Podcast Summary: The Ancients – Stegosaurus: Titan of the Jurassic

Host: Tristan Hughes
Guest: Dr. Susannah Maidment, Natural History Museum
Date: December 14, 2025
Duration: approx. 47 minutes

Episode Overview

In this lively, in-depth episode, host Tristan Hughes brings on paleontologist Dr. Susannah Maidment, one of the world’s leading experts on armored dinosaurs, for a deep dive into Stegosaurus – one of the most famous and enigmatic dinosaurs of the Jurassic period. Together, they explore its anatomy, evolutionary mysteries, ecology, and the latest cutting-edge discoveries, from the iconic plates and spikes to little-known relatives and fossil finds from across the globe.

Main Discussion Points & Insights

1. Why Stegosaurus Captivates (03:40–04:37)

• Stegosaurus's Iconic Status
  • Tristan and Susie agree Stegosaurus is a perennial childhood favorite.
  • Susie notes: “Every seven year old knows what stegosaurus is… everyone puts their hand up, everyone knows what stegosaurus is.” (03:46)
• UK Fossil Heritage
  • The UK is privileged to have key stegosaur specimens at the Natural History Museum (NHM), notably “Sophie”—Europe’s most complete Stegosaurus.

2. Stegosaurus, Stegosaurs, and Their World (04:37–11:58)

• Clarifying Terminology
  • Stegosaurus refers to a single genus; stegosaurs denotes the broader group.
• Timeline & Geography
  • Stegosaurs first evolved in the Middle Jurassic (~167 million years ago), peak diversity in Late Jurassic, extinct by Early Cretaceous (~100 million years ago). (05:43)
  • Found in North America, Europe, China, Africa, and South America—absent (so far) in Australia and Antarctica but likely once present. (07:01)
• Who Lived With Stegosaurus?
  • Large sauropods (Diplodocus, Brontosaurus, Brachiosaurus) and predators like Allosaurus were contemporary with Stegosaurus.
  • Common misconception: Stegosaurus and T. rex did NOT coexist—T. rex is closer to us in time than to Stegosaurus.
    • “T. rex…66 million years ago. Stegosaurus…150 million years ago. So T. rex is actually closer to us in time than it is to Stegosaurus.” (06:12)

3. Fossil Rarity and Environment (07:48–11:58)

• Fossil Record
  • Despite fame, stegosaur fossils (esp. complete skeletons) are rare, with North America and China as exceptions.
• Jurassic Habitats
  • North America: seasonally arid to wet. Europe: mostly marine rocks, suggesting stegosaur carcasses sometimes washed out to sea.
  • Example: Fossil stegosaur tail spikes with marine bivalves attached, evidence of “whale fall”–type sea floor communities. (11:28)

4. Anatomy: Head to Tail

a. Head & Brain (12:28–16:31)

• Brainpower
  • Stegosaurus had a notably small brain—“about the size of a walnut… the smallest brain volume per body mass of any terrestrial animal that’s ever lived.” (12:59)
  • “They did what they needed to do… which was to eat and mate… smart enough to live for millions of years.” (14:26)
• Teeth & Diet
  • Small teeth suggest a diet of soft plants, but engineering studies indicate they could likely crop tougher vegetation with a turtle-like beak.
• Senses
  • No evidence of exceptional senses in the fossil record.
  • Did not chew—food was likely processed in the gut, possibly with the aid of gastroliths.

b. Neck & Body (17:15–21:24)

• Neck Length Variation
  • Most had average necks; Miragaia (Portuguese genus) had an unusually long neck (17 vertebrae), possibly for high browsing. (17:25)
  • Raised the possibility that some stegosaurs could rear up tripodally for feeding.
• Posture & Locomotion
  • Shorter forelimbs than hindlimbs; likely presented a sloped back, with a sometimes “awkward” crouched posture by mammalian standards. (19:02–20:09)

c. Plates: Structure and Purpose (20:12–27:37)

• Plate Arrangement
  • Stegosaurus had two staggered rows of plates, not a single line; “Sophie” has 19 plates and spikes. (20:28–21:21)
• Composition & Location
  • Plates were bone with a keratin sheath, richly supplied with blood vessels, and embedded in the skin (not attached to vertebrae)—“osteoderms”, similar to those in crocodiles. (21:24–21:54)
• Functions Theorized
  • Armor: Could resist attacks from above, though flanks remained exposed.
  • Display: Likely important for species/dating recognition or mate attraction (analogy to peacocks or deer antlers). Lack of juvenile fossils or sexual dimorphism data makes this hard to prove.
  • Thermoregulation: Plates as radiators for heat loss via blood vessel networks.
    • “They probably flushed hot blood into these plates and it would radiate heat out.” (25:51)
  • Likely multi-purpose, as in living species with similar structures. (27:10)

d. Spikes: “Thagomizer” and Variations (29:44–34:34)

• Tail Spikes
  • Four spikes on Stegosaurus’s tail—colloquially ‘Thagomizer’ (from a Far Side cartoon), but Dr. Maidment prefers “spikes.” (30:08–31:16)
  • Biomechanical models show they could strike with bone-crushing force, probably effective against predators. (31:23)
  • Number and arrangement of tail spikes varies by species—Kentrosaurus (Africa) had spikes all down its tail. (32:08–32:36)
  • Tails were highly muscular, likely swung side-to-side. (33:01–33:30)
• Other Armor
  • Some species had shoulder spikes (e.g., Gigantspinosaurus from China with 1.5m shoulder spines), throat armor (“chainmail”-like ossicles in some Stegosaurus), and skin generally scaly and unarmored. (28:50–29:56)

e. Social Structure, Reproduction, and Living Habits (34:34–37:52)

• Juveniles & Eggs
  • Virtually no juvenile stegosaurs or eggs known—possibly due to soft-shelled eggs that don’t preserve well. Only one fragmentary juvenile specimen known. (34:43–36:44)
• Herding/Habits
  • Lack of fossil evidence for herding, but group living would have been useful for defense. (36:44–37:52)
• Predators
  • Allosaurus was the predominant stegosaur predator in North America (“Allosaurus roared the Morrison.”), with others like Ceratosaurus less common. (38:03–38:33)

5. New Discoveries and Continuing Mysteries (38:33–45:15)

• Adratiklit boulahfa (Morocco)
  • Dr. Maidment’s work led to the identification of the first North African stegosaur from Middle Jurassic Morocco, tracking its provenance from the fossil market back to the original site. (39:04–41:39)
  • Highlights the poor sampling of Africa’s fossil record; likely many stegosaurs remain undiscovered due to geographical and sociopolitical barriers. (42:07)
• Evolutionary Fate
  • Stegosaurs went extinct by the Cretaceous—“they don’t evolve into anything; they went extinct.” (45:15)

6. Stegosaurus in Popular Media (45:30–46:46)

• Media Depictions
  • Generally accurate, especially in older series like Walking with Dinosaurs—iconic plates, small head, face-offs with Allosaurus.
  • Major complaint: Scenes showing armored dinosaurs running at speed are implausible due to anatomical limitations.

Memorable Quotes & Moments

• On Stegosaurus’s brain:
  “Their brains are about the size of a walnut… of any terrestrial animal that’s ever lived.” (12:59 – Dr. Susannah Maidment)
• On T. rex and Stegosaurus:
  “T. rex is actually closer to us in time than it is to Stegosaurus.” (06:12 – Dr. Susannah Maidment)
• On the purpose of plates:
  “I sometimes say that I think that Allosaurus could have chomped through Stegosaurus plates like us eating Doritos.” (27:56 – Dr. Susannah Maidment)
• On the ‘Thagomizer’:
  “We don’t need this... It’s literally a made up word that was made up in a comic.” (30:16 – Dr. Susannah Maidment)
• On lack of fossils from Africa:
  “Africa is virtually unsampled... relative to North America and Europe. We just haven’t been looking there very long.” (42:07 – Dr. Susannah Maidment)
• On what Stegosaurs became:
  “They went extinct, so they don’t evolve into anything.” (45:15 – Dr. Susannah Maidment)

Timestamps for Key Segments

| Timestamp | Topic/Highlight | |--------------|---------------------------------------------------------------------------------------------------| | 03:40–04:37 | Stegosaurus’s iconic status; NHM’s Sophie specimen | | 05:43–06:40 | Stegosaur evolution, diversity, and extinction; T. rex comparison | | 07:48–08:32 | Rarity and global distribution of stegosaurs | | 11:28–11:58 | Fossilized tail spikes with bivalves—evidence of marine transport | | 12:28–14:39 | Stegosaurus head, brain, and dietary adaptations | | 17:15–18:51 | Neck and posture differences among stegosaurs; possible feeding strategies | | 20:12–21:21 | Plate arrangement and evidence from Sophie | | 22:45–27:37 | Plate function theories: armor, display, thermoregulation | | 29:44–31:23 | Tail spikes (“thagomizer”), their power and evolutionary significance | | 34:43–36:44 | Lack of juvenile fossils and reproductive mysteries | | 39:04–41:57 | Discovery of Moroccan stegosaur (Adratiklit boulahfa) | | 45:15 | Stegosaurs did not evolve into anything, they simply went extinct | | 45:30–46:46 | Stegosaurus in TV/media and pop culture depictions |

Tone & Style

The episode is friendly, enthusiastic, and accessible, with both host and guest displaying infectious interest and humor. Dr. Maidment is candid about what we don’t know and injects fun paleontological skepticism—especially on pop-culture terminology (“thagomizer”) and depictions of dinosaur behavior.

Summary

• Stegosaurus remains a perennial favorite not only for its bizarre appearance but also because it embodies ongoing scientific mystery—a dinosaur as famous as it is rare in the fossil record.
• Key anatomy: Tiny head/brain, large armored plates, spiked tail; lived across much of the Jurassic world, especially North America, Europe, and China, alongside giant sauropods and predators like Allosaurus.
• Recent advances include new discoveries from Africa and South America, but many questions—about reproduction, behavior, and even basic biology—remain due to the sparse fossil record.
• Function of plates and spikes—likely multi-purpose: some protection, some display, some temperature control.
• Popular media generally gets Stegosaurus right—with the exception of implausibly fast or agile movement!

Final Note

Dr. Maidment’s expert insights underline both what science can unravel about these prehistoric icons and how much remains mysterious—a true example of paleontology as a living, evolving science.