310-million-year-old horseshoe crab brain discovery

By Rebecca Dzombak:

August 20, 2021 at 8:00 am

How fossilization preserved a 310-million-year-old horseshoe crab’s brain

A newly analyzed specimen is a ‘one-in-a-million’ find, researchers say

Paleontologists can spend years carefully splitting rocks in search of the perfect fossil. But with a 310-million-year-old horseshoe crab brain, nature did the work, breaking the fossil in just the right way to reveal the ancient arthropod’s central nervous system.

Of all soft tissues, brains are notoriously difficult to preserve in any form (SN: 10/31/16). Stumbling across such a detailed specimen purely by chance was “a one-in-a-million find, if not rarer,” says evolutionary paleontologist Russell Bicknell of the University of New England in Armidale, Australia.

The fossilized brain is remarkably similar to the brains of modern horseshoe crabs, giving clues to the arthropods’ evolution, Bicknell and colleagues report July 26 in Geology. And the brain’s peculiar mode of preservation could point paleontologists toward new places to look for hard-to-find fossils of soft tissues.

Extinct sea scorpions could breathe on land

This April 2019 video says about itself:

Sea scorpions thrived for 200 million years, coming in a wide variety of shapes and sizes. Over time, they developed a number of adaptations–from crushing claws to flattened tails for swimming. And some of them adapted by getting so big that they still hold the record as the largest arthropods of all time.

From West Virginia University in the USA:

Coming up for air: Extinct sea scorpions could breathe out of water, fossil detective unveils

September 10, 2020

Summary: Through computed tomography (CT) imaging, geologists found evidence of air breathing in a 340 million-year-old sea scorpion, or eurypterid.

Scientists have long debated the respiratory workings of sea scorpions, but a new discovery by a West Virginia University geologist concludes that these largely aquatic extinct arthropods breathed air on land.

James Lamsdell dug into the curious case of a 340 million-year-old sea scorpion, or eurypterid, originally from France that had been preserved at a Glasgow, Scotland museum for the last 30 years.

An assistant professor of geology in the Eberly College of Arts and Sciences, Lamsdell had read about the “strange specimen” 25 years ago while conducting his doctoral studies. Existing research suggested it would occasionally go on land.

Yet nothing was known on whether it could breathe air. The closest living relative to the eurypterid is the horseshoe crab, which lays eggs on land but is unable to breathe above water.

These details puzzled Lamsdell through the years until he reached out to a colleague, Victoria McCoy at the University of Wisconsin-Milwaukee, and asked, “Do you have access to a CT scanner?”

“We wondered if we could apply new technology to look further into what was preserved of this specimen,” said Lamsdell, who heads a paleobiology lab at WVU. “I like the science and detective work that goes into research. And this was a cold case where we knew there was potential evidence.”

Through computed tomography (CT) imaging, Lamsdell and his team found that evidence, which is published in Current Biology.

Researchers managed to study the respiratory organs of the three-dimensional eurypterid, leading to two findings that stood out to Lamsdell. First, he noticed that each gill on the sea scorpion was composed of a series of plates. But the back contained fewer plates than the front, prompting researchers to question how it could even breathe.

Then they zeroed in on pillars connecting the different plates of the gill, which are seen in modern scorpions and spiders, Lamsdell said. These pillars, or small beams of tissue, are called trabeculae.

“That props the gills apart so they don’t collapse when out of water,” Lamsdell explained. “It’s something that modern arachnids still have. Finding that was the final indication.

“The reason we think they were coming onto land was to move between pools of water. They could also lay eggs in more sheltered, safer environments and migrate back into the open water.”

The discovery of air-breathing structures in the eurypterids indicate that terrestrial characteristics occurred in the arachnid stem lineage, the researchers wrote, suggesting that the ancestor of arachnids were semi-terrestrial.

In addition to Lamsdell and McCoy, co-authors include Opal Perron-Feller of Oberlin College and Melanie Hopkins of the American Museum of Natural History.

Now that Lamsdell has cracked the case living in the back of his head for 20-plus years, he believes there’s more to unearth from the fossil. He noted that the sea scorpion’s back legs expand into a paddle shape, which he suspects would have been used to swim. The bases of their legs also had spikes that ground up food for them that they maneuvered into their mouths, Lamsdell added.

“One of the things that would be really cool to do is to flesh out this model and try to reconstruct exactly how the legs could move and how they were positioned,” Lamsdell said, “like reconstructing the fossil as a living animal.”

Carboniferous animal trackway discovery, Grand Canyon, USA

From the National Park Service in the USA:

Cliff collapse reveals 313-million-year-old fossil footprints in Grand Canyon National Park

August 21, 2020

Paleontological research has confirmed a series of recently discovered fossils tracks are the oldest recorded tracks of their kind to date within Grand Canyon National Park. In 2016, Norwegian geology professor, Allan Krill, was hiking with his students when he made a surprising discovery. Lying next to the trail, in plain view of the many hikers, was a boulder containing conspicuous fossil footprints. Krill was intrigued, and he sent a photo to his colleague, Stephen Rowland, a paleontologist at the University of Nevada Las Vegas.

The trailside tracks have turned out to be even more significant than Krill first imagined. “These are by far the oldest vertebrate tracks in Grand Canyon, which is known for its abundant fossil tracks” says Rowland. “More significantly,” he added, “they are among the oldest tracks on Earth of shelled-egg-laying animals, such as reptiles, and the earliest evidence of vertebrate animals walking in sand dunes.”

The track-bearing boulder fell from a nearby cliff-exposure of the Manakacha Formation. The presence of a detailed geologic map of the strata along the Bright Angel Trail, together with previous studies of the age of the Manakacha Formation, allowed the researchers to pin down the age of the tracks quite precisely to 313 +/- 0. 5 million years.

The newly discovered tracks record the passage of two separate animals on the slope of a sand dune. Of interest to the research team is the distinct arrangement of footprints. The researchers’ reconstruction of this animal’s footfall sequence reveals a distinctive gait called a lateral-sequence walk, in which the legs on one side of the animal move in succession, the rear leg followed by the foreleg, alternating with the movement of the two legs on the opposite side. “Living species of tetrapods―dogs and cats, for example―routinely use a lateral-sequence gait when they walk slowly,” says Rowland. “The Bright Angel Trail tracks document the use of this gait very early in the history of vertebrate animals. We previously had no information about that.” Also revealed by the trackways is the earliest-known utilization of sand dunes by vertebrate animals.

Carboniferous fossil fish sturgeon-like, no sturgeon

From the University of Pennsylvania in the USA:

300-million-year-old fish resembles a sturgeon but took a different evolutionary path

June 22, 2020

Sturgeon, a long-lived, bottom-dwelling fish, are often described as “living fossils,” owing to the fact that their form has remained relatively constant, despite hundreds of millions of years of evolution.

In a new study in the Zoological Journal of the Linnean Society, researchers led by Jack Stack, a 2019 University of Pennsylvania graduate, and paleobiologist Lauren Sallan of Penn’s School of Arts & Sciences, closely examine the ancient fish species Tanyrhinichthys mcallisteri, which lived around 300 million years ago in an estuary environment in what is today New Mexico. Although they find the fish to be highly similar to sturgeons in its features, including its protruding snout, they show that these characteristics evolved in a distinct evolutionary path from those species that gave rise to modern sturgeons.

The find indicates that, although ancient, the features that enabled Tanyrhinichthys to thrive in its environment arose multiple times in different fish lineages, a burst of innovation that was not previously fully appreciated for fish in this time period.

“Sturgeon are considered a ‘primitive’ species, but what we’re showing is that the sturgeon lifestyle is something that’s been selected for in certain conditions and has evolved over and over again,” says Sallan, senior author on the work.

“Fish are very good at finding solutions to ecological problems,” says Stack, first author on the study, who worked on the research as a Penn undergraduate and is now a graduate student at Michigan State University. “This shows the degree of both innovation and convergence that’s possible in fishes. Once their numbers got up large enough, they started producing brand new morphologies that we now see have evolved numerous times through the history of fishes, under similar ecological conditions.”

The first fossil of Tanyrhinichthys was found in 1984 in a fossil-rich area called the Kinney Brick Quarry, about a half-hour east of Albuquerque. The first paleontologist to describe the species was Michael Gottfried, a Michigan State faculty member who now serves as Stack’s advisor for his master’s degree.

“The specimen looks like someone found a fish and just pulled on the front of its skull,” Stack says. Many modern fish species, from the swordfish to the sailfish, have protuberant snouts that extend out in front of them, often aiding in their ability to lunge at prey. But this characteristic is much rarer in ancient fishes. In the 1980s when Gottfried described the initial specimen, he posited that the fish resembled a pike, an ambush predator with a longer snout.

During the last decade, however, several more specimens of Tanyrhinichthys have been found in the same quarry. “Those finds were an impetus for this project, now that we had better information on this enigmatic and strange fish,” Stack says.

At the time that Tanyrhinichthys roamed the waters, Earth’s continents were joined in the massive supercontinent called Pangea, surrounded by a single large ocean. But it was an ice age as well, with ice at both poles. Just before this period, the fossil record showed that ray-finned fishes, which now dominate the oceans, were exploding in diversity. Yet 300 million years ago, “it was like someone hit the pause button,” Sallan says. “There’s an expectation that there would be more diversity, but not much has been found, likely owing to the fact that there just hasn’t been enough work on this time period, especially in the United States, and particularly in the Western United States.”

Aiming to fill in some of these gaps by further characterizing Tanyrhinichthys, Stack, Sallan, and colleagues closely examined the specimens in detail and studied other species that dated to this time period. “This sounds really simple, but it’s obviously difficult in execution,” Stack notes, as fossils are compressed flat when they are preserved. The researchers inferred a three-dimensional anatomy using the forms of modern fishes to guide them.

What they noticed cast doubt on the conception of Tanyrhinichthys as resembling a pike. While a pike has an elongated snout with its jaws at the end of it, allowing it to rush its prey head-on, Tanyrhinichthys has an elongated snout with its jaws at the bottom.

“The whole form of this fish is similar to other bottom dwellers,” Stack says. Sallan also noticed canal-like structures on its snout concentrated in the top of its head, suggestive of the locations where sensory organs would attach. “These would have detected vibrations to allow the fish to consume its prey,” says Sallan.

The researchers noted that many of the species that dwelled in similar environments possessed longer snouts, which Sallan called “like an antenna for your face.”

“This also makes sense because it was an estuary environment,” Sallan says, “with large rivers feeding into it, churning up the water, and making it murky. Rather than using your eyesight, you have to use these other sensory organs to detect prey.”

Despite this, other features of the different ancient fishes’ morphology were so different from Tanyrhinichthys that they do not appear to have shared a lineage with one another, nor do modern sturgeon descend from Tanyrhinichthys. Instead, the long snouts appear to be an example of convergent evolution, or many different lineages all arriving at the same innovation to adapt well to their environment.

“Our work, and paleontology in general, shows that the diversity of life forms that are apparent today has roots that extend back into the past,” says Stack.

Carboniferous rainforest collapse and animal evolution

This 19 February 2020 video says about itself:

The Carboniferous Rainforest Collapse set the stage for a takeover that would be a crucial turning point in the history of terrestrial animal life. If it weren’t for that time when the rainforests collapsed – in an extinction event that you probably haven’t heard of – our ancestors might never have made it out of the swamps.

The Tully Monster, mysterious extinct animal

This 16 February 2020 video says about itself:

One of the weirdest prehistoric creatures that ever existed was The Tully Monster, an animal so bizarre that palaeontologists still don’t know for sure what it was.

Prehistoric sharks invented suction feeding, new research

This 26 February 2019 video says about itself:

SHARKS and other prehistoric fish. Size comparison chart. Paleoart

INCLUDED TAXA: Harpagofututor, Echinochimaera, Falcatus, Stethacanthus, Cladoselache, Hybodus, Orthacanthus, Edestus, Mawsonia, Xiphactinus, Great White Shark, Helicoprion, Rhizodus, Onchopristis, Dunkleosteus, Carcarocles megalodon, Leedsightys.

From the University of Chicago in the USA:

Long before other fish, ancient sharks found an alternative way to feed

3D reconstructions of a 335-million-year-old shark fossil show how it evolved suction feeding 50 million years before bony fish

September 11, 2019

Researchers from the University of Chicago have used tools developed to explore 3D movements and mechanics of modern-day fish jaws to analyze a fossil fish for the first time. Combined with CT imaging technology able to capture images of the fossil while it is still encased in rock, the results reveal that the 335-million-year-old shark had sophisticated jaws capable of the kind of suction feeding common to bony fishes like bass, perch, carp and also modern-day nurse sharks.

Remarkably, these ancient shark jaws are some 50 million years older than the earliest evidence of similar jaws adapted for suction feeding in bony fishes. This shows both the evolutionary versatility of sharks, and how sharks responded quickly to new ecological opportunities in the aftermath of one of the five big extinctions in Earth’s history.

“Among today’s aquatic vertebrates, suction feeding is widespread, and is often cited as a key factor contributing to the spectacular evolutionary success of ray-finned fishes”, said Michael Coates, PhD, professor of organismal biology and anatomy at the University of Chicago and senior author of the new study. “But here we show that high-performance aquatic suction feeding first appeared in one of the earliest known sharks.”

A complete construction kit to rebuild a shark

The study, published this week in Science Advances, describes the fossil of Tristychius arcuatus, a 2-foot long shark similar to a dogfish. It was first discovered by Swiss biologist Louis Agassiz in 1837, and later described in detail by John Dick, a former classmate of Coates’, in 1978. Tristychius, and other Devonian period sharks like it, are found in ironstone rock nodules along the shores of the Firth of Forth near Edinburgh, Scotland.

Shark fossils are rare because their cartilage skeleton usually rots away before there’s any chance of fossilization. For decades, researchers studying ancient sharks have been limited to isolated teeth and fin spines. Even if they do find a more complete skeleton, it’s usually flattened, or, if it’s encased in one of these stones, it crumbles when they try to remove it.

Coates and his lab have been leading the field in applying modern imaging technology and software to study these challenging fossils. CT scanning allows them to create 3D images of any fossilized cartilage and the impressions it left while still encased in the stone. Then, using sophisticated modeling software originally developed to study structure and function in modern-day fish, they can recreate what the complete skeleton looked like, how the pieces fit together and moved, and what that meant for how these sharks lived.

“These new CT methods are releasing a motherlode of previously inaccessible data,” Coates said.

His team started reexamining some of the same fossils Dick studied, as well as specimens left untouched in earlier research. “Some of this is superbly preserved,” Coates said. “We realized that when we got all the parts out [virtually], we had the complete construction kit to rebuild our shark in 3D.”

Beating underwater physics

That virtual construction kit also allowed them to create 3D plastic printouts of the cartilages that build a shark’s skull. These, in turn, allowed Coates and his team to model movements and connections, both physically and virtually, to see how the skull worked.

Fish that use suction feeding essentially suck water in through their mouths to catch elusive prey, such as worms, crustaceans and other invertebrates from the ocean floor. To do so, they have to draw water in when they open their mouth, but not force it back out when they close it.

Suction feeders overcome these challenging physics by funneling the water back out through their gills. The amount of suction they create can be enhanced by flexible arches and joints that expand the cheeks and the volume inside the mouth to draw the water through (imagine the feeling when you hold your hands together underwater and slowly pull your palms apart).

Today’s fish have perfected this process, but Tristychius had a similar feeding apparatus that could expand as it opened and closed its mouth to control the flow of water (and food). Crucially, this included a set of cartilages around the mouth that limited the size of the opening to control the amount of suction. The circular mouth was pushed forward at the end of its muzzle like a modern-day carpet shark or nurse shark, not a gaping, toothy maw like a great white.

While other sharks at the time did have the more typical snapping jaws, the combination of expanding cheeks and a carefully controlled mouth aperture provided Tristychius with access to previously untapped food resources, such as prey taking refuge in shallow burrows or otherwise difficult-to-capture schools of shrimp or juvenile fish, around 50 million years before bony fish caught on to the same technique.

“The combination of both physical and computational models has allowed us to explore the biomechanics in a Paleozoic shark in a way that’s never been done before,” Coates said. “These particular sharks were doing something sophisticated and new. Here we have the earliest evidence of this key innovation that’s been so important for multiple groups of fishes and has evolved repeatedly.”

Additional authors for the study include Kristen Tietjen from the University of Chicago, Aaron M. Olsen from Brown University, and John A. Finarelli from University College Dublin, Ireland.

Ancient Carboniferous amphibian, new research

From the University of Lincoln in England:

Research reveals surprisingly powerful bite of tiny early tetrapod

May 9, 2019

Micro-CT scanning of a tiny snake-like fossil discovered in Scotland has shed new light on the elusive creature, thought to be one of the earliest known tetrapods to develop teeth that allowed it to crush its prey.

Detailed scans of Acherontiscus caledoniae showed a unique combination of different tooth shapes and sizes as well as a deep lower jaw which scientists believe would have given the creature the ability to pierce, cut and grind the hard-shelled crustaceans that made up its diet.

Scientists led by the University Museum of Zoology in Cambridge alongside the University of Lincoln, the Natural History Museum in London and the University of Southampton, found that the dental pattern of Acherontiscus is at odds with that of several other tetrapods of this period, which tended to have uniform rows of cone-like teeth sometimes curved backwards at the tip. The variation in the shape and size of teeth shown in this fossil displays a level of dental adaptation that is unprecedented in such an early tetrapod.

As co-author Dr Marcello Ruta from the University of Lincoln’s School Of Life Sciences explains: “We found that Acherontiscus preceded the origin of modern tetrapod lineages and joined an array of primitive groups that independently acquired long and often miniaturized bodies, and exhibited either reduced or no limbs.”

The fossil is the only known specimen of this limbless tetrapod, which measured just 6 inches long and existed in swampy marshlands on the outskirts of Edinburgh some 330 million years ago. The delicate nature of the fossil meant that scientists were unable to use mechanical or chemical methods to free its skeleton from the surrounding rock, or study the specimen under a microscope.

Lead author Professor Jennifer Clack from the University Museum of Zoology in Cambridge said: “Using advanced techniques of micro-CT scanning, we were able to make sense of Acherontiscus’ complex skull, revealing minute anatomical details that allowed us to produce a greatly revised and much more complete reconstruction.

“We were particularly surprised to realize the great variety of shapes and sizes of its teeth. Acherontiscus is the earliest known tetrapod showing a crushing dentition, a feature with a rather discontinuous distribution in fossil and modern tetrapods.”

Fragments in the surrounding matrix have also revealed more about Acherontiscus’ habitat which will inform further research into the area as co-author Professor John Marshall from the University of Southampton’s School of Ocean and Earth Science explains: “Our study provided impetus for exploring the ecology and environments of the Scottish wetlands where Acherontiscus lived. Analysis of the content of fossil spores from about 0.2 grams of the matrix surrounding the creature suggests that this animal lived close to or within a still water body surrounded by herbaceous plants related to clubmosses. A more distant forest of larger, tree-like relatives of modern quillworts was also present.”

Carboniferous ice age geology of Namibia

This 2015 video says about itself:

The “Karoo Ice Age” from 360–260 million years ago was the second major ice age of the Phanerozoic Eon. It is named after the tillite found in the Karoo region of South Africa, where evidence for this ice age was first clearly identified in the 19th century.

From West Virginia University in the USA:

Researcher unearths an ice age in the African desert

February 4, 2019

A field trip to Namibia to study volcanic rocks led to an unexpected discovery by West Virginia University geologists Graham Andrews and Sarah Brown.

While exploring the desert country in southern Africa, they stumbled upon a peculiar land formation — flat desert scattered with hundreds of long, steep hills. They quickly realized the bumpy landscape was shaped by drumlins, a type of hill often found in places once covered in glaciers, an abnormal characteristic for desert landscapes.

“We quickly realized what we were looking at because we both grew up in areas of the world that had been under glaciers, me in Northern Ireland and Sarah in northern Illinois,” said Andrews, an assistant professor of geology. “It’s not like anything we see in West Virginia where we’re used to flat areas and then gorges and steep-sided valleys down into hollows.”

After returning home from the trip, Andrews began researching the origins of the Namibian drumlins, only to learn they had never been studied.

“The last rocks we were shown on the trip are from a time period when southern Africa was covered by ice,” Andrews said. “People obviously knew that part of the world had been covered in ice at one time, but no one had ever mentioned anything about how the drumlins formed or that they were even there at all.”

Andrews teamed up with WVU geology senior Andy McGrady to use morphometrics, or measurements of shapes, to determine if the drumlins showed any patterns that would reflect regular behaviors as the ice carved them.

While normal glaciers have sequential patterns of growing and melting, they do not move much, Andrews explained. However, they determined that the drumlins featured large grooves, which showed that the ice had to be moving at a fast pace to carve the grooves.

These grooves demonstrated the first evidence of an ice stream in southern Africa in the late Paleozoic Age, which occurred about 300 million years ago.

“The ice carved big, long grooves in the rock as it moved,” Andrews said. “It wasn’t just that there was ice there, but there was an ice stream. It was an area where the ice was really moving fast.”

McGrady used freely available information from Google Earth and Google Maps to measure their length, width and height.

“This work is very important because not much has been published on these glacial features in Namibia,” said McGrady, a senior geology student from Hamlin. “It’s interesting to think that this was pioneer work in a sense, that this is one of the first papers to cover the characteristics of these features and gives some insight into how they were formed.”

Their findings also confirm that southern Africa was located over the South Pole during this period.

“These features provide yet another tie between southern Africa and south America to show they were once joined,” Andrews said.

The study, “First description of subglacial megalineations from the late Paleozoic ice age in southern Africa” is published in the Public Library of Science’s PLOS ONE journal.

“This is a great example of a fundamental discovery and new insights into the climatic history of our world that remain to be discovered,” said Tim Carr, chair of the Department of Geology and Geography.

Edaphosaurus, ancient sail-backed mammal-like reptile

This 28 January 2019 video says about itself:

Edaphosaurus, meaning “pavement lizard” for dense clusters of teeth) is a genus of extinct edaphosaurid synapsid. It lived in what is now North America and Europe around 300 to 280 million years ago, during the late Carboniferous to early Permian periods.

Edaphosaurus is important as one of the earliest known large plant-eating (herbivorous) amniote tetrapods (four-legged land-living vertebrates). In addition to the large tooth plates in its jaws, the most characteristic feature of Edaphosaurus is a sail on its back which is unique in shape and morphology. Edaphosaurus species measured from 0.5 metres (1.6 ft) to almost 3.5 metres (11.5 ft) in length and weighed over 300 kilograms (660 lb).

Like its more famous relative Dimetrodon, Edaphosaurus had a sail-like fin that was supported by bones of the vertebral column. Edaphosaurus differs from Dimetrodon in having cross-bars on the spines that supported its fin. Edaphosaurus and other members of the Edaphosauridae evolved tall dorsal sails independently of sail-back members of the Sphenacodontidae. Dimetrodon and Secodontosaurus that lived at the same time are an unusual example of parallel evolution.