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Chilly morning at Montbrook


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The spring 2021 digging session opened last week at the Montbrook site in north central Florida. It is a short drive from Gainesville where Tammy and I relocated last summer. One of the reasons for choosing Gainesville as our new home is so that we can volunteer more with the Florida Museum of Natural History (FLMNH). It is really great to be able to do a day of volunteer digging at the Miocene Montbrook site without a 5 hour trip up from South Florida and hotel reservations. Previously, we'd book a 3-4 day span of volunteer digging to make the trip worth the effort. Being able to dig for a single day and then rest up after (consuming fistfuls of ibuprofen) has its advantages. ;)

 

Usually, the museum would open this dig to a group of nearly 500 volunteers (students, retirees, and even out-of-state visitors) who have all put in countless hours of digging this site since 2016. Safety concerns due to the pandemic have forced the museum to limit the attendance at the digs to a smaller number of individuals and only locals with years of experience at the site. Luckily, we fit that category. We wear masks at the site and though we are not in one of the higher priority groups for the COVID vaccine many of the other retirees have had at least their first shot. While we are fortunate to be able to dig as part of the skeleton crew (pun certainly intended) we look longingly forward to being past the pandemic and seeing many old friends at the dig site.

 

We were out for the season opener last Wednesday and Richard Hulbert assigned Tammy and me to a pair of adjoining (1m x 1m) grid squares. At this section of the dig site the underlying layers of the formation slant down steeply from west to east--possibly the sloping bank of the river which is what we intuit this site to represent. I spent the morning removing the soft "sugar" sand on the top layer of my grid square. We know from other adjacent grid squares (several of which I've excavated) that this layer seems to be above the good fossiliferous layers and only rarely has isolated fossils (usually only small bits of Trachemys slider turtle shell). Being soft like beach sand, this layer can be dug out quickly and efficiently with our usually excavation tool--a standard blade screwdriver. I filled and hauled out dozens of plastic cat litter containers of this sand, dumping them on the spoil pile out of the pit in which we were digging. Good exercise and useful excavation but did not add many fossils to my "bone bag" for that day.

 

Tammy worked the adjacent square "up-slope" of my square. She was already at the level of the gritty layer below the sugar sand. This gritty layer contains larger rocks and has a more grainy appearance. It also seems to have a lot of clay particles mixed in which makes it concrete hard when dried out. We infer that these layers may represent major storms that raised the river level and increased its flow rate. As the storm subsided the more coarse material in suspension with the faster flow started to drop out and form this layer. Often, it contains interesting micro-fossils (and occasionally larger fossils as well). Tammy was digging out this layer and putting it into sandbags so it could be processed later washing it through screens to separate the micro-matrix from the silty fine sand. This was to be reserve material for an outreach project for science teachers in Florida who will be receiving matrix to pick through with their classes. Tammy needed the hose to soften the matrix--we have a gravity-fed water supply with a large tank and a jumble of hoses. She worked down her corner of the square and bagged it but it was like melting concrete with a hose and scraping it with a screwdriver. My gritty layer was under the layer of sugar sand and so was already somewhat damp and not nearly so hardened. By the end of the day I had taken down the top part of what I had been calling the "ski slope". The second photo is how we left the site at the end of the day.

 

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We were busy last Saturday (we now dig every Wednesday and Saturday) and didn't make it out. Some of the other long-term volunteers worked our squares that day removing more material and exposing a partially articulated Macrochelys snapping turtle carapace. At the end of the day they had also uncovered a small section of bone that looked like it might be part of a skull. Alligator was a good candidate and that's what we were told when we picked up work on this square yesterday (Wednesday).

 

It was a chilly morning (starting out below freezing) and this is why they have delayed the starting time to 10am. Because it was a sunny day, before long we were able to ditch many of the multiple layers we had started out with. Richard reassigned us to this pair of squares and Tammy worked the square with the snapping turtle carapace starting by uncovering more of the suspected alligator skull. I worked my adjacent square again. It had some of the gritty layer removed but sitting out in the sun for several days meant that it had hardened and I ended up making copious use of the hose this time trying to soften this "concrete" and get through to a hopefully fossiliferous layer below--the same layer that held Tammy's snapping turtle and mystery bones.

 

Once I got down to the bottom edge of my hard gritty layer I uncovered the layer of softer sand below it. At the interface of these two distinct layers I started finding some fossils. If this gritty layer represents material laid down during a flood event then it makes sense that some of the larger objects would have dropped out of the flow first followed by the gritty material. The finer clay particles would have settled last and then probably percolated between the grains of the grit and completed the "paving" for this weather event recorded in the layers at this site. I started to find a few bits like a pieces of a Trachemys plastron (2 left xiphiplastron elements--so not an associated set) and some gator osteoderms (which we call "cookies") and a really sweet large shark vert. They were all at the bottom of a chunk of the gritty material where it separated from the softer sand layer below.

 

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While I was busy "unpaving" the "ski slope" in my grid square Tammy was uncovering more around the suspected alligator skull. She had switched from the screwdriver to a dental pick as she worked closer towards the area with the uncovered bone. When she came upon a tooth and started uncovering it she was surprised that it did not look like a gator tooth. A little more excavation revealed a row of teeth. It was quite obvious they were mammal teeth and not gator and so we called over Richard who used a hose set to a fine mist to help gently wash away the matrix to reveal more. It turned out to be a lower jaw from a peccary (Protherohyus brachydontus)! They have a few other pieces of peccary skull but this is the first lower jaw complete with teeth. An excellent find that would be plaster jacketed and removed for preparation in the lab.

 

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I switched over to Tammy's square for a bit and we worked together to dig a trench around the jaw so that it would be raised on a pedestal for jacketing. There were a few Trachemys turtle bones discovered while trenching but luckily the were isolated finds. Occasionally, an interesting find (like the jaw) ends up in a cluster of different sets of bones and it gets complicated to figure out how to decide what gets included in the jacket. Smaller jackets are, of course, easier to remove, transport and prepare so it is always good to be able to isolate a particular specimen. We were able to create a roomy trench around most of the jaw but could only make a more narrow slot between the pedestal we were forming and the snapping turtle carapace adjacent to it. Thankfully, it was just enough to be able to jacket the specimen and remove it safely. We covered the articulated snapping turtle carapace bones with a sandbag so we would not get plaster slopped onto the specimens. Now that the peccary jaw is out it will be easier to excavate the snapping turtle to see how much is there. We protected the jaw by packing on some clean damp sand and made a more level base so this jacket would rest properly when it is flipped and worked in the lab from the underside. Tammy gets recorded as the co-collector along with the volunteer that first spotted it.

 

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I could have easily titled this post "The Day of the Peccary" or "Peccary Appreciation Day" but that would have spoiled the surprise. We had an additional surprise to this peccary-themed day. Sue, another long-time volunteer (pictured in a blue sweatshirt in a photo above and a gray jacket the week before in the very first photo) was working a few squares over and mostly finding turtle bones and a fish vertebrae came across something interesting. When she showed it to Richard he was amazed to see it was half a broken peccary tusk. A good portion of the tip was missing and though it looked to be an old (not fresh) break at the end he asked Sue if she had the other part. She didn't but she said she'd go through her bucket of matrix again before dumping it to make sure it wasn't hiding in some clump. She went through her bucket twice and set aside any of the bits she found. Amazingly, the missing piece turned up. She had not recognized it and though it had turned up earlier she methodically searched through her bucket of matrix with a fine-tooth comb (twice). The effort was well rewarded with a fine looking tusk that may very well be associated with the nearby jaw in Tammy's square.

 

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By the time we left at the end of the day I had leveled and cleared about half of my square down below the hardened gritty layer to the softer sandy layer below. You can see the neat smooth layer that I'm known for while digging at this site in the left in photo below. In Tammy's square to the right you can see the deeper pit in the upper right corner where the jacket containing the peccary jaw was removed. The sandbag with sand holding it down next to that is where the snapping turtle carapace is being protected. While Tammy was finishing off the day removing the higher level material shown at the middle of the right edge in the photo she came across a bit of bone. It was getting late and we were starting to clean up and get ready to leave. She showed Richard the bone that she had exposed and asked him if she should continue exposing it or leave it for later. We were wondering if it might be associated with a gomphothere scapula that is in the adjacent square. You can see a sandbag along the lower right edge in the image that is protecting and indicating where this fossil is positioned. It can't be removed till the adjacent material is dropped sufficiently to allow the extent of this scapula to be determined and allow for proper trenching and jacketing. The more that Tammy uncovered this bone the more it didn't seem to be related to the scapula. In the end she marked it with an empty plastic bone bag we had handy and weighted it down with a handful of sand so it would not blow away.  We'll likely get back to these squares this Saturday and Tammy can investigate this bone more fully and work to get the snapping turtle carapace pedestalled and jacketed. I'll probably continue removing material from the square I've been working on and hope to get to some nicely fossiliferous material that was hiding below the gritty pavement. Who knows what will turn up next? And that's precisely why we keep coming back--even on chilly mornings. ;)

 

Cheers.

 

-Ken

 

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Thanks Ken. Your reports are amongst the finest to be found on the forum and are the benchmark the rest of us should strive for. 

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Great write up Ken, looks like you had a blast out there. Thanks for sharing :thumbsu:

Every once in a great while it's not just a big rock down there!

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Fieldwork is the ultimate detective story. ;) I try to write these reports so the reader experiences the same surprises as we do in the field. :)

 

 

Cheers.

 

-Ken

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When volunteer spots open back up post-pandemic you'll have to sign-up and come play in our big sandbox. ;)

 

 

Cheers.

 

-Ken

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  • 1 month later...

Update to the story. It is no longer chilly in any stretch of the imagination at the Montbrook site. We were around 86F (30C) today with few clouds to cool things down. Luckily, there was a bit of a breeze which occasionally reached us down in the pit we were digging. Copious sunscreen and frequent breaks to guzzle lots of water. A great tip is to fill your plastic water bottles half full and freeze them solid. Top off with water and toss in the cooler. When you pull a bottle out it stays nicely cool for some time. Despite the heat the chunk of ice on one reusable bottle lasted well over an hour. Digging with masks certainly was appreciated on the cool mornings a last month but were a bit sniffling today.

 

Last night I saw photos of the tapir jaw after being prepped out of its plaster jacket. Since this is an uncommon species at the site with few nice specimens and because it was a relatively small and compact jacket, it jumped to the head of the line of jackets waiting to be worked and the peccary mandible was consolidated and freed from its sand and plaster jacket. The front of the jaw was not preserved well but the back was in nice shape with the teeth well preserved.

 

Cheers.

 

-Ken

 

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Fantastic report and update Ken ! That seems to be a very productive site.

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