A study led by Capital Normal University in China has discovered that the Mudsaurus rex, which lived 150 million years ago, had teeth when it first hatched. Researchers reported in the journal *Current Biology* that as the young dinosaur grew, it likely transitioned from a carnivorous to a herbivorous diet, and its carnivorous teeth were replaced by a beak more suited for consuming plants. This is unprecedented in other reptile or dinosaur studies until about 10 years ago when the Mudsaurus rex fossil was unearthed in Wucaiwan, Xinjiang.
The adult and juvenile dinosaurs, unable to escape the mud pit, were almost separated into two different types of dinosaurs.
Wang Shuo, who led the research, said that they initially thought they had discovered fossils of two different dinosaurs, one with teeth and one without, and had even begun to classify them separately. However, the researchers gradually discovered that, apart from the difference in their teeth, the two dinosaurs were very similar in all other characteristics.
Later research suggested that *Mudosaurus* gradually lost its teeth as it grew, making it the only known reptile to exhibit this characteristic. Among extant creatures, only the platypus may have similar growth patterns, while *Mudosaurus* belongs to the theropod suborder, along with Tyrannosaurus Rex and Velociraptor.
This discovery may help explain or unlock the key to the relationship between dinosaurs and birds.
