Medium-sized meat-eaters dinosaurs missing in the fossil record, and paleontologists think they have figured out why.
Paleontologists have discovered giant dinosaurs and small dinosaurs, but according to a new study, there is a noticeable lack of medium-sized carnivorous dinosaurs, especially from the Chalk period (145.5 million to 65.5 million years ago).
The investigators put on their detective hats and quickly found a suspect; megatheropods – the largest of the dinosaurs that eat meat, such as Tyrannosaurus rex and Gorgosaurus, who as adults weighed more than 2,200 pounds (1,000 kilograms). It is possible that juvenile megateropods extinct the mediocre animals, the researchers said.
“The juvenile megateropod surpassed other medium-sized dinosaurs, leading to empty global dinosaur diversity,” lead researcher Katlin Schroeder, a doctoral student in the Department of Biology at the University of New Mexico, told WordsSideKick in an email.
However, not everyone is convinced that there is a case of missing medium-sized dinosaurs; it is possible, for example, that fossils of medium-sized animals have yet to be found, said Michael D’Emic, associate professor in the Department of Biology at Adelphi University in New York, who was not involved in the study.
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Small, medium, large
As egg-laying animals, all dinosaurs started small and weighed no more than 15 kg. As dinosaurs grew, some probably occupied different niches and ate different foods than adults of the same species did – for example, a young T. rex probably could not accept a Triceratops, and probably went after smaller prey.
To investigate the medium-sized mystery, Schroeder and her colleagues reported to the Paleobiology database, a non-profit source for paleontological data, and they categorize more than 550 species of dinosaurs as small (22 to 220 pounds, or 10 to 100 kg), medium (220 to 2200 pounds, or 100 to 1000 kg) or large ( more than 2200 lbs), or 1 000 kg). These dinosaurs lived in 43 communities (groups living at the same time and place) in seven continents throughout the country Jurassic period (201 million to 145.5 million years ago) and the Cretaceous.
The researchers found that although communities often had herbivorous dinosaurs in each size category, they were rarely a medium-sized carnivorous dinosaur in communities with megateropods.
“It is possible that the ‘gap’ is caused by young people of the large megateropods, who may have eaten other things than their parents and therefore compete with medium-sized carnivores,” Schroeder said.
The team found that the medium-sized dinosaur gap was more pronounced in the Cretaceous than in the Jurassic period. During the Cretaceous, the tyrannosaurs and the abelisaurs reigned supreme, and they also “looked very different from juveniles than adults,” unlike the megatopotes of the Jurassic, she said.
In other words, during the Jurassic period, the megateropods, such as Allosaurus, did not change much as they grew, ‘and possibly shared food sources, such as giant sauropods [long-neck herbivorous dinosaurs] with their parents, “Schroeder said. This made it possible for more carnivores to exist in the same communities, leading to a smaller [medium-size] gaping in carnivore. ‘
But at the end of the Jurassic many sauropods died, and dinosaurs like Allosaurus. ‘They may have been replaced by dinosaurs like Tirannosaurus Schroeder said a wider range of different sources is used.
Next, Schroeder’s team wondered if the youthful megateropod had a greater influence on the composition of their communities than the adults. To find out, the researchers calculated how many juveniles and adults each species had in a community. Then the team discovered the biomass – the number of individuals in a species multiplied by their mass at a certain age.
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The researchers found that in some megateropod species, such as Allosaurus and Tirannosaurus, the juveniles represent a larger share of the mass than the adults, probably because it was a dinosaur-eating-dinosaur world at the time, and megateropods did not always make it to adulthood. This indicates’ that the youths had just as much (if not more ”) influence on their community as the adults did ”, Schroeder said in the email. In fact, there were so many medium-sized juveniles of megateropods that they could even be seen as their own species.
‘When we added the youth to their communities [species]”The gap has largely disappeared,” said Schroeder.
However, it is possible that something else could explain this medium-sized mystery, D’Emic said. Twelve out of 43 of the paleo-communities examined in the study apparently do not follow the pattern derived in the study – that medium-sized carnivorous dinosaurs were rare in communities with megateropods. In these twelve communities, “they have large and medium-sized teropods,” D’Emic said. The study explains these exceptions in different ways, but perhaps there were medium-sized carnivorous dinosaurs there, only paleontologists have yet to find their fossils in every community, D’Emic said. “Even in relatively well-researched places around the world, new dinosaur species are discovered every year, so that’s not unlikely,” D’Emic said in an email to WordsSideKick.
I am also possible that some dinosaur species were misidentified in the study. Only recently have paleontologists begun to evaluate bone microstructure, which may reveal the age of a dinosaur at death. “This may indicate that some small dinosaur individuals belonging to one species were merely juveniles of other species, or conversely, that some small dinosaur individuals considered to be juveniles of one species are rather adults of new dwarf species,” he said. D’Emic said.
The study was published online in the journal on February 25. Science.
Originally published on Live Science.