Undersaurus

Undersaurus (name meaning Underdog reptile) is an extinct species of sauropod that lived in what is now North America during the Late Cretaceous period. It was one of the last ever species of Brachiosaurids in existence, living from 76 million years ago to about 66 million years ago. Like many other sauropods, they were gentle giant plant eaters that fed on nothing but leaves, ferns, cycads, and horsetails. They grew to about the size of a Jurassic North American Brachiosaurus or an African Giraffatitan, as the nearly complete skeleton of an Undersaurus suggests, and they had the same body plan as the two Jurassic Brachiosaurids, so Undersaurus could have had a similar niche to the two Brachiosaurids of the Jurassic. They most likely became extinct due to the the asteroid impact on the Gulf of Mexico and its effects.