Numerous non-avian dinosaurs possessed pennaceous feathers on their proto-wings and tail. Their functions remain unclear. Seoul National University researcher Jinseok Park and colleagues propose that these pennaceous feathers were used in displays to flush hiding prey through stimulation of sensory-neural escape pathways in prey, allowing the dinosaurs to pursue the flushed prey.
Diversity of avian flush-pursuers, prey with simple neural escape pathways, and the Caudipteryx robot used in behavioral experiments. Image credit: Park et al., doi: 10.1038/s41598-023-50225-x.
“The early function of pennaceous feathers remains unclear,” Park and co-authors said.
“Over the past three decades, spectacular dinosaur fossils with diverse feather types have been discovered.”
“Among these fossils, pennaceous feathers, the type of feathers that is adaptively modified for flying in modern birds, are limited to Pennaraptora.”
“The earliest pennaceous feathers were present on the distal forelimbs as small ‘proto-wings’ and around the tip of the tail as distal caudal plumage in the early-diverging pennaraptorans, as preserved in Caudipteryx, a two-legged, peacock-sized pennaraptoran dinosaur that lived approximately 124 million years ago.”
“Proto-wings were too small to be used for powered flight. The functions of proto-wings and caudal plumage might have been related to foraging/hunting or other behaviors.”
The authors hypothesized that the proto-wings may have been used for ‘flush-pursuit’ foraging, a hunting strategy observed in multiple species of contemporary insectivorous and omnivorous bird species such as the greater roadrunner (Geococcyx californianus) and the northern mockingbird (Mimus polyglottos).
This strategy consists of predators using displays of contrasting-colored feathers on their wings and tails to startle prey out of hiding and into fleeing, at which point they can be pursued and caught.
To test their hypothesis, the researchers built a robot named Robopteryx, basing it on the size, shape, and estimated movement range of Caudipteryx.
They then used Robopteryx to imitate several variations of flush-pursuit display behaviors — with the full sequence consisting of spreading the proto-wings and raising a tail, pausing with them outstretched, then folding them back — and observed the behavioral response of grasshoppers to the display behavior.
Grasshoppers were used as they respond to flush-pursuit display behavior and belong to the order Orthoptera which existed concurrently with Caudipteryx.
The scientists found significant positive associations between the use of the proto-wings in the display behavior and both the likelihood of the grasshopper fleeing — with 93% of tested grasshoppers fleeing when the proto-wings were used compared to 47% without — and how far away Robopteryx was when they fled.
They also found significant associations between both the presence of white patches on the proto-wings and the presence of feathers on the tail and the likelihood of the grasshopper fleeing.
“Our results with Robopteryx support the flush-pursuit hypothesis, and provide a new perspective on why feathered wings and tails may have initially evolved in dinosaurs,” they concluded.
Their paper was published in the journal Scientific Reports.
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J. Park et al. 2024. Escape behaviors in prey and the evolution of pennaceous plumage in dinosaurs. Sci Rep 14, 549; doi: 10.1038/s41598-023-50225-x
Source : Breaking Science News