Triceratops skull delivers a Wow! of a Christmas gift

Removing dinosaur bone from rock is much like opening a Christmas gift: you never know what to expect. Sometimes, if you are really lucky, what’s revealed makes you take a step back and say, Wow!

And that’s exactly the early holiday surprise I got several weeks ago working on the museum’s one-of-a-kind Triceratops skull. It might contain the world’s first fossil evidence of this horned-dinosaur’s skin from the area of the neck frill.

When I last wrote about the partial skull of a large Triceratops prorsus in our collections, I had just started preparation work on the specimen. From reading Charles M. Sternberg’s 1929 original field notes, our expectations were already high. The complete frill and both horn cores he collected and preserved in two plaster jackets could be the world’s largest Triceratops.

Drawing of a Triceratops prorsus skull collected by the pioneering American palaeontologist Othniel Charles Marsh. The first fossils of this famous horned dinosaur were found in the late 19th century in Colorado, and have since been collected from Wyoming, South Dakota, Alberta and Saskatchewan. © Biodiversity Heritage Library (CC BY-SA 2.0)

Now, after five months of meticulous work on the backside of the bony frill, a completely unexpected find has emerged that could change our view of what Triceratops looked like.

A major challenge in preparing this Triceratops specimen is that much of the skull is fractured, and between these thin gaps in the fossil, tiny fragments and rock dust have accumulated. Before the fractures can be repaired, this accumulation must be removed.

A section of the bony shield that flared out around the neck of our Triceratops specimen, seen here sitting in a plaster jacket in the museum’s palaeontology workshop. The surface has been partially cleaned revealing many fractures. When C. M. Sternberg examined this fossil soon after its discovery in 1929, he made note of its exceptionally large size. Catalogue number: CMNFV 56508. Image: Alan McDonald, © Canadian Museum of Nature.

View of the frill section from above following complete exposure and cleaning of the numerous fractures that riddle the surface. One such fracture held a fragment containing a very interesting surprise — what appears to be preserved skin. Catalogue number: CMNFV 56508. Image: Alan McDonald, © Canadian Museum of Nature.

One afternoon in early October, as I was removing and sifting through the dust trapped in the fractures, I noticed a small, broken section of fossil.

A triangular-shaped piece of fossilized bone had separated from the main frill, but remained largely in place.  As I cleared the rock fragments and lifted out this small bit of fossil bone, what I saw underneath it made me quickly set down my brush.

To my surprise, there was a small section of what looks to be beautifully fossilized dinosaur skin.

This block of sediment covered a portion of the Triceratops frill and bears the impression of its surface features, including deep channels and pits. These may have once harboured blood vessels and other soft-tissue structures. One theory concerning the frills of horned dinosaurs is that they were covered in a hard sheath, perhaps composed of keratin, just like our fingernails. It’s possible that this protective covering was so dense and tight against the skull that the blood vessels providing oxygen and nutrients normally found in the soft tissue instead grew into the outer layers of the bone of the skull. Catalogue number: CMNFV 56508. Image: Alan McDonald, © Canadian Museum of Nature.

If so, it is the first evidence of skin from the head of this dinosaur species. Since it was first discovered in 1887, there has been no fossil material found to give any clear indication of what covered this horned dinosaur’s iconic frill. For more than a century, it was assumed that a mosaic of scales covered the surface of the frill, but others have more recently suggested that it was instead covered by a tough, horny sheath. Until now, we had no way to be sure.

The polygonal features seen in this photo appear to be the remains of fossilized skin preserved in association with the frill. The fossil has been removed for further study to confirm this initial identification. Once preparation of the top side of the frill is underway, it may finally provide some answers regarding the nature of the skin on a horned dinosaur’s neck shield, and perhaps also earn the specimen the title of the largest Triceratops skull ever described. Catalogue number: CMNFV 56508. Image: Alan McDonald, © Canadian Museum of Nature.

Taking a closer look at the section of distinctly patterned features with Dr. Jordan Mallon, the Canadian Museum of Nature’s dinosaur specialist, we decided we needed to re-examine how best to approach preparing the opposite side of the frill. We want to not only preserve any delicate fossilized skin it may retain, but if possible, also keep it from separating from the bone.

With this in mind, I am proceeding even more carefully and slowly in continuing the finer preparation and stabilization of the currently exposed side of the frill. Over the next few weeks, we will create a new plaster jacket to support the specimen, flip it over, and then see what new surprises the other side might have for us.

For now, though, I am quite content to enjoy this early, unique Christmas gift of probable fossilized Triceratops skin!