Palaeontologists in Japan have uncovered the fossilised remains of a 120-million-year-old flying dinosaur that’s seriously shaking up the bird family tree.
Many of you have likely heard of Archaeopteryx – a winged, long-tailed dinosaur that lived during the Late Jurassic period some 160 million to 140 million years ago. This creature, with its flight and tail feathers, is the earliest known flying dinosaur and a critically important species in furthering our understanding of the origin of birds and the evolution of flight.
New research published last week in Communications Biology now describes the second-most primitive, or basal, flying dinosaur in the evolutionary record, an entirely new genus and species known as Fukuipteryx prima. The newly described species supplants Jeholornis, which is now the third-most primitive bird.
Found in Japan, this dinosaur lived 120 million years ago during the Early Cretaceous period (145 million to 100 million years ago), but the authors of the new study, led by palaeontologist Takuya Imai from the Institute of Dinosaur Research at Fukui Prefectural University in Japan, have good reason to believe this species emerged before that time.
Artist’s depiction of Fukuipteryx prima. (Image: Masanori Yoshida)
Archaeopteryx is still the king of basal birds, but many important physical characteristics associated with modern birds didn’t appear until the Early Cretaceous. Most notable of these characteristics is the pygostyle – a triangular plate located at the tip of the backbone, which modern birds use to support flight feathers. As the new paper reveals, Fukuipteryx was an early pygostylian bird capable of limited flight, but its tail end likely didn’t contribute to this capacity.
Fukuipteryx was unearthed in the Kitadani Dinosaur Quarry near the city of Katsuyama in Japan’s Fukui Prefecture, and it’s the first bird from this crucial time period to have been found outside of northeastern China. The fossil, a three-dimensionally preserved specimen, was nearly fully grown – about the size of a pigeon – when it died. Its 3D preservation is a rarity, as most other bird fossils from this time period have been squished into flat slabs, producing two-dimensional impressions. Consequently, the Fukuipteryx fossil was able to yield more anatomical information than usual.
One observation came as a big surprise to the researchers. Though the species is the most anatomically primitive bird from the Early Cretaceous, it was found in relatively young sediment, and more evolutionarily advanced species have been found in sediment older than the Fukuipteryx fossil.
“We were so surprised that we did the whole analysis again as we thought we did something wrong,” Imai told Gizmodo in an email. But it turned out the same no matter “how many times we checked our data and methods – the result did not change.”
Left: The fossil of Fukuipteryx prima. Right: Illustration of the bones contained within. (Image: T. Imai et al., 2019)
To conduct the analysis, Imai and his colleagues carefully measured the specimen and performed a comparative physical analysis with other fossil birds. The palaeontologists could not remove the fossilised bones from the rock for fear of damaging the specimen, so they used a micro-CT scanning technique to observe the skeleton embedded within the rock, in a procedure similar to how medical x-rays work but with microscopic accuracy and the ability to churn the data into a digital 3D model.
The physical analysis revealed some distinct similarities to Archaeopteryx, such as a large wishbone, unfused pelvis, and similar forelimbs.
“Fukuipteryx shows a somewhat unexpected combination of adaptations when seen in the context of early dinosaurian flight,” Dennis Voeten, a palaeontologist at Palacký University in the Czech Republic who was not involved in the study, said in an email to Gizmodo. “Certain shoulder and wing bones that would have played an important role during aerial locomotion appear quite primitive and are broadly similar to those in the oldest flying dinosaur discovered to date – Archaeopteryx.”
Unlike Archaeopteryx, however, Fukuipteryx had a fully formed pygostyle. Importantly, Imai and his team don’t believe the pygostyle was connected to flight and was instead a byproduct of shrinking tails among these dino-birds over evolutionary time. The authors believe Fukuipteryx could fly, but it wasn’t as proficient as modern birds and it probably glided or flapped short distances.
Despite its much more modern-appearing tail end, the researchers positioned Fukuipteryx “as the second-most primitive flying dinosaur, after only Archaeopteryx,” due to its very primitive shoulder and wing bones, said Voeten.
The detection of the pygostyle on Fukuipteryx is not as big a deal as it may sound in terms of its evolutionary role in avian flight, but it is a big deal in terms of where it places birds in the phylogenetic family tree.
“A couple of theropod dinosaurs [i.e. non-avian dinosaurs, such as T. rex and raptors] that apparently did not fly apparently possessed the pygostyle,” said Imai. “Studies of Fukuipteryx indicates that the pygostyle evolved at least twice independently during the evolution of birds, once in the lineage of Fukuipteryx and once in the lineage of modern birds. The observation that long-tailed Jeholornis is phylogenetically more advanced than short-tailed Fukuipteryx, together with the presence of pygostyle in non-avian theropods, suggests that the pygostyle was not a ‘must have’ for flight.”
Michael Pittman, a palaeontologist from the Vertebrate Palaeontology Laboratory at the University of Hong Kong, added some colour to these details.
“The earliest-diverging fossil birds had long tails and are known from Late Jurassic rocks from southern Germany and Early Cretaceous rocks from northeastern China. What makes Fukuipteryx special is that its tail is short instead and ends in a fused tip called a pygostyle,” explained Pittman, who wasn’t involved with the new research, in an email to Gizmodo. “This is surprising because this type of tail was previously only known in later-diverging fossil birds like Jinguofortis, Confuciusornis and Sapeornis and is what we now see in living birds.”
Pittman said the discovery is also significant in that it extends the fossil record of the earliest birds to the Early Cretaceous of Japan.
Voeten said the researchers presented “a detailed overview of Fukuipteryx that will certainly help in reconstructing the broader context of early dinosaurian flight,” but he did point out one important limitation.
“Although quite a good number of its bones have been found, the highly informative skull is unfortunately too damaged to include in the description,” Voeten told Gizmodo. “Since many informative adaptations are identified in the skull, only time will tell whether Fukuipteryx indeed maintains its primitive position among the dinosaurian pioneers of flight. This is, however, not something that the authors could have prevented. Fossilisation is a rare process and because the bones of flying animals tend to be fragile, they are often already damaged upon discovery.”
More conceptually, Voeten said the term “primitive” doesn’t always accurately reflect ancestry over time. He explained:
In fact, Fukuipteryx and Jeholornis shared the skies with a broad variety of contemporaneous bird-like dinosaurs that likely already enjoyed much more advanced flight capabilities. Fukuipteryx lived about 35 million years after Archaeopteryx and may therefore not preserve the exact adaptations that enabled the very first flying dinosaurs to take to skies after all. It nevertheless fits in neatly with a theory that has been gaining traction over the last few years.
Where the evolution of dinosaurian flight was traditionally viewed as having started in a single species that give rise to all other feathered flyers, including modern birds, we are now starting to see that the Mesozoic period may have been the stage of very diverse dinosaurian experiments with flight that were not necessarily restricted to a single lineage. Because comparable habits may lead to very similar skeletal adaptations, reconstructing the family relations of a diverse group of extinct flying dinosaurs may very well prove to be much more difficult than presently assumed. Since modern birds with very advanced flight adaptations are the only dinosaurs that survived the catastrophic end-Cretaceous meteorite impact, no comparable primitive feathered flight styles can be directly observed today. This makes the interpretation of bizarre flight experiments during the Mesozoic not only very challenging, but also very important for retracting the lost diversity of dinosaurs.
Funny how science works. The beginnings of a field may produce overly simplistic theories, but they often only appear that way in hindsight. The truth is almost always more complicated, as we’re learning with human evolution, for example. The more we learn about the past, the more complicated it seems to get. But what seems intractably complex now may not always stay that way. We just have to keep digging, both literally and figurative, for more evidence.
Featured image: Masanori Yoshida