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

Will NASA’s Dragonfly Mission Encounter Dust Devils on Titan?

Dust Devils on Titan

Brian Jackson, Ralph D. Lorenz, Jason W. Barnes, and Michelle Szurgot

Summarized by Lisette Melendez

What data were used? In 2019, NASA announced a brand-new mission: Dragonfly. The objective? To visit Titan, the largest moon of Saturn and the only place in our universe (besides Earth) where distinct evidence of surface liquid has been discovered. Titan’s environment is very similar to that of very early Earth, with a nitrogen-rich atmosphere and volcanic activity. By studying Titan’s chemistry, scientists can discover more about the origin of life itself. It’s a very exciting mission, but it’s important for scientists to prepare for all the different obstacles the rotorcraft will encounter on Titan’s surface, including hazardous weather phenomena like dust devils.

An illustration of NASA’s Dragonfly rotorcraft-lander approaching the dunes on Saturn’s exotic moon: Titan. Credits: NASA/JHU-APL

We’ve learned more about weather patterns on Titan through NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017. This study focuses on how dust storms are identified on other celestial bodies and what implications they hold for the Dragonfly mission. Cassini identified three regional dust storms within the equator near the “Shangri-La” dune fields that were chosen as Dragonfly’s landing spot. The study of these dust storms in Titan’s unique environment (with clouds and rain of methane!) can help us learn more about how they operate and life dust in the first place. This study also draws from observations by the Huygens probe for information on Titan’s temperatures and atmosphere.

Methods: In order to determine the weather conditions necessary for a dust storm on Titan, scientists need data on various atmospheric circumstances, such as temperature, elevation, and pressure. By analyzing the images and observations collected by Cassini and Huygens and combining these findings with data collected by observing dust devils here on Earth, scientists were able to model the surface conditions that were suitable for dust devil formation as well as the size of these storms. The study focused on dust devils on the equator because that’s where we have the most data available about Titan’s weather conditions.

An illustration of the Cassini-Huygens space-research mission, which was a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ISA) to study Saturn and its many moons. Credit: NASA/JPL

Results: Many of the atmosphere conditions identified on Titan are favorable for the formation of dust devils. On Earth, dust devils are generally hindered by the presence of liquid because the increased particle cohesion (i.e., how sticky the particles are to one another) prevents wind from being able to lift the dust particles. Observations show that the equator of Titan is very arid and dry, with methane downpours only occurring in areas once every 10 Earth years. By looking at surface humidity levels measured by Huygens, it shows that the surface is too dry for even cloud formation. The abundance of dunes and dust storms provides further evidence that Titan has the ideal environment for dust devils.

An image of a dust devil in Kansas. Credit: The Thunderbolts Project

However, there are some surface conditions on Titan that may reduce the occurrence of dust devils, including the possibility of insufficient wind speeds. Additional work is required to model typical speeds on Titan’s surface.

Why is this study important? This study is important because it helps predict the occurrence of dust devils on Titan when Dragonfly is scheduled to arrive in 2034. This study outlines what remains unknown about the formation of dust devils and how Dragonfly presents the opportunity to study wind-related phenomena in a novel environment.

The big picture: After analyzing the environment on the surface of Titan based on the data currently available, it is concluded that the dust devils will most likely not pose a threat to the Dragonfly rovercraft (since they are too slow in the given conditions). Nevertheless, the mission can provide crucial insight to the creation of dust devils and how frequently they occur on other celestial bodies. Dragonfly provides us the opportunity to learn so much more about extraterrestrial worlds, and we’re all very excited for its departure!

Citation: Jackson, B., Lorenz, R. D., Barnes, J.W., & Szurgot, M. (2020). Dust devils on Titan. Journal of Geophysical Research: Planets, 125, e2019JE006238. https://doi.org/10.1029/2019JE006238

Climate Change and Encephalitis

The potential impact of climate change on the transmission risk of tick-borne encephalitis in Hungary

Kyeongah Nah, Ákos Bede-Fazekas, Attila János Trájer, and Jianhong Wu

Summarized by Kailey McCain

What data were used? The data collected for this study includes the monthly average temperature values in Hungary from the years 1961-1990. Specifically, for the past climate data,researchers used the CarpatClim-Hu database. For future climate predictions, the researchers used two distinct climate models: ALADIN-Climate 4.5 and RegCM 3.1. Additionally, previously established models for Tick-borne Encephalitis virus (i.e., a human viral infectious disease) transmission was used. Models help us hypothesize how different scenarios will look, by allowing us to input a lot of different types of data to understand large future patterns, like the one in this article! 

Methodology: By using the previous climate data for the years 1961-1990, the researchers established a predictive warming model for the years 2021-2050 and 2071-2100 in Hungary. This data was then compared to the tick-borne encephalitis virus (TBEV) transmission model to establish correlations between the data sets. This model broke down the transmission into various factors: reproduction numbers, duration of infestation, and density. The dynamics of transmission can be visualized in figure 1.

Figure 1: This figure shows an extensive diagram of how an infected tick spreads the disease to humans, livestock, and other animals. The inner circle represents the stages from larva, to nymph, to mature tick; then it branches to external transmission.

Results: The predictive climate model showed a steady increase in temperature for the age ranges 2021-2050 and 2071-2100, and the TBEV model resulted in an increase in tick population and transmission. These increases can be positively correlated (linked) to warming climate because previous data shows that a higher temperature speeds up the rate of sexual maturity in ticks; meaning, this allows the tick to reproduce at an increased rate. Moreover, research has shown that a warming climate leads to the elongation of tick questing season; which increases the chance for transmission. When a tick is questing (shown in figure 2), it is strategically placed on vegetation in order to grab a hold of by passers. 

Figure 2: This image represents a questing tick sitting on the edge of a lead with their legs spread out, and ready for attachment.

Why is this study important? This study is important because it shows the dynamic effects climate change has on global health. It also conveys an important message that the prevention of climate change is not only a biological and geological problem, but a public health problem, too. This means that solutions for reducing the impacts of climate change have to be creative and have to be from a lot of different types of researchers! 

The big picture: This study helps us understand the ways in which infectious diseases, (e.g., Tick-Borne Encephalitis Virus) are affected by climate change. As well as giving a glimpse into the future of what disease transmission will look like if prevention protocols are not put in place.

Citation: Kyeongah Nah, Ákos Bede-Fazekas, Attila János Trájer, & Jianhong Wu. (2020). The potential impact of climate change on the transmission risk of tick-borne encephalitis in Hungary. BMC Infectious Diseases, 20(1), 1–10. https://doi.org/10.1186/s12879-019-4734-4

How Climate Change in Serbia is Impacting the Rate of Cancer and Infectious Diseases

Assessment of climate change impact on the malaria vector Anopheles hyrcanus, West Nile disease, and incidence of melanoma in the Vojvodina Province (Serbia) using data from a regional climate model 

By: Dragutin T. Mihailović, Dusan Petrić, Tamas Petrović, Ivana Hrnjaković- Cvjetković, Vladimir Djurdjevic, Emilija Nikolić-Đoric, Ilija Arsenić, Mina PetrićID, Gordan Mimić, Aleksandra Ignjatović-Cupina 

Summarized by: Kailey McCain

What data were used? Researchers assessed climate change and UV radiation (UVR) and compared it to data collected over ten years from mosquito field collections at over 166 sites across Serbia. Additionally, public health records for the circulation of vector-borne disease (I.e., illnesses spread by mosquitoes and ticks), specifically the West Nile Virus, and the incidence of melanoma (i.e., a serious form of skin cancer) were collected and compared.

Methods: The climate change and UVR doses were collected by using EBU-POM model (a type of regional climate model) for the time periods: 1961-2000 and 2001-2030. As for the collection of the mosquito data, two different dry-ice baited traps (dry-ice is a solid form of carbon dioxide, which is a natural attractive substance for mosquitos) were used. The various sites were chosen by entomologists (i.e., scientists who study insects) to obtain a diverse data set. The mosquitoes collected were then anesthetised, separated by location, species, sex, and then tested for a specific RNA (I.e., a single stranded molecule) strand that would indicate the mosquito was carrying the West Nile Virus.

Furthermore, the researchers measured the rate of melanoma incidences in Serbia by using two different indicators: new number of cases versus time and number of new cases versus population size. The defined time period for data collection was 10 years (1995-2004). With this data, the researchers compared the rate of incidence to the climate data previously collected.

Fig 1: This diagram shows the linear trend in annual temperature fluctuations throughout Serbia from the time period 1990-2030; as well as depicts the mosquito prevalence found at the various collection sites.

Results: From the data collected via the regional climate model, a linear upwards trend in temperature in Serbia was recorded. The prevalence of mosquitoes was also found to increase linearly throughout the time period. The culmination of these results can be seen in figure 1.

As for the melanoma data, the researchers found a linear increase in UVR doses for the time period. This data was found to be correlated to an increase in melanoma incidences throughout Serbia and this data can be visualized in figure 2.

Why is this study important? Disease prevalence and distribution have always been difficult to predict due to the varying ecological factors that play important roles. Research like this is especially important because it allows scientists to simulate future spreads of vector-borne diseases within European countries. This can eventually lead to the development of public health surveillance technology and overall prevention.

Fig 2: Diagram (a) depicts the increased temperature rates throughout Serbia, and diagram (b) depicts the UV radiation doses on the various provinces throughout Serbia. Diagram (c) shows the linear relationship of UV doses versus the time period 1990-2030. The data shows a clear increase in “hot days” (HD) and “warm days” (WD) through time. Diagram (d) shows a linear relationship between UVR dose versus melanoma incidence rate from 1995-2004.

The big picture: This study aimed to correlate changes in temperature and UV radiation to the spread of diseases and cancer. With vector-borne diseases being the most sensitive to ecological conditions, researchers chose the West Nile Virus to act as a proxy to all mosquito transmitted diseases. As expected, the data supports the claim that increased temperatures trigger an enhanced risk for not only infectious diseases, but certain cancers as well.

Citation: Mihailović, D. T., Petrić, D., Petrović, T., Hrnjaković-Cvjetković, I., Djurdjevic, V., Nikolić-Đorić, E., Arsenić, I., Petrić, M., Mimić, G., & Ignjatović-Ćupina, A. (2020). Assessment of climate change impact on the malaria vector Anopheles hyrcanus, West Nile disease, and incidence of melanoma in the Vojvodina Province (Serbia) using data from a regional climate model. PLoS ONE, 15(1), 1–17. https://doi.org/10.1371/journal.pone.0227679

How coastal wetlands can help reduce property damage from storm surge and sea level rise

Valuing natural habitats for enhancing coastal resilience: Wetlands reduce property damage from storm surge and sea level rise

by: Ali Mohammad Rezaie, Jarrod Loerzel, Celso M. Ferreira

Summarized by: Mckenna Dyjak

What data were used?: This study used coastal storm surge modeling and an economic analysis to estimate the monetary value of wetland ecosystem services (positive benefits of natural communities to people). One of the ecosystem services provided by wetlands is that  they are great at controlling flooding; their flood protection value was estimated using the protected coastal wetlands and marshes near the Jacques Cousteau National Estuarine Research Reserve (JCNERR) in New Jersey. 

Methods: Storm surge flooding was determined for historical storms (e.g., Hurricane Sandy in 2012) and future storms that account for habitat migration and sea level rise. Each storm had modelled flooding scenarios for both the presence and absence of the coastal wetland/marsh. The model also incorporated ways to account for monetary value of physical damage by using property values.

Results:  This study found that coastal wetlands and marshes can reduce flood depth/damage by 14% which can save up to $13.1 to $32.1 million in property damage costs. The results suggest that one square kilometer (~0.4 square miles) of natural coastal wetland habitats have a flood protection value of $7,000 to $138,000 under future conditions (Figure 1).

Figure 1. This graph shows the estimated monetary value of coastal marshes flood protection in different storm scenarios per square kilometer. A “25 year Storm” or “50 year Storm” is a storm event that occurs once on average in the time span given.

Why is this study important?: Natural coastal wetlands and marshes contribute many vital ecosystem services such as providing habitats for wildlife, helping protect against coastal erosion, and purifying water. Assigning a monetary value to these natural habitats for their flood protection can highlight another aspect of their importance and urge people to protect these important coastal communities. The results from this study can allow the public and private sectors to develop and practice sustainable methods to preserve the ecosystems.

The bigger picture: Storm events, such as hurricanes, are predicted to become more frequent and more severe due to climate change. As the oceans continue to warm (an estimated increase of 1-4 degrees Celsius in mean global temperatures by 2100) hurricanes are predicted to intensify in wind speed and precipitation. Storm surge is known to be the most dangerous aspect of hurricanes and causes deadly flooding. As sea levels rise and ocean water expands due to warming, storm surges will become more severe during major storm events. This study has shown that coastal wetlands and marshes are considered our “first line of defense” in these circumstances. We must take care of and protect our natural habitats because they provide us with many services that we are unaware and likely unappreciative of.

Citation: Rezaie AM, Loerzel J, Ferreira CM (2020) Valuing natural habitats for enhancing coastal resilience: Wetlands reduce property damage from storm surge and sea level rise. 

How fossil collection methods can affect paleoecological datasets

The influence of collection method on paleoecological datasets: In-place versus surface-collected fossil samples in the Pennsylvanian Finis Shale, Texas, USA

Frank L. Forcino, Emily S. Stafford

Summarized by Mckenna Dyjak

What data were used?: Two different fossil collecting methods were compared using the Pennsylvanian marine invertebrate assemblages of the Finis Shale in Texas. In-place bulk-sediment methods and surface sampling methods were used to see how these different methods could influence taxonomic (groups of animals) samples. 

Methods: The bulk-sediment sampling method involves removing a mass of sediment and later washing and sieving the material to retrieve the fossil samples; surface sampling is a simpler method in which the top layer of sediment is removed and the exposed fossils are collected by hand. The samples were collected in the Finis Shale in Texas at stratigraphically equivalent (layers of rock deposited at the same time) locations to ensure continuity in the two methods. The bulk-sediment and surface pick-up samples were analyzed for differences in composition and abundance of fossil species (i.e., paleocommunities) using PERMANOVA (a type of analysis used to test if samples differ significantly from each other).

Results: The study found that the bulk-collected samples differed from the surface-collected samples. The relative abundance of the major taxonomic groups (brachiopods and mollusks), composition, and distribution varied considerably in both collecting methods. For example, there was a higher relative abundance of brachiopods in the bulk-collected samples and a higher relative abundance of gastropods in the surface-collected samples.

Figure 1. Comparison of relative abundance of fossil groups between in-place and surface samples. Note the different abundances from each of the collection methods.
(SpE = Spillway East outcrop, SpW = Spillway West outcrop, CW = Causeway Road outcrop)

Why is this study important?: Bulk-sediment sampling and surface sampling methods produce significantly different results, which would end up affecting the overall interpretation of the history of the site. The surface-collected fossils may be influenced by stratigraphic mixing (mixing of materials from different rock layers), collector bias (which can influence a fossil’s potential to be found and collected; for example, larger fossils are more likely to be collected), and destruction of fossils due to weathering. Bulk-sediment sampling will likely have a more accurate representation of the ancient community, because the fossils likely experienced the least amount of alteration during the process of the organism becoming a fossil (also known as taphonomy).

The bigger picture: The amount of things that have to go right in order for an organism to become a fossil is a lengthy list (read more about the fossilization process here). There are many biases that can contribute to the incompleteness of the fossil record such as environments that favor preservation (e.g., low oxygen), as well as poor preservation value of soft tissues, like skin. Scientists must do what they can in order to collect accurate data of the fossil record since there are already so many natural biases. Knowing which fossil collecting methods produce the most accurate results is important when advocating for the paleocommunity.

Citation: Forcino FL, Stafford ES (2020) The influence of collection method on paleoecological datasets: In-place versus surface-collected fossil samples in the Pennsylvanian Finis Shale, Texas, USA. PLoS ONE 15(2): e0228944. https://doi.org/10.1371/journal.pone.0228944

Organic carbon stored in Florida lakes

Organic carbon sequestration in sediments of subtropical Florida lakes

Matthew N. Waters, William F. Kenney, Mark Brenner, Benjamin C. Webster

Summarized by Mckenna Dyjak

What data were used? A broad range of Florida lakes were chosen based on size, nutrient concentrations (nitrogen and phosphorus), trophic state (amount of biologic activity that takes place), and location. The lakes were surveyed using soft sediment samples to identify the best drilling sites for sediment cores. After drilling, the cores were dated and the organic carbon (OC) content and burial rates were calculated. Organic carbon can be stored in sediments and buried, which temporarily removes it from the atmosphere.

Methods: The sediment cores were taken using a piston corer commonly used to retrieve soft sediments. Each core was dated using ²¹⁰Pb which is a common radioactive isotope found in lake environments and can be used to date sediments up to 100 years. Radioactive isotopes can be used to date rocks and sediments based on their natural decay rate (half-life). The organic carbon content of the cores was measured using a Carlo-Erba NA-1500 Elemental Analyzer which is an instrument that can determine the total carbon present in a sediment sample. To calculate the organic carbon deposition rates, the accumulation of sediment rates were multiplied by the proportion of OC found in the sediment. A recent increase of eutrophication (high amount of nutrients present in lakes) needed to be taken into account when calculating the OC deposition rate, so the sediments were divided into pre-1950 and post-1950 deposits to depict the change in industrial activity and agriculture. 

Results: The OC burial rate was highest in the shallower lakes and decreased as the depths increased (can be seen in Figure 1). This is different from the rates for temperate (mild temperatures) bodies of water, where OC burial rates decreased as the lakes got bigger. They found a 51% increase in OC burial rates in the post-1950 deposits which corresponds to the increase in eutrophication in the lakes.

Figure 1. Graph showing the correlation between depth and organic carbon (OC) burial rate. The OC burial rate increases as the depth decreases in meters.

Why is this study important? Cultural eutrophication is caused by an increase of nutrients in waterways such as phosphorus and nitrogen (commonly found in lawn fertilizers) which cause harmful algal blooms; these algal blooms remove oxygen from the water and can mess up the entire ecosystem. The lack of oxygen and harmful algal blooms can lead to habitat loss and loss of biodiversity. This study highlights the effects and severity of cultural eutrophication in Florida’s subtropical lakes.

The bigger picture: Managing carbon and removing it from the atmosphere (i.e., carbon sequestration) is an important aspect of climate mitigation. The carbon can be removed from the atmosphere and stored in places known as carbon sinks (natural environments that can absorb carbon dioxide from the atmosphere). This study shows that subtropical Florida lakes are effective carbon sinks for organic carbon that deserve to be protected from nutrient runoff that causes eutrophication.

Citation: Walters, M. N., Kenney, W. F., Brenner, M., and Webster, B. C. (2019). Organic carbon sequestration in sediments of subtropical Florida lakes. PLoS OnE 14(12), e0226273. doi: 10.1371/journal.pone.0226273

The Clues Ancient Glaciers Leave Behind on Mars

Transient post-glacial processes on Mars: Geomorphologic evidence for a paraglacial period

by: Erica R. Jawin, James W. Head, David R. Marchant 

Summarized by: Lisette Melendez

Figure 1: A map of the crater in the midlatitudes on Mars, showing the geologic features that were created due to deglaciation, like gullies and spatulate depressions. These same features can be found in post-glacial environments on Earth!

What data were used? Mars, just like Earth, goes through a cycle of glaciation and deglaciation. The rise and fall of glaciers on Mars is influenced primarily by the planet’s obliquity, or the tilt of its axis. During times of higher obliquity, the planet’s tilt is greater, hence its poles are exposed to more sunlight and the glaciers leave the poles and travel towards the middle of the planet. As the cycle continues and the tilt is lower, the glaciers leave the midlatitudes and migrate towards the poles once again. The period of time where environments are adjusting to deglaciation is known as a paraglacial period, and it comes with a group of identifying features that are well studied here on Earth. This study applies what we’ve learned about the kinds of geologic features that are left behind by glaciers on Earth to the environment on Mars. The area that is left behind by a glacier is known as a glacial deposit. By analyzing images of craters on Mars taken by cameras aboard the Mars Reconnaissance Orbiter, scientists are able to find evidence of paraglacial periods and how long they last on Mars.

Figure 2: A photo of two retreating glaciers in the Antarctic Valley that are leaving behind ridges that are comparable to the ones found on the Martian surface.

Methods:  After choosing a crater in the midlatitudes of Mars, the scientists began breaking down the features found in the images of the crater and mapping out the terrain, as shown in Figure 1. Glaciers leave behind special signatures in the rocks on Earth (e.g., here are some Time Scavengers posts about glacial geology on Earth: glaciers in Connecticut River Valley and glaciers in the Bay of Fundy), and the objective was to identify these same features on Mars. In order to further understand the processes that were occurring in the crater on Mars, analyses of places with the same climate and geologic features on Earth were used! The climate on Mars is arid and freezing, similar to the McMurdo Dry Valleys in Antarctica.

Figure 3: A diagram that shows the process of forming gullies and debris fans (piles of sediment), which can be seen in real-life in the next figure.

Results: Several geologic features that, when found together, are indicative of glaciers migrating away were found in this crater on Mars. Some of these features include ridges becoming increasingly deformed as one looks further downslope, as shown in Figure 2, where the ridges of the glacial deposits in Antarctica are more deformed at the bottom of the picture. Spoon-like holes, called spatulate depressions, were also found on both the Antarctic glacial deposits and the Martian crater, formed by ice weathering away. As glaciers retreat, they often leave behind steep slopes in their wake. These slopes are unstable, and over time, sediment flows downward and builds up on the sides to stabilize the slope, as shown in Figure 3. Gullies, which are a geologic feature formed by the path that the sediment took to travel downward, and the resulting triangular piles of sediment can be found both in the crater on Mars and on Earth, shown side by side in Figure 4.

Why is this study important? This study is important because it increases our understanding of the time frames of climate cycles on Mars, and also highlights the similarities and differences between Mars and Earth. On Earth, paraglacial periods are relatively short, and the features left behind are likely to be eroded away by rainfall, rivers, and vegetation. These features are better preserved on Mars, an extremely cold and dry planet that doesn’t have the same erosive forces.

Figure 4: An example of gullies and debris fans on Mars (left) and on Earth (right).

The big picture:  Understanding the formation of geologic features on Earth is essential to uncovering the geologic history of the rest of our planets. This study showed that several features that form after a glacier migrates away can be found both on Earth and on Mars. The key difference is the time frame: on Earth, the paraglacial period is relatively rapid, while on Mars, it takes place on the scale of millions of years. 

Citation:mJawin, E. R., Head, J. W. & Marchant, D. R. Transient post-glacial processes on Mars: Geomorphologic evidence for a paraglacial period. Icarus 309, 187–206 (2018).

Tracing the Body Plans of Echinoderms through Time

Evolution and Development at the Origin of a Phylum

by: Bradley Deline, Jeffrey R. Thompson, Nicholas S. Smith, Samuel Zamora, Imran A. Rahman, Sarah L. Sheffield, William I. Ausich, Thomas W. Kammer, and Colin D. Sumrall

Summarized by: Lisette Melendez

What data were used? In this paper, changes in the bodies of early echinoderms (the group that includes marine animals such as starfish and sea urchins!) are tracked in order to understand the trends that separate groups from the rest of the animal kingdom. The main question is: why are all the body plans so different from one another? Figure 1 shows the range of body plans for early echinoderms, but the distinction carries on even today, considering how starfish and sea cucumbers look so different from one another! In order to quantify these changes, the scientists directly studied specimens from various natural history museums, sifted through past echinoderm papers, discussed with experts in organism classification, and consulted the Treatise on Invertebrate Paleontology. Since the scientists were looking specifically at early echinoderms, we are talking about fossils that date back to the Cambrian and Ordovician periods, about 541-444 million years ago! Usually, data from fossils this old is limited because many significant characteristics are worn away with time. However, echinoderms have notable skeletons that retain a great deal of important characteristics, making their skeletons excellent indicators of evolutionary changes through time.

Figure 1: a collection of different early Paleozoic echinoderm body plans. The one featured in (A) is non-radial, (B) is pentaradial attached, (C) is mobile and able to move around freely, and (D) – (F) are pentaradial stalked (hence the stem-like structures).

Methods: Once all the data was gathered, the next step was to find a way to accurately portray the changes of early echinoderm bodies through time. A morphospace, or a representation of every possible shape of echinoderms, was created, as shown in Figure 2. Four major echinoderm body plans were revealed in the graph. Three of the groups had radial symmetry (symmetry around a central part), while one was non-radial. Two of the groups were characterized by stem-like stalks that attached the echinoderm to the sea floor, while another group was mobile and free to move around. While Figure 2 shows the overall body plans of early echinoderms, this graph was further broken down into specific time intervals (each about 20 million years long) in order to study how the body plans changed over time. Figure 3 depicts how different the body plans were from one another throughout time.

Results: By studying the graphs, several important evolutionary trends can be picked out. Take, for example, Figure 3. The Cambrian was when the first major echinoderm body plans appeared, but the Ordovician was really where each body plan became more complex and different from one another, pointing to the Great Ordovician Biodiversification Event. Each body plan became more well-defined over time, and the differences between the various body plans are highlighted by the extinction of the transitional forms that connected one body plan to another. Even as evolution continued to progress, sometimes certain species would “readapt” a characteristic that they lost thousands of millions of years previously, showing how flexible evolution can really be.               

Figure 2: A graph that shows all the different body types of Echinoderms, separated by characteristic differences like mobility and radial symmetry (or lack thereof).

Why is this study important?  This study is important in studying the mechanisms behind the nature of the Cambrian explosion: why do all of these major animal groups start appearing and how have the groups changed over time? This study shows how fluid characteristics are throughout time, with the introduction, removal, and possibly even a re-introduction of characteristics to body plans as time progresses (this is called homoplasy). It highlights the various patterns of body types within Echinodermata and the patterns of gaining or losing characteristics over time, indicating the complexity in studying how animals change over time.

Figure 3: A graph that shows the diversity of echinoderms between the Cambrian and the Ordovician (541 – 444 million years ago).

The big picture: This study helps us fill in some of the gaps in our knowledge about the Cambrian Explosion, a consequential chapter in the history of living creatures, and how animals have evolved since that point. It shows how evolution has changed the bodies of animals within the same group over time and helps us understand how some animals (like sand dollars and brittle stars) can look so different, yet be closely related to one another. 

 Citation: Deline et al., Evolution and Development at the Origin of a Phylum, Current Biology (2020), https://doi.org/10.1016/ j.cub.2020.02.054

The relationship between rodents and Homo floresiensis

Temporal shifts in the distribution of murine rodent body size classes at Liang Bua (Flores, Indonesia) reveal new insights into the paleoecology of Homo floresiensis and associated fauna

by: E. Grace Veatch, Matthew W. Tocheri, Thomas Sutikna, Kate McGrath, E. Wahyu Saptomo, Jatmiko, and Kristofer M. Helgen.

Summarized by: Kailey McCain

What data were used? Researchers once believed that Homo sapiens (i.e., modern humans) were the only hominid to reach the Indonesian islands. However, in the past few decades anthropologists, archeologists, and paleontologists have discovered an early hominid species’ cultural and skeletal remains, belonging to Homo floresiensis, on the island of Flores. Along with the hominid remains, 257,000 additional vertebrate skeletal elements were identified and 80% of the collected belonged to the murine rodent taxa (i.e., rats). The main rodent genera identified and used in this study varied in body size, which was used as a proxy (i.e., representative) to identify the paleoecology of the environment. The five genera used were: Papagomys, Spelaeomys, Hooijeromys, Komodomys, Paulamys, and Rattus (Figure 1).

Methods: The excavation site for the murine skeletal remains, as well as H. floresiensis, was within the Liang Bua, a limestone cave on Flores Island. The stratigraphy of Liang Bua was divided into sectors based on age, with the oldest being approximately 190-120 ka (thousand years ago) and the youngest sector at less than 3 ka. Once the sites were identified, researchers began excavating the remains by using a method called wet-sieving, which is the process of sediment separation using water to remove certain grain sizes and break apart agglomerates (i.e., a mass of sediment grains).

Once the murine remains were collected, researchers began identifying the different species by using molar and jaw sizes, as well as comparing the skeletal body to size to extant (i.e., living) rodents. In addition to dividing the remains into their different species, they were also further divided by size. The five distinct body size categories are: small (<100 g), medium (100-300 g), large (300-600 g), huge (600-1100 g), and giant (>1100 g).

Figure 1: This image represents how the different murine taxa, Papagomys, Spelaeomys, Hooijeromys, Komodomys, Paulamys, and Rattus, differ in body size and molar size.

Results: The data collected showed that the small and medium sized murines dominated the cave during the first two sectors (190-60 ka) but researchers noted a sharp decline in the medium sized murines during the 60-50 ka age range. This decrease in species can be correlated to the paleoclimate record, which indicated a substantial decrease in available vegetation. As time progressed to the age range 47-12 ka, researchers noticed no significant change in body size. This was a surprise to the researchers due to the geologic record indicating high levels of volcanic activity. The next range, 12-5 ka, exhibited a decrease in overall murine size that can be attributed to the high rainfall and monsoon season recorded for this time period. Finally, the age range 5-3 ka, showed the first increase of medium sized murines which could be correlated to the dispersal of Homo floresiensis and the subsequent opening of habitats, but will need further research to support the claim.

Why is this study important? This study is important because it shows the relationship between the dominant non-human animals and Homo floresiensis within the Liang Bua cave. Additionally, the researchers explored other ecological factors (e.g, weather, resource availability, volcanic activity) and showed how it affects not only the fauna in general, but showed the difference in responses between sizes.

Figure 2: This figure shows two images. Image (a.) shows researchers measuring a large modern cave rat, Papagomys armandvillei. Image (b.) shows a reconstructed image of H. floresiensis carrying a large rat over their shoulder.

The big picture: The researchers set out to determine the ways in which the dominant fauna, second to the hominid species, responded throughout time with the introduction and dispersal Homo floresiensis. While there was a relationship noted between murine size/distribution and hominid involvement, the data also suggested that additional ecological factors may have contributed; therefore, no significant conclusions can be made without additional research regarding the true impact of Homo floresiensis

Citation: Veatch, E. G., Tocheri, M. W., Sutikna, T., McGrath, K., Saptomo, E. W., & Helgen, K. M. (2019). Temporal shifts in the distribution of murine rodent body size classes at Liang Bua (Flores, Indonesia) reveal new insights into the paleoecology of Homo floresiensis and associated fauna. Journal of human evolution130, 45-60. https://doi.org/10.1016/j.jhevol.2019.02.002