How birds got their wings
The origin of a structure in bird wings essential to flight has been
found in dinosaurs

Date:
February 24, 2023
Source:
University of Tokyo
Summary:
Modern birds capable of flight all have a specialized wing structure
called the propatagium without which they could not fly. The
evolutionary origin of this structure has remained a mystery,
but new research suggests it evolved in nonavian dinosaurs. The
finding comes from statistical analyses of arm joints preserved
in fossils and helps fill some gaps in knowledge about the origin
of bird flight.


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FULL STORY ========================================================================== Modern birds capable of flight all have a specialized wing structure
called the propatagium without which they could not fly. The evolutionary origin of this structure has remained a mystery, but new research suggests
it evolved in nonavian dinosaurs. The finding comes from statistical
analyses of arm joints preserved in fossils and helps fill some gaps in knowledge about the origin of bird flight.


==========================================================================
For a long time now, we have known modern birds evolved from certain
lineages of dinosaurs that lived millions of years ago. This has led researchers to look to dinosaurs to explain some of the features unique
to birds, for example, feathers, bone structure and so on. But there's something special about the wings of birds in particular that piqued
the interest of researchers at the University of Tokyo's Department of
Earth and Planetary Science.

"At the leading edge of a bird's wing is a structure called the
propatagium, which contains a muscle connecting the shoulder and
wrist that helps the wing flapping and makes bird flight possible,"
said Associate Professor Tatsuya Hirasawa. "It's not found in other vertebrates, and it's also found to have disappeared or lost its
function in flightless birds, one of the reasons we know it's essential
for flight. So, in order to understand how flight evolved in birds,
we must know how the propatagium evolved. This is what prompted us to
explore some distant ancestors of modern birds, theropod dinosaurs."
Theropod dinosaurs, such as Tyrannosaurus rex and Velociraptor, had arms
not wings. If the scientists could find evidence of an early example of
the propatagium in these dinosaurs, it would help explain how the modern
avian branch of the tree of life transitioned from arms to wings. However,
it's not so simple, as the propatagium is made up of soft tissues which
do not fossilize well, if at all, so direct evidence might not be possible
to find. Instead, the researchers had to find an indirect way to identify
the presence or lack of a propatagium in a specimen.

"The solution we came up with to assess the presence of a propatagium
was to collect data about the angles of joints along the arm, or
wing, of a dinosaur or bird," said Yurika Uno, a graduate student
at Hirasawa's lab. "In modern birds, the wings cannot fully extend
due to the propatagium, constraining the range of angles possible
between connecting sections. If we could find a similarly specific set
of angles between joints in dinosaur specimens, we can be fairly sure
they too possessed a propatagium. And through quantitative analyses of
the fossilized postures of birds and nondinosaurs, we found the telltale
ranges of joint angles we hoped to." Based on this clue, the team found
that the propatagium likely evolved in a group of dinosaurs known as
the maniraptoran theropods, including the famous Velociraptor. This was
backed up when the researchers identified the propatagium in preserved
soft tissue fossils, including those of the feathered oviraptorosaurian Caudipteryx and winged dromaeosaurian Microraptor. All the specimens
they found it in existed prior to the evolution of flight in that lineage.

This research means it's now known when the propatagium came into being,
and it leads researchers on to the next question of how it came to be. Why these particular theropod species needed such a structure to better adapt
to their environment might be a harder question to answer. The team has
already begun exploring possible connections between the fossil evidence
and embryonic development of modern vertebrates to see if that will
shed any light on it. The team also thinks some theropods might have
evolved the propatagium not because of any pressure to learn to fly,
as their forelimbs were made for grasping objects and not for flying.

"Dinosaurs portrayed in popular media are becoming more and more
accurate," said Hirasawa. "At least now we get to see features like
feathers, but I hope we can see an even more up-to-date representation
soon where theropods have their propatagium too."
* RELATED_TOPICS
o Plants_&_Animals
# Birds # Bird_Flu_Research # Zoology #
Evolutionary_Biology
o Earth_&_Climate
# Geology # Weather # Earth_Science
* RELATED_TERMS
o Feathered_dinosaurs o Whooping_Crane o Convergent_evolution
o Archaeopteryx o Fossil o Dinosaur o Bioinformatics o Biology

========================================================================== Story Source: Materials provided by University_of_Tokyo. Note: Content
may be edited for style and length.


========================================================================== Related Multimedia:
* Wing_evolution_in_birds ========================================================================== Journal Reference:
1. Yurika Uno, Tatsuya Hirasawa. Origin of the propatagium in non-avian
dinosaurs. Zoological Letters, 2023; 9 (1) DOI:
10.1186/s40851-023-00204- x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/02/230224135058.htm

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