First Remote Touch Birds

Some probe-foraging birds locate their buried prey by detecting vibrations in the substrate using a specialized tactile bill-tip organ. This remarkable ‘sixth sense’ is known as remote touch, and the associated organ is found in probe-foraging species belonging to both the palaeognathous (in kiwi) and neognathous (in ibises and shorebirds) groups of modern birds. Intriguingly, a structurally similar bill-tip organ is also present in the beaks of living, non-probing palaeognathous birds (e.g. emu and ostriches) that do not use remote touch. A team of researchers from South Africa provides evidence that the lithornithids — the earliest known palaeognathous birds which evolved in the Cretaceous period — had the ability to use remote touch.

A pair of kiwi by John Gerrard Keulemans in A history of the birds of New Zealand, 1873. Image credit: National Library NZ.

“What’s been really exciting to paleobiologists studying the evolution of birds, aside from remote-touch being a remarkable sensory adaptation that has cropped up multiple times in the avian record, is that this bill-tip organ has the potential to be preserved in the fossil record, as it appears to potentially be characterized by large numbers of bony pits on the surfaces of the beak bones,” said lead author Carla du Toit, a Ph.D. candidate in the FitzPatrick Institute of African Ornithology at the University of Cape Town.

Toit and her colleagues hypothesized that the bill-tip organs found in all living paleognaths might be a vestigial organ remaining from their most recent common ancestor.

“Luckily, exquisitely preserved beaks of the lithornithids have been found in North America and Europe,” they said.

“These small birds with relatively long beaks and legs are believed to have co-existed with dinosaurs in the Cretaceous period before the extinction event that killed-off all non-avian dinosaurs.”

“Our study shows that some if not all the wetland-dwelling lithornithids were likely able to use remote-touch to locate buried prey, in much the same way that modern day ibises and kiwi do.”

The findings suggest that modern paleognaths retained the structural components of the ancestral bill-tip organ even though it became functionally redundant, much like the hind limb bones of whales or pythons.

“We’ve been puzzled by the bill-tip organs of ostriches and emus, ever since they were first described by South African researchers about five years ago,” said senior author Dr. Susan Cunningham, also from the FitzPatrick Institute of African Ornithology at the University of Cape Town.

“We knew what this kind of beak was for in probe-foraging birds like kiwis, which are also paleognaths, but it didn’t make sense that these structures were present in their giant non-probing relatives as well, especially as ostrich and emu brains are not wired to deal with the kind of tactile information a bill-tip organ provides.”

“Discovering that the earliest known paleognaths — the lithornithids — were thought to be probe-foraging wetland birds, and that there were beautifully preserved fossils available, was really a light-bulb moment for us.”

The results suggest that remote-touch evolved very early in modern birds, perhaps from snout tactile specializations of their non-avian dinosaur ancestors.

“This is such an incredibly cool study,” said co-author Professor Anusuya Chinsamy-Turan, also from the FitzPatrick Institute of African Ornithology at the University of Cape Town.

“We’ve been able to show that the Mesozoic ancestor of ratites (such as, ostriches, rhea, and emu) was a probe-feeding bird like modern ibises and kiwi.”

“Furthermore, our finding suggests that the remote-sense organ in the beaks of birds most likely originated from the sensitive snouts of their dinosaurian ancestors.”

The study was published in the Proceedings of the Royal Society B: Biological Sciences.

_____

C.J. du Toit et al. 2020. Cretaceous origins of the vibrotactile bill-tip organ in birds. Proc. R. Soc. B 287 (1940): 20202322; doi: 10.1098/rspb.2020.2322