that, in spite of some differences, they were similar enough to be considered part of the same genus, albeit granted separate species. Apatosaurus was named first, so it had priority, and so Brontosaurus excelsus became Apatosaurus excelsus.

A modern reconstruction of the Apatosaurus, showing Diplodocus-like skull and spines.

However, Brontosaurus is by far the superior name for a dinosaur, and it is not surprising that it caught on in a way that Apatosaurus never has. Aside from the simple sound of it, the meaning is far more stirring. Apatosaurus has the rather wishy-washy translation of "deceptive lizard," while Brontosaurus has the far more fitting meaning of "thunder lizard," as befits such a mighty beast. When mounting the second specimen at the American Museum of Natural History, Henry Fairfield Osborn labelled it Brontosaurus, perpetuating the name. Brontosaurus became a hugely famous dinosaur, appearing in many textbooks and popular media, in spite of the fact that, according to scientific consensus, it never technically existed. The lack of a skull also caused problems. The creature was far stockier than its close relative Diplodocus, and was reconstructed with a heavy, boxlike skull based on that of the more distantly-related sauropod Morosaurus (itself later recognised as a junior synonym of Camarasaurus). It was years before the correct skull was considered to be similar to the gracile, almost snakelike head of the Diplodocus. Over the years, three more species have been reliably assigned to Apatosaurus: A. louisae, A. parvus and A. yahnahpin.

An outdated reconstruction of the Brontosaurus

Nonethless, Brontosaurus, boxy head or no, has remained a hugely recognisable dinosaur, far more so than the correct name. It even maintains an influence in palaeontological circles. The genus Eobrontosaurus, meaning "dawn thunder lizard," was suggested as an ancestral form, but has itself been absorbed into Apatosaurus (and now Brontosaurus). The Diplodocoidea, the sauropod clade that contains the families most closely related to Apatosaurus, is often referred to as "the brontosaurs" by palaeontologists, purely colloquially. It's an evocative name, and everyone can imagine a brontosaur.

After all this time, however, Tschopp's team's analysis has suggested that there are indeed enough differences between A. ajax and A. excelsus that the latter be removed from the genus and reassigned to its own, resurrecting the name Brontosaurus for scientific use. A similar move occurred a number of years ago when the species Brachiosaurus brancai was removed from the genus and assigned to its own, Giraffatitan. Under the proposal, A. louisae remains, while the other two species are reassigned to become B. parvus and B. yahnahpin.

I remain on the fence; as I've stated before, I'm not keen on the tendency to split similar fossils into dozens of genera, when modern animals feature many species, often with major differences, in the same genus. As this article states, it's really an issue of semantics rather than science. Tschopp's paper is available here and does list a number of differences between the species, and exhaustive analysis that should be applauded. Wiipedia, while never the most reliable of sources, has already moved the species concerned to a new Brontosaurus article, which is a good indication of the direction popular opinion will go. 

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