Bryozoan Fauna of the Lake Valley Formation (Mississippian), New Mexico
By: Andrej Ernst, Karl Krainer, Spencer G. Lucas
Summarized by: Johnathan Cook. Johnathan Cook is a fourth-year undergraduate at the University of South Florida. He spent most of his life involved in missionary work overseas in Argentina. After graduating from an Argentine high school, he returned to the United States to receive his Associates Degree from Hillsborough Community College before transferring the University of South Florida. He is set to graduate in December of 2019 and plans to pursue a career in hydrogeology and water management.
What data were used? Bryozoans (aquatic colonial organisms that survived by filtering nutrients from the water they live in) that had been overlooked in previous studies of the Mississippian-age Lake Valley Formation were re-examined by researchers. They also took a fresh look at the environment they were found in to help gain a better understanding of past climate and how the environment has changed through time. Researchers also looked at the type of sediment and the size of the grains to determine the prevalent geologic processes at the time of its deposition.
Methods: The researchers examined the layers (also called members) of the Lake Valley Formation, noting sedimentary structures and characteristics. Bryozoans specimens were made into thin sections and studied through binocular microscopes to determine the genus and species of each specimen found (which is the only accurate way to determine bryozoan taxonomy).
Results: The study of this area found there to be ten species of Bryozoa in the rock record, one of which had been previously overlooked. The studied samples were taken from two members of the formation and indicate changes in the environment. The older layer, named the Andrecito Member, showed deep marine conditions which were quiet and calm, while the younger layer, named the Tierra Blanca Member, showed shallower conditions with higher energy. The characteristics of these two members are good indicators of environmental conditions present during their creation. The deep conditions of the Andrecito member suggest transgression (meaning sea level was high or rising) and the shallow conditions of the Tierra Blanca suggest regression or sea level falling. The species found in these environments demonstrated physical characteristics in support of this hypothesis. Bryozoans in the calmer environment had thinner branches, whereas those in higher energy were thicker.
measuring the spacing between structures-the zoaria (individual animals in a single colony) in the bryozoan fossil specimens. This was done under the microscope, as these measurements are quite small.
Why is this study important? This study shows further diversification of a fossil type thought to be well understood, as well as the importance of understanding the stratigraphy in combination with fossils to construct a picture of the processes that formed our continent. These specific species are endemic to North America and can give us an idea of the evolution of climate and its effect on North American rocks.
The Big Picture: The discovery of the diverse fossils along with the sedimentary layers provides a reminder that science is not infallible but often misses details that can alter our understanding or hypotheses of past life. How creatures adapt says a lot about the environment they inhabited and with every new data, we can create a clear and more accurate picture of the past. It is important to remember that a hypothesis is not set in stone but can be edited or even disproved as more data are collected.
Citation: Andrej Ernst, Karl Krainer, Spencer G Lucas. Bryozoan Fauna of the Lake Valley Formation (Mississippian), New Mexico. Journal of Paleontology, 92(4), 2018, p. 577–595.