Understanding the transition from gliding to flapping in the ancestors of birds

The origins of flight in birds, along with the possibilities of gliding and flapping in various animals, remains a huge area of ​​research.

We have a good idea of ​​the main issues in the animal mass in question; their anatomical arrangement how they extend their various wings and use them as control surfaces (the arms, legs, and tail), and the amount of lift generated. Development remains strong here and so while there are places that need to be filled and more to come, this is not an area that has not been explored or is likely to make major breakthroughs, as most of them are, if not in hand, surely strongly pointing to the answers. However, one of the two main areas that still needs work in terms of the origins of flight is the transition from gliding to flapping.

Powered flight evolved only four times: in insects, bats, pterosaurs, and birds. Insects are not very helpful in bird flight; the origins of pterosaurs (the flying reptiles that lived alongside the dinosaurs) remain poorly understood in general and even less so in terms of their flight development; and fossil bats are extremely rare. So, all practical research is about the birds themselves and their dinosaur ancestors, and while the information we have from the fossil record is now exquisite and detailed, with dozens of species known from hundreds or thousands of specimens between them, the transition from gliding. in flapping is less understood.

Ongoing discoveries from China in particular, where there are many feathered dinosaurs that seem to be from the very point where flapping appeared, will likely help fill this gap soon, but there remains one more area that also needs additional work.

In order to fly in some ways, animals need to be launched and airborne. Most birds get most of their launching power from their legs, so even though their wings pump hard, it’s their running and/or jumping that gets them up. Very little emphasis has been placed on this important aspect of bird flight (both by paleontologists and science journalists), and the jumping capacity of various small dinosaurs needs to be investigated to see how it compares with apparent capacity. for flying, because there must be a fairly strong relationship between them. That said, perhaps jumping is a precursor to flying and it’s intriguing to see how far back in different lines the ability to jump properly. And for the larger theropods (the carnivorous dinosaurs) in particular, could they jump?

A related issue in terms of launching is the ability to climb vertical surfaces, mostly trees. Various studies strongly advocate small bird-like theropods as capable of climbing, but very likely did not engage in this behavior. Both obviously cannot be true, and as usual, the truth may be somewhere in between, as some animals do not seem to have many obvious adaptations for climbing but are surprisingly good at it, as seen by the number of goats that goes to the trees.

If flight evolved from primarily terrestrial non-climbing animals, that would be somewhat surprising, and so establishing their abilities in trees was an important part of the exercise in which these animals were launching from and by extension what evolutionary pressures trigger flight . After all, there is a big difference in terms of getting an initial elevation from the ground or from a tree branch. Sure, it looks like a lot of small gliders climb, or how else can they get to a high point if gliding can only bring you down, but that doesn’t mean first flappers have to take this approach. In addition, small theropods weren’t the only dinosaurs that could do this in trees, and there were many other small species from other groups that were light and agile and had relatively grasping hands.

Admittedly, none of them seem particularly well-suited to an arboreal life, especially given their lack of classic climbing signs such as well-developed claws for grasping, or arms with a wide range of motion. to reach awkward branches. But again, this does not eliminate the possibility that they get in and around some trees, and this is an area where all the work is focused on the origin of the birds and almost none on any other group.

Dinosaurs were primarily terrestrial animals and we have commented here on issues surrounding flight, but sooner or later most species will encounter large bodies of water. Dinosaurs seem strangely extinct as semi-aquatic or even highly aquatic species, but that doesn’t mean they didn’t swim or couldn’t swim. In fact, while some great work has been done on how various dinosaurs floated thanks to their large lungs and other pneumatic bits, it doesn’t say much about how well they did in water. .

There may be only a few good swimmers (even credible candidates for a semi-aquatic life do not have an in-depth analysis of their likely forms of locomotion), but it would certainly be interesting to know which species which can swim well and which are stranded. Several bonebeds of larger horned dinosaurs are known where the animals appear to have drowned, but we do not know whether these were relatively competent swimmers overcome by floodwaters or unexpectedly difficult crossings, or animals which would barely make it ashore at the best of times. , or even that mass drowning may be a fairly regular occurrence.

The role of excavation

A final terrestrial aspect that is less studied is excavation. Many dinosaurs probably dug holes to create nests in which to lay their eggs, and while the giant claws on the hands of some sauropods have been linked to digging nests, few others had anything like attention. The small insectivorous alvarezsaur, for example, has been shown to be well adapted to making burrows to uncover their food, and the small ornithischian Oryctodromeus seems to have lived in burrows and also shows some digging adaptations, but there has been little systematic study of the mechanics of their burrowing potential, let alone the host of other dinosaurs that were in some way likely capable of burrowing.

As with the point about goats above, animals do not necessarily exhibit a set of adaptations to be decent and active diggers in some circumstances. The (orange and somewhat hairy) Sumatran rhinoceros can dig fairly large and deep pits to make mud pits for themselves, despite lacking any real specialization for the activity. Although for rhinos it probably helped in the relatively soft and moist terrains of the rainforest, it seems really strange that no other dinosaurs engaged in similar behaviors and, when studied, the some can easily reveal something of an anatomical link to the production of this type. of thing.

In general, biomechanics is an emerging area of ​​research for dinosaurs, with continuous advances in technology allowing better and easier studies of complex motions and stresses and enabling to researchers who delve deeply into the physics of posture and movement. Of all the aspects covered in this book, this is probably the one area where most of the major pieces are played out and it is often only a matter of time until enough researchers address these questions and then we will have basic answers.

In the background, the work of non-paleontologists developing new technologies and software to allow better and faster calculations, and anatomists providing a deeper understanding of living animals, continues. to push this field into greater precision. So far, the overlap between paleontology and biomechanics is limited, as few researchers have the expertise to dive deep into this area, but it is growing in depth and breadth, and it is certainly an area with some major new innovations and answers to come. in the near future.

This essay is from HOW FAST DID T. REX RUN: UNSOLVED QUESTIONS FROM THE FRONTIERS OF DINOSAUR SCIENCE by David Hone. Copyright © 2022 by Princeton University Press. Reprinted by permission of Princeton University Press. Learn more about the book.

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