Theropods: The trace of one of the fastest dinosaurs found in La Rioja | Science

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Reconstruction of a theropod running over lake sediments during low water times.
Reconstruction of a theropod running over lake sediments during low water times.Francesc Gascó

Some of the fastest bipedal predatory (theropod) dinosaurs left their trail in La Rioja between 100 and 145 million years ago. An investigation into 12 fossilized tracks found at the La Torre site, in the municipality of Igea, has determined that the specimens that marked the ground as they passed could reach up to 45 kilometers per hour. This speed makes them one of the fastest, behind other theropods such as a young specimen of Tyrannosaurus rex, that could reach 50 kilometers per hour, and the smallest Compsognathus (64 kilometers per hour). However, they surpassed the velociraptor (38 kilometers per hour). The work has been published in Scientific Reports and headed by Pablo Navarro-Lorbés, paleontologist from the University of La Rioja.

The tracks analyzed correspond to specimens from the Early Cretaceous and present the three characteristic functional toes of the “beast’s foot” (translation of the Greek word theropod) as well as a longer shape (28.9 centimeters) than wide (26.9 cm ). Research has been able to confirm that these are fossilized traces of agile and medium-sized specimens of this suborder of saurischian dinosaurs. The paleontologist specifies: “By our estimates from the footprints, they had a height to the hips of between 1.3 and 1.4 meters, which could mean that we are talking about dinosaurs up to two meters high and about four meters of length”.

One of the tracks found in the Igea site called 6A.  / PABLO NAVARRO-LORBÉS
One of the tracks found in the Igea site called 6A. / PABLO NAVARRO-LORBÉS

However, the investigation has not been able to pin down the exact species. In this sense, Navarro-Lorbés explains: “The configuration of the icnitas [huellas fosilizadas] The size of a dinosaur depends on several factors: the shape of the animal’s foot, the characteristics of the mud in which they stepped and the movement made by the foot when generating the footprint. Since the shape of the foot of carnivorous dinosaurs is broadly similar in many species (three relatively graceful toes ending in claws), it is difficult to assign a specific footprint to a specific species. In addition, we know some of the species that inhabited the Iberian Peninsula during the Lower Cretaceous, but we do not know all of them, so it is not possible to know which species of dinosaur produced them. From the fossil remains that exist in the Iberian Peninsula and the characteristics of the footprints, we know that they were produced by a carnivorous dinosaur (theropod) belonging to either the group of carcharodontosaurids or spinosaurids ”.

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The remains of La Torre are divided into two groups, one with five tracks (6A-14) and the other with seven (6B-1). The first track belongs to a larger theropod and the track is estimated to correspond to a progressive run of between 23.4 and 37 kilometers per hour. The second specimen was more agile and left traces of abrupt speed changes, as if maneuvering, and at a faster pace (between 31.7 and 44.6 kilometers per hour at its fastest pace).

The authors of the study emphasize that, beyond the singular finding, “the study of the tracks of the dinosaurs can help to answer some questions about the behavior and the biodynamics as well as the interaction of these animals with the environment”. According to Navarro-Lorbés, “they allow us to know more and more precisely the way in which dinosaurs moved and lived, providing valuable information about their capacities and relationship with the environment.”

Walkers more than runners

Thus, according to research on fossil footprints, for these dinosaurs, “walking was the most common behavior” (96%), although some cases of trotting, in most cases, and running have also been identified.

According to the study, the footprints of La Rioja – “as far as we know”, according to the authors – correspond to those of “one of the fastest dinosaurs known,” only surpassed by two specimens, one from the Early Jurassic and another from the Lower Cretaceous, whose traces were found in the American deposits of San Juan (Utah) and in Texas. “The trail of La Torre 6B”, according to Navarro-Lorbés, “is today the third fastest known trail of theropod”. The Spanish researcher explains that the Utah dinosaur could reach 55 kilometers per hour, “although this trail only has two preserved tracks.”

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Preliminary measurement of one of the tracks during field work.
Preliminary measurement of one of the tracks during field work.Alberto Labrador

According to the research, “the dinosaur tracks found at the La Torre site correspond to the three highest speeds ever calculated for non-avian theropod tracks.” Furthermore, in the case of the most agile specimen, the trail shows its ability to execute and control substantial changes in speed while running and that the ecological conditions “were conducive for the medium-sized theropods to move by running.”

The study also details that these “good corridors” from La Rioja, with masses of less than 1,000 kilograms, developed this capacity “due to their dual status as hunters of smaller species and prey for larger predators.” According to Navarro-Lorbés, “for the animals that produced these footprints (medium-sized carnivorous dinosaurs), being fast and agile gave them an important advantage when it came to predating, but also so as not to be preyed upon by other larger carnivores” .

In this sense, Tom Cullen, a scientist at the Field Museum in Chicago, agrees: “Different growth patterns can make a big difference in the way an animal fits into its ecosystem. Getting big quickly can be a competitive advantage: it makes it easier for other animals to hunt and more difficult for other animals to hunt ”. And the other animals also evolved to adapt to these conditions, as the Spanish paleontologist explains: “Probably, their prey, biped herbivorous dinosaurs (ornithopods), could also reach high speeds and possess good maneuverability to flee from their predators.”

The Tyrannosaurus rex, the most popular prehistoric predator, walked at a speed of about 4.6 kilometers per hour, according to a scientific team from the Netherlands that established this data with the analysis of the swing of its tail, as published in the magazine Royal Society Open Science. According to Pasha van Bijlert, lead author of the work and Movement Sciences researcher at the Free University of Amsterdam (Vrije Universiteit), “the swinging of the tail, thanks to the ligaments, served as a counterweight. It is comparable to the suspension of a bridge and produced part of the force necessary to rhythmically push the body forward on two legs. The speed of the tread had to correspond to the natural frequency with which the tail rises and falls and we indicated that the step of the Tyrannosaurus rex it was 1.28 meters per second ”.

The research led by Navarro-Lorbés is part of his thesis, directed by Angélica Torices, director of the chair of Paleontology at the University of La Rioja, and has been carried out in collaboration with scientists from the Center for Paleontological Interpretation of La Rioja and from the Complutense Universities of Madrid, the Basque Country and the National University of Río Negro (Argentina).

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George Holan

George Holan is chief editor at Plainsmen Post and has articles published in many notable publications in the last decade.

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