Fossil sites are usually points: a quarry, a cave, a road cut. A place where a few bones turned up and where digging continues carefully. There is one exception of a different scale, and it is in southern Alberta.
In a park of 73.29 square kilometres — an area smaller than many medium-sized cities — 58 different dinosaur species have been identified and more than 500 specimens taken out, today spread across museums around the world. The interesting question is not how many there are, but why they are all there together.
01 The figure and what it means
It is worth putting the number in context. Fifty-eight species is a very high fraction of everything known from the end of the Cretaceous in North America, and it comes from a single park. Across the province at least 38 type specimens were collected, that is, the reference specimens used to define a new species.
The park was established on 27 June 1955 and UNESCO inscribed it as a World Heritage Site on 26 October 1979. It sits in the Red Deer river valley, in a badlands landscape that opens abruptly in the middle of the prairie.
That contrast is part of the story. From the road the plain stays flat right up to the valley rim, and the site is invisible until you are on top of it. What lies beneath the whole prairie is the same; what changes is that here it is exposed.
02 One million seven hundred thousand years
The second figure is the one that impresses most once understood. The exposed sediments belong to three formations: Oldman at the base, Dinosaur Park in the middle and Bearpaw on top. Most of the articulated skeletons come from the middle one.
And that middle formation was laid down between 76.5 and 74.8 million years ago. That is, an interval of one million seven hundred thousand years. Fifty-eight species concentrated in a time window that, on a geological scale, is an instant.
The ground where they were deposited explains the abundance. These were floodplains and coastal plains, crossed by river systems that flowed east and south-east. A river that floods regularly buries what lies on its plain quickly, and quick burial is the condition for anything to fossilise.
03 The gash that opened it all
What was missing was bringing it to light, and the ice took care of that. At the end of the last glaciation, when the Laurentide ice sheet retreated, enormous quantities of meltwater were released at once and cut rapid channels into the plain. That was some 13,000 years ago.
Those gashes cut through the soft Late Cretaceous rock that forms the bedrock of southern Alberta and left very steep valley walls. The badlands of the Red Deer valley reach 200 metres deep and flank the river for some 300 kilometres.
Without that episode, all the bone would still be under the prairie. The site does not exist because there were more dinosaurs there than elsewhere: it exists because there the meltwater opened a 300-kilometre window into the layer that holds them.
04 Half a centimetre a year
And here is the mechanism that keeps it alive. The average erosion of Alberta's badlands is around 0.5 centimetres a year, and in the Red Deer valley 1 to 2 centimetres a year have been measured. That is an enormous figure for a rocky landscape.
The comparison makes it clear: it is roughly a thousand times the erosion rate of the Rocky Mountains. The rock is soft, there is no vegetation holding it and rain and ice break it down without resistance.
The consequence is that the site renews itself. Each season, erosion brings to the surface material that was buried the year before, and the teams working there do not dig blind: they walk the ground looking for what has just appeared.
05 Five hundred specimens spread around the world
The record of removals explains something that surprises visitors. More than 500 specimens have been taken from the park and are displayed in museums across the planet: the Royal Ontario Museum in Toronto, the Canadian Museum of Nature in Ottawa, the American Museum of Natural History in New York, the Field Museum in Chicago.
That was the pattern above all before 1985. That year the Royal Tyrrell Museum opened nearby, and since then much of the material stays in the province. It is an important change for the traveller: today you can see the site and the finds without crossing an ocean.
The earlier dispersal, by contrast, is the reason this park was for a century a familiar name in museums across half the world and almost unknown as a destination.
06 How to look at it
The first practical consequence is not to go looking for bones. Access to most of the ground is restricted precisely because material appears continuously and a footstep in the wrong place destroys a specimen. What you can walk freely is a fraction of the park.
The second is that the landscape reads better in low-angle light. First thing or last, the horizontal layers on the slopes pick up shadow and you can tell the three superimposed formations apart: Oldman at the bottom, Dinosaur Park in the middle, Bearpaw on top.
And the third is the one that changes how you look. What you see there is not an exceptional graveyard: it is an ordinary layer of southern Alberta that happens to be cut open. Beneath the prairie surrounding the park lies the same thing, intact and unseen, waiting for water to open another window.
