An identity crisis is afflicting the world's most famous dinosaur.

A group of scientists said in February that the dinosaur was actually three different species. The paper made the case for a royal family of supersized predator lizards. The king would be joined by the emperor and the slimmer queen.

The paleontology community was struck by the proposal to reclassify T. rex. The first peer-reviewed rebuttal was published on Monday.

Thomas Carr, a paleontologist at Carthage College in Wisconsin, is one of the authors of the new rebuttal. The multiple species hypothesis would not have made sense to the public.

The rebuttal was published in a journal. Gregory Paul is one of the authors of the original study and is working on a new paper.

Mr. Paul is an independent researcher and influential paleo artist. The evidence is very strong that there are more than one species.

This debate is going to rage for a long time. It is hard for researchers to differentiate prehistoric species. The lines between two fossil species are messy. The size and shape of a bone are measured by paleontologists. Spending millions of years underground can distort bone. Sexual differences, injuries, illness and natural variation are just some of the things that can affect bones.

Large data sets balance warped trait in living populations. The sample sizes of dinosaurs like T. rex are very small according to Philip Currie, a paleontologist at the University ofAlberta. There is a fundamental problem with the estimate of 100 known tyrannosaurus rex fossils.

The field is filled with mistaken identities and extinct species names. Triceratops experienced its own naming drama in 1996 when scientists split it into two species.

ImageThe skull of Stan, one of the most complete Tyrannosaurus specimens discovered.
The skull of Stan, one of the most complete Tyrannosaurus specimens discovered.Credit...Mike Segar/Reuters
The skull of Stan, one of the most complete Tyrannosaurus specimens discovered.

It is possible that no scientific name is as sacred as the tyrannosaurus rex. The world's most-studied dinosaur has remained its name since 1905. The study threatened to send shock waves through the halls of museums.

Scientists had their doubts. There were two sets of incisor teeth found in the predator's lower jaw.

Dr. Carr claims in the rebuttal study that neither trait is distinct from any of the dinosaurs. The features that were claimed to be different between the three species were not. We have to have a higher standard than that, because there wasn't any break between the different species. Several well-preserved tyrannosaurus fossils do not fit into any proposed species due to their teeth and heft.

They want to puncture the analyses used in the paper. According to James Napoli, a paleontologist at the American Museum of Natural History in New York and a co-author on the rebuttal, the statistics used were misleading because the authors defined the number of species. If you know how many groups are in your data, it is a good test. It will always group the data into the number of groups you tell it to.

The researchers compared the variation between individual tyrannosaurs and Allosaurus skeletons. The Allosauruses come from a single bone bed in Utah while the T-Rex fossils come from a variety of sites over a long period of time, according to the rebuttal. Regional and temporal variation in the data set should be expected.

The team looked at the variability of T. rex's living relatives. The team concluded that the differences between T. rex and other birds were not significant.

Mr. Paul thinks another feature could make it more obvious. He theorizes that the style of horns on the skulls of dinosaurs are different to each other. The horn-encrusted brow of T. imperator was similar to T. rex's. Mr. Paul said this should be the end of the matter.

Dr. Napoli doesn't think it's true. Like the armor of modern crocodiles, these outgrowths were encased in a substance that protected them from the elements. The shape of the T. rex's horns may have changed as it aged.

Both sets of researchers agree that more tyrannosaurus fossils are needed. According to W. Scott Persons, a paleontologist at the College of Charleston, when more skeletons are found, the statistical support is going to be so strong that reasonable scientists can't disagree.

While neither side is ready to give up, Peter Makovicky, a paleontologist at the University of Minnesota who was not involved with either study, believes the continued back-and-forth will benefit paleontology.

The lay person can understand why we care so much about distinguishing new species in the fossil record. If it is a brachiopod, it would be difficult to convince someone of that.