Fearsome tyrannosaurs were social animals

The fearsome tyrannosaur dinosaurs that ruled the northern hemisphere during the Late Cretaceous period (66-100 million years ago) may not have been solitary predators as popularly envisioned, but social carnivores similar to wolves, according to a new study.

The finding, based on research at a unique fossil bone site inside Utah’s Grand Staircase-Escalante National Monument containing the remains of several dinosaurs of the same species, was made by a team of scientists including Celina Suarez, University of Arkansas associate professor of geosciences.

“This supports our hypothesis that these tyrannosaurs died in this site and were all fossilized together; they all died together, and this information is key to our interpretation that the animals were likely gregarious in their behavior,” Suarez said.

The research team also include scientists from the U.S. Bureau of Land Management, Denver Museum of Nature and Science, Colby College of Maine and James Cook University in Australia. The study examines a unique fossil bone site inside Grand Staircase-Escalante National Monument called the “Rainbows and Unicorns Quarry” that they say exceeded the expectations raised even from the site’s lofty nickname.

“Localities [like Rainbows and Unicorns Quarry] that produce insights into the possible behavior of extinct animals are especially rare, and difficult to interpret,” said tyrannosaur expert Philip Currie in a press release from the BLM. “Traditional excavation techniques, supplemented by the analysis of rare earth elements, stable isotopes and charcoal concentrations convincingly show a synchronous death event at the Rainbows site of four or five tyrannosaurids. Undoubtedly, this group died together, which adds to a growing body of evidence that tyrannosaurids were capable of interacting as gregarious packs.”

In 2014, BLM paleontologist Alan Titus discovered the Rainbows and Unicorns Quarry site in Grand Staircase-Escalante National Monument and led the subsequent research on the site, which is the first tyrannosaur mass death site found in the southern United States. Researchers ran a battery of tests and analyses on the vestiges of the original site, now preserved as small rock fragments and fossils in their final resting place, and sandbar deposits from the ancient river.

“We realized right away this site could potentially be used to test the social tyrannosaur idea. Unfortunately, the site’s ancient history is complicated,” Titus said. “With bones appearing to have been exhumed and reburied by the action of a river, the original context within which they lay has been destroyed. However, all has not been lost.” As the details of the site’s history emerged, the research team concluded that the tyrannosaurs died together during a seasonal flooding event that washed their carcasses into a lake, where they sat, largely undisturbed until the river later churned its way through the bone bed.

“We used a truly multidisciplinary approach (physical and chemical evidence) to piece the history of the site together, with the end-result being that the tyrannosaurs died together during a seasonal flooding event,” said Suarez.

Using analysis of stable carbon and oxygen isotopes and concentrations of rare earth elements within the bones and rock, Suarez and her then-doctoral student, Daigo Yamamura, were able to provide a chemical fingerprint of the site. Based on the geochemical work, they were able to conclusively determine that the remains from the site all fossilized in the same environment and were not the result of an attritional assemblage of fossils washed in from a variety of areas.

“None of the physical evidence conclusively suggested that these organisms came to be fossilized together, so we turned to geochemistry to see if that could help us. The similarity of rare earth element patterns is highly suggestive that these organisms died and were fossilized together,” said Suarez.

Excavation of the quarry site has been ongoing since its discovery in 2014 and due to the size of the site and volume of bones found there the excavation will probably continue into the foreseeable future. In addition to tyrannosaurs, the site has also yielded seven species of turtles, multiple fish and ray species, two other kinds of dinosaurs, and a nearly complete skeleton of a juvenile (12-foot-long) Deinosuchus alligator, although they do not appear to have all died together like the tyrannosaurs.

“The new Utah site adds to the growing body of evidence showing that tyrannosaurs were complex, large predators capable of social behaviors common in many of their living relatives, the birds,” said project contributor, Joe Sertich, curator of dinosaurs at the Denver Museum of Nature & Science. “This discovery should be the tipping point for reconsidering how these top carnivores behaved and hunted across the northern hemisphere during the Cretaceous.”

Future research plans for the Rainbows and Unicorns Quarry fossils include additional trace element and isotopic analysis of the tyrannosaur bones, which paleontologists hope will determine with a greater degree of certainty the mystery of Teratophoneus’ social behavior.

In stark contrast to the social interaction between humans and among many species of animals, paleontologists have long debated whether tyrannosaurs lived and hunted alone or in groups.

Based on findings at a site in Alberta, Canada, with over 12 individuals, the idea that tyrannosaurs were social with complex hunting strategies was first formulated by Philip Currie over 20 years ago. This idea has been widely debated, with many scientists doubting the giant killing machines had the brainpower to organize into anything more complex than what is observed in modern crocodiles. Because the Canadian site appeared to be an isolated case, skeptics claimed it represented unusual circumstances that did not reflect normal tyrannosaur behavior. Discovery of a second tyrannosaur mass death site in Montana again raised the possibility of social tyrannosaurs, but this site was still not widely accepted by the scientific community as evidence for social behavior. The researcher’s findings at the Unicorns and Rainbows Quarry provides even more compelling evidence that tyrannosaurs may have habitually lived in groups.

Story Source:

Materials provided by University of Arkansas. Original written by Bob Whitby. Note: Content may be edited for style and length.

Journal Reference:

  1. Alan L. Titus, Katja Knoll, Joseph J.W. Sertich, Daigo Yamamura, Celina A. Suarez, Ian J. Glasspool, Jonathan E. Ginouves, Abigail K. Lukacic, Eric M. Roberts. Geology and taphonomy of a unique tyrannosaurid bonebed from the upper Campanian Kaiparowits Formation of southern Utah: implications for tyrannosaurid gregariousnessPeerJ, 2021; 9: e11013 DOI: 10.7717/peerj.11013

Tiny cat-sized stegosaur leaves its mark

A single footprint left by a cat-sized dinosaur around 100 million years ago has been discovered in China by an international team of palaeontologists.

University of Queensland researcher Dr Anthony Romilio was part of the team that investigated the track, originally found by Associate Professor Lida Xing from the China University of Geosciences (Beijing).

“This footprint was made by a herbivorous, armoured dinosaur known broadly as a stegosaur — the family of dinosaurs that includes the famed stegosaurus,” Dr Romilio said.

“Like the stegosaurus, this little dinosaur probably had spikes on its tail and bony plates along its back as an adult.

“With a footprint of less than six centimetres, this is the smallest stegosaur footprint known in the world.

“It’s in strong contrast with other stegosaur prints found at the Chinese track site which measured up to 30 centimetres, and prints found in places like Broome in Western Australia where they can be up to 80 centimetres.”

The tiny footprint has similar characteristics of other stegosaur footprints with three short, wide, round toe impressions.

However researchers found the print wasn’t elongated like larger counterpart prints discovered at the track sites, which suggests the young stegosaur had a different behaviour.

“Stegosaurs typically walked with their heels on the ground, much like humans do, but on all fours which creates long footprints,” Dr Romilio said.

“The tiny track shows that this dinosaur had been moving with its heel lifted off the ground, much like a bird or cat does today.

“We’ve only previously seen shortened tracks like this when dinosaurs walked on two legs.”

Associate Professor Xing said that it was plausible young stegosaurs were toe-walkers.

“This could be possible as this is the ancestral condition and a posture of most dinosaurs, but the stegosaur could also have transitioned to heel-walking as it got older,” Dr Xing said.

“A complete set of tracks of these tiny footprints would provide us with the answer to this question, but unfortunately we only have a single footprint.”

Finding the tiny tracks on crowded track sites will be challenging for the researchers.

“The footprints made by tiny armoured dinosaur are much rarer than those formed by other groups of dinosaurs,” Associate Professor Xing said.

“Now that our study has identified nine different dinosaur track sites from this locality, we will look even closer to see if we can find more of these tiny tracks.”

Story Source:

Materials provided by University of QueenslandNote: Content may be edited for style and length.

How many T. rexes were there? Billions

Analysis of what’s known about the dinosaur leads to conclusion there were 2.5 billion over time

How many Tyrannosaurus rexes roamed North America during the Cretaceous period?

That’s a question Charles Marshall pestered his paleontologist colleagues with for years until he finally teamed up with his students to find an answer.

What the team found, to be published this week in the journal Science, is that about 20,000 adult T. rexes probably lived at any one time, give or take a factor of 10, which is in the ballpark of what most of his colleagues guessed.

What few paleontologists had fully grasped, he said, including himself, is that this means that some 2.5 billion lived and died over the approximately 2 1/2 million years the dinosaur walked the earth.

Until now, no one has been able to compute population numbers for long-extinct animals, and George Gaylord Simpson, one of the most influential paleontologists of the last century, felt that it couldn’t be done.

Marshall, director of the University of California Museum of Paleontology, the Philip Sandford Boone Chair in Paleontology and a UC Berkeley professor of integrative biology and of earth and planetary science, was also surprised that such a calculation was possible.

“The project just started off as a lark, in a way,” he said. “When I hold a fossil in my hand, I can’t help wondering at the improbability that this very beast was alive millions of years ago, and here I am holding part of its skeleton — it seems so improbable. The question just kept popping into my head, ‘Just how improbable is it? Is it one in a thousand, one in a million, one in a billion?’ And then I began to realize that maybe we can actually estimate how many were alive, and thus, that I could answer that question.”

Marshall is quick to point out that the uncertainties in the estimates are large. While the population of T. rexes was most likely 20,000 adults at any give time, the 95% confidence range — the population range within which there’s a 95% chance that the real number lies — is from 1,300 to 328,000 individuals. Thus, the total number of individuals that existed over the lifetime of the species could have been anywhere from 140 million to 42 billion.

“As Simpson observed, it is very hard to make quantitative estimates with the fossil record,” he said. “In our study, we focused in developing robust constraints on the variables we needed to make our calculations, rather than on focusing on making best estimates, per se.”

He and his team then used Monte Carlo computer simulation to determine how the uncertainties in the data translated into uncertainties in the results.

The greatest uncertainty in these numbers, Marshall said, centers around questions about the exact nature of the dinosaur’s ecology, including how warm-blooded T. rex was. The study relies on data published by John Damuth of UC Santa Barbara that relates body mass to population density for living animals, a relationship known as Damuth’s Law. While the relationship is strong, he said, ecological differences result in large variations in population densities for animals with the same physiology and ecological niche. For example, jaguars and hyenas are about the same size, but hyenas are found in their habitat at a density 50 times greater than the density of jaguars in their habitat.

“Our calculations depend on this relationship for living animals between their body mass and their population density, but the uncertainty in the relationship spans about two orders of magnitude,” Marshall said. “Surprisingly, then, the uncertainty in our estimates is dominated by this ecological variability and not from the uncertainty in the paleontological data we used.”

As part of the calculations, Marshall chose to treat T. rex as a predator with energy requirements halfway between those of a lion and a Komodo dragon, the largest lizard on Earth.

The issue of T. rex‘s place in the ecosystem led Marshall and his team to ignore juvenile T. rexes, which are underrepresented in the fossil record and may, in fact, have lived apart from adults and pursued different prey. As T. rex crossed into maturity, its jaws became stronger by an order of magnitude, enabling it to crush bone. This suggests that juveniles and adults ate different prey and were almost like different predator species.

This possibility is supported by a recent study, led by evolutionary biologist Felicia Smith of the University of New Mexico, which hypothesized that the absence of medium-size predators alongside the massive predatory T. rex during the late Cretaceous was because juvenile T. rex filled that ecological niche.

What the fossils tell us

The UC Berkeley scientists mined the scientific literature and the expertise of colleagues for data they used to estimate that the likely age at sexual maturity of a T. rex was 15.5 years; its maximum lifespan was probably into its late 20s; and its average body mass as an adult — its so-called ecological body mass, — was about 5,200 kilograms, or 5.2 tons. They also used data on how quickly T. rexes grew over their life span: They had a growth spurt around sexual maturity and could grow to weigh about 7,000 kilograms, or 7 tons.

From these estimates, they also calculated that each generation lasted about 19 years, and that the average population density was about one dinosaur for every 100 square kilometers.

Then, estimating that the total geographic range of T. rex was about 2.3 million square kilometers, and that the species survived for roughly 2 1/2 million years, they calculated a standing population size of 20,000. Over a total of about 127,000 generations that the species lived, that translates to about 2.5 billion individuals overall.

With such a large number of post-juvenile dinosaurs over the history of the species, not to mention the juveniles that were presumably more numerous, where did all those bones go? What proportion of these individuals have been discovered by paleontologists? To date, fewer than 100 T. rex individuals have been found, many represented by a single fossilized bone.

“There are about 32 relatively well-preserved, post-juvenile T. rexes in public museums today,” he said. “Of all the post-juvenile adults that ever lived, this means we have about one in 80 million of them.”

“If we restrict our analysis of the fossil recovery rate to where T. rex fossils are most common, a portion of the famous Hell Creek Formation in Montana, we estimate we have recovered about one in 16,000 of the T. rexes that lived in that region over that time interval that the rocks were deposited,” he added. “We were surprised by this number; this fossil record has a much higher representation of the living than I first guessed. It could be as good as one in a 1,000, if hardly any lived there, or it could be as low as one in a quarter million, given the uncertainties in the estimated population densities of the beast.”

Marshall expects his colleagues will quibble with many, if not most, of the numbers, but he believes that his calculational framework for estimating extinct populations will stand and be useful for estimating populations of other fossilized creatures.

“In some ways, this has been a paleontological exercise in how much we can know, and how we go about knowing it,” he said. “It’s surprising how much we actually know about these dinosaurs and, from that, how much more we can compute. Our knowledge of T. rex has expanded so greatly in the past few decades thanks to more fossils, more ways of analyzing them and better ways of integrating information over the multiple fossils known.”

The framework, which the researchers have made available as computer code, also lays the foundation for estimating how many species paleontologists might have missed when excavating for fossils, he said.

“With these numbers, we can start to estimate how many short-lived, geographically specialized species we might be missing in the fossil record,” he said. “This may be a way of beginning to quantify what we don’t know.”

Story Source:

Materials provided by University of California – Berkeley. Original written by Robert Sanders. Note: Content may be edited for style and length.

Journal Reference:

  1. Charles R. Marshall, Daniel V. Latorre, Connor J. Wilson, Tanner M. Frank, Katherine M. Magoulick, Joshua B. Zimmt, Ashley W. Poust. Absolute abundance and preservation rate of Tyrannosaurus rexScience, 2021 DOI: 10.1126/science.abc8300

450-million-year-old sea creatures had a leg up on breathing

First evidence of trilobites’ bizarre breathing organs uncovered

A new study has found the first evidence of sophisticated breathing organs in 450-million-year-old sea creatures. Contrary to previous thought, trilobites were leg breathers, with structures resembling gills hanging off their thighs.

Trilobites were a group of marine animals with half-moon-like heads that resembled horseshoe crabs, and they were wildly successful in terms of evolution. Though they are now extinct, they survived for more than 250 million years — longer than the dinosaurs.

Thanks to new technologies and an extremely rare set of fossils, scientists from UC Riverside can now show that trilobites breathed oxygen and explain how they did so. Published in the journal Science Advances, these findings help piece together the puzzle of early animal evolution.

“Up until now, scientists have compared the upper branch of the trilobite leg to the non-respiratory upper branch in crustaceans, but our paper shows, for the first time, that the upper branch functioned as a gill,” said Jin-Bo Hou, a UCR paleontology doctoral student who led the research.

Among the oldest animals on earth, this work helps situate trilobites on the evolutionary tree more securely in between older arthropods, a large group of animals with exoskeletons, and crustaceans.

The research was possible, in part, because of unusually preserved fossil specimens. There are more than 22,000 trilobite species that have been discovered, but the soft parts of the animals are visible in only about two dozen.

“These were preserved in pyrite — fool’s gold — but it’s more important than gold to us, because it’s key to understanding these ancient structures,” said UCR geology professor and paper co-author Nigel Hughes.

A CT scanner was able to read the differences in density between the pyrite and the surrounding rock and helped create three-dimensional models of these rarely seen gill structures.

“It allowed us to see the fossil without having to do a lot of drilling and grinding away at the rock covering the specimen,” said paleontologist Melanie Hopkins, a research team member at the American Museum of Natural History.

“This way we could get a view that would even be hard to see under a microscope — really small trilobite anatomical structures on the order of 10 to 30 microns wide,” she said. For comparison, a human hair is roughly 100 microns thick.

Though these specimens were first described in the late 1800s and others have used CT scans to examine them, this is the first study to use the technology to examine this part of the animal.

The researchers could see how blood would have filtered through chambers in these delicate structures, picking up oxygen along its way as it moved. They appear much the same as gills in modern marine arthropods like crabs and lobsters.

Comparing the specimens in pyrite to another trilobite species gave the team additional detail about how the filaments were arranged relative to one another, and to the legs.

Most trilobites scavenged the ocean floor, using spikes on their lower legs to catch and grind prey. Above those parts, on the upper branch of the limbs, were these additional structures that some believed were meant to help with swimming or digging.

“In the past, there was some debate about the purpose of these structures because the upper leg isn’t a great location for breathing apparatus,” Hopkins said. “You’d think it would be easy for those filaments to get clogged with sediment where they are. It’s an open question why they evolved the structure in that place on their bodies.”

The Hughes lab uses fossils to answer questions about how life developed in response to changes in Earth’s atmosphere. Roughly 540 million years ago, there was an explosive diversification in the variety and complexity of animals living in the oceans.

“We’ve known theoretically this change must have been related to a rise in oxygen, since these animals require its presence. But we have had very little ability to measure that,” Hughes said. “Which makes findings like these all the more exciting.”

Story Source:

Materials provided by University of California – Riverside. Original written by Jules Bernstein. Note: Content may be edited for style and length.

Journal Reference:

  1. Jin-bo Hou, Nigel C. Hughes, Melanie J. Hopkins. The trilobite upper limb branch is a well-developed gillScience Advances, 2021; 7 (14): eabe7377 DOI: 10.1126/sciadv.abe7377

Ancient meteoritic impact over Antarctica 430,000 years ago

A research team of international space scientists, led by Dr Matthias van Ginneken from the University of Kent’s School of Physical Sciences, has found new evidence of a low-altitude meteoritic touchdown event reaching the Antarctic ice sheet 430,000 years ago.

Extra-terrestrial particles (condensation spherules) recovered on the summit of Walnumfjellet (WN) within the Sør Rondane Mountains, Queen Maud Land, East Antarctica, indicate an unusual touchdown event where a jet of melted and vaporised meteoritic material resulting from the atmospheric entry of an asteroid at least 100 m in size reached the surface at high velocity.

This type of explosion caused by a single-asteroid impact is described as intermediate, as it is larger than an airburst, but smaller than an impact cratering event.

The chondritic bulk major, trace element chemistry and high nickel content of the debris demonstrate the extra-terrestrial nature of the recovered particles. Their unique oxygen isotopic signatures indicate that their interacted with oxygen derived from the Antarctic ice sheet during their formation in the impact plume.

The findings indicate an impact much more hazardous that the Tunguska and Chelyabinsk events over Russia in 1908 and 2013, respectively.

This research, published by Science Advances, guides an important discovery for the geological record where evidence of such events in scarce. This is primarily due to the difficult in identifying and characterising impact particles.

The study highlights the importance of reassessing the threat of medium-sized asteroids, as it likely that similar touchdown events will produce similar particles. Such an event would be entirely destructive over a large area, corresponding to the area of interaction between the hot jet and the ground.

Dr van Ginneken said: ‘To complete Earth’s asteroid impact record, we recommend that future studies should focus on the identification of similar events on different targets, such as rocky or shallow oceanic basements, as the Antarctic ice sheet only covers 9% of Earth’s land surface. Our research may also prove useful for the identification of these events in deep sea sediment cores and, if plume expansion reaches landmasses, the sedimentary record.

‘While touchdown events may not threaten human activity if occurring over Antarctica, if it was to take place above a densely populated area, it would result in millions of casualties and severe damages over distances of up to hundreds of kilometres.’

Story Source:

Materials provided by University of Kent. Original written by Olivia Miller. Note: Content may be edited for style and length.

Journal Reference:

  1. M. Van Ginneken, S. Goderis, N. Artemieva, V. Debaille, S. Decrée, R. P. Harvey, K. A. Huwig, L. Hecht, S. Yang, F. E. D. Kaufmann, B. Soens, M. Humayun, F. Van Maldeghem, M. J. Genge, P. Claeys. A large meteoritic event over Antarctica ca. 430 ka ago inferred from chondritic spherules from the Sør Rondane MountainsScience Advances, 2021; 7 (14): eabc1008 DOI: 10.1126/sciadv.abc1008