Researchers used digital modelling and computer simulation to uncover a common trend of jaw strengthening in theropods — expanding the rear jaw portion in all groups, as well as evolving an upturned jaw in carnivores and a downturned jaw in herbivores.

Publishing their findings today in Current Biology, scientistsrevealed that biomechanical analysis showed these form changes made jaws mechanically more stable when biting — minimising the chance of bone fracture.

The international team, led by scientists at the University of Birmingham, created digital models of more than 40 lower jaws from five different theropod dinosaur groups, including typical carnivores like Tyrannosaurus and Velociraptor, and lesser-known herbivores like ornithomimosaurs, therizinosaurs and oviraptorosaurs.

Fion Waisum Ma, PhD researcher at the University of Birmingham, who led the study, said: “Although theropod dinosaurs are always depicted as fearsome predators in popular culture, they are in fact very diverse in terms of diets. It is interesting to observe the jaws becoming structurally stronger over time, in both carnivores and herbivores. This gives them the capacity to exploit a wider range of food items.

“Theropod dinosaurs underwent extreme dietary changes during their evolutionary history of 165 million years. They started off as carnivores, later on evolved into more specialised carnivores, omnivores and herbivores. Studying how their feeding mechanics changed is key to understanding the dietary transitions in other vertebrate animals too.”

For example, in carnivores like tyrannosauroids, an early form like Guanlong had a relatively slender and straight jaw. But later forms such as Tarbosaurus and Tyrannosaurus evolved deeper jaws with the front portion bending upward, which increase jaw strength.

Having a strengthened jaw is especially important to herbivorous theropods, as their jaws experience considerable stress from repetitive plant cropping. Herbivores like Erlikosaurus and Caudipteryx have extremely downward-bending jaws that could help dissipate such stress.

Dr Stephan Lautenschlager, Senior Lecturer at the University of Birmingham and senior author of the study, said: “It is fascinating to see how theropod dinosaurs had evolved different strategies to increase jaw stability depending on their diet. This was achieved through bone remodelling — a mechanism where bone is deposited in regions of the jaw that experience high stresses during feeding.”

The researchers studied the feeding mechanics of tyrannosaurids through growth and observed that the deeper and more upturned jaws of adult theropods, such as Tyrannosaurus and Tarbosaurus, are structurally stronger compared to those of their juvenile forms.

Dr Lautenschlager further explained: “The similarity between jaw strengthening through growth and through time suggests that developmental patterns in juvenile dinosaurs ultimately affected the evolution of the whole group. This likely facilitated the jaw evolution of theropod dinosaurs and their overall success for over 150 million years.”

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

Using climate data from 1979 to 2019, the researchers found that the number of heatwaves occurring simultaneously in the mid- to high-latitudes of the Northern Hemisphere was seven times greater in the 2010s than in the 1980s. On average, there were concurrent heatwaves on 143 days each year of the 2010s — almost every day of the 153 days of the warm months of May through September.

The concurrent heat events also grew hotter and larger: their intensity rose by 17% and their geographic extent increased 46%.

“More than one heatwave occurring at the same time often has worse societal impacts than a single event,” said Cassandra Rogers, a WSU post-doctoral researcher and lead author of the study in Journal of Climate. “If certain regions are dependent on one another, for instance for agriculture or trade, and they’re both undergoing stresses at the same time, they may not be able to respond to both events.”

Heatwaves can cause disasters from crop failures to wildfires. Concurrent heatwaves can multiply those threats, the authors pointed out, exhausting the ability of countries to provide mutual aid in crises as was seen during the multiple wildfires in the U.S., Canada and Australia associated with the 2019 and 2020 heatwaves. A previous study also found that concurrent heatwaves caused about a 4% drop in global crop production.

This study defined large heatwaves as high temperature events lasting three days or more and covering at least 1.6 million square kilometers (about 620,000 square miles), which is roughly equivalent to the size of Mongolia or Iran.

The researchers analyzed ERA5 data produced by the European Center for Medium-Range Weather Forecasts, which blends vast amounts of observational data from weather stations on land, water buoys and aircraft as well as data from satellites with weather forecasting models. ERA5 provides globally complete estimates of hourly data for various climate variables from 1979, when satellite data became available, which is why the study focused on this time period.

Using these observational data, the researchers found that the primary driver of the heatwaves was the overall rise in global mean temperature due to climate change. The world has warmed 1 degree Celsius (about 1.8 degrees Fahrenheit) over the last century with the vast majority of the rise, two-thirds, occurring since 1975. The researchers also found that increasing occurrence of two hemisphere-wide circulation patterns made particular areas more vulnerable to concurrent heatwaves, including eastern North America, eastern and northern Europe, East Asia and eastern Siberia.

The study adds more evidence for the need to curb greenhouse gas emissions and mitigate climate change, the researchers said, and the continued rise in temperature means the world should prepare for more concurrent heatwaves.

“As a society, we are not currently adapted to the types of climate events we’re experiencing right now,” said co-author Deepti Singh, WSU associate professor in the School of the Environment.

“It’s important to understand how we can reduce our vulnerability and adapt our systems to be more resilient to these kind of heat events that have cascading societal impacts.”

In addition to Rogers and Singh, authors on the study include Kai Kornhuber of Columbia University, Sarah Perkins-Kirkpatrick of the University of New South Wales in Australia and Paul Loikith of Portland State University. This research was supported by the National Science Foundation and the Australian Research Council.

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Materials provided by Washington State University. Original written by Sara Zaske. Note: Content may be edited for style and length.