(LINKS TO PAST FOSSIL
FRIDAYS)
Community College (LRCCD)
Geology & Earth
Science Instructor: Arthur Reed, P.G.
Happy
Fossil Friday!
Friday April 9, 2021
Who
developed sight first, the Hunter or the Hunted?
Complex animals
first showed up in the fossil record beginning in the Cambrian, that time in
geologic history known for the ‘explosion of life’. A particular predator at
the time is speculated to have developed eyesight far exceeding other
contemporary creatures. Additionally, this creature, named Anomalocaris’ briggsi, was an apex
predator that was in an evolutionary race.
Those creatures that developed better sight would be the hunters, those
with lesser or no sight would be the hunted.
Following
is a summary of research published last year in the Journal of Science
Advances
This ancient bottom feeder could have ‘invented’
modern sight.
If you like seeing defined shapes, you should thank
this little fellow.
A new paper examines how life first developed advanced
eyes and sight, and how this led to an “evolutionary arms race” around 500 million
years ago. The findings rely on radiodont fossils, a group of arthropods that
were abundant in the ocean at the time.
Artist’s reconstruction of ‘Anomalocaris’ briggsi., Sea Monster
The radiodont order, meaning “radiating teeth”, is
comprised of many species with a similar body layout — a head and a pair of
segmented limbs that would capture prey. They had circular mouths with sharp,
serrated teeth, and were roughly squid-shaped. They
likely inhabited the deeper layers of the ocean, at around 1000 meters in
depth. Due to the low light levels there, they evolved large, sophisticated
eyes in order to catch prey. But this ‘sensor’ upgrade
would send ripples throughout life on the planet, the authors explain, making
vision a driving force in evolution as it pitted predator against prey.
See food, eat food
“Our study provides critical new information about the
evolution of the earliest marine animal ecosystems,” said Professor John
Paterson from the University of New England’s Palaeoscience
Research Centre, lead author on the study.
“In particular, it supports the idea that vision played a crucial role
during the Cambrian Explosion, a pivotal phase in history when most major
animal groups first appeared during a rapid burst of evolution over half a
billion years ago.”
The development of complex eyes allowed animals to
perceive their surroundings better than ever before, which also helped
predators spot prey more easily. But sight can also warn the hunted of the
hunter, so it became a very powerful driver of
evolution — after all, the one with poorer sight might not make it through the
day. It has retained its importance up to today when virtually every ecosystem
and ecological interaction on the planet is shaped by sight.
Acute zone–type eye of ‘A.’ briggsi. Image credits John R. Paterson, Gregory D. Edgecombe, and Diego C. García-Bellido, (2020), Science Advances.
The fossils used in this study were first unearthed
around a century ago at Emu Bay Shale on South Australia’s Kangaroo Island and
were comprised of isolated body parts. However, initial attempts to reconstruct
the animals based on their fossils were quite unsuccessful and resulted in
several “Frankenstein’s monsters”, the authors note. Over the decades, as more
radiodont material was discovered, including whole bodies, we’ve
gained a better understanding of these animals, their body structure,
diversity, even possible lifestyles. Still, the specimens from Emu Bay Shale
had some unique properties.
“The Emu Bay Shale is the only place in the world that
preserves eyes with lenses of Cambrian radiodonts. The more than thirty
specimens of eyes we now have, have shed new light on the ecology, behavior,
and evolution of these, the largest animals alive half-a-billion years ago,”
says Associate Professor Diego García-Bellido from the University of Adelaide
and South Australian Museum, a co-author of the paper.
The team worked with these fossils before. They
published two papers describing the fossilized eyes recovered from the site.
The first one looked at isolated eye specimens of up to one centimeter in
diameter, which remain unassigned to a species up to now. The second paper
analyzed the eyestalks of Anomalocaris, a top predator in its day
that grew up to one meter in length. The current paper, according to the
authors, identifies that first, unknown species: ‘Anomalocaris’ briggsi,
a new genus that “is yet to be formally named,” Prof. Paterson said.
Acute zone–type eye of ‘A.’ briggsi. Image credits John R. Paterson, Gregory D. Edgecombe, and Diego C. García-Bellido, (2020), Science Advances.
“We discovered much larger specimens of these eyes of
up to four centimeters in diameter that possess a distinctive ‘acute zone’,
which is a region of enlarged lenses in the center of the eye’s surface that
enhances light capture and resolution.”
The large lenses of these animals suggest that they
could work in the dim light of the deep sea, and were
likely very similar to those of modern amphipod crustaceans (a type of
prawn-like creature). Anomalocaris briggsi primarily hunted
plankton by filtration through its appendages; its eyes helped it spot its
meals from the bottom of the ocean.
