“Scotty” – The World’s Biggest T. rex

A scientific paper on what is regarded by many scientists as the world’s biggest Tyrannosaurus rex has been published.  It is time for the “T. rex” specimen nicknamed “Scotty” to step into the spotlight.  It measures around thirteen metres in length and represents an individual more than thirty years of age, remarkably old for a tyrannosaur.  Based on the diameter of the leg bones and other measurements, the body weight of this formidable carnivore has been estimated at 8.8 Tonnes.  It has been suggested that this specimen (RSM P2523.8), is a little longer and heavier than “Sue” (BHI2033), which resides in the Evolving Planet exhibit at the Field Museum in Chicago.

The “Scotty” T. rex Exhibit Preparing to Make Its Debut at the Royal Saskatchewan Museum

A reconstruction of the skeleton of “Scotty” the T. rex

Picture credit: Amanda Kelley

Gracile and Robust T. rex Forms

On August 16th, 1991, Robert Gebhardt, a high school teacher by profession but also a keen fossil hunter, was working with Tim Tokaryk (palaeontologist at the Eastend Fossil Research Station).  They were exploring the strata exposed along the Frenchman River Valley in Saskatchewan Province, for Robert this was an opportunity to learn more about field work.  However, within a few hours, Robert had found the base of a heavily worn tyrannosaur tooth, along with a caudal vertebra, the sort of discoveries that seasoned palaeontologists dream about.  Robert had discovered the oldest individual T. rex specimen.

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Excavation Work Begins

It was not until June 1994, that the excavation work began on this new T. rex specimen in earnest.  The dig site became a visitor attraction in its own right with several thousand people coming to see how the huge bones representing about sixty-five percent of the skeleton were being excavated.  Unfortunately, the sandstone matrix surrounding the fossil bones and teeth was extremely hard, extracting the fossils from their 66-million-year-old rock tomb has proved to be one of the most challenging large theropod fossil preparations so far undertaken.

Scientists are aware that there seem to be two main types of Tyrannosaurus rex adult body plan – a robust form and a gracile form.  It is not known what these two different body types represent, one could be male, the other female, however, “Scotty”, so named after a celebratory drink of scotch after the initial fossil discovery, is a very robust Tyrannosaurus rex.

A Silhouette Showing the Fossil Material Associated with RSM P2523.8

A silhouette outline showing the anatomical position of the known skeletal material of “Scotty”.

Picture credit: University of Alberta, via Agence France-Presse – Getty Images

Scott Persons, (University of Alberta) and one of the authors of the scientific paper published in The Anatomical Record, explained:

“This is the rex of rexes!”

There is considerable size variability among Tyrannosaurus.  Some individuals were lankier than others and some were more robust.  Scotty exemplifies the robust.  He comes out a bit heftier than other T. rex specimens.

Indeterminate Growth

Multiple measurements (including those of the skull, hip, and limbs) show that this was a robust individual with an estimated body mass exceeding all other known T. rex specimens and representatives of all other gigantic terrestrial theropods.  A histological analysis of the fibula (lower leg bone), indicates that Scotty was a mature, adult animal that was over thirty years of age when it died.

“Scotty” T. rex

Dinosaurs exhibit indeterminate growth, as opposed to most other extant tetrapods that have determinate growth.  Simply put, this means that a dinosaur grows rapidly when young (T. rex growth spurts in the teenage years for example), but when fully mature, the animal keeps growing albeit at a much reduced pace.  Therefore, a very old individual such as RSM P2523.8, could be larger than other tyrannosaurs, such as T. rex “Sue”, which is believed to have been around twenty-years of age when it died.

Persons stated:

“Scotty is the oldest T. rex known.  By which I mean, it would have had the most candles on its last birthday cake.  You can get an idea of how old a dinosaur is by cutting into its bones and studying its grown patterns.  Scotty is all old growth.”

Evidence of Pathology – Signs of a Violent Life

Although the fossil material is not as complete as the Field Museum T. rex, just like Sue, the fossilised bones of Scotty show plenty of pathology (evidence of injury or disease).  This dinosaur may have had a long life, but it was a tough life too.  A number of caudal vertebrae are damaged, it has been suggested that this pathology was caused by a bite from another T. rex.  As with many theropod specimens ribs show evidence of having been broken and subsequently healed and the jaw shows signs of an infection.

Palaeontologist Scott Persons Stares into the Jaws of “Scotty”

Scott Persons stares into the jaws of “Scotty”.

Picture credit: University of Alberta,  Amanda Kelley via Agence France-Presse – Getty Images

Cranial Armour?

Intriguingly, the skull exhibits a number of lumps and bumps which suggests that T. rex could have had armoured skin, a feature not seen in other T. rex cranial material.   A cast of the fossils will help to form a new mounted Tyrannosaurus rex display, part of an exhibit that is due to open at the Royal Saskatchewan Museum in May 2019.

Scott Persons added:

“I think there will always be bigger discoveries to be made, but as of right now, this particular Tyrannosaurus is the largest terrestrial predator known to science.”

Bigger Specimens Awaiting Discovery

The big, robust bones of this Tyrannosaurus rex probably represent the largest of this species so far described.  To most scientists and academics, which dinosaur was the biggest does not really matter, after all, the mass estimates for tyrannosaurs vary considerably.  However, the authors of the scientific paper, which include Phil Currie and Gregory Erickson, propose that RSM P2523.8 adds weight to the prior hypothesis that there is a sampling bias throughout the Dinosauria.  “Scotty” with its mature, thick-set bones indicates that many other dinosaur taxa grew to significantly greater sizes than currently recognised.

This means, that there are likely to be even bigger dinosaur specimens awaiting discovery…

For the time being, the Royal Saskatchewan Museum can claim that they are putting on display a cast of the heaviest T. rex known to science, a claim that they can make, at least for now.

The Fossilised Remains of Even Older and Larger Specimens Probably Await Discovery

The skull of the T. rex exhibit on display at Wollaton Hall until August 2022.  Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The scientific paper: “An Older and Exceptionally Large Adult Specimen of Tyrannosaurus rex” by W. Scott Persons IV, Philip J. Currie, Gregory M. Erickson published in the journal The Anatomical Record.

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