A mass extinction of fish 360 million years ago hit the reset button on Earth's life, setting the stage for modern vertebrate biodiversity. The mass extinction scrambled the species pool near the time at which the first vertebrates crawled from water towards land.
Those few species that survived the bottleneck were the evolutionary starting point for all vertebrates--including humans--that exist today, according to results of a study published this week in the journal Proceedings of the National Academy of Sciences (PNAS).
"Everything was hit; the extinction was global," said Lauren Sallan of the University of Chicago and lead author of the paper. "It reset vertebrate diversity in every single environment, both freshwater and marine, and created a completely different world."
The Devonian Period, which spanned from 416 to 359 million years ago, is also known as the Age of Fishes for the broad array of species present in Earth's aquatic environments.
Armored placoderms such as the gigantic Dunkleosteus and lobe-finned fishes--similar to the modern lungfish--dominated the waters, while ray-finned fishes, sharks and tetrapods were in the minority, according to Maureen Kearney, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research, along with NSF's Division of Earth Sciences.
But between the latest Devonian Period and the subsequent Carboniferous period, placoderms disappeared and ray-finned fishes rapidly replaced lobe-finned fishes as the dominant group, a demographic shift that persists to today.
"The Devonian period is known as the Age of Fishes, but it's the wrong kind of fish," Sallan said. "Just about everything dominant in the Devonian died at the end of the period and was replaced."
"There's some sort of pinch at the end of the Devonian," said the paper's second author, Michael Coates, an organismal biologist and anatomist at the University of Chicago.
"It's as if the roles persist, but the players change: the cast is transformed dramatically. Something happened that almost wiped the slate clean, and, of the few stragglers that made it through, a handful then re-radiate spectacularly."
Scientists have long theorized that the Late Devonian Kellwasser event--considered to be one of the "Big Five" extinctions in Earth's history--was responsible for a marine invertebrate species shake-up.
But an analysis of the vertebrate fossil record by Sallan and Coates pinpointed a critical shift in diversity to the Hangenberg extinction event 15 million years later.
Prior to the extinction, lobe-finned forms such as Tiktaalik and the earliest limbed tetrapods such as Ichthyostega had made the first tentative "steps" toward a land-dwelling existence.
But after the extinction, a long stretch of the fossil record known as "Romer's Gap," is almost barren of tetrapods, a puzzle that had confused paleontologists for many years.
Sallan and Coates' data suggest that the 15-million-year gap was the hangover after the traumatic Hangenberg event.
"Something that's seen after an extinction event is a gap in the records of survivors," Sallan said. "You have a very low diversity fauna, because most things have been killed off."
When tetrapods finally recovered, those survivors were likely the great-great-grandfathers to the vast majority of land vertebrates present today.
Modern vertebrate traits--such as the motif of five-digit limbs that is shared by all mammals, birds and reptiles in utero--may have been set by this early common ancestor, the authors propose.
"Extinction events remove a huge amount of biodiversity," Coates said. "That shapes in a very significant way the patchiness of biodiversity that persists to the present day."
The analysis benefitted from recent advances in filling in the vertebrate fossil record, Coates said.
Previously, estimates of the earlier extinction had been made using fossils of invertebrates such as mollusks and clams, which are far more abundant.
With a larger dataset of vertebrates and analytical techniques borrowed from modern ecology, Sallan and Coates were able to see the abrupt changes in species composition before and after the Hangenberg event.
"It's a big extinction during what was already considered a critical time in vertebrate evolution, so it's surprising that it went unnoticed for so long," Sallan said. "But it took the right methods to reveal its magnitude."
What remains mysterious is exactly what happened 360 million years ago to trigger this mass extinction.
Other researchers have found evidence of substantial glacier formation at the end of the Devonian period, which would have dramatically lowered sea levels and affected life.
The first appearance of forest-like environments in some regions might also have produced atmospheric changes catastrophic to animal life.
The research also raises questions about the pattern of evolution after the extinction event.
It remains unclear why groups that were abundant before the event did not recover, while other groups spread and diversified in radical new ways.
Regardless of these questions, the consequences are still being felt hundreds of millions of years later.
"It is a pivotal episode that shaped modern vertebrate biodiversity," Coates said. "We are only now beginning to place that important event in the history of life and the history of the planet, which we weren't able to do before."
Funding was also provided by the University of Chicago Hinds Fund, the Paleontological Society, the Palaeontological Association, the American Society of Ichthyologists and Herpetologists, and the Evolving Earth Foundation.
Cheryl Dybas | EurekAlert!
Working the switches for axon branching
26.09.2018 | Max-Planck-Institut für Biochemie
Diversity in the brain – How millions of neurons become unique
26.09.2018 | Universität Basel
Our brain is a complex network with innumerable connections between cells. Neuronal cells have long thin extensions, so-called axons, which are branched to increase the number of interactions. Researchers at the Max Planck Institute of Biochemistry (MPIB) have collaborated with researchers from Portugal and France to study cellular branching processes. They demonstrated a novel mechanism that induces branching of microtubules, an intracellular support system. The newly discovered dynamics of microtubules has a key role in neuronal development. The results were recently published in the journal Nature Cell Biology.
From the twigs of trees to railroad switches – our environment teems with rigid branched objects. These objects are so omnipresent in our lives, we barely...
The Fraunhofer FEP has been involved in developing processes and equipment for cleaning, sterilization, and surface modification for decades. The CleanHand Network for development of systems and technologies to clean surfaces, materials, and objects was established in May 2018 to bundle the expertise of many partnering organizations. As a partner in the CleanHand Network, Fraunhofer FEP will present the Network and current research topics of the Institute in the field of hygiene and cleaning at the parts2clean trade fair, October 23-25, 2018 in Stuttgart, at the booth of the Fraunhofer Cleaning Technology Alliance (Hall 5, Booth C31).
Test reports and studies on the cleanliness of European motorway rest areas, hotel beds, and outdoor pools increasingly appear in the press, especially during...
The building blocks of matter in our universe were formed in the first 10 microseconds of its existence, according to the currently accepted scientific picture. After the Big Bang about 13.7 billion years ago, matter consisted mainly of quarks and gluons, two types of elementary particles whose interactions are governed by quantum chromodynamics (QCD), the theory of strong interaction. In the early universe, these particles moved (nearly) freely in a quark-gluon plasma.
This is a joint press release of University Muenster and Heidelberg as well as the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt.
Then, in a phase transition, they combined and formed hadrons, among them the building blocks of atomic nuclei, protons and neutrons. In the current issue of...
Thin-film solar cells made of crystalline silicon are inexpensive and achieve efficiencies of a good 14 percent. However, they could do even better if their shiny surfaces reflected less light. A team led by Prof. Christiane Becker from the Helmholtz-Zentrum Berlin (HZB) has now patented a sophisticated new solution to this problem.
"It is not enough simply to bring more light into the cell," says Christiane Becker. Such surface structures can even ultimately reduce the efficiency by...
A study in the journal Bulletin of Marine Science describes a new, blood-red species of octocoral found in Panama. The species in the genus Thesea was discovered in the threatened low-light reef environment on Hannibal Bank, 60 kilometers off mainland Pacific Panama, by researchers at the Smithsonian Tropical Research Institute in Panama (STRI) and the Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) at the University of Costa Rica.
Scientists established the new species, Thesea dalioi, by comparing its physical traits, such as branch thickness and the bright red colony color, with the...
21.09.2018 | Event News
03.09.2018 | Event News
27.08.2018 | Event News
26.09.2018 | Life Sciences
26.09.2018 | Trade Fair News
26.09.2018 | Life Sciences