Reviewing the relationship between the molars of small mammals and climate change during the Paleocene-Eocene transition (~55.5 million years ago)

Evaluating the responses of three closely related small mammal lineages to climate change across the Paleocene–Eocene thermal maximum

Summarized by Matthew Eisenson, a geology major at the University of South Florida (USF) at the Tampa campus. Currently, he is in his third year. He plans on attending graduate school to earn his PhD in volcanic hazards. From that, he plans on working on different volcanoes and examining their hazards so that he can help the people in those areas during times of natural disasters caused by volcanic eruptions. He may potentially become a university professor after working in the field for a few years. When he is not studying for school, he likes to play tabletop roleplaying games with people or play games with friends.

What was the hypothesis being tested? The main hypothesis that was being tested in this study was whether abiotic- climate change (driven (i.e., nonliving variables like temperature, precipitation, salinity, and humidity) can be traced in the dental molars of three mammalian species: cf. Colpocherus sp , Macrocranion junnei, and Talpavoides dartoni. These are all small mammals that were rodent-like in appearance. 

What data was used? The data used in this study were fossils of the three most common species of stem erinaceids (the group containing hedgehogs) that were alive during the Paleocene-Eocene Thermal Maximum (PETM), listed above. As the name suggests. The Paleocene-Eocene Thermal Maximum, the climate warmed drastically on Earth. From these, this study looked at the teeth (molars) of these animals. They got the specimens used for this experiment from the Florida Museum of Natural History (FMNH), Gainesville, FL., and National Museum of Natural History (USNM), Washington, D.C. These teeth were taken from a range of time surrounding the PETM: early, mid, late, and post. The three teeth belonging to each species can be seen in Figure 1. 

Methods: This study used several methods to study changes in the molars of the listed species through time. One method used was done by measuring the size change of the molars. This was done by calculating the log transformed crown area (length × width). The other strategy used was measuring the shape change of the molars. This was done by looking at three-dimensional model analysis of the shape change with dental topographic metrics and 3D geometric morphometrics. The shape change was also measured by univariate parameters (or based on one attribute) created from the linear and angular measurements (Figure 1).

Results: This experiment had results that neither supported the hypothesis that abiotic change as a direct driver of altered dental morphology or the null hypothesis that biotic change as a direct driver of altered dental morphology. This came as a surprise, as previous studies have shown that molar teeth can change due to a changing climate. Much of the data was limited by sample size, making most seen changes fall within an error range (i.e., that the size changes are not significant enough to indicate true change). Even though there were changing climates during this period, there were no significant changes in these animals’ molars. 

The figure above shows the way the researchers broke down the measurements for the molars. Shown are three views of the tooth with the measurements marked on them (A= top down view; B= side view; C= angled view). First, they measured the crown area by doing the natural log of the length times the width. Next was the relative talonid by dividing the width by the length. Next, they measured the relative metaconid length by dividing the metaconid length by the length. They also measured the relative metaconid-entoconid intercusp by dividing the metaconid-entoconid intercusp by the length. They measured the relative hypoconid−hypoconulid intercusp distance by dividing the hypoconid−hypoconulid intercusp distance by the length. Finally, they measured the relative trigonid height by diving the trigonid height by the length.
Figure 1. This image shows how the researchers did their linear and angular measurements to get their univariate parameters. This was done by measuring several parts of each molar and putting it through a code to get a univariate parameter that could be used. Each tooth was measured 3 separate times. The acronyms are CA, crown area; HHID, hypoconid−hypoconulid intercusp distance; L, length; MEID, metaconid−entoconid intercusp distance; ML, metaconid length; R-, relative; TH, trigonid height; TW, talonid width; W, width. A= top down view; B= side view; C= angled view

Why is this study important:  This study is important to look at because it showed contradicting data from what has been found before. As stated, these species seemed to have been minimally affected (at least in their molar shape and size) by climate change, while other studies on other species have shown far larger effects from climate change. More thought, analysis, and retesting is needed in this area for a more correct answer to be brought forth.

Broader Implications beyond this study?  The broader implications for this study all relate to climate change. As this study looks at relating certain characteristics across time and climate change, there is an implication about using it to better understand our geologic past, by using data gathered here to correlate molars with climate change. Another implication is looking at current climate change and how mammals will/are responding to it. Looking at how mammals may respond to the current global climate change can give us a lot of information. We can also see how past events predict what are seeing with current climate change and use that information for conservation purposes. 

Citation: Vitek, N. S., Morse, P. E., Boyer, D. M., Strait, S. G., & Bloch, J. I. (2021). Evaluating the responses of three closely related small mammal lineages to climate change across the Paleocene–Eocene thermal maximum. Paleobiology, 47(3), 464-486.

New Fossil Evidence Reveals How Killer Whale And Other Hunting Whales’ Feeding Preferences Evolved

The origins of the killer whale ecomorph

Summarized by Lara Novalvos, a senior at the University of South Florida, majoring in Marine Biology and with a double minor in Geology and Environmental Science and Policy. After graduation, she expects to earn a Ph.D. in Oceanography. In her free time, she enjoys traveling, reading, and working out.

What was the hypothesis being tested: Scientists in this study are testing the hypothesis that hunting mammals is a trait that evolved more than once in whales and dolphins. The killer whale (Orcinus orca) and the false killer whale -a species of dolphin that resembles killer whales in feeding habits- (Pseudorca crassidens) are the only cetaceans (the group that contains whales and dolphins) that hunt marine mammals, a trait that was thought to have evolved once.

What data were used?:  A cetacean partial skeleton fossil found on Rhodes, Greece. The fossil skeleton preserved (among other bones) was its mandible (lower jaw), some teeth, and otoliths (“earstones”) belonging to fish that were eaten as the whale’s last meal.

Methods:  Morphological traits of the discovered species Rododelphis stamatiadisi were compared to those of other extinct and extant cetaceans (especially teeth count, size, and shape and upper jaw size) to build and infer an evolutionary tree that shows how the killer whale, the false killer whale, and the newly discovered Rododelphis stamatiadisi are related.

ResultsRododelphis stamatiadisi, the species found on the beach in Greece, is an extinct whale from the Pleistocene (2.59 million years ago – 11,700 years ago) that fed on fish. The results of the evolutionary (phylogenetic) analysis indicates that Rododelphis’ skull morphology is more closely related to that of false killer whales, placing them as sister taxa on the tree. However, another fish-feeding whale fossil previously discovered, Orcinus citoniensis, is considered killer whales’ closest relative. Researchers analyzed the teeth, jaws, and size of many cetaceans, extinct and extant, and concluded that delphinids (small whales with teeth such as dolphins, killer whales, pilot whales, and close relatives) evolved in six different lineages, half of them having many small teeth, and three of them having bigger, fewer teeth. From one of the lineages with few big teeth, killer whales evolved; false killer whales also appeared in a lineage of whales with big few teeth but not from the same one killer whales evolved.. These results indicate that the trait of feeding on other marine mammals appeared twice in the evolutionary history of whales, rather than having a single origin.

The figure above displays different delphinid species and its relationship based on morphological and molecular analysis. The phylogenetic tree shows a group of branches towards the middle of the tree colored in orange; these represent the lineage where the present killer whale evolved and its closest known ancestors. Towards the bottom of the tree, branches containing today’s false killer whale and its known lineage are colored in purple. The most closely related species to Orcinus orca is Orcinus citoniensis, while the most closely related species to Pseudorca crassidens is the recently discovered Rododelphis stamatiadisi; both extinct species fed on fish, whereas both killer whales species feed on other mammals, suggesting that the trait evolved in two separate instances.
The evolutionary tree containing extant killer whale and false killer whale. Orange branches show species in the killer whale’s lineage; purple branches show the false killer whale’s ancestors and lineage. Killer whales belong to a lineage that evolved before the false killer whale’s lineage did. Rododelphis stamatiadisi is more closely related to false killer whales than it is to killer whales; moreover, false killer whales are more closely related to Rododelphis stamatiadisi than to killer whales.

Why is this study important?: This study provided an opportunity to revise the evolutionary groups of the whale group. It focused on how different feeding habits evolved within the group, allowing for a deeper understanding on how the different species adapt to new environments, food abundance, or even climate change. Whaling has caused killer whales to switch to smaller prey, allowing us to observe how these whales adapt their feeding habits to different food abundance.

Broader Implications beyond this study: Research suggests that the coexistence of many large predators lead to the selection for even larger creatures; this study suggests that marine mammal predation can be correlated with whale’s gigantism. Both Orcinus orca and Pseudorca crassidens feed on marine mammals, but their most common ancestors did not.  Although the exact origin of why whales became so large is still unknown, it has been hypothesized that gigantism drove these two killer whales to develop their particular feeding preference.

Citation: Bianucci, Geisler, J. H., Citron, S., & Collareta, A. (2022). The origins of the killer whale ecomorph. Current Biology, 32(8), 1843–1851.e2.  

The diversity of 85-million-year-old European freshwater snails was influenced by global climate change

Onset of Late Cretaceous diversification in Europe’s freshwater gastropod fauna links to global climatic and biotic events

Summarized by Jordan Orton. Jordan Orton is a geology major at the University of South Florida. Currently, he is a senior. He plans to work for the water management district to help protect and preserve the aquifer system to ensure we have plenty of safe water to drink and use. When he’s not studying geology, he loves to watch movies, garden, play board games, and go on little adventures. 

What was the hypothesis being tested? The hypothesis of this paper is to determine which factors influenced the rate of speciation (the rate that new distinct species evolve from a common ancestor) to increase so rapidly. Was it because of annual precipitation, average temperature, geographic distance, or continental area (which is determined by the sea level)?

What data were used? Data for this study was collected previously by the same authors and includes estimates of temperature, precipitation, and other variables by geographic location. Their data set also included taxonomic records of 3,122 species of snails represented in this fossil record.

Methods: They compared the results of a birth-death model (a statistical model of how the population of a species changes over time) and a multivariate birth-death analysis (a more complex statistical model to estimate population changes over time that takes into account several contributing factors) with shifts from a 10-million-year timeframe before the peak in speciation of snails to a 10-million-year timeframe after the peak in speciation of snails in order to determine which of the four variables in the hypothesis most affected the rate of speciation.

Results: The researchers analyzed four factors that may have contributed the most to this increase in diversity of snails: annual precipitation, mean annual temperature, geographic distance, and continental area (which is a function of sea level rise and fall). According to the results of the analyses and models, the factors that had the most influence for so many species of snails evolving was a reduction in continental area (i.e., sea level rise) and an increase in geographic distance. 

A reduction in continental area means that sea levels rose and flooded parts of the continent, creating new niche habitats that are brackish (slightly saline) to freshwater. This allows species that can tolerate the less salty waters have a place to flourish and escape predation from marine organisms. This coincided with the Cretaceous Terrestrial Revolution, a bloom in diversity of flowering plant life, and high global water surface temperatures, which also increased marine animal diversity. The creation of these new habitats allowed multiple species to develop and feed from varying types of new flowering plants that were also diversifying in the new habitats. Over time, these organisms evolved into new species that specialized which plants they consumed (similar to the example of Darwin’s finches). The secondary factor that allowed for this increase in diversity of snails is that there was a greater distance between continents, so there was more habitable area for the snails to spread out into. Because the snails venture out further apart, they don’t have the opportunity to intermingle with each other as much, which causes more species to develop

The rate of extinction of snails was consistent through each of these 10-million-year windows, so the rate of extinction wasn’t particularly affected by these four factors. It is likely that there was a decline in the rate of speciation from 85 Mya to 80 Mya due to interspecies competition. Interspecies competition is when there are too many different species competing for a limited resource, so there is a decline in population.

This figure consists of four bar graphs: speciation rate from 95-85 Mya, speciation rate from 85-75 Mya, extinction rate from 95-85 Mya, and extinction rate from 85-75 Mya. The x axis is a range from -7.5 to 2.5 and the y-axis is the time period for that graph. Each graph has 5 factors that are correlated to rate of speciation or extinction: diversity, annual precipitation, mean annual temperature, geographic distance, and continental area. The factors that correlate most with increasing the rate of diversity from 95-85 Mya are an increase in geographic distance and a decrease in continental area, the factor that correlates most with the decline of the rate of speciation from 85-75 Mya is diversity. The rate of extinction from 95-85 Mya was not correlated to any of the factors, and the rate of extinction from 85-75 Mya was correlated to a decrease in continental area. The other variables: annual precipitation and mean annual temperature had a small effect on the data.
This figure shows the correlation strength of the four variables from the hypothesis plus the effect diversity has on the rate of speciation and extinction in the time period 95-85 Mya and 85-75 Mya. The factors that correlate most with influencing the rate of speciation in the period of 95-85 Mya are a decrease in continental area and an increase in geographic distance, while the factor that correlates most to influencing the rate of speciation in the period of 85-75 Mya was diversity. The rate of extinction was not heavily influenced by any of these variables from 95-85 Mya, but the drop in extinction rate from 85-75 Mya was influenced by a decrease in continental area.

Why is this study important? This study is important because there hasn’t been much research into the factors that drove the diversity of species of European freshwater snails; the marine and terrestrial snails are more studied and better understood.

Broader Implications beyond this study: Sea levels and average annual temperature are rising today. If we want to understand what sort of impact human activity is having on the increasing and decreasing rates of speciation of snails, we need to understand how they were affected by the paleoclimate (historical climate). We need to see how snails reacted to these conditions in the past to have a baseline that we can compare to how they react now to the same conditions (which are now being driven by humans).  Scientists can then determine how human activity (habitat destruction, nutrification, etc.) is affecting their rates of speciation. 

Citation: Neubauer, T. A., & Harzhauser, M. (2022). Onset of late cretaceous diversification in Europe’s freshwater gastropod fauna links to global climatic and biotic events. Scientific Reports, 12, 1–6. 

First evidence of fossilized ‘earstones’ in Cretaceous-aged cephalopods

First Cretaceous cephalopod statoliths fill the gap between Jurassic and Cenozoic forms

Summarized by: Gabrielle Scrogham completed her Bachelor’s of Marine Biology degree in 2020 and is currently a Geology Master’s student at the University of South Florida, Tampa. She is studying methods for tracking changes in diet of fish over time based on stable isotope and trace metal analysis. Their interests include marine ecology and biogeochemistry. Outside of academia, Gabrielle enjoys snorkeling, painting, and practicing martial arts.  

What was the hypothesis being tested? Cephalopods are a group of animals which include octopuses and squids. In this paper, researchers compared recently discovered fossils of cephalopod statoliths, also known as earstones, from the Cretaceous Period (145 – 66 million years ago) to older earstone fossils from the Jurassic Period (201 – 145 million years ago) and to earstones found in modern squid and cuttlefish to see how they change over time. Earstones are small, calcified parts found in the head of animals to help with navigation, movement, and balance. Earstones, or other structures for sensing balance, are found in most animals and even some plants. Statoliths in cephalopods are analogous to structures called otoliths in bony fish, as they perform the same function. The researchers hypothesized that differences in the shapes and abundances of earstone fossils would reflect evolutionary changes in cephalopod lineages. They also hypothesized these newly discovered fossils would support evidence from other paleontologists that a large-scale shift in animal dominance from cephalopods to fish occurred during the Cretaceous. 

What data were used? Five fossilized cephalopod earstones were collected from two sites in Poland and England. Several images from scanning electron microscopes were used in this study, including the newly collected earstones, a Jurassic earstone fossil, and earstones from modern squids and cuttlefish. This allowed for detailed comparisons of their shapes. The earstone structures were then compared to data compiled from previous studies on cephalopod lineages. The number of earstones found for both cephalopods and fish from each time period were also counted. 

Methods: Sediments were wet sieved using a fine (0.375 mm) mesh to separate fossils from the clay and silts in the rocks. Both collection sites were chosen due to being known Lower Cretaceous formations and for being uniquely accessible at the time of sampling. The collection site in Poland is now flooded, meaning additional samples from this area cannot be accessed. Once identified, the fossils were photographed using a scanning electron microscope. 

Results: The shape of the single earstone fossil from Poland differ than those found in England, which are more similar to earstones from Jurassic fossils. Some differences in traits include the shape and angle of the rostrum, the spur, and the lateral dome (see Figure 1 for what these features look like). Since the earstone from Poland has unique features not seen in other fossils, this likely represents a new lineage of cephalopod. There are some indications that the Poland specimen may have been a juvenile organism, so in addition to only having one fossil available, this data cannot be considered comprehensive. The earstones from England are more similar to fossils from the Jurassic, which means they may be more closely related. In addition to the analysis of the shape differences, the number of cephalopod and fish earstones were compared. Cephalopod earstones were more abundant than fish earstones in the Jurassic sediments, while fish earstones become more dominant in Cretaceous sediments. Thus, this is evidence for a shift in dominance from cephalopods to fish around 145 million years ago.

Four rows of earstone fossils pictured at different angles with significant features labelled. Figures are labelled by letter for specimen and by number for angle, with a total of six angles showing differences in the structures. Most are shaped loosely like ovals, but have thicker and thinner parts to them distorting the shape. Average size is just over 200 microns.
Images from scanning electron microscope comparing cephalopod earstones, also called statoliths, from different angles. Four samples are represented including A: modern pygmy squid; B: Cretaceous cephalopod fossil from Poland; C: Jurassic cephalopod fossil from Poland, and D: modern cuttlefish. Some distinguished features include the rostrum (r), spur (sp), and the lateral dome (ld). Scale bar = 200 microns.

Why is this study important?: Cephalopod statoliths have been found and recorded from both the Jurassic and the Cenozoic (modern), but not from the time period between those two, which is the Cretaceous (145 – 66 million years ago). This type of comparative data can reflect changes in animal lifestyle, such as shallow versus deep water environments, which can be used to reconstruct ancient habitats. Similarities between these fossils also allow researchers to look for connections in evolutionary lineages over time. Some of these fossils are also collected from sites that are no longer accessible, increasing their scientific value as it would be difficult to collect new evidence from the same regions. 

Broader Implications beyond this study: This study documents shapes of new cephalopod earstones, which could be used to examine ancient environments and reconstruct what types of animals lived in those habitats. The proposed shift in dominance of cephalopods during the Middle Jurassic to a dominance of bony fish in the Early Cretaceous would demonstrate a large-scale change in marine ecology. This dominance shift would also additionally explain the noticeable increase of fish abundance over cephalopods in the fossil record and modern oceans.

Citation: Pindakiewicz, M, K., Hyrniewicz, K., Janiszewska, K., & Kaim, A.  (2022). First Cretaceous cephalopod statoliths fill the gap between Jurassic and Cenozoic forms. Comptes Rendus Palevol, 21, 801–813. 

New spider family discovered in Europe

First Record of the spider family Hersiliidae from the Mesozoic of Europe

Summarized by Devan Legendre, a geology major at the University of South Florida. He is currently a senior in his last semester. Once he earns his degree, he plans to work in the geotechnical industry and gain experience to actively promote himself within the field. When he’s not studying geology, he enjoys running long distances to clear his head and gain new insight. 

Hypothesis: The aim of this study is to describe a new male spider found in ajkaite (sulfur-bearing resin found in brown coal) from the Ajka Coal Formation in Hungary and place the male spider in a new taxonomic group. The climate and the environment in which the resin was found was used to evaluate the current environmental description for the Ajka Coal Formation and better predict past environments. 

Data used: Arachnid fossils that are found preserved in amber resin offer a unique glimpse into the build of arachnid fossils, which usually don’t have their legs preserved.  The amber provides a preservation that is often entirely complete, shows the entire body build, and has a level of detail not often found in other methods of preservation for fossils. This can also help to understand the behavior and ecology of arachnids. The amber fossils used in this study are from the Ajka Coal Formation in Hungary that is one of two areas known for Mesozoic amber inclusions dated between 86 to 83 million years of age.

Methods: The chunk of ajkaite resin for this study was almost completely opaque, making it too dark for examination by light microscope. An X-ray tomograph from the University of Pannonia in Veszprem, Hungary was used to scan the large chunk of ajkaite. Upon scanning, multiple arthropod inclusions were discovered inside the chunk, including a relatively large sized spider. To achieve a better resolution scan on the spider, the ajkaite was broken to a smaller size for easier scans. A micro-computed tomography scanner in Hamburg, Germany used multiple images taken at various specifications along with specialized computer programs in Matlab, and the Astra Toolbox. 

Results: The images taken allowed scientists to identify a short third pair of legs and lateral spinnerets unique to the Hersiliidae family of spiders, that differs from the extinct and extant families. The specimen can be seen in Figure 1.  This is why scientists proposed the Hungarosilia genus to accommodate the new arachnid fossil. Based on drill cores samples, the climate for the Ajka Coal Formation has been projected as tropical, with large amounts of rain. The forests were likely fern dominated in the subtropical or tropical environment.

A dark mass with multiple protruding stick like objects (the spider body and limbs), as well as two pointy objects coming from the rear of said dark mass. The pointy objects are the spinnerets, it appears. Entire body is about 3 mm in height; with legs, about 6 mm in width.
An image of the spider scanned from the amber inclusion, that was found in the Ajka Coal Formation in Europe. Hails from the Mesozoic time period. Scale bar = 2 mm

Why is this study important? This specimen is unique in that it is a new genus of spider from the Mesozoic. The only other genera in this spider family that have been described so far are Burmesiola and Spinasilia, both of which were found in amber from Myanmar. These two genera have distinct differences that set them apart from the newly found specimen, which differs mainly with the longer rear end, triangular separation between the spinnerets, and short middle section. 

Broader implications beyond this paper: Up until this specimen was found, there have been very few spiders or spider-related inclusions found in the Ajka Coal Formation . With the identification of this specimen, the Hersiliidae family of spider establishes the oldest known record for this family in Europe, as well as being the second record of this fossil from the Mesozoic. The discovery of this specimen has greatly improved the knowledge on the Mesozoic diversity of the family Hersiliidae, and the Ajka Coal formations paleoenvironment. Further specimens may help to expand the diversity of spiders in the Mesozoic of Europe.

Citation: Szabo, Marton, Jörg U. Hammel, Danilo Harms, Ulrich Kotthoff, Emese Bodor, Janos Novak, Kristof Kovacs, and Attila Ősi. “First record of the spider family Hersiliidae (Araneae) from the Mesozoic of Europe (Bakony Mts, Hungary).” Cretaceous Research 131 (2022): 105097.

Determining the Maturity of Bivalves in Puerto Rico and the Dominican Republic to Determine Historical Processes that Affected Deposition

Strontium Isotope Stratigraphy for Oligocene-Miocene Carbonate Systems in Puerto Rico and the Dominican Republic: Implications for Caribbean Processes Affecting Depositional History

Ortega-Ariza, D., Franseen, E. K., Santos-Mercado, H., Ramírez-Martínez, W. R., and Core-Suárez, E. E.

Summarized by Andrea Gann, a graduate student pursuing a master’s degree in Environmental Science and Policy at The University of South Florida. Currently, she is in her second year. After graduation, she plans to work as an environmental science analyst for an environmental consulting firm in Tampa. When she’s not studying environmental science, she enjoys kayaking and swimming in the many springs located in Florida. 

What was the hypothesis being tested? This paper aims to establish the ages of two fossil clam species, Kuphus incrassatus and Ostrea haitensis, by using absolute dating methods. Absolute dating is when scientists calculate the amount of radioactive decay in the isotopes of minerals found inside the fossil. Isotopes are known as elements that share the same number of protons while differing in their number of neutrons. This data was used to better understand under what conditions certain shallow marine systems in Puerto Rico and the Dominican Republic were deposited. 

What data were used? The data collected in this study is called strontium (Sr) isotope data. Strontium is known as a common trace element, which is a chemical component present in many organisms that includes both essential and non-essential elements. For example, zinc is considered an essential element in most organisms, while other elements like aluminum or uranium are deemed non-essential. To study and determine the ages of certain fossils – in this case, bivalves – the authors are applying the 87Sr/86Sr ratio. Within strontium are four isotopes, and these two are the closest to each other in abundance. The ratio involves the decay of rubidium isotope 87Rb, a trace element, into  87Sr over geologic time. By studying the increase of 87Sr/86Sr, researchers can determine the absolute age and origin of certain fossils by calculating ratios.  

Methods: The researchers began by collecting shell samples of both Kuphus incrassatus and Ostrea haitensis bivalves and drilling small amounts of their shell to chemically analyze. These shells are composed of low-magnesium calcite, which means that they tend to be fairly stable where other forms of minerals would change in the fossilization process.  Scientists compared the ratio of the bivalve fossils to modern-day fossils to ensure no chemical changes would have affected the 87Sr/86Sr ratio. Here, a Thermo- Finnigan MAT 253 isotope ratio mass spectrometer was used to calculate the isotopic ratios of the bivalves, which were then juxtaposed with the ratios of modern mollusks. Concentration levels of other trace elements such as iron and manganese were also confirmed and compared with Sr values as another indicator of chemical alteration. Finally, the Sr isotope ratio produced three values – each with a corresponding minimum and maximum age. The 87Sr/86Sr ratio value reflects the mean age, while the minimum and maximum values exist as a range for any error or uncertainty.  

Results: 117 samples were collected, and 41 of those samples were at values expected of a shallow-water environment. . The authors also discovered a depletion in carbon values that could have been caused by freshwater runoff or an insufficiency of open-ocean water interchange. The absolute age of the bivalves, used to determine the ages of the rocks in which they were found, were included in the results. For example, the San Sebastian Formation in Northern Puerto Rico was set in the middle-late Oligocene at a mean age range of 29.78 to 26.51 Ma. Another formation named the Yanigua-Los Haitises Formations were set in the Middle Miocene at a mean age range of 15.75 to 15.25 Ma.

A four panel figure labeled A to D. A- shelly layer of fossils with a sharpie for scale. B- shelly layer of fossils with a pointer finger indicating to a zigzag break in the structure. C-horizontally striped microstructures that appear similar to a ripple effect. D. layered fossilized tissue with round edges and smooth overlapping structure that resembles a palmetto leaf.
The images above display the samples of Kuphus incrassatus and Ostrea haitensis bivalves tested in the study. Images (A) and (C) are Kuphus incrassatus which show that the interior shell texture is still intact, as well as the outer layers which have recrystallized. Images (B) and (D) display Ostrea haitensis bivalves with consecutive layers of preserved tissue and partially recrystallized shell texture. The condition of these bivalves demonstrates the lack of chemical alteration found in the study.

Why is this study important? The framework created in this study provides insight into how the chronostratigraphy of bivalves is directly correlated with time and surrounding local processes and regional processes. The meaning behind chrono is time, while the meaning behind strat is ‘layer’. Thus, chronostratigraphy is the analysis of rock layers over time. By identifying the absolute age of these shells, the authors can then determine what global and local processes influenced its deposition. 

Broader Implications beyond this study: This model will allow other stratigraphers and geologists to replicate this study with bivalves or other shells in their own regions globally. The authors describe methods using multiple pieces of scientific equipment (e.g., a Thermo- Finnigan MAT 253 isotope ratio mass spectrometer, microscope-mounted dental drill, transmitted light microscope petrography, plasma atomic emission spectroscope, and more). There is in-depth detail about the formulas utilized to calculate for chemical alteration that can help guide other geologists with their own chronostratigraphy and absolute dating analyses. Overall, absolute dating helps construct a structured timeline and establishes the depositional conditions and processes that were occurring. 

Citation: Ortega-Ariza, D., Franseen, E. K., Santos-Mercado, H., Ramírez-Martínez, W. R., & Core-Suárez, E. E. (2015). Strontium Isotope Stratigraphy for Oligocene-Miocene Carbonate Systems in Puerto Rico and the Dominican Republic: Implications for Caribbean Processes Affecting Depositional History. The Journal of Geology, 123, 539–560.

Diversification Patterns of Trilobites during the Ordovician

Post-Ordovician Trilobite Diversity and Evolutionary Faunas

Bault, V., Balseiro, D., Monnet, C., and Crônier, C.

Summarized by Alexa Milcetic, a senior at the University of South Florida studying geology, with minors in astronomy and geographic information systems (GIS). She plans on furthering her education by obtaining a master’s degree in planetary geology. After she earns her degree, she plans to work for the National Aeronautics and Space Administration (NASA). When she isn’t studying geology, she loves to listen to music, watch movies, and read.

What was the hypothesis being tested? The hypothesis being tested required an investigation of the evolutionary history of trilobites, marine fossils, after the Late Ordovician Mass Extinction (LOME). Scientists wanted to evaluate the amount of diversity of trilobites after the LOME and understand the shifts in the broad groupings of diversity, called ‘evolutionary faunas’. Researchers asked what kind of environment did these different groups of trilobites live in? How did their differing regions they were acclimated to help or harm them during extinction events that happened after the LOME. 

What data were used? Trilobite data was downloaded from the Paleobiology Database which spanned 23 families. Where they were found, specifically the rock they were found in (lithology), can be used to estimate where they lived and where in the ocean they were found. For this, the Paleobiology Database was primarily used. This database was used to determine the post-Ordovician biodiversity of trilobites. Essentially, researchers put the data into the database, and these scientists then downloaded the information. This was then represented through the creation of a plotted graph (Figure 1), showing the diversity of trilobites throughout this range in geologic time. Using this same database, habitat conditions and the location of where these organisms lived was also collected. The lithology (the geology of their habitat) data became separated into the categories of carbonate, siliciclastic, or mixed. The preference for sediment that these trilobites had changed throughout time, and scientists wanted to see if there was any correlation with this preference and how certain groups became extinct. Bathymetrical data also became separated into categories of shallower or deeper, showing if a certain group preferred living in a certain region of the water where another group would not be able to survive. The latitude locations of their habitats also became separated into categories of low latitude, middle latitude (equatorial), and high latitude.

Methods: These trilobites within this period of the Post-Ordovician were in four distinct groups according to their similar characteristics, environments, and time they lived in. These were then used as variables to evaluate the evolutionary faunas. What the fauna was made of was determined by the latitude, lithology, and overall environment of the habitat they lived in. They looked at who was present, and the features of their environments, to better understand if things like lithology, etc. might explain more of their survival. They took all the data and ran tests to determine if there were patterns driving the biodiversity in these trilobites and tested the results to see if they were statistically significant. 

Results: Four groupings of trilobites showed up in four different chunks of time from the Silurian until the Permian–Triassic extinction (444 to 252 million years ago), where trilobites ultimately went extinct. Throughout the Silurian period, trilobites were highly diverse (i.e., many genera were present; more genera means more diversity). These are called the Silurian fauna. During this same period, these trilobites still maintained a high diversity even at higher latitudes and in richer siliciclastic (i.e., more sand and mud instead of limestone) environments, especially when compared to the more recent faunas. Next, there is the Devonian fauna, where especially in the Early Devonian there was the highest post-Ordovician diversity found within this study. In the Middle Devonian, there was a large reduction in trilobite diversity. This was likely due to the decrease in the amount of atmospheric oxygen, as well as with changes in sea level. The evolutionary fauna that developed here, within the Devonian, occurred during environmental changes, like an increased greenhouse environment, more carbonate environments, and high sea levels, indicating  a warmer climate. In the Late Devonian, diversity within trilobites was still low and the fauna is called the Kellerwasser Fauna.This was still due to the abrupt environmental changes that occurred during the Middle Devonian, that decimated previous evolutionary faunas. After this, there was the Hangenberg Event, known as the end-Devonian Extinction, which affected all existing trilobite groups. The survivors of this are called the Late Paleozoic Fauna (Figure 2). Since there was a decrease in diversity during the Mississippian (Early Carboniferous), there were only a select few faunas able to survive until the Permo-Triassic extinction. 

Figure showing 11 different types of trilobite groups that lived and or died during the time of the Cambrian (521 million years ago) to the end of the Permian (252 million years ago). The great diversity when many of these groups lived, ended as the Devonian ended (360 million years ago). Since this study focuses on Post-Ordovician, the diversity during this time interval was greatest in the Early Devonian. Overall, the diversity of trilobites was greatest in the Ordovician.
Figure 1: Evolutionary history of the different types of trilobites, from the Cambrian where they are first found in the geologic record, to the Permian-Triassic extinction where all trilobites became extinct. The Y-Axis is time in a Logarithmic scale.

Why is this study important? In the trilobites, the diversity ranged vastly across different geologic times, which allowed them to make it through multiple extinction events. With this, we can begin to study who survived and who didn’t, and the common characteristics they shared or did not share with each other, such as: what made them more likely to live, and what characteristics made it more likely for them to die. This study is important because trilobites were an extremely common part of the early Paleozoic and why they went extinct in the pattern that they did (across multiple mass extinctions) isn’t well understood. The variables that likely controlled this include climate change and the environment each of these distinct trilobite groups lived in. While they never recovered from the Late Ordovician mass extinction, there were slight increases in diversity in the Early Devonian, possibly caused by warmer climates and large inland seas. 

Broader Implications beyond this study: These trilobites left us a blueprint. Since something with so much diversity has died out, it is important to find out what could have caused this. Their extinction was heavily affected by high greenhouse gasses. It is important to use this information in the past to decide how to best mitigate and protect the organisms we have today, as human activity is releasing high greenhouse gasses today. Understanding how trilobites responded to these mass extinctions can help us understand how other animals did too. We can use this information to see how current and future trends in climate will affect organisms today.  

Citation: Bault, V., Balseiro, D., Monnet, C., & Crônier, C. (2022). Post-Ordovician trilobite diversity and evolutionary faunas. Earth-Science Reviews, 230.

Small tracks found in Southern Colorado, USA show scientists details about the fossil record in an area that experienced volcanism

Small bird and mammal tracks from a mid-Cenozoic volcanic province in Southern Colorado: implications for paleobiology

Lockley, M. G., Goodell, Z., Evaskovich, J., Krall, A., Schumacher, B. A., and Romilio, A.

Summarized by Brysen Pierce, a geology major, working on Geographic Information Systems and Technology, as well as environmental science and policy minors. Currently, he is a senior who has not decided what to do for his career path. When he is not studying geology, he enjoys watching movies and hiking. 

What was the hypothesis being tested? Several fossilized animal tracks have been discovered in Rio Grande National Park (Colorado, USA). After locating samples containing tracks near the first site, the authors hypothesized that since there was already one set of tracks located, there could be others nearby in a similar geologic setting. The purpose of this study was to define the tracks and identify what kind of creatures may have made them.

What data were used? Samples were collected from the field and analyzed. The source of the data was in southwestern Colorado in the San Juan Volcanic Field and from a smaller site in New Mexico. At the first site, there were two tracks that indicated two different birds and another unfinished track, which contained small prints that did not follow a distinct trail or were not able to be identified. The second site had four completed tracks that were left by birds and mammal traces that formed another track and there were some more traces that did not complete tracks. 

Methods: The tracks were found close to fifty meters apart from each other in two different locations. The tracks were preserved in a piece of a volcanic block, which had since been moved from its original position; once the rock had been moved, it became exposed. A volcanic block is a piece of a solidified fragment that has been ejected thrown from a volcano by an eruption and is measured to be larger than sixty-four millimeters in diameter. Since these trace fossils were the first of their kind that have been recorded in this type of volcanic environment, researchers wanted to expand on this topic. From here, the scientists were able to collect samples and take casts so that they could do measurements of the prints and better analyze the trace fossils and define what they could have been from. 

Results: Three total samples were collected or casted and brought to museums to study. Three species were identified in this study: two of them were bird species and the last was a species of mammal related to modern day rodents. The birds were some of the smallest found in the fossil record and have relations to creatures like the sandpiper whose habitat is shorelines. Some tracks were not easily identifiable because they are incomplete. The bird tracks in this area were identified Avipeda circumontis named after the region it was found in and the mammal tracks are Musvesigium minutus whose name means small mouse footprints. Both species share similarities between other closely related species that are found in the western United States, which makes identification of the species difficult.

This image shows three smaller images labeled a, b, and c. a) is a picture of the broken off block that is showing the tracks with a measuring tape across the broken surface that measures across at about 23 inches. b) is a drawn model of the block that includes two complete fossil tracks and other markings around the surface that measures 23 inches and shows a 30 cm scale next to it. This image is reversed from a) and shows the clear impressions compared to the photograph. This bird is tridactyl and we can see 8 steps in a row and another set of a couple steps following a separate path in a similar direction of northeast. c) is a 3d modeled created from images of the surface that shows the fossil tracks and two small measuring tools to show the scale of the sample measuring 23 inches and scale of 25 centimeters.
These images show the first site where the bird tracks can be located. a) is the image of the bird tracks in the block which it was found inside of. b) shows a drawn replication of the bird tracks but flipped it. c) a 3d model of the bird tracks on the block in situ. This is telling us that fossil tracks are visibly seen on this site and shows in varying amounts of detail.

Why is this study important? This study is important because it shows us that trace fossils can be found in a volcanic setting, which has previously been unreported. The study shows us what kind of species lived in this area during the mid-Cenozoic and could provide additional information about an environment that has not been preserved in the past with fossils. New types of trace fossils were identified in a setting that previously had produced no fossils. We learned that not only small birds, but also small mammals, once lived in the volcanic province of south Colorado. 

Broader Implications beyond this study: Since this is the first study that has described animal tracks found preserved in volcaniclastic setting, this could lead to other discoveries within similar environments in the geologic record . There is a lot to learn from sites like this because the species that the footprints were left by were previously undiscovered. The bird and mammal fossil tracks found here could be unique to this setting, but this means that tracks are able to be preserved in this type of environment and that the animals were, in fact, leaving evidence behind.

Citation: Lockley, M. G., Goodell, Z., Evaskovich, J., Krall, A., Schumacher, B. A., & Romilio, A. (2022). Small bird and mammal tracks from a mid-Cenozoic volcanic province in Southern Colorado: implications for palaeobiology. Historical Biology34, 130-140.

Fossilized Lynx skulls from Southern Italy provide a window into the Evolutionary History of the Endangered Lynx pardinus

The tale of a short-tailed cat: New outstanding late Pleistocene fossils of Lynx pardinus from southern Italy

Mecozzi, B., Sardella, R., Boscaini, A., Cherin, M., Costeur, L., Madurell-Malapeira, J., Pavia, M., Profico, A., & Iurino, D. A.

Summarized by Vincent Levin, a geology major at the University of South Florida in his third year. He loves geochemistry and is contemplating graduate school. While he isn’t splitting rocks with a tile saw, Vincent loves to spend time at the USF Catholic Student Union, where he is a very active member and part of their leadership team. He also enjoys video games and playing the bass guitar. 

What data were used? This study was conducted on the fossilized remains of a group of large cats, the lynxes, and particularly the Iberian lynxes (Lynx pardinus) (L. pardinus). These fossils were found at the site of Ingarano in Foggia, South Italy. Unearthed there were 415 late Pleistocene Lynx remains. Of these remains, this study focuses exclusively on craniodental fossils, or fossils of the skull and teeth. 

Methods: The fossils were gathered throughout the 1990s by different researchers. To collect the data used in the study, they used CT scans and CT imaging software on the complete skull fossils. This allowed them to create 3D models of the two skulls. They also used ZBrush 4R6, a modeling software, to restore missing points of the skull. They also incorporated other Lynx fossil data from different sites in France, Spain, and other parts of Italy. Lastly, they estimated Lynx body mass using a method that uses skull measurements to determine overall body mass.

This is a map of Europe and part of the middle east. The fossils of Lynx issiodorensis, Lynx pardinus, Lynx lynx, Lynx sp., and the Lynx remains from the Ingarano site are listed here. Lynx pardinus fossils have been found ranging from the middle to late Pleistocene, moving from France and Italy into Spain. The Lynx remains from the Ingarano site are represented by a pink circle in Southern Italy.
The geographic distribution of Pliocene and Pleistocene lynx fossils in Europe. This figure covers a large portion of Europe and shows the distribution of the different species of lynx. In pink is the Ingarano site in southern Italy. The Iberian Lynx, in green, is shown to arise in the early Pleistocene and spread into the Iberian peninsula and into modern day France and Italy.

Results: Researchers determined that all of the cranial remains contained permanent teeth, indicating that they were all from adult cats. Many of the skull pieces and whole skulls still retained many upper teeth, which were beneficial in the final analysis. The lower teeth and mandibles (jawbones) also showed that all the remains were from adult specimens. However, these fossils showed much more size variation, and none of the lower incisors were preserved.

All the characteristics of the fossils found fit the overall morphology of L. pardinus. Overall, the Ingarano samples have larger cranial dimensions than other data sets. They concluded that there was also little sexual dimorphism, with the male to female body mass ratio being mostly equal. Sexual dimorphism is what accounts for biological differences between the sexes of a species.. Due to the limited sample size, it is hard to determine a correlation between Lynx body size and any potential environmental factors.

The most important result of this study was found in the cranium (skull) fossils. The cranium fossils provided a new insight into the evolutionary history of Lynx issiodorensis (L. issiodorensis) as a possible ancestor to Lynx pardinus and the still-living Eurasian lynx (Lynx lynx). L. issiodorensis, hypothesized to be representative of an ancestor of the modern Lynx, was shown to have similar cranial features to L. pardinus. The data found in this study supported the hypothesis that these cranial features were homologous, or features inherited from an ancestor. 

Why is this study important? This study compiled data on 68 craniodental (skull and teeth) Lynx fossils. Teeth and skulls are an important window into the morphology, what it looked like, and ecology, how it lived and interacted with its environment. Many of the studies done on Lynx fossils have lacked any substantial cranium (skull) data. This study was able to add that to the overall discussion on Lynx evolutionary history. Lynx evolutionary history was hard to nail down due to the coexistence of the two modern species of Lynx, Lynx pardinus and Lynx lynx, during the same time period. The addition of the cranium data added some clarity to the overall discussion.

The big picture: The Iberian Lynx (L. pardinus) is currently endangered. This study adds to a decades-long effort to better understand the ecological and biological characteristics of these cats. This could add data to create better conservation efforts for the preservation of this species against natural and manmade threats. 

Citation: Mecozzi, B., Sardella, R., Boscaini, A., Cherin, M., Costeur, L., Madurell-Malapeira, J., Pavia, M., Profico, A., & Iurino, D. A. (2021). The tale of a short-tailed cat: New outstanding Late Pleistocene fossils of Lynx pardinus from southern Italy. Quaternary Science Reviews, 262, 106840.

A Tooth for a Tooth: Evolutionary Development of Dental Structure Based on Common Mutations of the Bearded Dragon

The developmental origins of heterodonty and acrodonty as revealed by reptile dentitions
by: Salomies, L., Eymann, J., Ollonen, J., Khan, I., & Di-Poï, N.

Summarized by Kat Cool, a fourth-year geology student studying at the University of South Florida. She is pursuing her major with a geophysics emphasis and a minor in Geographic Information Systems and Technology. She is also the proud owner of three bearded dragons that have inspired her interest in this article. In the future she hopes to study meteorology at the graduate level and hopefully specialize in severe weather forecasting.

What data were used?  Discovering evolutionary mechanisms for dental changes could have implications in phylogenetics, taxonomy, and ecological identification of animals that are extinct as well as those still here today. This could be especially useful in key taxa groups that have a poor fossil record or a more mysterious evolutionary history. One group of reptiles the lepidosaurs (snakes and lizards), are a perfect candidate for this research due to their diversity in dental structures. Mutations in the genetic codes of lepidosaurs could provide key insight to the mechanisms behind their dental evolution. One mutation commonly seen is variation of the ectodysplasin (EDA) pathway. This mutation can be observed in many vertebrate species, including humans, and causes changes in the appearance of hairs, feathers, scales, nails, and teeth. The subject for this study group will be the humble bearded dragon (Pogona vitticeps), due to the different stages of EDA mutations one can easily observe. Since this mutation is also known to influence tooth development, scientists decided to look at the dental structure of these morphs as well.

Methods: To analyze the tooth development of bearded dragons, scans were taken to take a closer look at the EDA mutation both during embryonic development and after the hatchlings have emerged from the egg. Then 3D-rendered bearded dragon skulls were compared at 14 days after hatching. The teeth of the wild-type bearded dragon, the leather-back (Sca/+), and the silk-back (Sca/Sca) were then compared based on the appearance (or lack thereof) of pleurodont and acrodont teeth (Figure 1 for images and descriptions of teeth; Figure 2 for images of the lizards).

Figure 1 (A) shows diagrams of different tooth structures. The jawbone, dental pulp, dentine, and enamel are color coded in each of five tooth structures. Bearded Dragons have two of these types of teeth. The first is pleurodont teeth which are shown in the diagram by having one side of the tooth connected to the jawbone while the other side is exposed. The second type of teeth in this diagram of interest to us are the acrodont teeth. The acrodont teeth are shown in the diagram by having the jawbone go about halfway up on both sides of the tooth.(B) A phylogenetic tree showing families and subfamilies of Acrodonta connected by lines based on their relationship. The tree stems off into two main groups: The Agamidae and the Chamaeleonidae. The Lepidosauria reptiles are on the Agamidae side of the tree. (C) 3D-rendered skulls of lizards representing the main Acrodonta subfamilies. Each skull shows an X ray of the bones and teeth in the lizard’s skull from a straight on angle as well as from the side of a lizard’s skull. The anterior pleurodont teeth are highlighted in red and the acrodont teeth are noncolored
Figure 1 (A) Different tooth attachment types in vertebrates. There are two main types of teeth present in these reptiles: Pleurodont teeth are set on the inside jaws, while acrodont teeth are generally larger and attach to the jaw by connective tissue. Pleurodont teeth are accepted as the norm for Lepidosauria; however, there are certain families like Agamidae, Chamaeleonidae, and Trogoniphidae that show an understudied mix of pleurodont and acrodont teeth or a singular acrodont tooth. Another unique feature of living lepidosaurs is the lack of or absence of tooth replacement in acrodont teeth. (B) Phylogenetic tree showing families and subfamilies of Acrodonta. The Lepidosauria clade includes the Rhynchocephalia order with the single surviving species, the Tuatara, as well as the Squamata order with many living members like lizards and snakes (C to J) 3D-rendered skulls of lizards representing the main Acrodonta subfamilies


Results:  It was found that wild-type hatchlings had eight acrodont teeth and one small pleurodont tooth per jaw. There is also a central egg tooth on the middle jaw bone (premaxilla) that is replaced with a pleurodont tooth soon after hatching. However, it was found that both scaleless bearded dragons (Sca/+ and Sca/Sca) often did not have pleurodont teeth on their premaxillary bone, leading to about half of juvenile dragons with an EDA mutation having few or no teeth on this bone at all. It was also found that bearded dragons with EDA mutations had fewer teeth in total than the wild-type dragons, as well as wider teeth. These observations were more evident in the silk-back juveniles (Sca/Sca).

Figure 2 Two female bearded dragons sitting next to each other on a pillow. They are laying on their stomach with their heads looking forward. Their round abdomen consolidates by their hind legs where their long tails extend out of frame. The bearded dragon on the left is a wild type bearded dragon. She is yellow and brown in color and her spikes are much more apparent than the bearded dragon on the right. The bearded dragon on the right is more orange and tan and lacks the same spiky texture as the other bearded dragon.
Figure 2. An image of a wild-type bearded dragon (left) and a leather-back bearded dragon or Sca/+ (right). If you are familiar with bearded dragon morphology, the EDA mutation is responsible for two of the most well-known morphs: the ‘leather-back’ and the ‘silk-back’. The leather-back bearded dragon (Sca/+) has one copy of the EDA mutation, resulting in reduced scale size than the bearded dragon’s without this mutation (also called wild type in this study). This reduction in scales creates a leathery appearance, earning these little mutants the colloquial name ‘leather-back’. The silk-back (Sca/Sca) bearded dragon has two copies of the EDA mutation: one from each parent. The result is a more extreme version of the features observed in the leather-back dragons: instead of reduced scales there appears to be an absence of scales all together.

Why is this study important: At the time of these results, the scaleless bearded dragon was the first known example that researchers had found of a gene mutation that resulted in position changes in teeth. These results provide a contrasting prospective to results found when studying the dental structures of mice. While the research with mice indicated that vertebrate tooth position was based on a complex model of gene expression patterns, the scaleless bearded dragon data suggests tooth identity can be produced with the modification of a simple gene.

The big picture: The simple modifications of the EDA gene had very observable effects on the position of the teeth. Though more research is necessary, this study shows that through observations of living species today, mechanisms of dentition diversity can be discovered through many different approaches to better understand evolutionary development. Though it is sometimes a long, slow process that can span across millions of years, it can also sometimes be isolated to a change in a single gene at a specific moment. 

Citation: Salomies, L., Eymann, J., Ollonen, J., Khan, I., Di-Poï, N. (2021) The developmental origins of heterodonty and acrodonty as revealed by reptile dentitions. Science Advances 7(51). DOI: 10.1126/sciadv.abj7912