Study sheds light on the evolution of the earliest dinosaurs

The classic dinosaur family tree has two subdivisions of early dinosaurs at its base: the Ornithischians, or bird-hipped dinosaurs, which include the later Triceratops and Stegosaurus; and the Saurischians, or lizard-hipped dinosaurs, such as Brontosaurus and Tyrannosaurus.

In 2017, however, this classical view of dinosaur evolution was thrown into question with evidence that perhaps the lizard-hipped dinosaurs evolved first — a finding that dramatically rearranged the first major branches of the dinosaur family tree.

Now an MIT geochronologist, along with paleontologists from Argentina and Brazil, has found evidence to support the classical view of dinosaur evolution. The team’s findings are published today in the journal Scientific Reports.

The team reanalyzed fossils of Pisanosaurus, a small bipedal dinosaur that is thought to be the earliest preserved Ornithiscian in the fossil record. The researchers determined that the bird-hipped herbivore dates back to 229 million years ago, which is also around the time that the earliest lizard-hipped Saurischians are thought to have appeared.advertisement

The new timing suggests that Ornithiscians and Saurischians first appeared and diverged from a common ancestor at roughly the same time, giving support to the classical view of dinosaur evolution.

The researchers also dated rocks from the Ischigualasto Formation, a layered sedimentary rock unit in Argentina that is known for having preserved an abundance of fossils of the very earliest dinosaurs. Based on these fossils and others across South America, scientists believe that dinosaurs first appeared in the southern continent, which at the time was fused together with the supercontinent of Pangaea. The early dinosaurs are then thought to have diverged and fanned out across the world.

However, in the new study, the researchers determined that the period over which the Ischigualasto Formation was deposited overlaps with the timing of another important geological deposit in North America, known as the Chinle Formation.

The middle layers of the Chinle Formation in the southwestern U.S. contain fossils of various fauna, including dinosaurs that appear to be more evolved than the earliest dinosaurs. The bottom layers of this formation, however, lack animal fossil evidence of any kind, let alone early dinosaurs. This suggests that conditions within this geological window prevented the preservation of any form of life, including early dinosaurs, if they walked this particular region of the world.

“If the Chinle and Ischigualasto formations overlap in time, then early dinosaurs may not have first evolved in South America, but may have also been roaming North America around the same time,” says Jahandar Ramezani, a research scientist in MIT’s Department of Earth, Atmospheric, and Planetary Sciences, who co-authored the study. “Those northern cousins just may not have been preserved.”

The other researchers on the study are first author Julia Desojo from the National University of La Plata Museum, and a team of paleontologists from institutions across Argentina and Brazil.

“Following footsteps”

The earliest dinosaur fossils found in the Ischigualasto Formation are concentrated within what is now a protected provincial park known as “Valley of the Moon” in the San Juan Province. The geological formation also extends beyond the park, albeit with fewer fossils of early dinosaurs. Ramezani and his colleagues instead looked to study one of the accessible outcrops of the same rocks, outside of the park.

They focused on Hoyada del Cerro Las Lajas, a less-studied outcrop of the Ischigualasto Formation, in La Rioja Province, which another team of paleontologists explored in the 1960s.

“Our group got our hands on some of the field notes and excavated fossils from those early paleontologists, and thought we should follow their footsteps to see what we could learn,” Desojo says.

Over four expeditions between 2013 to 2019, the team collected fossils and rocks from various layers of the Las Lajas outcrop, including more than 100 new fossil specimens, though none of these fossils were of dinosaurs. Nevertheless, they analyzed the fossils and found they were comparable, in both species and relative age, to nondinosaur fossils found in the park region of the same Ischigualasto Formation. They also found out that the Ischigualasto Formation in Las Lajas was significantly thicker and much more complete than the outcrops in the park. This gave them confidence that the geological layers in both locations were deposited during the same critical time interval.

Ramezani then analyzed samples of volcanic ash collected from several layers of the Las Lajas outcrops. Volcanic ash contains zircon, a mineral that he separated from the rest of the sediment, and measured for isotopes of uranium and lead, the ratios of which yield the mineral’s age.

With this high-precision technique, Ramezani dated samples from the top and bottom of the outcrop, and found that the sedimentary layers, and any fossils preserved within them, were deposited between 230 million and 221 million years ago. Since the team determined that the layered rocks in Las Lajas and the park match in both species and relative timing, they could also now determine the exact age of the park’s more fossil-rich outcrops.

Moreover, this window overlaps significantly with the time interval over which sediments were deposited, thousands of kilometers northward, in the Chinle Formation.

“For many years, people thought Chinle and Ischigualasto formations didn’t overlap, and based on that assumption, they developed a model of diachronous evolution, meaning the earliest dinosaurs appeared in South America first, then spread out to other parts of the world including North America,” Ramezani says. “We’ve now studied both formations extensively, and shown that diachronous evolution isn’t really based on sound geology.”

A family tree, preserved

Decades before Ramezani and his colleagues set out for Las Lajas, other paleontologists had explored the region and unearthed numerous fossils, including remains of Pisanosaurus mertii, a small, light-framed, ground-dwelling herbivore. The fossils are now preserved in an Argentinian museum, and scientists have gone back and forth on whether it is a true dinosaur belonging to the Ornithiscian group, or a ” basal dinosauromorph” — a kind of pre-dinosaur, with features that are almost, but not quite fully, dinosaurian.

“The dinosaurs we see in the Jurassic and Cretaceous are highly evolved, and ones we can nicely identify, but in the late Triassic, they all looked very much alike, so it’s very hard to distinguish them from each other, and from basal dinosauromorphs,” Ramezani explains.

His collaborator Max Langer from the University of São Paulo in Brazil painstakingly reanalyzed the museum-preserved fossil of Pisanosaurus, and concluded, based on certain key anatomical features, that it is indeed a dinosaur — and what’s more, that it is the earliest preserved Ornithiscian specimen. Based on Ramezani’s dating of the outcrop and the interpretation of Pisanosaurus, the researchers concluded that the earliest bird-hipped dinosaurs appeared around 229 million years ago — around the same time as their lizard-hipped counterparts.

“We can now say the earliest Ornithiscians first showed up in the fossil record roughly around the same time as the Saurischians, so we shouldn’t throw away the conventional family tree,” Ramezani says. “There are all these debates about where dinosaurs appeared, how they diversified, what the family tree looked like. A lot of those questions are tied to geochronology, so we need really good, robust age constraints to help answer these questions.”

This research was mainly funded by the National Council for Scientific and Technical Research (Argentina) and the São Paulo State Research Support Foundation (Brazil). Geochronologic research at the MIT Isotope Lab has been supported in part by the U.S. National Science Foundation.

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What happens in Vegas, may come from the Arctic?

A cave deep in the wilderness of central Nevada is a repository of evidence supporting the urgent need for the Southwestern U.S. to adopt targets aimed at reducing greenhouse gas emissions, a new UNLV study finds.

UNLV climate scientist Matthew Lachniet and colleagues have compiled a detailed, 13,000-year climate history from stalagmite specimens in Leviathan Cave, located in the southern Great Basin, which provides clues for the mitigation of climate change today.

These ancient climate records show that Nevada was even hotter and drier in the past than it is today, and that one 4,000-year period in particular may represent a true, “worst-case” scenario picture for the Southwest and the Colorado River Basin — and the millions of people who rely on its water supply.

At that time, the long-term hot and dry climate of the region was linked to warm Arctic seas and a lack of sea ice, as well as warming in the western tropical Pacific Ocean, the cave record shows.

This parallels today and the near future, as the release of human carbon emissions into the atmosphere will warm the Arctic and possibly the western tropical Pacific, and is expected to result in long-term arid conditions for Nevada and the broader Colorado River Basin.

If the arid conditions become permanent, then the water supply in the Colorado River Basin is expected to decrease, which researchers say would imperil critical water resources for millions of people who live in the Southwest U.S.

“The last few decades have seen increasingly severe ‘hot droughts’ in the Colorado River Basin, when high temperatures coincide with less rainfall, and which have startled climate scientists and water policy managers,” Lachniet said. “But these dry intervals don’t usually last more than a few decades. In contrast, our new data show that Nevada climate can experience an extended interval of aridity for thousands of years, not just a few decades.”

The recent Southwestern U.S. drought that began in 2001, which has resulted in historic low reservoir levels in Lake Mead, is one indicator of the gravity of the problem. The Colorado River and Rio Grande basins are critical human support systems as their headwaters in the Rocky Mountains supply snow-fed water for myriad economic uses and support 56 million residents throughout the region.

“‘Business as usual’ scenarios for anthropogenic warming carry the risk of tipping the Southwest into an extended state of aridification,” researchers wrote.

The paper, published in the journal Paleoceanography and Paleoclimatology, provides a clearer and more comprehensive picture of the Southwest’s climate history compared to tree ring records which extend only 2,000 years into the past.

Stalagmites — like those located in Leviathan Cave — are common cave formations that act as ancient rain gauges to record historic climate data. Stalagmites grow upward at rates of inches every few hundred years as mineral-rich waters seep through the ground above and drop from the tips of stalactites on cave ceilings.

These deposits more accurately represent a long-term shift toward a more arid climate as they hold data that extends deeper into the past.

A former analysis of one tree ring record, for example, pointed to a 10-year drought in the Medieval era as being a “worst case” predictor of a future, comparable drought, as compared to the more persistent and sustained 4,000-year period of aridity presented in Lachniet’s new study.

Regionally, paleoclimate records from other sources like lakes, landforms, pollen, and others, also support the conclusion of warmth and aridity during the same 4,000-year period.

Researchers also found that the Leviathan Cave region, where the stalagmite specimen was collected, is representative of climate conditions in most of the Mojave Desert and the southern Great Basin, and that the data has implications for the broader desert region.

Lachniet and colleagues say that their study can be a resource for policymakers today in adopting measures to reduce greenhouse gas emissions which will in turn “minimize oceanic and Arctic warming.”

“There already is evidence that droughts in the Southwest are partly caused by humans because of the higher temperatures and more evaporation in surface waters like Lake Mead,” Lachniet said. “The new fossil-fuel climate might end up making these droughts permanent.”

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Materials provided by University of Nevada, Las Vegas. Original written by Natalie Bruzda. Note: Content may be edited for style and length.

Growth rate of common trilobites

If you’ve ever held a trilobite fossil, seen one in a classroom, or walked by one in a store, chances are it was Elrathia kingii, one of the most common and well-recognized trilobites, and collected by the hundreds of thousands in western Utah. But despite the popularity of this species, scientists had not determined how it grew — from hatchling to juvenile to adult — until now. New work from the American Museum of Natural History published today in the journal Papers in Palaeontology describes the development and growth rate of Elrathia kingii — only the second such dataset to be compiled for a trilobite — allowing for the first comparison among trilobite species.

“There’s quite a big size range among trilobites. Some never got bigger than about a centimeter, while the largest on record is 72 centimeters (28 inches),” said Melanie Hopkins, an associate curator in the Museum’s Division of Paleontology and the study’s author. “Growth-rate studies like this one can help us tackle some of the big-picture questions: How did some trilobites get so big? What was the environmental context for that? And how did body size evolve over the evolutionary history of the clade?”

Trilobites are a group of extinct marine arthropods — distantly related to the horseshoe crab — that lived for almost 300 million years. They were incredibly diverse, with more than 20,000 described species. Their fossilized exoskeletons are preserved in sites all over the world, from the United States to China. Like insects, they molted throughout their lifetimes, leaving clues to how they changed during development. But to calculate the species’ growth rate, scientists need fossils representing all stages of the animal’s life — and lots of them.advertisement

“There are tons of specimens of Elrathia kingii out there but most of them are adults, and data from exactly where they were collected is inconsistent,” Hopkins said. “I needed material that I could collect from as small a section as possible that included a lot of juveniles.”

So in May 2018, Hopkins spent five days in Utah with a crew consisting of Museum staff and volunteers at a new fossil site said to preserve bucketloads of Elrathia kingii. By the end of the trip, they had collected about 500 specimens — many of them juveniles, which can be as small as half a millimeter long — from a section of outcrop just 1.5 meters (about 5 feet) long.

Hopkins estimated the growth rate and compared it to previously published data on a different trilobite, Aulacopleura konincki — the first time two trilobite species have been compared in this way. The two species look very similar and Hopkins found that they also grow in similar ways: for example, the growth of the trunk — the area immediately below the trilobite’s head made up of segments that increase with age — was controlled by a growth gradient, with those that were younger and closer to the back of the body undergoing faster growth. But while Elrathia kingii was smaller in early development and went through fewer molts before adulthood, it had faster growth rates, ultimately reaching sizes on par with Aulacopleura konincki, the largest of which are about 4 centimeters long.

In future studies, Hopkins is planning to add growth-rate data on different, more diverse-looking trilobite species to her models.

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Fossil jawbone from Alaska is a rare case of a juvenile Arctic dromaeosaurid dinosaur

A small piece of fossil jawbone from Alaska represents a rare example of juvenile dromaeosaurid dinosaur remains from the Arctic, according to a study published July 8, 2020 in the open-access journal PLOS ONE by Alfio Alessandro Chiarenza of the Imperial College London, UK, and co-authors Anthony R. Fiorillo, Ronald S. Tykoski, Paul J. McCarthy, Peter P. Flaig, and Dori L. Contreras.

Dromaeosaurids are a group of predatory dinosaurs closely related to birds, whose members include well-known species such as Deinonychus and Velociraptor. These dinosaurs lived all over the world, but their bones are often small and delicate and rarely preserve well in the fossil record, complicating efforts to understand the paths they took as they dispersed between continents.

The Prince Creek Formation of northern Alaska preserves the largest collection of polar dinosaur fossils in the world, dating to about 70 million years ago, but the only dromaeosaurid remains found so far have been isolated teeth. The jaw fossil described in this study is a mere 14mm long and preserves only the tip of the lower jaw, but it is the first known non-dental dromaeosaurid fossil from the Arctic. Statistical analysis indicates this bone belongs to a close relative of the North American Saurornitholestes.

North American dromaeosaurids are thought to trace their origins to Asia, and Alaska would have been a key region for the dispersal of their ancestors. This new fossil is a tantalizing clue toward understanding what kinds of dromaeosaurs inhabited this crucial region. Furthermore, the early developmental stage of the bone suggests this individual was still young and was likely born nearby; in contrast to previous suggestions that this part of Alaska was exclusively a migratory pathway for many dinosaurs, this is strong evidence that some dinosaurs were nesting here. The authors suggest that future findings may allow a more complete understanding of these mysterious Arctic dromaeosaurids.

Chiarenza summarizes: “There are places where dinosaur fossils are so common that a scrap of bone, in most cases, cannot really add anything scientifically informative anymore: this is not the case with this Alaskan specimen. Even with such an incomplete jaw fragment, our team was not only able to work out the evolutionary relationships of this dinosaur, but also to picture something more on the biology of these animals, ultimately gaining more information on this Ancient Arctic ecosystem.” Fiorillo adds: “Years ago when dinosaurs were first found in the far north, the idea challenged what we think we know about dinosaurs. For some time afterwards, there was a great debate as to whether or not those Arctic dinosaurs migrated or lived in the north year round. All of those arguments were somewhat speculative in nature. This study of a predatory dinosaur jaw from a baby provides the first physical proof that at least some dinosaurs not only lived in the far north, but they thrived there. One might even say, our study shows that the ancient north was a great place to raise a family and now we have to figure out why.”

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Different tracks, same dinosaurs: Researchers dig deeper into dinosaur movements

When picturing dinosaur tracks, most people imagine a perfectly preserved mold of a foot on firm layer of earth. But what if that dinosaur was running through mud, sinking several inches — or even up to their ankles — into the ground as it moved?

Using sophisticated X-ray-based technology, a team of Brown University researchers tracked the movements of guineafowl to investigate how their feet move below ground through various substrates and what those findings could mean for understanding fossil records left behind by dinosaurs.

They found that regardless of the variability in substrates, or the guineafowl moving at different speeds, sinking at different depths or engaging in different behaviors, the birds’ overall foot movement remained the same: The toes spread as they stepped onto the substrate surface, remained spread as the foot sank, collapsed and drew back as they were lifted from the substrate, and exited the substrate in front of the point of entry, creating a looping pattern as they walked.

And part of what that means is that fossilized dinosaur tracks that look distinct from each other, and appear to be from different species, might instead come from the same dinosaurs.

“This is the first study that’s really shown how the bird foot is moving below ground, showing the patterns of this subsurface foot motion and allowing us to break down the patterns that we’re seeing in a living animal that has feet similar to those of a dinosaur,” said Morgan Turner, a Ph.D. candidate at Brown in ecology and evolutionary biology and lead author of the research. “Below ground, or even above ground, they’re responding to these soft substrates in a very similar way, which has potentially important implications for our ability to study the movement of these animals that we can’t observe directly anymore.”

The findings were published on Wednesday, July 1, in the Royal Society journal Biology Letters.

To make the observations, Turner and her colleagues, Professor of Biology and Medical Science Stephen Gatesy and Peter Falkingham, now at Liverpool John Moores University, used a 3D-imaging technology developed at Brown called X-ray Reconstruction of Moving Morphology (XROMM). The technology combines CT scans of a skeleton with high-speed X-ray video, aided by tiny implanted metal markers, to create visualizations of how bones and muscles move inside humans and animals. In the study, the team used XROMM to watch guineafowl move through substrates of different hydration and compactness, analyzing how their feet moved underground and the tracks left behind.

Sand, typically a dense combination of quartz and silica, does not lend itself well to X-ray imaging, so the team used poppy seeds to emulate sand. Muds were made using small glass bubbles, adding various amount of clay and water across 107 trials to achieve different consistencies and realistic tracks.

They added metal markers underneath the claws of the guineafowl to allow for tracking in 3D space. It’s these claw tips that the researchers think are least disturbed by mud flow and other variables that can impact and distort the form of the track.

Despite the variation, the researchers observed a consistent looping pattern.

“The loops by themselves I don’t think are that interesting,” Gatesy said. “People are like, ‘That’s nice. Birds do this underground. So what?’ It was only when [Turner] went back into it and said, ‘What if we slice those motion trails at different depths as if they were footprints?’ Then we made the nice connection to the fossils.”

By “slicing” through the 3D images of the movement patterns at different depths, the researchers found similarities between the guineafowl tracks and fossilized dinosaur tracks.

“We don’t know what these dinosaurs were doing, we don’t know what they were walking through exactly, we don’t know how big they were or how deep they were sinking, but we can make this really strong connection between how they were moving and some level of context for where this track is being sampled from within that movement,” Turner said.

By recognizing the movement patterns, as well as the entry and exit point of the foot through various substrates, the team says they’re able to gain a better understanding of what a dinosaur track could look like.

“You end up generating this big diversity of track shapes from a very simple foot shape because you’re sampling at different depths and it’s moving in complicated ways,” Gatesy said. “Do we really have 40 different kinds of creatures, each with a differently shaped foot, or are we looking at some more complicated interaction that leaves behind these remnants that are partly anatomical and partly motion and partly depth?”

To further their research, the team spent time at the Beneski Museum of Natural History at Amherst College in Massachusetts, which is home to an expansive collection of penetrative tracks discovered in the 1800s by geologist Edward Hitchcock.

Hitchcock originally believed that his collection housed fossil tracks from over 100 distinct animals. Because of the team’s work with XROMM, Gatesy now thinks it’s possible that at least half of those tracks are actually from the same dinosaurs, just moving their feet in slightly different ways or sampled at slightly different depths.

“Going to museum together and being able to pick out these features and say, ‘We think this track is low in the loop and we think this one is high,’ that was the biggest moment of insight for me,” Turner said.

Turner says she hopes their research can lead to a greater interest in penetrative tracks, even if they seem a little less pretty or polished than the tracks people are used to seeing in museums.

“They have so much information in them,” Turner said, “and I hope that this gives people a lens, a new way to view these footprints and appreciate the movement preserved within in them.”

This work was supported by the US National Science Foundation (EAR 1452119 to SMG and PLF; IOS 0925077 to SMG), a Marie Curie International Outgoing Fellowship within the 7th European Framework Programme to PLF, and the Bushnell Research and Education Fund to MLT.

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Tiny Japanese dinosaur eggs help unscramble Cretaceous ecosystem

When most of us think of dinosaurs, we envision large, lumbering beasts, but these giants shared their ecosystems with much smaller dinosaurs, the smaller skeletons of which were generally less likely to be preserved. The fossilized egg shells of these small dinosaurs can shed light on this lost ecological diversity.

Led by the University of Tsukuba, researchers scoured an exceptional fossil egg site first discovered in 2015 in Hyogo Prefecture, southwestern Japan, and reported their findings in a new study published in Cretaceous Research.

The Kamitaki Egg Quarry, found in a red-brown mudstone layer of the Ohyamashimo Formation, deposited in an Early Cretaceous (about 110 million years old) river flood plain, was carefully and intensively excavated in the winter of 2019, and yielded over 1300 egg fossils. Most were isolated fragments, but there were a few partial and almost complete eggs.

According to lead author Professor Kohei Tanaka, “our taphonomic analysis indicated that the nest we found was in situ, not transported and redeposited, because most of the eggshell fragments were positioned concave-up, not concave-down like we see when egg shells are transported.”

Most of these fossil eggs belong to a new egg genus and species, called Himeoolithus murakamii, and are exceptionally small, with an estimated mass of 9.9 grams — about the size of a modern quail egg. However, biological classification analysis implies that the eggs belonged not to early birds, but to their cousins, the non-avian theropod dinosaurs (the group that includes well-known carnivores like Tyrannosaurus and Velociraptor). That puts Himeoolithus murakamii among the smallest non-avian theropod eggs reported to date. These tiny eggs were notably elongated in shape — unusual for similarly small eggs among Cretaceous birds, but typical among larger non-avian theropod eggs.

In addition to the abundant Himeoolithus murakamii egg shells, five more ootaxa (distinct types of egg fossils) were recognized in the Kamitaki locality. All of these ootaxa belonged to small non-avian theropods.

As Professor Tanaka explains, “the high diversity of these small theropod eggs makes this one of the most diverse Early Cretaceous egg localities known. Small theropod skeletal fossils are quite scarce in this area. Therefore, these fossil eggs provide a useful window into the hidden ecological diversity of dinosaurs in the Early Cretaceous of southwestern Japan, as well as into the nesting behavior of small non-avian theropods.”

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

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.

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First egg from Antarctica is big and might belong to an extinct sea lizard

In 2011, Chilean scientists discovered a mysterious fossil in Antarctica that looked like a deflated football. For nearly a decade, the specimen sat unlabeled and unstudied in the collections of Chile’s National Museum of Natural History, with scientists identifying it only by its sci-fi movie-inspired nickname — “The Thing.”

An analysis led by researchers at The University of Texas at Austin has found that the fossil is a giant, soft-shell egg from about 66 million years ago. Measuring in at more than 11 by 7 inches, the egg is the largest soft-shell egg ever discovered and the second-largest egg of any known animal.

The specimen is the first fossil egg found in Antarctica and pushes the limits of how big scientists thought soft-shell eggs could grow. Aside from its astounding size, the fossil is significant because scientists think it was laid by an extinct, giant marine reptile, such as a mosasaur — a discovery that challenges the prevailing thought that such creatures did not lay eggs.

“It is from an animal the size of a large dinosaur, but it is completely unlike a dinosaur egg,” said lead author Lucas Legendre, a postdoctoral researcher at UT Austin’s Jackson School of Geosciences. “It is most similar to the eggs of lizards and snakes, but it is from a truly giant relative of these animals.”

A study describing the fossil egg was published in Nature on June 17.

Co-author David Rubilar-Rogers of Chile’s National Museum of Natural History was one of the scientists who discovered the fossil in 2011. He showed it to every geologist who came to the museum, hoping somebody had an idea, but he didn’t find anyone until Julia Clarke, a professor in the Jackson School’s Department of Geological Sciences, visited in 2018.

“I showed it to her and, after a few minutes, Julia told me it could be a deflated egg!” Rubilar-Rogers said.

Using a suite of microscopes to study samples, Legendre found several layers of membrane that confirmed that the fossil was indeed an egg. The structure is very similar to transparent, quick-hatching eggs laid by some snakes and lizards today, he said. However, because the fossil egg is hatched and contains no skeleton, Legendre had to use other means to zero in on the type of reptile that laid it.

He compiled a data set to compare the body size of 259 living reptiles to the size of their eggs, and he found that the reptile that laid the egg would have been more than 20 feet long from the tip of its snout to the end of its body, not counting a tail. In both size and living reptile relations, an ancient marine reptile fits the bill.

Adding to that evidence, the rock formation where the egg was discovered also hosts skeletons from baby mosasaurs and plesiosaurs, along with adult specimens.

“Many authors have hypothesized that this was sort of a nursery site with shallow protected water, a cove environment where the young ones would have had a quiet setting to grow up,” Legendre said.

The paper does not discuss how the ancient reptile might have laid the eggs. But the researchers have two competing ideas.

One involves the egg hatching in the open water, which is how some species of sea snakes give birth. The other involves the reptile depositing the eggs on a beach and hatchlings scuttling into the ocean like baby sea turtles. The researchers say that this approach would depend on some fancy maneuvering by the mother because giant marine reptiles were too heavy to support their body weight on land. Laying the eggs would require the reptile to wriggle its tail on shore while staying mostly submerged, and supported, by water.

“We can’t exclude the idea that they shoved their tail end up on shore because nothing like this has ever been discovered,” Clarke said.

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Tracking Australia’s gigantic carnivorous dinosaurs

North America had the T. rex, South America had the Giganotosaurus and Africa the Spinosaurus — now evidence shows Australia had gigantic predatory dinosaurs.

The discovery came in University of Queensland research, led by palaeontologist Dr Anthony Romilio, which analysed southern Queensland dinosaur footprint fossils dated to the latter part of the Jurassic Period, between 165 and 151 million-year-ago.

“I’ve always wondered, where were Australia’s big carnivorous dinosaurs?” Dr Romilio said.

“But I think we’ve found them, right here in Queensland.

“The specimens of these gigantic dinosaurs were not fossilised bones, which are the sorts of things that are typically housed at museums.

“Rather, we looked at footprints, which — in Australia — are much more abundant.

“These tracks were made by dinosaurs walking through the swamp-forests that once occupied much of the landscape of what is now southern Queensland.”

Most of the tracks used in the study belong to theropods, the same group of dinosaurs that includes Australovenator, Velociraptor, and their modern-day descendants, birds.

Dr Romilio said these were clearly not bird tracks.

“Most of these footprints are around 50 to 60 centimetres in length, with some of the really huge tracks measuring nearly 80 centimetres,” he said.

“We estimate these tracks were made by large-bodied carnivorous dinosaurs, some of which were up to three metres high at the hips and probably around 10 metres long.

“To put that into perspective, T. rex got to about 3.25 metres at the hips and attained lengths of 12 to 13 metres long, but it didn’t appear until 90 million years after our Queensland giants.

“The Queensland tracks were probably made by giant carnosaurs — the group that includes the Allosaurus.

“At the time, these were probably some of the largest predatory dinosaurs on the planet.”

Despite the study providing important new insights into Australia’s natural heritage, the fossils are not a recent discovery.

“The tracks have been known for more than half a century,” Dr Romilio said.

“They were discovered in the ceilings of underground coal mines from Rosewood near Ipswich, and Oakey just north of Toowoomba, back in the 1950s and 1960s.

“Most hadn’t been scientifically described, and were left for decades in museum drawers waiting to be re-discovered.

“Finding these fossils has been our way of tracking down the creatures from Australia’s Jurassic Park.”

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Ancient crocodiles walked on two legs like dinosaurs

An international research team has been stunned to discover that some species of ancient crocodiles walked on their two hind legs like dinosaurs and measured over three metres in length.

University of Queensland palaeontologist Dr Anthony Romilio said the researchers first thought the similar-shaped fossilised footprints were from another ancient animal known as the pterosaurs.

“At one site, the footprints were initially thought to be made by a giant bipedal pterosaur walking on the mudflat, we now understand that these were bipedal crocodile prints,” Dr Romilio said.

“The footprints measure around 24 centimetres, suggesting the track-makers had legs about the same height as human adult legs.

“These were long animals that we estimate were over three metres in length.

“And while footprints were everywhere on the site, there were no handprints.”

The research team, led by Professor Kyung Soo Kim from Chinju National University of Education, soon found clues as to why there were no handprints.

“Typical crocodiles walk in a squat stance and create trackways that are wide,” Professor Kim said.

“Oddly, our trackways are very narrow looking — more like a crocodile balancing on a tight-rope.

“When combined with the lack of any tail-drag marks, it became clear that these creatures were moving bipedally.

“They were moving in the same way as many dinosaurs, but the footprints were not made by dinosaurs.

“Dinosaurs and their bird descendants walk on their toes.

“Crocodiles walk on the flat of their feet leaving clear heel impressions, like humans do.”

The footprints dated between 110-120 million years ago and were discovered after analysing animal track sites in what is now known as South Korea.

Researchers initially questioned the absence of hand impressions from the trackways, given that today’s typical crocodiles are ‘four-legged’ or quadrupedal.

“Fossil crocodile tracks are quite rare in Asia, so finding an abundance of nearly one hundred footprints was extraordinary,” Dr Romilio said.

“As an animal walks, the hind feet have the potential of stepping into the impression made by the hand and ‘over-printing’ it, but we find no evidence of this at these Korean sites.

“It isn’t due to poor preservation either, because these fossils are spectacular, they even have the fine details of the toe-pads and scales on their soles preserved.”

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Journal Reference:

  1. Kyung Soo Kim, Martin G. Lockley, Jong Deock Lim, Seul Mi Bae, Anthony Romilio. Trackway evidence for large bipedal crocodylomorphs from the Cretaceous of KoreaScientific Reports, 2020; 10 (1) DOI: 10.1038/s41598-020-66008-7