The hummingbird family now includes some of the smallest bird species in the world. But even in the Cretaceous period there were apparently bird-like creatures in miniature. This is now indicated by an exciting find from Myanmar: Researchers have discovered a 99 million year old piece of amber in which the tiny skull of a saurian has been preserved. He was probably only the size of the smallest hummingbird during his lifetime – making him the smallest dinosaur ever found. The fossil thus provides exciting insights into the evolution of dinosaurs and birds, as the team reports.
Bernstein always provides unique insights into the living environments of the past. Because parts of plants, animals and other organisms remain preserved in the fossil tree resin for millions of years. Paleontologists have already discovered numerous insects, primeval flowers, fungi and even blood-sucking ticks. Vertebrate fossils are very rarely found in amber clumps. In recent years, these rare finds have included the foot of an anole lizard, the wing of a primeval bird and the tail of a young dinosaur. Another of these rare fossils from the Dino era has now been discovered by researchers led by Lida Xing from the Chinese University of Earth Sciences in Beijing: the head of a miniature bird-like dinosaur.
A tiny predator
The roughly 99 million year old amber piece comes from the Angbamo site in northern Myanmar. The skull enclosed in it appears to belong to a fully grown animal, but is only 7.1 millimeters long. According to the scientists, this suggests that this dinosaur was only about the size of a bee elf – this Kolobriart is considered the smallest bird in the world and weighs just under two grams. However, this means that the newly discovered fossil could be the smallest known dinosaur from the Middle Ages. More detailed investigations of the find using high-resolution synchrotron scans confirmed that the mini-dinosaur has a combination of features never seen before. Xing’s team therefore assigned him to a new genre and type: Oculudentavis khaungraae.
Oculudentavis is derived from the Latin words for eye, tooth and bird. The name thus indicates the characteristic properties of the fossil. At first glance, as the researchers explain, the skull looks like that of a bird. What is striking, however, are the two relatively large eye sockets – they resemble the structures known from today’s lizards and only have a narrow opening that lets in little light. This indicates that Oculudentavis was active mainly in daylight. Individual bone elements are fused together in a unique way in the dinosaur. He also has a whole series of sharp teeth, a feature that can also be found in primeval birds such as the Enantiornithes. The scientists estimate that Oculudentavis had 29 or 30 teeth on the upper and lower jaw during their lifetime. These “weapons” suggest: Despite its tiny size, this bird-like dinosaur may have been a predator. He may have been feeding on small invertebrates like insects – unlike today’s mini-birds, which have no teeth and live on nectar.
Unclear relationship
“The conservation of vertebrates in amber is rare and this fossil gives us an insight into the world of dinosaurs at the lower end of the body size spectrum,” said co-author Lars Schmitz from the Natural History Museum of Los Angeles County. “Its unique anatomical properties point to one of the smallest and at the same time the most primitive birds ever found.” However: How exactly Oculudentavis is related to other dinosaurs and birds is unclear. “The skull has no features that clearly indicate its phylogenetic position,” the scientists explain. According to their analyzes, there are two possibilities: On the one hand, the mini saurian could belong to the Enantiornithes and thus to the most widespread group of primeval birds in the Cretaceous period. A closer relationship with dinosaurs like the Archeopteryx seems more likely, but Oculudentavis is more developed than this icon of the theory of evolution. It could therefore lie on the evolutionary family tree between the Archeopteryx and the Cretaceous primeval birds.
Regardless of the exact assignment, however, one thing is clear: mini-versions of bird-like dinosaurs developed much earlier than previously thought. “Birds had apparently reached their minimum height shortly after they appeared in the late Jurassic period,” comments paleobiologist Roger Benson from the University of Oxford, who was not involved in the study, in the journal “Nature”. In the opinion of Xing and his colleagues, the extreme miniaturization of oculudentavis also confirms a common hypothesis that the Cretaceous amber from the Angbamo site was created in a so-called island arch – an arch-shaped island chain that mostly arises in regions with high seismic and magmatic activity . Because: “Miniaturization often occurs in island environments,” they explain.
Hoping for more finds
Researchers are now hoping for more fossil finds to find out more about Oculudentavis and its evolutionary importance. “The past decade has provided much insight into the dinosaur-bird transition and significantly improved our understanding of this important evolutionary event. Bernstein has provided surprising insights such as previously unknown springs and skeletal structures, ”says Benson. “Oculudentavis suggests that the potential for further discoveries is far from being exhausted – also and especially with regard to small animals,” he concludes.
Source: Lida Xing (Chinese University of Earth Sciences, Beijing) et al., Nature, doi: 10.1038 / s41586-020-2068-4