Gargoyleosaurus

When people think of “armored dinosaurs”, they generally think of two kinds of creature: the stegosaurs and the ankylosaurs. Both of these groups belong to the dinosaur sub-order Thyreophora, which means “armor-bearing” in ancient Greek. The dinosaur group Ankylosauria or Ankylosauroidea is divided into two families called “Ankylosauridae” and “Nodosauridae”. There are several differences between the two, including skull structure and body armor, but the most diagnostic difference is that ankylosaurids have tail clubs and nodosaurids don’t. In general, it seems that the ankylosaurids placed a heavier reliance upon weaponry with their club tails and possessed moderate body armor, whereas the nodosaurids placed a much higher value on defensive armament. As such, the nodosaurids were some of the most heavily-armored dinosaurs to have ever existed, often possessing fearsome spikes and blade-like fins sticking out of their back and sides.

Stegosaurs like Stegosaurus and Kentrosaurus are generally associated with the Jurassic Period, while the ankylosaurs such as Ankylosaurus and Euoplocephalus are associated with the later Cretaceous Period. Were there any ankylosaurs living in the Jurassic? The answer is a definite “Yes!”. During the 1970s, fossils of an ankylosaurian were discovered in China in rocks dating to the middle Jurassic Period about 170-165 million years ago. Originally named Jurassosaurus, it was re-named to Tianchisaurus in 1993. It was the first time that any ankylosaurian was found in Jurassic-aged rock.

Meanwhile in the United States during the 1980s, a large abundance of fossil bones were discovered in Colorado at a place called Mygatt-Moore Quarry, in rocks that dated to about 150 million years ago, within the Morrison Formation of the late Jurassic Period. Among the fossils which were found at this site were bones and pieces of armor from an ankylosaurian dinosaur – the first time that an ankylosaurian had been found in North America within rocks that weren’t from the Cretaceous Period. In 1994, it was officially named Mymoorapelta, “Mygatt-Moore shield”. It is currently in the collections of the Museum of Western Colorado (collections ID code: MWC 1815) (1).

In 1995 in Wyoming at a place called Bone Cabin Quarry, also within the rocks of the Morrison Formation dated to approximately 150 million years ago, a partial skeleton was discovered by Jeffrie Parker and Tyler Pinegar, who worked for Western Paleontology Labs. The bones clearly belonged to an ankylosaurian dinosaur, and they included a nearly-complete skull, a partial right shoulder, a right humerus, numerous vertebrae from the neck, sacrum, and tail, several partial ribs, a piece of the hip, a right femur, and an abundance of osteoderms on its neck and back. Three years later in 1998, they were classified as a new species of armored dinosaur, and it was given the name Gargoyleosaurus, “the gargoyle lizard”. The species name was originally G. parkpini, named after Jeffrie Parker and Tyler Pinegar who found the bones. However in 2001, it was changed to G. parkpinorum, which was judged to be the correct use of the names in Latin. The holotype is currently in the collections of the Denver Museum of Nature and Science, formerly known as the Denver Museum of Natural History (collections ID code: DMNH 27726) (2).

Quarry map of the fossil remains of Gargoyleosaurus parkpinorum, discovered at Bone Cabin Quarry, Wyoming. The polka-dotted pieces represent armor. From Brandon Killbourne and Kenneth Carpenter (2005), “Redescription of Gargoyleosaurus parkpinorum, a polacanthid ankylosaur from the Upper Jurassic of Albany County, Wyoming”. Neues Jahrbuch für Geologie und Paläontologie, volume 237 (July 2005). Page 113.

Based upon the size of the skull, and comparing this with the skulls of other ankylosaurians, Kenneth Carpenter and his associates estimated that Gargoyleosaurus measured 12 feet (3.7 meters) long (3). In 2005, Carpenter slightly lowered the size to being 10 to 11.5 feet (3 to 3.5 meters) long (4). Most estimates which I have seen state that the animal reached 10 to 12 feet long. However, we don’t have a complete tail from this animal, so we cannot be absolutely certain of this measurement.

Gargoyleosaurus was a nodosaurid, and it’s classified as a member of the nodosaur sub-family Polacanthinae, which includes animals such as Polacanthus of England and Gastonia of the United States. Gargoyleosaurus is noteworthy because it still has teeth in the front of its mouth in both its upper and lower jaws. This is important because nearly all anklyosaurians have premaxillae which are entirely toothless, which is only further evidence that Gargoyleosaurus is a very primitive member of this group (5).

Gargoyleosaurus’ triangular head was very small in proportion with the rest of its body. It had a flat top covered in bony nodules, and just behind each eye there were two stubby triangular horns, one pointing up and the other pointing down. Its neck was protected by five curved armor plates known as “cervical rings” (even though they aren’t technically “rings”). Its back was covered with numerous small circular and oval-shaped osteoderms, most of them being “keeled”, or possessing a ridge running along the middle. It is unknown how many osteoderms the animal’s back would have had, so reconstructions of the animal are somewhat conjectural. Sticking out horizontally along the animal’s side, from its shoulders to the end of its tail, were large blade-like osteoderms which resembled shark fins. Positioned over its hips was a large armored plate consisting of numerous circular and oval osteoderms which were embedded into a pebble-textured slab of bone. Based upon the size and shape of the caudal vertebrae and chevrons, Gargoyleosaurus’ tail appears to have been shaped like an upside-down egg in cross-section and heavily-muscled. This anatomical structure would make the tail well-suited to be swung side-to-side rather than raising it up-and-down. The tail also appears to have been far less armored than the animal’s main body, likely to allow the tail to retain flexibility while whipping and smacking at potential threats like Allosaurus, Ceratosaurus, and Torvosaurus. It must also be taken into consideration that the osteoderms would not have been exposed bone – they would have been covered in a protective layer of keratin, which would have made them larger and more pronounced in real life than what the fossils themselves suggest.

Mounted skeleton of Gargoyleosaurus parkpinorum (DMNH 27726). Much of the left half of the skeleton has been reconstructed. From Brandon Killbourne and Kenneth Carpenter (2005), “Redescription of Gargoyleosaurus parkpinorum, a polacanthid ankylosaur from the Upper Jurassic of Albany County, Wyoming”. Neues Jahrbuch für Geologie und Paläontologie, volume 237 (July 2005). Page 153.

File:Gargoyleosaurus.png

Skeleton of Gargoyleosaurus on display at the Denver Museum of Nature and Science (2007). Creative Commons Attribution-Share Alike 3.0 Unported license.
https://commons.wikimedia.org/wiki/File:Gargoyleosaurus.png.

Below is a reconstruction that I made of the armor of Gargoyleosaurus when viewed from above. This reconstruction was based upon the illustration of the layout of the bones and armor as seen in Killbourne and Carpenter’s 2005 article, photographs and measurements of the pieces of armor within that same article, and also based upon reconstructions of the skeleton which are on display in the Denver Museum of Nature and Science and the Museum of Ancient Life in Lehi, Utah. It must be noted that the two skeletal reconstructions are constructed slightly differently, with different numbers and positioning of the dorsal osteoderms. There are very few osteoderms known from the animal’s tail, so the number and positioning of the osteoderms on the tail is, for the time being, left up to personal interpretation. The drawing was made with No.2 and No.3 pencil on printer paper.

Gargoyleosaurus armor. © Jason R. Abdale (August 25, 2021).

Keep your pencils sharp, everybody.

Source citations

  1. James I. Kirkland and Kenneth Carpenter (1994), “North America’s first pre-Cretaceous ankylosaur (Dinosauria) from the Upper Jurassic Morrison Formation of western Colorado”. Brigham Young University Geology Studies, volume 40 (January 1994). Pages 25-42.
  2. John H. Ostrom and John S. McIntosh, Marsh’s Dinosaurs: The Collections from Como Bluff. New Haven: Yale University Press, 1999. Page xii; Brandon Killbourne and Kenneth Carpenter (2005), “Redescription of Gargoyleosaurus parkpinorum, a polacanthid ankylosaur from the Upper Jurassic of Albany County, Wyoming”. Neues Jahrbuch für Geologie und Paläontologie, volume 237 (July 2005). Pages 112-114; Kenneth Carpenter, Clifford Miles, and Karen Cloward (1998), “Skull of a Jurassic ankylosaur (Dinosauria)”. Nature, volume 393 (June 25, 1998). Pages 782; Kenneth Carpenter, ed., The Armored Dinosaurs. Bloomington: Indiana University Press, 2001. Page 376.
  3. Kenneth Carpenter, ed., The Armored Dinosaurs. Bloomington: Indiana University Press, 2001. Page 235.
  4. Brandon Killbourne and Kenneth Carpenter (2005), “Redescription of Gargoyleosaurus parkpinorum, a polacanthid ankylosaur from the Upper Jurassic of Albany County, Wyoming”. Neues Jahrbuch für Geologie und Paläontologie, volume 237 (July 2005). Page 111.
  5. Kenneth Carpenter, ed., The Armored Dinosaurs. Bloomington: Indiana University Press, 2001. Page 41.

Bibliography

  • Carpenter, Kenneth, ed. The Armored Dinosaurs. Bloomington: Indiana University Press, 2001.
  • Carpenter, Kenneth; Miles, Clifford; Cloward, Karen (1998). “Skull of a Jurassic ankylosaur (Dinosauria)”. Nature, volume 393 (June 25, 1998). Pages 782-783.
  • Killbourne, Brandon; Carpenter, Kenneth (2005). “Redescription of Gargoyleosaurus parkpinorum, a polacanthid ankylosaur from the Upper Jurassic of Albany County, Wyoming”. Neues Jahrbuch für Geologie und Paläontologie, volume 237 (July 2005). Pages 111-160.
  • Kirkland, James I.; Carpenter, Kenneth (1994). “North America’s first pre-Cretaceous ankylosaur (Dinosauria) from the Upper Jurassic Morrison Formation of western Colorado”. Brigham Young University Geology Studies, volume 40 (January 1994). Pages 25-42.
  • Ostrom John H.; McIntosh, John S. Marsh’s Dinosaurs: The Collections from Como Bluff. New Haven: Yale University Press, 1999.


Categories: Paleontology, Uncategorized

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1 reply

  1. Thank you for sharing another great post! I must admit I missed seeing one of your reconstructions, but I still find the illustration of Gargoylesaurus’ armor arrangement very helpful and interesting. 🙂 I really like how you focus on a wide variety of creatures. 🙂

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