Horseshoe crab eyes, 400 million years old


This July 2018 video is called What If The Jaekelopterus rhenaniae Didn’t Go Extinct?

From the University of Cologne in Germany:

Compound eyes: The visual apparatus of today’s horseshoe crabs goes back 400 million years

December 3, 2019

The eyes of the extinct sea scorpion Jaekelopterus rhenaniae have the same structure as the eyes of modern horseshoe crabs (Limulidae). The compound eyes of the giant predator exhibited lens cylinders and concentrically organized sensory cells enclosing the end of a highly specialized cell. This is the result of research Dr Brigitte Schoenemann, professor of zoology at the Institute of Biology Didactics at the University of Cologne, conducted with an electron microscope. Cooperation partners in the project were Dr Markus Poschmann from the Directorate General of Cultural Heritage RLP, Directorate of Regional Archaeology/Earth History and Professor Euan N.K. Clarkson from the University of Edinburgh. The results of the study ‘Insights into the 400 million-year-old eyes of giant sea scorpions (Eurypterida) suggest the structure of Palaeozoic compound eyes’ have been published in the journal Scientific Reports — Nature.

The eyes of modern horseshoe crabs consist of compounds, so-called ommatidia. Unlike, for example, insects that have compound eyes with a simple lens, the ommatidia of horseshoe crabs are equipped with a lens cylinder that continuously refracts light and transmits it to the sensory cells.

These sensory cells are grouped in the form of a rosette around a central light conductor, the rhabdom, which is part of the sensory cells and converts light signals into nerve signals to transmit them to the central nervous system. At the centre of this ‘light transmitter’ in horseshoe crabs is a highly specialized cell end, which can connect the signals of neighbouring compounds in such a way that the crab perceives contours more clearly. This can be particularly useful in conditions of low visibility under water. In the cross-section of the ommatidium, it is possible to identify the end of this specialized cell as a bright point in the centre of the rhabdom.

Brigitte Schoenemann used electron microscopes to examine fossil Jaekelopterus rhenaniae specimens to find out whether the compound eyes of the giant scorpion and the related horseshoe crabs are similar or whether they are more similar to insect or crustacean eyes. She found the same structures as in horseshoe crabs. Lens cylinders, sensory cells and even the highly specialized cells were clearly discernible.

‘This bright spot belongs to a special cell that only occurs in horseshoe crabs today, but apparently already existed in eurypterida,’ explained Schoenemann. ‘The structures of the systems are identical. It follows that very probably this sort of contrast enhancement already evolved more than 400 million years ago,’ she added. Jaekelopterus most likely hunted placoderm[i fish]. Here, its visual apparatus was clearly an advantage in the murky seawater.

Sea scorpions, which first appeared 470 million years ago, died out about 250 million years ago, at the end of the Permian age — along with about 95 percent of all marine life. Some specimens were large oceanic predators, such as Jaekelopterus rhenaniae. It reached a length of 2.5 meters and belonged to the family of eurypterida, the extinct relatives of the horseshoe crab. Eurypterida are arthropods, which belong to the subphylum Chelicerata, and are therefore related to spiders and scorpions.

Among the arthropods there are two large groups: mandibulates (crustaceans, insects, trilobites) and chelicerates (arachnid animals such as sea scorpions). In recent years, Schoenemann has been able to clarify the eye structures of various trilobite species and to make decisive contributions to research into the evolution of the compound eye. ‘Until recently, scientists thought that soft tissues do not fossilize. Hence these parts of specimens were not examined until not so long ago’, she concluded.

The new findings on the eye of the sea scorpion are important for the evolution of the compound eyes not only of chelicerates, but also for determining the position of sea scorpions in the pedigree of these animals and for the comparison with the eyes of the related group of mandibulates.

Ancient carnivorous amphibian discovery


This 25 October 2019 Russian video says about itself (translated):

Found in Komi republic: the remains of the oldest ancestor of all terrestrial vertebrates

In Komi, the remains of one of the first tetrapods were discovered – an animal, thanks to which vertebrates were able to go on land, becoming the ancestors of amphibians, reptiles, birds and mammals. The Russian tetrapod was called Parmastega aelidae. Its age is 372 million years. Parmastega bones were discovered in the vicinity of the city of Ukhta.

From the University of Lincoln in England:

Massive fangs and a death crush: How a 370 million year old tetrapod hunted and killed

October 24, 2019

The habits of a needle-toothed tetrapod which lived more than 370 million years ago have filled in a piece of the evolutionary puzzle thanks to new research.

An international team of palaeontologists pieced together the fossilised skeletons of a new species of tetrapod called Parmastega aelidae and found it had a skull which resembled a crocodile — a unique feature among the earliest tetrapods — with eyes situated well above the top of its head, suggesting it was capable of “keeping an eye” on unsuspecting prey while swimming close to the surface of a tropical lagoon.

The unusual combination of anatomical features has cast new light on how one of [our] most distant ancestors hunted and its life-style. Researchers believe it would have used its slender needle-like teeth and elastic jaw to snatch prey before crushing it to death with massive fangs protruding from its palate.

The team also found that part of its shoulder girdle consisted of cartilage, and its vertebral column and paired limbs could also be made of cartilage, indicating it probably spent most or all its time in water. The concentration of the fossil remains also suggests that it may have lived in large groups.

Tetrapods are represented today by amphibians, reptiles, birds and mammals, and Parmastega predates the former earliest records of complete or almost complete tetrapod skeletons by nearly 12 million years.

The new study was led by the Ural Branch of the Russian Academy of Science, in partnership with the Universities of Lincoln and Cambridge in the UK, the University of Latvia, and the University of Uppsala in Sweden. It was funded by the National Geographic Society, the Latvian Council of Science, and the Knut and Alice Wallenberg Foundation.

Professor Per Ahlberg from the University of Uppsala in Sweden, explained that a clue to the lifestyle of Parmastega was provided by its sensory canals, used to detect vibrations in the water, which Parmastega inherited from its fish ancestors.

“These canals are well developed on the lower jaw, the snout and the sides of the face, but they die out on top of the head behind the eyes,” he said. “This probably means that it spent a lot of time hanging around at the surface of the water, with the top of the head just awash and the eyes protruding into the air.

“We believe there may have been large arthropods such as millipedes or ‘sea scorpions‘ to catch at the water’s edge. The slender, elastic lower jaw certainly looks well-suited to scooping prey off the ground, its needle-like teeth contrasting with the robust fangs of the upper jaw that would have been driven into the prey by the body weight of Parmastega.

“These fossils give us the earliest detailed glimpse of a tetrapod: an aquatic, surface-skimming predator, just over a metre in length, living in a lagoon on a tropical coastal plain.”

Dr Marcello Ruta from Lincoln’s School of Life Sciences added: “The evolution of tetrapods is one of the most important events in the history of backboned animals, and ultimately led to the appearance of our own species. Early in their history, tetrapods evolved many changes in their feeding strategies, movement abilities, and sensory perception, but many of these are still shrouded in mystery.

“Like all fossil organisms, Parmastega occupies a special and unique place in the tree of life. Our study welcomes a new, very early member of that tree which shows considerable anatomical, functional and ecological experimentation.

“These new findings demonstrate that the sequence of evolutionary changes that occurred during the transition from fish-like creatures to tetrapods were much less linear than previously thought. This helps us to amend or challenge previous evolutionary scenarios and give new insights into the life and environments of our most distant forerunners. Findings like those of Parmastega can help us grasp the complex patterns and processes that have shaped life’s diversity for hundreds of millions of years.”

Ancient trilobites, new study


This 2017 video is called The Trouble With Trilobites.

From the Fundação de Amparo à Pesquisa do Estado de São Paulo in Brazil:

Reconstruction of trilobite ancestral range in the southern hemisphere

January 9, 2019

Summary: Brazilian researchers used biogeographic analysis to study trilobites — arthropods that became extinct over 252 million years ago.

The first appearance of trilobites in the fossil record dates to 521 million years ago in the oceans of the Cambrian Period, when the continents were still inhospitable to most life forms. Few groups of animals adapted as successfully as trilobites, which were arthropods that lived on the seabed for 270 million years until the mass extinction at the end of the Permian approximately 252 million years ago.

The longer ago organisms lived, the more rare are their fossils and the harder it is to understand their way of life; paleontologists face a daunting task in endeavoring to establish evolutionary relationships in time and space.

Surmounting the difficulties inherent in the investigation of a group of animals that lived such a long time ago, Brazilian scientists affiliated with the Biology Department of São Paulo State University’s Bauru School of Sciences (FC-UNESP) and the Paleontology Laboratory of the University of São Paulo’s Ribeirão Preto School of Philosophy, Science and Letters (FFCLRP-USP) have succeeded for the first time in inferring paleobiogeographic patterns among trilobites.

Paleobiogeography is a branch of paleontology that focuses on the distribution of extinct plants and animals and their relations with ancient geographic features. The study was conducted by Fábio Augusto Carbonaro, a postdoctoral researcher at UNESP’s Bauru Macroinvertebrate Paleontology Laboratory (LAPALMA) headed by Professor Renato Pirani Ghilardi. Other participants included Max Cardoso Langer, a professor at FFCLRP-USP, and Silvio Shigueo Nihei, a professor at the same university’s Bioscience Institute (IB-USP).

The researchers analyzed the morphological differences and similarities of the 11 species of trilobites described so far in the genus Metacryphaeus; these trilobites lived during the Devonian between 416 million and 359 million years ago (mya) in the cold waters of the sea that covered what is now Bolivia, Peru, Brazil, the Malvinas (Falklands) and South Africa.

The Devonian Period is subdivided into seven stages. Metacryphaeus lived during the Lochkovian (419.2-410.8 mya) and Pragian (410.8- 407.6 mya) stages, which are the earliest Devonian stages.

The results of the research were published in Scientific Reports and are part of the project “Paleobiogeography and migratory routes of paleoinvertebrates of the Devonian in Brazil,” which is supported by São Paulo Research Foundation -FAPESP and Brazil’s National Council for Scientific and Technological Development (CNPq). Ghilardi is the project’s principal investigator.

“When they became extinct in the Permian, 252 million years ago, the trilobites left no descendants. Their closest living relatives are shrimps, and, more remotely, spiders, scorpions, sea spiders and mites”, Ghilardi said.

Trilobite fossils are found abundantly all over the world, he explained — so abundantly that they are sometimes referred to as the cockroaches of the sea. The comparison is not unwarranted because anatomically, the trilobites resemble cockroaches. The difference is that they were not insects and had three longitudinal body segments or lobes (hence the name).

In the northern hemisphere, the trilobite fossil record is very rich. Paleontologists have so far described ten orders comprising over 17,000 species. The smallest were 1.5 millimeters long, while the largest were approximately 70 cm long and 40 cm wide. Perfectly preserved trilobites can be found in some regions, such as Morocco. These can be beautiful when used to create cameos or intaglio jewelry. Trilobite fossils from Brazil, Peru and Bolivia, in contrast, are often poorly preserved, consisting merely of the impressions left in benthic mud by their exoskeletons.

“Although their state of preservation is far from ideal, there are thousands of trilobite fossils in the sediments that form the Paraná basin in the South region of Brazil, and the Parnaíba basin along the North-Northeast divide,” said Ghilardi, who also chairs the Brazilian Paleontology Society.

According to Ghilardi, their poor state of preservation could be due to the geological conditions and climate prevailing in these regions during the Paleozoic Era, when the portions of dry land that would one day form South America were at the South Pole and entirely covered by ice for prolonged periods.

During the Devonian, South America and Africa were connected as part of the supercontinent Gondwana. South Africa was joined with Uruguay and Argentina in the River Plate region, and Brazil’s southern states were continuous with Namibia and Angola.

Parsimonious analysis

The research began with an analysis of 48 characteristics (size, shape and structure of organs and anatomical parts) found in some 50 fossil specimens of the 11 species of Metacryphaeus.

“In principle, these characteristics serve to establish their phylogeny — the evolutionary history of all species in the universe, analyzed in terms of lines of descent and relationships among broader groups,” Ghilardi said.

Known as a parsimonious analysis, this method is widely used to establish relationships among organisms in a given ecosystem, and in recent years, it has also begun to be used in the study of fossils.

According to Ghilardi, parsimony, in general, is the principle that the simplest explanation of the data is the preferred explanation. In the analysis of phylogeny, it means that the hypothesis regarding relationships that requires the smallest number of characteristic changes between the species analyzed (in this case, trilobites of the genus Metacryphaeus) is the one that is most likely to be correct.

The biogeographic contribution to the study was made by Professor Nihei, who works at IB-USP as a taxonomist and insect systematist. The field of systematics is concerned with evolutionary changes between ancestries, while taxonomy focuses on classifying and naming organisms.

“Biogeographic analysis typically involves living groups the ages of which are estimated by molecular phylogeny, or the so-called molecular clock, which estimates when two species probably diverged on the basis of the number of molecular differences in their DNA. In this study of trilobites, we used age in a similar manner, but it was obtained from the fossil record,” Nihei said.

“The main point of the study was to use fossils in a method that normally involves molecular biogeography. Very few studies of this type have previously involved fossils. I believe our study paves the way for a new approach based on biogeographic methods requiring a chronogram [a molecularly dated cladogram] because this chronogram can also be obtained from fossil taxa such as those studied by paleontologists, rather than molecular cladograms for living animals.”

As a vertebrate paleontologist who specializes in dinosaurs, Langer acknowledged that he knows little about trilobites but a great deal about the modern computational techniques used in parsimonious analysis, on which his participation in the study was based. “I believe the key aspect of this study, and the reason it was accepted for publication in as important a journal as Scientific Reports, is that it’s the first ever use of parsimony to understand the phylogeny of a trilobite genus in the southern hemisphere,” he said.

Gondwanan dispersal

The results of the paleobiogeographical analyses reinforce the pre-existing theory that Bolivia and Peru formed the ancestral home of Metacryphaeus.

“The models estimate a 100% probability that Bolivia and Peru formed the ancestral area of the Metacryphaeus clade and most of its internal clades,” Ghilardi said. Confirmation of the theory shows that parsimonious models have the power to suggest the presence of clades at a specific moment in the past even when there are no known physical records of that presence.

In the case of Metacryphaeus, the oldest records in Bolivia and Peru date from the early Pragian stage (410.8-407.6 mya), but the genus is believed to have evolved in the region during the Lochkovian stage (419.2-410.8 mya).

Parsimony, therefore, suggests Metacryphaeus originated in Bolivia and Peru some time before 410.8 mya but not earlier than 419.2 mya. In any event, it is believed to be far older than any known fossils.

According to Ghilardi, the results can be interpreted as showing that the adaptive radiation of Metacryphaeus to other areas of western Gondwana occurred during episodes of marine transgression in the Lochkovian-Pragian, when the sea flooded parts of Gondwana.

“The dispersal of Metacryphaeus trilobites during the Lochkovian occurred from Bolivia and Peru to Brazil — to the Paraná basin, now in the South region, and the Parnaíba basin, on the North-Northeast divide — and on toward the Malvinas/Falklands, while the Pragian dispersal occurred toward South Africa,” he said.

Fossil trilobites have been found continuously in the Paraná basin in recent decades. Trilobites collected in the late nineteenth century in the Parnaíba basin were held by Brazil’s National Museum in Rio de Janeiro, which was destroyed by fire in September 2018.

“These fossils haven’t yet been found under the rubble and it’s likely that nothing is left of them. They were mere shell impressions left in the ancient seabed. Even in petrified form, they must have dissolved in the blaze,” Ghilardi said.

How plant roots originated


This 2014 video from India says about itself:

Rhynia by (B.Sc, M.Sc) Dr. Ruby Singh Parmar

In this video, Dr. Ruby Singh, HOD Science, Biyani Group of Colleges explains the morphological and anatomical structure of “Rhynia“. It is a fossil plant. In this video characters and structure of sporangia are discussed.

From the University of Oxford in England:

Getting to the root of plant evolution

August 22, 2018

Despite plants and vegetation being key to the Earth’s ecosystem, little is known about the origin of their roots. However in new research, published in Nature, Oxford University scientists describe a transitional root fossils from the earliest land ecosystem that sheds light on how roots have evolved.

The findings suggest that plant roots have evolved more than once, and that the characteristics of roots developed in a step-wise manner — with the central root organ evolving first. And the root cap subsequently coming later.

Dr Sandy Hetherington and Professor Liam Dolan — both of Oxford’s Department of Plant Sciences and Magdalen College Oxford, conducted a microscopic study of the oldest known plant ecosystem — the 407 million-year-old Rhynie chert.

Dr Hetherington said: ‘The level of preservation in the Rhynie chert is truly remarkable — it never ceases to amaze me that I am able to examine the cellular organisation of plants that were growing 407 million years ago. It provides an exceptional window into life on the terrestrial surface at that time.’

The defining feature of modern-day plant roots is the meristem — a self-renewing structure that is covered by a cap at its apex. Root meristems are hard to spot in the fragmentary fossil record, which can make it challenging to unearth the evolutionary origin of roots.

The authors found evidence of root meristems belonging to the lycopsid plant Asteroxylon mackiei. Lycopsids — commonly known as club mosses, are vascular plants (those with tissues that internally move resources) whose lineage branched off early, before the other higher plants (the euphyllophytes).

The team were able to build a 3D reconstruction of the fossil meristem.

The fossil analysis reveals that the meristems of A. mackiei lack both root hairs and caps — they are covered instead by a continuous layer of surface tissue. This structure makes these roots unique among the vascular plants.

The paper’s conclusion suggests that these roots are a transitional step towards modern-style, rooted vascular plants. The findings support the idea that, as this cap-less transitional structure appears in a plant that is already a lycopsid, roots with caps evolved separately in lycopsids and euphyllophytes from their common, root-less ancestors.

Discussing plans to expand on this work, Professor Dolan said: ‘Our discovery suggests that plant organs were built up step-by-step during the course of plant evolution.

‘The evolution of roots was a critical time in Earth’s history and resulted in a dramatic reduction of atmospheric carbon. Now that we know that roots evolved in a step by step manner, we can go back to ancient rocks looking for structures that are missing “parts” that are present in extant roots.

‘I really want to find out where root caps came from. They seemed to have appeared out of thin air. They are very important in extant roots; the root cap is important to protect the root as it pushes through the soil and it is the site where roots detect gravity. How did these ancient roots manage without a cap to provide these functions?’

Fossil fish and human skeletons


This 24 July 2018 video says about itself:

420 million years ago, some fish were more medieval. They wore armor, sometimes made of big plates, and sometimes made of interlocking scales. But that armor may actually have served a totally different purpose, one that many animals still use today.

From the University of Manchester in England:

160-year-old mystery about the origin of skeletons solved

July 31, 2018

Scientists at The University of Manchester and the University of Bristol have used powerful X-rays to peer inside the skeletons of some of our oldest vertebrate relatives, solving a 160-year-old mystery about the origin of our skeletons.

Living vertebrates have skeletons built from four different tissue types: bone and cartilage (the main tissues that human skeletons are made from), and dentine and enamel (the tissues from which our teeth are constructed). These tissues are unique because they become mineralised as they develop, giving the skeleton strength and rigidity.

Evidence for the early evolution of our skeletons can be found in a group of fossil fishes called heterostracans, which lived over 400 million years ago. These fishes include some of the oldest vertebrates with a mineralised skeleton that have ever been discovered. Exactly what tissue heterostracan skeletons were made from has long puzzled scientists.

Now a team of researchers from the University of Manchester, the University of Bristol and the Paul Scherrer Institute in Switzerland have taken a detailed look inside heterostracan skeletons using Synchrotron Tomography: a special type of CT scanning using very high energy X-rays produced by a particle accelerator. Using this technique, the team have identified this mystery tissue.

Lead researcher Dr Joseph Keating, from Manchester’s School of Earth of Environmental Scientists, explained: “Heterostracan skeletons are made of a really strange tissue called ‘aspidin’. It is crisscrossed by tiny tubes and does not closely resemble any of the tissues found in vertebrates today. For a 160 years, scientists have wondered if aspidin is a transitional stage in the evolution of mineralised tissues.”

The results of this study, published in Nature Ecology and Evolution, show that the tiny tubes are voids that originally housed fibre-bundles of collagen, a type of protein found in your skin and bones.

These findings enabled Dr Keating to rule out all but one hypothesis for the tissue’s identity: aspidin is the earliest evidence of bone in the fossil record.

Co-author, Professor Phil Donoghue from the University of Bristol concludes: “These findings change our view on the evolution of the skeleton. Aspidin was once thought to be the precursor of vertebrate mineralised tissues. We show that it is, in fact, a type of bone, and that all these tissues must have evolved millions of years earlier.”

Fish-amphibian transition fossils discovered in South Africa


This video from South Africa says about itself:

The Centre of Excellence in Palaeosciences based at the University of the Witwatersrand today announced the discovery of two new Devonian tetrapod species and the first Devonian tetrapods discovered in Africa (8 June 2018). The species have been named Tutusius umlambo (named in honour of Archbishop Emeritus Desmond Tutu) and Umzantsia amazana and were discovered by Dr Rob Gess of the Albany Museum and supported by the Millenium Trust.

Thank you to Rhodes University journalism department for the video clip.

From the Times in South Africa:

Not so fishy: Africa’s first ever fish-with-legs discovered

07 June 2018 – 20:07

By Tanya Farber

An extraordinary find has been made near the university town of Grahamstown in the Eastern Cape.

Up until today‚ when a paper was published in Science‚ it was believed that Devonian tetrapods (fish that had developed four legs as the evolution from aquatic to land animals began) had only existed in the tropics.

But‚ in a groundbreaking study that shakes up our entire notion of the moment we adapted to move beyond the water‚ it has now been discovered that that is simply not true.

The newly discovered tetrapods – which would have resembled a cross between a crocodile and a fish‚ with a crocodile-like head‚ stubby legs‚ and a tail with a fish-like fin – were found in the Devonian Waterloo Farm near Grahamstown‚ and were living within the Antarctic circle some 360 million years ago.

The two new species are named Tutusius and Umzantsia. The metre-long Tutusius umlambo‚ named in honour of Archbishop Emeritus Desmond Tutu‚ and the somewhat smaller Umzantsia amazana‚ are both incomplete.

Tutusius is represented by a single bone from the shoulder girdle‚ whereas Umzantsia is known from a greater number of bones‚ but they both appear similar to previously known Devonian tetrapods.

This find represents two dramatic shifts. Firstly, it means the first appearance of tetrapods on African soil shifts to 70-million years earlier than thought‚ but it also means that one of the most fundamental understandings of our shift from the water to the land has to be reassessed.

The evolution of tetrapods from fish during the Devonian period was a major turning point in our ancestry‚ and all research on that turning point has up until now‚ hinged on the fact that this happened (or so we thought) between 30 degrees north and south of the equator. Almost all come from Laurussia‚ a supercontinent that later fragmented into North America‚ Greenland and Europe.

“Whereas all previously found Devonian tetrapods came from localities which were in tropical regions during the Devonian‚ these specimens lived within the Antarctic circle”, explains lead author‚ Dr Robert Gess of the Albany Museum in Grahamstown‚ and co-author Professor Per Ahlberg of Uppsala University in Sweden.

Minister of Science and Technology‚ Mmamoloko Kubayi-Ngubane‚ congratulated Dr Gess‚ saying this groundbreaking discovery places South Africa at the forefront of the study of the evolution of land-living vertebrate animals‚ including the ancestry of all the wildlife we see in the country’s game parks.

The research was supported by the South African DST-NRF Centre of Excellence in Palaeosciences‚ based at the University of the Witwatersrand and the Millennium Trust.

See also here.

Oldest amphibians not in freshwater


This 2015 video is called Ancestral Evolution – Ichthyostega to Varanops.

By Carolyn Gramling, 5:29pm, May 30, 2018:

The first land-walking vertebrates may have emerged from salty estuaries

An analysis casts doubt on views that the ancient creatures arose in freshwater

Earth’s earliest land-walking vertebrates didn’t paddle about in freshwater lakes or rivers. Instead, these four-footed creatures, which appeared about 375 million years ago, lived in the brackish waters of an estuary or delta, researchers report online May 30 in Nature.

Early tetrapods, such as Ichthyostega and Acanthostega, lived an amphibious existence between land and sea: They had feet, but also gills and tails made for swimming. A new study by paleontologist Jean Goedert of Université Lyon in France and colleagues suggests that the animals also could have tolerated rapid changes in salinity, such as is found in an estuary.

The researchers analyzed sulfur and oxygen isotopes — forms of these elements with the same number of protons, but different masses — in 51 fossilized tetrapod bones from locations in what’s now Greenland and China. Compared with freshwater, seawater has a higher ratio of the sulfur-34 isotope relative to sulfur-32. The tetrapod bones tended to show elevated sulfur-34, the researchers report, suggesting that the creatures spent at least some time in seawater. But oxygen isotope analyses of the bones show that freshwater was also present, arguing against a purely salty environment such as an ocean.

The results challenge a long-held view that the earliest tetrapods emerged from freshwaters, such as rivers or lakes. In 1929, the first Ichthyostega fossils were found in a series of red sandstone layers in eastern Greenland that geologists once thought had been deposited in a freshwater environment. But later discoveries of tetrapod fossils found associated with known marine species suggested that the early walkers may have lived in saltier waters than once thought.

An ability to tolerate different salinity environments could have helped tetrapods — a group that includes today’s amphibians, reptiles and mammals — survive a mass extinction of ocean-dwellers that occurred by the end of the Devonian Period about 359 million years ago, the researchers say.