An artist's conception shows Archaeopteryx, a creature that had the wings of a bird but the tail and teeth of a dinosaur.
John Sibbick / NHM
Powered flight has evolved three times in vertebrates, the long-extinct Triassic pterosaurs, in a Jurassic dinosaur lineage that would become birds and in the Early Cenozoic ancestors of today's bats.
Of those, the easiest to study the evolution of flight in is the dinosaur lineage that became birds, because there is a large and available group of birds and a rich fossil record to study.
Now a team of Evolutionary biologists at Johns Hopkins Medicine, including assistant professor of functional anatomy and evolution, Amy Balanoff, Ph.D. have combined PET scans of modern pigeons with studies of fossil dinosaurs to answer one of the enduring questions in evolutionary biology - how did powered flight evolve in birds?
Having established the role of the cerebellum in flight with the PET scans on pigeons, they then found that there was a progressing increase in the size and complexity of the cerebellum in the ancestral dinosaurs as they evolved into flying birds.
Their results are published in Proceedings of the Royal Society B.
As the Johns Hopkins Medicine news release explains:
Scientists have long thought that the cerebellum should be important in bird flight, but they lacked direct evidence. To pinpoint its value, the new research combined modern PET scan imaging data of ordinary pigeons with the fossil record, examining brain regions of birds during flight and braincases of ancient dinosaurs.In the abstract to their paper in Proceedings of the Royal Society B, the authors say:
"Powered flight among vertebrates is a rare event in evolutionary history," says Amy Balanoff, Ph.D., assistant professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine and first author on the published research.
In fact, Balanoff says, just three groups of vertebrates, or animals with a backbone, evolved to fly: extinct pterosaurs, the terrors of the sky during the Mesozoic period, which ended over 65 million years ago, bats and birds.
The three species are not closely related on the evolutionary tree, and the key factors or factor that enabled flight in all three have remained unclear.
Besides the outward physical adaptations for flight, such as long upper limbs, certain kinds of feathers, a streamlined body and other features, Balanoff and her colleagues designed research to find features that created a flight-ready brain.
To do so, she worked with biomedical engineers at Stony Brook University in New York to compare the brain activity of modern pigeons before and after flight.
The researchers performed positron emission tomography, or PET, imaging scans, the same technology commonly used on humans, to compare activity in 26 regions of the brain when the bird was at rest and immediately after it flew for 10 minutes from one perch to another. They scanned eight birds on different days.
PET scans use a compound similar to glucose that can be tracked to where it's most absorbed by brain cells, indicating increased use of energy and thus activity. The tracker degrades and gets excreted from the body within a day or two.
Of the 26 regions, one area — the cerebellum — had statistically significant increases in activity levels between resting and flying in all eight birds. Overall, the level of activity increase in the cerebellum differed by more than two standard statistical deviations, compared with other areas of the brain.
The researchers also detected increased brain activity in the so-called optic flow pathways, a network of brain cells that connect the retina in the eye to the cerebellum. These pathways process movement across the visual field.
Balanoff says their findings of activity increase in the cerebellum and optic flow pathways weren't necessarily surprising, since the areas have been hypothesized to play a role in flight.
What was new in their research was linking the cerebellum findings of flight-enabled brains in modern birds to the fossil record that showed how the brains of birdlike dinosaurs began to develop brain conditions for powered flight.
To do so, Balanoff used a digitized database of endocasts, or molds of the internal space of dinosaur skulls, which when filled, resemble the brain.
Balanoff identified and traced a sizable increase in cerebellum volume to some of the earliest species of maniraptoran dinosaurs, which preceded the first appearances of powered flight among ancient bird relatives, including Archaeopteryx, a winged dinosaur.
Balanoff and her team also found evidence in the endocasts of an increase in tissue folding in the cerebellum of early maniraptorans, an indication of increasing brain complexity.
The researchers cautioned that these are early findings, and brain activity changes during powered flight could also occur during other behaviors, such as gliding. They also note that their tests involved straightforward flying, without obstacles and with an easy flightpath, and other brain regions may be more active during complex flight maneuvers.
The research team plans next to pinpoint precise areas in the cerebellum that enable a flight-ready brain and the neural connections between these structures.
Scientific theories for why the brain gets bigger throughout evolutionary history include the need to traverse new and different landscapes, setting the stage for flight and other locomotive styles, says Gabriel Bever, Ph.D., associate professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine.
"At Johns Hopkins, the biomedical community has a wide-ranging set of tools and technology to help us understand evolutionary history and link our findings to fundamental research on how the brain works," he adds.
AbstractSo, a clear pattern of transition from the relatively small cerebellum of the avian dinosaurs to the larger cerebellum of modern birds; what creationists would call 'transitional' until shown it, then it becomes 'not-transitional'.
The evolution of flight is a rare event in vertebrate history, and one that demands functional integration across multiple anatomical/physiological systems. The neuroanatomical basis for such integration and the role that brain evolution assumes in behavioural transformations remain poorly understood. We make progress by (i) generating a positron emission tomography (PET)-based map of brain activity for pigeons during rest and flight, (ii) using these maps in a functional analysis of the brain during flight, and (iii) interpreting these data within a macroevolutionary context shaped by non-avian dinosaurs. Although neural activity is generally conserved from rest to flight, we found significant increases in the cerebellum as a whole and optic flow pathways. Conserved activity suggests processing of self-movement and image stabilization are critical when a bird takes to the air, while increased visual and cerebellar activity reflects the importance of integrating multimodal sensory information for flight-related movements. A derived cerebellar capability likely arose at the base of maniraptoran dinosaurs, where volumetric expansion and possible folding directly preceded paravian flight. These data represent an important step toward establishing how the brain of modern birds supports their unique behavioural repertoire and provide novel insights into the neurobiology of the bird-like dinosaurs that first achieved powered flight.
Balanoff, Amy; Ferrer, Elizabeth; Saleh, Lemise; Gignac, Paul M.; Gold, M. Eugenia L.; Marugán-Lobón, Jesús; Norell, Mark; Ouellette, David; Salerno, Michael; Watanabe, Akinobu; Wei, Shouyi; Bever, Gabriel; Vaska, Paul
Quantitative functional imaging of the pigeon brain: implications for the evolution of avian powered flight
Proceedings of the Royal Society B: Biological Sciences; 291 2015, 20232172. DOI: 10.1098/rspb.2023.2172.
© 2023 The Royal Society.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.
And as we've come to expect of science papers, not a hint of any abandonment of the TOE as the explanation for these observations, as creationists frauds have been telling their dupes has been imminent for the last 50 years, during which time the mountain of supporting evidence for the TOE has grown massively, due to DNA recovery and analysis and better technology such as the PET scanning equipment used in this work, and still not a single scrap of definitive evidence for any god or for creation by magic.
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