Stan the T. rex

Actual skull of STAN, now considered to be the second most complete T. rex ever found.

REPORT FROM REXBERG
THE TYRANNOSAURUS REX CAPITAL OF THE WORLD

by Paul R. Janke

Amateur fossil hunter Steve Sacrison was on a fossil walkabout in searing 100+ degree heat when he noticed a small patch of ground that seemed to reflect the afternoon sunlight in a slightly unusual way. He kneeled down for a closer look and found a few loose chunks of weathering bone next to the small patch. A quick look at the structure in one of the larger bone chunks and he immediately knew it was T. rex. Pete Larson of the Black Hills Institute of Geological Research (BHIGR) soon confirmed his discovery. The small patch that caught Steve's eye turned out to be the bone surface of a nearly complete femur, still mostly buried in the siltstone, mudstone and ironstone of the Hell Creek Formation.

Finding T. rex fossils used to be a rare event. Thanks to the efforts of some dedicated amateurs, they're now being found all over the place. Especially if the place is near Harding County, South Dakota. The area around the town of Buffalo has produced so many (6 new specimens in the last 8 years) that it has become the T. rex capital of the world. Researchers are using these new finds to re-write the book on T. rex as each new site and every new bone adds to our growing knowledge of this most famous dinosaur.

The high number of recent discoveries near Buffalo can be attributed in part to the excellent exposures of the Hell Creek Formation in the surrounding badlands. However, what really sets this area apart from similar Hell Creek localities is the superb job done by amateurs in locating new sites. Twin brothers Stan and Steve Sacrison are persistent, experienced fossil hunters. They have already found 3 major T. rex specimens near their home town of Buffalo. It's a testimony to amateur dedication when two brothers from South Dakota account for around 15% of the entire known inventory of T. rex bone. Stan Sacrison is the discoverer of Stan and Duffy, while brother Steve found his namesake Steven.

Amateur fossil hunter Stan Sacrison, the discoverer of 2 T.rex! (STAN and Duffy)

I had the opportunity to do some fieldwork and digging at these sites in August, 1995, right after Steven was discovered. Our camp area is affectionately referred to as "Rexberg". The sites for Stan, Duffy, and Steven are all within a mile of camp. These digsites are managed by scientists from the BHIGR who run a paleo lab and non-profit natural history museum in Hill City, SD. The game plan was to begin documenting and then digging at the Steven site and also do some follow-up work at the Stan and Duffy sites.

The fieldwork on Steven began with a meticulous surface examination. We spent several days bagging and labelling every piece of bone on the surface. We took lots of pictures and videos, screened for small fossil fragments and explored downhill for pieces of bone that may have washed down from the site. Excitement almost reached a fever pitch when fossil eggshell fragments were spotted by Leon "the eggman goo goo goo joob" Theisen. Based on their curvature, these fragments came from an original egg measuring around 20 x 8 inches. They display a telltale knobby texture with pores and were found in direct association with the main group of Steven bones. Bob Farrar of the BHIGR described these fragments as "definitely matching Chinese theropod eggshell". They most likely represent the first T. rex egg fossils ever found in the Hell Creek Fm. We started to speculate about possible T. rex nesting grounds and considered the option of changing the specimen name from Steven to Stevie!

Along with the surface analysis, a grid was set up so the bones could be mapped in context as we began to dig. In the week I was on site we uncovered several ribs and vertebrae along with the femur. The bones seem to continue under a small hill, which won't be opened up until next field season. There are two things you learn about the T. rex fossils of Harding County: 1) they're all over the place, and 2) when you find one, it's all over the place. Often the remains cover a wide area surrounding the main group of bones. It will be a while before we know just how much of Steven's skeleton has been preserved.

My first visit to the Stan site turned up a nice surprise as well. Spring rains had neatly uncovered a gastralia (almost certainly from Stan) which Neal Larson of the BHIGR instantly recognized. This is one of the reasons that you have to keep visiting sites periodically. The forces of weathering are steady and unforgiving. Freeze/thaw cycles, wind, plant roots and especially "gully-washer" rainstorms constantly attack fossil treasures and turn them into dust. Thanks to the innovative field techniques of the BHIGR and assistance of amateurs, Stan is now considered to be the second most complete T. rex ever found.

Work on the Duffy site may have been the most interesting of all. Several days of digging saw the discovery of 4 new whole teeth, complete with roots, along with quite a bit of well preserved skull material. These finds were made more than 50 feet away from the main bone concentration, outside the radius that scientists usually explore. It really got me wondering about the other T. rex specimens found earlier this century. I'd be willing to wager that a lot more skeletal material could be found at those sites if they had the same amateur involvement and used the same field techniques as the BHIGR scientists.

The T. rex of Harding County were some of the last dinosaurs to walk the earth. The Cretaceous/Tertiary(K/T) boundary defines the end of the age of dinosaurs. This boundary is evident near the tops of many of the taller buttes in the Buffalo area, where bright white Paleocene sediments overlay a dark black layer of Cretaceous coal. The actual boundary is near the middle of the coal layer at the Rexberg locality. Although no distinctive boundary clay is present here, the abrupt pollen changes and iridium/siderophile anomalies characteristic of K/T sections worldwide have been documented. The boundary is a just a short climb (less than 100 feet) up from the Stan and Duffy sites, while Steven appears to rest even closer to the boundary. These three animals do not appear to have been contemporaries back in the Cretaceous. Stratigraphy indicates they were separated in time by perhaps a few thousand years.

I would like to give special thanks to Pete and Neal Larson, Bob Farrar and Terry Wentz of the BHIGR for sharing their expertise and knowledge with me both in the field and back at the lab. Their mounted T. rex specimens along with their famous collection of beautiful fossils are on display at the Black Hills Museum of Natural History in Hill City, SD. This team of dinosaur experts is lifting T. rex science to new heights. The specimens found, excavated and prepared by the BHIGR are widely renowned for what they have revealed about behavior, pathology, taphonomy, anatomy, sexual dimorphism and even possible cannibalism! Future reports from Rexberg will examine Stan, Duffy and Steven in more detail to see how in spite of their similarities, each individual has its own story to tell.

Pete and Neal Larson working at the STAN site.

Sites managed by the Black Hills Institute receive hundreds of visitors.

A young student discovers the serrations on a T. rex tooth.

Overview of the STAN site.