Fossil Friday 12/18/15: An extinct carcharhiniform shark

UF 262186, a lower tooth of Physogaleus contortus. Photo VP FLMNH.

UF 262186, a lower tooth of Physogaleus contortus. Photo © VP FLMNH.

This week’s Fossil Friday feature is the tooth of an extinct species of shark called Physogaleus contortus. This specimen was found in the Las Cascadas locality of the Culebra Formation and is early Miocene in age. This shark had a widespread distribution during the middle Miocene.

To learn more about this specimen, read the publication that includes it here.

Reference:

Pimiento C., Gonzalez G., Hendy A., Jaramillo C., MacFadden B.J., Montes C., Suarez S.C., Shippritt M. 2013. Early Miocene chondrichthyans from the Culebra Formation, Panama: A window into marine vertebrate faunas before closure of the Central American Seaway. Journal of South American Earth Sciences 42: 159-170
www.dx.doi.org/10.1016/j.jsames.2012.11.005.

Fossil Friday 12/11/15: a Springvale Cup and Saucer Limpet

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UF 214431, a Springvale cup and saucer limpet. (Photo © IVP FLMNH).

This week’s Fossil Friday is the Springvale cup and saucer limpet, Crucibulum springvaleense. This specimen was collected from the Gatún Formation and the mollusc that inhabited it would have been found filter-feeding while attached to rocks in Late Miocene oceans. Although this mollusc looks similar to a limpet, it is not a true limpet and is not closely related.

Studying Panama’s Microfossils

Hello from the lab!

While I spend most of my time in the field looking for new fossils, I also have the opportunity to work on original research while I am working with the PCP-PIRE project. I have previously worked with microfossils, specifically ostracods, so I decided to look at the types of ostracods preserved in the Canal deposits.

In particular, I am looking at the ostracods from the new locality we discovered two weeks ago that is full of gastropods and bivalves. When we returned to the site, I discovered nummulites, which led me to believe that foraminifera and ostracods would be present in the deposit as well. However, these fossils require a microscope to see in detail. I collected four sample bags of sediment from different rock layers in the outcrop, and returned to the lab to process them.

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The new invertebrate locality, in which I am searching for microfossils.

Another intern at the Smithsonian Center for Paleoecology and Archaeology, Andrés Ríos, also studies fossil ostracods, and helped me prepare the sediment to view under the microscope. We used a dilution of hydrogen peroxide to disaggregate the rock. Andrés sieved the sediment into different grain sizes and let the sediment dry in the lab’s drying oven.

Under the microscope, I use a small paint brush to sift through the grains to locate ostracod individuals and place them on a microfossil slide. Though I have only just begun going through the sediment samples, I have found several types of ostracods, both juveniles and adults. The following ostracods are from a portion of one sediment sample I collected.

I will continue to comb through my sediment samples in search of ostracods, and then work on identifying all the different genera present in the new outcrop. With this information, we will be able to identify the type of environment in which the locality was deposited–whether it was marine, brackish, or freshwater–as well as its relative age based on the microfossil biostratigraphy. I’m looking forward to learning more about this new site based on these minuscule fossils!

-Dipa Desai

New Fossil Finds at Puente Centenario

This week we had an exciting time in the field, specifically at our site under Puente Centenario. Under the shadow of the bridge and nestled among tall stands of elephant grass lies a locality deposited there some 14 to 17 million years ago. These fluvial deposits contain the remains of Panama’s Miocene animals and plants: The ancient river or stream carried teeth, bones, leaves, and other remnants, then gently buried them in sediment. After millions of years entrapped in the rock, these fossils are exhumed by our field team.

Our first excursion to this site yielded several teeth from crocodiles, fish, and even one carnivore molar.

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My field supervisor, Jorge Moreno, suspects this is a carnassial molar. 

Teeth are common finds in the field because they are composed of durable enamel that preserves well over time. The enamel also lends a sheen to the fossil which makes it easy to pick out among the dark pebbles and sediment. The color of the fossil tooth is not white, as it was when the animal was alive. When the tooth gets buried, minerals in the surrounding water infiltrate the porous bone and replace the original material, resulting in a darker color.

As our field day was ending, I brushed around the area where I collected the carnassial molar and found something surprising.

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An unknown large bone peeking out from the rock where I discovered the carnivore molar.

We returned the next day to carefully excavate this bone. Not knowing how large this bone was, we systematically removed all the rock above and around it until we approached the bone. To strengthen and stabilize it, Jorge covered the exposed bone in paraloid, a type of thin glue that absorbs into the fossil. Using chisels and brushes, we finally freed the bone from the rock and discovered it to be a large astragalus, or ankle bone.

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Jorge identified the astragalus as possibly belonging to a large, early type of horse.

We are excited to send these finds to the University of Florida for further study, and to head back to the field to find more fossils!

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-Dipa Desai