Scelidosaurus

The “Blueprint” of Thyreophora: Ancestor of the Big Names

Scelidosaurus is the common ancestor, or an existence extremely close to it, before the divergence of “Stegosauria” (with plates on their backs) and “Ankylosauria” (armored with plates).
It is an important dinosaur standing at a branching point in evolution; without it, the later Stegosaurus and Ankylosaurus might not have existed.

Basic Specs and Origin of Name

It is a medium-sized herbivorous dinosaur with a total length of 3 to 4 meters and a weight of approximately 270 kg.
It had a weight similar to a modern large cow or a small rhino.
The scientific name means “Limb Lizard.”
It was named by the renowned paleontologist Richard Owen.

Elaborate “Living Armor”

Its greatest feature is the elaborate armor of “osteoderms” covering its entire body.

Dorsal Armor

From the neck to the tail, bony plates with keels (ridges) were lined up in several rows.

Flank Spikes

On the flanks, there were sharp osteoderms curved like goat horns, blocking the approach of enemies.

Throat and Gaps

The throat was also firmly guarded, and small granular scales were densely embedded in the gaps of the armor.

Because these bones were not fused and remained independent, the armor combined mobility with defense.
Indeed, the “blueprint” for later heavily armored dinosaurs was completed here.

Evolutionary Missing Link: Transition to Quadrupedalism

Evolution from Scutellosaurus

While its ancestor “Scutellosaurus” was small and bipedal, Scelidosaurus had a large body and heavily developed armor.
To support this increased weight, they chose a sturdy “quadrupedal walk.”
This embodies the evolutionary process where Thyreophorans abandoned agility to become heavily armored.

The Oldest Ornithischian Dinosaur?

As of June 2025, it is considered one of the “oldest currently known ornithischian dinosaurs.”
It occupies an extremely important position in understanding the origin of the ornithischians, which had been shrouded in mystery.

150 Years of Sleep and the “Rosetta Stone”

“Rediscovery” via Acid

The fossil was discovered in 1858.
It is one of the first dinosaurs for which a “nearly complete skeleton” was found, but because it was buried in hard limestone, complete cleaning was impossible, and it slept in storage for over 150 years.

However, since 2020, Dr. David Norman succeeded in freeing the fossil from the rock using a method of dissolving the limestone with acid.
What appeared was an astonishing specimen with details ranging from the skull to traces of skin.
Because of this overwhelming amount of information, it came to be called the “Rosetta Stone of dinosaur research,” likened to the stone tablet used for deciphering ancient scripts.

Jurassic Life Scenery: Standing on Two Legs and Herds

Diet and Bipedal Stance

It was a herbivorous dinosaur that ate ferns and shrubs with its beak and leaf-shaped teeth.
Although basically quadrupedal, because its hind limbs were long and developed, it is speculated that it could “stand on two legs” when eating plants in high places or when alert.

Living in Herds

Having become slow due to heavy armor, it is considered highly likely that they moved in herds to protect themselves from carnivorous dinosaurs.
They likely traveled in groups to protect their young while seeking good feeding grounds.