Abundant Ornithischian Fossils shed light on Late Cretaceous mega-fauna
With the re-examination of many of the lost quarries within the Dinosaur Provincial Park of Alberta more data on the palaeocommunities from this region has been collected. This has provided some intriguing information that may indicate a succession line of ornithischian genera (both ceratopsia and hadrosauridae) and lead to a greater understanding of the type of habitats preferred by many types of dinosaur.
Between 1898 and 1954 nearly 40 large palaeontological expeditions were sent out into the Dinosaur Provincial Park many led by the famous Charles Sternberg and his sons, collecting museum quality specimens for institutions such as the Royal Ontario museum, the American museum of Natural History and the then British museum (London Natural History museum). However, poor and incomplete field documentation as well as incorrectly catalogued field photographs has led to a number of these sites being “lost”. The rapid erosion of the messas and buttes within the local landscape has further complicated the finding of these fossil sites from just the photographic evidence alone.
Researchers from the Royal Tyrrell museum have been playing detective and gathering evidence so that these old quarries can be located and mapped using modern global positioning technology. Re-visiting these sites once they had been found again has yielded more specimens and important micro-fossils, overlooked by the scientists during the first excavations. It is a good job some palaeontologists are untidy, many of the sites have been found again as site rubbish dumps have been located. Dates when expeditions first visited a site have been calculated by studying old newspapers left behind by the original scientists. During the early to mid part of the 20th Century, expeditions would carry bundles of old newspapers with them to wrap fossils. Fragments of newspaper recovered from the dumps and from around old quarries has helped the Royal Tyrrell team to accurately date when these quarries were first explored.
Modern palaeontological techniques have helped produce more finds and the sites have been properly numbered and accurately recorded. This helped provide a clearer picture of the changes in environment and the resulting fauna over the 2 million years or so that the Dinosaur Park Formation represents (believed to cover 76 million – 74 million years ago).
Using this new information and the stratigraphic distribution of ornithischian dinosaurs, a time frame for major genera can be plotted. For example, no Chasmosaurines have been found in the Oldman Formation, but Chasmosaurs have been found in upper Campanian sediments dating from 76 million years ago, with Chasmosaurus russelli being found in the earliest strata with Chasmosaurus belli being found in later strata, indicating a succession. Another ceratopsian group, the Centrosaurines are confined to a zone of sediments about 40 metres deep dating from 76.5 mya to about 75 mya, after this their place in the fossil record seems to be taken by Styracosaurs.
A similar pattern of succession can be seen in the main hadrosaur types around at the time when these sediments were laid down. In earlier sediments, roughly equating to the time of Centrosaurine dominance in the ceratopsia fauna, Corythosaurus genera dominate. These give way to increasing numbers of Lambeosaurs such as Lambeosaurus magnicristatus.
This does not mean that the animals that preceded the later ones are directly ancestral to them, but it might indicate that certain genera were better able to adapt to the changing environment in this part of western North America during the latter stages of the Cretaceous. The Dinosaur Park Formation was deposited in the last stages of the transgressive phase of the Bearpaw cycle. Rising sea-levels would have made the area much more coastal and the climate would have been greatly affected by the encroachment of the sea. Perhaps the Centrosaurs and Corythosaurs were less able to adapt to the changing environment and preferred more inland habitats. This allowed the Styracosaurs and the Lambeosaurs to move in and out compete these other dinosaurs.
Ornithischian Faunal Zones within upper Campanian Stratigraphy of Alberta
74 mya – “Pachyrhinosaurid” – L. magnicristatus – C. irvinensis faunal zone?
Styracosaurus – Lambeosaurus faunal zone C. belli
76 mya – Centrosaurus – Corythosaurus faunal zone C. russelli
78 mya – New Centrosaurus Species No Chasmosaurines found
Ref: Dinosaur Provincial Park (Ecosystem Revealed) – P. J. Currie and E. B Koppelhus