Sometimes science gets a bad rap for changing its mind. First Pluto is a planet, and then it’s not. Scientists and policy makers started by talking about “global warming,” but have since come to prefer the term “climate change.” And now the beloved long-necked dinosaur of our childhoods, Brontosaurus, has been redeemed and acknowledged as a prehistoric beast unique and separate from that of Apatosaurus.
In what is surely to be one of the science stories that receives more than its fair share of time in the popular press, Emanual Tschopp et al.’s manuscript (“A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae”) detailing their “revival” of Brontosaurus was published today (April 7, 2015) in the journal PeerJ. The study is not only noteworthy for its simultaneous breadth and depth of work, but also for the reinstatement of Brontosaurus as a genus distinct from that of Apatosaurus, whereas previously Brontosaurus had been considered an incorrect and outdated name for Apatosaurus.
If you were a dinosaur buff as a child (or simply a know it all), you may have annoyed your parents by providing continual correction whenever the name “Brontosaurus” was used. Paleontologists have long held that the fossils of Brontosaurus are really just members of the genus Apatosaurus, and it is funny that the name “Brontosaurus” has gained such a prominent place in culture since that verdict was first made way back in 1903. (Talk about some severe cultural resistance to change!)
The search for discovering new fossils was fierce in the late 1800s, and while some potential prospectors were heading out to the American West in hopes of striking gold, paleontologists Edward Cope and Othniel Marsh were in a fierce competition to discover and name the ferocious prehistoric beasts known as dinosaurs. As may be expected, along with the intensively competitive research came the occasional lapse in attention to detail, and sometimes papers were published in a slapdash fashion with conclusions that wouldn’t fly by today’s standards.
Specifically, Marsh published short papers describing his discovery of Apatosaurus and Brontosaurus in 1877 and 1879 respectively, but by 1903 the paleontology community decided that the specimens were far too similar to be classified in separate genera (plural of “genus”), resulting in the “official” adoption of the name “Apatosaurus” for the genus since it was the specimen named first. (Remember that species are classified in a taxonomically appropriate manner as “Genus species,” such as “Homo sapiens” for humans and “Mus musculus” for the house mouse.)
In case it has been a while since you have studied taxonomy, let me provide a brief review. Taxonomy is the study of the organization and classification of living organisms. It is an old field that had its first modern conception in the 1700s with Carl Linnaeus. Taxonomy seeks to understand the relationships between all living organisms by studying their physical and morphological similarities and differences. This is a related, but distinct field from that of phylogeny, which seeks to map evolutionary relationships between organisms through genetic methods. Such evolutionary relationships for prehistoric animals such as dinosaurs are primarily formulated through careful comparison of the fossil record, although organisms whose close relatives are still alive today can benefit from phylogenetic analysis.
Sauropods, the “long-necked” dinosaurs whose members include the genera Brachiosaurus, Apatosaurus, and Diplodocus represent a completely extinct lineage of organisms that have no relatives alive today. This is in contrast to the two-legged theropods which include famous examples such as Velociraptor and Tyrannosaurus that scientists believe formed a group of organisms that eventually gave rise to birds. But because there are no living descendants of sauropods today, scientists must rely on careful anatomical studies from the available fossils to make conclusions about the species relationships. This is exactly what Tschopp et al. did in their new study.
The publication on PeerJ is incredibly long, and extremely thorough. Tschopp analyzed 477 skeletal features from 81 different specimens from museums around the world and online. You can check out the open-access paper for yourself if you so desire, complete with a whopping 120 figures (quite a few more than a publication like Science or Nature would allow). The details allow for other paleontologists to check their work, and provide further clarity to the family tree of the “Diplodocidae.” However, it will suffice to say, as Tschopp et al. are aware, that the exciting take-home message from their work that will interest the public is that the “existence” of Brontosaurus has been rightfully restored as a genus unique from that of Apatosaurus.
As for why the name “Brontosaurus” stuck around all these years since it was deemed “unofficial” in 1903…? Your guess is as good as mine. Suffice to say, the Jurassic-period dinosaurs Apatosaurus and Brontosaurus must have been similar enough in appearance to allow the debate about their identity to continue for well over 100 years. In other words, paleontologists might forgive you for interchangeably referring to “long-necked” dinosaurs as either Brontosaurus or Apatosaurus.
Hopefully paleontologists will now work to clearly define the differences between the Brontosaurus and Apatosaurus, so that a new generation of dinosaur-loving kids can grow up droning on to their parents about variations in the bone morphology of their favorite sauropods. (This brings to mind the image of a younger version of myself…) Regardless of the details of the difference however, this story is an excellent example in the process of science, and how ideas can change with the right degree of evidence.
Science is an always changing and continually developing endeavor, where facts and theories are only as good as the evidence that supports them. This is why Pluto has now been reclassified as a “dwarf planet,” why we no longer speak merely of “global warming” but of “climate change,” and why Brontosaurus and Apatosaurus can now be rightfully considered as their own species. It is good to stir up the dirt every once in a while, and Tschopp et al. bringing back our beloved Brontosaurus was definitely an excellent way to do so.