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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

A new change in heart: a new species of heart urchins found in South Korea

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Brissopsis pohangensis sp. nov., a New Echinoid Species (Spatangoida) from the Middle Miocene Duho Formation, Pohang Basin, Korea

By : Bong Jin Lee and Dal-Yong Kong

Summarized by: Joshua Rivera. Joshua Rivera is a geology major and an Asian studies minor in Binghamton University. He is currently a senior and has no plans post-graduation. He hopes to one day get into an exploration program and find things related to his field, be it fossils, minerals or fossil fuels. In his free time, he currently writes short stories, poetry, and novels. He enjoys exploring the world on hikes, and enjoys playing video games.

Data: Researchers found 428 fossil samples from the Duho Formation, which is a subdivision along the Pohang Basin in southern South Korea. It can be dated to around the middle Miocene Epoch, which is roughly 12 million years old. Among these samples were a never-before discovered sea urchin (related to sea stars), in a group called the spatangoids or the“heart urchins”. Upon a closer look at these fossils, there were a few notable things which stood out. Its petals held a unique shape. The groove along it had a deeper indentation compared to others of its kind. One of its plates was significantly longer as well (Fig. 1). This was common among all found 428 samples. The samples were preserved in a flattened manner, likely from the weight of sediment pressing on it.

Hypothesis: These heart urchins seemed quite similar to others in their group, specifically a genus called Brissopsis. However, the various outliers in plate length and other aspects of its morphology had the researchers asking if these were sufficient enough to determine this finding as an entirely new species or a species already known in the genus Brissopsis.

Methods: These researchers collected and recovered these samples from the field. They began the process of cleaning and preparing the samples, removing any sediment and making sure details on the body were visible. Once clean, they measured the samples. To the best of their ability, they measured the length and width. However, some differences in morphology, or simply the form the critter takes, required microscopy in order to gauge. And so they were measured under a microscope. There were specific urchin related- anatomical parts that they noticed the most difference in. These were namely: the test, the apical disc, the fascioles, and the plastron. To help visualize, the test is the outer hard shell as a whole. The apical disc is the top most disc on the test. The fasciole is a flattened groove along the test. Lastly, the plastron is the bottom shell, or the bottom side of the test. Figure 1 shows these details.

An image of the findings Brissopsis pohangensis. It is relatively round, with many plates and grooves along it., much like a knight’s armor. On its top it is divided into 5 segments, like a person with all of their limbs extended. These are the ambulacra, and they have a rounded plated texture. Between the ambulacra, are the interambulacra. If a person had all their limbs opened wide, this would be the empty space between all of them but it is actually solid. The signature of the top are two heart shaped structures, one along the arm like ambulacra, and the other upside down along the leg like ambulacra. The bottom side, the same ambulacra are much more prominent, and are larger. In the center where all the ambulacra meet, the “chest”, this is where its mouth is. The interambulacra are also there, but they are less in number, but larger.
Fig. 1. A mockup of the new species Brissopsis pohangensis. Side A represents the top, the side not containing the mouth. Side B indicates the bottom, the side which does contain the mouth, which can be seen as the pitch-black groove in the center of the ambulacra. The Roman numerals indicate the five radial bands, the ambulacra, a signature of echinoderms. Through the ambulacra, echinoderms are capable of movement through their tube feet which emerge. Numbers 1-5 indicate the space between the ambulacra, the interambulacra. The blue solid line represents a fasciole, which was measured during tests. On side B, letters a and b refer to the columns designated by ambulacra and inter ambulacra. Numbers indicate the order of plates. The solid blue line represents the path of the subanal fasciole, while the dotted line is the inferred path as samples are missing this portion.

Results: The different body measurements, among others, were enough to find similarities, and therefore confirm they belonged to the genus Brissopsis. It is primarily the measurements and morphology of the labral plate (a small plate near the mouth), which is larger here than other species. The petals were quite different in shape and pattern than other species. Finally, the patterns of the fasciole were also quite different, as they were much deeper than other closely related species. Whilst being a spatangoid, its morphology was far different, to warrant it being a newly discovered species within Brissopsis.
Also of note, their preservation was significant. These spatangoids were found not only preserved in high numbers together, they were also found alongside scallops and snails. Typically, these spatangoids are not very communal, spread anywhere from the shallower tidal flats to the abyssal depths, thousands of meters below sea level. Spatangoids would burrow beneath the sands where they would dwell, predate, far away from most other life. Should something happen to the condition of the sediments, like the oxygen content running low, they would abandon their burrows. Upon leaving the sediments they would typically die, overturning on the surface of the ocean floor. This suggests these spatangoids, in addition to scallops and gastropods, did not die naturally, like of age. Likely, they faced something far more catastrophic, killing them all quickly with little notice.

Significance: This discovery is a breakthrough for spatangoid research. Not only was a new species discovered, but a hypothetical new “piece of the puzzle” is now unlocked in the ecosystems of Miocene East Asia. The assemblage they were found in may now also be a starting point on any investigation studying how they lived and how their preservation can tell us more about how they died.

Broader Implications: This new heart urchin is the new piece of the puzzle, in the larger scheme of East Asian paleontology. Spatangoids feed by burrowing, in the ocean floor. They ate whatever they could. Brissopsis pohangensis may play a yet to be found role in the environment as both predator and prey. Further work to understand how their preservation tells us about their lifestyles or about the moments leading up to their death is warranted to better understand the broader ecological role these organisms played.

Lee, B. J., & Kong, D.-Y. (2025, June 30). Brissopsis pohangensis sp. nov., a new echinoid species (Spatangoida) from the Middle Miocene Duho Formation, Pohang Basin, Korea. Economic and Environmental Geology. https://www.kseeg.org/journal/view.html?uid=2300&vmd=Full#n

Taking a look at an ancient crinoid (relative of seastars) lineage that nearly died out

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Phylogeny and macroevolution of a “dead clade walking”: a systematic revision of the Paragaricocrinidae (Crinoidea)

by Richard G. Keyes, David F. Wright, and William I. Ausich

Summarized by Alberto Farfan, Alberto lives in the Bronx, New York, and is a student at Binghamton University who is seeking a B.S. in Biology. He is also the president of the Binghamton University Fencing Club. His dream is to pursue infectious disease research to help others dealing with sickness and disease.

What data were used? The scientists collected data about features of the body from previously discovered crinoids (sea creatures with a stem and many arms, within the group that includes sea stars), as well as a new fossil that they discovered. The new fossil was discovered in the Tuscumbia Limestone on the East Warrior Platform in Northeastern Alabama, USA. The limestone in this region was formed over 336 to 340 million years ago during the Middle Mississippian Period. The new fossil was found in three disarticulated pieces in a quarry in Madison, Alabama, which is a part of the Tuscumbia Limestone. The feature that sets this fossil apart from other discovered fossilsis that it has spikes covering its anus.  

What was the goal of the paper? Initially, the goal was to analyze and place the new crinoid fossil into the currently existing crinoid family tree. But once they saw the results of their data, it caused them to change their goal. The goal then shifted to examining the entire crinoid group to reestablish the evolutionary relationships of the entire family that the new fossil is a member of. 

Methods: The scientists first collected the recently discovered fossil and removed it from the limestone. Because of some of the preserved features, they suspected it to belong to a group of crinoids (a family) called the Paragaricocrinidae. Due to this, they compared the fossil to four species in the Paragaricocrinidae family from the middle to late Paleozoic Era (~340 million years ago). They then compiled every characteristic visible from the fossils’ bodies together and used it to create an evolutionary tree..The scientists then used two different methods to determine how every species is related to each other. They first used parsimony analysis to determine the relation based on their inherent features. This is done by arranging the relationships of the fossils in the tree in a way that uses the fewest number of changes in the characteristics. The scientists also used Bayesian statistics to infer an evolutionary tree, as well, which uses probability to arrange the relationships of the included species. For example, if you flip a coin, you have a 50% (0.5) chance of getting heads. If you flip it twice, the probability of it being heads twice is 0.5*0.5 (25%). Bayesian statistics uses probability to understand the likelihood of how the species evolved and calculates that probability from the ancestors to the descendents of the tree.This allowed them to get a full analysis of the family to determine where each member of the family fits in an evolutionary tree.

Figure 7 shows the diversity of Paragaricocrinidae branches throughout the Early Carboniferous 350MYA to the middle Permian 280MYA. There is a sharp decline after the Late Carboniferous. The X axis is the Time in MYA from 340MYA to 260MYA, while the Y axis is Diversity(Number of Lineages), ranging from 0 to 10. The highest number of observed lineages was the Upper Carboniferous, with 8 lineages. At the end of the Late Carboniferous, there is a sharp decline, leaving 1 lineage and then 2 and then back to 1 lineage, marking when it became a "dead clade walking", which is the text on the graph referring to this point.
Figure 7 shows how diversity of Paragaricocrinidae crinoids branches throughout the Lower Carboniferous to the middle Permian. There is a sharp decline in biodiversity after the Late Carboniferous. 

Results: The researchers determined that a reorganization of the Paragaricocrinidae family tree was needed due to the differences observed in species. The scientists determined that, of the fossils they studied, four new genera, four new species, and one preexisting species had to be created or moved to a pre-existing taxon. Some uncertainty remains, so some species were not yet moved to different taxonomic groups and will need to be restudied. Previously, scientists thought that the family was very diverse with six different species in the entire family but underwent an unexplained decline (Fig 1) around 300 million years ago in the Late Carboniferous. After the steep decline, the species still clung on with one to two species leading into the Middle Permian. It was originally believed that their sudden decline was a result of a mass extinction event and so the family was given the term “dead clade walking”. A DCW is defined as a group of species that barely survive a mass extinction event with the majority of its members dying except for a few. But the issue with this is that there has been no documented mass extinction event during the time of their decline. However, now that scientists have a better understanding of the true diversity in this group, these scientists no longer think a “dead clade walking” is an appropriate term, nor do they think this was due to the result of a mass extinction. Instead, they called the group a “dead clade staggering” since they believe that their decline is due to another outside factor not related to a mass extinction and more inline with a slower, less extreme background extinction, possibly due to ecological changes.

Why is this study important?: This study is important because it helped the scientists better understand a more accurate picture of the family Paragaricocrinidae as a whole. It then became a question of what caused the biodiversity in the Paragaricocrinidae clade to decline so abruptly. It was shown that this pattern was not as a result of mass extinction but potentially as a result of possible ecological changes. Understanding the history of Paragaricocrinidae helps to give us insight into how crinoids respond to ecological pressure (more limited resources, competition, etc). This shows that species can lose biodiversity not just as a result of a major mass extinction-level event (asteroids, volcanoes, etc), but also as a result of environmental factors such as potential competition or small natural changes in the environment.

Broader implications beyond this study: A better handle on the taxonomic diversity of the fossil record can change how we identify extinction events in the fossil record. The authors revised the understanding of Paragaricocrinidae from a “dead clade walking” to a “dead clade staggering” since the family went extinct less rapidly and less dramatically than thought as a result of small environmental factors such as competition or a lack of resources. This can aid scientists in better understanding the amount of ecological changes that are needed to bring a species this close to extinction.

Citation: Keyes, R. G., Wright, D. F., & Ausich, W. I. (2025). Phylogeny and macroevolution of a “dead clade walking”: a systematic revision of the Paragaricocrinidae (Crinoidea). Journal of Paleontology, 99(1), 144–162. doi:10.1017/jpa.2024.70, https://doi.org/10.1017/jpa.2024.70

The Glypheid Lobsters: The Living Fossils that Escaped Extinction

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An overview of the stratigraphic and paleobiogeographic occurrences of the lobster family Glypheidae, including a reappraisal of Early Jurassic Paraglyphea eureka from Argentina

By: Susana E. Damborenea, Miguel O. Manceñido, Javier Echevarría, Francisco M. Harguindeguy

Summarized by: Kayla Said. Kayla is a senior at Binghamton University studying biology with a minor in health and wellness! After graduation she hopes to attend medical school and pursue her dreams of becoming a doctor in Dermatology. In her free time, Kayla loves to crochet, exercise at the gym, and bake! 

What was the point of the paper? A group of lobsters, called the glypheid lobsters, was thought to be extinct for over 50 million years. In the 1970s, a living species of the taxonomic family was discovered in the deep Pacific Ocean. The point of the paper is to deduce the full story, or history, of the glypheid lobster family, and understand how these organisms went undetected for years, giving them their nickname of “living fossils.” With previous data from published literature and new fossil evidence from Argentinian rock, the authors were able to piece together a clearer story of how the glypheid lobster family escaped the forces of extinction.

Data:  To understand the fascinating history of Paraglyphea eureka, a species within the glypheid lobster family, paleontologists first compiled research from different decades. Sorting through peer reviewed paleontologic literature helped paleontologists develop a story of the lobsters’ history, including where they lived, how they lived, and which environments they preferred. However, when sifting through the literature, the researchers noticed missing details in the known information about P. eureka. To patch up the missing details in the lobster’s whereabouts throughout time, new data was collected. Researchers took off to Mendoza, Argentina, where they found a sheet of rock from the Toarcian Age, in the Jurassic period, that formed nearly 180 million years ago. From this bed of rock, the researchers found exoskeletons of the P. eureka, and they were able to study their anatomy in much greater detail than ever before, as seen in Figure 1. 

The figure represents a hand drawn sketch of the Paraglyphea eureka lobster. The drawing depicts a hard outside covering around the entirety of the organism, aside from the lobster’s eyes and antenna. Certain portions of the drawing are shaded in a light orange tone. The lobster appears to have six long legs in the image, with a segmented tail. The drawing represents a side view of the lobster, excluding portrayals of the lobster’s upper and lower body from a bird’s eye view.
Figure 1. Paraglyphea eureka, a restoration sketch. After analyzing components of fossilized portions from Toarcian Age rock originally found in Mendoza, Argentina, researchers were able to resketch the morphology of the P. eureka based on this new evidence. This particular fossil has 10 legs, 6 abdominal segments, and 2 main claws.

Methods: In their study of glypheid lobsters, researchers first reorganized the literature that was already published about them. By doing this, they unraveled inadequate evidence in the survivorship of the lobster family and were able to better understand what was and was not known about them. Researchers found that P. eureka was one of three living species to this day of the glypheid lobster family. In hopes of revealing more fossilized evidence of the lobsters, researchers then extracted a patch of 180-million-year-old rock from Mendoza, Argentina. By analyzing the bed of rock, the researchers found exoskeletons of P. eureka, and thoroughly reevaluated the species based on anatomy found in new fossils. This allowed the researchers to revise the lobsters’ scientific classifications and reassess their geographic distribution over time. This process that the researchers underwent is called a systematic reappraisal, meaning that they combined new fossil evidence with previously published literature to better understand the anatomy of P. eureka. 

Results: After evaluating new fossil findings and piecing together older research, paleontologists classified P. eureka as a cosmopolitan species. This means that these glypheid lobsters are able to thrive in a variety of environmental conditions and can live across a wide geographic range. Scientists found that due to their large geographic range and distribution, the P. eureka was likely able to escape extinction by migrating to cold, deeper waters. Due to a habitat shift of moving from warm, shallow waters to deeper, colder waters, P. eureka were able to escape forces of extinction after a rough period of volcanic eruptions. This series of volcanism released greenhouse gases into the atmosphere and thus increased ocean acidification dramatically. This event is known as the Toarcian Oceanic Anoxic Event, and it occurred over 100 million years ago, marking the sharp decline in glypheid lobster diversity. 

Why is this study important? This study is important for several reasons. Firstly, it helps us understand the full story of P. eureka, or “living fossils.” This study helps us understand how glypheid lobsters were thought to be extinct for over 50 million years, but with new evidence, are now understood to be habitat shifting organisms that can dwell in many different conditions. This study also demonstrates how a wider geographic range of an organism helps increase its survivorship abilities, making it more likely to survive. By piecing together new fossil evidence with previously studied literature, this study focuses on anatomical features of Paraglyphea eureka, providing clear correlations between cosmopolitan groups and their survival abilities.  

Broader Implications of this Study: This study impacts science on a broader level, as it helps us decipher how gaps in fossilization records can influence our knowledge of biological presences on our Earth. This study demonstrates why it is important for us to understand cosmopolitan species, due to what is happening in our environment today with increased ocean acidification. The acidity of our oceans is influenced by the amount of greenhouse gases we exude into the atmosphere. By understanding the migration potential for cosmopolitan organisms, especially with the changes occurring currently in our environment, we are able to understand more about modern day organisms. This also helps us predict changes to species populations in the future! 

Citation: Damborenea, S. E., Manceñido, M. O., Echevarría, J., & Harguindeguy, F. M. (2025). An overview of the stratigraphic and paleobiogeographic occurrences of the lobster family Glypheidae, including a reappraisal of Early Jurassic Paraglyphea eureka from Argentina. Journal of Paleontology, 1–14. doi:10.1017/jpa.2024.41 

500-million-year-old fossils uncovered in the Grand Canyon (USA) reveal evolution driven by animal competition

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Evolutionary escalation in an exceptionally preserved Cambrian biota from the Grand Canyon (Arizona, USA)

By: Giovanni Mussini, James W. Hagadorn, Anne E. Miller, Karl E. Karlstrom, Rhydian Evans, Carol M. Dehler, Salvador Bastien, and Nicholas J. Butterfield 

Summarized by: Kayla Adeyemi is a senior biochemistry major at Binghamton University. She plans to attend medical school in pursuit of becoming a physician. In her free time, Kayla likes to ballroom dance and read fantasy novels. 

What data were used? 29 shales, or hardened mud, around 15 cm thick, were collected in the Grand Canyon in the Bright Angel Rock Formation in Arizona, USA. The shales contained 1,539 non-biomineralized, or soft-bodied, fossil organisms, from the Cambrian (~500 million years ago). Hard-bodied, or biomineralized, organisms are more likely to be fossilized than soft-bodied organisms since they have hard parts like bones that are more resistant to decay. The fossils found are referred to as small carbonaceous fossils (SCFs), meaning they are under a millimeter (for scale, that’s smaller than a sesame seed) and preserve small details of soft-bodied organisms. Since the fossils were preserved in shale, a rock of small grains, scientists interpreted the environment to be low-energy and not frequently disturbed by strong ocean currents. Trace fossils (fossils that show behavior, rather than the body) previously found in the area were used to estimate the environment: they show evidence of seafloor animal activity through traces left by feeding, burrowing, and resting. 

What was the hypothesis being tested? Researchers tested the evolutionary escalation hypothesis. The escalation hypothesis proposes that animal competition and predators influenced evolution (i.e. the biological change in populations over time). Over time, less competitive organisms would be confined to less resourceful environments, while more competitive organisms would inhabit resource-rich environments. The researchers here propose that the escalation hypothesis happens in stable and resource-rich environments. Most Cambrian non-biomineralized fossils are found in environments that would have had limited oxygen and information about their ecosystem. However, this study found non-biomineralized fossils from an environment with oxygen availability and an abundance of animal activity and nutrients, as evidenced by diverse trace fossils. Therefore, they could infer a resource-rich environment, and the escalation hypothesis could be tested with their data. If escalation occurred, researchers would expect to find non-biomineralized Cambrian organisms with adaptations for catching food and similarity in their body shapes that would indicate similar pressures (like how sharks and dolphins have similar bodies due to similar environments, not evolution). 

Methods: The researchers collected 29 shales around 15 cm thick, along the Bright Angel Rock Formation in the Grand Canyon. The formation contains 100 m thick rock from shallow marine environments during the Cambrian. The scientists unearthed the fossils carefully by dissolving the shale in hydrofluoric acid and filtering the residue through a tiny strainer. The residue contained the fossils, which were viewed and separated under a microscope. 

Results: The researchers found 1,539 well-preserved small carbonaceous fossils, SCFs. They also found bacteria microfossils which were interpreted as photosynthetic; that means this environment must have received at least some sunlight. All of the SCFS were disarticulated organisms, but had some intact body parts. Most of the fossils were of priapulids (the group containing worms), crustaceans (the group containing lobsters, clams, and barnacles), and molluscs (the group containing squid, clams, and snails). The organism parts ranged in size from four µm to three mm long, or the height of two U.S. pennies. They were identified by their feeding structures and similarities to modern-day critters. Priapulids are smooth and round predatory worms. The researchers discovered a new species of priapulid with hundreds of branched teeth in rows. Its teeth were likely too delicate for catching larger prey, but thicker towards the outside, with fine bristles in between for scraping food off sediment. Its feeding structure was notably more complex than other known Cambrian priapulids that lacked branching and bristles. Crustaceans were identified by their lined and scaly crescent-shaped teeth. They showed adaptations for breaking down larger food with long incisors and comb-like teeth structures to filter out particles. Scientists found two types of crustacean teeth: one with uniform scales and short incisors, and another with asymmetric scales and longer incisors. The first type could be useful for eating plankton, and the second type could be useful for predation. This shows how different organisms in the same environment can adapt to utilize different resources and reduce competition. The mollusks the researchers found have distinct boot-shaped radula or “teeth” that vary in shape, as seen in Figure One. 

13 images of mollusk “teeth” labeled from A–M. The teeth range in size from 150 to 450 μm long. Pictures A–M are in color and are brown, while pictures L and M are in black and white. All teeth are connected in a series by a long, dark connective tissue. Surrounding the root of the teeth appear to be small, thin fibers. Picture A shows shovel-shaped teeth that are symmetrical on both sides. Picture B also shows shovel-shaped teeth. Picture C shows cone-shaped teeth. Picture D shows more rectangular, wedge-shaped teeth that are marked by wear. Picture E shows a close-up of five of the teeth in picture D, noting the wear on the teeth. Picture F shows more cone-shaped teeth. Picture G boxes in six of the teeth from image F to show the wear of the teeth. Figure H shows another set of cone-shaped teeth. Picture I shows a partial series of shovel-shaped teeth. Pictures J and K have black boxes around parts of the series of teeth in image I to show the inward curve of the teeth surface. Picture L shows a microscopy image of an organism with shovel-shaped teeth. Picture M is a magnified image of teeth from Picture L to show the texture and inward curve of the tooth surface.
Figure One: This figure depicts the various shapes of fossilized mollusc radula or “teeth.” The teeth range from 150 to 450 μm long. Images A, B, I, and L show shovel-shaped teeth. Images C, F, G, and H show cone-shaped teeth. Image D shows wedge-shaped teeth with an emphasis on the tooth wear. The scale bar is 50 μm for each image except for E, which is 25 μm. 

The teeth have either a shovel-shaped form, pictured in Figure One, Image A, B, and L, or a thinner cone-shaped form, as seen in Images C and F. These particular mollusks possessed both sets of specialized teeth to shovel and scrape their food from sediment, as evidenced by the wear shown in Image E in Figure One. This is far more advanced than the teeth of organisms that lived in more resource-limited environments (like Wiwaxia and Odontogriphus). Their resource-limited counterparts had weaker, fewer, and generalized teeth. These fossilized organisms’ dissimilarity to resource-limited Cambrian organisms and similarity with current species led the researchers to believe that escalation occurred in this Cambrian environment. Their environment was oxygenated and nutrient-filled, allowing them to invest their energy in more specialized feeding structures.

Why is this study important? It is rare to find fossils from the Cambrian that are soft-bodied, well-preserved, and from environments better suited for hosting diverse life. The fossils found had unexpectedly well-adapted feeding structures for selective feeding and were comparable to living species. The fossilized organisms existed in a pivotal time during the Cambrian Explosion, where there was a surge in marine animal diversity within the fossil record. This study fills a gap in our fossil record for soft-bodied animals and proposes escalation as a driver of evolution.  

Broader Implications beyond this study: The evolution of predation is an active area of study within paleobiology. The arms race theory is a type of escalation theory that claims prey adapt to avoid predators. This can be used to explain the abundance of hard-bodied organisms that evolve for the first time during the Cambrian. However, organism adaptation in this study appeared to be mainly driven by competition and resource acquisition, despite them being soft-bodied and more vulnerable to predators. It suggests that predation was not a primary pressure for organisms in this particular ecosystem. Furthermore, predators may have evolved from these organisms. We see evidence of this from the crustacean fossils researchers found with larger incisors associated with predation. This study can give insight into ways escalation occurred and how modern animals evolved from these Cambrian species. 

Citation: Mussini G., Hagadorn J.W., Miller A.E., Evans R., Dehler C.M., Bastien S., and Butterfield N.J. (2025). Evolutionary escalation in an exceptionally preserved Cambrian biota from the Grand Canyon (Arizona, USA). Science Advances, 11(30). https://doi.org/10.1126/sciadv.adv6383