Little Morning Bird

This week, a [paper] describing a new fossil bird was published. Lots of cool things going on with this fossil.

The fossil was found on Navajo lands in New Mexico. It is from the Early Paleocene (around 62 million years ago), only a few million years after the end-Cretaceous extinction. The fossil preserves parts of the arms and legs, a couple of vertebrae, and a tiny bit of the skull.

Figure 2 from the paper showing the different parts of the fossil.

Its feet are particularly interesting. This little bird had the ability to turn one of its toes backward whenever it wanted to. Most birds have 1 toe that’s permanently backwards for grasping branches. Some birds, like parrots and woodpeckers, have two toes like this. This new bird could decide when it wanted a second toe pointed backwards.

Different bird feet. The parrot and woodpecker have two toes turned backward. Most birds only have one toe turned backward. From here.

By comparing it to other birds in a phylogenetic analysis, the authors discovered that it’s the oldest mousebird ever found. Today, there are only 6 species of mousebirds and they all live in Africa.

A modern mousebird. From here.

The fossil is a new species of mousebird. The authors named it Tsidiiyazhi abini, meaning “little bird” and “morning” in Navajo. The cool thing is, because this fossil is so old, it pushes back the origin of several bird lineages into the Paleocene. This means that most of the modern bird groups were already present only 4 million years after the extinction! Birds evolved very quickly after the extinction event (a process called an explosive radiation). Flowering plants (the plants that produce fruits and nuts) were also explosively radiating at this time and probably provided homes and food for all of these bird groups.

An illustration of what Tsidiiyazhi abini might have looked like. By S. Murtha.

A New Whale with Crazy Teeth

This week, a [paper] came out that described a new fossil whale from South Carolina (USA). The fossil is from the Oligocene (~ 30 million years ago) and it has a basically complete skull, some vertebrae, and a few ribs.

A reconstruction of Coronodon by A. Gennari.

The authors named the fossil Coronodon havensteini, meaning ‘crown tooth.’ It was found by Mark Havenstein, so the specific epithet (the second part of the name) is in his honor. The teeth of this fossil are particularly interesting.

Figure 2 from the paper showing the teeth of Coronodon.

Instead of simple, conical teeth (like in dolphins), or baleen (like in the blue whale), Coronodon has teeth with many bumps, giving each tooth the appearance of a little crown. Food and other particles left little scrape marks on the teeth, which indicate the direction of water flow through the mouth, and how the teeth were used during feeding. When the mouth was closed, the upper teeth sat on the outside of the lower teeth, providing just enough space for water to escape through the teeth, leaving delicious food bits inside the mouth.

Figure 2f from the paper showing how water would have flowed between the teeth.

Coronodon was using its crazy teeth to filter feed! Why is this important? Because understanding how filter feeding began in whales is an ongoing question. Coronodon is one of the earliest relatives of the mysticetes (baleen whales), but it has no baleen itself. It used its teeth the same way mysticetes use their baleen. Later on in mysticete evolution, baleen began to develop and finally took over as the dominant feeding structure. Coronodon represents the first step in that process. Another idea is that whales went through a toothless, suction-feeding phase before filter-feeding with baleen came about, but Coronodon shows that suction-feeding wasn’t part of the evolution of filter-feeding.

We can learn a lot about how extinct animals ate their food through looking at the shape and tiny scrape marks on the teeth (called microwear), and Coronodon is new amazing example of that!

A Fluffy Double-Feature

This week, two articles were published that discussed feathers in two different dinosaurs. We’ll start with the cooler one…. uhhhh… I mean…. the…. one with better preservation. Yes, that’s it!

The first [article] described a bird fossil in amber, the third one from Myanmar that has been recently described. It is of an enantiornithine, an extinct lineage of toothed birds from the Cretaceous, and it’s spectacular. Most of the animal is preserved because it’s trapped in amber and many of the feathers are preserved in detail.

Figure 6c from the paper showing the 99 million year old enantiornithine foot in amber. Behold its beauty! Scale bar is 5 millimeters.

The authors wrote a thorough report of each part of the specimen, along with descriptions of the feathers found on each portion of the body. By CT scanning and examining it under dissecting microscopes, the authors were able to see both bone and feather morphologies. The morphologies indicated that the specimen was a juvenile. The feathers show that enantiornithines were precocial at hatching. Precocial means that they were able to walk around, and potentially even fly, from the day they hatched (like a chicken or a brush-turkey). Baby birds that need a lot of care before they can manage by themselves are altricial. This new specimen, along with other enantiornithines, are pointing to most enantiornithines being precocial. They are also known to be mostly arboreal (tree-dwellers). The combination of precocial and arboreal is not something that modern birds are doing: the precocial birds of today are ground-dwellers and the altricial birds of today are tree-dwellers. This means that enantiornithines were superficially similar to modern birds, but living different sorts of lifestyles than what we see today and this could have impacted the places they could live in and the body-shapes they had.

The graphical abstract from the paper showing the amber chunk with the fossil (bottom), the CT scan (middle), and a line drawing interpretation (top).

The second [article] was about tyrannosaurids. This group contains Tyrannosaurus rex, Gorgosaurus, Tarbosaurus, and a few other large-bodied theropods that are known for their large heads and tiny arms. There has been an ongoing debate on whether or not they had feathers covering their bodies. This debate originated because we know feathers were present on a lot of other theropods, including on the most basal members of the group, like Dilong. The issue is that we’ve never found a larger bodied tyrannosaur with feathers preserved on it.

An illustration of Dilong by P. Sloan.

To address this question, the authors examined fossilized skin impressions of several specimens of this group. They found that scales covered parts of the neck, abdomen, hips, and tail and concluded that most of these large-bodied tyrannosaurids were covered in scales. If feathers were present, they would have been limited to the back of the animal. There are many hypotheses (testable scientific ideas) out there about why these big tyrannosaurids lost their feathers, but I’m not going to address those here.

Figure 1b from the article showing a piece of fossilized skin from T.rex. You can see the outline of each scale.

The main point I want to make about this paper, and I’m going to quote my undergraduate mentor (Dr. Tom Holtz) here, the absence of evidence is not evidence of absence. That means just because we haven’t found feathers preserved on big tyrannosaurids, does not mean they didn’t have them. The conditions needed for feather preservation are very specific, and the places where we find these big tyrannosaurids are not the same types of places that preserve feathers. So maybe T. rex had feathers and they just weren’t preserved. Maybe T.rex didn’t have any feathers. Maybe it had feathers as a baby and lost them as an adult. Maybe it had feathers in some places on its body. For now, we don’t really know. We might never know. And that’s ok because science is a process of continuous discovery and interpretation. We’ll just have to keep digging.

Oceans, Whales, and Time

I don’t always talk about whales on this blog, but when I do, I prefer to talk about their size or echolocation. This time it’s about size. We all know many whales are really, really big. What we hadn’t quite understood yet is when they got big, or why.

A photo of several baleen whales surfacing as they engulf tiny krill. Source unknown.

Thankfully, a new [article] ran an analysis to figure out these two missing pieces. The authors used a dataset of 13 living and 63 extinct whales, including DNA (for the living ones) to create an evolutionary tree with time estimates for each branching point (called branch lengths). Using this tree and a dataset of body sizes, the authors used a model-testing approach to assess how the timing of whale evolution took place.

What’s a model testing approach? A model-testing approach is when we use computers to test the fit of different models to the data we give it. In this case, the authors gave the computer the tree and the body size data. The authors picked several different models for the computer to test. One of the models was based on random events driving evolution. One of them was based on evolution with a trend towards one trait. Some of the models were combinations of the others, where the model changes at a certain point during evolution. Once the computer is done testing each model, it produces a few statistical values that tell us how well each model fit the data.

A representation of the authors hard at work.

For this study, the authors wanted to know which model of evolution best fit the evolution of giant sizes in whales. The computer’s analysis showed that body size evolved randomly until around 3 million years ago when there was a shift to evolution with a trend of becoming very large. Even though filter feeding using baleen had been present in whales since 25 million years ago, it wasn’t until recently that they became very large. Around 3 million years ago, during the Plio-Pleistocene, wind-driven upwelling (where wind patterns on the surface bring up nutrients from the ocean floor) started getting stronger. This concentration of small food items is probably what lead to whales getting gigantic.

How upwelling works. Higher winds on the surface push the warmer surface water away from the coast. Colder, nutrient-filled water from the bottom gets pulled up. From NOAA.

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.