Sharp size reduction in dinosaurs that changed diet to termites
Dinosaurs were generally huge, but a new study of the unusual alvarezsaurs show that they reduced in size about 100 million years ago when they became specialised ant-eaters.
The new work is led by Zichuan Qin, a PhD student at the University of Bristol and Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. He measured body sizes of dozens of specimens and showed that they ranged in size from 10-70 kg, the size of a large turkey to a small ostrich, for most of their existence and then plummeted rapidly to chicken-sized animals at the same time as they adopted a remarkable new diet: ant-eating.
The alvarezsaurs lived from the Late Jurassic to Late Cretaceous (160 to 70 million years ago) in many parts of the world, including China, Mongolia, and South America. They were slender, two-legged predators for most of their time on Earth, pursuing lizards, early mammals, and baby dinosaurs as their diet.
“Perhaps competition with other dinosaurs intensified through the Cretaceous,” says Prof Michael Benton, one of Zichuan’s supervisors, at Bristol’s School of Earth Sciences. “The Cretaceous was a time of rapidly evolving ecosystems and the biggest change was the gradual takeover by flowering plants. Flowering plants changed the nature of the landscape completely, and yet dinosaurs mostly did not feed on these new plants. But they led to an explosion of new types of insects, including ants and termites.”
This restructuring of ecosystems has been called the Cretaceous Terrestrial Revolution, marking the time when modern-style forests and woodlands emerged, with diverse plants and animals, including insects that specialised to pollinate the new flowers and to feed on their leaves, petals and nectar.
A key problem with many alvarezsaur specimens, especially the chicken-sized ones, was to be sure they were all adults. “Some of the skeletons clearly came from juveniles,” says Dr Qi Zhao, a co-author and an expert on bone histology, “and we could tell this from sections through the bone. These showed the ages of the dinosaurs when they died, depending on the number of growth rings in the bone. We were able to identify that some specimens came from babies and juveniles and so we left them out of the calculations.”
Ant-eating might seem an amazing diet for dinosaurs. “This was suggested years ago when the arms of Mononykus were reported from Mongolia,” says Professor James Clark in Washington, DC, a co-author of this paper, and also one of the first discoverers of tiny alvarezsaurs from Mongolia. “Mononykus was one of the small alvarezsaurs, just about 1 metre long, but probably weighing 4-5 kilograms, a decent-sized Christmas turkey. Its arm was short and stout and it had lost all but one of its fingers which was modified as a short spike. It looked like a punchy little arm, no good for grabbing things, but ideal for punching a hole in the side of a termite mound.”
“Interestingly, alvarezsaur dinosaurs were indeed not small in size or ant eaters at start,” says Professor Jonah Choiniere in South Africa, a co-author of this paper, who was first to report the earliest alvarezsaurs in China. “Their ancestors, like Haplocheirus, are relatively large, close to the size of a small ostrich, and their sharp teeth, flexible forelimbs and big eyes suggest they had a mixed diet.”
Zichuan Qin took all the measurements of body size and mapped these across a dated evolutionary tree of the alvarezsaurs. “My calculations show how body sizes went up and down for the first 90 million years they existed, ranging from turkey to ostrich-sized, and averaging 30-40 kg,” says Zichuan. “Then, 95 million years ago, their body size suddenly dropped to 5 kg, and their claw shapes changed from grabbing and cutting to punching.”
“This is a very strange result, but it seems to be true,” says Professor Xing Xu, a co-supervisor to Zichuan in Beijing. “All other dinosaurs were getting bigger and bigger, but one group of flesh-eaters miniaturized, and this was associated with living in trees and flying. They eventually became birds. We’ve identified a second miniaturization event — but it wasn’t for flight, but to accommodate a completely new diet, switching from flesh to termites.”
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Journal Reference:
- Zichuan Qin, Qi Zhao, Jonah N. Choiniere, James M. Clark, Michael J. Benton, Xing Xu. Growth and miniaturization among alvarezsauroid dinosaurs. Current Biology, 2021; DOI: 10.1016/j.cub.2021.06.013
New beetle species found pristinely preserved in fossilized dropping of dinosaur ancestor
Fossilized feces are common finds at paleontological dig sites and might actually contain hidden treasures. By scanning fossilized dung assigned to a close dinosaur relative from the Triassic period, scientists discovered a 230-million-year-old beetle species, representing a new family of beetles, previously unknown to science. The beetles were preserved in a 3D state with their legs and antennae fully intact. The finding appears June 30 in the journal Current Biology.
The discovery that fossilized droppings, also known as coprolites, can preserve ancient insect species offers a new alternative to amber fossils — fossilized tree resin, which normally yield the best-preserved insect fossils. The oldest insect fossils from amber, however, are approximately 140-million-years old, and thus from relatively recent geological times. With coprolites, researchers can now look even further into the past, allowing them to learn more about insect evolution and food webs of yet unexplored time intervals.
“We didn’t know how insects looked in the Triassic period and now we have the chance,” says Martin Fiká?ek (@fikacek_martin), an entomologist at National Sun Yat-sen University, Taiwan and a co-author on the paper. “Maybe, when many more coprolites are analyzed, we will find that some groups of reptiles produced coprolites that are not really useful, while others have coprolites full of nicely preserved insects that we can study. We simply need to start looking inside coprolites to get at least some idea.”
“I was really amazed to see how well preserved the beetles were, when you modeled them up on the screen, it was like they were looking right at you,” says first author Martin Qvarnström (@M_Qvarnstroem), a paleontologist at Uppsala University, Sweden and a postdoctoral fellow in the lab of Per Ahlberg. “This is facilitated by coprolites’ calcium phosphatic composition. This together with early mineralization by bacteria likely helped to preserve these delicate fossils.”
The research team named the new beetle species Triamyxa coprolithica, which refers to its Triassic age and indicating that it belongs to the suborder Myxophaga — whose modern rep-resentatives are small and live on algae in wet environments — and that it was found in a cop-rolite. Triamyxa likely lived in semiaquatic or humid environments and were likely consumed by Silesaurus opolensis — the probable producer of the coprolite — a beaked dinosaur ancestor about 2 meters long and 15 kilograms that lived in what is now Poland at the same time.
“Although Silesaurus appears to have ingested numerous individuals of Triamyxa coprolithi-ca, the beetle was likely too small to have been the only targeted prey,” says Qvarnström. “Instead, Triamyxa likely shared its habitat with larger beetles, which are represented by disarticulated remains in the coprolites, and other prey, which never ended up in the copro-lites in a recognizable shape. So it seems likely that Silesaurus was omnivorous, and that a part of its diet was comprised of insects.”
The coprolite was scanned using synchrotron microtomography at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The method, which works like a CT scanner in a hospital except with strong x-ray beams, makes it possible to visualize internal structures in fossils in three dimensions with great contrast and resolution,
“So if you find an insect in the coprolite, you can scan it using microCT in the same way as we do with amber insects, and you can see all the tiny details of the insect body as we do in amber,” says Fiká?ek. “In that aspect, our discovery is very promising, it basically tells people: ‘Hey, check more coprolites using microCT, there is a good chance to find insects in it, and if you find it, it can be really nicely preserved.'”
“There are heaps of things you can study based on fossilized droppings but it had been hard to understand what to do with it, hard to recognize what is inside, and hard to draw conclusions from it, but now there are tons of data,” says Qvarnström. “The ultimate goal is to use the coprolite data to reconstruct ancient food webs and see how they changed across time.”
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Journal Reference:
- Martin Qvarnström, Martin Fikáček, Joel Vikberg Wernström, Sigrid Huld, Rolf G. Beutel, Emmanuel Arriaga-Varela, Per E. Ahlberg, Grzegorz Niedźwiedzki. Exceptionally preserved beetles in a Triassic coprolite of putative dinosauriform origin. Current Biology, 2021; DOI: 10.1016/j.cub.2021.05.015
Dinosaurs were in decline before the end
The death of the dinosaurs 66 million years ago was caused by the impact of a huge asteroid on the Earth. However, palaeontologists have continued to debate whether they were already in decline or not before the impact.
In a new study, published today in the journal Nature Communications, an international team of scientists, which includes the University of Bristol, show that they were already in decline for as much as ten million years before the final death blow.
Lead author, Fabien Condamine, a CNRS researcher from the Institut des Sciences de l’Evolution de Montpellier (France), said: “We looked at the six most abundant dinosaur families through the whole of the Cretaceous, spanning from 150 to 66 million years ago, and found that they were all evolving and expanding and clearly being successful.
“Then, 76 million years ago, they show a sudden downturn. Their rates of extinction rose and in some cases the rate of origin of new species dropped off.”
The team used Bayesian modelling techniques to account for several kinds of uncertainties such as incomplete fossil records, uncertainties over age-dating the fossils, and uncertainties about the evolutionary models. The models were each run millions of times to consider all these possible sources of error and to find whether the analyses would converge on an agreed most probable result.
Guillaume Guinot, also of the Institut des Sciences de l’Evolution de Montpellier, who helped run the calculations, added: “In all cases, we found evidence for the decline prior to the bolide impact.
“We also looked at how these dinosaur ecosystems functioned, and it became clear that the plant-eating species tended to disappear first, and this made the latest dinosaur ecosystems unstable and liable to collapse if environmental conditions became damaging.”
Phil Currie, a co-author of the study, from the University of Edmonton (Alberta, Canada), said: “We used over 1,600 carefully checked records of dinosaurs through the Cretaceous.
“I have been collecting dinosaurs in North America, Mongolia, China, and other areas for some time, and I have seen huge improvements in our knowledge of the ages of the dinosaur-bearing rock formations.
“This means that the data are getting better all the time. The decline in dinosaurs in their last ten million years makes sense, and indeed this is the best-sampled part of their fossil record as our study shows.”
Professor Mike Benton from the University of Bristol’s School of Earth Sciences, another co-author, added: “In the analyses, we explored different kinds of possible causes of the dinosaur decline.
“It became clear that there were two main factors, first that overall climates were becoming cooler, and this made life harder for the dinosaurs which likely relied on warm temperatures.
“Then, the loss of herbivores made the ecosystems unstable and prone to extinction cascade. We also found that the longer-lived dinosaur species were more liable to extinction, perhaps reflecting that they could not adapt to the new conditions on Earth.”
Fabien Condamine added: “This was a key moment in the evolution of life. The world had been dominated by dinosaurs for over 160 million years, and as they declined other groups began their rise to dominance, including the mammals.
“The dinosaurs were mostly so huge they probably hardly knew that the furry little mammals were there in the undergrowth. But the mammals began to increase in numbers of species before the dinosaurs had gone, and then after the impact they had their chance to build new kinds of ecosystems which we see today.”
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Journal Reference:
- Fabien L. Condamine, Guillaume Guinot, Michael J. Benton, Philip J. Currie. Dinosaur biodiversity declined well before the asteroid impact, influenced by ecological and environmental pressures. Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-23754-0
Research team discovers Arctic dinosaur nursery
Images of dinosaurs as cold-blooded creatures needing tropical temperatures could be a relic of the past.
University of Alaska Fairbanks and Florida State University scientists have found that nearly all types of Arctic dinosaurs, from small bird-like animals to giant tyrannosaurs, reproduced in the region and likely remained there year-round.
Their findings are detailed in a new paper published in the journal Current Biology.
“It wasn’t long ago that people were pretty shocked to find out that dinosaurs lived up in the Arctic 70 million years ago,” said Pat Druckenmiller, the paper’s lead author and director of the University of Alaska Museum of the North. “We now have unequivocal evidence they were nesting up there as well. This is the first time that anyone has ever demonstrated that dinosaurs could reproduce at these high latitudes.”
The findings counter previous hypotheses that the animals migrated to lower latitudes for the winter and laid their eggs in those warmer regions. It’s also compelling evidence that they were warm-blooded.
For more than a decade, Druckenmiller and Gregory Erickson, a Florida State University professor of biological science, have conducted fieldwork in the Prince Creek Formation in northern Alaska. They have unearthed many dinosaur species, most of them new to science, from the bluffs above the Colville River.
Their latest discoveries are tiny teeth and bones from seven species of perinatal dinosaurs, a term that describes baby dinosaurs that are either just about to hatch or have just hatched.
“One of the biggest mysteries about Arctic dinosaurs was whether they seasonally migrated up to the North or were year-round denizens,” said Erickson, a co-author of the paper. “We unexpectedly found remains of perinates representing almost every kind of dinosaur in the formation. It was like a prehistoric maternity ward.”
Recovering the bones and teeth, some no larger than the head of a pin, requires perseverance and a sharp eye. In the field, the scientists hauled buckets of sediment from the face of the bluffs down to the river’s edge, where they washed the material through smaller and smaller screens to remove large rocks and soil.
Once back at their labs, Druckenmiller, Erickson and co-author Jaelyn Eberle from the University of Colorado, Boulder, screened the material further. Then, teaspoon by teaspoon, the team, which included graduate and undergraduate students, examined the remaining sandy particles under microscopes to find the bones and teeth.
“Recovering these tiny fossils is like panning for gold,” Druckenmiller said. “It requires a great amount of time and effort to sort through tons of sediment grain-by-grain under a microscope. The fossils we found are rare but are scientifically rich in information.”
Next, the scientists worked with Caleb Brown and Don Brinkman from the Royal Tyrrell Museum of Palaeontology in Alberta, Canada, to compare the fossils to those from other sites at lower latitudes. Those comparisons helped them conclude that the bones and teeth were from perinatal dinosaurs.
Once they knew the dinosaurs were nesting in the Arctic, they realized the animals lived their entire lives in the region.
Erickson’s previous research revealed that the incubation period for these types of dinosaurs ranges from three to six months. Because Arctic summers are short, even if the dinosaurs laid their eggs in the spring, their offspring would be too young to migrate in the fall.
Global temperatures were much warmer during the Cretaceous, but the Arctic winters still would have included four months of darkness, freezing temperatures, snow and little fresh vegetation for food.
“As dark and bleak as the winters would have been, the summers would have had 24-hour sunlight, great conditions for a growing dinosaur if it could grow quickly enough before winter set in,” said Brown, a paleontologist at the Royal Tyrrell Museum.
Year-round Arctic residency provides a natural test of the animals’ physiology, Erickson added.
“We solved several long-standing mysteries about the dinosaur reign, but opened up a new can of worms,” he said. “How did they survive Arctic winters?”
“Perhaps the smaller ones hibernated through the winter,” Druckenmiller said. “Perhaps others lived off poor-quality forage, much like today’s moose, until the spring.”
Scientists have found warm-blooded animal fossils in the region, but no snakes, frogs or turtles, which were common at lower latitudes. That suggests the cold-blooded animals were poorly suited for survival in the cold temperatures of the region.
“This study goes to the heart of one of the longest-standing questions among paleontologists: Were dinosaurs warm-blooded?” Druckenmiller said. “We think that endothermy was probably an important part of their survival.”
This research was supported by the National Science Foundation.
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Journal Reference:
- Patrick S. Druckenmiller, Gregory M. Erickson, Donald Brinkman, Caleb M. Brown, Jaelyn J. Eberle. Nesting at extreme polar latitudes by non-avian dinosaurs. Current Biology, 2021; DOI: 10.1016/j.cub.2021.05.041