Mud-slurping chinless ancestors had all the moves

Date:
October 1, 2020
Source:
University of Bristol
Summary:
Researchers have revealed our most ancient ancestors were
ecologically diverse, despite lacking jaws and paired fins.



FULL STORY ==========================================================================
A team of researchers, led by the University of Bristol, has revealed
our most ancient ancestors were ecologically diverse, despite lacking
jaws and paired fins.


==========================================================================
Long before they evolved out of the water, our ancient ancestors were
simple fish-like creatures, but without fins or chins, who survived by filtering nutrients from sediment.

They have long been thought of as the lazy lumps who spent most of their
lives resting on or near to the sea floor. The belief was that everything changed with the evolution of jawed vertebrates whose paired fins made
them the super- swimmers and active predators, driving their jawless
relatives to extinction.

However, a new study published in the journal Current Biology overturns
this classical evolutionary story.

Researchers from the University of Bristol used computer simulations
to explore how avatars of our extinct ancestors interacted with water
currents. These experiments revealed the bizarre spikes and spines
that ornamented the heads of these jawless vertebrates were actually hydrodynamic adaptations, passively generating lift from water currents
flowing over the body. The varying head shapes of different species
allowed them to adapt to different positions, some high, others low,
within the water. Our ancient ancestors were already ecologically diverse,
long before the evolution of their jawed vertebrate relatives.

Dr Humberto G. Ferron, a postdoctoral researcher from the University of
Bristol and one of the paper's co-authors, said: "The evolution of jaws
and fins have classically been seen as the key evolutionary inventions
that allowed vertebrates to diversify their lifestyles.



==========================================================================
"In this context, jawless ancestors, characterized by the presence
of heavy rigid headshields, were assumed to be cumbersome fish-like
creatures, living on the bottom of rivers and seas, with poor
manoeuvrability." The question of how our ancient ancestors made a
living has long been a mystery because there are no animals like them
alive today. The 'osteostracans' (their latin name, meaning bony shells)
were heavily armoured, encased in thick bone from snout to tail. They
lacked a rear pair of legs and some had none at all; many possessed
bizarre horn-like extensions from the front of their heads.

Ferro'n and colleagues tackled this problem using state-of-the-art computational engineering techniques that simulate the behaviour of
fossil avatars in water currents.

Dr Imran Rahman, from the Oxford University Museum of Natural History,
said: "The application of computational fluid dynamics, has allowed us
to study the swimming performance of ancient vertebrates and learn more
about their position in evolutionary history.

Dr Carlos Martinez Perez, from the University of Valencia (Spain), added:
"Our simulations reveal that the different species of osteostracans show equally different hydrodynamic efficiencies. Some of them performed
better when moving close to the sea floor or riverbed while others
performed better when swimming freely in the water." Professor Phil
Donoghue, another Bristol co-author, concluded: "The different species'
body shapes are adapted to different environments, revealing distinct lifestyles among these groups of jawless early vertebrates.

"Our results calls into question the prevailing view that these extinct
groups of jawless vertebrates were ecologically constrained, and reveals
the main evolutionary hypothesis for the origin of jawed vertebrates is
more complex than previously thought."

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


========================================================================== Journal Reference:
1. Humberto G. Ferro'n, Carlos Marti'nez-Pe'rez, Imran A. Rahman,
Vi'ctor
Selles de Lucas, He'ctor Botella, Philip
C.J. Donoghue. Computational Fluid Dynamics Suggests Ecological
Diversification among Stem- Gnathostomes. Current Biology, 2020;
DOI: 10.1016/j.cub.2020.09.031 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201001113623.htm

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