{"id":439951,"date":"2024-01-02T19:09:06","date_gmt":"2024-01-03T00:09:06","guid":{"rendered":"https:\/\/platohealth.ai\/new-research-shows-juvenile-t-rex-fossils-are-a-distinct-species-of\/"},"modified":"2024-01-02T20:02:23","modified_gmt":"2024-01-03T01:02:23","slug":"new-research-shows-juvenile-t-rex-fossils-are-a-distinct-species-of","status":"publish","type":"post","link":"https:\/\/platohealth.ai\/new-research-shows-juvenile-t-rex-fossils-are-a-distinct-species-of\/","title":{"rendered":"New research shows \u201cJuvenile T. rex\u201d fossils are a distinct species of","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"
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A new analysis of fossils believed to be juveniles of T. rex<\/em> now shows they were adults of a small tyrannosaur, with narrower jaws, longer legs, and bigger arms than T<\/em>. rex<\/em>. The species, Nanotyrannus lancensis<\/em>, was first named decades ago but later reinterpreted as a young T<\/em>. rex<\/em>.<\/strong><\/p>\n

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A new analysis of fossils believed to be juveniles of T. rex<\/em> now shows they were adults of a small tyrannosaur, with narrower jaws, longer legs, and bigger arms than T<\/em>. rex<\/em>. The species, Nanotyrannus lancensis<\/em>, was first named decades ago but later reinterpreted as a young T<\/em>. rex<\/em>.<\/strong><\/p>\n

The first skull of Nanotyrannus<\/em> was found in Montana in 1942, but for decades, paleontologists have gone back and forth on whether it was a separate species, or simply a juvenile of the much larger T. rex<\/em>.<\/p>\n

Dr Nick Longrich, from the Milner Centre for Evolution at the University of Bath (UK), and Dr Evan Saitta, from the University of Chicago (USA) re-analysed the fossils, looking at growth rings, the anatomy of Nanotyrannus<\/em>, and a previously unrecognized fossil of a young T<\/em>. rex<\/em>.<\/p>\n

Measuring the growth rings in Nanotyrannus<\/em> bones, they showed that they became more closely packed towards the outside of the bone \u2013 its growth was slowing. It suggests these animals were nearly full size; not fast-growing juveniles.<\/p>\n

Modelling the growth of the fossils showed the animals would have reached a maximum of around 900-1500 kilograms and five metres \u2013 about 15 per cent of the size of the giant T<\/em>. rex<\/em>, which grew to 8,000 kilograms and nine metres or more.<\/p>\n

The researchers have published their findings in Fossil Studies<\/em>.<\/p>\n

\u201cWhen I saw these results I was pretty blown away,\u201d said Longrich. \u201cI didn\u2019t expect it to be quite so conclusive.<\/p>\n

\u201cIf they were young T<\/em>. rex<\/em> they should be growing like crazy, putting on hundreds of kilograms a year, but we\u2019re not seeing that.<\/p>\n

\u201cWe tried modeling the data in a lot of different ways and we kept getting low growth rates. This is looking like the end for the hypothesis that these animals are young T<\/em>. rex<\/em>.\u201d<\/p>\n

Supporting the existence of distinct species, the researchers found no evidence of fossils combining features of both the Nanotyrannus<\/em> and T<\/em>. rex <\/em>\u2013 which would exist if the one turned into the other.  Every fossil they examined could be confidently identified as one species or the other.<\/p>\n

Neither did the patterns of growth in other tyrannosaurs fit with the hypothesis that these were young T. rex.<\/p>\n

Dr Longrich said: \u201cIf you look at juveniles of other tyrannosaurs, they show many of the distinctive features of the adults. A very young Tarbosaurus <\/em>\u2013 a close relative of T<\/em>. rex <\/em>\u2013 shows distinctive features of the adults.<\/p>\n

\u201cIn the same way that kittens look like cats and puppies look like dogs, the juveniles of different tyrannosaurs are distinctive. And Nanotyrannus<\/em> just doesn\u2019t look anything like a T<\/em>. rex<\/em>.<\/p>\n

\u201cIt could be growing in a way that\u2019s completely unlike any other tyrannosaur, or any other dinosaur- but it\u2019s more likely it\u2019s just not a T. rex<\/em>.\u201d<\/p>\n

But that raises a mystery \u2014 if Nanotyrannus<\/em> isn\u2019t a juvenile Tyrannosaurus<\/em>, then why hasn\u2019t anyone ever found a young T<\/em>. rex<\/em>?<\/p>\n

\u201cThat\u2019s always been one of the big questions. Well, it turns out we actually had<\/em> found one,\u201d said Longrich. \u201cBut the fossil was collected years ago, stuck in a box of unidentified bones in a museum drawer, and then forgotten.\u201d<\/p>\n

The research led Longrich and co-author Evan Saitta to a previous fossil discovery, stored in a museum in San Francisco which they identified as a juvenile Tyrannosaurus.<\/em><\/p>\n

That young T<\/em>. rex<\/em> is represented by a skull bone \u2013 the frontal bone \u2013 with distinctive features that ally it with Tyrannosaurus<\/em>, but which aren\u2019t seen in Nanotyrannus<\/em>. It comes from a small animal, one with a skull about 45 cm long and a body length of around 5 metres.<\/p>\n

Dr Longrich said: \u201cYes, it\u2019s just one specimen, and just one bone, but it only takes one. T<\/em>. rex<\/em> skull bones are very distinctive, nothing else looks like it. Young T. rex<\/em> exist, they\u2019re just incredibly rare, like juveniles of most dinosaurs.\u201d<\/p>\n

The researchers argue these findings are strong evidence that Nanotyrannus<\/em> is a separate species, one not closely related to Tyrannosaurus<\/em>. It was more lightly-built and long-limbed than its thick-set relative. It also had larger arms, unlike the famously short-armed T<\/em>. rex<\/em>.<\/p>\n

\u201cThe arms are actually longer than those of T<\/em>. rex<\/em>. Even the biggest T<\/em>. rex<\/em>, has shorter arms and smaller claws than in these little Nanotyrannus<\/em>. This was an animal where the arms were actually pretty formidable weapons. It\u2019s really just a completely different animal \u2013 small, fast, agile.<\/p>\n

\u201cT. rex<\/em> relied on size and strength, but this animal relied on speed.\u201d<\/p>\n

The long arms and other features suggest it was only distantly related to T<\/em>. rex <\/em>\u2013 and may have sat outside the family Tyrannosauridae, which T<\/em>. rex<\/em> is part of, in its own family of predatory dinosaurs.<\/p>\n

The new study is the latest in a series of publications on the problem, going back decades.<\/p>\n

Longrich said: \u201cNanotyrannus<\/em> is highly controversial in paleontology. Not long ago, it seemed like we\u2019d finally settled this problem, and it was a young T<\/em>. rex<\/em>.<\/p>\n

\u201cI was very skeptical about Nanotyrannus<\/em> myself until about six years ago when I took a close look at the fossils and was surprised to realise we\u2019d gotten it wrong all these years.\u201d<\/p>\n

The authors suggest that, given how difficult it is to tell dinosaurs apart based on their often-incomplete skeletons, we may be underestimating the diversity of dinosaurs, and other fossil species.<\/p>\n

Longrich said: \u201cIt\u2019s amazing to think how much we still don\u2019t know about the most famous of all the dinosaurs. It makes you wonder what else we\u2019ve gotten wrong.\u201d<\/p>\n

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Journal<\/h4>\n

Fossil Studies<\/p>\n<\/div>\n

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DOI<\/h4>\n

10.3390\/fossils1010009 <\/i><\/p>\n<\/div>\n

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Method of Research<\/h4>\n

Experimental study<\/p>\n<\/div>\n

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Article Title<\/h4>\n

Taxonomic status of Nanotyrannus lancensis (Dinosauria:Tyrannosauroidea) \u2013 a distinct taxon of small-bodied tyrannosaur<\/p>\n<\/div>\n

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Article Publication Date<\/h4>\n

3-Jan-2024<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n