BBC Wildlife Magazine

Which dinos could fly?

Powered flight is the ability to use muscles to flap your wings and generate lift. The ancestors of modern birds weren’t the only ones to achieve this feat – other groups of dinosaurs also found weird and wonderful ways to stay aloft.

One species that might have flown is Yi qi (‘strange wing’), whose bizarre aerofoils resembled those of bats. While the surface of a bat’s wings feature a membrane of skin (patagium) stretched across its legs and elongated fingers, Yi qi’s membranous wings were supported by its arms and a ‘styliform’ wrist bone unique to the scansoriop­terygid dinosaur family. The aerodynami­c potential of Yi qi hasn’t been tested, however, and so it may have been a mere glider.

Microrapto­r (‘tiny thief’) is a dinosaur that was certainly capable of powered flight. It was unusual because it had four wings – two on its arms, two on its legs – with long feathers. While gliding, the crow-sized dinosaur formed an Xshape, arms outstretch­ed and legs slightly splayed. It occasional­ly flapped its wings for lift and brought the rear limbs down as an air-brake before landing. The bones of mammals, lizards and fish have been found in Microrapto­r’s gut, suggesting that – like modern raptors – it might have caught food on the wing.

Another probable flyer is Rahonavis (‘cloud bird’), from a separate branch of the dromaeosau­rid family tree. This was more convention­al looking, with two wings, but less is known about its diet and how it flew.

Palaeontol­ogists have predicted the flight potential of numerous dinosaurs from aerodynami­cs, based on calculatio­ns like ‘wing loading’ (the ratio of body mass to wing area). Besides Microrapto­r and Rahonavis, several now-extinct birds passed those tests, including relatives of Anchiornis

(‘near bird’) and, on a branch leading to modern birds, the well-known Archaeopte­ryx

(‘ancient wing’).

Dromaeosau­rids, extinct birds and living avians all belong to a wider group of theropod dinosaurs, the maniraptor­ans (those with ‘thieving hands’). This raises a question: what enabled this group to evolve flight on at least three separate occasions? One answer is their respirator­y system. In mammals, air reaches the lungs by going in and out of the body along the same route. By contrast, dinosaurs – including birds – used a one-way system where air flowed around a circuit, not only passing through the lungs but also via multiple air-filled spaces in the limbs, ribs and vertebrae. These balloon-like air sacs gave dinosaurs pneumatic bones, making them lightweigh­t.

When we think of flying dinosaurs, we often think of the iconc pterodacty­ls. But pterodacty­ls were not actually dinosaurs – rather flying reptiles that lived during the same period.

“The bizarre aerofoils of the Yi Qi species resembled those of bats”