Bruce MacFadden and John Turner talk about possible localities. Photo by Karen Schmidt
Today, we returned to do field work at Lago Alajuela where we had our first field work experience a week ago. After a succulent breakfast, we headed to the field more confident and excited about this field experience. On our bumpy ride to the Lake we stopped by the Madden Lake dam and took some pictures of the scenery.
The goals for today’s expedition were to find invertebrates fossils on the limestone bedrock cap of Lake Alajuela; to search for fossilized wood as well as collect sediment samples and other vertebrate fossils. The group was divided in smaller groups. Dr. McFadden led the group that decided to do the cracking of rock and the postdoctoral fellow, Nathan Jud, led the group looking for fossilized wood. Other participants led by Dr. Gary Morgan searched for vertebrate fossils and others decided to look for more shark teeth, the most popular fossil so far!
Despite the brutal heat, this field experience was successful! The group that cracked rocks was exhausted but found lots of small invertebrates, razer clams, snails, scallops, oysters and barnacles. Nathan got distracted in the forest as he examined the plants in the location but finally was able to collect multiple samples of fossilized wood with the help of one of the participants, Erin who has developed a special interest on fossil wood.
Another group led by Ian Cannon, collected samples of sediment from different areas that will be screen washed and examined for microfossils. Other particpants found shark teeth, crocodile teeth and turtle bones.
With Gina’s help, I learned how to catalogue the fossils. When you find a fossil, you need to record the coordinates of the site it was found using a GPS. Then, using toilet paper the fossil is carefully wrapped and protected as it travels and is transferred to the STRI facility. This wrapped fossil is placed in a plastic bag and the following information is recorded on the bag: location, date, coordinates, name of person that collected the fossil, name of organism and size. For example, I found a fossil of a scallop. The following information was recorded on the bag:
Lake Alajuela, invertebrate (scallop), 2 cm in diameter, 7/27/2015, coordinates(N 09.21202, W079.59325
Finally, on a field notebook, the context of the rock in which you found the fossil (lithology), is recorded. You may include the features of the rock, such as texture, color, size and how round the rocks are. It is preferable to use quantitative data.
After a successful expedition we traveled to the NAOS center, another facility of the STRI for research of marine organisms.
We met the archaeologist, Dr. Richard Cooke. At the archaeology lab we first went to the fish facility. Dr. Cooke discussed the abundance of different
species of fish in archaeological sites in Panama. We moved to another room with samples of arrow-like tools, a fossil of a possum, a bone from a crocodile. Dr. Cooke also shared his work with a miniature deer found in the Pearl Islands of Panama.
As I listened to Dr. Cooke, I made connections between the work that scientists do in different areas like paleontology and archaeology. In the facility, there were magnifying lenses to make observations of the sub fossils; the graduate student shared evidence to support the explanation about the miniature deer; and collaboration with scientists of other places like Colombia was mentioned in various occasions. But the most memorable part of the visit to the NAOS facility was to see the passion with which Dr. Cooke still shares so many anecdotes of his years in the archaeology field!
To end the day, Elizabeth led the pool chat for our daily reflection and to discuss the review article: The closure history of the Central American seaway: evidence from isotopes and fossils to models and molecules (Schmidt, 2007).
The group working in the limestone bedrock formation found a lot of very small invertebrates. These fossils point to the existence of a habitat dominated by two or three species, meaning this environment had less biodiversity than the Gatun formation we visited last week. At this moment it is difficult to provide an explanation for this difference in biodiversity.
Lots of samples of fossilized wood we found. The next step will be to identify the species found. Many of the samples of fossil wood were rounded indicating that these samples were transported from another area. This observation brings concerns about the time of the specimens as they could be older wood transported to the lake. This experience allowed us, the teachers of the GABI Ret program, to recognize a search image to find fossilized wood.
Dr. Jud briefly explained the process used to prepare fossilized wood for observation. Three views are needed: a cross section, a tangential section and a radial section. Using these views, scientists can identify the cellular features and organization which can be helpful in paleoclimatic studies.
The significance of the invertebrates fossils was also discussed. Many vertebrates fossils and shark teeth have been found at Lake Alajuela but no invertebrates fossils have been collected. In situ collection of invertebrates fossils provide evidence of the time context of the different layers found at Lake Alajuela as well as support to the uplift explanation.
Maggie shared that this article was a great review to understand all the factors and evidence that have been gathered to understand the events that led to the closure of the isthmus of Panama and further explained the AHA moment she experienced at the BioMuseo visit on Sunday when she saw the modeling of the closure of the isthmus of Panama.
Karen shared that many other events happened as the result of this closure, for example glaciation. Dr. Amanda Waite will further discuss these events with emphasis on the ocean current studies on Wednesday at the CTPA Paleo Talk.
Jessica asked about other alternate theories for the glaciation event. Dr. Waite mentioned that the rising of the West Indies is a possible theory but it is still not well studied.
Mayra inquired about the closure of other seaways as models of the isthmus of Panama closure. Dr. Waite explained that there is analogy with the Indonesian seaway closure in terms of land speciation but not in terms of global ocean circulation patterns.
Erin asked about the insular effect mentioned in the review. Dr. McFadden explained that this effect involves the phenomenon of having large animals become small and small animals become larger. Evidence from La Cucaracha formation supports a peninsula formation but no insular effect because there were no differences in the sizes of the animals found.
Finally, Elizabeth shared that this review article “connects the dots to allow us to see the big picture”. Dr. Waite reiterated that this article was a good example of the wealth of data existent to explain the closure of the isthmus of Panama.