Episode 120 – Tyrannosaurs

Listen to Episode 120 on PodBean, YouTube, Spotify, or your favorite alternative!

The most famous dinosaur of all time didn’t come out of nowhere. T. rex has a long history of cousins and ancestors, whose evolution and lifestyles have been the subject of mountains of research, debate, and popular depictions. This episode, we discuss the whole family tree of Tyrannosaurs.

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The Tyrants

Tyrannosaurus rex was first named and described in 1905, the largest and most complete carnivorous dinosaur known at the time, and it soon earned super-stardom among paleontologists and the public. For a long time, T. rex represented nearly everything we knew about its lineage, the tyrannosaurs. But in the 21st century, a bevy of new discoveries and innovative research has revealed more details of this group: their early members, their diversity, and trends in their evolution.

Even before T. rex was named, tyrannosaur fossils were being found across North America, some of which were given names that were later changed. Specimens named Manospondylus (left) and Dynamosaurus (right) were later reclassified as Tyrannosaurus rex.
Images: Evolutionnumber9, CC BY-SA 4.0 and Gary Todd, Public Domain

The earliest tyrannosaurs didn’t look much like T. rex. Many were relatively small (3-5 meters long), with slender skulls and long arms, and some, like Proceratosaurus and Guanlong, had flashy head crests. The oldest known tyrannosaurs are from the Middle to Late Jurassic, and at that time they had already spread to Asia, Europe, and North America. Throughout the Cretaceous, tyrannosaurs further diversify across these northern continents, and in the Late Cretaceous, we see the emergence of a more familiar group called Tyrannosauridae.

Two early tyrannosaurs:
Early CretaceousYutyrannus (left). Art by Tomopteryx, CC BY-SA 4.0
Late Jurassic Guanlong (right). Art by Durbed, CC BY-SA 3.0
*These two did not live at the same time

The members of Tyrannosauridae include T. rex and many of its cousins: Albertosaurus, Tarbosaurus, Alioramus, and more. These dinosaurs have heavily built skulls with thick teeth and reinforced bones that supported a powerful bite. They also have long, slender legs well-adapted for efficient running and walking. And many of them were quite large, often reaching 10 meters (35 feet) long and weighing over a ton, while the largest species, including T. rex itself, could be over 12 meters (40 feet) and weigh several tons. These were dominant predators, superbly adapted for chasing prey and crushing bones.

Top: Tyrannosaurid skeletal mounts from Wikimedia Commons (details here)
Bottom: Tyrannosaurid size comparison by PaleoGeekSquared, CC BY-SA 4.0

Tyrannosaur lifestyles

Lots of research has been dedicated to the details of tyrannosaur diets. Evidence from coprolites and bite-marked bones suggests these predators were in the habit of shattering bone, which might have provided them with extra mineral nutrients. Research on T. rex suggests that tyrannosaurs had excellent senses of smell (with large olfactory lobes in their brains) and vision (with large, forward-facing eyes), and their limb and body proportions made them not only agile, but also quick and energy-efficient in motion.

T. rex through time.
Left: Earliest artistic reconstruction of T. rex from 1905. Image: Public Domain
Right: Modern T. rex mount in the American Museum of Natural History, NY. Image: Evolutionnumber9, CC BY-SA 4.0

Tyrannosaurs would have been striking to look at. They likely all had some degree of feathers (Yutyrannus and Dilong from China have been found with preserved feathers, and all tyrannosaurs are descended from ancestral feathery coelurosaurs), many had ornamented heads (proceratosaurids had crests and tyrannosaurids had skulls covered in bumps and knobs, with two small bosses over the eyes), and occasional skin impressions provide evidence of scales of varying shapes and sizes.

Left: An “ontogram” showing how T. rex changed over time, with images highlighting changes in the skull. Image: Thomas Carr, CC BY 4.0. See more details here.
Right: Growth curve of tyrannosaurids, highlighting change in body mass with age.
Image redrawn from Erickson et al. 2004.

In recent years, a lot of research has been devoted to tyrannosaur ontogeny – growth and development. Though there is only scant evidence of tyrannosaur embryos, some species, like Tyrannosaurus, Tarbosaurus, and Albertosaurus, are known from many specimens of various ages, giving us a great look at how these animals changed as they grew. When it came to the largest species, teenage tyrannosaurs were so different from adults that they’re thought to have lived very different lifestyles, occupying different ecological niches as they grew.

Learn More

If you want an accessible overview of all things tyrannosaur, we recommend Dr. David Hone’s book The Tyrannosaur Chronicles: the Biology of the Tyrant Dinosaurs

If you prefer videos, here are some recent virtual talks about tyrannosaur biology:
Dr. Thomas Holtz, 2021
Dr. David Hone, 2017
Dr. Stephen Brusatte, 2015

T. rex growth series studied in incredible detail, 2020 (semi-technical)
Brusatte and Carr 2016. The phylogeny and evolution of tyrannosauroid dinosaurs (technical)

Stevens 2004. Binocular vision in theropod dinosaurs (Technical, paywalled) This includes the information on T. rex vision that we discussed in the episode

Some recent tyrannosaur finds we mentioned in the episode:
Moros, 2019
Dynamoterror, 2018
Nanuqsaurus, 2014

If you enjoyed this topic and want more like it, check out these related episodes:

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2 thoughts on “Episode 120 – Tyrannosaurs

  1. Rick Farrand September 27, 2021 / 9:20 pm

    I am a few podcasts behind, but I listened to the T Rex episode today and found it great to hear the details and your discussion at the end about the popularity of T Rex. I totally agree that T Rex is bigger than life (literally) but that is good for the science even if it is a bit sensationalized. I wanted to share that I am a docent at the Denver Museum of Nature and Science and every kid says that T Rex is their favorite dinosaur. We have some great specimens to show them including a replica of a tooth that is as long as many of the kids arms!
    I have also been the caption of running team that I have named Trail Rex and we run relays. My t-shirt design includes a depiction of a T Rex on the front and on the back it says Trail Wrecks for the finish line with the Rex upside down and dead. It’s been alot of fun and included T rex costumes, blow up T Rexes on our vans, sayings like “Running to Extinction!, etc.
    I obviously enjoyed the podcast and look forward to more from you guys keep up the great work with your research and your presentation it makes these topics very understandable!

    Liked by 1 person

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