One Year of Integrative Paleontology!

It has been one year since our inaugural post, and time has indeed flown by. In honor of this milestone, each blogger highlighted a favorite post from the last 12 months.

The Jurassic moth Mesokristensenia sinica

The Jurassic moth Mesokristensenia sinica, modified from Zhang et al. 2013. CC-BY.

Blogger Favorites
Sarah Werning picked her post on “Why Paleontology is Relevant” as a personal favorite. Although paleontologists are great at talking about why we are important, Sarah posited that at least some of the oft-cited reasons (e.g., we’re great at teaching anatomy) don’t cut the mustard. Instead, we need paleontology to understand our world today and the changes that it is undergoing. A vigorous discussion resulted.

Andy Farke cheated a bit, and picked a series of posts on proposed United States Forest Service regulations for paleontology on Forest Service lands. The series stimulated lots of productive discussion, largely thanks to the good faith participation of many people from all backgrounds–government paleontologists, museum paleontologists, private citizens, and the like.

Shaena Montanari selected her post on “Paleoecology and Poop” as a highlight for the past year, in which she highlighted the surprising amount of recent research on prehistoric droppings. It’s a poop renaissance, if you will!

So, check out these posts–and don’t forget to check out some exciting new posts that are on the way from our bloggers in the next few weeks!

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The Colorado Plateau Coring Project: Getting Dates in the Triassic

Yesterday I wrote about how rocks layers are aged. After rock layers are lined up and put in relative order, they are dated radiometrically to get their age in years. Terrestrial rocks are difficult to date using relative ages alone, because the divisions of geologic time are defined based on changes in marine fossils (like ammonites and conodonts), which are rare in terrestrial rocks. We can make rough correlations if terrestrial layers are bracketed above and below by marine layers, which happens when sea level rises and oceans spill onto the edges continents. But the oceans reach continental centers  rarely, so long stretches of time may occur between the marine “brackets” that allow terrestrial correlations.

A lot of neat stuff has happened on land during the history of life, from the birth of flowering plants to the origins of humankind. If we had a better grasp on the exact dates that these important events happened, then we could place them in context of things happening elsewhere on the planet: volcanic eruptions, asteroid impacts, climate change, etc.

One time of particular interest is the Triassic Period. Not only is it bounded by two enormous mass extinctions, but the Triassic is when all the major groups of land vertebrates alive today got their start: the ancestors of crocodiles and birds, frogs and salamanders, mammals and lizards all first appear or begin to diversify in the Triassic. What caused this burst of diversity – recovery from the biggest mass extinction of all time, climate change, rifting continents, or something else?  How long did it take – was it simultaneous around the world or region; did it have pulses? The answers are in the rocks, but unfortunately, Triassic terrestrial rock layers are poorly correlated and poorly dated compared to other parts of the global geologic column.

Colorado Plateau Coring Project

Logo by Steven Seppi. Used with permission from the Colorado Plateau Coring Project.

Enter the Colorado Plateau Coring Project. The Colorado Plateau is an area covering about 130,000 square miles of Utah, Colorado, Arizona, and New Mexico. It’s well known for its dramatic geology and incredible national parks, including the Grand Canyon, Arches, Canyonlands, and Petrified Forest. It’s also rich in Triassic rocks and fossils. If the Colorado Plateau was better aligned to the global rock record and better dated radiometrically, it would be key to answering those questions above. The Colorado Plateau Coring Project (CPCP) is funded by the International Continental Drilling Program (ICDP)-funded and National Science Foundation to do just that.

Petrified Forest National Park preserves an especially rich record of the terrestrial Triassic, and comprises nearly 100 million years of continuous rock layers, many rich in fossils. So it makes sense that the CPCP would begin their alignment and dating efforts here. This is a large, collaborative project involving scientists at several universities: Randall Irmis (University of Utah; Natural History Museum of Utah), George Gehrels (University of Arizona), Paul Olsen (Lamont-Dougherty Earth Observatory, Columbia University), Dennis Kent (Rutgers University), John Geissman (University of Texas at Dallas), and Roland Mundil (Berkeley Geochronology Laboratory). For the past two weeks, the team has been at Chinde Point in Petrified Forest drilling a core half a kilometer deep to get the basic rock data to align and date the Colorado Plateau.

Last week, I interviewed Randall about the details of this important research project.

Chinde Point, petrified forest

Chinde Point at Petrified Forest National Park preserves a nearly continuous sequence of Triassic rocks spanning ~100 million years. Image courtesy of the Colorado Plateau Coring Project.

SW: What are the main goals of the CPCP?

RI: The CPCP aims to recover a nearly-continuous record of sedimentary rocks from the Early Mesozoic (252-150 million years ago) of the Colorado Plateau. This record will be recovered using continuous rock cores recovered from at least five different locations around the plateau. Our first stage is to core the entire sequence of Triassic sedimentary rocks at Petrified Forest National Park; these are the Chinle and Moenkopi formations.

SW: What are you hoping to learn? Will the CPCP tell us anything about the biology of extinct animals or climate change?

RI: We hope to answer the following major questions:

  • What is the tempo of climatic and biotic change during the Triassic, such as the rise of dinosaurs?
  • How did changes in greenhouse gases (e.g., CO2) affect ecosystems and the environment during the Triassic Period?
  • What caused a sudden change in plant and animal species at about 215 million years ago – could it have been a meteorite impact that hit Quebec at about the same time?
  • How do Triassic ecosystems and environments in western North America compare with those from the same time in eastern North America, Europe, South America, and Africa?

SW: What is a core – is it a common way to study rocks? Do you find fossils in the cores?

RI: Cores are basically columnar cylinders of rock drilled from a borehole using a diamond-studded bit, which is hollow in the middle.  Cores are a common way to study subsurface rocks in the petroleum and economic geology industry.  They’re also the primary way we study deep sea sediments.  However, the application of scientific drilling (i.e., not for industry) to continents has been a fairly recent phenomenon.  Fossils can be found in the core, particularly invertebrates and microfossils, but the primary goal of the core is not to recover vertebrate fossils.

sediment cores

Triassic sediment cores from Chinde Point. Image courtesy of the Colorado Plateau Coring Project.

SW: What do you do with this column of rock once you have it?

RI: We can do almost everything with the core that one would do with traditional rock samples from surficial outcrops.  The first step is to characterize the stratigraphy and sedimentology – to understand where in section we are and what depositional environments are represented.  The core is precisely oriented relative to both north and vertical, which allows us to look at paleomagnetism to develop a magnetic polarity stratigraphy.  We will take samples for radioisotopic dating, organic and inorganic geochemistry, etc.

SW: Where will most of the research take place?

RI: Once we finish drilling, the cores will go to University of Texas-Austin to be CT scanned.  They will then travel to LacCore at University of Minnesota where the cores will be split in half lengthwise, imaged, and analyzed for natural gamma radiation and other variables.  One half will be permanently archived at LacCore, and the other half will go to Rutgers University where the science party will meet to describe the core and sample it.  Most of the actual research will happen at a host of different institutions, including but not limited to Columbia University, Rutgers University, University of Texas-Dallas, University of Arizona, Berkeley Geochronology Center, University of Utah, and University of Oslo.  In addition to the PIs (Paul Olsen, Dennis Kent, John Geissman, George Gehrels, Roland Mundil, and myself), a number of graduate students and postdocs are involved in the project, and I’m sure undergraduates will be involved as well.

CPCP fieldwork is an all day, every day operation that lasts several weeks. Image courtesy of the Colorado Plateau Coring Project.

CPCP fieldwork is an all day, every day operation that lasts several weeks. Image courtesy of the Colorado Plateau Coring Project.

SW: How does coring differ from traditional paleontology fieldwork?

RI: The timeframe of drilling varies greatly, depending on the characteristics of the rock and how long of a core you want to drill (or how many cores).  This core will be somewhere between 450-500 meters long, and we expect it to take a couple of weeks to drill.  One big difference from traditional fieldwork is that drilling occurs 24 hours a day, 7 days a week.  The equipment is so expensive that it’s best to maximize time on the site.  We work in two twelve hour shifts – in this case one from 8am to 8pm, and another from 8pm to 8am.  The crew consists of two to three drilling staff from the contracted drilling firm, and 3-5 folks on the science team who log and process the core as it comes out of the ground.

SW: Why can’t you get these data from looking at rocks on the surface?

RI: The two main keys to the core are that it gives you unambiguous stratigraphic superposition, and completely unweathered fresh rock. What the first point means is that you know that you have a single column of rock and don’t have to worry about inferences from horizontal stratigraphic correlation. In most cases the advantage of the core over sampling surficial outcrop is data quality and resolution.  For detailed sedimentologic/stratigraphic, paleomagnetic, and geochemical sampling, one would have to dig trenches at least 1-2 meters deep to reach fresh unweathered rock. The time it takes to do this limits the density of sampling to a couple of samples per meter at best, and would take many months to complete over the ~450 meters of section we are coring.  One other main benefit of our core is an innovation of my co-PI Dennis Kent – drilling the core at a 30° angle from vertical.  This means we can very precisely orient the samples for paleomagnetic work, and it gives us more rock per stratigraphic layer, which is useful when you’re taking so many samples from a 2.5 inch diameter core.

The outside of a hill is weathered and potentially chemically altered. Cores sample unaltered rock from the inside of the hill. They can also sample below ground.

Rocks on the surface are weathered and chemically altered from exposure to the environment. Cores sample unaltered, unweathered rock in a single column, and can sample far below ground, which is hard to reach with shovels and picks. Sampling at an angle results in more rock to analyze (the diagonal is longer than the vertical).

SW: Why hasn’t coring been attempted before?

RI: The proximate reason is cost – this core costs just under US $1 million, and that doesn’t include any of the science we’ll be doing.  That being said, scientific continental drilling is quickly becoming more common in deep time rocks (i.e., before the Pleistocene), particularly as specific funding sources for these types of projects are becoming available.  A broader answer is that as scientists refine their scientific questions, we need better age control and data resolution, so we haven’t necessarily needed the resolution provided by coring until recently.

SW: Why did you start with Petrified Forest?

RI: We wanted to start with a core that was both logistically manageable and maximized integration of existing data. Petrified Forest National Park has been a great partner in the project, and has been very supportive the entire way.  They’ve provided housing for the science team, and encouraged visitors to stop by to learn about CPCP.  We’re drilling in the gravel parking lot at Chinde Point, so its easy to get equipment/personnel in and out, and that way we’re also not adversely affecting any park resources.  The Triassic rocks at Petrified Forest NP and surrounding areas have been well-studied for quite a while, so there’s a very large dataset of environmental and paleontologic information that we can immediately integrate with the core to get a holistic picture of the story during the Middle and Late Triassic.

SW:  How many of these cores do you have scheduled and where else are you going to drill?

RI: Currently we are focusing on the first core at Petrified Forest National Park, which will cover nearly all of the Upper Triassic Chinle Formation and all of the Lower-Middle Triassic Moenkopi Formation.  Some late-breaking news is that we’ve just received additional supplemental funding from the International Continental Drilling Program (ICDP) to drill a second shorter core in the Chinle Fm in the southern part of the park. This will allow us to precisely test using geochronology the stratigraphic correlations that have been proposed between the northern and southern part of the park, and therefore also test the biostratigraphic schemes built on these correlations (e.g., Parker & Martz 2011).  This is particularly relevant for understanding the biotic turnover at ~215 Ma that might correlate with the Manicouagan impact event in Quebec. In the longer term, we have plans to core a total of five sites across the Colorado Plateau, which span rocks that range in age from 250 million years old to 145 million years old.  Coring of these future sites will require additional separate funding.

The Manicouagan crater in northern Quebec is an  impact crater so large it can be observed from space. The impact occurred at the end of the Triassic. Image in the public doman, originally from NASA and accessed on Wikipedia.

The Manicouagan crater in northern Quebec is an impact crater so large (70 km diameter) that it can be seen from space. The impact occurred at the end of the Triassic (~212 million years ago). Image in the public domain, originally from NASA and accessed on Wikipedia.

SW: Who is funding the CPCP, and how long did it take to get the money together for such a big endeavor?

RI: The Petrified Forest core is graciously funded by the National Science Foundation and International Continental Drilling Program.  Just the costs associated with the drilling alone are almost US $1 million.  The project was initiated with workshops in 2007 and 2009, and we submitted our first proposals for funding in late 2009.

SW: Are there economic benefits or museum exhibits planned? Will the research benefit people outside the sciences? 

RI: There are definitely plans for a strong component of outreach and communication about the results of the project, through exhibits and public programs at Petrified Forest National Park as well as at each PI’s individual institution.  In fact, the drilling site itself can be visited by anyone who is visiting the park – so we’re an active ‘living exhibit’ at the moment.  The research that will come out of the core has direct societal benefits in that it will elucidate how ecosystems change in a warming world with high CO2, something we all face with anthropogenic climate change over the next century.  The project directly or indirectly supports dozens of jobs in the drilling industry, both through the drilling contractor itself as well as a wide variety of sub-contractors for everything from drilling mud to water supply to rental of generators and work lights.

SW: Thanks so much for all your time, Randy! How can we keep track of CPCP progress between now and publication?  

RI: The best way to follow the CPCP is via our Facebook page and blog.  I should give a shout out to Steven Seppi for designing the beautiful project logo.

Literature cited: Parker WG  and JW Martz. 2011. The Late Triassic (Norian) Adamanian-Revueltian tetrapod faunal transition in the Chinle Formation of Petrified Forest National Park, Arizona. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 101: 231-260.

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Geologic time vs. absolute time

Tomorrow I’ll post an interview with Dr. Randall Irmis, a geologist and paleobiologist working on the Colorado Plateau Coring Project. Today, I offer some background information on the geologic time scale and why it is so hard to figure out how old rocks are.

Earth’s history is divided into different chunks of geologic time, going all the way back to the formation of our planet. Unlike calendars or clocks, which divide time into units of equal length (e.g., days or seconds), the divisions of geologic time aren’t the same length.  For example, the Mesozoic Era was ~186 million years long, whereas the preceding Paleozoic Era lasted ~289 million years. At 2.6 million years, the Pleistocene Epoch was much shorter than the Miocene Epoch (20.4 million years long).  These divisions may seem arbitrary at first, but they’re not; geologic time is based on the succession of rock layers. Geologic time was the first method scientists used to understand the sequence of events in Earth’s history. More recently, we’ve used other methods to associate actual dates with different rock layers, thus linking geologic time (a relative method) with absolute time (= numbers of years old). This merger of geologic time and absolute time is the geologic time scale. (Don’t have a geologic time scale handy? Get one here for free!)

Geologic time is hard to sort out. The first step requires understanding the relative order of the rock layers. For almost 1000 years, we’ve recognized that rock layers are organized in the order in which they were deposited. This idea was first put forth by the Persian polymath Avicenna, and later presented more formally by the geologist and Catholic bishop Nicholas Steno. They proposed that within a vertical column of rock layers, the oldest ones are on the bottom, and the youngest are on top. Today, we call this the principle of superposition. Related to superposition is the principle of original horizontality, which just means that rock layers are more or less horizontal when they are first deposited. Horizontality is important because today’s rocks are not always in their original orientation.

According to the principle of superposition, each rock layer is younger than the one it sits on, and older than the one it lies beneath. In this image, layer I is the oldest layer, and layer A is the youngest.   Image © 2013 Sarah Werning.

Superposition: each rock layer is younger than the one it sits on, and older than the one it lies beneath. In this image, layer I is the oldest layer, and layer A is the youngest.

Of course, the real world is more complicated than the above image. After rock layers form, their position can change through faulting or deformation. For example, the entire column can become tilted, in which case the rock layers get older or younger as you move horizontally along the ground, rather than vertically up a cliff:

syncline! look it up!

Tilted rock layers in the Rainbow Basin Natural Area near Barstow, CA. The rocks were originally deposited as a stack of horizontal layers but were later tilted through geologic processes. As you move from left to right in this picture, the rock layers go from oldest to youngest. Image © 2008 Sarah Werning.

There’s no place on Earth where rock layers going back to the beginning of the planet are visible all in one place, for several reasons. First, some of the layers are underground, so even if they’re present, we can’t always see them. Second, conditions aren’t always ideal for new rock formation, so there are times/places where new rock layers aren’t deposited. Also, rock layers erode at different rates in different places. For example, if there is a river running between two hills, the old rock layers will erode faster there than at the top of the hills. New rock layers are more likely to form in the riverbed and adjacent floodplains than on the hilltops. Different rates of erosion, deposition, and tectonic activity mean that the relative order of rock layers can be difficult to sort out in some places. To illustrate, look at the first image of rock layers above, with layers A through I. Let’s pretend that after layer A was deposited, a river carved out a valley:

CPCP layers erodedDepending on which  mountain you’re on, you might not see layers B or C. Also, there is no trace of layer A in this whole region, although it may be preserved somewhere else. Now, let’s say that after some more time, sediments accumulate in the valley and new rock layers begin to form:CPCP layers eroded new These processes occur over thousands or millions of years, so we can’t observe them in real time. But we can reconstruct the relative sequence of some events. For example, Layer 1 is older than layers 2, 3, and 4, which lie on top of it (thanks, superposition!). Layer 1 is younger than layer E (and F, G, H, and I), because it sits on top of E. Based on how layers 1-4 fill in the valley, we can also conclude that the erosion creating the valley likely happened after layer C was deposited. However,  in order to figure out if layer 1 is younger than layer B, we would need to look at another mountain that preserved both B and 1 in the same vertical column.

Once you have the correct order of your rock layers sorted out, you can begin to associate the rock columns in your area with columns in other regions. If at least one rock layer stretches for miles and miles, it’s easy to confirm you’re dealing with the same layer. In the image below, you can just walk along the grey layer from point 1 to 2 to establish that it’s the same layer in both places. You might then hypothesize that the red layers are the same layer, based on their position relative to the grey layer.

CPCP walk outcrop

More often than not, aligning rock columns is more complicated than this. Parts of your column might be underground, you might be missing rock layers from erosion, and/or the layers might vary regionally in thickness. Also, not all rocks deposited at the same point in time are identical. The appearance of rock layers depends on the local chemical and environmental conditions when they formed. Layers forming under the deep ocean will look very different than those forming in a coral reef, riverbed, desert, or swamp. Even more confusing, if environmental conditions are very similar, rocks deposited at two different points in time might look similar. So what’s a geologist to do?

One line of evidence for simultaneous deposition is when two layers contain the same fossil species. This is much easier to do for oceanic rock layers, because some ocean species (e.g., foraminifera, conodonts) are found around the globe. The types and sequence of these fossils can be helpful in lining up distant rock columns.

layers with seaLet’s say columns 1, 2, and 3 are rock columns separated by thousands of miles. In this picture, fossils are white, blue layers were deposited underwater, and the other colors formed in terrestrial environments. Columns 1 and 3 are mostly terrestrial, but there are three times when the ocean invaded the land – times of high sea level or inland seas. Because the oceanic fossil species are identical, these are probably the same layers seen in column 2; if so, these layers represent the same points in time in all three columns. The sequence of the oceanic fossil species is important, too: triangles, then hearts, then circles in all three columns. It’s more evidence that we are dealing with the same overall sequence of events. If these are the same oceanic layers  in columns 1 and 3, that means that the terrestrial layers between them are roughly correlated in time (I say “roughly” because there might be erosion or deposition gaps in one or both of the columns). Using the sequence of fossil species to correlate rock layers across big distances is called biostratigraphy, and it was extremely important for understanding the basic succession of rock layers on a global scale. Biostratigraphy is still important today for oil exploration, and is also used to align bores when drilling tunnels.

Once scientists had the rock layers aligned and their basic relative sequence sorted out, they noticed large-scale patterns in the succession of the fossils at a global scale. For example,  individual species of ammonites were good for correlating very small chunks of the rock record. At the same relative point in the rock column, all ammonite species disappeared in rock formations all around the world. Globally, blastoids, trilobites, and acanthodians were common in oceanic rocks up until a certain point, after which those types of fossils were never found again. Above that point, totally different types of fossils were found, such as plesiosaurs. Similar patterns were found in oceanic fossils as in terrestrial animal and plant fossils. Because these major shifts in fossil faunas and floras occurred simultaneously all around the world, biostratigraphers recognized that they could be used to bracket and define major regions of the rock column. Smaller shifts (between species rather than faunas) could be used to bracket smaller subregions of the rock column.

This is still how geologic time divisions are defined; saying “Triassic Period” is just shorthand for “the time represented by the chunk of the global geologic column between when we first see the conodont species Hindeodus parvus, up until we start to see the ammonite Psiloceras spelae tirolicum and the foraminiferan Praegubkinella turgescens” (seriously).

Metapolygnathus praecommunisti

Triassic conodonts. Image modified from Mazza et al. (2011), figure 2.

You might be asking yourself, “Well, if the fossils define the geologic time periods, isn’t it circular to use geologic time to tell us how long ago those fossils lived?”

Good question, but no. Remember that geologic time only tells you relatively how old something is; it doesn’t give us an age in terms of number of years ago. Let’s use this analogy: my High School Era is defined as “the time between when I first started attending high school up until I graduated high school”.  In the stratigraphic column of my life, the High School Era came after the Junior High Era, before the Undergraduate Era, and partially overlapped with the I Worked At A Movie Theater Epoch. If I find an essay I wrote for Mrs. Strutzel’s AP English class, I can tell you that it was written sometime during High School Era, and therefore before Undergraduate Era. But that doesn’t tell you how old I was in high school, or how many years ago that happened.

Can you believe those early-2000s fashions? Good Lord!

Sometime during the I Worked At A Movie Theater Epoch.

To find out how old something is in terms of years, you need a different metric, one that can determine absolute time. One common way to do this is radiometric dating. Radioactive isotopes are unstable. They break down (decay) over time, until they become stable isotopes (ones that don’t decay). Each radioactive isotope decays at a specific rate and results in specific stable isotopes – these are just basic properties of the atoms themselves. To estimate when that process started, you first take a substance and figure out its ratio between the radioactive isotopes and the stable (post-decay) isotopes. Then, you can use the rate of isotopic decay (also known as the half-life) to determine how many years of decay it took to result in that ratio – in other words, how many years since the process began, when the substance was 100% radioactive isotope and 0% stable isotope.

Carbon-14 is a radioactive isotope you’ve probably heard of. We use carbon dating to determine the ages of once-living things because it is present in plant and animal tissues. Carbon-14 decays pretty fast; a rate of 50% decay every 5,730 years. That rate of decay means Carbon-14 will completely convert to the stable isotopes Carbon-12 and Carbon-13 within ~60,000 years. This is a long time compared to the High School Era, but really short compared to the age of most rocks. So, we use other isotopes to date rocks; ones that decay at a slower rate. Common methods for dating rocks include uranium-lead dating and potassium-argon dating. These isotopes have much slower rates of decay (i.e., longer half-lives): the radioactive Uranium-235 converts to Lead-207 at a rate of 50% every 704 million years, and Potassium-40 converts to Argon-40 at a rate of 50% every 1.3 billion years.

Using radiometric dating methods, we can link absolute time to geologic time. These methods have already been used to date the rock layers containing the oceanic fossils that define and bracket the divisions of geologic time. So we now know how long each major division of geologic time lasted. Radiometric methods also have been used to date some terrestrial rock layers. Rather than roughly correlating terrestrial layers based on their associations with oceanic rock layers, we can now compare dates of terrestrial layers directly. As more and more rock layers are tagged with absolute dates, the geologic time scale is getting finer and finer resolution. As a result, we have a much better understanding the timing of events in Earth’s history and in Life’s history.

Tomorrow, I’ll talk more about a major new NSF-funded project that is extremely important both for aligning rock columns (calibrating geologic time) and putting absolute dates on individual rock layers (calibrating absolute time) from the Triassic Period.

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Prehistoric Platypus: Revenge of the Monotremes

(I tried to make the title of the post sound like a SyFy movie title, let me know how I did)

 Obdurodon tharalkooschild is not your garden-variety platypus.

Today, the platypus is one of two remaining varieties of living monotreme (the other being echidnas). I could go on and on about the platypus- it does too many cool things to mention them all.  Ok, ok, I will name one. The male platypus both has pointy ankle spurs that contain venom (females have the spur, but no venom).  This venom isn’t fatal to humans, but is, of course, extremely painful. How is this known? Well apparently a guy wanted to test it out by getting stabbed in the hand by a platypus in the early 90s (paper here) and it really, really hurt. Additionally, “significant functional impairment of the hand persisted for three months”. So no need to try that at home people.

Foot spur! Copyright (c) 1995 E.Lonnon Wikimedia Commons

Foot spur! Copyright (c) 1995 E.Lonnon Wikimedia Commons

We don’t know if O. tharalkooschild was venomous, but we know that it was huge! This new species is described on the basis of one singular tooth. The beautiful part about mammalian teeth is that even one tooth can be so different than any other known specimen and it diagnoses an entire species.  When then-Honors student Rebecca Pian (now a PhD student at Columbia University/AMNH) was looking through the vast amount of fossil material from Riversleigh, she adeptly noticed that this monotreme tooth was not like the others. The tooth in question is a lower first molar, and based on its size, O. tharalkooschild was at least two times larger than its modern counter part Ornithorhyncus anatinus! An adult male platypus is ~50cm long, so O. tharalkooschild was at least 1 meter long!

Reconstruction of O. tharalkooschild by Peter Schouten

Reconstruction of O. tharalkooschild by Peter Schouten

Riversleigh, the fossil locality this specimen was discovered at, is a famous World Heritage site in the outback of Queensland, Australia. Some of the most spectacular fossil marsupials and monotremes that define the evolutionary history of Oz’s most iconic animals have been found here. Previously, the only fossil platypus known from Riversleigh was Obdurodon dicksoni and all vaguely platypus-y material was referred to that species.

The variation in morphology of this tooth really shakes things up in the world of monotreme relationships. All of the platypus relatives had very similar looking molars, indicating the evolutionary history of these animals was fairly simple. This big ol’ platypus throws a wrench in things—it is lacking twin lophs (ridges) on a certain part of the tooth, which indicates this is a separate radiation from the previously discovered modern and fossil platypuses.

The molar. Photo by Rebecca Pian.

The molar. Photo by Rebecca Pian.

The age of this specimen is a bit vague, based on current stratigraphic knowledge it could be middle Miocene (~15 Ma) or as young as Pliocene (~5 Ma). Either way, it is still an extremely unique specimen that changes what we know about fossil monotremes. The oldest fossil monotremes include animals like Steropodon and Kollikodon, both Cretaceous (~100 Ma) in age, from the Lightning Ridge locality in New South Wales, Australia. Besides being some of the oldest known monotremes, these specimens are unique because most of the fossils at Lightning Ridge are opalised—meaning the minerals in the bones and teeth have been replaced with shiny opal.

Steropodon opalised jaw. (c) Carl Bento Australian Museum

Steropodon opalised jaw. (c) Carl Bento Australian Museum

Besides the fossils I’ve mentioned, there are a few other fossil monotremes, but the record is relatively sparse. The origin of these animals is still a mystery, although the presence of yet another platypus relative fossil in Argentina (Paleocene in age) gives the indication there was, at one point, a Gondwanan distribution of these enigmatic creatures. Rebecca says “Other than the Patagonian platypus Monotrematum sudamericanum, we have nothing in between the early Cretaceous and the late Oligocene. No fossils have be found from Antarctica either despite evidence that they should be there.” There are a few fossil localities in Australia that seem promising for the discovery of monotreme teeth, so hopefully the record will be filled in in the coming years.

(This research is from an article in the Journal of Vertebrate Paleontology that is not yet available online)

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How Big? How Tall? And…How Did It Happen?

The long-necked sauropod dinosaurs are perhaps the most culturally iconic prehistoric animals, appearing in everything from the Flintstones cartoons to the Sinclair gas station logo. Slide 4_Mamenchisaurus_youngi_steveoc_86 (1)The first live dinosaur glimpsed by the paleontologists in Jurassic Park was a sauropod, and even the first animated dinosaurs—Gertie (in 1914)—was a sauropod. Every parent knows Brontosaurus, and every kid knows that it’s actually called Apatosaurus. Some of the most awe-inspiring skeletons at a natural history museum are the sauropods. Much of this influence comes down to one thing: immense size. Sauropods were the biggest animals ever to walk the land, and even Hollywood is hard-pressed to come up with something more imaginative than that which evolution wrought.

Argentinosaurus_skeleton Sellers_1

Argentinosaurus Skeleton Sellers

Extremes in biology beg the question of how. How did sauropods achieve their massive size? Was it something in their metabolism? Something in their food supply? Something in their reproductive cycle? How did sauropods carry themselves? Did they have erect necks like an ostrich, or something more horizontal? Or was every sauropod a little different? These questions may seem best answered by the impossibility of a living sauropod. Indeed, there is only so much one can tease from a skeleton. However, there is also great power in this limitation.

Sauropods not only pushed biological limits—they also push the limits of our own biological knowledge. A new PLOS ONE collection on sauropod dinosaurs, Sauropod Gigantism: A Cross Disciplinary Approach, explores these boundaries. Based in part on the results of a grant and workshops funded by the German Research Foundation, the papers in this collection cover virtually every aspect of sauropod biology—anatomy, physiology, reproduction, function, and more. Perhaps the most powerful aspect of the collection is that its results are not myopic, but have implications for multiple endeavors within biology. Want to understand how sauropods held their necks? We have to understand something about neck anatomy and function in modern animals. Want to understand how sauropods got so big? We have to understand something about growth in dinosaurs. Want to understand how sauropods evolved their reproductive strategies? It is essential to explore the topic in modern animals! Sauropods undoubtedly serve as the backdrop to better understand our modern world, and can help us learn which questions about modern animals haven’t even been asked yet.


Collection Image: Kent A. Stevens, University of Oregon

The papers in the collection cover a variety of topics, and sum up nearly a decade of concentrated work by a variety of researchers. Although some of the contributions will not be without contention within the research community (arguably a good mark of relevance!), all of the papers measurably advance our knowledge. The most powerful aspect of this is in exploring the biological limits that guide both modern and extinct animals. These limits are a moving target, the product of a virtually infinite number of variables. By identifying the most critical variables, it is possible to both explain modern biological systems as well as infer the behavior of prehistoric ones. Although we may never know the exact details of sauropod biology, the research presented here goes a long way towards marking those boundaries of biological probability. Not too bad for animals that have been dead for over 65 million years.

Check out a new slideshow version of this post on


(Disclosure: Andy Farke served as a PLOS ONE academic editor on multiple Sauropod Gigantism Collection papers)

GO TO THE COLLECTION NOW on the PLOS Collections page  Sauropod Gigantism: A Cross-Disciplinary Approach 

The PLOS ONE Sauropod Gigantism Collection will be launched at the meeting of the Society of Vertebrate Paleontology (#2013SVP) in Los Angeles October 30-November 2, 2013, of which PLOS is a Gold Sponsor. Come to the PLOS ONE booth #4 to meet the editors and receive a free USB drive of the entire collection!

Read other PLOS Network blogger posts on the PLOS ONE Sauropod Gigantism Collection elsewhere:

On “The Crux”  How Brachiosaurus  (and Brethren) Became So Gigantic

On HuffingtonPost/Science    A tail’s tale: Holey bones found in sauropod tails


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Opening the Fossil Record for Open Access Week

OAlogoOpen Access Week was somewhere between hectic and insanely hectic for me. I was part of a research team (including fellow PLoS blogger Sarah Werning) that published an open access paper describing the smallest, most complete, and youngest skeleton yet known for the tube-crested dinosaur Parasaurolophus. Beyond the gee-whiz factor and the fact that one of my high school students found the fossil after I walked past it, the fossil provides some important information on how dinosaurs grew up. The paper was accompanied by a massive release of open data (including 3D scans of nearly the entire specimen via Figshare and high resolution images of the bone microstructure via Morphobank), as well as a dedicated website for the general public. I have blogged elsewhere about the experience before and after publication, so won’t say much more on that here. Instead, this post will focus on a few reflections / comments about the whole process.

Reconstructed skeleton of a baby <i>Parasaurolophus</i>, by Scott Hartman. From Farke et al. 2013, CC-BY.

Reconstructed skeleton of a baby Parasaurolophus, by Scott Hartman. From Farke et al. 2013, CC-BY.

What do we hope to accomplish in the long run?

  • Most importantly, we want to publicize the utility and importance of open data within paleontology. By opening up virtually everything associated with the project and having a high profile press release associated with it, we hope other paleontologists who have not already done so will be more likely to open up their own research.
  • Regarding CT scan data, we posted the segmentation files used to generate the 3D models. Because segmentation (the process in which structures are highlighted prior to modeling) has a subjective element, particularly for fossils, we want to get folks thinking about opening up this aspect of the research process so that it can be more easily verified and corrected if necessary. 3D models based on CT data are an important research tool for many labs, and it would be great to make them as open as possible!

What would I do differently next time?

  • If I had more time, I might have used more 3D renderings in concert with the interpretive drawings (instead of just straight line drawings to accompany the photographs).
  • Given more time, I would have had more high resolution scans of the specimen and its bones. Ideally, this would include all of the little unidentified fragments. Then again, the return on time investment would probably be minimal.

Pleasant surprises

  • Tech bloggers had some nice things to say about the open data.
  • One artist, independent of our prompting, made some really gorgeous renderings of the discovery. It was fun to another conception of how the dinosaur looked!
  • The response to the website for the public was overwhelming–over 100,000 visitors within the first day after it went live. If we have another discovery of this caliber again, I will definitely consider making a similar website. It is a great outreach tool!
  • The media response was overwhelming, too. It was an unexpected chance to get to spread the message of open access and open data, as well as highlight the awesome specimens at my museum and the talented high school students involved in our program.

And now it’s only another year until Open Access Week 2014…

Farke AA, Chok DJ, Herrero A, Scolieri B, Werning S. (2013) Ontogeny in the tube-crested dinosaur Parasaurolophus (Hadrosauridae) and heterochrony in hadrosaurids. PeerJ 1:e182

Category: Dinosaurs, Navel Gazing, Open Access, Open Data, Paleontology | Tagged , | 1 Comment

Paleontological Art and the Creative Commons

During the past few years, I’ve been making more and more of an effort to incorporate artwork licensed via Creative Commons (CC) into my blog posts and presentations. Two reasons underlie this–for one, PLOS requests that its bloggers license their blogs under a Creative Commons license, and thus I have to be careful about the artwork I use (i.e., even if I get permission from an artist, they have to be okay with a CC license–more on this below). The second reason is that I want to make more of my presentation slides (and videos of my presentations) available via CC license. Although fair use allows many uses of copyrighted material for classroom lectures, etc., it doesn’t necessarily allow me to distribute those more widely (particularly with a CC license on them). Thus, using only CC-licensed work (and public domain work, when available) allows me more freedom in what I do with it.

Sinocalliopteryx eating a hapless dromaeosaur. From Xing et al. 2012. CC-BY.

Sinocalliopteryx eating a hapless dromaeosaur. Illustration by Cheung Chungtat, from Xing et al. 2012. CC-BY.

Finding Sweet, Sweet CC Artwork
It’s actually fairly easy to find artwork licensed under various Creative Commons licenses. Wikimedia Commons is my usual go-to, and a Google Images Search (with licenses specified) works adequately. PLOS ONE articles also function as sources, particularly if I have a particular topic in mind (the image above originally appeared in the journal). My other new favorite is Phylopic, for its broad coverage. That site focuses just on silhouettes–very handy for abstractly showing a whole bunch of taxa in a uniform style. It’s not just a bunch of Velociraptors drawn and redrawn, but lots of obscure insects, modern mammals, and the like (full disclosure: I submitted a silhouette of myself for the site).

This search strategy usually works pretty well, but I consistently run into three issues:

  1. Images are often of variable quality. On the Tyrannosaurus page at Wikimedia, for instance, they range the gamut from cartoony to inaccurate to woefully inaccurate to actually pretty good.
  2. Licensing. There are many flavors of Creative Commons license, ranging the gamut from permissive (attribution only) to quite restrictive (no commercial use, no modification, all derivative work must use same license). I usually err on the permissive side (CC-BY / CC-By), because I want others to be able to reuse my own work as easily as possible. Plus, the commercial clause freaks me out a little bit – if the artwork goes on an exhibit in a museum that charges admission, does that count as commercial use? Probably not, but I’m not inclined to test the waters.
  3. Permissions. In many cases, photos licensed under CC licenses are images of specimens in museums with restrictive photography policies. Thus, I suspect that they may not validly licensed as CC, particularly for casual snapshots from museum exhibits. I don’t necessarily agree with this (if museums argue that fossils shouldn’t be commercial commodities, why commercialize all of their images, even by casual photographers? This is what some call a mixed message.), but as a person who works at a museum I want to abide by the rules when possible.

Fortunately, the situation is steadily improving. The selection of artwork and specimen images available via Creative Commons expands daily, and I’ve found that the average quality is also getting better. I’m not a huge fan of some of the art styles, but at least it is something to use! In light of all of this, here are some of my own closing thoughts:

  1. Whenever possible, we should make our work available via Creative Commons licenses or a public domain dedication. A recent project required a human silhouette–so once I made it, I uploaded it to Phylopic under a CC-BY license. If going to that effort, it isn’t much harder to share the wealth.
  2. That said, if you commission an artist to produce original art for a publication that will be released via CC-BY (or another CC license), make sure the artist is aware of this. In talking with one artist, they said they aren’t always kept in the loop on the plans for a piece of work, and were surprised to see it released as CC-BY. Such a CC license could potentially affect their income down the road (especially for commercial artists). For a forthcoming paper, we alerted the artist as to our plans, and compensated the artist appropriately for releasing the work as CC-BY. It’s good to be good to artists (and they appreciate the concern, too).
  3. For those of you just starting out on designing lectures and the like, use Creative Commons and public domain images from the start. I have found it a real pain to retrofit some of my class lectures!

And that’s all I have to say about that (for now).

A ctenophoran, by Scott Hartman. Public domain.

A ctenophoran, by Scott Hartman. Public domain, from Phylopic.

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Paleoecology of Magnificent Megafauna: The Moa

There was a time not so long ago (thousands of years ago, not millions, which is not so long ago to a paleontologist) when ecosystems around the world had something that is generally lacking today: really big herbivores. I’m talking beasts such as giant armadillos, giant sloths, mastodons, and mammoths. Obviously there aren’t any mastodons lumbering around your neighborhood today, so what happened to them? In general, there are two main hypotheses: either humans ended their reign or climate change eliminated their preferred habitats. These hypotheses are hotly debated in the literature, but as it is difficult to prove any absolute cause in certain cases, the debate still rages on.

No matter what caused their extinction, extinct herbivore megafauna can still be extremely useful in studying climate change. What evidence is there about the structure of habitats where megafauna lived? Just this week a paper in PNAS seeks to answer this questions in great detail. And how did they do it? Ancient bird poop, of course.

The New Zealand moa was a giant herbivorous bird that has been extinct since 1400 AD. The two largest species of moa would have been around 12 feet tall and weighed up to 500lbs! Their extinction, like other megafauna, has been debated to be caused by overhunting and/or habitat loss. Due to the fact the moa only lived with one other animal that was big enough to eat it- Haast’s eagle- it is likely humans caused their extinction. The moa is a relatively well studied animal for being extinct: we have even been able to sequence their genome and see what kinds of parasites lived in their guts. The nine extinct species of moa were endemic to New Zealand and they likely shaped the plant communities they lived in, but it is difficult to know for sure when we were unable to critically assess their impact. The study of ancient poop (coprolites, which I also talked about here) can remedy these issues.

Artists rendition of a Haast's eagle attacking a moa. By John Megahan. Distributed under CC-BY license, PLOS Biology

Artist’s rendition of a Haast’s eagle attacking a moa. By John Megahan. Distributed under CC-BY license, PLOS Biology

In this study, the authors analyzed 51 coprolites rigorously: they were carbon dated, and individually assessed for ancient DNA (aDNA), plant macrofossils, and fossil pollen. Ancient DNA is critical in this type of study because not only does the DNA tell us that these coprolites are from four different moa species, but they can also provide DNA identification of the plant remains contained in the coprolite. Additional pollen and macrofossil study provide a detailed list of what plants were present at this site 400 years before the extinction of the moa. This combination of methods is extremely rigorous, and an incredible way of measuring paleoecology quantitatively. The results indicate that there were four species of moa living at the same time in the same area but occupying different dietary niches.

Figure 3 from Wood et al. 2013. Plant data from coprolite aDNA, fossils, and pollen. The different species had distinct diets.

Figure 3 from Wood et al. 2013. Plant data from coprolite aDNA, fossils, and pollen. The different species had distinct diets.

It stands to reason that ecosystems can be vastly changed when key organisms are removed. Large birds like moa likely had an impact on habitats through altering vegetation composition and seed dispersal. The species of moa from this study had dietary preferences from forest plants to grasses, and everything in between. In response to the idea that other herbivores could be introduced into ecosystems to mimic the effect a moa might have had on the vegetation community, the authors note modern ostriches and emus do not occupy the same dietary niche spaces as the extinct moa, and would be a poor replacement herbivore in a New Zealand ecosystem.

I think this study is so great because it really drives home the power of a multiproxy approach for understanding paleoecology. Combining traditional methods of fossil analysis with “newer” methods of aDNA and carbon creates a very clear picture of an ancient environment that otherwise would be impossible to obtain.


Resolving lost herbivore community structure using coprolites of four sympatric moa species (Aves: Dinornithiformes). Jamie R. Wood, Janet M. Wilmshurst, Sarah J. Richardson, Nicolas J. Rawlence, Steven J. Wagstaff, Trevor H. Worthy, and Alan Cooper. PNAS 2013 ; published ahead of print September 30, 2013, doi:10.1073/pnas.1307700110

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Not Just Jaws…Claws Mark Bone Too!

After a long journey through the millennia, fossils inevitably arrive in the present as damaged goods. Bacteria, scavengers, erosion, wind, rain, and even sunlight conspire to destroy the remains of previously living organisms. Although this loss of information is a bad thing for understanding many aspects of a long-gone organism, some post mortem adventures actually add data to the fossil record. A whole subfield of paleontology–taphonomy–focuses on this very topic.

Some of my favorite taphonomic artifacts are feeding traces–particularly the bite marks left behind by carnivorous animals. These traces tell us who fed on whom, and how they did so. Spend some time with fossil bones, and you are quite likely to run across these bite marks. For instance, a recent study in PLOS ONE documented croc bite marks on juvenile dinosaur bones, with one croc even leaving a tooth embedded in the bone. These kinds of fossils help paleontologists reconstruct the long-vanished food webs of prehistoric ecosystems.

Probable bite marks from a 75 million year old croc, left on the shoulder blade of a plant-eating dinosaur. Modified from Figure 2 in Boyd et al. 2013. CC-BY.

Probable bite marks from a 75 million year old croc, left on the shoulder blade of a plant-eating dinosaur. The blue lines point to the bite marks. Modified from Figure 2 in Boyd et al. 2013. CC-BY.

Because bite marks are so common, it’s easy to get in a rut and assume that all traces on bone result from bite marks. One great counterexample is trample marks–if a bone is pressed into the ground, sand and gravel can score the bone surface, mimicking bite marks or even human tool marks. Several colleagues and I also hypothesized that Triceratops may have injured each other with their horns, and Joe Peterson and colleagues inferred head-butting damage in the skulls of pachycephalosaur dinosaurs. A new study in PLOS ONE comes up with an even more interesting possibility–claw marks.

Claws–whether they are in birds, tyrannosaurs, or tigers–are covered by a keratinous sheath, pretty much equivalent to our fingernails. We all know that this keratin is fairly soft, particularly relative to bone. (If you’re a meat-eater, try to scratch the bony surface of that t-bone or pork chop next time you throw one on the grill) So, you really wouldn’t expect to see claw marks in the fossil record. To investigate this assumption, Bruce Rothschild and colleagues set up a nifty experiment.

Tyger! Tyger! burning bright Photo by Nick Jewell, CC-BY.

Tyger! Tyger! burning bright (apologies to William Blake)
Photo by Nick Jewell, CC-BY.

Rather than try to simulate claw damage in the laboratory, Rothschild and colleagues went straight to the source–a real, live tiger. Conveniently, zoos strive to give their animals a variety of boredom-alleviating enrichment activities. These can be a simple puzzle with a piece of food inside, or a ball to bat around, or in this case, a scientific experiment. The researchers devised a simple but effective contraption–a beef bone bolted into a piece of wood, inset so that sharp tiger teeth couldn’t get to it. If anything was going to mark the bone, it had to be the claws. Add the contraption to the tiger enclosure at a local zoo, and see what happens.

Contrary to expectations, the bone was quite prominently marked by tiger claws. These marks showed up at all levels of magnification (see image below).

Tiger claw marks on a beef bone, modified from Rothschild et al. 2013. Scale bar equals 5 cm in lower figure, and 1 cm in upper figure. CC-BY.

Tiger claw marks on a beef bone, modified from Figures 2 and 3 in Rothschild et al. 2013. Scale bar equals 5 cm in lower figure, and 1 cm in upper figure. CC-BY.

So, this means that paleontologists should probably be on the look-out for claw marks in the fossil record. As noted by Rothschild and colleagues, potential claw damage was previously spotted in monkey carcasses that had been feasted upon by eagles. The next step, of course, will be to see if the signatures of teeth and claws can be adequately distinguished by their traces. It would also be great to repeat the experiment with other kinds of bones and other animals.

All in all, this paper presents some pretty cool results. My only “major” quibble concerns part of the abstract, which seemingly refers to the marks as “pathology” (this came up in a recent discussion about the paper with some friends on Facebook). Pathology generally refers to disease processes in living organisms, and “taphonomy” is far more appropriate terminology here. I think the authors may be angling towards distinguishing claw- and tooth-induced injuries that occurred within the lifetime of the animal, but that topic isn’t covered by the paper. That too, presents an interesting question, and is definitely one for future research.

You can read the new paper here. For another look at the research, check out Brian Switek’s blog post.

Boyd CA, Drumheller SK, Gates TA (2013) Crocodyliform Feeding Traces on Juvenile Ornithischian Dinosaurs from the Upper Cretaceous (Campanian) Kaiparowits Formation, Utah. PLoS ONE 8(2): e57605. doi:10.1371/journal.pone.0057605

Rothschild BM, Bryant B, Hubbard C, Tuxhorn K, Kilgore GP, et al. (2013) The Power of the Claw. PLoS ONE 8(9): e73811. doi:10.1371/journal.pone.0073811

Category: Dinosaurs, Paleontology, PLOS ONE, Zoology | 2 Comments

Dinosaurs Come Through In The Clutch

In the last few months, a lot has been going around about a pretty interesting topic—dino sex. Besides the mechanics of dinosaur sex and reproduction (some people love talking about that)- there are some more interesting questions to consider. For example, how many eggs did most dinosaurs lay? Some have suggested that enormous dinosaurs, such as sauropods, had many offspring per year, and this contributed to their gigantism. Previously, the only things we were able to discern about dinosaur reproduction were what was uncommonly preserved in the fossil record—such as complete fossil egg clutches, very rarely with a brooding parent on top. These finds are amazing and interesting, but because they are so rare, it is difficult to use these fossils to make broad generalizations about reproduction in different groups of dinosaurs.

Although rare, this brooding Citipati osmolskae is probably my favorite fossil ever. Uploaded by Dinoguy2, distributed under Creative Commons ShareALike 1.0 license.

In a paper out yesterday in PLOS ONE, authors Jan Werner and Eva Maria Griebeler looked at extant birds and reptiles in order to better understand how many eggs some dinosaurs may have laid during the year. They constructed a really cool allometric regression model based on modern species and found a close correlation between body mass, egg mass, clutch mass, and annual clutch mass.

Figure 2 from Werner and Griebeler 2013 showing the allometries of reptile, bird, and turtle body mass and egg mass.

Figure 2 from Werner and Griebeler 2013 showing the allometries of reptile, bird, and turtle body mass and egg mass.

When there is a clear idea of how extant animal size relationships function, the same equation can be applied to dinosaurs using extant phylogenetic bracketing. In other words, non-avian dinosaurs will be plugged into the same allometric equation as their closest ancestor. Theropods were plugged in to the “bird model” because they are most closely related to modern birds. Hadrosaurs and sauropodomorphs were plugged into the “reptile model” because the authors decided these dinosaurs were less related to birds than to reptiles since they were outside Therapoda. The results indicate that theropods probably only had one clutch per year, but hadrosaurs and sauropodomorphs may have had several. Surprisingly, using these calculations, most of the dinosaurs studied had less than 200 eggs per year. Enormous 75,000kg sauropods had around 400 eggs per year, which is less than extant sea turtles that can lay over 500 eggs per year!

But why did these different types of dinosaurs have different egg-laying strategies? Well, that is fairly open to interpretation. It is possible that the environments these animals lived in were so different that theropods were able to get by on one clutch per year, while other dinosaurs may have lived in environments where their clutches did not experience good survival rates. It is definitely clear though that there was a shift at some point during the evolution of non-avian dinosaurs to birds relating to egg and clutch size. Theropods had larger eggs than sauropodomorphs relative to body size, but had fewer eggs in their clutch. Modern birds have the largest eggs compared to body size of all, but by far the smallest clutch size, only laying 2.2-4.5 eggs per clutch. It will be interesting to explore and hypothesize about the drivers of this trend.

I always enjoy elegant studies like this one that utilize mostly published data to make new inferences about extinct animals. There are already so many data out there that paleontologists can utilize without relying on new fossil finds, so get (data)mining!


Werner J, Griebeler EM (2013) New Insights into Non-Avian Dinosaur Reproduction and Their Evolutionary and Ecological Implications: Linking Fossil Evidence to Allometries of Extant Close Relatives. PLoS ONE 8(8): e72862. doi:10.1371/journal.pone.0072862

Category: Dinosaurs, Paleontology, PLOS ONE | Tagged , , , , | 2 Comments