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Big skulls and slow gaits: paleontology in 2021

Yes, you probably could have outrun a Tyrannosaurus rex.

Is it really that time already? Another end-of-the-year paleontology article, and I have to be honest, I feel like I missed a lot.

Sure, I caught some of the big stories, like the two new spinosaurids from the U.K. Indeed, 2021 ended with a really amazing description of an oviraptorid egg with a preserved embryo, although one of the lead authors, Lida Xing, has also been lead of papers on Burmese amber specimens, including the since-retracted study describing Oculudentavis. I wrote a bit on this crisis in last year’s summary, so there’s a bit of irony in the timing.

But, despite 2021 flying by faster than a Quetzalcoatlus, there was some really cool work in paleontology, so let’s take a look.

Big skulls and slow gaits: paleontology in 2021
A life recreation of Cymbospondylus youngorum, by Stephanie Abramowicz.

A whale of a reptile

Ichthyosaurs are a famous group of extinct marine reptiles. Unlike dinosaurs — which are still present in our modern ecologies as birds — or mosasaurs, the animals made famous by Jurassic World which were evolutionarily nestled with lizards and snakes, the ichthyosaurs have no close relationship to modern-day animals. Ichthyosaurs are a stunning example of convergent evolution, bearing a striking resemblance to dolphins (mammals) and sharks (fish). And while we’ve known that these animals could attain great sizes, a new specimen described in 2021 reveals new aspects about the speed at which these animals evolved into giants.

A new species of the ichthyosaur genus Cymbospondylus was described based on a specimen with a 2-meter-long skull. This animal, named Cymbospondylus youngorum, was estimated to reach a length of 17 meters (that’s about 55 feet). But what makes this stunning is that this ichthyosaur attained that relatively large body size very early in the group’s appearance. Cymbospondylus lived approximately 246 million years ago, only a few million years after it’s believed that ichthyosaurs first evolved. When compared to animals like whales, which took tens of millions of years to reach their large body size, this discovery highlights just how quickly evolution can create a diverse range of phenotypes.

Gimli’s favorite dinosaur

Ankylosaurs are a famous group of dinosaurs known primarily for their armored bodies and massive tail clubs. Evolutionary cousins of the spike-tailed stegosaurs, ankylosaurs have traditionally been split into two groups: ankylosaurids, which had tail clubs, and nodosaurids, that lacked them. But a new discovery from Chile showed it wasn’t just clubs these animals were developing.

The new dinosaur, named Stegouros elengassen, was a small, early ankylosaur, that had an assortment of sideways projecting osteoderms over the the lower half of its tail, giving it the appearance of a battle-axe. Analyses performed by the team of scientists led by Sergio Soto-Acuña show that Stegouros’ closest known relatives were the Australian Kunburrasaurus and Antarctica’s aptly-named Antarctopelta, forming an early group of southern ankylosaurs that had branched off from their relatives.

These tails are made for walking

While Jurassic Park made Tyrannosaurus fast enough to pursue a jeep, a new study by Pasha van Biljert, A. J. van Soest and Anne Schulp suggests that T. rex preferred to walk. Unlike other studies which have focused on the musculature and proportions of the legs, this one also factored in the ligaments of the tail. Since theropod tails were actively used in locomotion, the authors were able to study the resonance of the tail ligaments and use a 3D model to determine the energy storage and step frequency of the animal.

The detailed analysis suggests that the Preferred Walking Speed (it’s important to note that this designation refers to an optimal energy output, not an anthropocentric presumption of a dinosaur’s preferences) of the tyrant lizard is 1.28 meters/second, or about 2.86 miles per hour. That might sound slow, but the authors note that while other methods have come up with higher speed estimates, this number is closely in line with the Preferred Walking Speed of many extant animals. So you might still want to hop in that jeep.

An animation of Tyrannosaurus rex walking according to the simulations in van Bijlert et al.
Credits: Rick Stikkelorum, Arthur Ulmann & Pasha van Bijlert.

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