The Tyrannosaurus rex is having a moment … 66 million years after it last roamed the Earth. The news this week has more T. rex stories than it has on the “Rex” of England. One is a newly discovered ancestor of everyone’s favorite dinosaur – and this frightening version had horns around its eyes. Another newly discovered dinosaur is being called the “T. rex of its time” … could it have held its own against the real one? Finally, the rare skeleton of an extremely pregnant T. rex went on display this week for the first time. What could be more frightening than a T. rex in labor? Who held its tiny hand and said, “Breathe”?
“Since their naming at the turn of the 20th century, tyrannosaurids have captivated public and scientific imagination alike, and are as a result among the best-studied groups of Cretaceous theropods. Perhaps the most successful group of tyrannosaurids were the latest-Cretaceous tyrannosaurines, including among them a diverse array of forms from the slender-snouted alioramins to robust and deep-jawed taxa like Teratophoneus and the eponymous Tyrannosaurus rex. However, much of the diversity of derived tyrannosaurines remains understudied or poorly understood, hampering understanding of paleobiogeographic and evolutionary trends.”
What paleontologist Elías A. Warshaw and Dickinson Museum Center curator Denver W. Fowler are trying to say in the opening to their new study, “A transitional species of Daspletosaurus Russell, 1970 from the Judith River Formation of eastern Montana,” is that there are plenty of T. rex fossils to study but most are from the same general era, so paleontologists have little to go by when trying to figure out how such a monstrous creature could have evolved. That changed in 2017 when paleontologist John “Jack” P. Wilson discovered a strange bone sticking out of a cliff in Badlands National Park in South Dakota. Initial careful excavations revealed that the bone was half of a tyrannosaur’s nostril, and more meticulous digging freed an entire premaxilla – a small cranial bone at the very tip of the upper jaw that generally holds teeth. The bone was labeled BDM 107 and from its size, Wilson and his team knew there could be a massive potential T. rex skeleton in the rock behind it. That meant digging through 26 feet (8 meters) of sediment – a task that caused the team to change the name of this specimen from BDM 107 to “Sisyphus” because it felt like they would be rolling rocks for all eternity.
Fortunately, ‘eternity’ arrived in 2020 as the paleontologists realized their tiny picks and shovels, which had uncovered a few broken vertebrae, were no match for this cliff, so they received permission to finish the job with jackhammers. By 2021, they uncovered enough of the partial skull and skeleton to determine that Jack Wilson had discovered a new ancestor of T. rex, earning the right to have it named after him. Daspletosaurus wilsoni (Daspletosaurus is Greek for 'frightful lizard') had some features from more primitive tyrannosaurs – especially prominent and scary-looking set of horns around the eye (you can see pictures of the dig and a recreation of the dinosaur here). It also had features from tyrannosaurs, including T. rex. By comparing the fossils to others from the area, the paleontologists determined that D. wilsoni was the descendant of Daspletosaurus torosus and the predecessor of Daspletosaurus horneri. That put its reign over the prehistoric badlands between 77 and 75 million years ago.
“If you saw Whatcheeria in life, it would probably look like a big crocodile-shaped salamander, with a narrow head and lots of teeth. If it really curled up, probably to an uncomfortable extent, it could fit in your bathtub, but neither you nor it would want it to be there. It would have made Whatcheeria the biggest thing in the lake: Go wherever you want, eat whoever you want."
The biggest thing to happen in What Cheer, Iowa, in both recent years and preshistoric times is the Whatcheeria deltae, a fierce apex predator that roamed the area 300 million years ago and whose 375 fossils — from bone fragments to nearly complete skeletons — were found recently in and around What Cheer. Ben Otoo, a doctoral candidate at Chicago's Field Museum and the University of Chicago and one of the authors of a new study published in Communications Biology, was trying to determine how fast this 6.5 feet (2 meters) long giant toothy salamander grew. (An artist's impression can be seen here.)
"You have this animal that is racing to get to reproductive age to get to at least a decent size really quickly, because the best way to get yourself out of a predator's range of prey items is to get bigger."
It turns out W. deltae got big fast and early in order to become the T. rex of its time. They reached half size by sexual maturity and then grew larger more slowly into adulthood. This was unusual for such an early tetrapod -- Otoo says it has only been seen in mammals, birds and reptiles with higher metabolisms than these tetrapods. Megan Whitney, the study’s lead author and a professor at Loyola University in Chicago, went so far as to say “this breaks all of the rules that we thought of for how growth is evolving in these early tetrapods.”
"It's a dirty secret, but we know next to nothing about sex-linked traits in extinct dinosaurs. Dinosaurs weren't shy about sexual signaling, all those bells and whistles, horns, crests, and frills, and yet we just haven't had a reliable way to tell males from females. Just being able to identify a dinosaur definitively as a female opens up a whole new world of possibilities. Now that we can show pregnant dinosaurs have a chemical fingerprint, we need a concerted effort to find more [medullary bone]."
Speaking of dinosaurs reaching sexual maturity, Lindsay Zanno, a paleontologist at North Carolina State University, talks about a "dirty little secret" discovery in 2005 in Montana’s Hell Creek Formation of medullary bone in the femur of a 68-million-year-old. It contained a porous and spongy layer of material inside of it that only happens when birds and dinosaurs are going to lay eggs. This made it a ‘medullary bone’ which is full of extra calcium the body uses to make egg shells. Theropod dinosaurs like T. rex are in the broad dinosaurian group that includes modern birds and this proved the fossil was of a pregnant one. Now named "Barbara", it is one of only three pregnant T. rexes ever discovered and it is finally going on display. The skeleton prominently shows the protruding abdomen that would have held eggs, and also a foot bone that was injured and healed, giving the pregnant mother a noticeable limp. Bones that were missing have been filled in with replicas from the famous the Tyrannosaurus rex skeleton ‘Stan’. (Photos can be seen here.)
This will be the first time in history that an adult male and female T-rex have been displayed together in the same museum. However, before you gas up or charge up the old family van, note that the museum is the Auckland War Memorial Museum Tāmaki Paenga Hira in New Zealand. Showings begin on December 2.
A horny one, a pregnant one and a small overachiever. That sounds like the perfect cast for a T. rex sitcom!