According to new research, large meat-eating dinosaurs took on the role of various species as they grew, resulting in a shocking lack of ecological diversity during the Mesozoic.
Megateropods: giant two-legged carnivores like Tyrannosaurus, Allosaurus, i Daspletosaurus—He did not instantly dominate the ecological space belonging to monstrously huge dinosaurs. Like other dinosaurs, they hatched from eggs and had to survive as they passed into adulthood. As new research paper published in Science shows, these stages of development were not just idle traps for megateropods; they were periods when dinosaurs, though juvenile, were still ecological forces to consider.
“This study puts numbers on something we suspected but didn’t really prove: that larger meat-eating dinosaurs filled different niches in the food chain as they grew from miniature cubs to older adults than buses, “said Steve Brusatte, a paleontologist at the University of Edinburgh who is not involved in the new research, said in an email.
The authors of the new study, led by Katlin Schroeder, a doctoral student at the University of New Mexico, have proposed a new term to describe this phenomenon: “morphospecies.” It basically means that megateropods, as they matured, grew and changed their hunting habits, took on the role of various species.
“Morphospecies is a very nice term,” Holly Woodward, a paleontologist at Oklahoma State University who is not affiliated with the new research, said in an email. “A youth T. rex for example, it remains a T. rex, but is playing the role of smaller carnivorous species, without being a different species.
G / O Media may receive a commission
By taking on the role of several species, however, megateropods managed to squeeze competitors and dominate multiple ecological niches, resulting in a surprising lack of species diversity and a notorious fossil gap, according to research. This gap exists throughout the Mesozoic, with possible explanations for the presence of non-dinosaurs in these niches (such as medium-sized mammals or crocodile-like creatures), or a selection bias with respect to the fossils found.
“Our study confirms the persistence of a gap in medium-sized carnivorous dinosaurs from many different communities across space and time,” Schroeder wrote in an email. “We knew that megateropods, especially Cretaceous megateropods, changed a lot as they grew, but we didn’t know what effect it would have on the structuring of their ecosystem. The discovery that young people are adapting to this gap and may have outgrown medium-sized carnivorous dinosaurs explains why they are largely absent from the fossil record.
In fact, the new study explains very well the lack of species diversity experienced during the three Mesozoic periods: the Triassic, the Jurassic, and the Cretaceous. As the fossil record shows, megaterapods – weighing more than 2,200 pounds (1,000 kilograms) – were prolific, but medium-sized carnivores, known as mesocarnivores, were surprisingly rare. This is a strange result, because environmentalists are used to seeing the opposite, at least among mammals. As a modern analogy, it would be as if only bones and lions existed, and also small carnivores such as cats, weasels and civets, but without medium-sized predators such as wolves, coyotes and hyenas. Basically, this describes the Mesozoic, a time when medium-sized dinosaurs weighing between 100 and 1,000 kilos were scarce and dinosaurs weighing less than 60 kilos were common.
“This seems to be a consistent pattern in dinosaurs, especially in those Cretaceous communities, towards the end of their reign,” Brusatte said. “There were few species of meat-eating dinosaurs of moderate body size for adults, and this is due to the young, adolescents and subadults of large despotic dinosaurs such as T. rex they controlled those niches “.
Dromaeosaurs like it Velociraptor they were quite successful, but unlike how they are portrayed in the film, they were actually quite small.
“Fans of Jurassic Park “Velociraptor” might be a little disappointed to find out that the real thing Velociraptor it was actually only the size of a turkey, “Schroeder said,” even relatively large dromeosaurs like it. Deinonychus they only reached 80 kilograms [176 pounds]”.
That said, there were medium-sized dinosaurs called megaraptors, such as Utahraptor, but they were rare, living only in places where megateropods were scarce, Schroeder explained. But there was one exception. Dakotaraptor, found in the Hell Creek Formation in South Dakota, weighed 300 kilograms (660 pounds), “but when the next largest carnivorous dinosaur in the community is the 7-ton Tyrannosaurus Rex, there is still a substantial gap, “he added.
Paleontologists are aware of this gap and the new article is not the first to propose this theory: large carnivorous dinosaurs filled multiple niches throughout evolutionary history. However, “despite their morphological disparity, adults and young people continue to be grouped in diversity [indexes], which is taxonomically accurate but not ecologically, “the authors wrote in the new study. As the paper notes, the new analysis is unique in that it” demonstrates the influence that juvenile megateropods would have had as morphospecies in their community. “
To make this analysis, Schroeder and colleagues examined 43 different dinosaur communities from seven continents over more than 136 million years of ecological history. The team analyzed more than 550 species of dinosaurs, classifying them by weight and diet, which allowed them, in turn, to compile meaningful community clusters made up of small, medium, and large-sized dinosaurs.
The results showed that mesocarnivores were largely absent in megateropod-ruled communities, and this was maintained regardless of time period or geographic location. That said, this ecological gap seemed to be more pronounced during the Cretaceous, which is no surprise given that megateropods were prolific at the time.
The team also posted the numbers to see if those results made sense. By considering factors such as growth and survival rates, the team was able to estimate the proportion of juvenile megateropods in the various dinosaur communities.
“Having observed the carnivorous dinosaur gap in many different communities that have different climates, from very different times, strongly indicated that it was being caused by [juvenile megatheropods]”Adding young megateropods to these communities and seeing them fit perfectly into the gap strongly indicated that they were at least part of the reason we observed a diminished diversity of dinosaurs,” Schroeder said.
This approach, in which researchers examined individual communities and compared dinosaurs of all shapes and sizes, is “the first attempt to quantitatively identify the ecological engines behind massive dinosaur distributions,” Schroeder said.
Brusatte really liked the new study, but was concerned that paleontologists would not take samples of smaller dinosaurs from the fossil record.
“We show so many fossils of small mammals, but this is because their durable teeth retain fossils well and are so complex that we can even use tooth fragments to identify mammal species. That’s not the case with dinosaurs, “he said.” This may affect some of the results of this study, but not the main finding that there is a gap in the distribution of body size of meat-eating dinosaurs, with young larger species that fill ecological niches that might otherwise be filled by different species of moderate body size for adults ”.
When asked about a possible selection bias in fossil samples, Schroeder dismissed it as a problem.
“I don’t think the selection bias came into play, as we examined many of the most well-known and sampled formations, which spanned 136 million years and represented all continents,” he said. “Our data set includes almost half of all known dinosaur species, so our data is unlikely to be representative of the dinosaur set.”
“It’s hard to say if anyone agrees with the conclusions of this article, because as the authors claim, no one has ever tried to rigorously quantify this ontogenetic niche in dinosaurs, so we really have nothing else to compare -lo, ”Woodward said.
In “changing the ontogenetic niche,” it refers to the changing ecological role of dinosaurs as they grow and grow.
“But I think his study reached the right level of detail and brevity,” Woodward added. “It will promote discussion on the topic and will likely encourage more specific research by other researchers.”