Sunday, December 15, 2019

What Good is Less Than Half a Beak?

One of the many distinctive features of modern birds is their complete lack of teeth, their jaws instead being sheathed in a keratinous beak. Modern birds are not the only beaked dinosaurs though; beaks have also been found in ornithischians, therizinosaurs, ornithomimids, caenagnathoid oviraptorosaurs, and confuciusornithiforms, just to name a few major groups. However, all of these examples appear to have acquired beaks independently; their beaks were not directly related to those of modern birds.

The beaks that did give rise to those of modern birds appear to have arisen relatively late, corresponding to the origin of the clade Euornithes*, which includes neornitheans (modern birds) and everything more closely related to them than to the enantiornitheans or "opposite birds". Contrary to a lot of paleoart, however, the beak in most non-neornithean euornitheans did not take up most of the jaw like it does in modern birds. Instead, both their upper and lower jaws generally had a short toothless section at the jaw tips; it is likely that the euornithean beak was originally restricted only to this small region.

*In recent literature, the most popular name for this group is Ornithuromorpha, which was originally named in 1999 and defined in 2002 as the clade uniting Patagopteryx and modern birds. Under the results of most phylogenetic studies, this would actually refer to a slightly smaller group within Euornithes instead of being equivalent to Euornithes itself. Furthermore, given that Euornithes was both named (in 1889) and explicitly defined as the "closer to modern birds than enantiornitheans" clade (in 1998) earlier than Ornithuromorpha was, I favor its use here.

The toothless portion of the lower jaw in non-neornithean euornitheans was particularly curious. In most vertebrates, the frontmost bones in the lower jaw are the dentaries. The toothless tip of the lower jaw in non-neornithean euornitheans, however, was composed of a small separate bone that lay in front of the dentaries, appropriately called the predentary.

The predentaries of various euornitheans, from Bailleul et al. (2019). The middle and right columns show the front end of each skull under microcomputed tomography (microCT) scanning. (And look, there's cranial material of Gansus!)

Not many vertebrates have a predentary. Some types of fish (such as marlins) have one, as did ornithischian dinosaurs. As many dinosaur geeks are eager to point out, even though ornithischians are known as "bird-hipped dinosaurs", birds are not ornithischians. The similarities between the hips of birds and ornithischians evolved convergently, and so too did the predentary.

Given that modern birds lack a separate predentary, and similar structures have only been found in fairly distantly related groups, analogues for the anatomy and function of the euornithean predentary are limited. In a recent study, Alida Bailleul and colleagues took the predentary from a specimen of the Cretaceous euornithean Yanornis and examined it in detail. They scanned the bone at extremely high resolution, took sections of it to view it in cross section under a microscope, and treated it with chemicals that react to specific tissue components.

The jaw tips of Yanornis, with special focus on the predentary (labeled "pd"), from Bailleul et al. (2019).

These methods allowed Bailleul et al. to identify traces of cartilage on both the predentary and dentaries of Yanornis where these bones would have attached to one another. The specific type of cartilage that forms on the dentaries is secondary cartilage, which generally forms at mobile joints that experience compressive forces. This, along with the shape of the bones themselves, led the authors to conclude that the euornithean predentary could move independently of the rest of the jaw, which has been previously suggested by other researchers. (Interestingly, this would provide another parallel with many ornithischians, in which the predentary allowed each half of the lower jaw to rotate along their long axes. In ornithischians, however, this movement probably occurred during chewing, which we have no evidence that any euornithean ever did.)

Unfortunately, we don't currently have enough information to reconstruct exactly what type of motion the euornithean predentary would have been capable of. However, this does imply that the predentary could have played a role in manipulating and processing food. Furthermore, Bailleul et al. identified canals for blood vessels and nerves that would have entered the predentary from the dentary, suggesting that the predentary could have also had a sensory function.

3D reconstruction of the dentary tips and predentary of Yanornis, from Bailleul et al. (2019). Blue represents patches of cartilage on the dentaries, whereas purple represents a patch of cartilage on the predentary.

Yanornis is known to have eaten fish, and it's not hard to see how a sensitive jaw tip might have helped it detect its prey. The authors point out that a piscivorous diet was probably not typical of all non-neornithean euornitheans though, so the mobile and sensory properties of the predentary were likely advantageous for euornitheans adopting a wide variety of ecologies. They could have even come in handy during behaviors other than feeding, such as preening and nest building.

Bailleul et al. note that the predentary in euornitheans is almost always paired with a corresponding toothless tip of the upper jaw. This may indicate that these two features were functionally linked. However, just a few weeks before the publication of Bailleul et al.'s study, a new Cretaceous euornithean, Mengciusornis, was described. Mengciusornis deviated from the usual euornithean pattern by having teeth at the tip of its upper jaw (in fact, it only had teeth at the tip of its upper jaw), and yet it still had a predentary. Perhaps, though, this is actually a point in favor of the idea that the predentary could be beneficial for many disparate feeding strategies.

Some euornitheans that don't appear to have much use for the predentary are the ones that lost teeth entirely. In addition to modern birds, a number of other euornitheans had independently evolved toothlessness, including Archaeorhynchus, Schizooura, Eogranivora, and Xinghaiornis, and it seems that none of these had a predentary. (The purportedly toothless Dingavis may preserve a surface at the tips of the dentaries where a predentary could have been present, but its describers also mention that they can't reject the possibility that it had small teeth.)

So what happens to the predentary in such taxa? Does it simply fail to form entirely? Does it fuse with the rest of the lower jaw? It would be interesting to find out whether any trace of the predentary can be detected in the developing embryos of modern birds. Bailleul et al.'s paper is by far the most detailed study on the euornithean predentary to date, but it's evident that there's much we still don't know about this interesting piece of avian evolution. I look forward to future research that aims to shed light on this enigmatic bone.

Reference: Bailleul, A.M., Z. Li, J. O'Connor, and Z. Zhou. 2019. Origin of the avian predentary and evidence of a unique form of cranial kinesis in Cretaceous ornithuromorphs. PNAS 116: 24696-24706. doi: 10.1073/pnas.1911820116

Tuesday, November 5, 2019

New "About" Page

Ever since the inception of this blog, the "About" page has largely remained unchanged. Seeing as it was written in an "answers to frequently asked questions that are not in fact frequently asked" format and much of the text pertained to my not-officially-cancelled-but-rarely-updated webcomic, I thought this would be a good time to overhaul into something that will potentially be more useful.

As a result, my "About" page now contains a very, very simplified overview of maniraptor diversity and evolution. In some ways, it can be considered a spiritual successor of my very old "What is a maniraptor?" post, which some readers have requested me to update in the past.

For the new "About" page, I had to cut out some of the material that I had planned (I would have liked to go into more detail regarding neoavian diversity), because it was already getting long for an introductory post. However, I hope that what I managed to fit in will be of some use in helping readers orient themselves regarding the groups and concepts that I regularly discuss on this blog.

Note for theropod taxonomy buffs: for the sake of simplicity and convention, I have not currently adopted the new definition for Dromaeosauridae proposed by Hartman et al. (2019). However, I would certainly be open to using it if it ends up in prevailing usage by theropod paleontologists.

As some "bonus material", here are three phylogenetic diagrams that didn't make it into the final write-up:

Tuesday, October 29, 2019

TetZooCon 2019

As much as I enjoyed Australia, I couldn't stay for long, and one of the reasons I couldn't was that TetZooCon was being held the following weekend. Despite my reluctance to leave behind a land of rich biodiversity and unique Southern Hemisphere clades, TetZooCon is always a good time and I had no intention of missing it. Building on its successful run last year, this year's TetZooCon also spanned two days, boasting events such as panel discussions (on archosaur paleontology and natural history filmmaking), parallel sessions, and more. With this year, we came ever closer to assembling the former crew of TetZoo Time in one place, seeing as comic inker Rebecca Groom, comic colorist Gareth Monger, and myself were all in attendance.

I've never seen a bad presentation at TetZooCon, but if I had to pick favorites from this year, my personal highlights would include Mike Dickison's talk on what makes a "native" New Zealand bird, Dave Hone's talk on the importance of defining terms in dinosaur paleontology, Lauren McGough's talk on her experiences hunting with golden and crowned eagles, and Tim Haines's talk on popularizing paleontology using digital media (e.g.: Walking with Dinosaurs).

One of the new features this year was the art show, showcasing work by a range of accomplished paleoartists. I was especially thrilled to see several of Luis Rey's original paintings on display. I remember seeing many of them in early 2000s paleontology books and they left a strong impression on me at the time, introducing me to then-new and exciting finds being unveiled in dinosaur paleontology.

One of Rey's iconic depictions of the Jehol Biota, featuring a trio of Beipiaosaurus as the centerpiece.
This Quetzalcoatlus looked familiar, but I don't remember having seen it carrying anything in its beak!

I chose to attend the paleoart workshop this year (in part as a show of support for paleoartist friends who were speaking), though this meant missing out on the nature documentary panel. Joschua Knüppe, Rebecca Groom, Agata Stachowiak, and Jed Taylor gave brief talks on their respective artistic endeavors, and throughout the session we were encouraged to exercise our creativity using provided art supplies. Joschua was granted the honor of selecting a theme for the workshop, and he suggested depicting prehistoric life in art styles reflective of the nations in which they were found.

Not being particularly familiar with different art styles, let alone enough to attempt replicating them at short notice, I mainly defaulted to my standard drawing style. In my defense, I did try to venture a little outside of my comfort zone by having a go at restoring some fossil birds that I hadn't before, such as the stem-mousebird Celericolius and the stem-flamingo Palaelodus. Being on a My Little Pony: Friendship is Magic kick with the recent conclusion of the series, I also couldn't resist drawing a My Little Maniraptor. Besides, I rationalized, it counted as non-standard paleoart and would be encouraged. In spite of my unadventurous efforts, it had been so long since I'd seriously drawn with pencil and paper that I ran into some unexpected challenges, like not being able to revert mistakes with the "undo" button or not being able to put items on different "layers".

In my recent forays into drawing My Little Maniraptor, I've found that I quite enjoy drawing my maniraptor design for Fluttershy, which is ironic because I used to consider her one of the hardest to draw. Also shown are my attempts at restoring Celericolius, Longipteryx, and Palaelodus (only the head of which is visible here).

Well, I certainly wasn't winning any prizes with that, especially considering some of the impressive work produced by other workshop attendees. As usual, I performed better on the TetZooCon quiz. Although I didn't come in first place like I did last year, I did tie for second with Kelvin Britton (who has also won first place in previous years, in his case several times)!

The day after the conclusion of the main event, Darren led an informal field trip to the London Zoo, which I gladly joined. We saw the vast majority of the zoo, including some of the more rarely-seen species. To paraphrase Ville Sinkkonen, only in a crowd like this could one find so many people excited about seeing a caecilian's cloaca. My favorite sighting though was probably the baby narrow-striped boky (though it was too active and the lighting was too dark for me to photograph)! As ever, TetZooCon did not disappoint, and I look forward to seeing how it develops next year.

A blue tree monitor.
A black-naped fruit dove.
A southern tamandua scaling a wall.

Monday, October 28, 2019

Lone Pine Koala Sanctuary

I didn't have much time to do touristy things during my time in Australia, but I did get to visit the Lone Pine Koala Sanctuary. As its name suggests, it was originally founded as a sanctuary for koalas specifically, but is now also home to a wide variety of Australian species.

One of the first animals one will see upon entering are these flying foxes.

Although I didn't get to see wild frogmouths in Australia, I did see several living individuals thanks to both the Koala Sanctuary and the Queensland Museum.

High on the list of the animals I wanted to see in Australia were platypuses, and the Koala Sanctuary gave me excellent views of them. They spent a lot of time swimming around actively while I was watching them, but this one was cooperative enough to lie still at the bottom of its tank for a short time.

Some Mary River turtles, an endangered turtle species that was only scientifically described in 1994.

Wildlife was abundant on the sanctuary grounds, and probably the most common were Australian water dragons and Australian brushturkeys. Here I managed to catch both in the same shot.

A wild maned duck.

A white-bellied sea eagle, one of several species flown in the Koala Sanctuary's raptor show. Others they showcased during my visit were barn owl, barking owl, and peregrine falcon.

Some lace monitors huddled in a hollow log.

A Mertens's water monitor not in the water.

A freshwater crocodile basking alongside a young wild water dragon. Presumably the crocodile isn't hungry, the young water dragon is very foolhardy, or both.

A wild bush stone-curlew shopping for postcards, or maybe for scraps of food dropped by visitors. Despite being shorebirds, these birds generally forage inland, usually at night.

Sunday, October 27, 2019

SVP 2019

This year's SVP was held in far-off Brisbane, Australia! (At least, "far-off" from the perspective of the usual majority contingent of North American and European delegates.) Australia has long been a bucket list location for me, so I was thrilled that I was fortunate enough to attend. This was not only my first time in Australia, but also my first time anywhere in the Southern Hemisphere.

It was amazing. Seeing all the Australian wildlife alone made the trip worth it. Before I saw a single rock pigeon in the city parks, I'd already seen seven species of birds I'd never seen previously. One of the most common, of course, was the Australian ibis (locally known as the "bin chicken"). In the background here is a maned duck, also known as the Australian wood duck due to its habit of nesting in trees, though it is not closely related to the North American wood duck.

An Australasian darter drying its wings.

I took one day away from the conference to go on a guided birding tour with my supervisor Daniel Field, my labmate Juan Benito, and fellow paleornithologist Adam Smith. As a group we saw or heard over 100 bird species, which means that I saw more bird species in three days in Australia than I have in three years of being in England.

Among the many birding hotspots we visited near Brisbane were these mangrove forests.

We saw three kingfisher species in or near the mangroves: laughing kookaburra, Torresian kingfisher, and sacred kingfisher (pictured).

A black-faced cuckooshrike. Cuckooshrikes arose from an early split within the clade Corvides, the songbirds more closely related to crows than to sparrows.

I'd been hoping to see woodswallows on the trip, and this white-breasted woodswallow granted my wish. Woodswallows are members of an Australasian radiation of songbirds called the artamids. This group also includes birds such as the Australian "magpie" and currawongs, which we also saw in Brisbane. As their name suggests, woodswallows are convergent on swallows in their ecology, catching insects by skillfully flying through the air.

I was also excited to comb-crested jacanas. We even saw a male leading three chicks around (though it was too far away for my camera).

Here's a flying tetrapod of a different sort. Flying foxes were a common sight throughout much of Brisbane, especially in flowering trees.

The highlight for me though was seeing two young powerful owls! (Daniel got a photo of one of them.) The wild koala was cool, too. Probably the only real mishap we encountered was that we got accidentally locked inside a campground after dark, but that was ultimately more of an inconvenience than anything. Also, the fact that we didn't get to see any wild frogmouths. On the whole though, I consider this year's trip to have been a great success, and I look forward to next year!

Oh, right, I was also there to attend a conference or something...

The conference itself was certainly a good time. The welcome reception took place in the Queensland Museum, where the museum staff brought out some of their live animals (used in their educational programs) for us to see. And though I didn't manage to see frogmouths in the wild on this trip, one of those education animals was a tawny frogmouth!

This wombat proved to be very popular.

In addition to the live frogmouth, there were also these taxidermied specimens on display.

The taxidermy displays in general were quite impressive. Here a barn owl is shown preying on a long-haired rat, a species whose population goes through dramatic boom-and-bust cycles.

A pair of striped possums (ecologically convergent with the Malagasy aye-aye), along with a white-lipped tree frog.

A perentie that had died trying to swallow an echidna. I first learned of this specimen from Tetrapod Zoology.

Befitting the occasion, the Queensland Museum also has a number of paleontological exhibits. Here are some paleontologists mingling near a skeletal mount of Muttaburrasaurus.

The ankylosaur Kunbarrasaurus, known from a nearly complete specimen.

Although I've presented talks at scientific conferences before, this year marks the first time I've given one at SVP. I talked about my recently published work on the phylogenetic relationships within Strisores, the nightjars, swifts, hummingbirds, and their kin. People seemed to like it, or at least everyone who mentioned it to me afterward did. As part of my presentation, I included a parody of the Twitter logo drawn as a nightjar. (I also made a turaco version for Daniel's talk and shared my existing Ichthyornis with Juan.)

As for the talks that I enjoyed, select highlights include the following:
  • Christopher Nedza's talk on changes in melanosome distribution during the decay of fish carcasses
  • Kieren Mitchell's talk on the phylogenetic position of dire wolves
  • Wang Shiying's talk on a new basal pygostylian from the Jehol Group
  • James Neenan's talk on convergent sensory ecologies between alvarezsaurs and owls
  • Patrick O'Connor's talk on an unusual avialan from the Maevarano Formation
  • Todd Green's talk on the development of bony crests in birds
  • Ian Miller's talk on how plants shaped vertebrate ecosystems during the Late Cretaceous and early Paleogene
My guide to paleocolor in dinosaurs had an unexpected presence at the meeting. Firstly, it was featured (and praised!) in Arindam Roy's talk on amniote paleocolor reconstruction. Secondly, my friend Jun-Hyeok Jang showed me a Korean dinosaur book that'd been illustrated with a multitude of entertaining cartoons, among them one that had almost certainly been inspired by my guide!
My original for comparison.

The SVP auction was fun as usual, though I was nodding off by the end of it all thanks to lingering jetlag. This year's auction theme was not any specific pop culture work, but a more generalized theme of "Australia"; thus, the hosts dressed up as kangaroos, cassowaries, and so on.

For the afterparty I'd thought that it would have been a missed opportunity not to play songs by Professor Flint, a science communicator who specializes in singing about Australian paleontology. The organizers more than met my expectations by treating us to a Professor Flint live performance! I got the sense that many attendees were somewhat perplexed by this, but songs with science-related lyrics are my jam, so I was honestly pretty delighted. In any case, Professor Flint's show was soon followed by a more conventional (at least by paleontologist standards) dance party, presumably putting the confused parties at ease. I'm not much of a partier though, so I retired for the night.

I'd enjoyed my time in Australia so much that I almost didn't want to leave, but all good things must come to an end. I do hope that I get to visit again someday. In the meantime, I did have TetZooCon to look forward to!

Hungry paleontologists/paleoartists/paleontology enthusiasts at SVP 2019 looking for food. Individuals represented are Tom Parker (Australovenator), myself (Albertonykus), Darren Naish (Eotyrannus), Jun-Hyeok Jang (Brachiosaurus), Henry Thomas (Zhejiangopterus), William Stout (Parasaurolophus), Joe Nicholson (Dinornis), and Tas (Iguanodon).

Saturday, August 31, 2019

Shining a Light on Nightbird Evolution: My First First-author Paper!

As I previously mentioned on this blog, I'd been hoping to have the first part of my PhD research submitted to a journal by the time I had reason to blog about it again. I'm pleased to report that my research has now not only been submitted, but published! Diversity (the journal I submitted to) processed the article unbelievably quickly, having it reviewed, edited, accepted, and published in less than a month! I was also fortunate in that the reviewers didn't request any major changes. I certainly don't expect to go through such a painless submission experience again anytime soon.

For this study, my coauthors and I looked at the phylogenetic relationships of a remarkable group of theropods, Strisores. Many strisoreans* are well-camouflaged birds that are active at night or twilight; these include the nightjars, oilbirds, potoos, frogmouths, and owlet-nightjars. However, the diurnal swifts and hummingbirds are also members of Strisores. Most strisoreans (including the predominantly nectar-feeding hummingbirds) eat insects, but the oilbird (Steatornis caripensis) feeds exclusively on fruit.

*I used this new paper as an opportunity to make the case that "strisorean" should be the vernacular form for Strisores, for much the same reasons that I now use "enantiornithean" instead of "enantiornithine". Time will tell whether anyone else follows this...

A cartoon depiction of the major strisorean subgroups and their inferred phylogenetic relationships based on our new study.

Traditionally, the nocturnal strisoreans have been classified as one group, but recent studies have presented strong evidence that the owlet-nightjars are more closely related to swifts and hummingbirds than to the rest. (The group uniting owlet-nightjars, swifts, and hummingbirds has been named Daedalornithes.) When it comes to the phylogenetic relationships among the remaining groups, however, little consensus exists. In fact, up until recently, no two phylogenetic datasets aimed at resolving their relationships found the exact same results!

We approached this problem by combining the largest genetic and anatomical datasets that have been assembled for Strisores so far. The genetic dataset was originally put together for a different study by my coauthors Noor White and Mike Braun (accepted at Molecular Phylogenetics and Evolution but not yet published online at the time of writing) and the anatomical dataset came from a 2013 study by Dan Ksepka and colleagues.

The results of selected previous studies on strisorean phylogeny. Up until White and Braun (2019) found an identical topology to Prum et al. (2015), no two datasets produced the same result!

When we analyzed our combined dataset, we found that nightjars were best supported as the most distantly related group to other living strisoreans. The oilbird and potoos were united in one group, which was in turn closely related to a clade containing the frogmouths and daedalornitheans. This result was not only identical to what we found when we analyzed our genetic dataset on its own, but also to the findings of a previous genetic study by Richard Prum and colleagues. Although it is never wise to unilaterally declare a case closed in science, the fact that two large datasets independently recovered the same results suggests to me that this is indeed the most likely phylogenetic tree for Strisores.

In fact, we felt that the support for a group including all strisoreans except nightjars was strong enough that we chose to give it a name: Vanescaves. This name translates to "vanishing birds", partly a nod to the Emily Dickinson poem "A Route of Evanescence", which describes a hummingbird flying near some flowers. The name also references the fact that many vanescavian subgroups currently have geographically restricted ranges (oilbirds and potoos in the Neotropics, frogmouths in Australia and Southeast Asia, and hummingbirds in the Americas), but are known from the fossil record to have once lived in other regions, such as Europe. In contrast, nightjars are distributed almost globally today, but have very little of a documented fossil record.

One of the resulting phylogenetic trees we recovered in our study, scaled to geologic time. (The divergence times are largely bare minima necessary to accommodate known fossil ages and should not be taken literally.)

Speaking of fossils, one of the main benefits of combining genetic and anatomical data in our study was that it allowed us to place fossil species in the context of our phylogenetic results. Despite their small body size and delicate, sometimes literally paper-thin bones, a diverse range of fossil strisoreans have been identified in Eocene fossil deposits (33.9-56 million years old). In general, most fossil strisoreans included in our study fell out in parts of the tree that we expected them to based on previous research, but we did find a few surprises.

For example, we found that the oilbird may be the closest living relative to Fluvioviridavis, a 52-million-year-old strisorean from Wyoming, unlike previous phylogenetic analyses which found Fluvioviridavis as a close relative of frogmouths. This is a notable result given that paleornithologist Gerald Mayr previously noted features in Fluvioviridavis that are more similar to oilbirds than to frogmouths.

The holotype of Fluvioviridavis, from Nesbitt et al. (2011), under CC BY 2.5.

We also discovered that Hassiavis, a 47-million-year-old strisorean from Germany that had not been previously subjected to phylogenetic analysis, was potentially an early member of the owlet-nightjar lineage, which would make it the oldest known stem-owlet-nightjar and the first one known from outside of Australasia, identifying owlet-nightjars as yet another vanescavian group with a formerly much broader distribution. (However, it should be noted that not all of our analyses recovered Hassiavis as a stem-owlet-nightjar. In any case, we found that it was most likely a daedalornithean.)

Our research additionally allowed us to make new inferences about the evolution of strisorean anatomy. Previous studies that considered only anatomical data tended to recover nightjars, potoos, and daedalornitheans as a group. These strisoreans are often specialized for snapping up insects in flight, in contrast to the fruit-eating oilbird and the big-beaked frogmouths (which instead more commonly pounce on prey on the ground). According to previous morphology-based hypotheses, this would imply that aerial insectivory originated relatively late in strisorean evolution. However, the phylogeny we found has the oilbird and frogmouths nested among the insect-hawking groups, suggesting that they descended from ancestors that similarly hunted insects on the wing.

Nightjars and other insect-hawking strisoreans have such specialized-looking anatomy that it may seem counterintuitive that they represent the ancestral state for Strisores. However, there may be a parallel example in other flying vertebrates: bats likely also started out as aerial insectivores, and they too evolved into fruit-eaters, vertebrate predators, and nectar-feeders. Furthermore, our phylogenetic results really only imply two losses of aerial insectivory (once in the oilbird and once in frogmouths), which does not come across as an unbelievably high number to me.

The skull of a common potoo (Nyctibius griseus), viewed from the right. The giant eyes and broad palate, among other things, make this a very bizarre skull!

Is there any support for this in the fossil record? Maybe! We found that Protocypselomorphus, a small strisorean from the Eocene of Germany that was likely an aerial insectivore, may have been more closely related to the oilbird than to any other living strisorean. If this is correct, it would provide evidence that the oilbird had insect-hawking ancestors. Indeed, the often-prescient Gerald Mayr had already pointed out that Protocypselomorphus shares certain features in common with the oilbird. That being said, the majority of fossil strisoreans in our study were already very anatomically similar to their closest living relatives, so a clearer picture of what the ancestral strisorean looked like may depend on the discovery of even older fossils.

One question I've frequently received when discussing this research is whether hummingbirds and swifts evolved from nocturnal ancestors. We did not focus on this interesting topic for this study, but I personally think that we do not yet have enough information to answer this question conclusively. If one assumes that gaining and losing nocturnality are equally likely, it's true that the most straightforward interpretation is that strisoreans were ancestrally nocturnal and then became diurnal on the line leading to hummingbirds and swifts. However, it is not clear that such an assumption is correct. Furthermore, there is evidence that different groups of nocturnal strisoreans have adapted to darkness in different ways: the eyes of nightjars and potoos have a reflective layer that helps them capture more light at night, whereas other strisoreans appear to lack this feature. Thus, the notion that nocturnality originated several times in strisoreans may also be plausible.

If you've seen me present this study at conferences, you may remember that I also intended to perform divergence time estimation on Strisores. We ultimately decided to forgo that part of the study, because the massive size of our genetic dataset made divergence time estimation very computationally expensive and time consuming. However, I may still attempt such an analysis on a smaller dataset for a future manuscript. Stay tuned...

Reference: Chen, A., N.D. White, R.B.J. Benson, M.J. Braun, and D.J. Field. 2019. Total-evidence framework reveals complex morphological evolution in nightbirds (Strisores). Diversity 11: 143. doi: 10.3390/d11090143

Tuesday, July 30, 2019

Chester Zoo

Having heard many good things about the Chester Zoo, it was only a matter of time before I planned a trip there. I was very impressed by both the exhibit design and collection of rarely-seen species. I took more than enough photos to split this trip report into several separate posts, but I unfortunately don't have time to write more than one at the moment, so a highlights reel will have to do.

It's not every zoo where you get to see an Indian rhinoceros right off the bat.

A nearby aviary houses several bird species, including northern bald ibises. This is such a large aviary that unless the birds are standing right next to the viewing area, it can be difficult to see them clearly without binoculars! (Luckily, I almost always carry a pair with me.)

Cinereous vultures also live in this aviary. (This one was cooperatively standing near the mesh.)

I spent a good amount of time in the Tropical Realm building, which houses numerous species of free-flying tropical birds. If this hadn't been my first trip to the zoo, I probably could have been persuaded to spend most of my day there just looking for all the species. (I did end up seeing most of them.) Here is a Palawan peacock pheasant.

A Madagascar fody taking a bath while a Java sparrow and a red-billed leiothrix look on.

A sunbittern on a light fixture.

In addition to the free-flying birds, lining the walls of the Tropical Realm are separate aviaries housing even more species. Here is a pink pigeon. In 1991, only ten individuals of this Mauritian bird were left and it was considered critically endangered. Thanks to successful conservation efforts, its conservation status has been downlisted to vulnerable.

A great hornbill, one of the largest hornbills. Chester Zoo has a great collection of hornbills; I counted at least five species on my visit (great, Visayan, wrinkled, rhinoceros, and red-billed).

Not a hornbill, but a toucan. A green aracari, to be specific.

Two blue-naped mousebirds. Picking favorite birds is always difficult for me, but mousebirds have to be high on the list for their distinctiveness and their rich Paleogene fossil record.

A Congo peafowl, a species that wasn't scientifically described until the 20th Century.

A superb fruit dove.

A blue-necked tanager.

A pair of collared trogons.

The Tropical Realm also contains exhibits for amphibians, such as this false tomato frog.

There are non-avian reptiles as well, like this Graham's anole.

The species I'd most wanted to see at Chester though was the tuatara, and I'm happy to report that my wish was granted! I've now seen the world's only extant rhynchocephalian.

I also saw bush dogs for what I think is the first time. These small South American canids are very social, allowing them to prey on animals larger than themselves. They are housed in a different tropics-themed exhibit, the Spirit of the Jaguar.

In general, I liked the exhibit signage at the Chester Zoo (as we shall see), but one of the accompanying signs for the bush dogs did contain a glaring error. (Coatis are not rodents.) (Update: Surprisingly, the outreach team at the zoo responded to my tweet about this and has said they're working on fixing this. Huzzah!)

Yet another tropics-themed exhibit is the Realm of the Red Ape, a two-story building that allows visitors to view orangutans and gibbons high above ground. It was quite impressive, but I was more distracted by the blue-crowned hanging parrots, and can you blame me?

Upon exiting the Realm of the Red Ape, the zoo suggests several animal-themed recipes that make use of products with sustainable palm oil.

A babirusa showing off its unusual upwards-curving tusks.

This red forest duiker is exhibited alongside okapis. No doubt it gets regularly mistaken for a juvenile okapi by visitors.

Dragons in Danger is another indoor exhibit, this time named after its Komodo dragons. However, it also houses a variety of other animals, including many Southeast Asian birds. Due to the dense vegetation and dim lighting, the birds were quite hard to spot, but I did see this (very loud) Asian fairy bluebird.

Nearby is a surprisingly large exhibit for giant Hispaniolan galliwasps (shared with mountain chickens, a type of frog).

Islands is a relatively new exhibition area at Chester (having opened in 2015), and it features animals from Southeast Asian islands and New Guinea, such as this southern cassowary.

Islands also includes a walkthrough aviary for even more Southeast Asian birds, including the critically endangered Bali myna. Unfortunately, one of the other major exhibits at Islands, the Monsoon Forest, was partially destroyed by a fire in December 2018. Most of the inhabitants were rescued and relocated to other parts of the zoo, but a number of smaller animals did not make it.

A large chunk of the Chester Zoo is devoted to African animals. Here is a black stork, part of a large wetland aviary.

A black crowned crane (with a wild magpie in the background that I hadn't noticed until after I took the picture).

Nearby are these wattled cranes, the largest cranes in Africa.

Some African wild dogs.

Rock hyraxes (with babies)!

Despite the gaffe with coatis shown earlier, I liked how informative many of Chester's exhibit signs were. I especially appreciated this sign at the hyrax exhibit.

Naturally, there is a walkthrough aviary in this part of the zoo as well. Here, a village weaver works on its nest.

A snowy-crowned robin chat, a skilled vocal mimic of other birds.

A hamerkop, a wading bird known for building massive nests that can be more than one meter across. Some of these nests were evident in the exhibit.

Africa is home to several spectacular starlings, including this aptly-named superb starling.

A blacksmith lapwing.

Some crested guineafowl (as opposed to the more commonly kept helmeted guineafowl).

Although the African aviary isn't especially large or densely-planted, many birds remained surprisingly well hidden. Fortunately, some keepers passed through while I was there and scattered some mealworms on the ground, which drew out a few of the shier birds. One of the birds that emerged to check out the commotion was this red-winged starling.

This lilac-breasted roller also showed up, to my delight.