Pipestone's
Pachyrhinosaurs

Though known in the palaeontology community since its first official announcement, efforts to tackle the huge undertaking of preparation, illustration, research and description of the many fossils from this site is ongoing. Dr. Phil Currie (University of Alberta), Dr. Wann Langston (University of Texas) and Darren Tanke (Royal Tyrrell Museum) are preparing a major research project on the animals and the site. When finished, the resulting monograph will be the largest ceratopsian study since 1933 and third largest ever.

It was not until June 1983 that Dr. Phil Currie saw the bonebed for the first time and collected a few specimens. He soon determined that a centrosaurine ceratopsian was present there.

Due to the extreme rarity of dinosaur bones in the Grande Prairie district and because Pachyrhinosaurus was at that time the rarest horned dinosaur, the decision was made to open up the Pipestone Creek bonebed. The very first fossil encountered there was a skull about 40% complete.

The resulting dig efforts yielded over 3500 ceratopsian bones and other fossils. Another pachyrhinosaur bonebed, located higher in section along the Wapiti River (some 30 kilometres to the West) was also discovered during this time. It produced several partial skulls and other bones. The Pipestone Creek site has become so popular with local residents that they consider the Pachyrhinosaurus "their" regional dinosaur and pachyrhinosaur logos have begun to appear as company and society logos.

Four size-classes of pachyrhinosaur are represented at Pipestone Creek from German Shepherd dog-sized juveniles (yearlings and young-of-the-year) to rhinoceros-sized adults.

The skeletons in the bonebed are disarticulated. The carcasses rotted, were scavenged on and the bones scattered before final burial. Most bones, especially the more robust ones were buried complete, or nearly so. However, elongated bones, such as ribs, tend to be broken into smaller fragments. Juvenile and subadult skulls are also fragmented. The site is particularly rich in skulls, no doubt due to the near total fusion of cranial elements later in individual development. One adult-sized skull ranging from 35% to 75% complete is found roughly every 2-2.5 metres. As a vivid demonstration of adult skull frequency, in the 1987 field season,three adult-sized skulls were found in the first hour of the first day and another was found later that day.

Some robust, adult skull bones seem to have been badly broken and abraded prior to burial. They have a markedly lighter surface colour and a soft yellow chalky appearance on the interior. These may represent older, more biologically and/or mechanically degraded bones that found their way into the deposit. Toothmarked bones are rare, yet shed theropod teeth are well know from the site. Unlike many ceratopsian bonebeds, the Pipestone Creek site preserves many smaller elements, such as small, delicate juvenile skull bones in perfect condition and smaller elements from adult animals (anklebones, fingerbones and tail vertebrae). The only elements that are noticeable rare are chevrons, which are unknown for immature animals and rare for adults.

Since four different sizes of animals were discovered at the site, individual development could be traced. Young pachyrhinosaurs began life with a small, semi-circular orbital horn. Later, upon reaching adult or near adult-size, these horns transformed into wrinkled, massive orbital bosses. In presumed older adult, holes developed in the floor of the orbital boss, the winkle texture was replaced by smooth bone and the boss seemed to be collapsing into itself. The concave or convex shape of the orbital boss in mature animals might indicate gender differences.

The bones are preserved at the Pipestone Creek site in a carbonaceous, fine, gray siltstone with no preferred orientation suggesting and overbank or crevasse splay (local flood) depositional environment. Virtually all (99+%) the bones are ceratopsian, although there are rare remains of other vertebrate groups.

A volcanic ash horizon, located downstream from the bonebed and about 30 metre higher in section yielded a date of 73.25 million years. This date is similar to the early Bearpaw Sea facies in Southern Alberta. Therefore we can say that when the Pipestone Creek pachyrhinosaurs were alive, much of Central and southern Alberta was awash under the shallow Bearpaw Sea. These dates show the Pipestone Creek bonebed is younger than the deposits at Dinosaur Provincial Park, and older than the rocks of the Horseshoe Canyon Formation exposed around Drumheller, Alberta, from where the Pachyrhinosaurus canadensis was described.

Since the Pipestone Creek excavations, other Pachyrhinosaurus-like forms were discovered. A skull and bonebed was located in Northern Alaska. However, whereas the Pipestone Creek adult pachyrhinosaurs have three prominent bosses on their skulls (one over the nose and one over each eye), the Alaskan animals had all three coalesced into one structure. This material still appeared somewhat similar to that of from Pipestone Creek, leading to early suggestions of annual dinosaur migration between what is now Alberta and Alaska. Radiometric data indicate the Alaskan material is about 69.1 million years old.

There is agreement the Pipestone Creek pachyrhinosaur is something “new”. It is currently referred to the Pachyrhinosaurus genus, possibly a as a new species. Whether it is an entirely new genus or a new species of Pachyrhinosaurus is the subject of ongoing investigation and research.

The Alaskan pachyrhinosaur (shown below) skull material appears similar to that from Pipestone Creek, leading to early suggestions of annual pachyrhinosaur and other dinosaur migrations between Alberta and Alaska. However, whereas the Pipestone Creek adult pachyrhinosaurs have 3 prominent humps atop their skull (one over nose and one over each eye), the Alaskan pachyrhinosaur has all three coalesced into one structure .

There is agreement the Pipestone Creek pachyrhinosaur is something "new", but whether it is an entirely new genus or a new species of Pachyrhinosaurus is not agreed upon.

The Pipestone Creek material will also provide crucial details on pachyrhinosaurine evolution.. Pachyrhinosaurus and other animals belonging to the Pachyrhinosaurus-like family are now known from Montana to Northern Alaska. Understanding their relationship requires further research.

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