Scientists have for the first time found embryonic remains of a group of carnivorous dinosaurs that include T. rex: fossilized jaws and claws that show these record-sized babies closely resembled adults and were "born ready" to hunt.
The bones indicate that these were larger than any other known dinosaur, 1 meter long, or the size of a medium dog, and that they hatched from what must have been huge eggs, perhaps exceeding 17 inches.
Smaller cousins of T. rex
The approximately 77 million-year-old jaw, about 3 cm in length, was unearthed in Montana and may belong to a species called Daspletosaurus .
The approximately 72-million-year-old wedge-shaped claw comes from the Canadian province of Alberta and may belong to a species called Albertosaurus.
They are both slightly smaller cousins of the Tyrannosaurus rex. The largest known tyrannosaurs exceeded 12 meters in length and 8 tons in mass. The jaw has distinctive tyrannosaurus features, including a deep groove on the inside and a prominent chin.
University of Edinburgh paleontologist Greg Funston , lead author of the research published in the Canadian Journal of Earth Sciences, noted that scientists were in awe of how similar embryonic bones were to adult tyrannosaurs and the jaws had functional teeth .