Rather like a newborn giraffe staggers to its feet or a freshly hatched snakelet can strike, pterosaur hatchlings may have been able to fly, paleontologists postulated on Thursday.
But like the neonatal herbivore’s first steps and baby snake’s first hunting efforts, the newly vivant pterosaur hatchling may not have flown very well. They almost certainly didn’t fly like the adults.
The report on the baby pterosaur’s postulated avian ability shores up previous work on the subject, and was published by Darren Naish of England’s University of Southampton and colleagues in Scientific Reports.
Qualitative work published in 2019 had already indicated that at least some pterosaur hatchlings were independent from early on. This new study supports that theory quantitatively, based on analysis of fossil embryonic bones still in the egg and of juvenile pterosaurs.
Pterosaurs were flying reptiles that lived from the Triassic about 230 million years ago through to the Cretaceous: the last ones apparently met their maker with the other non-avian dinosaurs 66 million years ago. Over this yawning span of time, they came in a vast range of sizes and forms. That makes it hard to distinguish between small adults and big babies, aka flaplings. Also, fossilized pterosaur eggs and embryos are extremely rare, the researchers explain.
Therefore, paleontologists have been at odds over whether the youngest pterosaurs could take to the air – and if they did, in what fashion.
There were three options: the “flap-early” model, in which the babies were independent and could fly by flapping their wings; the “fly late” model, which posits they could only fly from the half-grown stage; and the “glide early” model, in which the young pterosaurs could only glide.
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We may never know for sure, but although fossil prenatal pterosaurs are rare, there are some; and infant pterosaurs can be distinguished from wee adults based on the immaturity of certain skeletal features.
To the paleontologists’ surprise, they write, it seems that even when in egg, the pterosaurs they checked had adult-like skeletal proportions and also flight membranes. (The state of feathering in pterosaurs is another story entirely; in any case, rather like bats, they flapped with the help of wing membranes.)
So, Naish and the team modeled the aviation ability of the infant pterosaur using existing data: wing measurements from four established hatchling and embryo fossils, compared with the parallel measurements of adults, in two pterosaur species: Pterodaustro guinazui and Sinopterus dongi. They also compared the relative strength of the wing humerus bone in 22 adults versus three babies.
They concluded that aviating ptero-babies was plausible. The hatchlings’ humeruses were stronger than those of many adult pterosaurs, indicating that they would have been strong enough for flight within hours or days of hatching, they explain. (Note that the baby giraffe takes some minutes to get to its feet and a little longer before it can speed away from predators on the savanna.)
But they weren’t just miniature adults. The wing shape in pterosaur hatchlings was shorter and broader than those of adults, which may speak to their distance ability. They had a larger wing area relative to their body mass and size, the researchers explain. And that could indicate they may have been beautifully agile fliers but were less efficient than their parents at long-distance flight.
Agility in the air is a euphemism for the ability to suddenly change direction and speed, which would be an advantage for a toothsome newborn aviating reptile. At the other end of the rainbow, it could have made them nimble hunters, the researchers point out.
One reason for the fog shrouding the flight of the baby pterosaur, beyond their being extinct, is that a baby Sinopterus specimen had been mischaracterized as a distinct taxon, the researchers explain.
Indeed, paleontology has long had issues with telling whether a specific small specimen is a new species or a juvenile of known species – i.e., is a “teacup T-rex” such as the diminutive Nanotyrannus a different species or a baby? (Suskityrannus, on the other hand, was apparently full sized at 3-feet, or nearly 1 meter, tall at the hip.)
Anyway, back to pterosaurs and the subgroup pterodactyls. If the adults could soar afar efficiently and the babies were relatively fleet and agile in the air, then possibly the young ones grew up to dense habitats where they would be safer, only traveling in more open environments when adult, the team hypothesizes.
Anyway, even if one given species were early-flappers, that doesn’t mean all were. Hamipterus tianshanensis of the Cretaceous may have been flightless when young, based on the lack of ossification found in some embryonic wing elements, another study indicates.
The fact that birds are non-volant upon hatching and for some time afterward is neither here nor there – and anyway, there are some exceptions to that generalization such as certain megapodes, which are born precociously with open eyes, full wing feathers, body strength and, in some cases, the ability run and/or to fly. They need these abilities because unlike so many other kinds of birds, the parents don’t provide parental care. These kids are on their own.
One wonders if pterosaurs had parental care. The 2019 team suggested that since the flaplings could apparently fly, that argued against parental nurture. But other studies deduced that at least in the Hamipterus, the hatchlings did not in fact feature advanced ossification in the egg, which suggests the babies were flightless.
But think of the abilities of newborns in animals we know. Where the giraffe baby gets to its feet and can run in minutes or hours, human babies can take more than a year. It is possible that pterosaurs too ran the gamut from helpless at hatchlinghood and dependent on the parent pterosaurs, to fully flight-capable and self-reliant from the very start.