Sleeping through tough times
US scientists have discovered fossil evidence of a hibernation-like state in an animal that lived in Antarctica during the Early Triassic, some 250 million years ago.
It is the oldest such find, they say, and suggests that torpor – a general term for hibernation and similar states in which animals temporarily lower their metabolic rate to get through a tough season – arose in vertebrates even before mammals and dinosaurs evolved.
The creature, a member of the genus Lystrosaurus, was a distant relative of mammals.
It spread across Earth’s then-single continent, Pangea, and fossils have been found in India, China, Russia and Africa, as well as Antarctica, which at the time experienced extended periods without sunlight each winter.
“Animals that live at or near the poles have always had to cope with the more extreme environments present there,” says lead author Megan Whitney. “These preliminary findings indicate that entering into a hibernation-like state is not a relatively new type of adaptation. It is an ancient one.”
Whitney carried out the work while at the University of Washington, with then colleague Christian Sidor. Their findings are published in the journal Communications Biology.
Lystrosaurus had no teeth but bore a pair of tusks in the upper jaw, Witney says, which made their study possible. As in elephants, the tusks grew continuously, so cross-sections of fossilised tusks provide information about metabolism, growth and stress or strain.
The researchers compared tusks from six Antarctic Lystrosaurus and four from South Africa and noticed similar growth patterns but one key difference: closely-spaced, thick rings that likely indicate periods of less deposition due to prolonged stress.
“The closest analogue we can find to the ‘stress marks’ that we observed… are stress marks in teeth associated with hibernation in certain modern animals,” Whitney says.
The face of a dinosaur embryo
The first dinosaur embryos were found in a nesting ground of titanosaurian at Auca Mahuevo in Argentinian Patagonia. Two decades later, an international research team has described the first near-intact embryonic skull.
The findings, published in the journal Current Biology, suggest that sauropod dinosaurs, a group characterised by the long neck and tails and small heads familiar in the Brontosaurus, may have had specialised facial features as hatchlings that changed as they grew into adults.
“The most striking feature is head appearance, which implies that hatchlings of giant dinosaurs may differ in where and how they lived in their earliest stages of life,” says lead author Martin Kundrat of Pavol Jozef Šafárik University, Slovak Republic.
“But because it differs in facial anatomy and size from the sauropod embryos of Auca Mahuevo, we cannot rule out that it may represent a new titanosaurian dinosaur.”
Kundrat’s team used an imaging technology called synchrotron microtomography to study the inner structure of bones, teeth and soft tissues of the embryonic dinosaur and found hidden details, including tiny teeth preserved deeply in tiny jaw sockets.
The specimen also is from Patagonia, although its precise origin isn’t known. It was illegally exported and came to researchers’ attention only later. It’s now housed with other embryos from Auca Mahuevo at Argentina’s Museo Municipal Carmen Funes.
Thinking about dinosaur sex
Speaking of dinosaurs, how do you tell boys from girls? The answer may be to use stats.
In a new paper in the Biological Journal of the Linnean Society, scientists led by the Field Museum, US, explain how a different kind of analysis can estimate the degree of sexual variation in a dataset of fossils.
“It’s a whole new way of looking at fossils and judging the likelihood that the traits we see correlate with sex,” says lead author Evan Saitta. “This paper is part of a larger revolution of sorts about how to use statistics in science but applied in the context of palaeontology.”
Palaeontologists have previously used significance testing, where you collect all your data points then calculate the probability that those results could have happened by pure chance rather than an actual cause. This sometimes works for big, clean datasets, Saitta says, but “with a lot of these dinosaur tests, our data is pretty bad”.
He and his colleagues turned to effect size statistics, which attempts to estimate the degree of sex differences and calculate the uncertainty in that estimate. This approach takes natural variations into account without viewing dimorphism as black-or-white. Many sexual dimorphisms can be subtle.
“We showed that if you adopt this paradigm shift in statistics, where you attempt to estimate the magnitude of an effect and then put error bars around that, you can often produce a fairly accurate estimate of sexual variation even when the sexes of the individuals are unknown,” says Saitta. The work continues.
Old fossil adds to old debate
US and Canadian researchers have uncovered fossils of a new species of marine animal, Gyaltsenglossus senis, that could help solve a longstanding debate.
Discovered at a Burgess Shale site in the Canadian Rockies, they are over 500 million years old and just two centimetres in length, but the remarkably preserved soft tissues reveal incredibly detailed anatomical structures.
These details include the oval-shaped proboscis of acorn worms (aka enteropneusta) and a basket of feeding tentacles similar to those of pterobranchs. And that’s where things get interesting, because this provides evidence connecting these two major groups of hemichordates.
“Acorn worms and pterobranchs look so different from each other that understanding the origins of their evolutionary relationship has been a major historical question in zoology,” says Karma Nanglu from the Smithsonian National Museum of Natural History, lead author of a paper in the journal Current Biology.
“Answering this question has been made much harder by the extreme lack of fossils of these soft-bodied hemichordates. Throughout the half-billion-year-long history of hemichordates you can count on one hand the number of exceptional preserved fossil species.”
An ancient animal with an intermediary anatomy between acorn worms and pterobranchs had been hypothesised before but “this new animal is the clearest view of what the ancestral hemichordate may have looked like,” says co-author Christopher Cameron, from the University of Montreal.
Hemichordates belong to a major division of animal life called Deuterostomia, which includes chordates like fish and mammals. When looking at Gyaltsenglossus, we’re actually looking at a very, very distant relative of our own branch of vertebrate and human evolution, Nanglu says.
Read science facts, not fiction...
There’s never been a more important time to explain the facts, cherish evidence-based knowledge and to showcase the latest scientific, technological and engineering breakthroughs. Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science. Financial contributions, however big or small, help us provide access to trusted science information at a time when the world needs it most. Please support us by making a donation or purchasing a subscription today.