Tracksite Facts and Resources
History
Geology
Clayton Lake State Park and Dinosaur Trackways is located on the Southern High Plains of northeastern New Mexico. Here, erosion of Seneca Creek and its tributaries has cut into the low, rolling and soil/grass-covered high plains surface to expose sedimentary rocks of Early Cretaceous age, about 100 million years old.
When those sedimentary rocks were formed, a seaway extended from the Gulf of Mexico to the Canadian Arctic, and Clayton Lake State Park and Dinosaur Trackways was near or at the western shoreline of that seaway. At Clayton Lake, the succession of rock formations (oldest to youngest) tells the story of the shoreline of the seaway about 100 million years ago:
- Below the dam and the spillway, shale of the Glencairn Formation was deposited on the seafloor. It has fossil shells of marine animals that lived in the seaway.
- As the shoreline retreated to the northeast, river deltas poured into the seaway. The deposits of the deltas and associated beaches became the Mesa Rica Formation.
- As the seaway retreated farther, the delta front moved to the northeast, and river floodplains landward covered the area of Clayton Lake, forming the Pajarito Formation.
- The seaway then advanced to the southwest again. Its new shoreline formed the Romeroville Formation and, when the sea inundated the area of Clayton Lake, rocks of the Graneros Formation were deposited on the seafloor.
The dinosaur tracks at Clayton Lake are in the transition from the Mesa Rica to the Pajarito Formation. These tracks were made near the shoreline of the seaway.
Tracksite Overview
Hundreds of dinosaur tracks and other trace fossils are exposed in the spillway of the dam at Clayton Lake State Park and Dinosaur Trackways. The footprints cover an area of Y on a single surface, which is called the main track surface. A few footprints are also present on three other rock layers exposed at the spillway.
In addition to the dinosaur tracks, invertebrate trace fossils (shallow burrows) and some fossil impressions of plant foliage are preserved on the main track surface. Almost all of the tracks on the main track surface were made by ornithopod dinosaurs, while a much lesser number of tracks were made by theropod dinosaurs, and one trackway made by an ankylosaur (armored dinosaur). These fossils formed on a subtropical seacoast about 100 million years ago.
The dinosaur tracksite at Clayton Lake is managed and interpreted as part of the Clayton Lake State Park and Dinosaur Trackways. Exhibits overlooking the tracksite and a boardwalk with signage around the main track surface facilitate visitor access to and understanding of the tracksite. Some of the tracks from Clayton Lake are on display at the New Mexico Museum of Natural History and Science.
The Tracks and Traces
Invertebrate Trace Fossils
Numerous invertebrate trace fossils are present on the main track surface at Clayton Lake State Park and Dinosaur Trackways. These are four kinds of shallow burrows commonly found in shoreline rock formations:
- Arenicolites are u-shaped tubes made by worms or worm-like organisms. These trace fossils appear as paired, circular openings on the main track surface.
- Planolites are filled tubes parallel or nearly parallel to the main track surface interpreted as the feeding structure of a worm or worm-like organism.
- Taenidium are the most common burrows on the main track surface. They are horizontal tubes with a “meniscate” internal structure interpreted as the feeding structure of an arthropod or worm-like organism.
- Thalassinoides are cylindrical, filled burrows that have y- or t-shaped branching to form networks or polygons on the main track surface. Crustaceans were the makers of these burrows.
These burrows likely indicate a freshwater environment, except Thalassinoides, which typically is formed in shallow marine waters.
Plant Fossils
Some fossilized impressions of plant foliage are present on the main track surface. These represent “leaf litter” of flowering plants that lived around the tracksite and may have been a source of food for the herbivorous ornithopod dinosaurs that made most of the tracks.
Crocodile Tracks
In 1982, in the dam spillway, the lowest layer with tracks contained a few tracks that are little more than near parallel scratch marks made by the digits. These are crocodilian tracks that have been eroded away. Fortunately, a replica of one of these tracks was made and is on display in the Visitor Center at Clayton Lake State Park and Dinosaur Trackways.
Ornithopod Tracks
Most of the dinosaur tracks on the main track surface at Clayton Lake were made by ornithopod dinosaurs similar to Tenontosaurus. These are pes tracks that have three stout, relatively short toes with pointed digit tips and broad, rounded, or squared-off heels. Manus tracks are rare, small subcircular impressions made when the ornithopod touched the ground with part of its forefoot. The range of shapes of the hundreds of ornithopod tracks on the main track surface reflect variable viscosity of the surface walked on and other factors such as the speed of ornithopod walking. Thus, ornithopod tracks range from “cookie cutter” three-toed tracks with clear digits and heels to less well-defined tracks and include those with metatarsal impressions that project backward.
Theropod Tracks
Two kinds of theropod dinosaur tracks on the main track surface were made by two kinds of meat-eating dinosaurs. The smaller tracks are 17-19 cm long and have three very slender digits. They were made by a bird-like ornithomimosaur.
The larger theropod tracks are 38-60 cm long and have relatively short and thick digit imprints. A large theropod like Acrocanthosaurus made these tracks.
Ankylosaur Tracks
On the main track surface, there is only one trackway of a quadrupedal dinosaur. These tracks are rectangular to broadly triangular pes imprints with smaller, crescentic manus prints in front of them. These tracks are those of an ankylosaur.
Additional Resources
Publications
Lucas and Dalman (2016) - The Early Cretaceous Clayton Lake Dinosaur Tracksite, Northeastern New Mexico (Download the PDF)
Lucas et al. (1986) - Cretaceous stratigraphy and biostratigraphy, Clayton Lake State Park, Union County, New Mexico (Download the PDF)
Gillette and Thomas (1985) - Dinosaur tracks in the Dakota Formation (Aptian-Albian) at Clayton Lake State Park, Union County, New Mexico (Download the PDF)
Kvasnak et al. (2021) - Clayton Lake Dinosaur Tracksite Project: Paleontology by Drone (Download the PDF)
Lucas et al. (2021) - The Early Cretaceous Dinosaur Tracksite at Clayton Lake: Overview and Previous Studies (Download the PDF)
Pitula et al. (2021) - Clayton Lake Dinosaur Tracksite – Surface Hydrology Analysis: Establishing a Baseline for Studies of Surface Erosion (Download the PDF)
Rogers et al. (2021) - The Early Cretaceous Dinosaur Tracksite at Clayton Lake: Sedimentological Observations on the Main Track Level (Download the PDF)
Videos
CNM Students Map Dinosaur Tracks (Watch on Vimeo)
Tracksite Walk Through with Spencer Lucas (Watch on YouTube)