It’s only 23 inches lengthy, however one tyrannosaur cranium has been a bone of significant competition amongst paleontologists for many years.
In 1988, a group of researchers named it Nanotyrannus lancensis, suggesting that it represented a definite animal that lived within the shadow of Tyrannosaurus rex. In 1999, one other group argued that the cranium and related specimens have been T. rex as an adolescent, earlier than the species underwent a unprecedented development spurt that preceded maturity.
For years, the teenager T. rex speculation gained traction.
“Most individuals purchased into it, together with me,” mentioned Nick Longrich, a paleontologist with the College of Bathtub in England.
However Dr. Longrich has modified his tune. In a examine printed Wednesday within the journal Fossil Research, he and colleagues argue that sufficient proof exists to resurrect Nanotyrannus as its personal species among the many bigger Tyrannosaur household. Primarily based on anatomical options, they argue, it isn’t even significantly intently associated to T. rex.
Different consultants say the examine is unlikely to finish the controversy.
“It’s type of like Schrodinger’s dinosaur,” mentioned Thomas Holtz, a paleontologist on the College of Maryland who was not concerned with the paper. “This paper’s going to maintain folks speaking about it, however it’s not going to essentially resolve it.”
To make its case, Dr. Longrich’s group studied the unique 23-inch cranium and newer finds named Jane and Petey, in addition to a long-disputed tyrannosaur specimen, the “dueling dinosaurs.” All of those have been argued to symbolize adolescent T. rex, Dr. Longrich mentioned. However his group mentioned it discovered round 150 variations of their anatomy, together with cranium particulars; an prolonged, bladelike snout; and longer arms and claws than grownup T. rex.
He additionally mentioned the specimens had options according to mature animals, not adolescents. The expansion rings contained in the bone from three specimens — together with Jane and Petey — likewise recommend slowing development charges. The animals have been on observe to weigh over a ton, fairly than the T. rex, which was 4 to 5 tons, the researchers estimated.
“We now have three people, which mainly guidelines out a person variation or aberrant development sample,” Dr. Longrich mentioned. “What we’re seeing is that the expansion patterns are inconsistent with these animals being juveniles.”
The place, then, are the precise juvenile T. rex? Dr. Longrich believes he’s discovered a fraction of 1 — a bit of cranium from the College of California, Berkeley, collections described within the paper. “In each single characteristic it was T.rex,” he mentioned.
Different paleontologists will not be able to throw out the teenage T. rex speculation, and so they raised sturdy objections to the paper.
The specimens in query do present options in frequent with grownup T. rex — amongst them the brow, snout and braincase, mentioned Thomas Carr, a paleontologist at Carthage School who first made the case that Nanotyrannus represented younger T. rex. Furthermore, he disagrees with the declare that they don’t match the expansion sample in different tyrannosaur skulls.
“With T. rex and tyrannosaurs on the whole, variations between juveniles and adults are fairly excessive and persons are simply thrown,” Dr. Carr mentioned.
Holly Woodward, a paleontologist at Oklahoma State College who produced among the development information utilized by Dr. Longrich’s group, additionally disputed their conclusions. The spacing of the innermost development rings within the bone tissue of almost full grown grownup T. rex suggests “decrease development charges at youthful ages earlier than the massive development spurt,” she mentioned.
Dr. Woodward added that the group’s selection of mathematical fashions dangers producing a distorted image that exhibits youthful animals which can be accomplished rising, even when that isn’t the case.
“I’m simply not satisfied that the expansion curve arguments help that speculation,” she mentioned.
Dr. Longrich responded that teenage T. rex proponents haven’t confirmed their case both: “I’d throw it again of their camp and say, ‘The place is the proof in your speculation?’”
He defined that “for Nanotyrannus to show into T. rex, this requires a unprecedented variety of transformations.” No different dinosaur develops like this, Dr. Longrich argues: All the things his group studied suits neatly into the Nanotyrannus kind or the T. rex one.
Credible paleontologists have traditionally argued either side of the problem, Dr. Holtz mentioned. A part of the problem is that the majority T. rex specimens are adults, with just a few subadults. Everybody acknowledges that hole; they merely disagree about its which means.
The invention of both an older grownup Nanotyrannus or a younger T. rex distinct from the Nanotyrannus kind would assist make clear issues, Dr. Holtz mentioned. So may forthcoming information about Jane and the “dueling dinosaurs” tyrannosaur. Whereas the group’s paper offers attention-grabbing strategies, Dr. Holtz mentioned it isn’t sufficient for him to reject the speculation “that these are juvenile T.rex.”
The argument continues. For an animal that will or could not have existed, Nanotyrannus is proving curiously troublesome to kill.