Day #7 on our Christmas Countdown is…

GIGANTSPINOSAURUS!

Gigantspinosaurus: the “Giant-Spined Lizard”

Gigantspinosaurus was a relatively small stegosaur from Late Jurassic China. There are many well known dinosaurs from the Shaximiao Formation, such as the club-tailed sauropod Shunosaurus, the really long-necked sauropod Mamenchisaurus, and the far more famous Chinese stegosaur Tuojiangosaurus.

Like many other formations, these layers of rock cover a large expanse of time, and so are divided into smaller pockets. For example, Shunosaurus is found in the “lower” Shaximiao Formation (also known as the Shunosaurus-Omeisaurus assemblage), alongside a small stegosaur known as Huayangosaurus, right at the beginning of the Late Jurassic.

Gigantspinosaurus comes in later in the “upper” Shaximiao Formation, which is also known as the Mamenchisaurus assemblage, because Mamenchisaurus is found at this layer.

Since the Shaximao Formation preserves a timeline from the Middle Jurassic to the Late Jurassic, we get a wonderful glimpse into how creatures adapted and changed over time. Take the stegosaurs for example. There are seven different genus of stegosaur that can be found here, including Bashanosaurus, the oldest stegosaur known to date.

Let’s take a peak at all of them and where they fit in the layers of time…

• Bashanosaurus: Middle Jurassic, 169-165 Ma. The earliest known stegosaur. It shares traits with Scelidosaurus and later stegosaurs.
• Huayangosaurus: Middle Jurassic, 165 Ma. One of the smallest stegosaurs, and only 13 feet long. It is known for its more spike-like, triangular plates.
• Chungkingosaurus: Late Jurassic, 160 Ma. Another small stegosaur with triangular plates that are almost more like spikes on the front half of its back, and then true spikes all the way to the end of the tail. These spikes start vertical, and then are horizontal towards the tail tip in a “pincushion” arrangement.
• Gigantspinosaurus: Late Jurassic, 163-157 Ma. Most famous for the gigantic, comma-shaped shoulder spikes.
• Tuojiangosaurus: Late Jurassic, 160 Ma. The most well researched and understood of the Chinese stegosaurs. It had a double row of plates that look like slightly flattened, modified spikes. These plates are small and pear-shaped by the head, but grow bigger and sharper towards the hips. The tail spikes are also in a “pincushion” arrangement.
• Chialingosaurus: Late Jurassic, 160 Ma. Only known from fossils of young animals. It is often reconstructed with rounded plates on the front half of the body, and spikes along the tail like Kentrosaurus.
• Yingshanosaurus: Late Jurassic, 155 Ma. This stegosaur had a double row of flat, rounded, relatively small plates along its back, and shoulder spikes that were large and curved like those of Gigantspinosaurus.

For just a little bit of context, Stegosaurus itself does not appear until 155-145 Ma.

For even more fun, I highly encourage looking back even further in the family tree to critters like Scutellosaurus and Scelidosaurus. It would be tons of fun to design a Pokemon evolution series based on the stegosaur family tree!

Do you have a favorite stegosaur?

See you tomorrow for day 8 of the Critter Christmas Countdown!