Life restoration of cephalaspis, a typical osteostracan that floats above the substrate. Photo credit: Hugo Salais (Metazoa Studio)
A research team led by Bristol Universitydemonstrated that despite the lack of jaws and paired fins, our oldest ancestors were ecologically diverse.
Long before they evolved out of the water, our ancient ancestors were simple fish-like creatures, but without fins or chins, that survived by filtering nutrients out of the sediment.
They have long been viewed as the lazy lumps that have lived on or near the ocean floor for most of their lives. The belief was that everything changed with the development of the jawed vertebrates, whose paired fins made them super swimmers and active predators, and brought their jawless relatives to extinction.
However, a new study was published in the journal Current biology overturns this classic evolutionary story.
Researchers at the University of Bristol used computer simulations to study how avatars of our extinct ancestors interacted with currents of water. These experiments showed that the bizarre spines and prickles that adorned the heads of these jawless vertebrates were actually hydrodynamic adaptations that passively created buoyancy from currents of water flowing over the body. The different head shapes of different species allowed them to adapt to different positions in the water, some high, some low. Our ancient ancestors were ecologically diverse long before their vertebrate relatives evolved.
Dr. Humberto G. Ferron, a postdoctoral fellow at the University of Bristol’s School of Earth Sciences and a co-author of the paper, said, “The evolution of the jaws and fins was classically viewed as the most important evolutionary inventions that allowed vertebrates to add to their lifestyle diversify.
“In this context, it was believed that jawless ancestors, characterized by the presence of heavy rigid head-shields, were clumsy fish-like creatures who lived at the bottom of rivers and seas and had poor maneuverability.”
The question of how our ancient ancestors made a living has long been a mystery, because animals like these no longer exist today. The ‘Osteostracans’ (their Latin name means bony shells) were heavily armored and wrapped in thick bones from snout to tail. They lacked a pair of back legs and some had none at all; Many had bizarre horn-like extensions from the front of their heads.
Ferrón and colleagues have approached this problem with state-of-the-art computational techniques that simulate the behavior of fossil avatars in water currents.
Dr. Imran Rahman of the Natural History Museum at Oxford University 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 show that the different types of osteostracans have different hydrodynamic efficiencies. Some of them did better when they were near the seabed or riverbed, while others did better when they were free to swim in the water. ”
Professor Phil Donoghue, another co-author from Bristol, concluded: “The body shapes of the different species are adapted to different environments and show different lifestyles in these groups of jawless early vertebrates.
“Our results challenge the prevailing view that these extinct groups of jawless vertebrates were ecologically restricted, and show that the main evolutionary hypothesis for the formation of jawed vertebrates is more complex than previously thought.”
Reference: “Computational Fluid Dynamics Proposes Ecological Diversification Between Tribe Gnathostomes” by Humberto G. Ferrón, Carlos Martínez-Pérez, Imran A. Rahman, Víctor Selles de Lucas, Héctor Botella and Philip CJ Donoghue, October 1, 2020, Current biology.
DOI: 10.1016 / j.cub.2020.09.031
