Small bird and mammal tracks from a mid-Cenozoic volcanic province in Southern Colorado: implications for paleobiology
Lockley, M. G., Goodell, Z., Evaskovich, J., Krall, A., Schumacher, B. A., and Romilio, A.
Summarized by Brysen Pierce, a geology major, working on Geographic Information Systems and Technology, as well as environmental science and policy minors. Currently, he is a senior who has not decided what to do for his career path. When he is not studying geology, he enjoys watching movies and hiking.
What was the hypothesis being tested? Several fossilized animal tracks have been discovered in Rio Grande National Park (Colorado, USA). After locating samples containing tracks near the first site, the authors hypothesized that since there was already one set of tracks located, there could be others nearby in a similar geologic setting. The purpose of this study was to define the tracks and identify what kind of creatures may have made them.
What data were used? Samples were collected from the field and analyzed. The source of the data was in southwestern Colorado in the San Juan Volcanic Field and from a smaller site in New Mexico. At the first site, there were two tracks that indicated two different birds and another unfinished track, which contained small prints that did not follow a distinct trail or were not able to be identified. The second site had four completed tracks that were left by birds and mammal traces that formed another track and there were some more traces that did not complete tracks.
Methods: The tracks were found close to fifty meters apart from each other in two different locations. The tracks were preserved in a piece of a volcanic block, which had since been moved from its original position; once the rock had been moved, it became exposed. A volcanic block is a piece of a solidified fragment that has been ejected thrown from a volcano by an eruption and is measured to be larger than sixty-four millimeters in diameter. Since these trace fossils were the first of their kind that have been recorded in this type of volcanic environment, researchers wanted to expand on this topic. From here, the scientists were able to collect samples and take casts so that they could do measurements of the prints and better analyze the trace fossils and define what they could have been from.
Results: Three total samples were collected or casted and brought to museums to study. Three species were identified in this study: two of them were bird species and the last was a species of mammal related to modern day rodents. The birds were some of the smallest found in the fossil record and have relations to creatures like the sandpiper whose habitat is shorelines. Some tracks were not easily identifiable because they are incomplete. The bird tracks in this area were identified Avipeda circumontis named after the region it was found in and the mammal tracks are Musvesigium minutus whose name means small mouse footprints. Both species share similarities between other closely related species that are found in the western United States, which makes identification of the species difficult.
Why is this study important? This study is important because it shows us that trace fossils can be found in a volcanic setting, which has previously been unreported. The study shows us what kind of species lived in this area during the mid-Cenozoic and could provide additional information about an environment that has not been preserved in the past with fossils. New types of trace fossils were identified in a setting that previously had produced no fossils. We learned that not only small birds, but also small mammals, once lived in the volcanic province of south Colorado.
Broader Implications beyond this study: Since this is the first study that has described animal tracks found preserved in volcaniclastic setting, this could lead to other discoveries within similar environments in the geologic record . There is a lot to learn from sites like this because the species that the footprints were left by were previously undiscovered. The bird and mammal fossil tracks found here could be unique to this setting, but this means that tracks are able to be preserved in this type of environment and that the animals were, in fact, leaving evidence behind.
Citation: Lockley, M. G., Goodell, Z., Evaskovich, J., Krall, A., Schumacher, B. A., & Romilio, A. (2022). Small bird and mammal tracks from a mid-Cenozoic volcanic province in Southern Colorado: implications for palaeobiology. Historical Biology, 34, 130-140.