Not many dinosaurs have been proven to be semi-aquatic. A new discovery adds a duck-like species to their narrow ranks.
For decades, paleontologists have been treating dinosaurs as land wanderers, while other ancient reptiles groups were launched. But increasing new fossil evidence reopens the question of whether some ancient dinosaurs can thrive on land and water in some form or way, like many modern creatures. Whether dinosaurs are some degree of "semi-aquatic" has been bothering researchers, because few dinosaur fossils have skeletal characteristics that clearly show evolution in engraving the body to obtain water.
Now, a new study provides another clue: velociraptor 's dental relatives over 68 million years show signs of streamlined shape in the ribs of diving birds. The fossils in southern Mongolia, published in the journal Communication Biology - known as the "polytoothed swimming hunter" after being called in Latin and Greek - marks the first time this trait has been discovered in dinosaurs that have become extinct in birds and their close relatives.
In many organisms, ribs extend from the spine at an angle of about 90°, but in modern diving birds, such as penguins and cormorants , the ribs tilt downward to the tail end of the animal. Inclined ribs can narrow the abdomen from the back to the abdomen. This feature is thought to help simplify the streamlined shape of animals swimming in water. It is exactly this adaptation that scientists see in Natovenator's fossils, which include part of the well-preserved chest cavity.
Natovenator's skull retains large eye sockets, many small teeth and noses, and will grow in life with sensitive nerve endings
The top, bottom and sides of the beak skull.
Natovenator's skull retains large eye sockets, many small teeth and noses, and will grow in life with sensitive nerve endings .
Today many existing dinosaurs—what we call birds—thrive on and off the water. Some of their ancient ancestors did the same, such as the marine primitive birds Ichthyornis and Hesperornis. However, birds are just a branch of the dinosaur family tree, and there is little evidence of non-birth dinosaurs immersed in lakes and rivers. Discovering dinosaurs like Natovenator whose bones are built for swimming means dinosaurs’ habitat and lifestyles are more diverse than previously thought.
In this spirit, Natovenator reveals "how diverse the ecological locations of dinosaurs are," said Yuong-Nam Lee, a paleontologist at Seoul National University in South Korea.
Swimmers, waders and everything in between
In the past decade, scientists have increasingly suspected that at least one group of dinosaurs have a close connection to water: Spironosauraceae . These predators are obviously more aquatic than other predatory dinosaurs, with multiple anatomical and chemical evidence that they lurk at least occasionally in the coastline and hunt for fish.
Some studies even believe that the largest member of this family, the school bus-sized Spinosaurus, is a kind of "river monster" that spends most of its time in the water. These claims have been challenged for years, and in a recent study published yesterday in the journal eLife, Spinosaurus is more of a wading ambush predator than a swimming chaser.
A 2017 study describes another potential swimmer: the quirky skeleton Halszkaraptor from Mongolia. Although this creature is a storm - a subgroup of dinosaurs including velociraptors - it has a long, absolutely goose-like neck. More importantly, its nose – covered with nerve holes – shows that it has facial touch like a modern crocodile, detecting the movement of prey in the water.
At the time, the team that first described the fossil proposed that its strange features might make it a semi-water swimmer like a modern goose or duck. However, for years, some scientists have been refuting whether the Halshkalapusaurus is semiaquatic, partly because the fossil ribs are not well preserved to identify key features.
New research on Natovenator helps clarify Halszkaraptor's pictures, and found that the two organisms are close relatives. Therefore, the chest cavity of the Halshkalapson also seems to be equally streamlined, which reinforces the claim that this strange little dinosaur is indeed closely linked to water.
Halz Kalapueron "certainly looks like a Raptor trying to be a goose...but it's a sample size," said Tom Holtz, a paleontologist at the University of Maryland, who reviewed the new Natovenator study before publication. "Obviously, more data points would be better - this is another.
Long neck, toothed hunter
Natovenator was exposed during the 2008 Korean-Mongolia International Dinosaur Expedition, an international team of 27 people who found nearly 200 fossils across Mongolia. On August 26 of the same year, team member Robin Sissons saw bones from the fossil-rich cliff edge of southern Mongolia Hermiin Tsav's rock protruded out of the rock, about 68 million to 75 million years old. Although she didn't know what the skeleton was, she applied it with protective plaster and prepared to return to the lab.
Sissons' discovery and other fossils from the expedition were transported to South Korea for preparation and later returned to Mongolia. When the preparers carefully scraped off the excess rock from the fossil, a well-preserved dinosaur began to appear: a long neck and a skull covered with tiny teeth. "We realized immediately that this was an important thing," said Lee.
Natovenato The fossil of R is one of the hundreds of fossils that Lee team has collected in Mongolia over the years, so preparations take a long time and intermittent. Then, a major announcement helped to understand the slowly emerging fossils: the unveiling of Halszkaraptor in 2017.
Deeper exploration
If there is any precedent in the fierce debate about Spinosaurus, then Natovenator may face controversy. But University of Southern California PhD candidate, paleontologist Kiersten Formoso isn't that sure. In her opinion, the small size of Natovenator makes its semi-aquatic traits easier to sell than the giant Spinosaurus. First, she says, "When you're smaller, you won't dive with huge lungs filled with air."
Natovenator's announcement is just the beginning of work to put it in the world of dinosaurs and increase our knowledge of swimming dinosaurs. Matteo Fabbri, a researcher at the Field Museum of Natural History in Chicago, suggested that future research should focus on Natovenator's bone density , because its thorax is similar to that of modern diving birds such as penguins and cormorants. In a March study, a team led by Fabry showed that penguins, hippos and other modern animals that often feed underwater tend to have dense bones as ballasts. The study also found that unlike penguins, the bones of Halshkalapusaurus are hollow, and that the bones of Spinosaurus and its cousin baryon are dense, consistent with spending a lot of time in water.
However, it is already clear that in the process of making a living from water, Natovenator follows a different evolutionary path than many relatives. For University of Maryland paleontologist Holtz, Natovenator is a powerful reminder that closely related species follow very different paths, just as today’s crunchy spotted hyena is a close relative of insect-chewing aardvark , “Just because you’re a dragon doesn’t mean you’re committed to being a predator like velociraptors,” he said, “they are all part of the same large family – but pursuing adaptive trends to different routes.
