Not all dinosaurs are considered to still be valid, which means they are dubious dinosaurs. These “doubtful names” are known as nomen dubium, and it happens when it’s too hard to tell if a specimen has enough features to be considered a unique species.
Sometimes it’s because the fossils are too fragmentary, and other times it’s because the only known fossils have been lost or destroyed.
Here are 10 dubious dinosaurs that have been named, and then often renamed, over the years.
If you want to learn more about each one, listen to our corresponding podcast episode.
A dubious ceratopsid that lived in the Late Cretaceous in what is now Wyoming, U.S. Only the hip bones, hip vertebrae, and ribs have been found.
This dinosaur was a Bone Wars dinosaur, and when it was discovered, it was the largest known land animal—estimated to be 30 ft (9 m) long and weigh 6 tonnes.
Learn more about Agathaumas in episode 234 of our show.
A tyrannosauroid that lived in the Cretaceous in what is now New Jersey, U.S. This dinosaur is famous because of Charles Knight’s painting of Leaping Laelaps.
Only one specimen was found, and it was estimated to grow up to 25 ft (7.5 m) long. Now Laelaps is known as Dryptosaurus.
Learn more about Laelaps in episode 268 of our podcast.
A maybe dubious ceratopsian that lived in the Late Cretaceous in what is now Montana, U.S. and Alberta, Canada.
Fossils were found before scientists knew much about horned dinosaurs, also known as ceratopsians, and the man who named Monoclonius at first thought Monoclonius was a hadrosaur, or duck-billed dinosaur. There’s been a lot of debate about Monoclonius and another ceratopsian, Centrosaurus.
Learn more about Monoclonius in episode 302 of our podcast.
A dubious tyrannosaurid that lived in the Late Cretaceous in what is now Mongolia.
The specimen was collected illegally and smuggled out of Asia, so it was difficult to figure out its origins. It’s considered to be a nomen dubium because it looks similar to juvenile Tarbosaurus, and there’s not adult version of Raptorex to compare to Tarbosaurus and make sure it’s unique.
Learn more about Raptorex in episode 94 of our podcast.
A dubious ankylosaur that lived in the Late Cretaceous in what is now China.
Multiple specimens have been found, but no two of the same bones were found, so it was difficult to compare them and see if they all belonged to the same type of dinosaur. Two species were named: Crichtonsaurus bohlini and Crichtonsaurus benxiensis. Crichtonsaurus bohlini was found to be dubious and Crichtonsaurus benxiensis became Crichtonpelta benxiensis.
Learn more about Crichtonsaurus in episode 208 of our podcast.
A possibly dubious sauropod that lived in the Early Cretaceous in what is now Utah, U.S.
Two fragmentary specimens have been found, probably of an adult and juvenile. These fossils may be too incomplete to know if Brontomerus is a valid dinosaur.
Learn more about Brontomerus in episode 325 of our podcast.
A possibly dubious coelophysoid that lived in the Triassic in what is now New Mexico, U.S.
The fossils thought to be Gojirasaurus turned out to be from two other dinosaurs, Shuvosaurus and another coelophysoid.
Learn more about Gojirasaurus in episode 165 of our podcast.
A dubious ankylosaur that lived in the Late Jurassic in what is now England.
Only part of a femur, or thighbone, has been found. At first, Cryptosaurus was thought to be related to Iguanodon, a hadrosaur. It took over 110 years to recognize the femur belonged to an ankylosaur.
Learn more about Cryptosaurus in episode 295 of our podcast.
A dubious ankylosaur that lived in the Late Cretaceous in what is now Montana, U.S.
At one point, there were multiple Palaeoscincus species named, but most of them were reassigned to different dinosaur names. Not all of these dinosaurs were ankylosaurs either. They included a stegosaurid and pachycephalosaurid. The type species, Palaeoscincus costatus, is based on only one tooth, which is why it’s dubious.
Learn more about Palaeoscincus in episode 364 of our podcast.
Hadrosaurs (Duck Billed Dinosaurs)
And last, but not least, there have been many lumpings and splittings of hadrosaur dinosaurs over the years. This includes lots of dubious dinosaurs!
Most hadrosaurs are known from their skulls, and some of the well known hadrosaurs whose names have changed over the years include Anatosaurus, Bactrosaurus, Claosaurus, Gryposaurus, Hypsibema, Kritosaurus, Orthomerus, and Trachodon.
We cover over 60 types of hadrosaurs in episode 350 of our podcast. Listen here: