0 Comments
For The Conversation article, click here.
Tyrannosaurs are perhaps the most famous dinosaur family of them all, and their growth from dog-sized hatchlings to gigantic, multi-tonne killers is an intensely studied area within dinosaur palaeontology. But disagreements remain about the way these animals aged and how fast they could move: did the juveniles look like miniature versions of their parents, and possess similar running abilities? Or were the adults comparably more bulky and less mobile? The research, published today in the Journal of Vertebrate Paleontology, analysed a collection of fossilised tyrannosaur footprints to learn more about the way these animals aged and how they moved. UNE PhD student and study leader, Nathan Enriquez — in international collaboration with the Philip J. Currie Dinosaur Museum, University of Alberta, Royal Ontario Museum, University of Bologna and the Grande Prairie Regional College — believes the findings contribute a new line of evidence to previous findings based on bone anatomy and computer models of muscle masses. “The results suggest that as some tyrannosaurs grew older and heavier, their feet also became comparably more bulky,” Mr Enriquez said. “Fully grown tyrannosaurs were believed to be more robust than younger individuals based on their relatively shorter hind limbs and more massive skulls, but nobody had explored this growth pattern using fossil footprints, which are unique in that they can provide a snapshot of the feet as they appeared in life, with outlines of the soft, fleshy parts of the foot that are rarely preserved as fossils. "If relative bulk increased as tyrannosaurs grew, and their ability to run decreased, we would expect to see differences in the shape of footprints made by older and younger animals." Footprints can be ambiguous and hard to interpret correctly — the shape of a footprint may be influenced by the type of ground surface that is stepped on and the motions of the animal making the footprints. In addition, the exact identity of the animal may not always be clear. These challenges have previously limited the use of fossil footprints in understanding dinosaur growth. The answer lay in the Grande Prairie region of Northern Alberta, Canada, where the research team worked with well-preserved samples of footprints of different sizes that are suggested to belong to the same type of animal. Image: A tyrannosaur footprint (left) that was discovered near Grande Prairie in Alberta, Canada, and graphic demonstration (right) of the relative increase in heel size as some tyrannosaurs grew. Image courtesy of Nathan Enriquez. Tyrannosaur black body silhouette credited to Matt Dempsey. “We explored a remote dinosaur footprint site where we discovered a new set of large carnivorous dinosaur footprints within very similar rocks to those which have produced tyrannosaur tracks in the past,” Mr Enriquez said. “Based on the relatively close proximity between these discoveries and their nearly equivalent ages — about 72.5 million years old — we suggest they may indeed belong to the same species. “We were also careful to assess the quality of preservation in each footprint, and only considered specimens which were likely to reflect the shape of the actual feet that produced them.” Once the team had a suitable sample, they analysed the outlines of each specimen using a method called geometric morphometrics. This process removes the effect of overall size differences between each footprint and shows what the most important differences in track shape are. “The greatest difference in shape was found to be the relative width and surface area of the heel impression, which significantly increased in size between smaller and larger footprints,” Mr Enriquez said. "The smaller tracks are comparably slender, while the biggest tyrannosaur tracks are relatively broader and had much larger heel areas. This makes sense for an animal that is becoming larger and needs to support its rapidly increasing body weight. It also suggests the relative speed of these animals decreased with age. “Increasingly bulky feet in the adults aligns with previous suggestions that juvenile tyrannosaurs would have been faster and more agile for their body size in comparison to their parents, and means that we can add footprints as another line of evidence in the debate over tyrannosaur growth. “Lastly, it demonstrates the usefulness of footprints for investigating a potentially wider range of ideas about the lives of extinct species than has been considered previously.” Publication link: Journal of Vertebrate Paleontology Image: Diversity of sauropods from the Griman Creek Formation. Image provided by Henry Sharpe (No reuse). For The Conversation article, click here.
Dinosaur teeth uncovered at Lightning Ridge, New South Wales, have offered fresh insight into how these giants co-existed and foraged. Lead researcher and PhD candidate at the University of New England Timothy Frauenfelder said the teeth reflect the high diversity of three sauropod species that once lived in the area. Sauropod dinosaurs, like Brontosaurus and Brachiosaurus, were the largest animals to have ever walked the earth; weighing up to 90,000kg and 40m long. Although their fossils are common in central Queensland, there has been limited evidence of their existence and lifestyle from NSW. Lightning Ridge has yielded a rich bounty in dinosaur fossils over the years and is unique in that all of the fossils found there are completely formed in opal. “While this makes the fossils beautiful to look at, it can often hinder the discovery and preservation of the fossils,” Mr Frauenfelder said. “Teeth are one of the smallest bones in a sauropod and there is an abundance of them at Lightning Ridge. Although small in comparison to other sauropod fossils, which can be over one metre long, teeth can be incredibly useful in assessing ecology and diversity,” Mr Frauenfelder said. “Unlike us, sauropod dinosaurs don’t have different types of teeth such as molars or incisors, and differing tooth shapes can give us an idea about how many species were living in a particular area. “Based on this, we can identify potentially three different species of sauropods that co-existed at Lightning Ridge.” The team also conducted a microwear analysis to view feeding features preserved on a tooth’s wear facet. “As sauropods eat, they produce large facets that preserve varying degrees of features such as pits and scratches. The frequencies of these features, enable us to determine how high an animal was feeding in the canopy, or how hard the food was. Comparing features between teeth, allows us to interpret how these giant dinosaurs co-existed.” Mr Frauenfelder was able to determine that at least two of the species fed at different levels within the canopy: one species fed at ground levels - less than one metre above ground - while the other was feeding mid-canopy, or one to 10 metres above ground. Mr Frauenfelder acknowledges support and access to specimens provided by the Australian Opal Centre and the Australian Museum during the research The study was published in the Journal Lethaia. Full Reference: Frauenfelder, T. G., Campione, N. E., Smith, E. T., & Bell, P. R. 2020. Diversity and palaeoecology of Australia's southern‐most sauropods, Griman Creek Formation (Cenomanian), New South Wales, Australia. Lethaia, doi.org/10.1111/let.12407. Image: The largest and the smallest: dinosaurs reached an amazing range in size through the Mesozoic Era. Image courtesy of Vitor Silva. For The Conversation article, click here.
How do you weigh a long-extinct dinosaur? A couple of ways, as it turns out, neither of which involve actual weighing — but according to a new study, different approaches still yield strikingly similar results. New research published today in the prestigious journal Biological Reviews involved a review of dinosaur body mass estimation techniques carried out over more than a century. The findings should give us some confidence that we are building an accurate picture of these prehistoric animals, says study leader Dr Nicolás Campione — particularly our knowledge of the more massive dinosaurs that have no correlates in the modern world. "Body size, in particular body mass, determines almost at all aspects of an animal’s life, including their diet, reproduction, and locomotion," said Dr Campione, a member of the University of New England’s Palaeoscience Research Centre. "If we know that we have a good estimate of a dinosaur's body mass, then we have a firm foundation from which to study and understand their life retrospectively." Estimating the mass of a dinosaur like the emblematic Tyrannosaurus rex is no small feat — it is a creature that took its last breath some 66 million years ago and, for the most part, only its bones remain today. It is a challenge that has taxed the ingenuity of palaeobiologists for more than a century. Scientific estimates of the mass of the biggest land predator of all time have differed substantially, ranging from about three tonnes to over 18 tonnes. The research team led by Dr Campione compiled and reviewed an extensive database of dinosaur body mass estimates reaching back to 1905, to assess whether different approaches for calculating dinosaur mass were clarifying or complicating the science. Although a range of different methods to estimating body mass have been tried over the years, they all come down to two fundamental approaches. Scientists have either measured and scaled bones in living animals, such as the circumference of the arm (humerus) and leg (femur) bones, and compared them to dinosaurs; or they have caluculated the volume of three-dimensional reconstructions that approximate what the animal may have looked like in real life. Debate over which method is ‘better’ has raged in the literature. The researchers found that once scaling and reconstruction methods are compared en masse, most estimates agree. Apparent differences are the exception, not the rule. "In fact, the two approaches are more complementary than antagonistic," Dr Campione said. The bone scaling method, which relies on relationships obtained directly from living animals of known body mass, provides a measure of accuracy, but often of low precision; whereas reconstructions that consider the whole skeleton provide precision, but of unknown accuracy. This is because reconstructions depend on our own subjective ideas about what extinct animals looked like, which have changed appreciably over time. “There will always be uncertainty around our understanding of long-extinct animals, and their weight is always going to be a source of it,” said Dr David Evans, Temerty Chair of Vertebrate Palaeontology at the Royal Ontario Museum in Toronto, senior author on the new paper. “Our new study suggests we are getting better at weighing dinosaurs, and it paves the way for more realistic dinosaur body mass estimation in the future.” The researchers recommend that future work seeking to estimate the sizes of Mesozoic dinosaurs, and other extinct animals, need to better-integrate the scaling and reconstruction approaches to reap their benefits. Drs Campione and Evans suggest that an adult T. rex would have weighed approximately seven tonnes — an estimate that is consistent across reconstruction and limb bone scaling approaches alike. But the research emphasizes the inaccuracy of such single values and the importance of incorporating uncertainty in mass estimates, not least because dinosaurs, like humans, did not come in one neat package. Such uncertainties suggest an average minimum weight of five tonnes and a maximum average weight of 10 tonnes for the ‘king’ of dinosaurs. "It is only through the combined use of these methods and through understanding their limits and uncertainties that we can begin to reveal the lives of these, and other, long-extinct animals," Dr Campione said. Full reference: Campione, N. E. and Evans, D. C. 2020. The accuracy and precision of body mass estimation in non-avian dinosaurs. Biological Reviews. doi: 10.1111/brv.12638 |
From time to time, we will post news about published articles and the lab's media presence.
Archives
May 2021
Categories |