Different tracks, same dinosaurs: Researchers dig deeper into dinosaur movements

Date:
July 1, 2020
Source:
Brown University
Summary:
Using X-ray-based technology, researchers uncover shared subsurface
movement patterns between birds and dinosaurs, adding a new
dimension of fossil track diversity.



FULL STORY ==========================================================================
When picturing dinosaur tracks, most people imagine a perfectly preserved
mold of a foot on firm layer of earth. But what if that dinosaur was
running through mud, sinking several inches -- or even up to their ankles
-- into the ground as it moved?

========================================================================== Using sophisticated X-ray-based technology, a team of Brown University researchers tracked the movements of guineafowl to investigate how their
feet move below ground through various substrates and what those findings
could mean for understanding fossil records left behind by dinosaurs.

They found that regardless of the variability in substrates, or the
guineafowl moving at different speeds, sinking at different depths
or engaging in different behaviors, the birds' overall foot movement
remained the same: The toes spread as they stepped onto the substrate
surface, remained spread as the foot sank, collapsed and drew back as
they were lifted from the substrate, and exited the substrate in front
of the point of entry, creating a looping pattern as they walked.

And part of what that means is that fossilized dinosaur tracks that
look distinct from each other, and appear to be from different species,
might instead come from the same dinosaurs.

"This is the first study that's really shown how the bird foot is moving
below ground, showing the patterns of this subsurface foot motion and
allowing us to break down the patterns that we're seeing in a living
animal that has feet similar to those of a dinosaur," said Morgan
Turner, a Ph.D. candidate at Brown in ecology and evolutionary biology
and lead author of the research. "Below ground, or even above ground,
they're responding to these soft substrates in a very similar way,
which has potentially important implications for our ability to study
the movement of these animals that we can't observe directly anymore."
The findings were published on Wednesday, July 1, in the Royal Society
journal Biology Letters.



==========================================================================
To make the observations, Turner and her colleagues, Professor of Biology
and Medical Science Stephen Gatesy and Peter Falkingham, now at Liverpool
John Moores University, used a 3D-imaging technology developed at Brown
called X-ray Reconstruction of Moving Morphology (XROMM). The technology combines CT scans of a skeleton with high-speed X-ray video, aided by tiny implanted metal markers, to create visualizations of how bones and muscles
move inside humans and animals. In the study, the team used XROMM to watch guineafowl move through substrates of different hydration and compactness, analyzing how their feet moved underground and the tracks left behind.

Sand, typically a dense combination of quartz and silica, does not lend
itself well to X-ray imaging, so the team used poppy seeds to emulate
sand. Muds were made using small glass bubbles, adding various amount
of clay and water across 107 trials to achieve different consistencies
and realistic tracks.

They added metal markers underneath the claws of the guineafowl to allow
for tracking in 3D space. It's these claw tips that the researchers think
are least disturbed by mud flow and other variables that can impact and
distort the form of the track.

Despite the variation, the researchers observed a consistent looping
pattern.

"The loops by themselves I don't think are that interesting," Gatesy said.

"People are like, 'That's nice. Birds do this underground. So what?' It
was only when [Turner] went back into it and said, 'What if we slice those motion trails at different depths as if they were footprints?' Then we
made the nice connection to the fossils." By "slicing" through the 3D
images of the movement patterns at different depths, the researchers found similarities between the guineafowl tracks and fossilized dinosaur tracks.



==========================================================================
"We don't know what these dinosaurs were doing, we don't know what they
were walking through exactly, we don't know how big they were or how
deep they were sinking, but we can make this really strong connection
between how they were moving and some level of context for where this
track is being sampled from within that movement," Turner said.

By recognizing the movement patterns, as well as the entry and exit point
of the foot through various substrates, the team says they're able to
gain a better understanding of what a dinosaur track could look like.

"You end up generating this big diversity of track shapes from a very
simple foot shape because you're sampling at different depths and
it's moving in complicated ways," Gatesy said. "Do we really have 40
different kinds of creatures, each with a differently shaped foot, or are
we looking at some more complicated interaction that leaves behind these remnants that are partly anatomical and partly motion and partly depth?"
To further their research, the team spent time at the Beneski Museum of
Natural History at Amherst College in Massachusetts, which is home to
an expansive collection of penetrative tracks discovered in the 1800s
by geologist Edward Hitchcock.

Hitchcock originally believed that his collection housed fossil tracks
from over 100 distinct animals. Because of the team's work with XROMM,
Gatesy now thinks it's possible that at least half of those tracks are
actually from the same dinosaurs, just moving their feet in slightly
different ways or sampled at slightly different depths.

"Going to museum together and being able to pick out these features and
say, 'We think this track is low in the loop and we think this one is
high,' that was the biggest moment of insight for me," Turner said.

Turner says she hopes their research can lead to a greater interest in penetrative tracks, even if they seem a little less pretty or polished
than the tracks people are used to seeing in museums.

"They have so much information in them," Turner said, "and I hope
that this gives people a lens, a new way to view these footprints
and appreciate the movement preserved within in them." This work was
supported by the US National Science Foundation (EAR 1452119 to SMG and
PLF; IOS 0925077 to SMG), a Marie Curie International Outgoing Fellowship within the 7th European Framework Programme to PLF, and the Bushnell
Research and Education Fund to MLT.


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


========================================================================== Journal Reference:
1. Morgan L. Turner, Peter L. Falkingham, Stephen M. Gatesy. It's
in the
loop: shared sub-surface foot kinematics in birds and other
dinosaurs shed light on a new dimension of fossil track
diversity. Biology Letters, 2020; 16 (7): 20200309 DOI:
10.1098/rsbl.2020.0309 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200701125504.htm

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