Unique and rare deposits in South Korea provide a glimpse of Cretaceous flowering plant ecosystems
It has been over a month since the closure of the UC Berkeley campus and the UCMP due to the ongoing pandemic. During the shelter-in-place, I have been fortunate enough to be able to continue research from home. Many images of fossils that I am working on at the moment are from a summer 2019 research trip to South Korea. Thanks to the research award I received from UCMP, I was able to do fieldwork in Jinju, a city in the southern part of South Korea, and study specimens at the Korea Geoheritage Institute in Jinju.
I am broadly interested in studying plant-animal interactions during major floral changes in the past. Perhaps one of the most significant periods in the history of terrestrial ecosystems is the rise and diversification of flowering plants during the Cretaceous (145-66 million years ago (Mya)). Flowering plants are dominant in most terrestrial ecosystems, representing approximately 90 percent of all living land plants. However, flowering plants are significantly younger than other major plant groups: the first fossil record of their pollen dates back to the Early Cretaceous (~135 Mya). Compared to the first appearance of land plants (~470 Mya) or the first seed plants (~400 Mya), flowering plants are relatively new members of terrestrial ecosystems. The appearance of flowering plants was followed by their diversification and the concomitant decline of conifers and other gymnosperms during the Aptian-Albian (125-110 Mya). Flowering plants became dominant across a broader range of habitats by end of the Cretaceous (83-66 Mya).
My study site is part of the Jinju Formation (110-106 million years old). It is famous for its rich trace fossils (footprints) of dinosaurs, pterosaurs, crocodiles, lizards, etc., and is recognized as a Lagerstätte (a fossil site exhibiting exceptional preservation and/or diversity). It is also rich in terrestrial and freshwater arthropod body fossils. I am interested in reconstructing the insect and other arthropod community during this unique time period. This formation was deposited during a unique time window of the global Aptian-Albian diversification of flowering plants. However, the Jinju Formation does not hold any flowering plant fossil records, neither pollen nor macrofossils. Comparing the angiosperm-poor Jinju assemblage with nearby older or similar-aged angiosperm-rich Chinese localities with insect fossils, will provide unique insights into Early Cretaceous insect evolution and the role of host plant diversity in insect communities.
During the summer of 2018, after finishing my Bachelor’s degree and before starting my PhD program, I began collecting fossil specimens. Like many other fossil localities, my study site is a construction site for an industrial complex. Rocks at the site were removed from underground and piled up, filling a large area, destined to be used as base flattening material for building construction. After receiving permission from the landlord, I began collecting plant and insect fossils. By the time I wrapped up the field collection season, there were vehicles temporarily unloading construction materials in my sampling area.
With support from the UCMP, I was able to go back to my field site in summer 2019. By that time, the rocks on the surface had been smashed by heavy vehicles and construction materials. However, there were still large slabs of shale that were undamaged when I removed the smaller pieces with a shovel, and I was able to continue field collection and conserve fossil specimens that would otherwise have been destroyed.
Doing fieldwork during the South Korean summer is challenging – daytime temperatures in Jinju are over 80 degrees, occasionally exceeding 90 degrees, with 70-90% humidity. Wearing fully covering clothes while actively working under full sun with high humidity was nearly impossible. Given that my field locality is not at risk of falling rocks from exposed outcrops, I wore eye protection and gloves, with shorts, and worked in the site in the cooler early morning and late afternoon.
During my daily breaks from fieldwork, I assessed specimens in the collections of the Korea Geoheritage Institute, in collaboration with Dr. Kyungsoo Kim. Dr. Kim’s team works on trace fossils of the Jinju Formation. When construction companies find vertebrate fossils while digging up the ground, they are required to contact the local government to report the finding. Then Dr. Kim’s team goes into the construction site, and studies and collects the fossils before the construction resumes. His team has saved many plant and insect fossil specimens over the past years alongside with vertebrate fossils, and he generously let me study the specimens in the collections. I was able to study and photograph the specimens, and it is those images that allow me to continue research during the COVID19 shelter-in-place.
The Jinju project is an important part of my dissertation research. I have gained invaluable experience designing and conducting fieldwork, and made important connections with collaborators, thanks to the UCMP’s funding and support. I will continue collecting in the field and assessing specimens in the Korean museums once the pandemic is over and I look forward to sharing the results of this study.