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Reinstate Brontosaurus as its own dino, study declares

March 30, 2005
Courtesy 
and World Science staff

Al­though one of the most famous di­no­saurs, Bron­to­sau­rus, whose name means “thun­der lizard,” has for over a cen­tu­ry been con­sid­ered wrongly named.

In 1903, sci­en­tists agreed that the animals formerly known as Bron­to­sau­rus ex­cel­sus should be clas­si­fied as part of an­oth­er group, Ap­atosaurus. The rea­son­ing was that their dif­fer­ences were too mi­nor to mer­it dif­fer­ent a clas­sifica­t­ion. Ap­atosaurus was an old­er name, ex­plain­ing why both groups ended up un­der that name rath­er than the other.

But the new study claims con­clu­sive ev­i­dence that Bron­to­sau­rus is dif­fer­ent enough to be its own ge­nus, a cate­gory that can the­oret­ically in­clude more than one spe­cies.

Bron­to­sau­rus is one of the most char­is­mat­ic di­no­saurs, in­spir­ing genera­t­ions of chil­dren thanks to its huge size and evoc­a­tive name. But eve­ry arm­chair pa­le­on­tol­ogist knows the “cor­rect” name is Ap­atosaurus.

Courtesy Davide Bonadonna

Bron­to­sau­rus was nev­er really gone, though. It was just treated as a spe­cies with­in the larg­er ge­nus Ap­ato­saur­us. So, while sci­en­tists thought the ge­nus Bron­to­sau­rus was the same as Ap­ato­saur­us, they al­ways agreed that the spe­cies ex­cel­sus was dif­fer­ent from oth­er Ap­ato­saur­us spe­cies.

The his­to­ry dates back to the 1870s, when the West­ern Un­ited States yielded doz­ens of specta­cular fos­sil finds, often under the direc­tion of the fa­mous, ri­val pa­le­on­tol­ogists Oth­ni­el Marsh and Ed­ward Cope.

Marsh’s team found two huge, par­tial skele­tons of long-necked di­no­saurs and shipped them to the Yale Pea­body Mu­se­um in New Hav­en, where Marsh worked. Marsh de­scribed the first of these as Ap­ato­saur­us ajax, the first word mean­ing “de­cep­tive lizard” and the sec­ond a ref­er­ence to the an­cient Greek he­ro. He lat­er he named the sec­ond ske­l­e­ton Bron­to­sau­rus ex­cel­sus, or “no­ble thun­der lizard.” 

But nei­ther ske­l­e­ton had a skull. Marsh re­con­struct­ed one for Bron­to­sau­rus. It was a mas­sive beast, like Ap­atosaurus, and like an­oth­er long-necked di­no­saur from the West­ern Un­ited States, Ca­ma­ra­saur­us. Be­cause of this si­m­i­lar­ity, it seemed log­i­cal at the time that Bron­to­sau­rus had a si­m­i­larly stout, box-like skull, but that was wrong.

Shortly af­ter Marsh’s death, a team from the Field Mu­se­um of Chi­ca­go found an­oth­er ske­l­e­ton that re­sem­bled some­thing of a mid­dle ground be­tween Ap­ato­saur­us and Bron­to­sau­rus. Pa­le­on­tol­ogists con­clud­ed they must be quite si­m­i­lar af­ter all. That was the end of Bron­to­sau­rus as a sep­a­rate name.

A fi­nal b­low to “Bron­to­sau­rus” hap­pened in the 1970s, when re­search­ers showed that Ap­ato­saur­us was­n’t closely re­lat­ed to Ca­ma­rasaurus, but to yet an­oth­er di­no­saur from the same ar­e­a: Dip­lo­do­cus. Be­cause that one had a slen­der, horse-like skull, Ap­atosaurus and thus al­so “Bron­to­sau­rus” must have had a skull more si­m­i­lar to Dip­lo­do­cus in­stead of to Ca­ma­rasaurus. Thus a pop­u­lar myth about Bron­to­sau­rus be­ing an Ap­ato­saur­us with the wrong head was born.

In the new stu­dy, pub­lished in the re­search jour­nal PeerJ and with al­most 300 pages of sup­port­ing ev­i­dence, sci­en­tists from Por­tu­gal and the U.K. cite a list of dif­fer­ences be­tween the di­no­saurs that they say are at least as nu­mer­ous as those used to tell apart gen­era in oth­er cases.

But why is this coming out now, after more than a century?  “Our re­search would not have been pos­si­ble at this lev­el of de­tail 15 or more years ago,” said Eman­u­el Tschopp, a Swiss na­t­ional who led the study dur­ing his PhD at Uni­ver­si­dade No­va de Lis­boa in Por­tu­gal. “In fact, un­til very re­cent­ly, the claim that Bron­to­sau­rus was the same as Ap­ato­saur­us was com­pletely rea­son­a­ble, based on the knowl­edge we had.” It is only with many new find­ings of di­no­saurs like Ap­ato­saur­us and Bron­to­sau­rus that a de­tailed re­in­ves­ti­ga­t­ion has been pos­si­ble, he ex­plained.

In sci­ence, the dis­tinc­tion be­tween spe­cies and ge­nus—the first, a sub­clas­sifica­t­ion of the sec­ond—lacks clear rules. Does this mean that the de­ci­sion to res­ur­rect Bron­to­sau­rus is just a mat­ter of per­son­al taste? “Not at all,” said Tschopp. “We tried to be as ob­jec­tive as pos­si­ble whenev­er mak­ing a de­ci­sion which would dif­fer­entiate be­tween spe­cies and ge­nus.” 

The re­search­ers used sta­tis­ti­cal ap­proaches to cal­cu­late the dif­fer­ences be­tween oth­er spe­cies and gen­era of “diplodocid di­no­saurs,” and were sur­prised by the re­sult. “The dif­fer­ences we found be­tween Bron­to­sau­rus and Ap­atosaurus were at least as nu­mer­ous as the ones be­tween oth­er closely re­lat­ed gen­era, and much more than what you nor­mally find be­tween spe­cies,” said Rog­er Ben­son, a co-author from the Uni­vers­ity of Ox­ford in the U.K.

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Although well known as one of the most iconic dinosaurs, Brontosaurus, whose name means “thunder lizard,” has for over a century been considered wrongly named. In 1903, the scientific community concluded that the genus, or lineage, previously known as Brontosaurus excelsus should be classified as part of another group, Apatosaurus. The reasoning was that their differences were too minor to merit different a classification. Apatosaurus was an older name, explaining why both groups ended up under that name rather than Brontosaurus. But the new study claims conclusive evidence that Brontosaurus is different enough to be its own genus, a biological classication that can include one or more species. Brontosaurus is one of the most charismatic dinosaurs, inspiring generations of children thanks to its huge size and evocative name. But as every armchair paleontologist knows, Brontosaurus was a misnomer, and it should be correctly referred to as Apatosaurus. The Brontosaurus was never really gone—it was simply treated as a species within the larger genus Apatosaurus. So, while scientists thought the genus Brontosaurus was the same as Apatosaurus, they always agreed that the species excelsus was different from other Apatosaurus species. Now, paleontologists Emanuel Tschopp, Octávio Mateus, and Roger Benson say that Brontosaurus was a unique genus all along. The history of Brontosaurus dates back to the 1870s, the Western United States yielded dozens of dinosaur and other fossil discoveries. Crews excavated many skeletons, mostly for the famous rival paleontologists Othniel Marsh and Edward Cope. Marsh’s team found two huge, partial skeletons of long-necked dinosaurs and shipped them to the Yale Peabody Museum in New Haven, where Marsh worked. Marsh described the first of these as Apatosaurus ajax, the first word meaning “deceptive lizard” and the second a reference to the ancient Greek hero. He later he named the second skeleton Brontosaurus excelsus, or “noble thunder lizard.” But because neither skeleton had a skull, Marsh reconstructed one for Brontosaurus. It was a massive beast, like Apatosaurus, and like another long-necked dinosaur from the Western United States, Camarasaurus. Because of this similarity, it seemed logical at the time that Brontosaurus had a similarly stout, box-like skull, but that was wrong. Shortly after Marsh’s death, a team from the Field Museum of Chicago found another skeleton that resembled something of a middle ground between Apatosaurus and Brontosaurus. Paleontologists concluded they must be quite similar after all. That was the end of Brontosaurus as a separate name. A final blow to “Brontosaurus” happened in the 1970s, when researchers showed that Apatosaurus wasn’t closely related to Camarasaurus, but to yet another dinosaur from the same area: Diplodocus. Because Diplodocus had a slender, horse-like skull, Apatosaurus and thus also “Brontosaurus” must have had a skull more similar to Diplodocus instead of to Camarasaurus. Thus a popular, but incorrect myth about “Brontosaurus” being an Apatosaurus with the wrong head was born. In the new study, published in the research journal PeerJ and with almost 300 pages of supporting evidence, scientists from Portugal and the UK point to a list of differences between the dinosaurs that they say are at least as numerous as those used to distinguish genera in other cases. How can a single study overthrow more than a century of research? “Our research would not have been possible at this level of detail 15 or more years ago,” said Emanuel Tschopp, a Swiss national who led the study during his PhD at Universidade Nova de Lisboa in Portugal. “In fact, until very recently, the claim that Brontosaurus was the same as Apatosaurus was completely reasonable, based on the knowledge we had.” It is only with many new findings of dinosaurs similar to Apatosaurus and Brontosaurus that a detailed reinvestigation has been possible, he explained. In science, the distinction between species and genus—the first, a subclassification of the second—lacks clear rules. Does this mean that the decision to resurrect Brontosaurus is just a matter of personal taste? “Not at all”, said Tschopp. “We tried to be as objective as possible whenever making a decision which would differentiate between species and genus.” The researchers applied statistical approaches to calculate the differences between other species and genera of “diplodocid dinosaurs,” and were surprised by the result. “The differences we found between Brontosaurus and Apatosaurus were at least as numerous as the ones between other closely related genera, and much more than what you normally find between species,” said Roger Benson, a co-author from the University of Oxford in the U.K..