Ice Age Fossils Discovered in Grande Ronde Valley, January 2010
On a cold mid-January day in 2010 an earthmover operator stripping 5 meters off the top of one of the Pleistocene terrace fragments in the southern Grande Ronde Valley so that the potato farmer who owned the land could move his farm equipment up and down the hillside ran over something white in the brown sand. When he stopped to look, it turned out to be a tibia from a mammoth. Further digging exposed two tusks, an articulated set of vertebrae, and other skeletal fragments. When some of the fragments were reassembled, it turned out that a radius had also been found at the site. The owner of the property generously donated the fossils to the Geology Program at Eastern Oregon University. He has requested that the location of the site be kept confidential.
Leg bones found at the site after the dirt has been cleaned off and the pieces glued back together again. The bone on the right hand side of the left photo is a mammoth tibia (~60 cm long). The bone on the left is the left radius (41 cm long) from a large male giant bison. The photo on the right shows an x-ray of the mammoth tibia made by Dr. Mark Omann of Country Animal Clinic in La Grande. The growth line (near the top) shows that the animal was a juvenile.
Mammoth tusks found at the site. One of the tusks measures 1.25 m from tip to tip and the other is 1 m from tip to tip. Photo on right by April Van Tassell.
Dr. William Orr of the University of Oregon's Thomas Condon Museum of Paleontology thinks that the curvature of the tusks suggests that they came from a mammoth, not a mastodon. Other mammoth fossils that have been found in the Grande Ronde Valley are from the Columbian mammoth Mammuthus columbi (also known as Mammuthus or Elephas washingtonii). It is likely that the new mammoth fossils are from the same species, but we do not know for sure. The small sizes of the tusks and the presence of growth structures in the tibia revealed in an x-ray taken by Dr. Mark Omann of La Grande's Country Animal Clinic suggest that the mammoth is a juvenile. Our best guesstimate based on measurements of the tibia and the tusks is that it was an 18 year old male that was about 3 meters high. The mammoth tusks are hollow—only the outer ivory remains. Because they are so fragile, the mammoth tusks shattered when they were transported and only half of one and the tip of the other are intact. We managed to preserve about half of one of the tusks and the tip of the other.
Only the tip of one mammoth tusk and about half of the other survived transport.
The Grande Ronde Valley Mammoth fossils may be from Columbian, not Woolly, Mammoths (diagram from the Web).
We assumed that the radius came from a mammoth but when we pieced it together and compared it with Columbian mammoth radii, it didn't match. That led us to look at radii of other types of large mammals that are frequently found with mammoths. We now think that the bone is the left radius, with part of the ulna fused to it, of a giant bison. Based on the size of the bone, we think this is from a large male adult bison whose hump was about 2.3 meters above the ground.
Skeleton and reconstruction of the giant bison, Bison latifrons. We this is the species found in the Grande Ronde Valley. Images from the Web.
The seven lumbar vertebrae, the proximal end of a femur and possible tailbone fragments found at the site are too small to be from a mammoth. The femur comes from a short-faced bear (Arctodus simus) that is similar in size to the bears at Rancho La Brea in California. We thought the vertebrae might be from the bear, but now that most of the pieces are back together we are suspicious they are from a giant bison. What we thought were tailbones turn out to be carpals ("wristbones") from the bison. .
The photo on the left, taken by one of the construction workers at the site, shows the vertebrae in the field. The photo on the left shows seven articulated vertebrae and the carpals of a giant bison after they were cleaned and glued back together again, along with the proximal end of the femur of a short-faced bear (Arctotus simus). We still don't know what the bone on the lower right is.
Pictures of what a short-faced bear may have looked like (from the Web). Short-faced bears, also known as megabears, were 1.6 meters high at the shoulder and were not pigeon-toed like modern bears. Some paleontologists think they were top predators, capable of killing saber-tooth tigers and sloths. Others think that they were mainly scavengers. Images from the Web.
Work at the site was shut down and the fossils were covered to protect them until Ann Rogers, an archaeologist with the U.S. Natural Resources Conservation Service in Pendleton, arrived on January 23rd to survey the site for artifacts. No artifacts were found, but while looking for the skull of the mammoth, a contractor's assistant found a lump of soil with a small tooth sticking out. When the soil was removed later, it held an almost complete skeleton of a ground squirrel. We also found a femur from a second ground squirrel. Measurements of the skull of the squirrel suggest that it is a Columbian ground squirrel (Spermophilus columbianus). Beldings ground squirrels are found at the site today, while Columbian ground squirrels are more common along the margins of the Grande Ronde Valley and up in the hills surrounding the valley.
This skull and bones from a Columbian ground squirrel (Spermophilus columbianus) were also discovered at the site (left).
Dr. John Rinehart and his students at Eastern Oregon University working hard to sequence the DNA of the mammoth and the bear, but were unsuccessful. We sent samples of the mammoth tusks out to Geochron Laboratories in Billerica, Massachusetts for radiocarbon dating. The preliminary results suggest that the tusks are ~10,650 +/- 340 radiocarbon years old. This is approximately 12,700 years in calendar years, making them the youngest mammoth fossils from the Grande Ronde Valley and some of the youngest Columbian mammoth fossils in the United States. This is important because it suggests that mammoths lived in the Grande Ronde Valley after the arrival of humans in Oregon ~14,000 years ago suggested by the human feces found near Fort Rock and at or after the impact event that occurred ~12,900 years ago that has been postulated to be the cause of the extinction of the Pleistocene megafauna. We have sent samples to another lab for more radiocarbon dating to confirm this age.
This is not the first time that fossils from the Pleistocene ice ages have been found in the Grande Ronde Valley. Two mammoth teeth were found in 1979 near the plate of the old EOU baseball field. One of these was radiocarbon dated at 15,280 ± 280 years old. In 1964 the skull of the ground sloth Mylodon harlani was found in a gravel quarry south of La Grande. This skull has a radiocarbon age of 11,030 ± 800 years. Other mammoth bones and teeth have also been found on the west side of the Grande Ronde Valley north of La Grande. It is interesting that the ages of the Pleistocene mammals found in the La Grande alluvial fan grow progressively younger toward the outer margin of the fan. This may record the outward growth of the fan into the Grande Ronde Valley.
Mammoth tooth found on Eastern Oregon University campus in 1979 (upper left); proximal end of a mammoth femur found north of La Grande in 1976 (upper right); skull of the ground sloth, Mylodon harlani, found south of La Grande in 1964 (bottom left; and an illustration of a giant Pleistocene ground sloth (bottom left, from the Web).
For the latest on the Airport Lane fossils, click here and scroll down to the issue 8 of Eastern Oregon Geology.