A team of paleontologists led by Emanuel Tschopp at the New University of Lisbon in Portugal has just completed a massive computer analysis of fossils in a group of dinosaurs called Diplodocids. They found that Brontosaurus are its own group. Its fossils share distinct, incomparable bone features—enough for it to reclaim its iconic genus name.
According to Tschopp, there are seven specific bone differences that make the body of the original Brontosaurus its own species and genus, not just some other big dino that’s been mislabeled. Most of are rather subtle, including facts like this: The tail vertebrae in dinosaurs related to Brontosaurus have spiny prominences called “neural spines,” he says, “and for most of these dinosaurs these spines project kind of backwards, but in Brontosaurus they’re more straight up.” Brontosaurus’s hips are unusual, with two bones (the ilium and pubis) meeting a curious junction. And its lower leg fibula meets its ankle bones in an equally unusual manner. Like we said, we’re talking about subtle differences. But these are the differences that make a species.
The paper increases knowledge about the phylogenetic relationships of diplodocid sauropods. In order to resolve relationships within Diplodocidae, a specimen-based phylogenetic analysis was performed, which included all holotypes that have been identified as belonging to a diplodocid sauropod at some point in history.
The numerical approaches established in the present analysis allowed a reassessment of the validity of the numerous taxonomic names proposed within Diplodocidae. Thereby, it was found that apatosaurine diversity was particularly underestimated in the past. One genus previously synonymized with Apatosaurus is considered to be valid based on our quantitative approaches: Brontosaurus forms the sister clade to Apatosaurus in the present analysis. On the other hand, Elosaurus and Eobrontosaurus were found to be junior synonyms of Brontosaurus, and one more cluster of specimens was recovered at the base of Apatosaurinae, which might even represent a further, new apatosaurine genus. Apatosaurus was found to include only the two species A. ajax and A. louisae. This results in three genera and six species belonging to Apatosaurinae. In a less inclusive and less detailed specimen-based analysis of Apatosaurus, Upchurch, Tomida & Barrett (2004) found five species as probably valid, but did not include Eobrontosaurus yahnahpin. The species count recovered by our analysis is comparable to that proposed by Upchurch, Tomida & Barrett (2004).
In total, nine to eleven different species in seven or eight genera are recognized within Diplodocinae and six to seven species in three genera within Apatosaurinae. Together with the probable non-apatosaurine, non-diplodocine diplodocid Amphicoelias altus, this totals 15–18 valid diplodocid species, 12–15 of which are from the Morrison Formation of the western United States.
SOURCE – peerj paper, popular mechanics