Paleoclimate implications from a sediment core taken in a frozen Antarctic lake

Limnological Investigation of Antarctic Lakes and their Paleoclimate Implications

By: Pawan Govil

Summarized by: Baron Hoffmeister 

What data were used?: A 78 cm sediment core from a freshwater lake in Larsemann Hills, East Antarctica was used to interpret historic climate patterns from the late Quaternary period. 

Methods: The sediment core was analyzed using grain size distribution, as well as biological productivity indicators such as organic carbon and biogenic silica. Biogenic silica makes up diatom cell walls and is commonly called opal. This study used radiocarbon dating to measure total organic carbon present, and the biogenic silica was also evaluated using a wet alkaline extraction. A wet alkaline extraction is a method that isolates plasmid DNA or RNA from bacteria. This was used to determine the biogeochemical attributes of this lake.

Results: Using radiocarbon dating, this study found that this core is from the Holocene Epoch, a time that began around 11,700 years ago. This core was dated to be 8,300 years old. Most of the material in the core was sand, and clay and silt were rarer (sand, clay, and silt are defined by grain size in geology- sand is the coarsest grain size in this example; figure 1)The silica content within this was very low, indicating a very low abundance of silicate microfossils. The total carbon was low or negligible in the lower part of the core, likely due to the high sedimentation rates of sand during this time. The area of the core that had the most organic carbon was the top of the core that contained the small amounts of clay and silt. This study showed that this was due to a build of algae. The particles of clay and silt prevented oxygen from  decomposing the organic matter. This indicates that during this time, approximately 4,000 years ago, there were low sedimentation rates and low oxygen levels in this lake. This algal mat at the top of the core indicates warming temperatures during this time, and that the lake had little interference with glacial ice. The fine grained sediments were deposited due to ice meltwater (as water slows down, fine grained sediments drop out of water suspension) and can be seen in the upper core. The lower portion of the core contains high sand content, which implies glacial river input (i.e.,fluvioglacial) before 6,000 ago. The overall paleoproductivity implications of the core are as follows.  From 8,300 ago to around 6,000 years ago there was a period of warming. Around 4,000 ago, the warm temperatures allowed the lake to be free of ice and exposed to sunlight, and therefore this was the highest level of productivity and can be reflected in the upper core’s higher total carbon content. 

Graph depicting age dating of a sediment core.
This is a chronological interpretation of the sediment core taken from this study. Sand dominated the core with low percentages of silt and clay. This graph shows records dating back to 8.22 thousand years ago (right) working its way to around 1 thousand years ago (left).

Why is this study important?: Antarctica and its surrounding oceans influence climate across the entire planet. Antarctica holds around 90% of the world’s ice and about 70% of the world’s freshwater trapped in ice. The ability to be able to interpret past climate conditions that influenced climate patterns in Antarctica can allow scientists to better predict current day climatic changes in Antarctica and its effects globally.  More information about Antarctica and its ice sheets can be found here

The big picture: Today, the ice sheets are melting at a rate that has never been seen before. The effects of this could be catastrophic to life on Earth. Studies like these can allow scientists to better understand current-day climate patterns that could potentially help reduce the impact of widespread climate change. 

Citation: Govil, P. (2019). Limnological Investigation of Antarctic Lakes and their Paleoclimatic Implications. Ministry of Earth Sciences, (24), 289-303. Retrieved May 24, 2020.

New Late Cretaceous Shark found in North America

A new large Late Cretaceous lamniform shark from North America, with comments on the taxonomy, paleoecology, and evolution of the genus Cretodus

by: Kenshu Shimada, Micheal J. Everhart

Summarized by: Baron Hoffmeister

What data were used? : This study examined a partial skeleton of the Late Cretaceous shark, Cretodus, collected from the Blue Hill Shale in north-central Kansas, U.S.A. It had unique teeth not present in any other species of Cretodus

Methods: This study used a taxonomic analysis of the fossilized remains found and compared them to other members of the Cretodus genus. 

Results: The study found that the species of the fossilized partial shark skeleton found does not share enough similar features with any of the other four known species within the genus Cretodus. Therefore it has been listed as a new species, C. houghtonorum. Researchers found that it had a unique tooth size and pattern that didn’t match any previously discovered species (figure 1). Its calcified cartilage scales along with the inference that this shark had a large girth due to its bone structure that was preserved, indicated that this organism was likely a sluggish shark that lived in a nearshore environment. This study examined growth bands in its vertebral column and found that this shark had a lifespan of around 51 years. 

Image of many shark teeth from various angles to showcase how many different types of teeth exist for sharks
These are the 115 well-preserved teeth of C. houghtonorum. Sharks shed their teeth over their lifespan, and have several rows of teeth in both their upper and lower jaws. As one tooth falls out, it is replaced by the one in the row behind it. Each species of shark has unique teeth and jaw structures.

Why is this study important? Aside from discovering a new species, this study recognizes the fact that the evolutionary relationships of several shark families is still relatively unknown. However, this new finding provides data linking it with other members at the genus level. Without understanding these relationships, it’s difficult to understand the distribution of these organisms, how they changed over time, and why they went extinct. 

The big picture: Overall, this study is useful in determining possible links between extant and extinct shark species. This study provides data that can rework our understanding of evolutionary traits between extinct and modern-day sharks as well. The skeletal and dental data found in this study can be useful for other studies incorporating evolutionary trends, prehistoric ecology, and the taxonomic differences within the genus Cretodus.

Citation:  Shimada, K., & Everhart, M. J. (2019). A new large Late Cretaceous lamniform shark from North America, with comments on the taxonomy, paleoecology, and evolution of the genus Cretodus. Journal of Vertebrate Paleontology, 39(4). doi: 10.1080/02724634.2019.1673399

How genetic research can help to explain carnivoran (dog and cat) evolution

FGF gene family characterization provides insights into its adaptive evolution in Carnivora

Qinquo Wei, Yuehuan Dong, Guolei Sun, Xibao Wang, Xiaoyang Wu, Xiaodong Gao, Weilai Sha, Guang Yang, Honghai Zhang

Summarized by Kale Headings,  a senior at the University of South Florida. They are getting a dual degree in geology and environmental science and policy. They intend to study planetary geology or glaciology in graduate school next, and then work as a researcher or professor after they finish graduate school. In their free time they like to draw, play video games, and hang out with friends!

What data were used? The researchers looked at FGF genes, or fibroblast growth factors, from humans, domestic dogs and cats, mice, and other Carnivora genes from GenBank. FGFs affect a variety of biological functions including metabolism and development.

Methods: The researchers searched for Carnivora genetic sequences in GenBank, which is a database of genetic information of various species and confirmed that the genetic sequences they found were FGF genes. They did a phylogenetic analysis on the Carnivora species to determine their evolutionary relationships and the relationships of their FGF genes, using the FGF genes of mice and humans as an outgroup (outgroups ‘root’ the tree). In other words, comparing carnivoran FGF genes to human and mice FGF genes could help researchers determine which FGF genes are unique to carnivorans, and which are present across many groups and species, including mice and humans. Much of this analysis utilized various advanced computer programs and techniques. The researchers referenced preexisting phylogenetic trees for Carnivora and used Bayesian inference methods to create phylogenetic trees that included FGF genes alongside the Carnivora tree. Bayesian inference methods use Bayes theorem, an equation, to help infer which evolutionary relationships between species are most supported by the data. 

Results: The researchers found 660 new FGF genes in 30 different carnivora genomes. The phylogenetic trees created both with and without the FGF data were similar, and the FGF genes were able to be classified into 10 subfamilies (Figure 1) based on their locations on the phylogenetic tree. There were positive selection sites for two FGF genes that control metabolism and muscle development in Carnivora, which is significant because these features are important to these animals’ predatory habits. There was also a positive selection gene for FGF19 in the group of carnivora that was semiaquatic, and this is notable because it may indicate that FGF19 helps semiaquatic animals to regulate their body temperature and keep their balance in water. 

Alt text: Image of two concentric color-coded wheels, with the outer wheel containing text to label FGF subfamilies 19, 22, 5, 3, 7, 8, 1, 9, 4, and 11. The inner wheel shows individual FGF genes that are a part of each subfamily. Inside the space in the center of the two wheels is a tree-like diagram representing the phylogenetic families of Carnivora, with each section of the tree lined up with and color-coded to match the FGF gene and subfamily that it corresponds to.
Figure 1. The phylogenetic tree of Carnivora with the corresponding FGF subfamilies and specific genes, as determined by the researchers using Bayesian inference methods.

Why is this study important? The researchers concluded that the FGF gene family of Carnivora should be divided into 10 subfamilies. The researchers also found positive selection for several individual FGF genes that may be related to the diet and predator status of Carnivora animals, as these genes help to metabolize fats and develop muscles. They also found that habitat plays a role in what FGF genes are selected for, as notably FGF19 was selected for in semiaquatic carnivorans, and several other FGF genes also showed a strong relationship with the animals’ habitat types. These conclusions show how FGF genes can be used to further understand the evolutionary relationships and significance of specific evolutionary traits across a variety of species of mammals, since other groups of mammals besides Carnivora also have FGF genes. 

The big picture:  This study may help researchers better understand the evolutionary pathways taken by earlier carnivorans in the fossil record. In the specific case of FGF genes, these genes contain key physiological processes, just a few of which are metabolism and muscle development. Therefore, better understanding of the FGF genes and how they function across groups of mammals and how they vary due to evolutionary relationships may also help us to better understand our own FGF genes and how they work in our own human bodies.  

Citation: Wei, Q., Dong, Y., Sun, G., Wang, X., Wu, X., Gao, X., Sha, W., Yang, G., & Zhang, H. (2021). FGF gene family characterization provides insights into its adaptive evolution in Carnivora. Ecology and Evolution, 11, 9837– 9847. https://doi.org/10.1002/ece3.7814

Updating the Fossil Record of Whales

THE AWKWARD RECORD OF FOSSIL WHALES

Publication Date: 29 November, 2019

Stefano Dominici, Silvia Daniseb, Simone Cauc, Alessandro Freschic

Summarized by Jacob T. Booe. Jacob is in his senior year at the University of South Florida pursuing a B.S. degree in Geology. Growing up on the east coast of Florida near Kennedy Space Center, science and engineering has surrounded him for much of his educational career. While Jacob’s current trajectory is geared towards Earth Sciences, at the time of high school graduation, Jacob had no clue what his future career path was. Therefore, he enrolled in his local community college, Eastern Florida State College, where he graduated with his A.A. degree. However before obtaining an A.A. degree, Jacob found himself as an avid musician, pursuing the idea of acoustics and audio engineering. It wasn’t until his last year before receiving his A.A. degree that Jacob decided to take an intro to geology elective. After that course Jacob found himself committed to a career in geology transferring to USF in Spring 2020.

What data were used: The research team began with the analysis of 719 records of fossil whales, whose first origins are in the Cenozoic Era, across the Miocene, Pliocene, and Pleistocene epochs, approximately 11,000 to 23 million years ago (Figure 1). Researchers also used fossil whale occurrences to supplement their dataset from the Paleobiology Database (PBDB), which is a public database of global fossil occurrences that researchers update with new fossil finds. Along with the fossil occurrences, researchers collected information about the characteristics of rocks (i.e., their lithology). in which the fossils were found, where in the world they were found, and the time at which they lived. 

Methods: Researchers created six categories of lithology based on composition and grain with carbonate (like limestone) and siliciclastic rocks (like sandstone); these can be considered to represent the environments they likely have lived in. The skeletal system of the whales was categorized into four parts: skull, teeth, limbs, and spinal column. In addition, each fossil was graded on its quality of preservation. These data were analyzed to determine what relationships these variables shared. Other data, like measurements of the whale bones, were used to determine growth patterns of the organisms.  

Results: The majority of whale fossils that have currently been described originated in the Northern hemisphere. The team compared their findings to that of the existing PBDB and found that the PBDB had a more global sampling, with more even coverage between the north and south hemispheres. Researchers note that more exploration for fossils in the southern hemisphere must continue; other areas for further research include West Africa and Antarctica. In regard to lithological findings, results show that whale fossils are mainly found in fine-grained siliciclastic rocks while carbonates contribute considerably fewer occurrences. This differs from the PBDB, where carbonate lithologies had more occurrences than fine-grained siliciclastic. In terms of the growth of an organism, the team compared the fossil whales against the growth of a modern whale, the river dolphin. The results showed that in ancestral whales, skull size increases while the tympanic bulla (an ear bone) decreases; however, modern whales show skulls that increase concurrently with the tympanic bulla, with a special type of growth called “isometric growth”. 

The figure shows a global map projection denoting whale fossil finding by colored dots. Each dot is assigned a color based on its region locality. Regions are classified into nine groups as follows: 1) Western coast of Central and North America, 2) Western Coast of Southern America, 3) Eastern Coast of North America, 4) Eastern Coast of South America, 5) Western Coast of Europe and North Africa, 6) Mediterranean, Central and Eastern Europe, and Asian Near East, 7) Eastern Coast of Asia, 8) Oceania, 9) Indian Ocean and Austral Africa. The figure visually identifies that most samples are present in regions of North America (regions one and three), Europe (regions five and six) and Japan/Eastern Asia (region seven); or simply put the Northern Hemisphere.
Figure: The figure above displays the various distributions of whale fossil findings. The team grouped together nine regions showcasing which areas have been sampled. This also shows which areas are under sampled and could provide excellent locations for future studies.

Why is this study important: The current information used to study whales and their evolution is incomplete and biased towards known fossil localities in the northern hemisphere. In order to fill in the gap of whale fossils, this study shows some trends towards what environments is more likely to hold preserved whale fossils. 

The big picture: In this study, the authors tried to determine the quality and quantity of fossil data of whales. Identifying the gaps in our knowledge, and discovering why those gaps currently exist, can have an impact on how scientists approach whale paleontology moving forward. As the authors point out, places like West Africa are under-sampled, which leads to biases in our dataset. It is critical to determine whether under sampled areas of the world are due to a lack of fossil record or if scientists are not approaching the search for fossils globally. 

Citation: Dominici, S., Danise, S., Cau, S., & Freschi, A. (2020). The awkward record of fossil whales. Earth-Science Reviews, 205, 103057.https://doi.org/10.1016/j.earscirev.2019.103057

A comprehensive report on the morphology of the scales adorning the iconic horned theropod dinosaur, Carnoturus sastrei

The scaly skin of the abelisaurid Carnotaurus sastrei (Theropoda: Ceratosauria) from the Upper Cretaceous of Argentina.

By: Christophe Hendrickx and Phil R. Bell

Summarized by: Israel J. Rivera-Molina, a senior Geology major at the University of South Florida. He plans to attend graduate school in paleontology in order to start a career within the field of dinosaur morphology and evolution. 

What data were used? The holotype (i.e., the fossil specimen that ‘defines’ a species) of Carnotaurus, which was recovered from La Colonia Formation in Argentina; scientists also looked  at skin casts and 3D models of various other dinosaur taxa.

Methods: In this study, fossilized skin impressions of Carnotaurus were studied and a 3D model was generated using a camera and various imaging softwares. The skin was examined and then compared to various other taxa of dinosaurs from repositories, museums and other places where researchers keep fossils, from around the world.

Results: The scales covering the Carnotaurus (Figure 1) were found to be different in shape, size, orientation, and distribution. It was previously thought that the scales of the Carnotaurus were the same throughout the animal’s body, but it turns out that that is not the case. On the contrary, the scales were diverse: coming in six different shapes from elliptical to diamond-shaped scales. The scales also differed in textures ,ranging from smooth to granular, and were oriented in more than one way depending on which part of the body being observed. The tail especially displayed scales of a wide array of shapes that were arranged in various directions, while also ranging in size. 

A slab of preserved Carnotaurus skin containing grooved skin and circular scales; important scaled features circled to show which parts were measured by the researchers. There are 17 marked features, but none are discussed in depth in this summary here.
Figure 1: Portion of the skin located on the tail of Carnotaurus; outlined are the areas containing scale structures whose areas were measured by Hendrickx and Belll this was done to categorize the size and shape of the scales, compared to scales on other regions of the body.

Why is the study important? This study is important because it calls to attention the lack of emphasis placed on the research done on the skin of the Carnotaurus. Carnotaurus has some of most well-preserved scales amongst the theropods (the bipedal, carnivorous dinosaurs), yet past articles made little to no mention of the skin of the dinosaur. The authors also suggested that regarding the function of scales, scientists should think outside the box when comparing dinosaurs to extant lifeforms. They encourage researchers to not be afraid to venture away from reptilian analogues to attempt to discern what use(s) the scales served.

Big picture: This research provided a more in-depth look into the architecture of the scales covering the Carnotaurus. This body of work encourages scientists to look at and think more critically about the scales of dinosaurs, not only to reconstruct their appearance, but also to possibly discern some of their behaviors. Whether the scales served as a means of thermoregulation or as sexual display structures, further studies done on scales can lead to a greater understanding of how extinct dinosaurs lived.

Citation: Hendrickx, C., Bell, P. B., 2021, The scaly skin of the abelisaurid Carnotaurus sastrei (Theropoda: Ceratosauria) from the Upper Cretaceous of Patagonia. Cretaceous Research, p. 1-18. https://doi.org/10.1016/j.cretres.2021.104994

How Much Bias Exists in Fossil Research?

Phylogenetic Signal and Bias in Paleontology

By Robert J. Asher and Martin R. Smith

Summarized by: Alyssa Anderson, a senior geology major at the University of South Florida. Her dream is to work with environmental sciences and geology in water-related fields, such as oceanography or hydrology. In her spare time, she enjoys writing or sketching.

What data were used? Six sets of morphological data (i.e., data about the physical characteristics of organisms) from previously published fossil studies were gathered and the genetic data (i.e., the DNA) from living examples of those organisms were matched with the fossils. This was used to create rudimentary evolutionary trees of mammals and birds, the primary subjects of the studies. The trees retained all of the character codes from previous studies, even if there had been critiques.  

Methods: This study only used taxa that had at least 50% of the molecular and morphological characters present. Researchers tested how missing data would affect the outcomes of the phylogenetic trees. To do this, researched used artificial extinction and artificial fossilization techniques. This means, the researchers used various computer programming packages to artificially remove all molecular data from fossil taxa (as most fossils do not have any molecular data preserved) and some of the morphological data was also removed, as is also common with fossils. 

Results: The researchers worked to test three hypotheses. The first hypothesis studied the reconstruction of evolutionary trees based on the missing fossil data and molecular data. The results found that the experiment created fairly accurate evolutionary trees from this. The second hypothesis tested how accurate morphological studies are without molecular data in creating evolutionary trees. This was also found to uncover accurate results. Finally, the third hypothesis tested if poorly fossilized data leads to misinformed conclusions. Results demonstrated that including poor fossil data with missing information created better trees than trees that had no fossil data. In summary, any data helps make the trees more accurate, and it generally does not result in inaccurate evolutionary relationships. The most accurate evolutionary trees are made when molecular data and morphology data are combined.

A picture of six different evolutionary trees of bird and mammal genera, each from previously published data. The trees are well resolved; broader clades (e.g., marsupials) are highlighted in each of the trees
Figure: Six trees gathered from the five studies investigated in this research paper. The animal groups focused on here are birds and mammals. The tips of the tree are the genera used in this study.

Why is this study important? Determining how important including fossil data is, even in cases of the fossils’ inevitable missing data, was important in this study. An additional question that researchers wanted to know was if fossil breakdown creates situations where unrelated fossils appear more similar to each other than they actually are. Many morphological features can look similar across species, even if they are not closely related, so the process of fossil decay can make it even more difficult to piece out how similar or different certain features are. However, it doesn’t seem that this bias of fossil decay affects the dataset very much. Their placement on the evolutionary tree were usually quite similar to the known trees the researchers used. 

The big picture: Identifying bias or limitations in scientific studies is one of the most important things scientist can do. Bias can never be fully removed, and limitations won’t ever be either, but investigating sources of bias and the ranges of our limitations can help reduce it in future studies. Studying fossils is a vital science as it shows the history of the world and how species have evolved over time. If the information gained from the fossils is misleading in evolutionary analyses, due to the fossils inability to provide DNA or or do not retain clear features that mean it can’t be properly identified, then that could mess up our study of history and evolution. Through this study, it was discovered that using multiple sources of data (i.e., morphology and molecular data) create far more accurate evolutionary trees than trees that don’t use both. The study of paleontology and other sciences can benefit from this knowledge to improve other experiments in the future and broaden our understanding of the world.

Citation: Asher, J. R. and Smith, R. M. 2021. Phylogenetic Signal and Bias in Paleontology. Syst. Biol. 0(0):1–23. DOI:10.1093/sysbio/syab072 

New Fossil Evidence From the Arctic Could Indicate that Mosasaurs Migrated

Arctic mosasaurs (Squamata, Mosasauridae) from the Upper Cretaceous of Russia

Dmitry V.Grigoriev and Alexander A.Grabovskiy

Summarized by Evan Kruse. Evan Kruse is a senior undergrad student at University of South Florida majoring in geology. He plans on attending graduate school in either paleontology or mineralogy. He enjoys hiking, rock tumbling, identifying the rocks that his friends bring to him, and, secretly, he wishes he could bring back dinosaurs and have his own raptor, hence his paleontology major.

What data were used?  New mosasaur fossils, consisting of a vertebral column, isolated teeth, and a jawbone were found by the researchers in the Zolotaya River in the Anadyr district of Russia. Mosasaurs belong to a superfamily of marine reptiles, all of which have a crocodile-like head, lizard-like body, flippers instead of feet, and a long, paddle-like tail. All three types of fossils were found in roughly the same location, within 5 m of each other. The researchers also used older mosasaur vertebrae fossils from Kotikovo, Russia and the River Lemva, Komi Republic, Russia. 

Methods: This study utilized morphological differences, such as vertebral length-to-height ratios and the distinct facets on the tooth crowns, to classify the newly-discovered mosasaur specimen as a member of the subfamily Tylosaurinae. More data is required to fully classify the specimen and for now they are simply classified as Tylosaurinae indet.(i.e., it is currently an indeterminate species within Tylosaurinae) In addition to the newly discovered fossils, the researchers use the same morphological comparative techniques on two other samples previously discovered elsewhere. These other specimens are very damaged and can only be identified as belonging to the family Mosasauridae indet. The researchers also analyze the geographical location where all three specimens, the vertebrae, jawbone, and teeth, were found in reference to their predicted geographical location during the Cretaceous Period, specifically the Turonian, Santonian, Campanian, and Maastrichtian ages. 

This image shows four images of globes as overhead views looking down at the North pole with red stars marked at various locations as well as dashed and solid white arrows. Each globe has a different continental and oceanic layout and represent the predicted layout during different ages in the Late Cretaceous, one each for the Turonian in the top left, Coniacian-Santonian in the top right, Campanian in the bottom left, and the Maastrichtian in the bottom right. Arrows of cold and warm currents in the ocean are on this chart as well; some of the mosasaur fossils found would have been in the cold water currents.
This diagram shows the predicted geographical location where the mosasaur remains referenced in the paper would have died and been fossilized at during the different ages in the Cretaceous Period. The red stars indicate mosasaur locations. The size of the star indicates the predicted amount of fossil remains at the location. Solid arrows represent warm currents; dashed arrows represent cold currents.

Results:  The mosasaur remains found in the paper were discovered in high latitudes in cold conditions. Researchers have studied the continental movements associated with plate tectonics and have predicted the longitudinal and latitudinal location of the remains during the Late Cretaceous when they were deposited. The fossils retain their position in high latitudes which would have been associated with frigid waters. This means that mosasaurs were much more widespread than previously thought and that they were able to survive in colder climates than previously believed. In the past several years, many studies have come out which discuss and theorize about the thermoregulation (i.e.., how an organism regulates their body temperature) of mosasaurs. Although mosasaurs are a part of the same large group as lizards and snakes (who are ‘cold blooded’, basking in the sun to maintain body heat), these new studies postulate that many or all mosasaurs were endothermic (meaning that they could self-regulate their own body temperature) like mammals are. Being endothermic implies that Arctic conditions were not a problem for mosasaurs and that they would have been able to survive staying part or all of the year in the polar seas. Evidence from this study supports this hypothesis. This study also takes the existence of polar mosasaur fossils as indirect evidence of yearly migration patterns. Today, the high latitudes go through extended periods of constant 24-hour light and darkness, a yearly cycle that does not differ much today from the same cycle during the Cretaceous. This study predicts that the polar regions would have at least two months of solid darkness and at least one month of constant twilight. It is unlikely that mosasaurs had binocular vision for nighttime hunting and it is even less likely that mosasaurs developed echolocation (locating objects by reflected sound, like many whales do) to deal with the absence of light. With this in mind, the presence of mosasaur fossils in the high latitudes can be taken as indirect evidence of mosasaur migration patterns, so it is possible that the mosasaurs did not remain in those high latitudes year-round.

Why is this study important?  This study is important because it hypothesizes that mosasaurs seasonally migrate to and from higher latitudes in much the same fashion as our modern-day whales. If this is true, then we may be able to take the patterns and behaviors of whales and apply them to mosasaur behaviors. 

The big picture:  Predicting the behavior of extinct animals is tough; we often have little to go on, except for what we find in the fossil record. By examining the location and preservation state of fossil assemblages, we are able to make certain predictions about behavior. If mosasaurs migrated in similar fashion to modern-day whales, then we can look at other behaviors whales have and make predictions as to whether or not mosasaurs also shared that behavior. We can look for fossil evidence to support or contradict the hypotheses we put out. This can allow us to consider new behaviors for extinct animals we might not have before, change the way we interpret fossil evidence for other species, recognize new patterns in existing data, and make new predictions that may clue us into new ways to look for fossils. 

Citation: Grigoriev, Dmitry V., and Alexander A. Grabovskiy. “Arctic Mosasaurs (Squamata, Mosasauridae) from the Upper Cretaceous of Russia.” Cretaceous Research, vol. 114, Oct. 2020, p. 104499., https://doi.org/10.1016/j.cretres.2020.104499. 

CT analysis shows new relationships of Euryodus, an extinct amphibian

Computed tomographic analysis of the cranium of the early Permian recumbirostran ‘microsaur’ Euryodus dalyae reveals new details of the braincase and mandible

Bryan M. Gee, Joseph J. Bevitt and Robert R. Reisz

Summarized by Danielle Miller, who is a geology major at the University of South Florida, working towards becoming a paleontologist. She loves watching hockey and listening to music. She has two dogs. She also loves spending time out on the boat, fishing, and hanging out in the Gulf of Mexico.

What data were used? The researchers used two specimens that were identified as Euryodus dalyae from the Richards Spur locality, a fossil site in Oklahoma. Researchers compared the specimens of Euryodus dalyae to the holotype fossils of this species; a holotype is a specimen that is used by paleontologists to define a species. These two specimens are gymnarthrids, which belong to an extinct family of amphibians called microsaurs. These new specimens were compared using data that was collected through a type of CT that is called neutron tomography and x-ray tomography. The researchers also performed a phylogenetic analysis to understand how the newly discovered specimens were related to other microsaurs. The researchers created a number of characters based on the cranial (skull) shapes across the taxa used, as well as on the vertebrate of the taxa. The collected morphological data was put into the matrix (i.e., all of the morphogical characters in total) to be analyzed to determine the evolutionary relationships between the specimens.

Methods: The researchers did tomographic and phylogenetic analyses of the specimens. The phylogenetic analyses were done to see the evolutionary relationship between the specimens and the holotype of Euryodus. During the phylogenetic analysis, the researchers coded the two new specimens into a phylogenetic matrix that was created in a previous study done in 2017. Coding of several other microsaurs were used in the analyses. One of the other microsaurs used in the analyses was from the same genus as the new specimens, while the others were from different genera. The analyses were done using PAUP*, which is a computer program that is used to infer evolutionary trees. For the tomographic analysis of the specimens, the researchers did neutron tomography and X- ray tomography. Tomographic analyses are techniques that are used to represent a cross section of solid objects through X- rays or ultrasound. Neutron tomography is performed by rotating the specimens 180°, then taking neutron radiographs, which are photos produced on film by x-rays, at defined angular positions. This can produce a 3D image of a specimen’s composition. 1200 radiographs of one of the new specimens were produced in this analysis. The other new specimen was analyzed using X- ray tomography. The photos from both tomographic analyses were then analyzed in ImageJ, which is an image processing program that can be used to measure and analyze images. 

There are three pictures of the skull of Euryodus sp. Picture A is a triangular shaped, brownish skull shown from the bottom. Picture B is a colorful computer-generated model of the skull in the same orientation of Picture A. Picture C is also a colorful computer-generated model of the skull, but this time it is looking from the back of the skull. The sky-blue colored bone in Picture B is the upper jaw of the specimen discussed in the article. The dark pink bone in Picture B is the mandible also discussed in the article. Pictures B and C have abbreviations pointing out the different bones of the skull.
Figure 1. The skull of a specimen of Euryodus sp. Picture A is a picture of Euryodus sp.’s skull, viewed from the bottom. Picture B is a rendering of Euryodus sp.’s skull in the same profile. This picture has different colors representing the different parts of the specimen. Picture C is a rendering of Euryodus sp.’s skull from the back of the skull angled from the bottom to the top. The colors in the pictures B and C represent different parts of the skull. The colors in C represent the same parts as they do in Picture B. There are abbreviations in pictures B and C that represent the different anatomical parts of Euryodus sp. The abbreviation ‘m’ stands for the maxilla which is the upper jaw and while it is not abbreviated in this photo, the darker pink section is the part of the jaw that was discussed in the article. Scale bar= 1 cm.

Results: The result of this study shows that there is an especially close relationship between one of the recently discovered specimens and the holotype of Euryodus dalyae. The majority of differences between the skeletons are probably due to damage to the specimen over millions of years in the rock record, and not due to biological differences; however, there were some differences between the specimens on the internal portion of the skeleton These two specimens are also very similar to other species of extinct amphibians. The two specimen that were identified as Euryodus dalyae are now described as Euryodus sp. because of this study. Euryodus dalyae and Euryodus sp. look almost the same on the outside, but they are different internally. One such internal difference is the presence or absence of a presphenoid, which is the front part of a bone that is found at the base of the skull of the specimen. The researchers are unsure if these differences are due to ontogeny, the growth of the specimens, or if this is a signal that the two specimens represent different species. This difference is one reason that the researchers encourage more exploration of recumbirostrans, which are the amphibian group that include the family that Euryodus is part of. There was also the presence of an offset partial tooth row in the new specimens. This feature has been seen in a group called the captorhinids, which are lizard-like reptiles. This helps us better identify the broader groups that Euryodus is related to, because the offset teeth are only in certain species. This means that scientists can more confidently say that these groups belong in the same group. However, the offset teeth weren’t identical across the specimens studied here, so further tests need to be done.

Why is this study important? This is important because it provides a new understanding of the Euryodus clade. It can also be used to help determine if microsaurs are really a sister clade (meaning, the most closely related clade) to captorhinids, lizard-like reptiles that ranged from small to large and lived during the Permian, as they have been hypothesized to be before. This study also provides a better understanding of the anatomy of gymnarthrids and other microsaurs. Understanding the anatomy of gymnarthrids and other microsaurs is useful since future researchers can use that data to put other specimen into the group, if they fit that description.

The big picture: If we know the evolutionary relationships between the specimens in this study, then we could start to ask other questions about the group. We could investigate how the group changed across different extinction events or we could better understand the anatomy of these amphibians and see how this anatomy developed in amphibians of today.  

Citation: Gee, B. M., Bevitt, J. J., & Reisz, R. R. (2020). Computed tomographic analysis of the cranium of the early permian recumbirostran ‘microsaur’ Euryodus Dalyae reveals new details of the braincase and mandible. Papers in Palaeontology, 7(2), 721–749. https://doi.org/10.1002/spp2.1304

Sauropods of the Mahajanga Formation, and Changing Lifestyles of the Middle Jurassic

Sauropod Teeth from the Middle Jurassic of Madagascar, and the Oldest Record of Titanosauriformes

Gabriele Bindellini and Cristiano Dal Sasso

Summarized by Reynolds Hansen. Reynolds Hansen is an undergraduate geography major / geology minor at the University of South Florida. With a lifelong passion for paleontology instilled from an early age, Reynolds always knew the academic path ahead had a singular destination. Along the way, he picked up equal affinities for history and geography, and by the time he was in college, he worried he might have to choose one over the others. With the help of the university’s esteemed academic professionals and resources, he shifted focus with the goal of becoming a science communicator, telling the story of our world from the formation of the earth to the modern day as an interconnected narrative. Reynolds is set to graduate in the spring of 2021, after which he wishes to seek a post-graduate degree in paleontology, and a career as an educator. His academic focus is utilizing GIS to research paleoecological phenomena.

Data used:  The 31 fossil sauropod (the group including long neck dinosaurs) teeth described in this work are all from the Mahajanga Formation of Madagascar. The teeth are often the only recoverable remains for these animals, as intense weathering typically reduces most other bones to a powder-like state.

Methods: Researchers took qualitative and quantitative measurements of the teeth to reconstruct the amount of physical wear and abrasion to record observations of physical wear or abrasion, and determine possible diet according to tooth features, positioning in relation to neighboring teeth, and evolutionary derivation. Measurements were obtained via the use of digital calipers on targeted areas of interest on the teeth, specifically, from four regions around the crown of the tooth. The results of these measurements grouped teeth into one of four categories: heart-shaped teeth, spatulate teeth, compressed cone-chisel teeth, and pencil-shaped teeth (or peg-like teeth; fig.1). Finally, these measurements were compared against known sauropod species tooth dimensions to come to conclusions on species taxonomy and ecology (fig. 2). 

Figure 1: The four tooth types outlined in the findings of the paper and labeled respectively. Notice the progression from left to right, where enamel wrinkling decreases and tooth becomes more peg-like. This spectrum is also representative of the progression in sauropod tooth morphology seen over time.

Results: With the methods described above, the researchers were able to categorize the 31 teeth into eight morphotypes, or broad shapes. They were then able to categorize these morphotypes further into four possible taxa (species), based on a number of factors including comparative analysis of tooth features, knowledge of local species (or lack thereof), and a combination of these two points against the total current knowledge of sauropod tooth shape. Most of the morphotypes are tentatively assigned to two possible species: Bothriospondylus madagascariensis, or Lapparentosaurus madagascariensis (taxa A and B). Scientists don’t yet understand the relationships of taxon A to other sauropods yet, but taxon B may be related to groups like brachiosaurs or titanosaurs. Two morphotypes (taxon C) are tentatively assigned to Archaeodontosaurus descouensi., which is classified as an ‘eusauropod’; a designation that remains somewhat flexible, but typically refers to animals making the transition from Triassic prosauropods and late Jurassic-Cretaceous ‘neosauropods’. The last remaining morphotype is set into a taxon of its own (D), although the identity is largely unknown, and only tentatively proposed to be a diplodocid or basal titanosaur of some kind. It has characteristics unlike any yet seen in this formation, having a mostly peg-like shape while all other teeth are stouter with some enamel wrinkling.

Figure 2: Sauropod teeth plotted chronologically and according to dimensions measured according to figure 1. Taxa proposed in this study are shown in larger colored points and highlighted at temporal location by light blue bar.

Why is this study important? The findings in this paper imply that titanosaurs may have been around just as long as other successful groups of sauropods, like brachiosaurs and diplodocids, and that the roots of titanosaurs extends into the middle Jurassic, a time where fossils are less commonly known. Discoveries like these from this time period provide valuable insight into the changing global climate that led to the late Jurassic boom in sauropod diversity. In this case, we see the partly bipedal Triassic prosauropods slowly evolving into the large, quadrupedal animals we are more familiar with. This change is highlighted here in the shifting tooth morphology: narrower, increasingly peg-like teeth are seen as an evolutionary deviation from the more multi-purpose, wrinkled teeth associated with prosauropods. Since most later sauropods have virtually pencil-shaped teeth associated with branch-stripping and gut-digesting rather than chewing and oral-processing, the appearance of traits leaning in this direction gives us evidence that these evolutionary changes may have been propelled by competition between species and niche-filling. Accessing higher vegetation borne from trees presents pioneering animals with an untapped resource. However, trees also present challenges in the form of tough branches and leaves that are harder to digest and also often less nutritious. The transition from wider, wrinkled teeth for processing and chewing, to peg-like teeth that strip leaves from branches, allows animals to acquire more food in less time and with higher efficiency. This also translates most or all of the digestion to the stomach, which passively grinds food with the aid of gastroliths (swallowed stones), further allowing for the animal to continually take-in food and remain on the move.

The Big Picture: Special attention should be awarded to those locales which are already underrepresented in the fossil record. If one could extract new taxonomic information from less than three dozen teeth, especially from a time without significant fossil representation, then it leads one to wonder what could be found with further excavation, and the insight of local knowledge, interest, and investment. That is not to say that every sparsely researched locale is a treasure trove awaiting plentiful fossil discovery, but the matter of the Mahajanga Formation is such that its potential for producing Middle Jurassic materials should certainly not be overlooked, and is mostly untapped. The teeth used in this study were not exclusively extracted for the research of this paper. Instead, they were found as a result of a field survey conducted in tandem by an Italian institution (Museo di Storia Naturale di Milano), and a couple of Malagasy geological ministries in the early 2000s. It is only recently, in 2019 that the teeth were pulled from archives for analysis. This means that this the geological deposits near Ambondromamy, Madagascar, likely have much yet to show us.   

Citation: Bindellini, G. and Dal Sasso, C. (2021), Sauropod teeth from the Middle Jurassic of Madagascar, and the oldest record of Titanosauriformes. Pap Palaeontol, 7: 137-161. https://doi.org/10.1002/spp2.1282

Newly discovered hatchling sea turtle fossil track marks allow paleontologists to compare ancient sea turtle breeding ranges and climate conditions compared to that of the modern day

New fossil sea turtle trackway morphotypes from the Pleistocene of South Africa highlight role of ichnology in turtle paleobiology

Martin G. Lockley, Hayley C. Cawthra, Jan C. De Vynck, Charles W. Helm, Richard T. McCrea, Ronel Nel

Summarized by Sophia Gutierrez, who is majoring in geology at the University of South Florida. She is currently a senior and plans to pursue some experience in the field before continuing to further her education with a graduate program majoring in sedimentary geology. When she’s not studying geology, she enjoys walking in nature and listening to music.

What data were used? Three coastal sites, showing never before seen fossilized sea turtle hatchling track marks were discovered on the south coast of South Africa originating from the late Pleistocene (~100,000 years ago). Two species of sea turtles were ultimately identified from their trace fossils at the sites as loggerhead (Caretta caretta) and leatherback (Dermochelyis coriacea) sea turtles. Some track marks showed multiple “footprints” coming out of a centralized area that could possibly represent the ancient nesting location.

The three coastal S. African sites with never before recorded sea turtle hatchling fossil traces (A) Site 1, 3 loggerhead hatchling track marks, Australochelichnus agulhasii. The 2 track ways on the right show overlap. (B) Site 2, a leatherback turtle hatchling curved trackway, Marinerichnus latus, with red marks to show the lengths of the inner and outer sidelines. (C) Site 3, the long arrows show two sets of loggerhead trackways, Australochelichnus agulhasii, from different hatchlings. The shorter arrow shows an uncertain trace, but this may signify the remains of a nest in the center where the circle is.

 

Methods: This study used two dimensional (2D) and three dimensional (3D) photographed images of the trackways in track sites 1 and 2, not far from each other, showing the sea turtle hatchling trails that were preserved in the large slab of rock. Tracing diagrams were then drawn to illustrate detailed trackway patterns of the two hatchling species. Site 3 fossils were found on a portable boulder. The boulder was photographed and taken to be preserved and studied at a separate location.

Results: After the fossil traces had been properly examined, it was concluded that the sets of tracks found in site 1, on a large slab of rock that had fallen off the side of a cliff, were those from hatchling loggerhead sea turtles. Site 2 is positioned close to site 1 in a narrow cliff pass filled with fallen rock slabs and boulders. One of those slabs holds fossilized hatchling leatherback sea turtle tracks. The final track site was found about 100 km (~62 miles) away from the other two, on a portable boulder that showed newborn loggerhead tracks appearing suddenly from the ground, likely representing the moment the hatchlings traveled out of their nest in the sand. Site 3 is especially interesting because it shows two sets of track marks emerging from the sand but paddling in opposite directions, 180° from each other. Site 2 also shows indications of the hatchling emerging suddenly from the sand but in this case, it’s unclear to say if this suggests a nest or shows signs of inadequate trace fossil preservation. These fossilized loggerhead and leatherback hatchling sea turtle tracks have never been documented before and are fairly distinct from other marine and terrestrial turtle track sites recorded. Due to these reasons, the paleontologists who discovered these tracks may assign these ichnotaxa (a taxonomic group based on the trace fossils of an organism) new, original names: Australochelichnus agulhasii for the hatchling loggerhead tracks and Marinerichnus latus for the hatchling leatherback tracks. These ichnotaxa provide us with copious information about ancient sea turtle breeding ranges, given that both loggerheads and leatherbacks nest in very specific conditions. This gives an insight on how the climate conditions in the late Pleistocene may have been in this area where temperatures were calculated to be about 25° to 35° C with a water level up to 6 meters (20 ft) higher than they are today. The presence of the Marinerichnus latus tracks made by leatherbacks (site 2) so close to the Australochelichnus agulhasii tracks made by loggerheads (site 1) in the area they were found in suggests that the breeding areas for the leatherback were twice as extensive in the Pleistocene than they are today.

Why is this study important? This study allows scientists to combine what is known about modern sea turtle hatchings with what was discovered from fossil tracks from about 100,000 years or so ago. The location that the trace fossils are preserved in can reveal to scientists the environmental and climatic conditions of the late Pleistocene, which could broaden the understanding of naturally changing climates of the past and the rapidly increasing climate change in the present day. Along with that, due to the close range of the leatherback and loggerhead turtle fossil nest sites in sites 1 and 2, this study demonstrated that modern breeding ranges of both leatherback and loggerheads have been halved in the past 100,000 years.

The big picture: This paper studied the ichnological evidence (the trace fossils made by an organism at the time it is alive) made by two distinct species of hatchling sea turtles. Scientists related the breeding ranges of modern sea turtles to the ancient breeding ranges they observed at the fossil sites and suggested the climate of the late Pleistocene ranged from 25° to 35° C and had sea levels up to 6 meters (20 ft). As of 2021, loggerhead sea turtles are endangered and leatherback sea turtles are vulnerable species. This study could potentially help future populations of these species due to the new knowledge of ancient breeding ranges relative to the specific nesting conditions.

Citation: Lockley, M. G., Cawthra, H. C., De Vynck, J. C., Helm, C. W., McCrea, R. T., Nel, R. 2019. . Quaternary Research 1–15. https:// doi.org/10.1017/qua.2019.40