72 million years ago: Kremmling Cretaceous Ammonite Locality takes trekkers into the past
August 11, 2008
Before the Rocky Mountains rose to touch the sky, a vast inland sea stretching from the Arctic to the Gulf of Mexico covered much of North America, including what would become Colorado’s Grand County. And in that primeval sea lived a species of odd-looking creatures that were half-giant snail and half-squid that scientists now call ammonites.
The ammonites were marine predators that hunted, reproduced, died and eventually became extinct 72 million years ago in that long-ago sea. The only thing that remains of them today is their fossilized bodies.
Last Saturday, about 25 local residents, tourists and fossil-lovers from around the region went in search of these prehistoric creatures during this summer’s Ammonite Trek organized by Frank Rupp, staff archaeologist at the Kremmling Field Office of the Bureau of Land Management (BLM). The trek was led by Dr. Emmett Evanoff, a professor of paleontology at the University of Northern Colorado (UNC) in Greeley, and Katie DeBell, a UNC geology student who lives in Kremmling.
The trek took the fossil hunters to the Kremmling Cretaceous Ammonite Locality (KCAL), which is famous among paleontologists and other fossil lovers because it has the highest concentration of those prehistoric marine animals to be found anywhere in the world. The present-day site is a high, sagebrush covered ridge about 10 miles north of Kremmling.
Bottom of the sea
“It’s hard to wrap your head around a figure like 72 million years ago and that this was the bottom of a sea then,” Rupp said after arriving at the KCAL with the trekkers Saturday. “But the Ammonites and other marine life thrived here at that time.”
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After a short but heart-pounding hike up the KCAL’s steep ridge, it quickly became apparent why this site is such a fossil-hunter’s dream. Scattered everywhere were the fossils of several large clams, followed by a string of ammonite fossils that trailed along the crescent-shaped ridge.
“About a hundred different marine species have been found here,” Dr. Evanoff said. “Clams, snails, brachiopods, crabs, gastropods and fish, along with four or five types of ammonites. This was a marine rich environment during the Cretaceous Period.”
The ammonite fossils at the KCAL are easy to spot. Found in sandstone slabs and outcroppings along the ridge, the fossils are almost circular depressions or “molds.” These molds, many as large as two feet in diameter, were made the ammonite’s curving outer shell, which is similar to today’s Nautilus.
In life, the creature had several tentacles like an octopus or squid which it could use to grasp its prey, but these fleshy parts did not survive the fossilization process.
“Bird baths” are the nickname that researchers at the KCAL have dubbed the ammonite fossils because the ones that lie horizontally easily catch rainwater. During Saturday’s trek, a few of the ammonite “bird baths” still held puddles of water from recent storms.
Mapping the ammonites
During the examination of the fossils by the trekkers, DeBell, the UNC geology student, told them that she is in the final stages of the GPS mapping of all the ammonite fossils within the KCAL as part of an internship project that she was doing for Evanoff. She has already found a total of 297 of the fossilized animals at the site, which is the first complete scientific mapping of the site.
She is also photographing the ammonites for the BLM’s Denver office, which wants to eventually place 3-D images of the KCAL’s ammonites on the Goggle Earth Web site.
“What’s really neat about this site is that it’s the only place in the world that we have this large a number of exposed ammonite fossils and in such density,” DeBell said.
Along with her cataloging of the ammonite fossils, DeBell discovered that the ratio between ammonite females and males at the site is 13 to 1. The large number of females, which are easily identified because they are four times larger than the male, has helped bolster an alternative theory by Dr. Evanoff that attempts to explain the mystery of why so many ammonites are found at that one place.
The conventional theory advanced by most paleontologists is that a “catastrophic event” took place 72 million years ago at the Kremmling site. A major hurricane or tidal surge drove the thousands of ammonites onto a sandbar where they died, became buried under sediment and eventually became fossilized.
Dr. Evanoff rejects that theory, arguing that there is no evidence of the “stacking” of the animals and other debris that would have been caused by a violent catastrophic storm. Instead, he points out that the fossils are found more spread out along the site.
Evanoff’s alternate theory is that the KCAL is was an ammonite “brooding ground” where the adult females came to lay their eggs and then died.
“That 13 to 1, female-to-male ratio suggests this was not a catastrophic event,” he said. “When we were digging up some of the ammonites, the lower sides are complete while the upper sides of the shells have been chipped away by marine scavengers. What this suggests to me is that this was a brooding ground where the ammonites, who probably mated only once in their lives and then died like modern squids and octopus, came here to lay their eggs in the sandy bottom. The females probably guarded their egg clutches until they fell over on their sides and died.”
After some preliminary scavenging by marine creatures, the dead ammonites were covered by sediments carried by the sea currents as well as the outflow of a prehistoric river delta that originated from a landmass near present-day Craig.
Whether Evanoff’s theory is correct or another explanation is finally found will be the work of future paleontologists and scientists. To insure that the ammonites are still there for their research purposes is a major reason why the 200-acre KCAL site was established in 1983.
“We set aside the KCAL for future scientific research as well as public enjoyment,” Rupp said. “We needed to preserve it for the future.”
Rupp explained the Kremmling ammonite site has been well known since the 1930s, and private individuals were allowed to collect fossils there by the BLM for years.
However, that changed in the early 1980s when a commercial fossil-prospecting company came in and attempted to loot the site. Rupp, Evanoff and other researchers pushed to have the KCAL established and have it designated an Area of Critcal Environmental Concern by the federal government.
Today, the KCAL site is fenced off with a gate and interpretative signs. The public is welcome to visit the site at no charge, but fossil collecting inside it is strictly forbidden. Rupp explained that fossil collectors and the general public are welcome to prospect and collect a reasonable number of fossils outside the site.
For more information about KCAL, contact Rupp at the BLM’s Kremmling Field Office at 2103 East Park Ave. (U.S. Highway 40) or call 724-3000.