Shark and bony fish evolution, new research


This 9 September 2020 video from England says about itself:

410-Million-Year-Old Fish Fossil Virtual 3D CT Scan

Virtual three-dimensional model of the braincase of Minjinia turgenensis generated from CT scan.

Credit: Imperial College London/Natural History Museum

From Imperial College London in England:

Ancient bony fish forces rethink of how sharks evolved

September 7, 2020

Sharks’ non-bony skeletons were thought to be the template before bony internal skeletons evolved, but a new fossil discovery suggests otherwise.

The discovery of a 410-million-year-old fish fossil with a bony skull suggests the lighter skeletons of sharks may have evolved from bony ancestors, rather than the other way around.

Sharks have skeletons made of cartilage, which is around half the density of bone. Cartilaginous skeletons are known to evolve before bony ones, but it was thought that sharks split from other animals on the evolutionary tree before this happened; keeping their cartilaginous skeletons while other fish, and eventually us, went on to evolve bone.

Now, an international team led by Imperial College London, the Natural History Museum and researchers in Mongolia have discovered a fish fossil with a bony skull that is an ancient cousin of both sharks and animals with bony skeletons. This could suggest the ancestors of sharks first evolved bone and then lost it again, rather than keeping their initial cartilaginous state for more than 400 million years.

The team published their findings today in Nature Ecology & Evolution.

Lead researcher Dr Martin Brazeau, from the Department of Life Sciences at Imperial, said: “It was a very unexpected discovery. Conventional wisdom says that a bony inner skeleton was a unique innovation of the lineage that split from the ancestor of sharks more than 400 million years ago, but here is clear evidence of bony inner skeleton in a cousin of both sharks and, ultimately, us.”

Most of the early fossils of fish have been uncovered in Europe, Australia and the USA, but in recent years new finds have been made in China and South America. The team decided to dig in Mongolia, where there are rocks of the right age that have not been searched before.

They uncovered the partial skull, including the braincase, of a 410-million-year-old fish. It is a new species, which they named Minjinia turgenensis, and belongs to a broad group of fish called ‘placoderms‘, out of which sharks and all other ‘jawed vertebrates’ — animals with backbones and mobile jaws — evolved.

When we are developing as foetuses, humans and bony vertebrates have skeletons made of cartilage, like sharks, but a key stage in our development is when this is replaced by ‘endochondral’ bone — the hard bone that makes up our skeleton after birth.

Previously, no placoderm had been found with endochondral bone, but the skull fragments of M. turgenensis were “wall-to-wall endochondral.” While the team are cautious not to over-interpret from a single sample, they do have plenty of other material collected from Mongolia to sort through and perhaps find similar early bony fish.

And if further evidence supports an early evolution of endochondral bone, it could point to a more interesting history for the evolution of sharks.

Dr Brazeau said: “If sharks had bony skeletons and lost it, it could be an evolutionary adaptation. Sharks don’t have swim bladders, which evolved later in bony fish, but a lighter skeleton would have helped them be more mobile in the water and swim at different depths.

“This may be what helped sharks to be one of the first global fish species, spreading out into oceans around the world 400 million years ago.”

Prehistoric fish teeth, new research


This July 2018 video says about itself:

When Fish Wore Armor

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 European Synchrotron Radiation Facility:

The origin of our teeth goes back more than 400 million years back in time, to the period when strange armoured fish first developed jaws and began to catch live prey. We are the descendants of these fish, as are all the other 60,000 living species of jawed vertebrates — sharks, bony fish, amphibians, reptiles, birds and mammals. An international team of scientists led by Uppsala University (Sweden), in collaboration with the ESRF, the European Synchrotron (France), the brightest X-ray source, has digitally ‘dissected’, for the first time, the most primitive jawed fish fossils with teeth found near Prague more than 100 years ago. The results, published today in Science, show that their teeth have surprisingly modern features.

Teeth in current jawed vertebrates reveal some consistent patterns: for example, new teeth usually develop on the inner side of the old ones and then move outwards to replace them (in humans this pattern has been modified so that new teeth develop below the old ones, deep inside the jawbone). There are, however, several differences between bony fish (and their descendants the land animals) and sharks; for example, the fact that sharks have no bones at all, their skeleton is made of cartilage, and neither the dentine scales nor the true teeth in the mouth attach to it; they simply sit in the skin. In bony fish and land animals, the teeth are always attached to jawbones. In addition, whilst sharks shed their worn-out teeth entire, simply by detaching them from the skin, bony fish and land animals shed theirs by dissolving away the tooth bases.

This diversity raises many questions about the origin of teeth. Until now, researchers have focused on fossils of a group of ancient fish that lived about 430 to 360 million years ago, called the arthrodires, which were the only stem jawed vertebrates in which teeth were known. However, they struggled to understand how they could have evolved into the teeth of modern vertebrates, as arthrodire teeth are so different in position and mode of tooth addition in comparison to bony fish and sharks.

Scanning the most primitive jawed fishes

A team from Uppsala University, Charles University (Czech Republic), Natural History Museum in London (UK), National Museum in Prague (Czech Republic) and the ESRF, the European Synchrotron (France) set out to determine whether this peculiar type of dentition was really ancestral to ours, or just a specialised offshoot off the lineage leading towards modern jawed vertebrates.

With this aim, they turned to the acanthothoracids, another early fish group that are believed to be more primitive than the arthrodires and closely related to the very first jawed vertebrates. The problem with acanthothoracids is that their fossils are rare and always incomplete. The very finest of them come from the Prague Basin in the Czech Republic, from rocks that are just over 400 million years old, and were collected at the turn of the last century. They have proved difficult to study by conventional techniques because the bones cannot be freed from the enclosing rock, and have therefore never been investigated in detail.

The researchers used the unique properties of the ESRF, the world’s brightest X-ray source and the synchrotron microtomography ID19’s beamline, to visualise the internal structure of the fossils in 3D without damaging them. At the ESRF, an 844 metre-ring of electrons travelling at the speed of light emits high-powered X-ray beams that can be used to non-destructively scan matter, including fossils.

“The results were truly remarkable, including well-preserved dentitions that nobody expected to be there” says Valéria Vaškaninová, lead author of the study and scientist from Uppsala University. Follow-up scans at higher resolution allowed the researchers to visualize the growth pattern and even the perfectly preserved cell spaces inside the dentine of these ancient teeth.

Like arthrodires, the acanthothoracid dentitions are attached to bones. This indicates that bony fish and land animals retain the ancestral condition in this regard, whereas sharks are specialized in having teeth that are only attached to the skin — in contrast to the common perception that sharks are primitive living vertebrates. Again, like arthrodires, the teeth of acanthothoracids were not shed.

More different from arthrodires than expected

In other ways, however, acanthothoracid dentitions are fundamentally different from those of arthrodires. Like sharks, bony fish and land animals, acanthothoracids only added new teeth on the inside; the oldest teeth were located right at the jaw margin. In this respect, the acanthothoracid dentitions look remarkably modern.

“To our surprise, the teeth perfectly matched our expectations of a common ancestral dentition for cartilaginous and bony vertebrates.” explains Vaškaninová.

The tooth-bearing bones also carry small non-biting dentine elements of the skin on their outer surfaces, a character shared with primitive bony fish but not with arthrodires. This is an important difference because it shows that acanthothoracid jaw bones were located right at the edge of the mouth, whereas arthrodire jaw bones lay further in. Uniquely, one acanthothoracid (Kosoraspis) shows a gradual shape transition from these dentine elements to the neighboring true teeth, while another (Radotina) has true teeth almost identical to its skin dentine elements in shape. This may be evidence that the true teeth had only recently evolved from dentine elements on the skin.

“These findings change our whole understanding of the origin of teeth” says co-author Per Ahlberg, professor at Uppsala University. And he adds: “Even though acanthothoracids are among the most primitive of all jawed vertebrates, their teeth are in some ways far more like modern ones than arthrodire dentitions. Their jawbones resemble those of bony fish and seem to be directly ancestral to our own. When you grin at the bathroom mirror in the morning, the teeth that grin back at you can trace their origins right back to the first jawed vertebrates.”

Devonian ancient plant discovery in Australia


Keraphyton mawsoniae: (A) specimen before preparation; (B) general view of stem showing the 4 rib systems (Ia, Ib, IIa and IIb); (C) central segment and four fundamental ribs; (D) rib system Ib showing a short branch dividing into two equal ultimate ribs at right and a long branch producing at least three long ultimate ribs at left; (E) long branch of rib system IIa producing short ultimate ribs; (F) short branch of rib system IIa dividing into two ultimate ribs; (G) long branch of rib system IIb producing short ultimate ribs; (H) long branch of rib system Ia producing long, but broken, ultimate ribs. Abbreviations: cs – central segment, fr – fundamental rib, ic – inner cortex, oc – outer cortex, Lb – long branch, sb – short branch. Yellow arrowheads indicate ultimate ribs. (DH) are all oriented with the cortex of the axis towards the top of the photo. Scale bars – 500 μm, (B) – 2 mm. Image credit: Champreux et al, doi: 10.7717/peerj.9321

From Flinders University in Australia:

Australian fossil reveals new plant species

June 16, 2020

Summary: Fresh examination of an Australian fossil — believed to be among the earliest plants on Earth — has revealed evidence of a new plant species that existed in Australia more than 359 Million years ago.

Antoine Champreux, a PhD student in the Global Ecology Lab at Flinders University, has catalogued the discovery of the new fern-like plant species as part of an international effort to examine the Australian fossil in greater detail.

The fossil was found in the 1960s by amateur geologist Mr John Irving, on the bank of the Manilla River in Barraba, New South Wales. The fossil was exposed after major flooding events in 1964, and Mr Irving gave the fossil to the geological survey of New South Wales, where it remained for more than 50 years without being studied.

It was dated from the end of the Late Devonian period, approximately 372-to-359 million years ago — a time when Australia was part of the Southern hemisphere super-continent Gondwana. Plants and animals had just started to colonise continents, and the first trees appeared. Yet while diverse fish species were in the oceans, continents had no flowering plants, no mammals, no dinosaurs, and the first plants had just acquired proper leaves and the earliest types of seeds.

Well-preserved fossils from this era are rare — elevating the significance of the Barraba plant fossil.

The fossil is currently in France, where Brigitte Meyer-Berthaud, an international expert studying the first plants on Earth, leads a team at the French laboratory of Botany and Modelling of Plant Architecture and Vegetation (AMAP) in Montpellier. This French laboratory is particularly interested in further examination of Australian fossils from the Devonian-Carboniferous geological period, to build a more detailed understanding of plant evolution during this era.

Mr Champreux studied the fern-like fossil during his master’s degree internship at AMAP and completed writing his research paper during his current PhD studies at Flinders University.

“It’s nothing much to look at — just a fossilised stick — but it’s far more interesting once we cut it and had a look inside,” says Mr Champreux. “The anatomy is preserved, meaning that we can still observe the walls of million-year-old cells. We compared the plant with other plants from the same period based on its anatomy only, which provide a lot of information.”

He found that this plant represents a new species, and even a new genus of plant, sharing some similarities with modern ferns and horsetails.

“It is an extraordinary discovery, since such exquisitely-preserved fossils from this period are extremely rare,” he says. “We named the genus Keraphyton (like the horn plant in Greek), and the species Keraphyton mawsoniae, in honour of our partner Professor Ruth Mawson, a distinguished Australian palaeontologist who died in 2019.”

An article describing the new plant — Keraphyton gen. nov., a new Late Devonian fern-like plant from Australia, by A Champreux, B Meyer-Berthaud and A-L Decombeix — has been published in the scientific journal PeerJ and It reinforces the partnership between the lab AMAP (Montpellier, France) and Flinders University.

Devonian-Carboniferous mass extinction and global warming


This 2015 video says about itself:

New Carboniferous Life

After the Devonian extinction, new types of tetrapods, fish, plants, and other organisms repopulated the world, some of which led to more modern fauna and flora.

From the University of Southampton in England:

Erosion of ozone layer responsible for mass extinction event

May 27, 2020

Researchers at the University of Southampton have shown that an extinction event 360 million years ago, that killed much of the Earth’s plant and freshwater aquatic life, was caused by a brief breakdown of the ozone layer that shields the Earth from damaging ultraviolet (UV) radiation. This is a newly discovered extinction mechanism with profound implications for our warming world today.

There have been a number of mass extinction in the geological past. Only one was caused by an asteroid hitting the Earth, which was 66 million years ago when the dinosaurs became extinct. Three of the others, including the end Permian Great Dying, 252 million years ago, were caused by huge continental-scale volcanic eruptions that destabilised the Earth’s atmospheres and oceans.

Now, scientists have found evidence showing it was high levels of UV radiation which collapsed forest ecosystems and killed off many species of fish and tetrapods (our four-limbed ancestors) at the end of the Devonian geological period, 359 million years ago. This damaging burst of UV radiation occurred as part of one of the Earth’s climate cycles, rather than being caused by a huge volcanic eruption.

The ozone collapse occurred as the climate rapidly warmed following an intense ice age and the researchers suggest that the Earth today could reach comparable temperatures, possibly triggering a similar event. Their findings are published in the journal Science Advances.

The team collected rock samples during expeditions to mountainous polar-regions in East Greenland, which once formed a huge ancient lake bed in the arid interior of the Old Red Sandstone Continent, made up of Europe and North America. This lake was situated in the Earth’s southern hemisphere and would have been similar in nature to modern-day Lake Chad on the edge of the Sahara Desert.

Other rocks were collected from the Andean Mountains above Lake Titicaca in Bolivia. These South American samples were from the southern continent of Gondwana, which was closer to the Devonian South Pole. They held clues as to what was happening at the edge of the melting Devonian ice sheet, allowing a comparison between the extinction event close to the pole and close to the equator.

Back in the lab, the rocks were dissolved in hydrofluoric acid, releasing microscopic plant spores (like pollen, but from fern-like plants that didn’t have seeds or flowers) which had lain preserved for hundreds of millions of years. On microscopic examination, the scientists found many of the spores had bizarrely formed spines on their surface — a response to UV radiation damaging their DNA. Also, many spores had dark pigmented walls, thought to be a kind of protective ‘tan’, due to increased and damaging UV levels.

The scientists concluded that, during a time of rapid global warming, the ozone layer collapsed for a short period, exposing life on Earth to harmful levels of UV radiation and triggering a mass extinction event on land and in shallow water at the Devonian-Carboniferous boundary.

Following melting of the ice sheets, the climate was very warm, with the increased heat above continents pushing more naturally generated ozone-destroying chemicals into the upper atmosphere. This let in high levels of UV-B radiation for several thousand years.

Lead researcher Professor John Marshall, of the University of Southampton’s School of Ocean and Earth Science, who is a National Geographic Explorer, comments: “Our ozone shield vanished for a short time in this ancient period, coinciding with a brief and quick warming of the Earth. Our ozone layer is naturally in a state of flux — constantly being created and lost — and we have shown this happened in the past too, without a catalyst such as a continental scale volcanic eruption.”

During the extinction, plants selectively survived, but were enormously disrupted as the forest ecosystem collapsed. The dominant group of armoured fish became extinct. Those that survived — sharks and bony fish — remain to this day the dominant fish in our ecosystems.

These extinctions came at a key time for the evolution of our own ancestors, the tetrapods. These early tetrapods are fish that evolved to have limbs rather than fins, but still mostly lived in water. Their limbs possessed many fingers and toes. The extinction reset the direction of their evolution with the post-extinction survivors being terrestrial and with the number of fingers and toes reduced to five.

Professor Marshall says his team’s findings have startling implications for life on Earth today: “Current estimates suggest we will reach similar global temperatures to those of 360 million years ago, with the possibility that a similar collapse of the ozone layer could occur again, exposing surface and shallow sea life to deadly radiation. This would move us from the current state of climate change, to a climate emergency.”

The remote locations visited in East Greenland are very difficult to access, with travel involving light aircraft capable of landing directly on the tundra. Transport within the vast field area was by inflatable boats equipped with outboard motors, all of which had to fit in the small aircraft.

All field logistics was organised by CASP, an independent charitable trust based in Cambridge specialising in remote geological fieldwork. Mike Curtis, Managing Director of CASP says: “We have a history of assisting research geologists such as John Marshall and colleagues to access remote field areas and we are particularly pleased that their research has proved to have such potentially profound implications.”

How giant prehistoric fish Titanichthys fed


This 30 December 2018 video says about itself:

Titanichthys is a genus of giant, aberrant marine placoderm from shallow seas of the Late Devonian of Morocco, Eastern North America, and possibly Europe. Many individuals of the species approached Dunkleosteus in size and build.

Unlike its relative, however, the various species of Titanichys had small, ineffective-looking mouth-plates that lacked a sharp cutting edge. It is assumed that Titanichthys was a filter feeder that used its capacious mouth to swallow or inhale schools of small, anchovy-like fish, or possibly krill-like zooplankton, and that the mouth-plates retained the prey while allowing the water to escape as it closed its mouth

From the University of Bristol in England:

Ancient giant armored fish fed in a similar way to basking sharks

May 19, 2020

Scientists from the University of Bristol and the University of Zurich have shown that the Titanichthys — a giant armoured fish that lived in the seas and oceans of the late Devonian period 380-million-years ago — fed in a similar manner to modern-day basking sharks.

Titanichthys has long been known as one of the largest animals of the Devonian — its exact size is difficult to determine, but it likely exceeded five metres in length; like in the basking shark, its lower jaw reached lengths exceeding one metre. However, unlike its similarly giant contemporary Dunkleosteus, there is no previous evidence of how Titanichthys fed.

Where the lower jaw of Dunkleosteus and many of its relatives had clear fangs and crushing plates, the lower jaw of Titanichthys is narrow and lacking any dentition or sharp edges suitable for cutting.

Consequently, Titanichthys has been presumed to have been a suspension-feeder, feeding on minute plankton by swimming slowly with the mouth opened widely through water to capture high concentrations of plankton — a technique called continuous ram feeding.

However, this has remained uncertain, as no fossilised evidence of suspension-feeding structures such as elongate projections that cover the gills in modern suspension-feeding fish has ever been found.

Instead, the team sought to investigate the question indirectly, using biomechanical analysis to compare the lower jaw of Titanichthys with those of other species. Their findings are reported today in the journal Royal Society Open Science.

Lead author Sam Coatham carried out the research while studying for his masters in palaeobiology at the University of Bristol’s School of Earth Sciences.

He said: “We have found that Titanichthys was very likely to have been a suspension-feeder, showing that its lower jaw was considerably less mechanically robust than those of other placoderm species that fed on large or hard-shelled prey.

“Consequently, those feeding strategies (common amongst its relatives) would probably have not been available for Titanichthys.”

The fossils of Titanichthys used in the study were found in the Moroccan part of the Sahara Desert by co-author Christian Klug, a researcher at the University of Zurich. He added: “When you do fieldwork in the Anti-Atlas, massive skull bones of placoderms can be found quite frequently.”

The team tested the resilience of the jaws by virtually applying forces to the jaws, using a technique called Finite Element Analysis (FEA) to assess how likely each jaw was to break or bend.

This revealed that the lower jaw of Titanichthys was much less resistant to stress and was more likely to break than those of the other placoderm species, such as the famous Dunkleosteus. Therefore, the jaw of Titanichthys probably would not have been able to withstand the higher stresses associated with their strategies of feeding on large prey, which thus exert more mechanical stress on the jaws.

This pattern was consistent in both sharks and whales, with the suspension-feeder proving less resistant to stress than the other species within the same lineage. Further analyses comparing the distribution of stress across the jaws showed similar patterns in Titanichthys and the basking shark, reinforcing this comparison.

It has been established that there were almost certainly giant suspension-feeding vertebrates living 380 million years ago, at least 150 million years before the suspension-feeding Pachycormidae (previously the earliest definitive example) and about 350 million years before the first baleen whales.

The research team believes that there are other extinct species that would have filled a similar ecological role, including other placoderms (armoured fish) and at least one species of plesiosaur.

Sam Coatham added: “Our methods could be extended to identify other such species in the fossil record and investigate whether there were common factors driving the evolution and extinction of these species.

“We suggest a link between oceanic productivity and the evolution of Titanichthys, but this should be investigated in detail in the future. An established link could have implications for our understanding of the conservation of modern suspension-feeders.”

Ancient Devonian fossil plant, new discovery


Barinophyton spp.

From Stanford’s School of Earth, Energy & Environmental Sciences in the USA:

New ancient plant captures snapshot of evolution

May 4, 2020

Summary: Researchers have discovered an ancient plant species whose reproductive biology captures the evolution from one to two spore sizes — an essential transition to the success of the seed and flowering plants we depend on

In a brilliant dance, a cornucopia of flowers, pinecones and acorns connected by wind, rain, insects and animals ensure the reproductive future of seed plants. But before plants achieved these elaborate specializations for sex, they went through millions of years of evolution. Now, researchers have captured a glimpse of that evolutionary process with the discovery of a new ancient plant species.

The fossilized specimen likely belongs to the herbaceous barinophytes, an unusual extinct group of plants that may be related to clubmosses, and is one of the most comprehensive examples of a seemingly intermediate stage of plant reproductive biology. The new species, which is about 400 million years old and from the Early Devonian period, produced a spectrum of spore sizes — a precursor to the specialized strategies of land plants that span the world’s habitats. The research was published in Current Biology May 4.

“Usually when we see heterosporous plants appear in the fossil record, they just sort of pop into existence,” said the study’s senior author, Andrew Leslie, an assistant professor of geological sciences at Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth). “We think this may be kind of a snapshot of this very rarely witnessed transition period in evolutionary history where you see high variation amongst spores in the reproductive structure.”

A major shift

One of the most important time periods for the evolution of land plants, the Devonian witnessed diversification from small mosses to towering complex forests. The development of different spore sizes, or heterospory, represents a major modification to control reproduction — a feature that later evolved into small and large versions of these reproductive units.

“Think of all the different types of sexual systems that are in flowers — all of that is predicated on having separate small spores, or pollen, and big spores, which are inside the seeds,” Leslie said. “With two discrete size classes, it’s a more efficient way of packaging resources because the big spores can’t move as easily as the little ones, but can better nourish offspring.”

The earliest plants, from between 475 million to 400 million years ago, lacked reproductive specialization in the sense that they made the same types of spores, which would then grow into little plantlets that actually transferred reproductive cells. By partitioning reproductive resources, plants assumed more control over reproduction, according to the researchers.

The new species, together with the previously described plant group Chaleuria of the same age, represents the first evidence of more advanced reproductive biology in land plants. The next example doesn’t appear in the fossil record until about 20 million years later.

“These kinds of fossils help us locate when and how exactly plants achieved that kind of partitioning of their reproductive resources,” Leslie said. “The very end of that evolutionary history of specialization is something like a flower.”

A fortuitous find

The researchers began analyses of the fossils after they had been stored in the collections at the Smithsonian National Museum of Natural History for decades. From about 30 small chips of rock originally excavated from the Campbellton Formation of New Brunswick in Canada by late paleobotanist and study co-author Francis Hueber, they identified more than 80 reproductive structures, or sporangia. The spores themselves range from about 70 to 200 microns in diameter — about a strand to two strands of hair. While some of the structures contained exclusively large or small spores, others held only intermediate-sized spores and others held the entire range of spore sizes — possibly with some producing sperm and others eggs.

“It’s rare to get this many sporangia with well-preserved spores that you can measure,” Leslie said. “We just kind of got lucky in how they were preserved.”

Fossil and modern heterosporous plants primarily live in wetland environments, such as floodplains and swamps, where fertilization of large spores is most effective. The ancient species, which will be formally described in a follow-up paper, has a medley of spores that is not like anything living today, Leslie said.

“The overarching story in land plant reproduction is one of increased division of labor and specialization and complexity, but that has to begin somewhere — and it began with simply producing small spores and big spores,” Leslie said. “With these kinds of fossils, we can identify some ways the plants were able to do that.”

Co-authors of the study are from Brown University, the University of North Carolina — Chapel Hill and the University of Sheffield.

Amphibian ancestor fossil fish discovery


This 20 March 2020 video says about itself:

This week, scientists discover something in a fish fossil that might give us a hand in finding our earliest land-dwelling ancestors.

Hosted by: Hank Green

That Devonian era fossil fish species is Elpistotege watsoni, discovered in Quebec.

Ancient fish fins before evolution to amphibians


This 2016 video says about itself:

The evolution of fish began about 530 million years ago during the Cambrian explosion. Early fish from the fossil record are represented by a group of small, jawless, armoured fish known as ostracoderms. Jawless fish lineages are mostly extinct. An extant clade, the lampreys may approximate ancient pre-jawed fish. The first jaws are found in Placoderm fossils. The diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors. The evolution of fish is not studied as a single event. since fish do not represent a monophyletic group but a paraphyletic one (by exclusion of the tetrapods).

From the University of Chicago Medical Center in the USA:

How fish fins evolved just before the transition to land

December 31, 2019

Research on fossilized fish from the late Devonian period, roughly 375 million years ago, details the evolution of fins as they began to transition into limbs fit for walking on land.

The new study by paleontologists from the University of Chicago, published this week in the Proceedings of the National Academy of Sciences, uses CT scanning to examine the shape and structure of fin rays while still encased in surrounding rock. The imaging tools allowed the researchers to construct digital 3D models of the entire fin of the fishapod Tiktaalik roseae and its relatives in the fossil record for the first time. They could then use these models to infer how the fins worked and changed as they evolved into limbs.

Much of the research on fins during this key transitional stage focuses on the large, distinct bones and pieces of cartilage that correspond to those of our upper arm, forearm, wrist, and digits. Known as the “endoskeleton”, researchers trace how these bones changed to become recognizable arms, legs and fingers in tetrapods, or four-legged creatures.

The delicate rays and spines of a fish’s fins form a second, no less important “dermal” skeleton, which was also undergoing evolutionary changes in this period. These pieces are often overlooked because they can fall apart when the animals are fossilized or because they are removed intentionally by fossil preparators to reveal the larger bones of the endoskeleton. Dermal rays form most of the surface area of many fish fins but were completely lost in the earliest creatures with limbs.

“We’re trying to understand the general trends and evolution of the dermal skeleton before all those other changes happened and fully-fledged limbs evolved,” said Thomas Stewart, PhD, a postdoctoral researcher who led the new study. “If you want to understand how animals were evolving to use their fins in this part of history, this is an important data set.”

Seeing ancient fins in 3D

Stewart and his colleagues worked with three late Devonian fishes with primitive features of tetrapods: Sauripterus taylori, Eusthenopteron foordi and Tiktaalik roseae, which was discovered in 2006 by a team led by UChicago paleontologist Neil Shubin, PhD, the senior author of the new study. Sauripterus and Eusthenopteron were believed to have been fully aquatic and used their pectoral fins for swimming, although they may have been able to prop themselves up on the bottom of lakes and streams. Tiktaalik may have been able to support most of its weight with its fins and perhaps even used them to venture out of the water for short trips across shallows and mudflats.

“By seeing the entire fin of Tiktaalik we gain a clearer picture of how it propped itself up and moved about. The fin had a kind of palm that could lie flush against the muddy bottoms of rivers and streams,” Shubin said.

Stewart and Shubin worked with undergraduate student Ihna Yoo and Justin Lemberg, PhD, another researcher in Shubin’s lab, to scan specimens of these fossils while they were still encased in rock. Using imaging software, they then reconstructed 3D models that allowed them to move, rotate and visualize the dermal skeleton as if it were completely extracted from the surrounding material.

The models showed that the fin rays of these animals were simplified, and the overall size of the fin web was smaller than that of their fishier predecessors. Surprisingly, they also saw that the top and bottom of the fins were becoming asymmetric. Fin rays are actually formed by pairs of bones. In Eusthenopteron, for example, the dorsal, or top, fin ray was slightly larger and longer than the ventral, or bottom one. Tiktaalik’s dorsal rays were several times larger than its ventral rays, suggesting that it had muscles that extended on the underside of its fins, like the fleshy base of the palm, to help support its weight.

“This provides further information that allows us to understand how an animal like Tiktaalik was using its fins in this transition,” Stewart said. “Animals went from swimming freely and using their fins to control the flow of water around them, to becoming adapted to pushing off against the surface at the bottom of the water.”

Stewart and his colleagues also compared the dermal skeletons of living fish like sturgeon and lungfish to understand the patterns they were seeing in the fossils. They saw some of the same asymmetrical differences between the top and bottom of the fins, suggesting that those changes played a larger role in the evolution of fishes.

“That gives us more confidence and another data set to say these patterns are real, widespread and important for fishes, not just in the fossil record as it relates to the fin-to-limb transition, but the function of fins broadly.”

Devonian era forest discovery in New York


This 2013 video from the USA says about itself:

Devonian forest

This scene is excerpted from the Colorado Geology: Devonian-Mississippian video (in progress). These trees are the Progymnosperm Archaeopteris, and the forest floor includes Racophyton. Major soils did not develop until the first trees evolved on land.

Animation by Joseph Rogers and Leo Ascarrunz. Special thanks to Ian Miller and James Hagedorn (DMNS) for their input.

Interactive Geology Project, University of Colorado-Boulder.

From ScienceDaily:

385-million-year-old forest discovered

December 19, 2019

While sifting through fossil soils in the Catskill region near Cairo, New York, researchers uncovered the extensive root system of 386-million-year old primitive trees. The fossils, located about 25 miles from the site previously believed to have the world’s oldest forests, is evidence that the transition toward forests as we know them today began earlier in the Devonian Period than typically believed.

“The Devonian Period represents a time in which the first forest appeared on planet Earth,” says first author William Stein, an emeritus professor of biological science at Binghamton University, New York. “The effects were of first-order magnitude, in terms of changes in ecosystems, what happens on the Earth’s surface and oceans, in global atmosphere, CO2 concentration in the atmosphere, and global climate. So many dramatic changes occurred at that time as a result of those original forests that basically, the world has never been the same since.”

Stein, along with collaborators, including Christopher Berry and Jennifer Morris of Cardiff University and Jonathan Leake of the University of Sheffield,have been working in the Catskill region in New York, where in 2012 they uncovered “footprint evidence” of a different fossil forest at Gilboa, which, for many years has been termed the Earth’s oldest forest. The discovery at Cairo, about a 40-minute drive from the original site, now reveals an even older forest with dramatically different composition.

The Cairo site presents three unique root systems, leading Stein and his team to hypothesize that much like today, the forests of the Devonian Period were composed of different trees occupying different places depending on local conditions.

First, Stein and his team identified a rooting system that they believe belonged to a palm tree-like plant called Eospermatopteris. This tree, which was first identified at the Gilboa site, had relatively rudimentary roots. Like a weed, Eospermatopteris likely occupied many environments, explaining its presence at both sites. But its roots had relatively limited range and probably lived only a year or two before dying and being replaced by other roots that would occupy the same space. The researchers also found evidence of a tree called Archaeopteris, which shares a number of characteristics with modern seed plants.

“Archaeopteris seems to reveal the beginning of the future of what forests will ultimately become,” says Stein. “Based on what we know from the body fossil evidence of Archaeopteris prior to this, and now from the rooting evidence that we’ve added at Cairo, these plants are very modern compared to other Devonian plants. Although still dramatically different than modern trees, yet Archaeopteris nevertheless seems to point the way toward the future of forests elements.”

Stein and his team were also surprised to find a third root system in the fossilized soil at Cairo belonging to a tree thought to only exist during the Carboniferous Period and beyond: “scale trees” belonging to the class Lycopsida.

“What we have at Cairo is a rooting structure that appears identical to great trees of the Carboniferous coal swamps with fascinating elongate roots. But no one has yet found body fossil evidence of this group this early in the Devonian.” Stein says. “Our findings are perhaps suggestive that these plants were already in the forest, but perhaps in a different environment, earlier than generally believed. Yet we only have a footprint, and we await additional fossil evidence for confirmation.”

Moving forward, Stein and his team hope to continue investigating the Catskill region and compare their findings with fossil forests around the world.

“It seems to me, worldwide, many of these kinds of environments are preserved in fossil soils. And I’d like to know what happened historically, not just in the Catskills, but everywhere,” says Stein. “Understanding evolutionary and ecological history — that’s what I find most satisfying.”

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.