Month: February 2026

Discovery of a new-found four-legged fish from the Devonian Period (419–359MYA) of central Australia

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A new stem-tetrapod fish from the Middle–Late Devonian of central Australia

By: Choo, B., Holland, T., Clement, A.M., King, B., Challands, T., Young, G., Long, J.A.

Summarized by: Allison Votteler. Allison Votteler is a senior at Binghamton University, majoring in Geology with a minor in Drawing. She enjoys learning about paleontology and hopes to pursue it as a career. In her free time she plays video games with her friends and draws. 

What data were used? The rock sections that were studied in this article were formed during the Devonian Period of Earth’s history (419–359MYA), where we can first observe the movement of aquatic vertebrate animals to land dwelling creatures. The Harajica Sandstone Member, a group section of sandstone preserved in central Australia, was studied due to the exceptional marine vertebrate fossil record preserved there. Scientists discovered an exceptionally well-preserved body fossil (a fossil that contains the species itself, instead of just a trace, such as a footprint or trail) contained within the rock. Combined with similar specimens found during previous expeditions in this area in 1991 and 2016, scientists analyzed the skull structures, fins, jaws, and scales of the preserved specimens. The discovery of this species, a new species of four-legged fish from the Devonian Period named in this study, can help bridge the gap in evolutionary theory. Previous data from other published evolutionary trees were also used to compare the new fossil find who it was most closely related to.

What was the hypothesis being tested? The scientists were trying to place the newly found fossil, which they hypothesized was a new species not yet described by scientists, among its most closely related relatives on an evolutionary tree, as well as understand and describe  the different characteristics of the species (such as features of its skull, fins, and structure).

Methods: The fossil was carefully removed from the surrounding rock on site and taken back to the lab for preparation. The surrounding sandstone that remained on the fossil had to be carefully removed from the sample. Smaller, loose sections were scrubbed with water and brushes while the larger sections that required more precise care were removed using specialized tools. Upon completing the careful removal of the specimen (Fig. 1), scientists began analyzing the characteristics of the new fossil in combination with samples collected from expeditions run in 1991 and 2016. 

A careful analysis by the scientists of the characteristics found in the specimen (such as skull shape/parts) was used to determine that the new fossil was closelyrelated toother tetrapods, such as Tiktaalik roseae. In order to create phylogenetic (evolutionary) trees, scientists use different features or characteristics found in fossils and compare them with other known characteristics of other species. A computer algorithm then sorts species based on which characteristics are shared between species. This is how the scientists were able to infer potential evolutionary  trees for the new species.

Three photos of Harajicadectetes zhumini (approximately 150 mm in length).as it appeared in the field, a long oval shaped creature encased in rock, with a triangular skull shape on the left. as a latex mold, following the same shape as in the field but showing only the fossil itself, triangular skull still on the left, fossil tapers out on the right into a tail like structure as an interpretive drawing, following the same oval shape, a line art drawing that shows the different structures visible after analysis of the specimen such as scales, skull sections, and bones.
Figure 1. Harajicadectetes zhumini fossil as seen A in the Harajica Sandstone Member, B as a latex mold of the fossil, C an illustration that showcases the different parts of the specimen. The triangular head and the elongated tail can be clearly seen. 

Results: Scientists determined that the new fossil was indeed a new species, which they named Harajicadectetes zhumini,The study of the fossil’s features and subsequent evolutionary  analysis indicated two probable evolutionary trees, both of which support the placement of Harajicadectetes zhumini as a member of the Osteolepididae–a paraphyletic group of lobe-finned tetrapods (meaning, four footed creatures that descended from lobe-finned fish, like coelocanths). Paraphyletic groups are a type of grouping of species that includes an ancestor and some, but not all of its descendents. It is possible that this placement isn’t entirely accurate because of missing samples, incomplete preservation of characteristics across species, as well as the possibility of convergent evolution (features that evolved separately of a common ancestor). These possibilities can mess with the results of the algorithm as they can lead to inaccurate placement of species on a tree. Convergent evolution was considered to play a role in the placement of Harajicadectetes zhumini, as it can lead scientists to believe that two distantly related species are closer on an evolutionary tree than they actually are. As different prehistoric fish may have felt the same environmental pressures, despite the distant relation they can evolve common mechanisms (similar to why dolphins and sharks are similarly shaped, even though sharks are fish and mammals are dolphins).

Why is this study important?: Understanding evolutionary history helps connect the current day to our past, and allows us to understand modern day processes. This study names a new species of tetrapod, continuing to close the gap in our evolutionary history and expanding our knowledge of the fossil record. 

Broader Implications beyond this study: This scientific discovery highlights some key factors for our understanding of the fossil record and helps us see the importance of finding these fossils. Despite the high-quality fossils that can be found in Australian deposits, the majority of these rocks have not been scoured, resulting in a lack of fossil data. With missing information, it can make understanding the evolution of these groups extremely difficult. This research is especially important as we can continue to bridge the gap between us and our fishy past. 

Citation: Choo, B., Holland, T., Clement, A.M., King, B., Challands, T., Young, G., Long, J.A. A new stem tetrapod fish from the Middle-Late Devonian of central Australia. Journal of Vertebrate Paleontology 43, 3 (2023). https://doi.org/10.1080/02724634.2023.2285000

Using Megatherium (Giant Sloth) bones to infer the past climate conditions in the Atacama Desert, Chile.

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Written in bones: palaeoclimate histotaphonomic history inferred from a complete Megatherium skeleton preserved in the Atacama Desert

Luisa Straulino Mainou, Jacqueline Correa-Lau, Rafael Labarca, Natalia A. Villavicencio, Vivien G. Standen, Susana Monsalve, Paula C. Ugalde, Sergey Sedov, Teresa Pi Puig, Alan Ulises Loredo-Jasso, Francisco J. Caro, Gabriela M. Jarpa, Patricia Hernández-Michaud, Claudio Latorre, Calogero M. Santoro

Summarized by William Pagan. William Pagan is an environmental earth systems major at Binghamton University. He plans to earn his degree and enter the workforce for a few years before attending graduate school. When he’s not busy with his studies, he is usually hiking or playing games with his friends.

What data were used? A nearly complete fossilized giant sloth skeleton found in the Atacama Desert in Chile was utilized, which was discovered prior to the study. The scientists collected carbonates from soils as well as rhyzoliths- trace fossils left by plant roots and cemented together by carbonates- that were found nearby the skeleton were also utilized.

What was the hypothesis being tested? The researchers aimed to understand how the climate of the Atacama Desert has changed since the deposition of the Megatherium skeleton since the end of Pleistocene Epoch (around 16,000-13,000 years ago) by analyzing the mineral composition and weathering patterns of the bones.

Methods:  Researchers set up a 1×1 m grid system throughout the site in the Atacama Desert (Fig.1 C), covering 54 m2 in total. The site is mainly sand-sized dry sediment, with little to no plant life and almost no water present. The giant sloth bones were present in 25 grids, and nine of these grids were excavated in 5 cm deep intervals. Loose sediment was put through a mesh sieve to gather the smaller bone fragments, while the larger pieces were carefully excavated from the rock.Scientists separated the bone fragment specimens used in the study into three sample groups. The scientists either kept the samples whole, sliced them into thin sections to look at under microscopes, or ground them in a mortar and pestle. The bone fragments kept whole were mostly pieces of teeth of the Megatherium and were used to analyze physical characteristics -such as color and pores in the bone; some tooth samples were set aside for more in depth analysis. The thin sections were analyzed under microscopes in order to get an understanding of the mineral composition of the bones as well as the internal structure and impacts of weathering. The bone section that was ground up was passed through a machine that uses X-ray waves to identify the minerals that were present in the samples. The carbonate rocks and a sample of bone were used for radiocarbon dating, which uses the isotope C14 to get a more accurate and precise idea of the age of the sample.

This figure is composed of four distinct images. Image A depicts scattered bones on a brown-reddish dirt surface. The area spans one full cell of the 25 box grid, roughly 2 square meters. Image b displays decaying fragments of bone in light brown sediment. There is a 2 cm scale bar present the size of one fragment, making the picture around 12 cm in total and the largest bone fragment around 3-4 cm. Image c displays the study area broken up into equal area squares by rope, with some of the squares excavated while others remain undisturbed. image d is a black and white drawing of the complete Megatherium skeleton and the position it was found in the ground. The bones take the shape of the giant sloth, which has two large hind legs with smaller front legs, a very large ribcage with a small head. A yellow box over the torso correlates to the bones in image a, and a much smaller box near the top of the skull correlates to the bone fragments in image b.
Fig 1. (a) Megatherium bones exposed on the surface before excavation took place. (b) fragments of bones from the skull. (c) site after excavation, showing the grid system used, showing the grid system used by scientists (d) line drawing indicating the placement of all of the bones on the specimen.

Results: Researchers found that the bones had increased levels of porosity and cavities that bioerosion- or the breakdown of the bones by bacteria- occurred shortly after the Megatherium specimen died. The bioerosion was thought to have happened before and after burial. Bacteria that cause bioerosion rely on environments with both oxygen and water, leading to the conclusion that the Megatherium skeleton was located in a place that was submerged in water, but dried out over time. After this bioerosion took place, iron and magnesium were deposited into the spaces left in the bone. Iron and magnesium deposition like this is known to take place in anoxic (lacking oxygen) conditions. This shift from oxygenated to un-oxygenated conditions could have been caused by the water becoming stagnant opposed to running or the water becoming deeper, but overall represents an environmental shift. The bones then started to crack as conditions became drier, and minerals such as calcium carbonate, halite, and gypsum were encrusted onto the bones. These minerals all dissolve well in water, and the fact that they were deposited around the bones hints towards the evaporation of water and the shift to more arid conditions in the environment. The dates obtained by the carbonate rocks and bone fragments show that the Megatherium is a minimum of 16,250 years old and as young as 13,000 years old., which lines up with a known large rainfall event in the area, further confirming the wet depositional environment. The increased rainfall would have lasted for roughly 4,000 years.  Overall, the Megatherium bones displayed excellent evidence of the changing conditions that line up well with the evidence found in the surrounding rock record.

Why is this study important? This study is important because it is a stellar example of how researchers can use bone samples- even smaller fragments with a lot of erosion and alterations- to get a better understanding of the paleoclimate of the Atacama Desert. This  study also gives direct evidence into the past climate of the Andes Region, highlighting times of drought and increased rainfall, while explaining what features of the Megatherium bones helped the researchers reach these conclusions.

Broader Implications beyond this study:  This study uses fossil data to better understand the broader pictures of how examining the fossilization of bones can give hints into past climate conditions. Scientists have used various methods in the past to try and reveal a broader picture of how regions and climates have changed, but the researchers in this study offer a unique angle of climate discovery by using the giant sloth bones to do it while combining many different disciplines and sciences to do it.

Citation: Straulino Mainou, L., Correa-Lau, J., Labarca, R., Villavicencio, N. A., Standen, V. G., Monsalve, S., Ugalde, P. C., Sedov, S., Puig, T. P., Loredo-Jasso, A. U., Caro, F. J., Jarpa, G. M., Hernández-Michaud, P., Latorre, C., & Santoro, C. M. (2025). Written in bones: Palaeoclimate histotaphonomic history inferred from a complete Megatherium skeleton preserved in the Atacama Desert. Palaeontology, 68(4), e70011. https://doi.org/10.1111/pala.70011

How Biogeographic Trends Influenced Ecological Adaptations in Mesozoic Dinosaurs

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The macroecology of Mesozoic dinosaurs

By: Alfio Alessandro Chiarenza

Summarized by: Olive Drury is a Biology and English undergraduate at Binghamton University. She spends most of her days typing stories and sewing dresses. She is generally a fan of ocean creatures such as the jellyfish and aspires to live in a submarine or perhaps a blimp. Olive’s favorite dinosaur is a Diplodocus. One fun fact about Olive is that she is very good at award winning board game Bananagrams.

Purpose: Large-scale geological shifts during the Mesozoic (251–65 million years ago)  brought about major transformations for global ecology. For non-avian dinosaurs, Earth’s tectonic remodeling across the Jurassic as continents moved (Figure 1) led to the permanent alteration of ecosystems, isolating dinosaur populations and impacting area availability, spatial patterns, and climate. The fallout of this fragmentation (particularly from the Late Triassic through the Cretaceous within the Mesozoic) drove the evolution of new species across terrestrial ecologies. Body mass, diet, and breeding habits all experienced major shifts, described in the study through a method called SAR (species-area relationship) modeling. This can offer insight into some interesting paleontological questions: how were enormous herbivories, which exerted great browsing pressure on their ecosystems, able to cohabitate with other organisms? How was the relative size of organisms impacted by vast geological changes, and how did these changes influence biodiversity? These inquiries, however, are unfortunately affected by undersampling. Certain areas of the globe are more sparsely recognized in the fossil record due to research bias—which only stresses the import of increased interdisciplinary (paleontology, geochemistry, climatology, sedimentology) research in less- studied regions.

Data: To describe how speciation was impacted by changes in macroecology shifts (that is, ecology shifts across millions of years), this study primarily utilizes a set of paleontological rules that have been developed by scientists through many studies. Allen’s rule describes how warm-blooded  creatures in cooler climates have a smaller surface area to volume ratio in order to conserve heat, and Bergmann’s rule states such organisms are typically larger for heat retention. These are both relevant to changes in body mass at higher latitudes due to continental shifts, for example, dinosaurs at higher latitudes would potentially appear stockier and with shorter limbs, allowing researchers to identify plausible habitats. Additionally, spatial rules such as Damuth’s Law, describes how the relationship between body mass and population density is inverse, such as in the case of Tyrannosaurus rex, where at its massive size, fewer were present in a region. However, because the Earth is not sampled equally, these ‘rules’ can be challenging to test scientifically. This ultimately challenges research, as potential fossil recovery diminishes with less dense populations. By reevaluating past data, broadening our scope of study, and persisting current research, more about the macroecology of the  fossil record can be understood

Results: Lower latitudes were more likely homes to populations of sauropods (four-legged, long-necked herbivores like Brachiosaurus). Ornithischian (like the Stegosaurus and Triceratops) populations, however, thrived at higher latitudes. Factors such as tooth size and variation in eggshells were notable features contributing to body-size and spatial-variation research. Teeth can be an indicator of size and diet, while eggshells are an eggcellent proxy for habitat—certain pigments in the shells were thermoregulators (i.e. heat-controlling) or could suggest a need for camouflage, as well as nesting habits. As an example, a sauropod’s sandy hole-nests were likely a reliance on using the heat from the ground,, thus, they likely lived in a warmer climate.

The image key including temperature (°C from -10 - 40), diet (red diamond for herbivore, green circle for carnivore), body mass, is included to the left of dinosaur silhouette images and species names marked with the diet status and colored to denote body mass for each taxa from dark purple to yellow (1 kg - 10,000 kg) in a phylogenetic tree arc around three stages of the Mesozoic through the Triassic (T), Jurassic (J), and Cretaceous (K), as displayed. The figure is a helpful interdisciplinary tool for a broad visual understanding of macroecological trends.
Figure 1: Development of macroecological features (like diet and body mass) in dinosaurs with respect to geological trends.
This image shows large-scale dinosaur evolution in terms of varying temperature and continental fragmentation over time, including a genus-level tree connecting included taxa.

Significance: By using paleontological principles including Allen’s Rule, Bergmann’s Rule, and Damuth’s Law, researchers can better investigate broad shifts in dinosaur macroecology, and their application to taxonomy, evolution, climate, and geography. The impact of these features’ development in Mesozoic terrestrial ecosystems could offer insight into modern organism’s response to environmental changes, including biotic and abiotic drivers in association with latitude. 

Broader Impacts: Going forward, anatomically precise descriptions and perpetually revisited data are essential for accurate descriptions of Mesozoic life, stressing the importance of further research. Sadly, incomplete patches in the terrestrial fossil record makes conclusive data for macroecological trends challenging. Increased data and more even sampling across the globe can help better construct the chronology for these prehistoric communities.

Citation: Chiarenza, A. A. (2024). The macroecology of Mesozoic dinosaurs. Biology Letters (2005), 20(11), 20240392. https://doi.org/10.1098/rsbl.2024.0392

Crustaceous fossils, relatives of shrimp, from 359 –299 million years ago found in glacial rock deposits of Argentinian basins

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Ostracod faunas from the Late Mississippian–Early Pennsylvanian, Calingasta–Uspallata Basin, central west Argentina: new records from glacial–postglacial successions

by: María José Salas, Andrea Fabiana Sterren and Gabriela Adriana Cisterna

Summarized by: Max Schwartzman; a senior geology major at Binghamton University. He is exploring various geology fields before going for his master’s degree in graduate school, and is considering possibly going further for a Ph.D. as well. When not studying geology, he is often playing games, trying to learn new things, or watching shows with his friends or family.

Data utilized: The authors and researchers of the original article acquired most of their fossil data through collected field samples in basins in Argentina from the Callingasta-Upallata Basin across four different locations. A majority of these collected samples and gathered data were fossils of ostracods; two-shelled critters most closely related to modern day shrimp, most of which resemble a ‘D’. These fossils that were collected were either fully preserved shells, or more commonly, molds of the species themselves which were imprinted into the sediment of the basins. These samples and collected data were then compared against data sets collected in a number of other previous analyses on these fossils by other researchers of the topic. In addition to these data sets, the researchers summarized findings from other authors regarding the study of the ostracod species from the Carboniferous–Permian Periods in Texas, USA (359–299 million years ago)

Hypothesis/Objective: The objective of the study was to perform a more in-depth exploration of ostracods from glacial periods during Earth’s history in order to construct a better record of both the time and place these ostracods existed, as well as uncover the taxonomic diversity of the group.

Methods: Data was collected from mudstone intervals and dropstones collected between 2005 – 2020. The material that the ostracods were preserved in was poorly preserved, with some external molds (when a fossil leaves their imprint behind in the rock without the fossil itself)showing more details of the valve features; to accurately collect these molds, the ostracods were prepared using a tool called a vibro-tool and fine needles for best accuracy, to clean off any extra sediment obscuring fossil details. The science team then used rubber latex to create a 3D replica of the imprint to better see the details. All of these samples were recorded and photographed.

Close up of 31 oval-shaped Argentinian ostracod fossils, averaging 200 μm in size, and varying in shape; some are more oval-shaped, some are bean-shaped, and some are flat and wide.
Figure 1. Photographs of many of the ostracod fossils or fossil imprints found in the Calingasta-Upallata Basin in Precordillera Argentina from the middle of the Carboniferous Period. Species 13–17 are the new species indicated by their bean-like shape and lump. Species 25–29 are fossils identified outside of Bolivia. Scale bar = 200 μm.

Results: The location of these fossils and the basins in which they were deposited tie into the glacial events in Southwest Gondwana, part of a former supercontinent that was made up of South America, Antarctica, and parts of Africa, much of which was centered around the south pole. The deposits these fossils were found in were found either below or between diamictites, a type of rock created by glaciers as they are moving. Using the location of these deposits, scientists were able to track how expansive the glaciers were, how their locations changed, and  how long it took for each deposit to be left behind. Along with the glacial data, eight species of ostracods, some already known to science and some new, were identified from the collected data. Figure 1 shows many of the ostracod samples and molds that were uncovered in the areas that were being investigated, with many of them displaying similar characteristics to one another, with differing species also having similar characteristics with one another. For example, one new species was identified: this new species was identified by a lump between where they curve. Two species were found outside of Bolivian geologic deposits for the first time, and two others were documented for the first time in South American geologic deposits. 

Importance of Study: This study is particularly important as it indicates the range of ostracods outside of where they were first documented. The Southern Gondwana glacier itself, due to its massive size, indicates colder climates globally. Using this knowledge, we can infer how organisms like ostracods lived in these colder conditions and how their ranges expanded or contracted along with the glaciations.

Broader implications: The ostracods are helpful in the study of both paleoclimate and paleobiology, and gives a better understanding between how life evolves through global climate changes, such as  through the Southern Gondwana glacier.

Citation: Salas, M. J., Sterren, A. F., & Cisterna, G. A. (2025, September 1). Ostracod faunas from the late Mississippian–early Pennsylvanian, Calingasta–Uspallata basin, Central West Argentina: new records from glacial–postglacial successions: Journal of Paleontology. Cambridge Core.

Revisiting the previously misunderstood Late Triassic (~205 million years ago) marine reptile, Pachystropheus rhaeticus

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The relationships and paleoecology of Pachystropheus rhaeticus, an enigmatic latest Triassic marine reptile (Diapsida: Thalattosauria)

By: Jacob G. Quinn, Evangelos R. Matheau-Raven, David I. Whiteside, John E. A. Marshall, Deborah J. Hutchinson & Michael J. Benton 

Summarized by: Kodi Biscardi, who is a transfer student at Binghamton University studying geology and hopes to one day study geophysics.

What data were used? Researchers present two major types of data in this study: fossil evidence of Pachystropheus rhaeticus, a marine reptile, and the fossilized pollen/spores found in the same rocks that contained Pachystropheus rhaeticus fossils.Researchers revisited all previously discovered and named  fossil specimens of Pachystropheus rhaeticus throughout Britain (particularly from rocks of the Westbury Formation, which dates back to the end of the Triassic ~205 million years ago. Namely, the studied fossils includes a “holotype” of the Pachystropheus rhaeticus, an incompletely preserved fossil of ~35 vertebrae and other bones. A holotype is a singular fossil that is used to define the features of a species, so that researchers can reference it when discovering new fossils. Researchers also present a new, similarly-aged specimen, suspected to belong to the same species of Pachystropheus, found in the same location as the holotype. This new discovery has 62 well-preserved backbones–almost double the amount of the holotype–as well as other preserved animal fossils and, fossilized pollens preserved within the rocks of the Westbury Formation.

What was the question or point of the paper? Researchers set out to establish a comprehensive history of Pachystropheus rhaeticus, a late Triassic marine reptile. This fossil is often misidentified because the preservation is often poor, which means that there can be conflicting information and interpretations about it. Scientists here focus on untangling some of the confusion by re-studying previously named fossils of this species, figuring out who it is closely related to, examining its ecological roles as a predator, and better defining the time that this species went extinct by using pollen fossils from the same layers as the reptiles.

Methods:  Researchers described consistent morphologic characteristics using the Pachystropheus rhaeticus holotype. Using bones from the holotype, the researchers conducted a comparative anatomy study of all previously and newly discovered Pachystropheus rhaeticus specimens, reidentifying many bones as coelacanth fish, instead of reptiles. Focusing on their newer fossil assemblage, having removed the non-reptilian bones from the study group, researchers utilized scanning techniques to produce 3D models that could be reconstructed to resemble what bones previously looked like during life. These scans gave researchers much easier ways to study harder-to-reach fossils and find common patterns in the bone structures, which is called the species’ morphology. By analyzing the morphology of specimens, researchers can infer the relationships between this species and possible ancestors/descendants, causing a shift in the Pachystropheus rhaeticus’ placement in evolutionary trees called a phylogenetic analysis. Some of the latest discovered specimens were believed to be from the early Jurassic (201.3 mya). However, preserved pollen and spores found within the rocks containing the specimen were focused on by researchers in this study. By running various tests on fossilized pollen/spores, researchers were able to precisely date the ages of the rocks these fossils were found in and, therefore, determine the age of the Pachystropheus rhaeticus fossils within it. Studying fossil pollen and spores is called palynology. 

Results: Scientists concluded that none of the named specimens of reptile had preserved teeth, jaws, or skulls; those specimens that had them actually belonged to the coelacanth fish. This means that the reptile’s ecology is speculative. Teeth are highly important in paleontology, as by studying them, paleontologists can guess a species’ diet and thus establish their role in the ecosystem. For instance, predators have sharper teeth designed to tear meat, while herbivores have teeth better designed for grinding down plants. Based upon their previously limited morphological information, the Pachystropheus rhaeticus was originally believed to be the oldest and first species of Choristodere (an order of ancient Jurassic reptiles). However, the results of their analysis of the fossilized pollen dated the youngest fossils to be around late Triassic (237 mya) in age, which means that the species did not survive a major extinction event at the end of the Triassic. Fossilized Pachystropheus rhaeticus ribs and upper leg bones showed specific features that are associated with nearshore aquatic lifestyles, but associated with the limited ability to move on land. These characteristics were highly similar to those of another marine reptile studied in other articles, Endennasaurus acutirostris; with this and the results of their phylogenies, researchers place the Pachystropheus rhaeticus in the same order as the Endennasaurus, which is called Thalattosauria. 

Imaged are 2 slender limb bones from 3 different angles, which were identified as Pachystropheus rhaeticus upper leg bones.. Sections labeled A–C display photographs of a real fossil of the specimen's right leg bone; the bone's surface is a pale brown color, weathered and cracked, however still shows anatomical landmarks at its proximal and distal ends. Sections labeled D–F display a pale yellow colored digital model reconstructed from CT scans of a left leg bone, showing the same anatomical landmarks as A–C. The bones are around 53 mm in length.
This figure displays two Pachystropheus rhaeticus upper leg bones from an assemblage. A–C is the right upper leg bone from a young individual. D–F are the remodeled and reconstructed left bone hidden within the assemblage but imaged via CT scans. Twisting and marked depressions (it, mc, lc, fh) of their bone indicate this specimen had adaptations for aquatic lifestyles,  rather than terrestrial. The scale bar represents 10 mm.

Why is this study important? Validity and reliability are important in any field of science. Previously, Pachystropheus rhaeticus specimens were believed to be much more abundant, leading to consistent misidentification. This study aimed and achieved to narrow down the standards of the species ecology, morphological identity, and chronological placements. This was exceedingly hard due to limited information from the fossil record. This study also closes a long-standing mystery of the evolutionary placement of Pachystropheus rhaeticus, labeling the species one of the last surviving members ofThalattosauria, not the earliest of the Choristodere.

Broader Implications beyond this study: This study has shifted many early marine reptile Choristodere and Thalattosauria evolution models, as well as set a standard for reevaluating old specimens for the possibility of misidentification and chronological mistakes. The accuracy of evolutionary trees is highly important for scientists as they allow us to infer more about how past ecosystems and lifestyles changed over time, especially during mass extinctions. Mass extinctions are especially periods of great interest to paleontologists, as understanding how animals responded to mass extinctions in the past can help us apply that information to modern day climate change science. 

Citation: Quinn, J. G., Matheau-Raven, E. R., Whiteside, D. I., Marshall, J. E. A., Hutchinson, D. J., & Benton, M. J. (2023). The relationships and paleoecology of Pachystropheus rhaeticus, an enigmatic latest Triassic marine reptile (Diapsida: Thalattosauria). Journal of Vertebrate Paleontology, 43(6). https://doi.org/10.1080/02724634.2024.2350408

How an extinct group of shelled animals expanded, thrived, and collapsed, after a mass extinction

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Diversification and disparity in a major Palaeozoic clade of Brachiopoda: the rise and fall of the Plectambonitoidea

By: Yves Candela, Zhen Guo, and David A.T. Harper

Summarized by Logan Mullin, an undergraduate student studying biological sciences at Binghamton University. Outside of school, Logan enjoys going to the gym, staying active outdoors, and spending time with friends and family. 

Purpose of Study: The purpose of this paper was to study the changes over time in population and characteristic traits of an extinct group of shelled organisms (brachiopods) called the Plectambonitoidea.. The Plectambonitoidea lived across the ocean floors more than 400 million years ago, and, at their peak, were one of the most common groups of brachiopods in the world. Scientists study Plectambonitoidea because of its rich fossil record, which can allow us to understand how marine organisms and oceans as a whole responded to major geological events. Using their collected data described below, the authors connected the rise of the Plectambonitoidea to major changes in the fossil record, which we call the the Great Ordovician Biodiversification Event and their extinction to the Late Ordovician Mass Extinction. These findings also help us understand how other ancient marine species reacted in times of global environmental change. This makes Plectambonitoidea a great example for broader debates in paleobiology, such as the Court Jester versus the Red Queen debate, which states that environmental events and interactions mold biodiversity over time.

Data Used: The authors created a large dataset of 4,586 individual fossil occurrences of 123 genera of Plectambonitoidea from the Paleobiology Database, a public, online website where scientists across the world can view and add to fossil records from all time periods. Their dataset was global, with many different fossil occurrences from all across different continents and regions. These occurrences were from the Early Ordovician Tremadocian(485 million years ago) to the Middle Devonian Eifelian(393 million years ago). In addition to their occurrence data, the authors created a table of 43 different physical characteristic traits for each genus. Some traits include shell shape, hinge structure, and muscle scar patterns. To create this table, the authors drew on previously published articles, scientific illustrations, and direct examinations in museums to identify the different traits. The authors organized each trait into categories to compare the different genera fairly, with unknown or missing data marked with a “?” to preserve accuracy. This table allowed the authors to see how the Plectambonitoidea body types changed through time and in different geological environments. 

Methods: After completing their fossil dataset, the authors checked how complete their fossil record was with a statistical analysis called Good’s u, which estimates if the dataset being studied is represented by enough samples.  Then, the authors plotted fossil occurrences by time and location to demonstrate how widely the distribution Plectambonitoidea fossils varied over time. After that, with the use of  a computer application called PyRate, the origination, extinction, and diversity of Plectambonitoidea throughout time were estimated. PyRate also accounts for biases as well, such as preservation bias by estimating how often fossils were likely to be preserved in each time interval.. Lastly, for the morphological analysis, the authors used their table of 43 morphological traits  to show how the variety of Plectambonitoidea body forms diversified over time. The authors compared how similar or different each genus was to the others and used a visualization tool called a Principal Coordinate Analysis to reconstruct the groups’ morphospace. A morphospace is the full range of shapes of an organism over time. These approaches allowed the authors to identify when the group expanded, declined, and how it changed over time during major geological events

Results: The authors found that the rise and fall of the Plectambonitoidea superfamily had a connection to major geological events.  During the Great Ordovician Biodiversification Event, a time when ocean life rapidly expanded and evolved, the Plectambonitoidea reached their highest levels in diversity. More specifically, it was during the Middle Ordovician about 460 million years ago. Morphological diversity and the number of organisms were the greatest at this time. After the Great Ordovician Biodiversification Event, the diversity began to decline. During the Late Ordovician Mass Extinction, an event caused by major climate and sea level changes, extinction rates started to surpass origination rates causing a sharp decline in population for most lineages. Although some lineages survived into the Silurian (444-419 million years ago), the superfamily was never able to recover and ultimately went extinct in the Middle Devonian (393-382 million years ago). Figure One supports the results by displaying statistics showing a shrinkage of morphospace occupied after the Late Ordovician Mass Extinction.

Four line graphs showing four measures of morphological diversification of Plectambonitoidea from the Early Ordovician to the Middle Devonian (480-400 million years ago). The y-axis on each graph ranges from 0 to 80 organisms. A, Sum of Ranges, shows how many different body shapes the group had, which stayed high until a sharp decline after the Late Ordovician Mass Extinction. B shows the Sum of Variances, which shows how different the genera were from each other, and followed the same pattern as the Sum of Ranges. C shows Average Nearest Neighbor Distance, showing how close or far the genera were in body shape, which showed no clear trend, but showed more variation after the Late Ordovician Mass Extinction. Lastly, D shows Average Displacement, which displays how the average body shape changed over time, and remained stable throughout, with peaks at the beginning and end of their lifetime.
Figure 5: Four bar graphs showing the trends of Plectambonitoidea over time from 480-400 million years ago.  Each graph uses a “morphospace,” which shows the range of body forms Plectambonitoidea can have. A, Sum of Ranges, shows how many different body shapes the group had. B, the Sum of Variances shows how different the genera were from each other. C, Average Nearest Neighbor Distance, shows how close or far the genera were in body shape. D, Average Displacement displays how the average body shape changed over time. All of these bar graphs indicate that the morphological diversification shrank after the mass extinction and stayed low until their extinction millions of years after this event.

Why is this study important? This study is important because it demonstrates how the Plectambonitoidea’s success and decline were shaped by major changes on Earth. By tracking when new genera appeared, changes in body shapes, and when extinction rates rose, the authors were able to reveal how Plectambonitoidea expanded during times such as the Great Ordovician Biodiversification Event and struggled during major environmental disruptions such as the Late Ordovician Mass Extinction. This study’s findings also contribute to larger debates in paleobiology. 

Broader Implications beyond this study: This study has many broader implications. It demonstrates how mass extinctions like the LOME can completely change evolutionary trends. The elimination of some clades opens more space in the environment for other clades to thrive. This study also discusses major debates in paleobiology, such as the Court Jester versus the Red Queen debate, which states that environmental events and interactions mold biodiversity over time. Lastly, this study provides information to better understand long term diversification and extinction patterns for other fossils.

Citation: Candela, Y., Guo, Z., & Harper, D. A. T. (2025). Diversification and disparity in a major Palaeozoic clade of Brachiopoda: the rise and fall of the Plectambonitoidea. Palaeontology, 68: e70010. https://doi.org/10.1111/pala.70010