Follow Seismosaurusto the museum

On August 1, 2004, tracks of Seismosaurus led visitors from the intersection of Rio Grande Boulevard and Mountain Road east to 18th Street and then to the museum's front door. These tracks were based on real-life trackways of sauropod dinosaurs like Seismosaurus. Fossil footprints have their own set of names, so the tracks painted on the above city streets are technically called Brontopodus. Museum scientists took published studies of Brontopodustracks and scaled them up to match Seismosaurus. All four feet of Seismosauruswould make tracks---the forefeet (manus, or "hand") make relatively small impressions, and the larger tracks are from the hind feet (pes, or "foot"). Covering almost 10 feet (3 m) with every stride, it would have taken Seismosaurusapproximately 230 strides with each foot to reach the museum from Rio Grande Boulevard.

Illustration modified from Figure 5.2a in Lockley, M.G., Tracking Dinosaurs: A new look at an ancient world. Cambridge University Press, Cambridge, 238 pp.

During their 160-million-year-long reign, dinosaurs made trillions of footprints, but only a small percentage of these footprints found their way into the fossil record.

In New Mexico, the oldest dinosaur footprints known come from 210-million-year-old rocks south of Tucumcari in Quay County. These are the footprints of small, meat-eating dinosaurs such as Rioarribasaurus. The only Jurassic dinosaur footprints from New Mexico are two tracks of a larger meat eater (probably an Allosaurus) found just south of Las Vegas in San Miguel County.

New Mexico's youngest dinosaur tracks are of duckbill dinosaurs and were found near Bisti, south of Farmington in San Juan County. These tracks are of Late Cretaceous age, about 70 million years old. New Mexico's most extensive dinosaur footprints come from Early Cretaceous (about 100 million years old) rocks at Clayton Lake and vicinity in Union and Harding counties.

These tracks are most easily seen at Clayton Lake State Park, where as many as 500 footprints are preserved in the spillway of the dam! Primitive ornithopod dinosaurs, the iguanodonts, made most of the tracks at Clayton Lake. These are the three-toed footprints of animals that either walked bipedally, or occasionally leaned forward to walk on all fours. They are easily recognized because of their square heels and lack of claw marks. In contrast, a few footprints at Clayton Lake are those of theropods, meat-eating dinosaurs. They are easily recognized by their pointed heels and sharp, clawed toes.

The Clayton tracks teach us something very important about dinosaur evolution in North America during the Cretaceous. Prior to 100 million years ago, the sauropod dinosaurs (brontosaurs of popular terminology) were the dominant dinosaurian plant eaters. Early Cretaceous footprint sites throughout Texas, Oklahoma and Arkansas were trampled by sauropods. But, at Clayton Lake and at other dinosaur tracksites of the same geologic age in northeastern New Mexico, Oklahoma and Colorado, there isn't a single sauropod footprint! Instead, the Footprints suggest ornithopods were the most abundant and conspicuous plant eaters.

This disappearance of sauropods appears to have been a real extinction of these dinosaurs in North America about 100 million years ago. After their disappearance, sauropod fossils (footprints or bones) are not found again in North America until about 70 million years ago, almost at the end of the Cretaceous. The last of the North American sauropods is Alamosaurus, originally discovered in the San Juan Basin of northwestern New Mexico and named for Ojo Alamo, a spring south of Farmington. Alamosaurus is the spitting image of South American sauropods, the titanosaurids, that thrived on the southern continent throughout the Cretaceous.

Clearly, Alamosaurus represents an immigrant from South to North America near the end of the Cretaceous. The 30-million-year-long absence of sauropod dinosaurs in North America, from 100 to 70 million years ago, has been called the "sauropod hiatus." The fossil footprints at Clayton Lake played a key role in identifying this important event in the evolutionary history of dinosaurs.

The public can view dinosaur footprints in their natural state at very few places in the United States. Clayton Lake State Park is one of these few places. Clayton is located in the extreme northeastern corner of New Mexico, but is only five or six hours by car from Albuquerque. Clayton State Park is a few miles north of Clayton. At the Park, you can walk among the dinosaur tracks and learn about them from educational labels and exhibits. The remarkable dinosaur tracksite at Clayton Lake State Park truly makes Clayton the "dinosaur track capital of New Mexico." For more information, contact Clayton Lake State Park at Rural Route, Box 20, Seneca, NM 88437 or by telephone at 505/374-8808.

Dr. Spencer G. Lucas
Curator of Paleontology
Email:  Dr. Spencer Lucas

FURTHER READING

Gillette, D. D. and Thomas, D. A. 1985. "Dinosaur tracks in the Dakota Formation (Aptian-Albian) at Clayton Lake State Park, Union County, New Mexico": New Mexico Geological Society, Guidebook to 36th Field Conference, pp. 283-288.

Lockley, M. G. and Hunt, A. P. 1995. Dinosaur tracks and other fossil footprints of the western United States. New York, Columbia University Press, 338 pp.

Lucas, S. G. 1993. Dinosaurs of New Mexico. Albuquerque, New Mexico Academy of Science, 130 pp.