The Campanian represents a distinct segment of Earth’s deep past, nestled within the Late Cretaceous Period. This age stands out as a dynamic interval, showcasing a flourishing of life across various ecosystems. It was a time marked by a notable increase in the diversity of many animal groups.
Placing the Campanian in Geologic Time
The Campanian Age spanned a significant period from approximately 83.6 to 72.1 million years ago. It holds a specific place within the broader geologic timescale as the fifth of six ages comprising the Late Cretaceous Epoch. This position means it followed the Santonian Age and directly preceded the final age of the Cretaceous, the Maastrichtian.
Global Environment and Geography
The Campanian Age presented a different Earth than today, characterized by a warm, “greenhouse” climate. While long-term trends show a progressive cooling towards the end of the Campanian and into the subsequent Maastrichtian, polar ice caps were absent during this period. This warmer global temperature contributed to a unique planetary landscape.
A defining feature of the Campanian was the higher global sea levels, which submerged vast continental areas and formed expansive, shallow inland seas. The continents continued their slow drift, gradually moving toward their modern configurations.
The prominent example of these inland seas in North America was the Western Interior Seaway. This immense body of water stretched for over 2,000 miles from the Gulf of Mexico to the Arctic Ocean, reaching widths of up to 600 miles and depths of approximately 2,500 feet. The seaway effectively divided North America into two distinct landmasses: Laramidia to the west and Appalachia to the east.
This vast inland sea influenced the climate and ecosystems of the surrounding landmasses. Its presence moderated temperatures and facilitated distinct evolutionary pathways for terrestrial life on either side. The seaway’s dynamic history, marked by periods of transgression and regression, left behind extensive sedimentary records providing insights into this ancient world.
Dominant Life Forms
The Campanian Age featured a rich array of life, both on land and in the expansive seas. Terrestrial environments were largely defined by the reign of dinosaurs, showcasing great diversity among herbivorous and carnivorous forms. Hadrosaurs, often called duck-billed dinosaurs, were abundant, grazing on available vegetation, while horned dinosaurs, or ceratopsians, were also widespread, likely feeding on mid-sized shrubs.
Apex predators on land included large tyrannosaurids such as Gorgosaurus and Daspletosaurus, which prowled the ancient landscapes of Laramidia, the western landmass of North America. Fossils suggest these carnivores preyed upon the numerous hadrosaurs and ceratopsians. Another tyrannosaur, Tyrannosaurus mcraeensis, a close relative of T. rex, also lived during the Campanian-Maastrichtian boundary, rivaling its famous successor in size.
The skies above were navigated by various pterosaurs, winged reptiles distinct from dinosaurs. These flying creatures, including types like pteranodontids and azhdarchids, exhibited diverse sizes, with some possessing wingspans estimated between 4.3 and 6.5 meters. Their tracks found in places like northern Patagonia indicate their widespread presence across different continents.
Marine ecosystems were dominated by large aquatic reptiles. Mosasaurs, marine lizards, became the apex predators of the warm, shallow inland seas, utilizing double-hinged jaws and flexible skulls to consume prey, including shelled ammonites. Long-necked plesiosaurs, another group of marine reptiles, propelled themselves through the water with four large flippers and were also common inhabitants of these ancient oceans.
Beyond the prominent reptiles, flowering plants, or angiosperms, experienced a proliferation during the Campanian, diversifying and outcompeting gymnosperms in many environments. Small mammals also coexisted with the dinosaurs, represented by diverse groups such as multituberculates and early eutherians, though their fossil record is less extensive.
Notable Fossil Discoveries
Our understanding of the Campanian Age is enriched by fossil discoveries from specific geological formations. These sites serve as windows into the past, preserving not just individual specimens but often entire ancient ecosystems.
Among the renowned is the Dinosaur Park Formation, located in southern Alberta, Canada. This formation, deposited between approximately 76.5 and 74.4 million years ago, is known for its dense concentrations of dinosaur skeletons. Many of these remains are found articulated, meaning they are still connected, and some even retain evidence of soft tissues, offering insights into dinosaur anatomy beyond bone.
The Dinosaur Park Formation represents ancient alluvial and coastal plain environments, where rivers and deltas flowed eastward towards the Western Interior Seaway. Along with numerous dinosaur species, the formation has also yielded abundant fossils of fish, turtles, crocodilians, and various plant remains. This rich assemblage makes the Dinosaur Park Formation, a UNESCO World Heritage Site, a valuable resource for reconstructing Campanian terrestrial communities.
Another important site is the Two Medicine Formation, found in northwestern Montana and southern Alberta. This formation, spanning from about 82.4 to 74.4 million years ago, is known for its bonebeds and well-preserved evidence of dinosaur nesting behaviors. Discoveries here include dinosaur nests, nesting grounds, embryos, and juvenile specimens, offering insights into dinosaur reproduction and growth.
The Two Medicine Formation consists largely of sandstones deposited by rivers and deltas, situated between the ancient Western Interior Seaway and the actively forming Cordilleran Overthrust Belt. The preservation of such detailed ecological data, including evidence of herd behavior in dinosaurs like Maiasaura peeblesorum, highlights the formation’s importance. These fossil-rich deposits collectively demonstrate why the Campanian Age is often described as a “peak of dinosaur diversity” in the Western Interior Basin of North America.