A paper published earlier this week in BMC Evolutionary biology suggests that one of only 12 known Archaeopteryx fossil skeletons is not in fact an Archaeopteryx at all but a new species of theropod dinosaur, Ostromia crassipes. One Dutch newspaper, perhaps over-egging it slightly, went as far as likening the discovery to finding out that your Monet painting turned out to be a Van Gogh. So what is Archaeopteryx and why has this paper got palaeontologists (a bit) excited?
What is Archaeopteryx?
You will find a cast of Archaeopteryx or two, or a model reconstruction in almost every natural history museum and Archaeopteryx is, quite rightly, described in the new paper as an iconic fossil. However, from personal experience in talking to museum visitors, it is not an extinct animal that many people are familiar with, being not quite on the same tier of recognisability as large dinosaurs.
First described in 1861, Archaeopteryx lithographica was the species name given to an isolated feather fossil, and later a fossilised feathered skeleton excavated from the lithographic limestone of Solnhofen in Germany. The Solnhofen limestone is one of the most widely known examples of a Konservat-Lagerstätte, a geological site of exceptional preservation. The discovery of the feather alone pushed the age of bird fossils back tens of millions of years, but the discovery and description of a the feathered skeleton could not have been better timed in the history of evolutionary biology, helping to build the iconic status of Archaeopteryx.
Icon of Evolution
Discovered just two years after the publication of Charles Darwin’s On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, Archaeopteryx ruffled feathers (boom boom) from the off. The fossil skeleton of Archaeopteryx showed typical reptilian features but also appeared to be covered in feathers. The discovery was met with incredulity by palaeontologists of the time, to whom the fixed nature of species was a long-ingrained idea. Feathers were firmly a characteristic of birds and could not be found associated with a reptile. Some scientists doubted the fossil until they saw it; others proposed that the structures superficially resembled feathers but were something else. Even renowned anatomist Richard Owen played down or ignored problematic reptile characteristics such as teeth in the skull and the anatomy of the limbs. The reason why the timing of the discovery couldn’t have been better timed is because many scientists were still debating Darwinian ideas of the transformation of species over time. For opponents, like Richard Owen, an almost perfect example of an “intermediate form” between birds and “saurians” like Archaeopteryx was problematic. Whether or not Archaeopteryx was a bird has been debated almost ever since, and very little else about this animal has been settled on. Amusingly, the Guardian fell foul of the Archaeopteryx bird-or-notcurse with Archaeopteryx being “knocked off its perch” in July 2011 and subsequently re-perched in October of the same year.
It’s a quirk of the history of discovery that Archaeopteryx has become a fulcrum for debates around evolution, the fixity of archetypes in animal groups and whether it’s a bird or the earliest true bird fossil. It’s only discoveries of other feathered reptiles, dino-birds and feather-like structures in reptiles in recent decades which have opened up the research in this area. It’s tempting to imagine how evolutionary biology may be completely different today had Archaeopteryx never been discovered exactly when it was. Would Richard Owen and allies have drawn out the acceptance of evolution without Archaeopteryx as a poster specimen for evolution (albeit not in the way we now understand it)? Because Archaeopteryx is an icon of evolution it’s also a target for creationists and there’s no doubt that the re-evaluation of this specimen will be hitting the print-on-demand creationist presses soon as yet further proof of the great palaeontological conspiracy or whatever it is we’re supposedly up to.
Following the discovery and description of the feather and first skeleton, over the years a number of other specimens came out of Solnhofen and one other locality and each gained a nickname, normally based on the museum they ended up in. After a long campaign to secure the specimen, the first skeleton ended up in the Natural History Museum London and became known as the London specimen. A second skeleton, the Berlin specimen, was discovered in 1876 and described in 1884. The Maxberg specimen, currently missing, was found in 1956. The Haarlem specimen was found in 1855 but not described until 1973. The Eichstätt specimen was found in 1951 and described in 1973. The mysterious Solnhofen specimen, original locality unknown, was described in 1988. The Munich specimen was discovered in 1992 and described in 1993. A further six specimens have been found since the late 1990s including a specimen held in a private collection and one specimen still awaiting scientific description.
These twelve specimens are all that is known about Archaeopteryx, and plenty of questions remain unanswered. A number of different identifications have been suggested, the number of species of Archaeopteryx is debated and size ranges across the known specimens have been posited as different developmental stages.
Whether Archaeopteryx was capable of true flight has also been the subject of much debate in the literature. Controversy around the origin, loss and rediscovery of some specimens means that interpreting the geographical, geological and temporal range of this species or group of species is also difficult. Twelve skeletons and a feather separated by thousands or tens of thousands of years in the geological record is an extremely limited data set to draw many firm conclusions from. Now, that list may be eleven skeletons and a feather thanks to the paper published this week: Re-evaluation of the Haarlem Archaeopteryx and the radiation of maniraptoran theropod dinosaurs (Foth & Rauhut 2017).
The ‘Haarlem specimen’, found in 1855 and described in 1975 is a part and a counter-part (two separate pieces of the same slab) which only preserves part of the right wing, part of the leg, some toes from both feet, a few vertebrae, belly ribs and fingers from the right hand. It is currently housed in the Teylers Museum in Haarlem, the Netherlands.
The research team re-examined the Haarlem specimen and found that, even given the poor preservation, anatomical details were different enough to distinguish it from Archaeopteryx and warrant an entirely new genus. Proportions of the fossil bones present were distinct from Archaeopteryx. The presence of furrows on both sides of the phalanges (fingers) is a character shared with theropod dinosaurs Anchiornis and Eosinopteryx from China. This specimen is distinct from both of those in the small size of the claw. This specimen is geologically younger than the supposed relatives from China and these characteristics and temporal difference are given as the basis for the new species, Ostromia crassipes.
As a number of palaeontologists have expressed on social media – and the research team themselves comment in the paper – the grounds for these differences aren’t as robust as they could be due to the partial preservation of the Haarlem specimen, but this is all part and parcel of the self-correcting process of science. No doubt this new research will prompt other scientists to reevaluate this specimen, other Archaeopteryx specimens and other closely related groups and it’s probable that consensus won’t be reached for a while.
Unfortunately for Ostromia crassipes, if the species holds up, it will likely always be associated with once being the iconic Archaeopteryx. As the researchers note, Archaeopteryx still holds onto one “perch” as the only Jurassic paravian theropod (the group of dinosaurs that also includes birds) outside of China, which isn’t quite as memorable as the first bird.
On a more personal and unprofessional note, if you do find yourself in the Netherlands and in the mood for a museum, I’d skip the Van Goghs and the Monets and make a pilgrimage to see Ostromia crassipes and the other geological wonders of the Teylers Museum for yourself.
There is quite a bit of literature about Archaeopteryx but two books stand out as an excellent overview of the history and discovery. Unfortunately, neither are up to date with recent discoveries. Bones of Contention: The Fossil that Shook Science by Paul Chambers is a popular science book that covers the controversy surrounding the discovery of Archaeopteryx, and the political and financial wrangling of scientists to get their hands on specimens. The second is Archaeopteryx: The Icon of Evolution by Peter Wellnhofer which is beautifully illustrated and packed with detail about the discovery, description and history of Archaeopteryx study.