In 1879, Othniel Charles Marsh, professor of palaeontology at Yale University's Peabody Museum of Natural History¹, announced the discovery of a large and fairly complete sauropod dinosaur skeleton. He named it Brontosaurus excelsus, meaning 'noble thunder lizard'. This mighty creature quickly caught the public's imagination, appearing in films such as Gertie the Dinosaur (1914) The Lost World (1925), King Kong (1933) and One Million Years BC (1966).

Yet from as early as 1903 scientists have questioned the Brontosaurus. Since the mid 1970s scientists insisted that this mighty creature, despite its inspiring name and appearance, should be struck out of books about dinosaurs and renamed 'Apatosaurus'. Once again the Brontosaurus looked doomed to extinction. How had the mighty fallen? And how did the Brontosaurus again make world headlines in 2015 after everyone had counted it out?

Brontosaurus

The Brontosaurus was a sauropod - a large four-legged dinosaur. It grew up to 72ft long and weighed approximately 15 tonnes. It had a long neck, long whip-like tail, and a large body with shorter forelegs than hind legs. At the time of its discovery it was the largest creature known to have walked on Earth, although remains of even larger sauropod dinosaurs have since been unearthed².

What Makes an Animal Species?

To understand the story, a quick layman's grasp of the rules of animal classification is needed. The classification of all living and fossil organisms in biology uses binominal nomenclature in which every organism has two names, the first referring to the animal's genus and the second the animal's species. So for instance humans are Homo sapiens, with 'Homo' being the genus and 'sapiens' the species. The same is true of dinosaurs. The most famous example in which both the genus and species names are well known is Tyrannosaurus rex.

A genus groups very closely-related species together while a species is usually defined as including all organisms which are capable of reproducing to create fertile offspring. So the different breeds of dogs (Canis familiaris), though they are all shapes and sizes, are the same species as they can still mate and have a litter of puppies that can reproduce. A donkey (Equus africanus) and a horse (Equus ferus), though both are in the same genus (Equus) are different species as their offspring, a mule, cannot reproduce.

This definition is not as straightforward as it sounds, even with well-known, hard-to-miss animals such as elephants and giraffes that are alive today. With elephants, traditionally scientists have believed that there are two species, the African elephant (Loxodonta africana) and the Asian elephant (Elephas maximus). However many biologists now believe that African bush elephants (Loxodonta africana) and African forest elephants (Loxodonta cyclotis) are separate species. In September 2016 it was realised that instead of there being one species of giraffe as has long been thought, there are actually four: southern giraffe (Giraffa giraffe), Masai giraffe (Giraffa tippelskirchi), reticulated giraffe (Giraffa reticulate) and northern giraffe (Giraffa camelopardalis³.

If scientists are still questioning how many species there are and making exciting new discoveries about the largest land animals alive today, which are rather well-known animals, it is unsurprising that there are still questions regarding dinosaurs that have been extinct for æons.

International Code of Zoological Nomenclature

How an animal is named is regulated by the International Code of Zoological Nomenclature, or ICZN for short. This covers how to properly write the binominal nomenclature, or 'binomen' for short. This system dates back to 1758 when it was introduced by Carl Linnaeus, the father of taxonomy. The rules state that the new name should be written in in italics, capitalising the genus but not the species. This name must be unique, based on a holotype type-specimen⁴ and the first scientifically-published name used for that animal is always correct.

Palaeontology and Taxonomy

With prehistoric animals, it is often almost impossible to know with concrete certainty the exact species of an animal from fragmented remains. Scientists might discover a tooth of a male, juvenile carnivorous dinosaur and a fractured pelvis of a mature female carnivorous dinosaur – from that, it is impossible to know if they are definitely from the same species or not. This leads to discussion, evaluation and research in which previously held beliefs are naturally challenged or reinforced, as is the scientific method.

An example of this is the story of the Eohippus, which means 'dawn horse'. In 1876 Othniel Marsh discovered a primitive horse skeleton which he named Eohippus angustidens. However remains of another primitive horse named Hyracotherium leporinum had been discovered in 1839 and published in 1841 by Sir Richard Owen, creator of the Natural History Museum. In 1932 the similarity between the two led to Eohippus the dawn horse being renamed 'Hyracotherium', which means 'hyrax-like beast'. Since then scientists have often debated whether or not these two discoveries are in fact the same species.

Bone Wars: The Brontosaurus' Discovery

The Brontosaurus was discovered in 1879 in the Morrison Formation rocks at Como Bluff, Wyoming during the period of palaeontology nicknamed the 'Bone Wars' due to Marsh's competition with rival palaeontologist Edward Drinker Cope. Due to this rivalry and to minimise the risk of the opposition stealing their discoveries, both Marsh and Cope rushed their discoveries from the excavation stage onwards⁵. They especially hurried their discoveries' publications and scientific descriptions in order to be the first to announce their findings.

In 1877 in the Morrison Formation rocks in Gunnison County, Colorado, Marsh discovered a few small, unspectacular remains missing the skull he named Apatosaurus ajax. 'Apatosaurus' meant 'deceptive lizard' and it was also named after Ajax in the Trojan War. Two years later, the first Brontosaurus fossil's remains were found at a different site. These much larger and far more impressive bones were remarkably well preserved, though the Brontosaurus was not complete; most notably the head had not survived.

When Marsh arranged to put the remains of his Brontosaurus on display he wanted a complete creature, not one missing a head. With no skull having been found, he used a conjectural design based on that of the Camarasaurus supremus, a species of sauropod discovered by Cope in 1878⁶. He even used Camarasaurus skull fragments to give his design veracity, which resulted in many scientists believing the fake skull shape to be genuine. It has since been accepted that this head shape is incorrect and that a Brontosaurus skull is not short and bulky after all, but long and thin like a Diplodocus. Marsh died in 1899.

Elmer Riggs Be Doubtful

Elmer Riggs was an American palaeontologist who worked for Chicago's Field Museum of Natural History and is most famous for discovering tall sauropod Brachiosaurus altithorax in 1900. In that year he discovered a fairly complete Apatosaurus skeleton, which he compared to Brontosaurus and Apatosaurus. Following this study he concluded that the Apatosaurus ajax skeleton that Marsh had uncovered had been a juvenile specimen and that therefore there were fewer differences between Apatosaurus and Brontosaurus than had been previously thought. After study, in the 1903 edition of Geological Series of the Field Columbian Museum he argued that the Brontosaurus, though clearly its own species, was not different enough from Apatosaurus to warrant its own genus. He proposed that it should be renamed Apatosaurus excelsus, which would differentiate it from the Apatosaurus ajax. Riggs concluded:

In view of these facts the two genera may be regarded as synonymous. As the term 'Apatosaurus' has priority, 'Brontosaurus' will be regarded as a synonym.

The 20th Century

At first Riggs' theory had little impact, especially as the apparent skull shapes of Apatosaurus and Brontosaurus were clearly different. The Brontosaurus became widely accepted into popular culture. In 1914 Gertie the Dinosaur was one of the very first animated films, pioneering many techniques still in use today⁷. In 1916 a Brontosaurus became the logo for petrol company the Sinclair Oil Corporation⁸ and a Brontosaurus is captured and brought to London in 1925 film The Lost World, animated by Willis O'Brien based on the classic novel by Sir Arthur Conan Doyle. Brontosauruses also feature in Ray Harryhausen's dinosaur films and The Flintstones (1960-66) to name but a few.

Meanwhile, other dinosaur remains were found. In 1909 the first Apatosaurus skull was discovered at what is now the Dinosaur National Monument in the Carnegie Quarry. The remains were named Apatosaurus louisae after Louise Carnegie, wife of library-building philanthropist Andrew Carnegie who sponsored dinosaur research⁹. However because this newly-discovered skull looked nothing like the existing fake skull of the Brontosaurus, palaeontologists at the time debated whether the skull was really that of the Apatosaurus. The consensus concluded that it was the skull of a diplodocus instead. When this Apatosaurus was displayed the skull was not attached.

Despite this, the notion that the Brontosaurus was a species of Apatosaurus continued to attract attention and increasingly more supporters. Doctor Who mentioned this in 1974's 'Invasion of the Dinosaurs'. In 1975 John Stanton McIntosh and David Berman published their study¹⁰ that re-examined the Apatosaurus skull compared to Diplodocus skulls. They concluded that the Apatosaurus had a skull very similar, but subtly different, to that of Diplodocus and quite unlike that of a Camarasaurus as shown on the Brontosaurus. Following this, in 1979 the Apatosaurus named after Louise Carnegie finally had its head reattached to its body and displayed once more, at the Carnegie Museum of Natural History.

This was considered persuasive enough for the majority of palaeontologists to agree that Brontosaurus excelsus was a species of the genus Apatosaurus, although different from both Apatosaurus ajax and Apatosaurus louisae, although some dispute remained. This scientific discussion reached the wider public awareness in 1989 after the US Post Office issued a rather nice set of dinosaur-themed stamps, including one showing a Brontosaurus, only for palaeontologists to denounce the name as inaccurate. Palaeontologists would not unite in anger in this manner again until the broadcast of the first episode of Walking With Dinosaurs controversially showed dinosaurs urinating.

Brontosaurus was officially renamed Apatosaurus excelsus over 75 years after this had been first proposed and dinosaur textbooks were rewritten to that 'Brontosaurus should be called Apatosaurus', although it was always believed to be a different species of Apatosaurus. Apatosaurus the 'deceptive lizard' had fooled everyone into thinking that it was all-but identical to the Brontosaurus.

Resurrection from Extinction

In the 21st Century an international team of palaeontologists has overturned this long-held belief. A team led by Emanuel Tschopp, a Swiss vertebrate palaeontologist at Portugal's Universidade Nova de Lisboa working with Octávio Mateus, and Roger Benson of the University of Oxford have travelled to museums around the world, analysing 477 physical features of 81 specimens, including many crucial recently-discovered finds. Professor Mateus stated:

It's the classic example of how science works, especially when hypotheses are based on fragmentary fossils, it is possible for new finds to overthrow years of research.

Though it was not the aim of their investigation, their 300-page study published in 2015 concluded the Brontosaurus was a separate genus from the Apatosaurus after all, although both belong to the Apatosaurinae sub-family. Tschopp concluded:

Our research would not have been possible at this level of detail 15 or more years ago. In fact, until very recently, the claim that Brontosaurus was the same as Apatosaurus was completely reasonable, based on the knowledge we had. The Brontosaurus can be distinguished from Apatosaurus most easily by the neck, which is higher and less wide.

Roger Benson agreed, stating:

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.

The study stated that there were three different species of Brontosaurus: as well as Marsh's original Brontosaurus excelsus, there is a Brontosaurus parvus and Brontosaurus yahnahpin. The Brontosaurus parvus was discovered in 1902 and initially named Elosaurus, although between 1994 and 2015 it was considered to be the same genus as Apatosaurus and named Apatosaurus parvus. This was a slightly smaller species, as apparently was Brontosaurus yahnahpin, a fairly complete skeleton of which was discovered in 1994, though only one substantial specimen has been discovered to date. This is believed to date from 155 million years BC, three million years earlier than Brontosaurus excelsus, which led to one palaeontologist in 1998 publishing their belief that it is a separate genus and suggesting the name Eobrontosaurus (Dawn thunder lizard) instead.

Although the Brontosaurus has now been restored to its rightful place on the prehistoric pantheon, its story does not end there. The scientific method calls for constant research, testing of theories and uncovering further evidence that supports, questions and/or challenges established views, which is as it should be. Not every palaeontologist has accepted this report without question, with many especially feeling that as the story has received more intense media scrutiny than normal the rigorous scientific process is being overlooked. This then may well lead to further research. Pushing the boundaries of knowledge, no matter the direction or conclusion, can only be a good thing.