Updates

Hello friends. Instead of a new paper this week, I’m going to give you a couple of updates.

First, back in November, I started a series of posts about women in paleontology. Since then, once a month, I’ve posted a biography about a woman paleontologist. However, since my book on the same topic got funded in March, I will reserve those stories for the book. Once the book is published, I will probably continue with the series. Until then, please check out [TrowelBlazers] for biographies about women in anthropology, geology, and paleontology (also on Twitter, Facebook, and Tumblr). And for updates on the book, look for the new tab at the top of the page (She Found Fossils), coming later this week.

Second, summer has arrived! In addition to the book project, field work is happening, and paleontology news slows down a bit. Because of that, I’m going to be posting every other week instead of every week. Unless something big gets published, in which case there will be a timely post.

Thank you for your continued support!
– DrNeurosaurus

Mining for Ankylosaurs

In another ankylosaur-related announcement this week, National Geographic has published an [article] discussing a new amazing fossil.

In 2011, miners in Alberta, Canada were excavating some rocks from 110 million years ago (Early Cretaceous) when several ankylosaur bones tumbled out of the hillside.

A photo of the new nodosaur specimen. Photo by R. Clark.

The mining company reached out to the Royal Tyrrell Museum for help, and the specimen was collected. After six years of work, enough of the fossil has been exposed to be able to publish a paper on it. The paper is almost ready for publication, so more discussion will come soon.

What we do know is that this fossil is of a nodosaur, a type of armored dinosaurs without club tails. The nodosaurs are part of the ankylosaur group, but form their own clade within it.

 

A cladogram of Ankylosauria showing Nodosauridae (the nodosaurs) and the rest of the ankylosaurs. From T. Holtz.

This particular nodosaur is almost perfectly preserved in three dimensions. It was likely washed out to sea and quickly buried upside down, keeping most of its skeleton, and all of its armor, intact. It almost looks like a statue since it’s so complete! We will have to keep a look out for more information once it’s published.

Kneel Before Zuul

This week, a new [akylosaur] was described! Ankylosaurs are great. They were like living tanks that roamed the Mesozoic, calmly eating plants that were low on the ground, and smashing threats with their fearfully great tail clubs (note: not all ankylosaurs had tail clubs, but the ones that did surely smashed things with them [I can only assume]).

A reconstruction of Zuul crurivestator by D. Dufault.

This new ankylosaur is the most complete akylosaurid ever found in North America. The paper described its skull and tail club, but a larger paper will come out later describing the rest of the fossil, once it gets prepared out of the rock.

The skull of Zuul. Photo from the Royal Ontario Museum.

The authors named it Zuul crurivestator, which means ‘Zuul’ (after the 1984 Ghostbusters creature) and ‘Destroyer of Shins’ because its tail club was at shin height. Its skull has a bunch of horns that aren’t present on other ankylosaurids, reminding the authors of Zuul.

A drawing of Zuul‘s head on the left and an image of Zuul from Ghostbusters on the right.

The tail club is the longest one from any ankylosaurid from North America and it preserves osteoderms (bone inside the skin layer) along the tail.

A photo of the tail showing the preserved skin, osteoderms, and the tail club. From B. Boyle (Royal Ontario Museum).

It’s from around 76 million years ago – a time for which we did not have ankylosaurs in the fossil record, even though they were present. And, to top it all off, the specimen has soft tissue preserved with it! There is a layer of black, shiny tissue on top of some of the osteoderms in the tail, which could be preservation of the keratin sheath that would have covered the osteoderms in life.

So, to wrap up, Zuul crurivestator is a brand new ankylosaurid. It’s one of the most complete ankylosaur fossils from North America, with a beautiful skull and tail club. And it has soft tissue preservation.

The Jurassic King of Scotland

Last week, a [paper] was published that described a new fossil of a previously known mammaliaform from Scotland. This animal is called Wareolestes rex, meaning Ware’s brigand King and it’s from the middle Jurassic Period (specifically the Bathonian, 168 to 166 million years ago). Mammaliaforms were starting to diversify in the middle Jurassic, and were relatively small, so finding any fossils of them is important to our understanding of how they lived.

A reconstruction of Wareolestes by E. Panciroli.

The new specimen of Wareolestes is a lower jaw with teeth. This fossil was CT scanned and the details of the teeth were recreated with computer software. The authors found that the jaw had two molars preserved in place, and several teeth that were hiding in the bone, waiting to erupt.

Figure 4 from the paper showing the CT scan of the jaw. The large molars are already erupted, but several premolars and another molar are still in the jaw. The purple is the mandibular nerve. The scale is 1mm.

The original fossil of Wareolestes is an isolated molar, but similarities with the molars preserved in this new specimen show that the two specimens come from the same species. The shape of the teeth indicate that Wareolestes is a morgonucodontan (an early mammal relative).

The un-erupted teeth show that Wareolestes replaced their teeth once in life. Most mammals have a set of baby teeth (also called ‘Milk’ teeth) and a set of adult teeth. This happens for two main reasons: 1) our mouths grow over time, but teeth cannot grow once they are formed, so we grow adult teeth to fit adult-sized mouths. And 2) our teeth fit precisely together so that we can chew our food really well (this is called precise occlusion), by only replacing our teeth once, we ensure that our teeth will fit together appropriately.

A photo showing how the different cusps of the premolars (labeled P4, for premolar 4) and the molars (labeled M1 and M2 for molar 1 and 2) fit together. From P.D. Polly.

By comparison, other animals (like crocodiles, for example), do not have a final adult size – they grow continuously as they age. They also replace their teeth as many times as they need to ensure they always have teeth for grabbing prey, but they don’t chew like mammals do, so their teeth don’t have to fit together.

This new specimen shows that morganucodontans had a similar tooth replacement pattern as modern mammals, and are the most basal mammaliaforms that have it.

If Not Us, Then Whom?

Last week, a [paper] came out that presented us with a new mystery. This paper discussed a fossil mastodon bone from San Diego, but the bone itself was not as interesting as what they found on it.

Let’s start with a bit of background. The mastodon is an extinct elephant, distantly related to modern elephants. They lived from the Miocene to the Pleistocene (23 million years ago to 11,000 years ago) in North America and Eurasia. The shape of their teeth tells us that they were browsers and ate a varied plant diet.

The American Mastodon (left) compared with the wholly mammoth and the African elephant. From Encyclopedia Britannica.

Mastodons were apparently very tasty and a food source for humans. This brings us to this week’s paper. In San Diego, there’s an archeological site in which these authors found a mastodon bone that had been broken apart with stone tools. The bone and molar that had been broken had spiral fractures indicating that they were broken while fresh and not from fossilization. Two large cobbles made of andesite (a volcanic rock) were found next to the bones and are interpreted as hammers and anvils.

Supplemental figure 3 from the paper. The figure on the left is showing an exposed mastodon rib on the left and a hammerstone on the right. The figure on the right is showing a different hammerstone.

Modern experiments using stone tools on cow and elephant bones create the same fracture patterns as those found in this mastodon specimen. It’s pretty clear that someone was using a stone tool to break apart the bone, probably to reach the nutritious bone marrow inside. The authors also analyzed the age of the specimen and found that it was buried approximately 130,000 years ago.

World map (from the North looking down) showing the migration routes and ages of Homo sapiens. From Wikipedia.

Here’s where it gets mysterious. Homo sapiens (our species) was hanging out in Africa and only just starting to migrate into Eurasia at that time. We didn’t make it to the Americas until around 15,000 years ago. The specimen in San Diego is 115,000 years older than that. So, I ask you, if not us, then whom?? Other species of Homo didn’t migrate into the Americas and other animals around this time and place didn’t use tools, so this question is very open ended. Maybe there was an unidentified species of Homo living in the Americas that we previously didn’t know about.

I’ll finish this post by noting that many experts in the field are debating this find and the conclusions the authors discuss, so we’ll have to stay tuned and see what the resolution is.

The Earliest Avemetatarsalians

The Triassic (251-199 million years ago) was an interesting time in the history of the Earth. Just after the largest mass extinction in Earth’s history (the Permian Mass Extinction at 252 million years ago), the Triassic was a time when new animals were starting to take over. The weird looking synapsids (distant relatives to mammals) were gone and early archosaurs were emerging.

Fauna of the Late Permian. From Pinterest.

Fauna from the Triassic. By deviantART user Apsaravis.

These archosaurs eventually divided into the Pseudosuchian (archosaurs closer to crocodylians: rauisuchians, thalattosuchians, aetosaurs, modern crocodylians, and more) and Avemetatarsalians (archosaurs closer to birds: pterosaurs, ornithischians, sauropods, theropods, and more). Understanding what these early Avemetetarsalians looked like has been difficult because complete, well-preserved specimens from the Triassic are hard to find. Other animals on these lineages that we do find are already very advanced: for example, early pterosaurs already look like pterosaurs.

An early pterosaur, Dimorphodon. From Wikipedia.

A new [paper] published this week described an early avemetatarsalian that they named Teleocrater rhadinus (Teleo – closed and crater– basin after the closed hip socket, and rhadinos – slender, for the animal’s slender body). It was found in Tanzania and it is from the lower portion of the Middle Triassic rock layers (247-237 million years ago), making it one of the oldest members of this group. The specimen has most of the limbs, some vertebrae, and a bit of the skull.

Figure 2 from the paper showing the Teleocaster specimens. Red bones are present in 1 individual. Blue bones are present in the second individual. Purple bones are present in both.

The bones of Teleocrater tell an interesting story. The way the ankle bones are shaped and the way they fit together is very much the same in this early avemetatarsalian and in early pseudosuchians. This means that the ankle seen in pterosaurs, dinosaurs, and one other group was evolved multiple times instead of just once for the whole group. Other features indicate that these early avemetatarsalians were long-necked, carnivorous, and not built for efficient running.

The authors also ran a phylogenetic analysis (an analysis of evolutionary relationships) and found that Teleocrater belongs to a small group of early avemetatarsalians, now called Aphanosauria, and is one of the earliest members of this group. This study provides much needed information about these early animals, and shows that the diversity of this group was much higher in the Triassic than previously thought.

Parasites and Primates

This week, a [study] was published that described a new amber fossil from the Dominican Republic, dated to 45-15 million years ago. The amber contained a tick. Ticks are small arachnids (like spiders, scorpions, mites, and other 8-legged invertebrates) and are responsible for latching on to mammals, sucking their blood, and potentially (and quite frequently) spreading diseases. In the US, ticks are known for spreading Lyme Disease, Rocky Mountain Spotted Fever, and about a dozen other infections according to the Centers for Disease Control (CDC).

Different types of ticks in the US. From Pennsylvania County Dog Club.

This fossil tick was no different: it was filled with blood from its last meal. The authors used high powered microscopes to examine the tick and found that it had 2 puncture marks in its back, through which some of the blood spilled.

Figure 1 from the paper showing the fossil tick. The arrows indicate the puncture locations.

Because of the openings, the amber preserved the blood perfectly and showed something hidden amongst the blood cells – microscopic parasites! The amber stained the blood cells and the parasites different colors, making them easily distinguishable under the microscope.

Figure 3 from the paper showing the blood cells as clear circles and parasitic cells as dark circles (with arrows). Scale bar is 20 micrometers.

They named this new species Paleohaimatus calabresi (“ancient blood” and “Calabrese” after the person who provided the fossil). Comparing it to modern tick-borne parasites, the authors identified the fossil parasite to be closest in size and shape to the modern Babesia genus, a known group of tick-borne parasites. These parasites feed off the juicy insides of blood cells, and have different shapes based on which part of their life cycle they’re in. They also infect the guts of the tick.

The authors also examined the healthy blood cells. Red blood cells are almost donut shaped and have no nucleus. They contain hemoglobin, which is a protein that transports oxygen to cells around the body. In mammals, the red blood cells are different sizes in different species, so by measuring the cells, the authors were able to confirm that the tick fed from a mammal, and what kind of mammal it was. Of the three types of mammals with red blood cell diameters of 6.9-7.3 micrometer (primates, canines, and lagomorphs), only primates were in the Dominican Republic at the time this tick was fossilized.

Cebus apella grooming each other.

Primates groom each other and some live in trees, so it is likely that this tick was feeding on a primate, was found while being groomed by another primate, was picked off, and tossed away, landing on a tree and getting trapped in the sap. A sad day for the tick, but a happy event for paleontologists to find.

Look at those suckers!

Cephalopods (octopus, squid, nautilis, and cuttlefish) are amazing for several reasons. The Nautilis is the closest living representation of what an ammonite would have looked like.

The Nautilis in all it’s cephalopod glory. From Wikipedia.

Octopi (or octopuses or octopodes) are really smart, and can change their skin color and *texture*.

One species of squid can grow to be 10-13 meters long (33-43 feet)! And cuttlefish are super cute.

Cuttlefish on the left, Bobtail Squid (closely related to cuttlefish) on the right.

Cephalopods are mollusks; mollusks also include snails, slugs, and bivalves. Cephalopods are mostly soft tissue, with the exception of the cuttlebone in cuttlefish, which is a remnant of a shell. As we know, soft tissue is harder to fossilize, so we don’t find many cephalopods in the fossil record if they don’t have big shells.

Figure 1A from the paper showing a photo of the specimen with the new arm numbering.

A [study] was published in December that re-described an octopus fossil from the Jurassic Period (201-145 million years ago) of France. Specifically, the fossil dates to 165 million years ago and is named Proteroctopus ribeti. The authors used synchrotron computed tomography (CT) to image the fossil. For those who are interested, synchrotron CT uses higher energy radiation and a different beam geometry to get higher contrast images than regular CT scanning.

Using these images, the authors found 2 well preserved eyes, were able to renumber the eight arms, and saw other details that were previously unknown. These included the absence of an ink sac, and the layout of the arm suckers. They found that the suckers are present in double-rows that are obliquely placed (so the suckers run down the arm in 2 rows, but they aren’t laid in pairs, rather they sit in a zig-zag down the arm).

Figure 1c from the paper showing a CT image of the suckers on the arm.

Using these details of the body, the authors added this species to an analysis of evolutionary relationships (called a phylogenetic analysis). This analysis placed Proteroctopus ribeti in the Vampyropoda clade. This means that Proteroctopus is more closely related to octopi than to squid, cuttlefish, or nautilis. The vampyropods also happen to include my favorite octopus: Vampyroteuthis infernalis (‘the vampire squid from hell’, which is actually an octopus, not a squid).

Vampyroteuthis infernalis showing off its tentacles. When threatened, it wraps its head with its tentacles and uses the hooks for protection. From here.

Now, Proteroctopus has suckers, not hooks, but the layout of the suckers shows that the diversity of suckers was high in the Jurassic. The authors point out that more fossils will need to be CT scanned to better understand the ancestral morphologies and the evolutionary relationships of this group.

See you next week!

A New Dinosaur Family Tree

Last week, a [study] was published that changed the fundamental relationships among dinosaurs. Traditionally, and for the last 130 years, dinosaurs have been split into two main groups: saurischians (‘lizard hipped dinosaurs’) and ornithischians (‘bird hipped dinosaurs’). The saurischians include the giant, long-necked sauropods, the meat-eating theropods, and eventually modern birds. The ornithischians include the horned dinosaurs, the armored dinosaurs (like Triceratops and Ankylosaurus), and the duck-billed dinosaurs.

The traditional view of dinosaur relationships.

This main distinction occurs because of differences in the hips of these dinosaurs, hence the names. The hips are made of three bones: the ilium, the ischium, and the pubis. The ilium attaches the other two bones to the spine. The ischium forms the back of the hips. The pubis forms the front. In saurischians, the pubis points forward, very similar to the hips of modern lizards. In ornithischians, the pubis points backwards, very similar to the bones of modern birds. Now we know that birds are actually saurischian dinosaurs, but we didn’t know that when these groups were named.

The differences in dinosaur hips. The dinosaur’s head would be to the left in these images. The ilium is in blue, the ischium is in red, and the pubis is in yellow. In saurischian dinosaurs, the pubis points forward. In ornithischian dinosaurs, the pubis points backwards. Source of image unknown.

The new study focused on the earliest dinosaurs. Here are the specifics: they examined 74 species and 457 characteristics of their bones and ran an analysis in a computer program called TNT (Tree analysis using New Technology). This program looks for the simplest way the characteristics can fit on an evolutionary tree, while creating the fewest amount of changes (a principle called parsimony).

This analysis found that the ornithischian dinosaurs are more closely related to the theropod dinosaurs and that saurischian dinosaurs are most closely related to a group called Herrerasaurids.

The new relationships among dinosaurs.

So, saurischian dinosaurs were split into two groups. This leads to at least one major problem: the definition of Dinosauria. Dinosauria is defined as: Megalosaurus (the first theropod discovered), Iguanodon (the first ornithischian discovered), their most recent common ancestor, and all of its descendants. When dinosaurs were split into two main groups, using Megalosaurus and Iguanodon to anchor the definition made sense because it included all of the animals we recognize as dinosaurs within the definition. Now that theropods and ornithischians are closer relatives, this definition would exclude the sauropods and herrerasaurids from the definition.

The traditional definition of Dinosauria. With the new relationships, sauropods would be outside of the dinosaur tree.

To fix that, the authors redefined Dinosauria as the least inclusive clade that includes Passer domesticus (the sparrow: a theropod), Triceratops horridus (an ornithischian), and Diploducus carnegii (a sauropod). That includes all the dinosaurs, and will keep including everyone even if the relationships in the tree change.

The new definition of Dinosauria is anchored with a species from each group, so even if the relationships change, all the dinosaurs are still included in it.

As interesting as this analysis is, there are issues with it. The main issue is that it’s the only analysis that gets this result. That’s not to say that it’s wrong! We just need to get the same answer with a lot more analyses before we start re-writing textbooks. Some of the technical aspects of the methods seem… off… as well, but I won’t get into those details until I can do more research. Basically, this is an interesting result and one that we should keep our eyes on, but we need more data to support it before we’re all on board.

*All skeletal images from Scott Hartman. Passer image from Birds of the World Handbook.

My Little Pony

Climate Change. It’s a topic that’s been in the media recently for a number of reasons, namely because we’re experiencing it now. We know that because we have climate records going back to 800,000 years (possibly [1.5 million years]) from ice cores. The gases trapped in the ice are made up of the atmosphere that was around when the ice formed. The atoms that make up the gas, like oxygen, carbon, and hydrogen, have different values of positive and negative particles (different isotopes) that relate directly to the temperature the planet was at the time. That’s how we know what temperature the planet used to be and how we can plot the data and form predictions about what the future holds (spoiler alert: it’s gonna get hot). For more on that, watch the video at the bottom.

This graph shows carbon dioxide levels over time. The higher the level of carbon dioxide, the hotter the temperature. From NASA. Credit goes to Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.

A [paper] was published this week that analyzed these same isotopes from the past. The Earth has gotten hotter in the past. One of these times, called the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) lasted for 200,000 years and caused the Earth to rise 5°-8°C over 10,000 years. (Note: we’ve risen [0.7°C over 100 years, which is about 10 times faster] than the natural warming cycles the planet has experienced.)

Lots of information in this graph. Here’s the breakdown. Time, in millions of years, is on the bottom (the x-axis) with present day on the right at 0 million years ago. The abbreviations above the time are for the names of the period (Pal = Paleocene, Eo = Eocene). Along the right, the y-axis shows the amount of a particular isotope of oxygen that tells us temperature. The green line in the graph is the amount of that isotope over time, and gives us a sense of temperature. The higher the line is the hotter the temperature, and the lower the line is, the cooler the temperature. Right between the Paleocene and the Eocene, you can see the spike that indicates a sudden hot temperature. You can also see the cooling trend that lead to the ice ages (“Rapid Glacial Cycles”).

This new study examined a time after the PETM (about 2 million years later, at 53.7 million years ago), called the Eocene Thermal Maximum 2 (ETM2). The record of this time is pretty complete in the Big Horn Basin of Wyoming. The authors analyzed the temperature before, during, and after the ETM2 using the isotopes contained in the soil and in the teeth of an early horse, Arenahippus pernix, and a couple of other mammal species. They also calculated the body size of these animals using the size of the first molar. Molar size corresponds well to overall body size in mammals, so we can use the molar size to estimate body size when we only have teeth.

Arenahippus pernix at the Swedish Museum of Natural History. From Wikipedia.

The authors found that as temperature increased, the size of the horse shrank (from 7.7 kg to 6.6 kg). As temperature fell again after the ETM2, body size increased (from 6.6 kg to 7.9 kg). One of the reasons for this shrinkage is that it’s easier to cool off a smaller body than it is to cool off a larger body. If the environment is warming up, then being able to cool off faster is an advantage. Also, there may have been fewer nutrients available if droughts were happening, so the horses may not have been able to grow to their full size. The last reason could be related to how much rain was available. Less rain means less plants and less food for herbivores. Whatever the reason or combination of reasons, what we do know is that climate change, like what we’re seeing now, will affect mammals in ways we are still discovering.

Figure 3 (A and C) from the paper. The first two columns show the carbon isotope levels in the soil through time. The further the points move to the left, the hotter the climate was. The right column shows molar size in Arenahippus. Points to the left are smaller molars and points to the right are larger molars. The molars get smaller just as temperature is the hottest, and then grow again when the climate cools down.

Video on atmospheric carbon dioxide from the Earth System Research Laboratory at the National Oceanic and Atmospheric Administration. More sources can be made available on request.