Wednesday, December 18, 2013

Back to the western Caribbean, Pt. 3

This will be, for now, the final part of this series. This is going to be a bit of a tease, as I'll go over some of the cetacean find we've made in the last several months won't go into many details as to what each of the fossils are. That will be the subject of future posts, once the fossils are properly described and published. There are a good amount of pictures to make up for it, so enjoy!

Trash road cetacean
As you may have read previously (here, here and here) collecting fossil vertebrates in the Chagres Formation is not an easy task and takes some planning before collecting each specimen. Back in the summer I found what seemed to be the remains of a fossil cetacean partially exposed on on the wave cut platform (see pictures below). To get to this locality we had to walk through a 10 meter stretch of road that is always full of trash, hence the locality name. As for the fossils, not a lot of it was exposed, and the day when we found it, we were on another mission. So we ended going back to the site to collect the fossils two days before Thanksgiving Day, and like most other digs here, we only had about four hours before the high tide took over.
Left: The exposed fossil; right: Chris (Summer 2013 intern) looking at it somewhat in disbelief. 
Finally, in November we collected the fossil. James and I started digging the trench around the fossil, soon after the other interns joined the digging party.
Zach, Sarah, Elena and James (Fall 2013 interns) are happily posing with the jacketed fossil, it only took us about 2 and a half hours. 
And liftoff!! We take the jacket to the truck and off to STRI where it will be properly prepared.

Chagres Norte dolphin
Back in early September, I had the chance to go prospecting in the Chagres Formation with two of my colleagues from invertebrate paleontology at the Florida Museum of Natural History, Roger Portell and Austin Hendy. They've previously done some more work in the marine units here in Panama, so it was good to go out with them and see new localities. One of these, was located further north of the village of Piña than I'm used to. Getting there involved a really muddy road, fortunately, we had all terrain vehicles, and it was actually fun driving through it.
The site, which I dubbed Chagres Norte, was one of the northern-most localities near the village of Piña.
At this site as with others along this whole coast, the Chagres Formation is exposed along the wave-cut platforms and sea cliffs. One of the fossils we knew was there (Roger and Austin had found it some days earlier) was part of the vertebral column of a small cetacean.
Elena (Fall 2014 intern), Roger and Austin collect the cetacean vertebrae. This is one of the reasons I like these guys, even of they specialize in invertebrates, they know not to ignore vertebrate fossils and will collect them.

This was Elena's second day in the field. She got hooked on the Chagres and even "claimed" the fossil saying that she was going to do the prep work, which she did.
The partial vertebral column we collected back in September. This is after Elena's careful and fantastic prep job.
Chagres Sur odontocete
Later that day, we went to another locality, this one south of Piña, so I gave it the obvious name of Chagres Sur. At this site I spotted some cetacean fossils sticking out of the sea cliff (see picture below).
One of the localities south of Piña, where I spotted some cetacean bones (you can see the bones towards the center right). For reasons I can't remember, Elena is staring in the wrong direction.
At that point, I didn't know what this fossil was, and we were also running out of daylight, so we left it there, and hoped to come back another day to collect it. It wasn't until a couple of weeks ago (1st week of December), that I decided to re-visit the locality with the interns. It was then, upon seeing this fossil again, that I had one of those, aha! moments and I realized what it was. So we had to collect it!
Here I am with the Chagres Sur odontocete, just before we removed it.
I won't go into details of what the fossil is at this moment (I warned you this was a post to spark your curiosity). But, if you plan on attending the 10th North American Paleontological Convention in Florida next February, you'll definitely find out more about it!

So stay tuned, you'll hear more about these discoveries in 2014!

Tuesday, December 3, 2013

Back to the western Caribbean, Pt. 2

The previous post was to give you a brief introduction into the geology of the Chagres Formation, which is where we are focusing part of our collecting efforts. This next post is to give you an idea of what happens when we find fossils of large marine vertebrates in the Chagres.

Often, when we find fossils in the Chagres these are on the rock exposed in the wave-cut platform along the beach (although there are exceptions). The benefit of this is the relatively easy access, the downside, is that we usually have only about 4 hours (spanning between the period before, during and after, the low tide) to collect the fossil. Back in April, during one of our trips to the Caribbean coast, we saw a partial marlin mandible exposed on one of the wave-cut platforms (picture below). That day we were prospecting, that is, looking for new localities and new fossils that were exposed so that we could plan to collect them in the near future. This was one of those finds.
A partial marlin mandible exposed on the wave-cut platform (anterior to the left).
The near future ended up being July. And so it was that together with Carlos De Gracia (a STRI intern whose main interest are fossil fishes), and my summer 2013 interns, Chris, Christina, and Silvia (previously featured here) we set out to the Caribbean to collect that fossil marlin.

Collecting the fossil took us three days. The first day was cut short and we couldn't do much work as the weather turned bad, and we had to leave after about an hour of work. Day two was purely devoted to digging a trench around the fossil so that we could wrap it in a protective plaster jacket for proper removal and transportation back to STRI (see picture below). This is a near obligatory task and method of proper collection of fossil vertebrates and has been used at least  since the late 1800's. While digging around it, we realized that we had more than we thought, the fossil consisted of mandible and skull, which meant we had to dig deeper, and wider around the fossil to be able to remove it completely.
Day 2 of the excavation. From left to right: Carlos De Gracia (STRI intern) and my summer 2013 interns, Christina, Chris and Silvia, make the trench around the marlin skull and mandible.
After we dug a deep enough trench around the fossil, we were ready to put a plaster jacket around it. Except that by then it was late, and the tide was coming back in, meaning we had to jacket the specimen another day. Finally, on our third day at this particular site, were were able to put a jacket around the fossil (see pictures below).
Day 3 of the excavation. Christina and Silvia are finish the jacket protecting the marlin skull and mandible.
This is the locality, if you click on the image you can see Silvia (near the center) and Christina (to the right); behind her is the jacket (the white blob on the ground).
After the plaster dried we undercut the block and flipped it so that we could remove excess rock and make it a bit lighter to carry back to the truck and then drive back to STRI (see pictures below). This specimen, as well as several other marlins that have been collected from the Chagres (including the one mentioned here), will be prepared and studied by Carlos.
After we popped and overturned the jacket,  me, Chris, and Carlos removed some of the excess rock in order to make it lighter.
Liftoff!! Even after trimming some of the rock off, this was still a pretty heavy block.
Other fishes known from the Chagres include a variety of bony fishes (mainly know from otoliths, which I mentioned in Part 1) as well as a several species of sharks (of which cookie-cutter sharks are one of the most common). Marlins are also relatively common and easy to recognize in the field; in fact, this year alone, we have collected several other skulls, mandibles and vertebrae.

Because they are common, the fossil marlins of the Chagres have not gone unnoticed, unlike the marine mammals. In 1978, Harry L. Fierstine described the first fossil marlin known from Panama. The fossil, consisting of a nearly complete skull, represented a new species, which he named Makaira panamensis. Modern relatives of Makaira panamensis include the black and the blue marlins. A second fossil marlin from Panama was described in 1999 (Fierstine, 1999). This one was found in the late Miocene Gatun Formation, which underlies the Chagres Fm. The fossil consisted of a partial rostrum, and was identified as Makaira cf. M. nigricans, the same species as the blue marlin (Fierstine, 1999). This implies that this particular species has been around for several million years, or more likely, that some extant members of this group are morphologically conservative and show very little differences from its fossil relatives.  

I'm sure we'll learn more about the fossil fishes of the Chagres and Gatun formations in the not so distant future. For now, stay tuned as this series is not yet over!

Literature Cited

Fierstine, H. L. 1978. A new marlin, Makaira panamensis, from the Late Miocene of Panama. Copeia 1978:1-11.

Fierstine, H. L. 1999. Makaira sp., cf. M. nigricans Lacépede, 1802 (Teleostei: Perciformes: Istiophoridae) from the Late Miocene, Panama, and its probable use of the Panama Seaway. Journal of Vertebrate Paleontology 19:430-437.