How Did Horses Get to Just One Toe?

Mechanics of evolutionary digit reduction in fossil horses (Equidae) *
Brianna K. McHorse, Andrew A. Biewener, Stephanie E. Pierce
Summarized by Time Scavengers contributor, Maggie Limbeck

What data were used? This study used metapodials (toe bones) from 12 fossil horse genera as well as from a tapir (herbivorous mammal that looks similar to a pig, but that also has an odd number of toes) to collect data. The metapodials were imaged in cross sectional views to determine load strength (how was weight distributed among the main three toes of fossil horses and the one toe of recent horses) and geometry of the metapodials.

Methods: The metapodials from the fossil horses and tapir were micro-CT scanned (3D x-ray scanning, like the human procedure but on a smaller scale) and the images were manipulated to see the cross sectional area and other views using the open source program ImageJ with the plugin BoneJ. The images were then measured and corrected for evolutionary changes using the open source statistical software, R. Estimates for bone stress were calculated using a toe reduction index (TRI), reconstructed body weights, and angle of metapodial during ground reaction at two speeds of forward locomotion. Additionally, the amount of stress that the metapodials could support was estimated using beam mechanics (an engineering process that looks at how much stress a hypothetical beam could withstand before bending and/or breaking).

Results: Looking at the geometry of the metapodials, it was determined that as the fossil horses grew in both size and weight, their need for four front and three back toes was decreased, and as such the digits gradually decreased to one on all four limbs. For the stress experiments, as the fossils moved forward in time to recent horses, it is seen that the amount of stress that can be placed on metapodial III (what we see expressed as the hoof) increases through time and the dependence on the two metapodials on either side of digit III decreases. This statement is true for both front and back metapodials at both a moderate speed (trotting) and performance (acceleration, jumping).

Figure 1. Image of the toe reduction index (TRI) shown across a phylogenetic tree (evolutionary tree) with the cross sectional view of the metapodial being analyzed. Based on the TRI it is apparent that there is a gradient for toe loss and that there is only one genus of horse, Equus, that truly has one toe. You can also see that for those early horses that still had side toes that the shape of the toe in cross section has a much different shape and therefore still needs side toes to some extent.

Why is this study important? This study is important because it supports two hypotheses that were held about digit reduction in horses. That a) the increased body mass of horses selected for a single, strong metapodial and b) that as horses grew taller, the cost of speed from the side toes outweighed their use in stabilization. This also contradicts the commonly held belief that horses experienced digit reduction as an adaptation to the replacement of forests by grasslands.

The big picture: The big picture here is sort of two-fold. Digit reduction in tetrapods (four-legged creatures) has been of interest to many scientists because as tetrapods emerged onto land 5, 8, even more digits was the ancestral state for these organisms. As we see today, that is not the case. The vast majority of the organisms that we think of have 5 or less digits on their hands and feet, so we want to understand what drove the process of digit reduction in every animal. Second, this study highlights that it is important to keep testing hypotheses even if they have been held for a while. The additional lines of evidence provided by this study give more credibility to two commonly held hypotheses while continuing to falsify the common explanation for digit reduction in horses.

Citation: McHorse BK, Biewener AA, Pierce SE. 2017. Mechanics of evolutionary digit
reduction in fossil horses (Equidae)
. Proceedings of the Royal Society B 284: 20171174.

*all samples in this study were fossils, no live animals were used

Ancient hydrothermal seafloor deposits on Mars

Ancient hydrothermal seafloor deposits in Eridania basin on Mars
Joseph R. Michalksi, Eldar Z. Noe Deobrea, Paul B. Niles, and Javier Cuadros
Summarized by Mike Hils

What data was used? High resolution imaging and spectroscopy data about mineralogy and geology

Methods: Used data from instruments on the Mars Reconnaissance Orbiter, a satellite currently orbiting Mars:

    HiRISE (High Resolution Imaging Science Experiment) was used to define the ancient basin boundaries and to inspect the types of features and rocks located in the Eridania basin. HiRISE is a camera onboard the Mars Reconnaissance Orbiter than can resolve objects to about a foot long on the surface of Mars.

    CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) to study the minerals and rocks found in the Eridania Basin. Materials bounce light off of them in a consistent pattern and energy, and spectrometers can analyze that light and identify the material on Mars’ surface.

Results: The Eridania Basin was probably up to 1.5 km (0.9 mi) deep, and flowed into a canyon named Ma’adim Vallis. Images from HiRISE show that the western half of the basin consists of massive stone that lacks bedding planes and has eroded into buttes and mesas. The basin would have held about as much water the Caspian Sea on Earth currently does. This basin is shaped different than many of the other Martian basins, and it is thought that a covering of ice kept sediment from settling on the bottom. A comparison of the craters in this part of the basin suggest that these rocks are about 3.77 Ga (G = giga, SI prefix for billion, a = annum, Latin for year) old.

Analysis from CRISM found evidence of minerals and rocks associated with deep ocean water on Earth, including iron and magnesium rich clays, serpentinite, carbonates, and chlorides. For example, serpentinite, a metamorphic rock that looks like green marble, forms when basalt reacts with warm, deep sea water. Carbonate minerals are common on Earth in the form of limestone, marble, seashells, and corals. The authors suspect that the carbonate formed due to hydrothermal interactions. Chlorides, such as salt (sodium chloride), form on Earth when water evaporates.

Map of the Martian terrane with colors indicating highs (orange) and lows (blue) of an ancient sea. The data points in the legend are minerals that were identified at each location.

Why is this study important? This study is important in two ways. First, one idea for the origin of life on Earth is that it developed around hydrothermal vents in the ocean. Although ancient rocks have been found suggesting such environments in the past, they have been significantly altered by weathering and metamorphism, and vital information has been lost. Martian sites, which haven’t been altered nearly as much as Terrestrial ones, might be a good proxy for understanding early environments on Earth. Secondly, the identification of such sites on Mars could provide key places to look for signs of life on Mars.

The big picture: Understanding how life began is a huge problem that scientists in many fields are exploring. Life may have evolved on Earth, or it may have arrived here from some other body. The identification of hydrothermal environments on Mars would allow scientists to gain a better understanding of hydrothermal environments on Earth as life was evolving and try to see if life could have started here. This would also allow astrobiologists to look for evidence of extraterrestrial life on Mars.
Two other bodies in our solar system may harbor life around hydrothermal vents. Jupiter’s moon Europa and Saturn’s moon Enceladus are both covered in salty water capped with ice, and both experience tectonic activity due to the gravitational pull from their host planets. In addition, organic molecules (chemicals made mostly of carbon that are often associated with organisms) have been detected in water escaping from Enceladus. If life could have evolved in hydrothermal environments on Earth and Mars, it is likely Europa and Enceladus both host extraterrestrial life now.

Citation: Michalski, J., Dobrea, E., Niles, P., Cuadros, J. 2017. Ancient hydrothermal seafloor deposits in Eridania basin on Mars. Nature Communications, 8:15978. doi: 10.1038/ncomms15978

Rapid decline of vertebrate populations

Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and decline

Gerardo Ceballos, Paul R. Ehrlich, and Rodolfo Dirzo

Global data from the study of terrestrial species. Species richness (maps on the left) indicates the number of species; number of decreasing species is presented on the middle maps; percentage of decreasing species is presented at right. The top 3 maps are for all vertebrate animals, and the lower maps are separated my the major groups (mammals, birds, reptiles, and amphibians). The cooler the color on the percentage decreasing maps, the more severe the loss of those animals.
Data: The scientists used a large data set of vertebrate populations (27,600 species and a more detailed data set of 177 mammal species from 1900 to 2015) to examine how the ranges of vertebrate animals have become smaller due to growing populations of humans that are pushing the animals out of their natural habitat. A lot of animals that are not considered endangered have experienced a huge decline in their numbers, indicating that animals all over the world are being IUCN Red List of Threatened Species. This data was was superimposed in a 22,000 grid of 10,000 km3 quadrats covering continental lands. A species was considered decreasing if their ranges (where that species lives) shrunk over time, or if there was a reduction in the number of species. This approach was also applied to 177 species of land mammals to see how their populations have changed through time.

Results: The scientists found that even in populations of animals that are not considered threatened, the rate of population loss is extremely high. In this study, 32% of the known vertebrate species are decreasing, meaning they have shrunk in population size and the ranges, or land in which they live. In the more detailed data set of 177 mammals, all of them have lost 30% or more of their ranges, and more than 40% of the mammal species have experienced severe population declines.

This map represents the percent of population extinctions in 177 species of mammals. The maps were made by comparing historic ranges of the animals to the current ranges. Cooler colors indicate areas that are experiencing the most severe population extinctions (for example, the east coast of the US, southern Australia, and northern Africa).

Why is this study important? This study uses a large data set of vertebrates to examine patterns of species through time to specifically assess how humans are impacting the ranges and populations of the animals. The current decline of species on Earth isn’t happening slowly; instead, it is happening at an accelerated rate. This study highlights the idea that Earth and all its creatures may be in the Sixth Mass Extinction, and remediation efforts are necessary and need to be enacted now in order to save animal populations.

The Big Picture: Humans are fundamentally changing the Earth and the animals that live on it. Through habitat destruction and expansion of housing and urban areas, to name just a few causes, we are taking habitats away from animals. Combined with climate change, the Earth’s animals are experiencing a biodiversity decline.

Citation: Ceballos, G., Ehrlich, P. R., and Dirzo, R., 2017. Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines. PNAS. DOI: 10.1073/pnas.1704949114

Unusual bird hatchling fossil preserved in amber (Burma)

A mid-Cretaceous enantiornithine (Aves) hatchling preserved in Burmese amber with unusual plumage
Lida Xing, Jingmai K. O’Connor, Ryan C. McKellar, Luis M. Chiappe, Kuowei Tseng, Gang Li, Ming Bai

What data was used? Newly discovered Cretaceous-age (~100-65 million years ago) amber specimens that contain parts of a bird hatchling; rarely found soft tissues of the plumage were also preserved. These specimens were found in Myanmar.

The fossil, preserved in amber (bottom right); CT scan of the fossil (bottom left) and the author’s reconstruction of it (top). You can see the rare fossil feathers in the amber!

Methods: The specimens, encased in amber, were CT scanned using a micro CT scanner. Each preserved piece of the bird skeleton (e.g., neck, foot, etc.) were scanned separately. Researchers then did a 3D reconstruction of the bird, combining all of the scanned pieces.

Results: Researchers found that a number of the bones in this specimen were unfused, which indicates that the bird was very young (bones typically fuse as an organism grows-human babies do this too!). The specimen preserved two types of feathers: downy-type feathers and outer feathers, similar to birds today and to some of the earliest birds in the Jurassic, like Archaeopteryx, the famous bird-dinosaur transitional fossil.

Why is this study important? Feathers and other types of soft tissue are exceedingly rare in the fossil record! Typically, the only things that get preserved are bones, shells, and other hard tissues. Amber is one of the ways that soft tissue can be preserved; when we find soft tissue preserved, it’s certainly a reason to celebrate! This data can shed a lot of light on how organisms looked from millions of years ago. This hatching’s preservation tells us a lot about how feathers in juvenile birds looked from the Cretaceous, and can be compared to the other soft tissue feathers that have been found previously belonging to adult birds. The bones also provide more information on how skeletal changes of birds occurred from juvenile to adult stages.

The big picture: Soft tissue preservation is an incredible opportunity to learn about organisms that lived a very long time ago-other soft tissue fossils have shown us what dinosaur skin looked like, how organs of extinct mammals look, and more. As you can imagine, it’s also rare to find well-preserved juveniles in the fossil record (many groups of fossils don’t have juvenile representatives at all!), so when we do find examples of younger organisms, it’s important to study them to understand how their bodies changed throughout their lifetime.

Citation: Lida, X., O’Connor, J.K., McKellar, R.C., Chiappe, L.M., Li, G., Bai, M., 2017, A mid-Cretaceous enantiornithine (Aves) hatchling preserved in Burmese amber with unusual plumage

The Dinosaur that Went Viral: Looking at the science behind the Facebook posts

An Exceptionally Preserved Three-Dimensional Armored Dinosaur Reveals Insights into Coloration and Cretaceous Predator-Prey Dynamics

Caleb M. Brown, Donald M. Henderson, Jakob Vinther, Ian Fletcher, Ainara Sistiaga, Jorsua Herrera, Roger E. Summons

Summarized by Time Scavengers contributor, Maggie Limbeck

What data were used? The holotype specimen (fossil or other specimen that all others are compared to to determine what it is) of Borealopelta markmitchelli was used for all experiments touched on in this article. Data was also collected from other members of the Ankylosauria (armored, herbivorous dinosaurs with a club on their tail) clade for comparison.

Methods: A phylogenetic analysis (family tree) was completed using this new dino as well as others from the Ankylosauria and Nodosauridae (Ankylosaurs missing the club on their tail) clades to determine where in the dinosaur tree B. markmitchelli belongs. This also provided data for comparison in life habit and some of the unusual features of this particular dinosaur. Additionally, geochemical studies were done on this specimen, including scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Both of these methods were used to get an idea of what the preserved organic material on the specimen was and determine what kinds of fossil melanins (pigments) were present.

Results: The resulting phylogenetic tree from this study does place B. markmitchelli where one would expect it to go within the Ankylosauria tree (within the Nodosauridae clade). The TOF-SIMS experiment showed that there were ions present that indicate benzothiazole and therefore pheomelanin was present. These particular chemicals would indicate that parts of this dinosaur were reddish-brown in color. However, not all parts of the osteoderm (bony skin) and epidermal coverings (scales) show this reddish-brown coloration.

Figure 1. A graphical summary of the paper. We see an image of B. markmitchelli that is exceptionally preserved, the results of the mass spectroscopy experiments that told us that there is countershading (camouflage) caused by the pigment pheomelanin that gave the dinosaur a reddish brown color. This reddish-brown color is a result of strong predation pressure and an attempt to better camouflage themselves.

Why is this study important? This study is important because it highlights how much we can learn from one extremely well preserved individual fossil. It was used in a phylogenetic analysis to determine where it belongs in the dinosaur-scheme of things, images were taken of the skull, and geochemical data was returned to determine the coloration of the skin. From these studies the scientists were able to determine that these dinosaurs used camouflage to help protect them from predators. This is very different from what we see today in predator-prey interactions. Borealopelta markmitchelli was by no means a small dinosaur (~5.5m long and ~1,300kg) and had significant body armor yet it still needed camouflage. Today, large mammals comparable to this size do not need camouflage because even the fiercest predator does not go after grown adults. This new relationship between Cretaceous predator and prey highlights major differences in large predator-prey interactions through time. This specimen will continue to play a major role in research for years to come.

The big picture: There are really two big picture things to take away from this article. The first being that science, and ground breaking science in particular, is always interdisciplinary. These paleontologists relied on geology, biology, ecology, and chemistry (to name a few) to come to their conclusions about B. markmitchelli. This is really important because people always think that science is very isolating and you only work on your own, when in actuality science is accomplished by a team of people who can support you and fill in knowledge gaps. Second, it is important to look into those flashy science articles that pop up on your newfeeds and on Twitter. Those articles are press releases to get you interested in the science that is being done on these fossils or rocks or bacteria. We scientists get excited about our work and want to share it with people-take the time to do so, get excited about nature, and keep reading!

Citation: Brown et al., An Exceptionally Preserved Three-Dimensional Armored Dinosaur Reveals Insights into Coloration and Cretaceous Predator-Prey Dynamics, Current Biology (2017), DOI: 10.1016/j.cub.2017.06.071

Global risk of deadly heat

Global risk of deadly heat

Camilo Mora, Benedicted Dousset, Iain R. Caldwell, Farrah E. Powell, Rollan C. Geronimo, Coral R. Bielecki, Chelsie W. W. Counsell, Bonnie S. Dietrich, Emily T. Johnson, Leo V. Louis, Matthew P. Lucas, Marie M. McKenzie, Alessandra G. Shea, Han Tseng, Thomas W. Giambelluca, Lisa R. Leon, Ed Hawkins, and Clay Trauernicht

Data: This study was conducted by gathering data from previous studies and looking at the number of lethal heat events that have occurred around the world from 1980 to 2014. The study also estimates the percentage of the population that is at risk from increased air temperatures and humidity due to human-induced climate change in the future.

The number of days per year that different areas are exposed to deadly heat and humidity (‘threshold’). The simulations, a-d, are from models into the year 2100. A) historical data from other published studies; B) RCP 2.6 scenario where nearly all emissions are cut; C) RCP 4.5 is a scenario where most emissions are cut; D) RCP 8.5 is the ‘business as usual’ scenario where emissions are not cut at all.

Methods: The authors used data from 911 previous studies to use in their analysis. They collected information on the place and dates of lethal heat events, or extreme heat events that led to human deaths. The number of days per year that surpassed the heat threshold for which humans can live in was assessed for each year (1980-2014). To determine how much of the population may be at risk of heat-related deaths in the future, the scientists used four different CO2 scenarios to model air temperature and humidity to year 2100.

Results: From the previous studies, the scientists found 783 cases of human mortality linked to excess heat from 164 cities in 36 countries. Cases of heat-related deaths were concentrated to mid-latitude regions, with high occurrences in North America and Europe. Temperature and relative humidity of an area were both found to be factors important to identifying regions where climate conditions may become deadly, as these are related to human’s ability to regulate their body temperature. Currently, around 30% of the Earth’s population is exposed to climate conditions that are considered deadly. By the year 2100, this number is projected to increase to 48% under a CO2 scenario where emissions are drastically cut, and 74% under a CO2 scenario of increased emissions.

Why is this study important? This study highlights the health risks posed to humans due to increased heating of the Earth. Several countries and large cities, mostly concentrated at the mid latitude regions and equator, are at most risk.

The big picture: Under all emissions scenarios, whether we cut emissions drastically or keep emitting CO2 at the same rate, an increased percent of the human population will be at risk of heat-related deaths. This study emphasizes the importance of aggressive mitigation to minimize the human population’s exposure to deadly climates linked to human-induced climate change.

Citation: Mora, C., Dousset, B., Caldwell, I. R., et al., 2017. Global risk of deadly heat. Nature Climate Change, 7, 501-506. DOI: 10.1038/nclimate3322

Evolution of the Arch of the Foot

Chimpanzee and human midfoot motion during bipedal walking and the evolution of the longitudinal arch of the foot
Nicholas B. Holowka, Matthew C. O’Neill, Nathan E. Thompson, Brigitte Demes
Summarized by Time Scavengers contributor, Maggie Limbeck

What data were used? The only data that were utilized in this study were five male humans and two male chimpanzees that were recorded while walking. The scientists applied markers on the joints and other key points in the feet of both the humans and chimpanzees based on where they hypothesized to see foot motion in both species. These markers provided the data points that were analyzed in film after the experiment was completed.

Methods: 3D kinematic data (a human or chimpanzee foot in motion) was collected by recording the subjects walking at a self-selected speed for 11 meters. The researchers then selected representative steps for each subject to analyze the motion and utilization in certain regions of the foot. The data was analyzed using the packages ProAnalyst and MATLAB to calculate joint angles and estimate speed of walking. These angles were then used to determine the motion between the markers placed on the foot and understand the differences between human foot motion and chimpanzee foot motion.

Image of both a human and chimpanzee subject while walking. The dots on each foot indicate the markers that the researchers were using for data collection. The percentages on each image indicate the amount of motion in the midfoot that is being utilized during each part of taking a step.

Results: It was found that humans have a much greater range of motion along the sagittal plane (imaginary plane that divides the body into left and right sides) than chimpanzees, but the range of motion along the coronal plane (imaginary plane that divides the body into front and back) were similar in both species. While there were some great differences in motion along other planes the results state that the motion and parts of the foot involved are still activated at some point while walking, they are just activated during different parts of walking in chimpanzees and humans.

Why is this study important? This study is important because it was thought that the arch in human feet evolved to stiffen the foot while walking upright on two legs (bipedally) and that therefore chimpanzees would have a much greater motion in the midfoot than humans would while walking bipedally. This experiment rejects that idea because it was found that humans actually use a significantly greater amount of motion in the midfoot while walking than chimpanzees. This does not however, mean that at all times when walking do humans have more motion in their midfoot. The researchers broke walking into separate phases and during some of those phases the chimpanzees did have much more motion in their feet than humans; but when looking at the step as a whole, humans do have more motion than chimpanzees.

Big picture: The big picture here is that the total difference in range of motion between humans and chimpanzees is pretty small, only 4°. Therefore we can’t rely on using only midfoot joints to explain evolutionary differences between humans and chimpanzees. The authors suggest that looking further into morphology (shape) affects the function of the midfoot throughout motion. Essentially, evolution cannot always be easily explained by differences in bone shape–we must observe the action that the bones might be influencing.

Citation: Holowka, N.B., O’Neill, M.C., Thompson, N.E., Demes, B., 2017, Chimpanzee and human midfoot motion during bipedal walking and the evolution of the longitudinal arch of the foot: Journal of Human Evolution, p. 23-31.

Global warming and bleaching of coral reefs

Global warming and recurrent mass bleaching of corals

Terry P. Hughes, James T. Kerry, Mariana Alvarez-Noriega, Jorge G. Alvarez-Romero, Kristen D. Anderson, Andrew H. Baird, Russel C. Babcock, Maria Beger, David R. Bellwood, Ray Berkelmans, Tom C. Bridge, Ian R. Butler, Maria Byrne, Neal E. Cantin, Steeve Comeau, Sean R. Connolly, Graeme S. Cumming, Steven J. Dalton, Guillermo Diaz-Pulido, C. Mark Eakin, Will F. Figueira, James P. Gilmour, Hugo B. Harrison, Scott F. Heron, Andrew S. Hoey, Jean-Paul A. Hobbs, Mia O. Hoogenboom, Emma V. Kennedy, Chao-yang Kuo, Janice M. Lough, Ryan J. Lowe, Gang Liu, Malcolm T. McCulloch, Hamish A. Malcolm, Michael J. McWilliam, John M. Pandolfi, Rachel J. Pears, Morgan S. Pratchett, Verena Schoepf, Tristan Simpson, William J. Skirving, Brigitte Sommer, Gergely Torda, David R. Wachenfeld, Bette L. Willis, and Shaun K. Wilson

Data: The authors surveyed Australian coral reefs around the Australian coast using aerial photographs and underwater images to assess the amount of bleaching experienced by the reefs. They compared these images and data to sea surface temperature data from the area to determine if there was a correlation between sea surface temperature and coral reef bleaching. Learn about what coral bleaching is by clicking here.

Methods: The authors first took aerial photographs of the reefs from an airplane and helicopter, which flew about 150 meters above sea level, for 10 days in 2016. The researchers then ranked the severity of coral bleaching using a scale from 0 to 4, with 4 being the worse bleaching (over 60% of corals). To check that their scale from the aerial images was correct, the scientists also conducted underwater surveys of the same reefs. The same methods were conducted in 1998 and 2002 by other researchers, so the authors of this study compared their data to previous data. In this way, they have 3 years of coral bleaching data from the years 1998, 2002, and 2016 to see if bleaching events are becoming more common and getting worse. The scientists then compared their bleaching scale to observed sea surface temperatures in the area where the surveys were conducted to observe the relationship between temperature and coral bleaching.

A). The severity of bleaching of coral reefs around the northeast coast of Australia from 1998, 2002, and 2016. Dark green areas indicate <1% of corals bleached, light green indicates 1-10% bleaching, yellow indicates 10-30% bleaching, orange areas indicate 30-60% bleaching, and and red areas are where more than 60% of the corals are bleached. B) Patterns of heat stress during mass bleaching events in 1998, 2002, and 2016. Hotter colors indicate maximum heat exposure.

Results: Coral reef bleaching increased significantly from 1998 to 2016. Associated with the bleaching was an increase in the water temperature around the coasts of Australia where the corals are living.

A) Aerial view of a reef that is close to 100% bleached; B) Severe bleaching of an older coral mass on the northern Great Barrier Reef; C) staghorn corals that were killed by the major bleaching event in 1998; D) the same site in C, but 18 years later and the corals have not recovered; E, F) mature staghorn corals that were killed by heat stress and colonized by algae in just a few weeks time in 2016.

Why is this study important? This study is one of the first to examine a huge amount of coral reefs (1,156 in 2016 alone) to assess the effects of increased water temperature on coral bleaching. The researchers indicate that some coral species can grow back in 10-15 years, but some of the corals that are dying in the reefs are slow growers and very old. It will likely take decades for these corals to return to their former glory. This study indicates that we must take action now to save our coral reefs, not just around Australia, but around the world.

The Big Picture: By using large data sets and looking at trends of corals through time, scientists can concretely state that rising sea surface temperatures due to increased CO2 levels are causing mass coral reef bleaching events. When corals are stressed for too long, they die. Coral reefs are considered the rainforests of the sea because they are home to so many species of marine animals. Once the coral reefs begin to die, other animals will lose habitat to live in, and thus their numbers will, and are, declining. This has huge implications on the fishing industry, as people who rely on the ocean to make a living will no longer be able to catch bountiful amounts of fish that live around the reefs. In short, the effects of dying corals has far-reaching implications that will hurt the marine ecosystem, collapse the marine food chain, and affect economies.

Citation: Hughes, T. P., Kerry, J. T., Alvarez-Noriega, M., Alvarez-Romero, J. G., et al., 2016. Global warming and recurrent mass bleaching of corals. Nature, 543 (7645). DOI: 10.1038/nature21707

Switching Up the Dinosaur Family Tree

A new hypothesis of dinosaur relationships and early dinosaur evolution
M.G. Baron, D.B. Norman, and P.M. Barret
Summarized by Time Scavengers contributor, Maggie Limbeck

What data was used? This study looked at a wide range of dinosaurs and dinosauromorphs (dinosaur-like animals) including those from around the world from the Middle Triassic to Cretaceous. The data were focused on the early dinosaurs, from which there previously wasn’t a lot of focus on evolutionary studies. By studying the fossils of all of these different dinosaurs the researchers were able to find similarities and differences in their morphologies (structure, shape, function) to create a character list to be used to create a new phylogenetic hypothesis (evolutionary hypothesis) for dinosaurs.

Methods: The character list that was created by studying the fossils of the dinosaurs in question was scored for each dinosaur. This means that every dinosaur had the same questions asked about it and answered as a yes/no question. This data set was then run through TNT 1.5-beta, a phylogenetics software that generates a phylogenetic tree based on those characters. After a new tree was created based on this data it was tested for support using Bremer support (which calculates the difference between the most parsimonious tree and the next most parsimonious tree that is missing a particular clade (grouping of organisms)) and constraint trees.

Results: The major result of this study is the reorganization of the dinosaur phylogenetic tree that changes the relationships that were thought to be true since 1887. Since that time the theropods (e.g., T. rex) and sauropods (e.g., Apatosaurus and Brachiosaurus) were thought to form a group because their hips have a classic “reptilian-hip” structure while ornithischians (Triceratops) have a “bird-hip” structure. After completing this study, it was found that contrary to this belief that the groups Ornithischia and Theropoda are more closely related to each other than Saurischians and Theropoda are. Additionally, this new hypothesis of the evolutionary relationships between the major dinosaur groups helps to provide an explanation for morphological features that were previously thought to be examples of convergent evolution (similar traits shared by organisms that are not closely related) between theropods and ornithischians.

The newly hypothesized phylogenetic tree for dinosaurs. B shows the reorganization of Ornithischia (bird hipped dinos) to be most closely related to Theropoda (T. Rex style dinos). This is different than the relationship that was believed since 1887 that Theropoda and Saurischia were most closely related.

Why is this study important? This study is important because it represents a critical shift in the way that we think about and study dinosaurs. A change in the evolutionary relationship between major groups of dinosaurs will require current studies to evaluate how this change may affect their results. However, this could aid research that had unanswered questions or odd data points that may now be explained by these relationships.

Big Picture: The big picture with this study is that even things that we as scientists and science enthusiasts have thought to be true for years can be redefined. We see here that the dinosaur “family tree” has changed dramatically with just this one study. However, this paper has sparked a lot of internal fact-checking and conversation that is an integral part of science that is often forgotten or hidden in the background. Many scientists have run their own phylogenetic analyses and have used different methods to decide if what these authors are claiming is, in fact, correct. All phylogenies are just hypotheses, especially with dinosaurs since we only have fossil data to use. Fossils are not always in the best shape to help us learn from them, and especially fossils from the early Triassic are lacking. By having the scientific community be so shaken by this news and running their own analyses, they are helping to strengthen the validity of this science and making it more powerful. So while yes, this is groundbreaking science, it is also a good reminder that scientific hypotheses are still extensively tested and retested parts of science, not just a guess or a hunch.

Citation:Baron, M.G., Norman, D.B., Barret, P.M., 2017, A new hypothesis of dinosaur relationships and early dinosaur evolution: Nature, p. 501-506.

How well do stable isotopes really work?

Defining uncertainty and error in planktic foraminiferal oxygen isotope measurements

Andrew Fraass and Christopher Lowery

Summary by Andy Fraass, website collaborator

Figure 1. Two different locations in the ocean. Temperature and salinity combine to give us the δ18O values. On the left are a few planktic foraminifera in their rough depth habitats (where each species likes to hang out in the water column) (Shiebel and Hemleben, 2005). Drawings are modified from Kennett and Srinivasan (1983) and Schiebel and Hemleben (2005).

Data: Chris and I developed a model to understand how good planktic foraminiferal isotopes actually are at recording temperature, and how important it is that a scientist uses a bunch of tests to measure the isotopes, rather than just a few. There’s actually no data in a traditional sense in this paper; we went back to theory, statistics, and math.

Methods: Chris and I wrote a theoretical model. Planktic foraminifera make their shells in a certain depth (or depths) in the water, and that depth has a certain chemistry. The model allows the scientist to say that the forams are mostly growing in a certain season and at a range of depths. Then the scientist has to decide to include how well the organism records the water chemistry (technically called ‘vital effects’), if the shell has its chemistry altered in the sediment (diagenesis), and a few other things including if there’s a chance that a different species (with a different ecology) got mixed in.

Results: Good results from stable isotope studies come from about 15 or so shells in an analysis, but it’s very dependent on the species and what the ocean structure is like.

Why is this study important? Given all the things that could go wrong, of which the parameters in the model are a part, it’s honestly a little surprising that planktic stable isotope records give the same results as the model. They do, which other folks have shown repeatedly. What Chris and I show here is that as long as you put in enough shells when you’re doing your analysis, then the record actually records what we think it does!

The big picture: Studying the ocean is tough, especially when we’re talking about the ocean from tens of millions of years ago. This paper helps show that despite statistical concerns some of us had with it, we’re doing a good job at recording the past.

Citation: Fraass, A. J., and C. M. Lowery (2017), Defining uncertainty and error in planktic foraminiferal oxygen isotope measurements, Paleoceanography, 32, 104–122, doi: 10.1002/2016PA003035.

References:

  • Kennett, J.P. and Srinivasan, M.S., 1983. Neogene planktonic foraminifera: a phylogenetic atlas. Hutchinson Ross.
  • Schiebel, R. and Hemleben, C., 2005. Modern planktic foraminifera. Paläontologische Zeitschrift, vol. 79(1), p.135-148.