When we talk about dinosaurs, almost automatically we mentally evoke huge beasts such as Brachiosaurus, Diplodocus, Triceratops, Tyrannosaurus, Spinosaurus or Stegosaurus. If we think a little deeper we find other smaller ones like Velociraptor —smaller than people think— or Compsognathus. However, there are even smaller dinosaur fossils. Talking about them is not easy; the remains are few, scattered and difficult to identify. In part because small animals fossilize worse than large ones, since the decomposition process is faster, and on the other hand, a small fossil goes more unnoticed in a site. However, and despite the difficulties, today we bring five dinosaurs so small that they could fit in our hands.
Microraptor zhaoianus , the little biplane
Despite being a dinosaur discovered a little over two decades ago, it is also one of the most information we have. Thanks to extraordinarily well-preserved fossils discovered in China, we know that this tiny dromaeosaurid—from the same family as Velociraptor —from the Cretaceous did, in fact, have four wings. Not only were the front legs feathered, but also the rear ones, all with rémige feathers —asymmetrically shaped feathers that allow birds to fly.
Perhaps the most fascinating thing about Microraptor , however, is that we know its coloration. Comparing the microscopic structure of fossil feathers with that of modern bird feathers, a research team led by Professor Quanguo Li, from the Beijing Natural History Museum, deduced that Microraptor must have a black and iridescent coloration, with greenish or bluish, similar to that of some modern crows and magpies. Interestingly, it weighed just over a kilo, about the weight of a modern crow.
Albinykus baatar , the (almost) complete fossil
One of the difficulties in identifying very small dinosaurs is resolving the question of whether they are adult specimens or hatchlings. When the fossils are quite complete, however, there are certain anatomical features that allow it to be estimated. In this case, we find an almost complete skeleton, of which only the skull is missing, and whose hind legs are perfectly articulated —that is, the bones are placed as they were in life—. Thanks to this, we know that the fossil is from a subadult that had reached a size close to the maximum of the adults of its species.
It lived at the end of the Cretaceous, and is one of the last members of the Alvarezsaurid group, like Ceratonykus or Alvarezsaurus itself, a family of dinosaurs that, exceptionally, showed a tendency to reduce their size as they progressed in their evolutionary history, instead of getting bigger, as usual. The weight of this animal was around 800 g, similar to a yellow-crested cockatoo.
BYU-2022, the solitary femur
Behind the name “Palaeopteryx thomsoni” hides one of the unknowns of paleontology. It is not at all clear what kind of dinosaur it was. The only rest that
What we have of this animal is a femur, and according to comparative anatomy, it may belong to a dromaeosaurid —the family of Microraptor and Velociraptor— or to a primitive bird from the end of the Jurassic.
Currently that scientific name is considered invalid, that is, it is not allowed to designate any animal, hence the inverted commas. What we do know, however, is that the fossil, however small, is very real — it is known as BYU-2022 — and whatever animal it belonged to, we do know it was an extraordinarily small dinosaur. The length of the femur is barely 45 millimeters, and according to mathematical models based on birds, it would correspond to an animal weighing about 400 grams, approximately the weight of an owl.
Epidexipteryx hui , strange little
This dinosaur, belonging to the scansoriopterígidos group, from the middle and end of the Jurassic can be described as peculiar, to say the least. It had a horny beak and the bony part of the tail was extraordinarily short, forming a kind of primitive, incipient pygostyle—the small, fused skeletal structure that modern birds have on their tails. However, the most characteristic feature was the plume of four feathers that it had for a tail. The structure of these feathers was quite simple, and did not seem to have the pilot function that those of modern birds have; therefore, Epidexipteryx is considered the first known dinosaur with ornamental feathers.
Only 6 years after its discovery, in 2015, a new scansoriopterigid called Yi qi was discovered, which allowed these dinosaurs to be reconstructed with a new appearance. Although their bodies were covered in feathers, they also had membranes on their front legs, forming wings similar to those of a bat.
The fossil from which Epidexipteryx is described is, as in the case of Albinykus, a subadult, so it would be expected that it could grow a little more, but not too much. Its estimated weight is just 164 grams, about the same as a kestrel or an owl.
Mellisuga helenae, the smallest dinosaur in history.
No, I have not gone crazy.
Mellisuga helenae is the scientific name of the hummingbird zunzuncito, also called fly bird. The reason we find it on this list is that birds are actually dinosaurs. Modern dinosaurs, who survived the cataclysm. Full-fledged dinosaurs, and without nuance.
This hummingbird measures just 6 cm from the tip of the beak to the tail, and weighs just 1.8 grams. The male is somewhat smaller than the female, and this makes it the smallest bird, and the smallest adult warm-blooded animal in the world.
Unfortunately, due to deforestation and the fragmentation of their habitat to obtain wood, the creation of crop fields and livestock, their population is decreasing year after year. It is currently in a “near threatened” state, but it would not be surprising if, sooner rather than later, its situation worsens. Let’s just hope that in a few years, this list won’t be made up entirely of extinct species.
REFERENCES:
Field, D. J. et al. 2013. Skeletal Correlates for Body Mass Estimation in Modern and Fossil Flying Birds. PLoS ONE, 8(11), e82000. DOI: 10.1371/journal.pone.0082000Jensen, J. A. et al. 1989. Small pterosaurs and dinosaurs from the Uncompahgre fauna (Brushy Basin Member, Morrison Formation: ?Tithonian), Late Jurassic, western Colorado. Journal of Paleontology, 63(3), 364-373. DOI: 10.1017/S0022336000019533Li, Q. et al. 2012. Reconstruction of Microraptor and the Evolution of Iridescent Plumage. Science, 335(6073), 1215-1219. DOI: 10.1126/science.1213780Nesbitt, S. J. et al. 2011. A small alvarezsaurid from the eastern Gobi Desert offers insight into evolutionary patterns in the Alvarezsauroidea. Journal of Vertebrate Paleontology, 31(1), 144-153. DOI: 10.1080/02724634.2011.540053Xu, X. et al. 2003. Four-winged dinosaurs from China. Nature, 421(6921), 335-340.DOI: 10.1038/nature01342Zhang, F. et al. 2008. A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature, 455(7216), 1105-1108. DOI: 10.1038/nature07447
