Fossil Friday 8/28/15: A Fossil Fruit and its Tree

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For today’s Fossil Friday, we have two plant fossils belonging to the genus Parinari in the family Chrysobalanaceae. Paleontologists always get excited when they find fossils from multiple parts of an organism, like finding the jawbone and vertebrae of a mammal, or in this case, the wood and fruit of the same tree. Obviously we don’t know if the fruit was attached to this exact tree, but these are the only two fossils that belong to the family Chrysobalanaceae, so it is likely that they are the same species!

The fruit is technically just the endocarp (think: pit). The outer, fleshy, edible parts of fruits don’t preserve so well in the fossil record. In this cross section we can see the two locules (chambers for holding seeds). In Parinari, only one of the locules is active and holding a seed, but in other types of fruit there may be one or many locules and seeds. In this specimen we can also see the germination plugs, which fall out of the endocarp when it is buried in the soil, allowing the seed to send a growing shoot out and up toward the sun, and a root down into the soil.

The wood sample is a cross section of the trunk or possibly a branch. The circles are the vessels, which transport water up the tree. One of the features that helped us identify this wood as Parinari is that almost all of the vessels are solitary: they are not directly connected to other vessels in clusters or rows (for an example of vessels in rows, check out our previous post on wood here and note the crescent shaped vessels in direct contact with neighboring vessels).

Both of these fossils come from the Lirio East site along the Panama canal and are 19 million years old.

Who’s Fault is it Anyway? Stratigraphy along the Panama Canal.

Who’s Fault is it Anyway?

Recognizing deformation (faults) of rocks within the Canal on three different scales can give context to the fossils that are found. Who’s fault? Well, that question is a bit harder to answer. We’ll start by looking at the ‘what’.

(1) Outcrop scale (meters/10s of feet) extensional faults reflect regional stress regimes.

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Early morning with overcast skies on the Panama Canal. Slightly north of Puente Centenario, along the Culebra Cut.

When reading geology in the field, one quickly learns that very little in the natural world is ‘random.’ The landscape around us appears inconceivably complex. Yet, the land as we experience it, from the height of mountains, to patterns in vegetation, the angles and shapes of topographic highs, and location of rivers, all that we see results from specific geologic processes (hence, the science of geomorphology).

By learning to identify these processes, one can read the landscape through a fascinating lens of cause and effect.

Take for example, the photograph below: a fantastic example of structural deformation (normal faulting) that has occurred to the sedimentary Canal formations. Here, layers of red and purple and tan sedimentary rocks (the colors most likely a product of iron oxidation) are bounded between bluish grey volcanic tuffs. Notice carefully the geometry which this sequence demonstrates, highlighted by the dotted lines. The central sedimentary sequence is bounded by beautiful 60 degree angles, (somewhat obscured by vegetation), highlighted  by the red linear dike (volcanic intrusion) that parallels the dotted line on the right side of the picture.

Sedimentary sequences exposed along the Panama Canal are highly faulted. Above, two photographs stitched together to give a shot of the entire outcrop. Sedimentary sequences of the Las Cascadas Formation bounded by basalts on either side.

Sedimentary sequences exposed along the Panama Canal are highly faulted. Above, two photographs stitched together to give a shot of the entire outcrop. Sedimentary sequences of the Las Cascadas Formation bounded by grey volcanic tuffs on either side.

As the schematic diagram illustrates below, the canal sediments in the photograph above display a fine example of extensional faulting.

A schematic diagram illustrating the structure that forms in an extensional faulting regime. As brittle rocks are stretched (whether on the scale of an entire portion of continental crust or simply a small rock formations), they break along characteristic angles, ~60 degrees.

A schematic diagram illustrating the structure that forms in an extensional faulting regime. As brittle rocks are stretched (whether on the scale of an entire portion of continental crust or simply a small rock formations), they break along characteristic angles, ~60 degrees.

For comparison, see the following example of a much larger outcrop in Colorado (viewed from the air).

 A beautiful example of extensional faulting of a large sequence of beds in Colorado. The down-dropping block is the graben. Source of image: Colorado Geologic Survey.

A beautiful example of extensional faulting of a large sequence of beds in Colorado. The down-dropping block is the graben. Source of image: Colorado Geologic Survey.

Hard to believe these textbook-worthy events happen on such a large scale? Visit here for more briefing on faulting.

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(2) Map scale (kilometers/miles) parallel faults reflect regional stress.

A map of the Panama Canal below highlights an area called the Culebra Cut (also known as the Gaillard Cut, named for the American engineer). It is along this portion of the Canal that the majority of the fossil localities for the PCP-PIRE project are located.

Map of the Panama Canal highlighting the area of the Gaillard (Culebra) Cut. The unstable nature of the soil and rock in the area of Gaillard Cut made it one of the most difficult and challenging sections of the canal excavation.

Map of the Panama Canal highlighting the area of the Gaillard (Culebra) Cut. The unstable nature of the soil and rock in the area of Gaillard Cut made it one of the most difficult and challenging sections of the canal excavation. Image source: rondougherty.com.

 

In 1992, the start of the Panama Canal expansion included a 10-year long project to widen the Canal channel as it passed through the Culebra Cut. The broader channel, along with larger locks, was needed in order to accommodate wider PANAMAX vessels. Prior to the work, the dimensions of these ships, built to the maximum size that will pass through a canal lock, limited them to one-way traffic while in the cut.

 

Follow the link to read more about the Historical Excavation of the Gaillard Cut. For more information on the Panama Canal Expansion, visit mipanamacanal.com.

Faulting on the outcrop scale, displayed in the picture of the Las Cascadas Formation at the start of this article, is mirrored in structural relationships on a much larger scale.

Zooming into the structure of formations within the Canal localities, notice how once-continuous belts of rock types are dissected and faulted. The approximate length of this map view is 4.5 miles, and encompasses over 20 major parallel faults.

Bedrock geologic map of the formations that oucrop along the Gailard Cut. Source: Kirby et al. 2008. Lower Miocene Stratigraphy along the Panama Canal and its Bearings on the Central American Peninsula.

Bedrock geologic map of the formations that outcrop along the Gailard Cut, south of Gatun Lake. The majority of rock types that outcrop in the area of the canal are early-Miocene (~20 million years old).  Source: Kirby et al. 2008. Lower Miocene Stratigraphy along the Panama Canal and its Bearings on the Central American Peninsula.

 

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(3) Hand samples (centimeters/inches) reveal a network of microfaults.

Of the rocks that outcrop along the southern half of the Panama Canal, (the Las Cascadas, Culebra and Cucaracha Formations), almost all are heavily faulted. This is apparent in micro-scale faults within the rocks we excavated (faults with a thickness maybe of several sheets of paper, cross cutting with a density similar to a cracked sidewalk).

PCP-PIRE Summer 2015 Intern Isaac Magallanes (foreground) and Gina Roberti (background) dig in the sedimentary sequences of the Panama Canal.

PCP-PIRE Summer 2015 Intern Isaac Magallanes (foreground) and Gina Roberti (background) dig in the sedimentary sequences of the Panama Canal. Notice the structure of the rock (slight bedding and hard to distinguish faults) visible on the excavated cross section.

When searching for fossilized remains embedded in bedrock, it is important to understand what has happened to the rocks since their deposition. For us digging in the canal, dark-colored slickenlines and deformation along the fault planes were at first easily confused with fossilized leaves and other remains. We quickly learned the fossils were more difficult to come by!

 

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Rocks along the Panama canal are faulted on a variety of scales, from the order of centimeters to kilometers. It is important to understand this geologic evidence when on the fossil hunt.

And so, to return to our primary question: Who’s fault is it anyway? We’ll settle with the conclusion that all our faults are stress related.

 

Photography and text original, Gina Roberti. Summer 2015.

PCP-PIRE Summer 2015 Interns, (from left to right) Isaac Magallanes, Michael Zeigler, Paris Morgan and Gina Roberti.

PCP-PIRE Summer 2015 Interns, (from left to right) Isaac Magallanes, Michael Zeigler, Paris Morgan and Gina Roberti.

Who’s Dating Whom, or rather, Who’s Sharing the Same Bed. Stratigraphic relationships along the Panama Canal

 

Distinguishing exact stratigraphic relationships between the sedimentary units that outcrop in the Canal remains a question of debate. Here, we will look at a series of figures used by geologists to interpret observations of rocks in the field.

(1) MAP VIEW

The first step is to create a map. What different types of rocks outcrop on the surface and where? Geologic maps are created by mapping the bedrock as it changes.

Below, a bedrock geologic map of the Canal region.  The majority of rock types that outcrop in the area of the canal are early-Miocene (~20 million years old).

Bedrock geologic map of the formations that outcrop along the Panama Canal. Different colored and fill textures distinguish different rock types. Note the abundance of volcanic rocks, as much of Panama was formed from a marine volcanic arc. Sedimentary sequences in which fossil excavation occurs formed in basins between volcanic islands, and thus exhibit a mix of shallow marine/brackish to deep water fossil fauna.

Bedrock geologic map of the formations that outcrop along the Panama Canal. Different colored and fill textures distinguish different rock types. Note the abundance of volcanic rocks, as much of Panama was formed from a marine volcanic arc. Sedimentary sequences in which fossil excavation occurs formed in basins between volcanic islands, and thus exhibit a mix of shallow marine/brackish to deep water fossil fauna.

 

 

The Miocene-aged Panama Canal rocks (the Las Cascadas, Culebra, Cucaracha and Pedro Miguel Formations- labeled ‘M’ in the bedrock map legend), are primarily sedimentary rocks (sandstones, siltstones and mudstones). This sedimentary detritus accumulated in basins between eroding volcanic islands, landmasses which eventually accumulated into a continuous isthmus connecting North and South America.

 

(2) CROSS SECTION

By noting structural relationships between different rock types, we can infer the three dimensional relationships of those rocks stacking underground. In this way we progress from a map in bird’s eye view to cross section. A cross section view often exhibits a vastly more complex picture than initially apparent on the surface. See the reference below.

Sample geologic cross section, 'step 2' in analyzing the bedrock geology. Different colors represent different rock units. This cross section was inferred using the bird's eye geologic bedrock map and information about the tilt (in structural geology called the dip) of various rock units. Project by Gina Roberti, Brown University 2013.

Sample geologic cross section, ‘step 2’ in analyzing the bedrock geology. Different colors represent different rock units. This cross section was inferred using the bird’s eye geologic bedrock map and information about the tilt (in structural geology called the dip) of various rock units. Project by Gina Roberti, Brown University 2013.

 

(3) STRATIGRAPHIC COLUMN

By analyzing structural relationships, geologists can move from a two-dimensional map to visualizing 3-D relationships between different rock units in cross section. Each rock unit, or geologic formation (in the column to the left), is mapped in detail. All textures and symbols have a specific meaning; even the contacts between units are denoted whether observed (and type) or inferred.

The figure below is a sample stratigraphic column for the primary formations which outcrop in the Gaillard Cut of the Panama Canal. Interpretations of the paleoenvironment are listed on the right.

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Sample stratigraphic cross section of rock units of the Gaillard Cut of the Panama Canal. Oldest rocks are on the bottom, with younger sequences forming on top. The environment of deposition is inferred from observations about the rocks (grain size, shape, etc.) and fossil fauna; interpretations are made in the column to the right. LCF = Las Cascadas Formation, P.MF. = Pedro Miguel Formation. Source: Kirby et al. 2008.

How do we determine the paleoenvironment? Interpretations based on observations.

The following illustration is a detailed and scientific reconstruction of the hypothesized paleoenvironment during the early Miocene. Centenario Fauna, ~19 million years ago. On display at the BIOMuseo, Panama City. Illustration by D. Byerley © Florida Museum of Natural History.

The following illustration is a detailed and scientific reconstruction of the hypothesized paleoenvironment during the early Miocene. Centenario Fauna, ~19 million years ago. On display at the BIOMuseo, Panama City. Illustration by D. Byerley © Florida Museum of Natural History.

Fossils uncovered in the Miocene-age Canal formations give clues to the environment in which these fossils accumulated (to a geologist, the ‘depositional environment’). The mix of fossil types, ranging from clams to plants, mammals and crocodilian teeth, all record changes in the environment over time. (Eg., Terrestrial vs. marine.) The sands, muds or silts in which those fossils are preserved reflect the depositional setting in which those fossils were preserved. (Fast moving river vs. quiet lagoon.) Geochemical parameters give information about the chemical conditions. (Carbon isotopes, paleotemperature, etc.).

A fragment of a fossilized crocodilian tooth, a common find in the PCP Canal Localities.

A fragment of a fossilized crocodilian tooth, a common find in the PCP Canal Localities. Paleoenvironmental conditions fluctuated from brackish near-shore, shallow marine environments to sandy river beds with many terrestrial mammalian fossils.

 

For example, the abundance of crabs, leaves and other marine invertebrates in the Culebra formation give evidence to multiple stages of marine transgression and regression, in which sea levels rose and fell. Clams and gastropods indicate saltwater environments. Fossils in the Cucaracha Formation, by comparison, include teeth of ancestral horses, camels, and other terrestrial species. Yet, these pieces have been rounded and broken by the flow of water, and are found along with many pebbles of similar size (1-3cm in diameter) and degree of rounding. This suggests the fossil pieces were transported and sorted by some mechanism, most likely by a river, accumulating as part of the rock.

Fossilized leaves are preserved within a relatively coarse grained sandstone of the Culebra Formation. Leaf margins, stomatal density and patterns in veination can all be used to determine not only the species or genera, but also the type of environment in which the plant was living.

Fossilized leaves are preserved within a relatively coarse grained sandstone of the Culebra Formation. Leaf margins, stomatal density and patterns in veination can all be used to determine not only the species or genera, but also the type of environment in which the plant was living.

(4) TECTONIC INTERPRETATION

If the stratigraphic column can provide an interpretation of the paleoenvironment, we return to the geologic map for the most complex interpretation: the tectonic history.

The stratigraphic column reveals the majority of rock types in the area of the canal are (1) volcanic and (2) sedimentary. Yet, volcanic tuffs and sedimentary rocks form in very different environments. Here then comes the geologic interpretation. The abundance of volcanic rocks suggest volcanism was common in Panama during the Miocene (~20 million years ago), around the same time that basins between the volcanos were filling with sediments. Hence, we see a mix of sedimentary rocks (sandstones, siltstones, mudstones) interspersed with volcanics (tuffs, basalts, volcanic conglomerates).

Below, a geologic map shows one way to interpret this setting. Volcanic ‘regimes’ of different ages are highlighted in different colors (yellow versus purple). Sedimentary sequences in which fossils accumulate are believe to have formed in basins between volcanic islands, and thus exhibit a mix of shallow marine/brackish to deep water fossil fauna.

Geologic interpretive map of Panama. Volcanic arcs (islands built from volcanic material, similar to Japan today) are colored in yellow and purple (distinguished by age). Sedimentary basins, including the basins in which sedimentary rocks of the Panama Canal formations formed, are hashed and dotted areas. It is believed that the sedimentary rocks accumulated in basins besides and between the volcanic arcs. The Panama Canal Basin is believed to be attached as a peninsula extending from North America. Source: Montes et al. 2012.

Geologic interpretive map of Panama. Volcanic arcs (islands built from volcanic material, similar to Japan today) are colored in yellow and purple (distinguished by age). Sedimentary basins, including the basins in which sedimentary rocks of the Panama Canal formations formed, are hashed and dotted areas. It is believed that the sedimentary rocks accumulated in basins besides and between the volcanic arcs. The Panama Canal Basin is believed to be attached as a peninsula extending from North America. Source: Montes et al. 2012.

And so, What is the role of a paleontologist? Thorough, steady, meticulous observation, documentation, interpretation.

 

Fossils are just one piece of the puzzle, as only as important as the context in which they are found. It is the combination of fossil evidence pLUS analysis of the bedrock geology which is necessary for a full interpretation of the rock sequence. Happy hunting!

PCP-PIRE Intern Paris Morgan observes the passage of a large ship through the Gaillard Cut, August 2015.

PCP-PIRE Intern Paris Morgan observes the passage of a large ship through the Gaillard Cut, August 2015.

Photography and text original, Gina Roberti. Summer 2015.

Fossil Friday 7/31/15: A sundial snail

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A lateral (left) and dorsal (right) view of the shell of the sundial snail Architectonica nobilis. Photo © IVP FLMNH.

The subject of this week’s Fossil Friday is the sundial snail Architectonica nobilis. This particular specimen is late Miocene in age and was found by former PCP PIRE Postdoc Austin Hendy in the lower Gatún Formation. This snail’s earliest occurence is in the early Miocene and can still be found in shallow marine waters today. These animals produce planktonic larvae that can travel great distances.

To find out more about this kind of snail, check out the Fossils of Panama page on it here.

Fossil Friday: A camel tooth

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UF/FGS 5680, the lower left first molar (m1) of Floridatragulus dolichanthereus. Left: occlusal surface; right: medial surface (side facing the tongue). Photo © VP FLMNH.

This Fossil Friday, we have a tooth from the camelid Floridatragulus dolichanthereus. This specimen was found by Stanley J. Olsen in 1956 at the early Miocene Thomas Farm locality in Florida. Camelid specimens referred to the genus Floridatragulus have also been found in Panama in the early Miocene Cucaracha Formation. F. dolichanthereus belongs to the same subfamily (Floridatragulinae) as Aguascalientia panamensis, which was featured in a previous Fossil Friday post.

Invertebrate Paleontology in the mid-Miocene: A trip to Lago Alajuela

A visit to Panama City by paleontologists Cristina Robins and Ian Cannon from the University of Florida this past week meant several field days focused on sampling invertebrate fossils. The goal: to obtain a better picture of the diversity of invertebrate communities within the formations in the Panama Canal, and increase collections of crustaceans and mollusks to be studied back at the University of Florida. Most exciting was our visit to a site outside the boundary of the Canal Excavation, to sample from the Alajuela Formation. Pictured below, Lago Alajuela, a man-made lake created along the Chagres River and major reservoir within the Canal watershed.

Invertebrate Paleo. collection team, July 15, 2015. Starting with the back row and moving left to right, Cristina Robins, project coordinator PCP-PIRE; Michael Ziegler, PCP-PIRE Intern; Ian Cannon, University of Florida; Jorge Moreno, PCP-PIRE Field Leader; Gina Roberti, PCP-PIRE Intern, Summer 2015.

Invertebrate Paleo. collection team, July 15, 2015, Lago Alajuela. The terraced shorelines and extremely low lake levels reflect record lows in rainfall during June, the third driest June on record in Panama in the last 100 years. So much exposed shoreline makes for fantastic fossil hunting. Starting with the back row and moving left to right, Cristina Robins, project coordinator PCP-PIRE; Michael Ziegler, PCP-PIRE Intern; Ian Cannon, University of Florida; Jorge Moreno, PCP-PIRE Field Leader; Gina Roberti, PCP-PIRE Intern, Summer 2015.

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7/17/15: A peccary tooth

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UF 236934, the upper left second molar of an indeterminate peccary. (Photo © VP FLMNH)

For this Fossil Friday I would like to present an upper tooth of a peccary (Family Tayassuidae). This specimen was found at El Lirio West in 2008 by Ph.D. student Aldo Rincon and is early Miocene in age. Peccaries have bunodont teeth, one of the two main tooth types attributed to artiodactyls (the other being selenodont). Bunodont teeth are characterized by low, rounded cusps. Human teeth are also bunodont.

Be sure to check out one of our past Fossil Friday posts on the peccary “Cynorca” occidentale here.

Fossil Friday 7/10/15: A flat sand dollar

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UF 2425, the test of Mellita tenuis. This specimen was found in Manatee County, Florida and is from the Late Pleistocene. (Photo © IVP FLMNH)

This Fossil Friday I would like to focus on the genus Mellita, a group of flat sand dollars (Class Echinoidea, Order Clypeasteroida). Members of this genus are restricted to the shores of North and South America, however they are found on both the Atlantic and Pacific sides of the continents. Members of Mellita feed by plowing through the surface of sand and collecting food particles. The split that resulted in two extant species of the genus, M. quinquiesperforata and M. notabilis, can be attributed to the closing of the Isthmus of Panama.

To learn more about the current distribution and phylogeography of this genus, read this paper that includes specimens from Panama.

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An extant Mellita longifissa plowing through sand. (Photo © Carolina~commonswik)

Reference: Coppard, S.E., Zigler, K. S., Lessios, H.A. Phylogeography of the sand dollar genus Mellita: Cryptic speciation along the coasts of the Americas. Molecular Phylogenetics and Evolution. (2013). doi:10.1016/j.ympev.2013.05.028

Bedrock Quest: Reflections on Fieldwork in the Azuero Peninsula

Delicate and intricate, the complexity of ecology and climate in the tropics presents a challenge for any scientist wishing to study more closely patterns of the naturaleza. Especially for geologists, accessing the bedrock, the layer of rock that forms the base of the land–underlying all soil and bodies of water–, is especially tricky. Hot and humid weather year round in tropical latitudes makes for incredible biological productivity, and happy microbes break down rocks into soils at a startling pace. Thus, to find exposures of rock outcrops that were fresh enough to determine the lithology, or composition, required a bit of effort.

A group of students from the University of the Andes examining an outcrop of basalt in Rio Verdadero.

A group of students from the University of the Andes discuss the orientation and lithology of an outcrop of basalt in Rio Verdadero. Plant growth in the rock’s cracks (fractures and faults) highlights patterns in the orientations of such features. Noting the primary direction and orientation of fractures can give information about regional stresses and tectonic changes.

In Azuero especially, it was difficult to see any bedrock beneath thick layers of red- iron rich tropical soils. The majority of land in the past 60 years has been deforested, and pasture land stretches for miles. Thus, to access the rocks, the majority of our time was spent in rivers, where water carved into the bedrock below.

Tiny sparkling grains of a blue-green metamorphic mineral (most likely epidote) that forms when volcanic basalts are hydrothermally altered. Notice the thin orange layer (perhaps microbial) on the surface, which shows weathering or breakdown of the rock ('meteorizado' in spanish). Oftentimes it requires a rock hammer to break open the rock and see past this superficial rind.

Tiny sparkling grains of a blue-green metamorphic mineral (most likely epidote) that forms when volcanic basalts are hydrothermally altered. Notice the thin orange layer (perhaps microbial) on the surface, which shows weathering or breakdown of the rock (‘meteorizado’ in spanish). Oftentimes it requires a rock hammer to break open the rock and see past this superficial rind.

And so, our group of geologists embarked on a quest to find bedrock exposures in the countryside of rural Panama. Pictured in the foreground PCP-PIRE intern Paris Morgan.

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Together with a group of twenty-plus students from the University of the Andes, de Bogota, Colombia, the Summer 2015 PCP-PIRE intern team shared in a three week mission to map the bedrock geology of western Panama.

A half-day’s drive from the Panama Canal Zone, the Azuero peninsula is comprised of rocks much older than those encountered in the Canal. Our goal was to learn more about the tectonic history of the region, to better inform our understanding of the ‘how’ and ‘why’ of the closure of the Isthmus of Panama.  To do this, we spent each day hiking through rivers and along beaches to access outcrops (‘afloramientos’ in spanish), where we would diligently document (in colored pencils on topographic maps) the rock types we encountered, their orientation and extent. By compiling bits of color day after day, it was possible to draw connections between similar rock types and infer (or, quite literally ‘color-in’) the bedrock geologic map of the south-western portion of the peninsula. Increíble!

Paleontologist Jorge Moreno-Bernal, field leader PCP-PIRE.

Paleontologist Jorge Moreno-Bernal, field leader PCP-PIRE.

Trekking through the rural countryside of Panama, the pursuit of a geologic field mapper is to learn the layout of the land…by foot. This caterpillar and paleontologist both captured in the view, caught moving at a slightly different pace.

 

July 2015. By Gina Roberti, PCP-PIRE Intern.

Fossil Friday 7/3/15: An otolith

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UF 264544, the left otolith of Paralonchurus trinidadensis. (Photo © VP FLMNH)

For this week’s Fossil Friday we have an otolith from a fish called Paralonchurus trinidadensis. This specimen was found at the San Judas site in the lower Gatún Formation and is Late Miocene in age. Otoliths or “earstones” are found in bony fishes and are used for hearing and balance. Otoliths also have growth rings similar to tree rings, allowing researchers to estimate the age of the fish when it died.

References:

Florida Fish and Wildlife Conservation Commission. (1999). Introduction to Aging Fish: What Are Otoliths? http://myfwc.com/research/saltwater/fish/age-growth-lab/aging-fish-otoliths/