Tuesday, June 11, 2019

ProgPal 2019

This year's ProgPal was held in the Lapworth Museum at the University of Birmingham. It's a small museum, but there are gems to be found. The most eye-catching item on display, however, is this cast of the Allosaurus specimen "Big Al".


"Big Al" was made particularly famous by a BBC documentary that also highlighted the many injuries preserved in this specimen. Here is an infected toe, which the documentary portrayed as having ultimately led to "Big Al"'s death.


The tree of life depicted in museum specimens. It's an appealing setup, though bats are incorrectly shown as being more closely related to primates and rodents than to pangolins.


In my few years of experience, ProgPal has always been a nice, relaxed conference for early-career researchers, and this year was no exception. It's surreal to me that among the delegates of ProgPal this year, I can probably now be considered relatively far along in terms of my career progression. Several individuals I'd met at previous ProgPals have since graduated or become too entangled in the final stages of their PhD research to come. Nonetheless, there were still a fair few friends and acquaintances around for me to catch up with, and I had a good time meeting many of the new faces, some of whom recognized me from the talk I gave at TetZooCon last year!

As usual, I will list off a personal highlights reel... though to be honest, I've met enough people now to feel somewhat guilty about not including the presentations of everyone I know (even with my colleagues from the same institution already excluded a priori). I suppose it should be clear that these are the presentations I found especially interesting or outstanding, as essentially every presentation I saw at ProgPal was enjoyable.
  • Emily Brown's talk on the endocranial anatomy of Proterosuchus
  • As with PalAss last year, the foraminiferan talks were surprisingly engaging, with special mention to Caitlin Lebel and Bridget Warren's presentations
  • Alessandro Chiarenza's talk on the Late Cretaceous distribution of sauropods
  • Richie Howard's talk on a sessile Cambrian worm
As for me, I gave an updated account of my work on the phylogeny of Strisores, which I've been presenting at conferences for over a year now. I hope that by the next time I mention that research on my blog, I will have submitted it as a manuscript!

Monday, May 20, 2019

What Were Adzebills?

New Zealand is renowned for its unique avifauna, hosting many distinctive bird clades found nowhere else in the world. And prior to the settlement of New Zealand by humans 700-800 years ago, this ensemble of unusual birds would have been even more diverse than it is now. The most famous of these recently lost birds are the moa (a group of large flightless birds) and the Haast's eagle (the largest known raptorial bird) that preyed upon them.

Less well known but no less remarkable were the two species of adzebills. Named after their robust, downcurved bills, these were another group of flightless birds. Although smaller than the largest moa species, adzebills probably weighed around 15-20 kg, making them large by the standards of most birds. The chemical composition of their bones suggests that they ate small animals, which they may have dug out of the ground or decaying wood by using their strong beaks and feet.

Skeleton of a South Island adzebill from the Auckland War Memorial Museum, under CC BY 4.0.

Unlike moa, adzebills clearly weren't paleognaths (a group of birds that also includes ostriches and kiwi), but their relationships to living birds have otherwise been difficult to figure out. Their overall anatomy doesn't obviously resemble any other group of birds; however, it has long been noted that they share similarities with members of the Gruiformes, a group that includes cranes, rails, and their close relatives. An alternative idea that became particularly popular starting in the 1980s is that adzebills were instead more closely related to the kagu, an unusual flightless bird from New Caledonia.

Initially, these ideas probably wouldn't have seemed dramatically discordant, given that the kagu and its closest living relative, the sunbittern of South America, were once thought to be gruiforms. However, with the advent of molecular phylogenetics, current evidence now suggests that they are more closely related to the marine tropicbirds. (In fact, many other ground-dwelling birds, such as bustards and seriemas, were traditionally classified as gruiforms, but are no longer considered members of that group.) Thus, a close relationship with the kagu would put adzebills in a quite different part of the bird family tree compared to potential affinities among gruiforms. Furthermore, a few researchers have even entertained the possibility that adzebills were closely related to yet a different group, the galloanserans (which includes chickens and ducks).

Adzebills went extinct recently enough that some genetic material can be extracted from their remains. Since the 1990s, small snippets of adzebill DNA have been available for study, and analyses that have included these have generally supported the gruiform hypothesis, placing adzebills as close kin of cranes and rails. However, the limited amount of data has prevented a confident assessment of where adzebills belong within Gruiformes.

In a recent study, Alexander Boast and colleagues sequenced nearly complete mitochondrial genomes from the two recent adzebill species. When they analyzed these sequences alongside those of a diverse sampling of other gruiforms, they consistently found a surprising result: the closest living relatives of adzebills are the flufftails, a group of small, rail-like birds from Africa.

Phylogeny of gruiform birds plotted against divergence times estimated by Boast et al. (2019), from their study.

Boast et al. made some novel findings about the relationships among living gruiforms as well. They found that the gray-throated rail (Canirallus oculeus), long thought to be closely related to the flufftail genus Mentocrex, is in fact a true rail. Flufftails in general were formerly considered to be a type of rail, and, especially given the absence of genetic samples for some obscure rail-like birds, it is evident that teasing the two groups apart remains an ongoing process.

But at least the adzebill problem is solved, right? Well... a second study on the phylogenetic position of adzebills has come out this year, and it came to a decidedly different conclusion. For this paper, Grace Musser and Joel Cracraft assessed the likely affinities of adzebills by assembling a new dataset of anatomical features in neornithean birds.

I was quite excited about this study when I first learned of it from Musser's presentation at SVP 2017. Our current understanding of neornithean phylogeny has been greatly refined by analysis of molecular data; however, morphological phylogenetic datasets for neornitheans (i.e.: the only way we can evaluate the phylogenetic relationships of most fossil neornitheans) have remained underdeveloped by comparison. Musser and Cracraft's dataset contains information on 368 skeletal characteristics, making it larger than nearly all other available morphological datasets for neornitheans.

The one morphological phylogenetic dataset on neornitheans that is larger than Musser and Cracraft's was published in Livezey and Zusi (2006). In fact, with over 2,900 characters, it is one of the largest morphological phylogenetic datasets of any kind. Although impressive in scope, however, Livezey and Zusi's study has been criticized for containing numerous errors as well as failing to recover many clades that are otherwise well supported by both molecular and morphological studies. I thus appreciated the fact that Musser and Cracraft built much of their dataset by reassessing the characters used in Livezey and Zusi (2006), building upon that previous work while (hopefully) not repeating its mistakes.

So how do the results of Musser and Cracraft's morphological analysis compare to those of recent molecular analyses? They certainly get closer to molecular results than any previous morphological analysis on neornitheans has gotten. Like Jarvis et al. (2014) and Prum et al. (2015) (the two largest recent molecular studies on bird phylogeny), nightjars and their kin were found to be an early-diverging branch among neoavians. Musser and Cracraft's dataset also placed the sunbittern, kagu, and seriemas outside of Gruiformes. Among gruiforms, rails were mostly recovered forming a clade excluding flufftails (though the Nkulengu rail, Himantornis haematopus, was unexpectedly found closer to flufftails), with Canirallus recovered as a true rail like in Boast et al.'s study.

Nonetheless, there are some notable differences. For example, seriemas were not found as close relatives to the other telluravians included in Musser and Cracraft's dataset (in this case vultures and courols), and grebes and loons were recovered as close relatives, a historically popular idea that is now considered outdated. (The convergent diving adaptations shared between grebes and loons have long been recognized as confounding factors in morphological phylogenies of birds.) Analyzing the morphological dataset in combination with a relatively small molecular dataset put some of these relationships (e.g.: the affinities of seriemas) more in line with molecular trees, though even this wasn't enough to pull grebes and loons apart in this study.

Simplified results of the phylogenetic analyses run by Musser and Cracraft (2019) compared to those of recent molecular analyses of modern birds.

Evidently, there is still much work to be done in the field of avian morphological phylogenetics. There are several bird groups that would have been interesting to see included in this study; flamingos, pigeons, and bustards come to mind. Regardless, I consider the assembly of this dataset to be a step in the right direction and the most valuable contribution of Musser and Cracraft's paper, irrespective of what it has to say about adzebills.

Speaking of which, what does it say about adzebills? Musser and Cracraft's analyses are consistent with molecular studies in putting adzebills among gruiforms. However, their results found the closest living relatives of adzebills to be the trumpeters, a group of South American, fruit-eating gruiforms that are more closely related to cranes than to rails. The analyses identified up to 15 similarities between adzebills and trumpeters, particularly in the hip and hindlimb bones. Their results also conflicted with molecular analyses when it came to another extinct New Zealand gruiform: Hawkins's rail (Diaphorapteryx hawkinsi) was found outside of a clade including both rails and flufftails, instead of being a true rail as previous studies suggested. (Note that even though Musser and Cracraft did run a combined molecular-morphological dataset, they did not include any molecular data from adzebills or Diaphorapteryx, as they had used nuclear instead of mitochondrial genes.)

Musser and Cracraft's study was evidently submitted for publication late enough to take into account the findings of Boast et al. (2019), because they explicitly tested the possibility of Boast et al.'s results by running additional analyses in which a close relationship between adzebills and flufftails was enforced. When this was done, the resulting tree was 18 steps longer (i.e.: it implied 18 more evolutionary changes) compared to the phylogenies in which adzebills were closely related to trumpeters. Phylogenetic trees that require so many more steps to explain are often thought to be less likely in phylogenetic studies. For this reason, Musser and Cracraft considered the potential adzebill-flufftail relationship to be inconsistent with their morphological dataset.

However, given that adzebills were aberrant forms that had been isolated from their closest relatives for more than 16 million years, it wouldn't seem farfetched to me if they really had undergone so many evolutionary changes since their last common ancestor with whatever their closest living relatives turn out to be. It's not as though there aren't any anatomical similarities that might indicate an adzebill-flufftail relationship: Musser and Cracraft found 16 shared features between the two groups. Although none of these features are unique to adzebills and flufftails, the same is true of the similarities between adzebills and trumpeters.

What would be particularly helpful for resolving this conundrum would be the discovery of early members of the adzebill lineage that shed light on their ancestral anatomy. Unfortunately, the oldest known fossil adzebills were already fairly similar to recent species, and thus aren't very informative in that regard.

Phylogenetic tree of gruiforms showing the conflicting positions for adzebills found by Boast et al. (2019) and Musser and Cracraft (2019).

Whether adzebills are more closely related to flufftails or trumpeters, either option raises some interesting biogeographic implications, as they imply that the closest living relatives of adzebills are either restricted to Africa (flufftails) or South America (trumpeters). Interestingly, there are parallels for both of these cases among other New Zealand birds: it is now thought that moa were most closely related to the South American tinamous, whereas kiwi are most closely related to the Malagasy elephant birds. What happened in the distant past that led to these unusual distributions in several different groups of birds?

My best guess is that the ancestral groups that gave rise to each of these closely related pairs were once more widespread across the Southern Hemisphere but have since died out, leaving recent descendants only in geographically restricted ranges. Antarctica would be a prime suspect for the place of origin of these groups, with its complete glaciation during the Neogene being a potential cause of extinction for their ancestral populations. Boast et al. (2019) and Musser and Cracraft (2019) both entertain similar possibilities, but we don't yet have the fossils to confirm this scenario. Oh, for a productive deposit of early Paleogene bird fossils from the Southern Hemisphere!

The two recent studies on the affinities of adzebills may not exactly agree with one another, but it's exciting that we've now received two new phylogenetic datasets devoted to resolving this problem in quick succession. If nothing else, we can probably be pretty confident in identifying adzebills as gruiforms now, and we can expect that their closest living relatives are likely one of the other Southern Hemisphere gruiform groups. Furthermore, these new datasets have paved the way for future studies to build upon them (or even combine them together). I certainly foresee Musser and Cracraft's dataset playing a big role in my future research...

References

Monday, April 1, 2019

The Walking with Beasts Evolution Game

Following my withdrawal from writing fake science articles for April Fools', I've been coming up with new ways to celebrate the occasion. In the end, I think Jamie Revell of Synapsida and Meig Dickson of A Dinosaur A Day had the right idea all along: instead of writing fake content for April Fools', they blog about subjects that don't fall under the typical purview of their blogs.

In that spirit, I could write about a recent discovery about some kind of non-maniraptoran animal. There is certainly no shortage of studies I could select from, and I expect that to be the direction I take in the future. However, for this first "rebranded April Fools'" post, I have decided to take the chance to reminisce about a small piece of paleo community internet history that appears to have been largely forgotten.


Fans of Walking with Dinosaurs who explored the series website in the 2000s likely remember the Big Al Game. This game allowed players to take on the perspective of a male Allosaurus, living out its life from hatchling to adulthood. (As far as I could tell, the final, adulthood level could go on indefinitely as long as you weren't killed.) It was a text-based game with point-and-click mechanics; the player could click the arrows on a compass to decide which direction the Allosaurus would travel, and click buttons to determine how to interact with the other animals they encountered.

Unfortunately, the BBC took the Big Al game offline in 2011. Despite the straightforward premise and simple layout, it had probably provided hours of entertainment to numerous paleontology enthusiasts. It is fondly remembered by many in the online communities that I'm a part of and has been cited as a source of inspiration for the ambitious Saurian video game project. The fanmade Walking with Wiki does a decent job at describing the contents and gameplay of the Big Al Game, enough so that a game developer who had never played the original has managed to recreate it with reasonable accuracy.

Far less well known is that Walking with Beasts, the sequel series to Walking with Dinosaurs, also had an accompanying online game with a similar gameplay style, known as the Evolution Game. Unlike the Big Al Game, which played out the life of an individual animal, the Evolution Game took players over the course of primate evolution, starting out the game as the Eocene primate Teilhardina. After playing for some time, the game would do a timeskip of several million years, upon which the player would assume the perspective of a descendant primate species, with different habitats and organisms to encounter. This would occur repeatedly throughout the course of the game.

Compared to the Big Al Game, few details of the Evolution Game have been publicly documented. Among the same circles in which the Big Al Game sparks immediate recognition, I've been hard-pressed to find anyone who even remembers it existed, let alone has memories of playing it. Its Walking with Wiki article contains little information that can't be gathered by Wayback Machine. As a result, this post reflecting on what I remember about the game might be of some interest to a certain portion of the online paleo-community. However, keep in mind that this is based on memories that are over a decade old, so I can't guarantee that it is entirely accurate.

Image showing the overall layout of the Evolution Game, screencapped from Wayback Machine. The archive doesn't appear to have captured the panel below "Hear", which contained information on what your character was perceiving through their sense of smell.

Overall gameplay mechanics were similar between the Evolution Game and the Big Al Game, but there were a few logistical differences reflecting the fact that the player characters were primates instead of an Allosaurus. For one, in addition to traveling through horizontal space using compass directions, players also had the option to climb and travel through the trees. For another, plant life was given a greater focus in the Evolution Game, and players could choose to feed on the leaves and fruits they came across. On the faunal side of things, very small animals such as insects and frogs could also be "eaten", whereas larger ones could be "attacked". At least in the beginning of the game, the largest animals that the player would be capable of killing included leptictids and opossums. Some animals in the game were identified only in general terms (e.g.: "arboreal hyaenodont"), but others were identified as members of specific genera (e.g.: Arctocyon, Kopidodon).

Making this post still somewhat relevant to maniraptors is that some birds could be encountered in the game (the few I recall being Eocene species referred to as "roller-like bird" or "woodpecker-like bird"). Most of the time, they were said to have flown off before you'd even get the chance to interact with them, but they were much too agile for you to catch even on the rare occasion that you did.

One characteristic of the game that I personally found memorable (and sometimes darkly humorous) were the "game over" messages that were shown if the player character died. Whereas the game over messages of the Big Al Game tended to be straightforward and repetitive (e.g.: "You attacked the [insert animal], but it was too strong and killed you"), the Evolution Game would go to the trouble of providing a somewhat detailed description of how you died. Miacids would "pounce on you" as you "tried to grab" them. Pangolins were surprisingly dangerous and could slash you fatally with their claws. Even a Propalaeotherium was too much for your early primate to handle, as it could kick you to death with its "tiny hooflets". And if you ever made the foolish decision to mess with a Pristichampsus, its long jaws would "close on you as you became history".

When the player came across a member of the same species in the game, the conspecific could be attacked as with any other animal, but one or two additional interactive options would appear. One was along the lines of "invite to group". I never fully grasped how group living altered your gameplay, though it required you to share food with other members of your group. It may have also allowed you to kill slightly larger prey than you normally could, but I am less certain about that. Every now and then, members of your group would leave of their own volition. Another option that occasionally showed up was "mate", evidently indicating that you'd encountered a member of the opposite sex. When this option was selected, the "species population" bar on the side panel would go up.

A fossil of the pantolestan Kopidodon, photographed by "Daderot", public domain. Kopidodon was one of the animals that could be encountered in the Evolution Game, and one of many species that could easily kill your Teilhardina if provoked.

Probably the biggest difference the Evolution Game had from the Big Al Game, however, was that it was hard. The Big Al Game had its own challenges, but a few rounds of trial and error were often enough for players to become familiar with in-game hazards and come up with a working strategy to get through the game. The Evolution Game, on the other hand, was much more difficult to figure out. I personally never made it past the Miocene (I remember my character being a Proconsul at that point, though my memory of the primate species in the game is hazy).

The main issue appeared to come to down to a lack of suitable food sources available to the player. Eating most types of leaves diminished the player character's energy instead of replenishing it, probably as a way to indicate that the player could not digest them properly. More baffling was the fact that larger prey items that the player could kill had the same result (even though one would expect meat to be fairly easy to digest). As a consequence, the only viable food for the player at the beginning of the game were small prey such as insects. However, as the game continued, there would come a point where the small animals would become too agile for the player to catch (likely reflecting the larger body size of the later primates), and yet foliage remained largely indigestible. The only substantial foods at that point were fruits and palm leaves, which were few and far between, leaving the player character doomed to starvation.

The game repeatedly hinted that the player's decisions could influence their evolutionary trajectory, and during some of my playthroughs I tried to get over the starvation hurdle in a Lamarckian way by having my early primate eat a diet with a higher proportion of plant material. Although this did alter the species that I ended up evolving into, I still did not gain specializations for folivory quickly enough to avoid going hungry. On one particular occasion, I died while desperately stuffing my face with acacia leaves, as though I could suddenly gain such specializations from doing so. According to the game over message, I lost my remaining strength before I could take another bite of the leaves, and plummeted from the tree.

I never got the chance to think of a better strategy than that, as the Evolution Game went offline in 2007, several years earlier than its predecessor. Naturally, I also never found out how the game depicted the Quaternary Period, or whether the game had any "end goal". On that note, the game over screen I keep mentioning provided tantalizing clues. Following the description of the player's cause of death, it also included a long list of extant primates, with the implication that the player could potentially evolve into any of them if they'd survived to present day. Given the lack of documentation available for the game, we may never know for sure.

A variety of extant primates, composited by "Miguelrangeljr", under CC BY-SA 3.0. Possible "end points" of the Evolution Game?

Friday, February 8, 2019

Finches Before There Were Finches: Eofringillirostrum and the Diversity of Stem-Passerines

Many types of modern birds eat seeds from time to time. It's a concept so familiar to us that the idea of "bird food" is likely to conjure up imagery of seeds, and indeed seeds probably comprise the majority of food that we offer to both pet and wild birds. It has even been suggested that seed-eating helped the ancestors of modern birds survive the end-Cretaceous mass extinction. However, living on a diet composed primarily of seeds is something that only a relatively small number of bird groups do.

Many of these seed-eating birds are passerines. Though most modern birds can perch, passerines are often called "perching birds" because their feet are particularly specialized for this task. As a whole, passerines account for about 60% of modern bird diversity, but most seed-eating specialists belong specifically to a group of passerines called Passeroidea. Seed specialist passeroids include finches, sparrows, buntings, cardinals, weaverbirds, estrildids (such as the colorful Gouldian finch of Australia), some tanagers (including Darwin's "finches", which are not really finches), and more. All of these birds have heavy-duty, cone-shaped beaks that they use for cracking open seeds. It's perhaps not surprising that bites from seed-eating passeroids are among those most dreaded by bird banders.

Based on the latest estimates, seed specialist passeroids evolved fairly recently during the Miocene, roughly 15 million years ago. Thanks to a new discovery, however, we now know that other birds led similar lifestyles to finches and sparrows long before these groups had even appeared. In a new study, Daniel Ksepka and colleagues named two new species of Eocene birds that exhibit adaptations for seed eating similar to those of seed-eating passeroids.

One of these new species, Eofringillirostrum boudreauxi, came from the early Eocene Green River Formation in North America, making it about 52 million years old. It was a small bird, about the size of a red-breasted nuthatch, and is known from an excellent specimen, a nearly complete skeleton preserved with feathers. Its most notable feature, however, is its stout, cone-shaped bill, which bears a strong resemblance to that of finches.

The holotype of Eofringillirostrum boudreauxi, from Ksepka et al. (in press).

The other new species was also assigned to the genus Eofringillirostrum, and was named Eofringillirostrum parvulum. This species came from the other side of the globe, the Messel Shale in Germany (which dates to about 47 million years ago). It was even smaller than E. boudreauxi, though its head was proportionately larger. The type specimen of E. parvulum is not quite as well preserved as that of E. boudreauxi, but the finch-like skull is evident.

The Green River and Messel are two of the richest fossil sites when it comes to preserving Eocene bird fossils, and Eofringillirostrum is not the only Eocene bird genus that has been found at both localities. Some other birds that are known to have had similar distributions include the stem-roller Primobucco and the rail relative Messelornis.

The holotype of Eofringillirostrum parvulum, from Ksepka et al. (in press).

Though their similarity to finches is striking, the skull of both Eofringillirostrum species is notably different from those of finches in having a prominent projection at the back of the lower jaw. This is a feature typically found in birds that can open their jaws widely. The describers of Eofringillirostrum speculate that this ability allowed it to swallow large seeds and deposit them in its crop (a pouch for temporary food storage at the base of the throat in birds), or helped it gulp down fruits as an alternative food source.

The skull of Eofringillirostrum (B), compared to that of a speckled mousebird (A), which has a similar projection behind the lower jaw, and an American goldfinch (C), which has a similar cone-shaped bill, from Ksepka et al. (in press).

To find out how Eofringillirostrum was related to modern birds, the describers included it in a phylogenetic dataset along with many other species of telluravians, a diverse group of mainly tree-dwelling birds including passerines, parrots, birds of prey, woodpeckers, and more. When this dataset was analyzed, Eofringillirostrum turned out to be a stem-passerine. In other words, passerines as a whole are its closest living relatives, but it was not a member of the group exclusive to extant passerine lineages. It certainly was not particularly closely related to finches or any of the other seed-eating passerines today.

Furthermore, Eofringillirostrum was found to be a member of a specific group of stem-passerines, the psittacopedids. This group includes several other Eocene birds, including Psittacopes and Pumiliornis from the Messel and Morsoravis from the Fur Formation in Denmark. Psittacopedids have not always been recognized as stem-passerines, partly because they had a fourth (outermost) toe that was at least partially reversed. This feature (known as zygodactyly) is not found in modern passerines, in which only the first or innermost toe points backwards (as is typical of most modern birds). However, genetic data have consistently shown that the closest living relatives of passerines are parrots, which do have zygodactyl feet. In light of this, it is not so surprising that passerines appear to have evolved from zygodactyl ancestors.

There are other noteworthy aspects of the phylogeny recovered by this study. One of the oldest known true passerines, Wieslochia from the early Oligocene of Germany, was found to be a suboscine, one of the two main passerine lineages. This makes sense given that the other main passerine lineage, the oscines or songbirds, is thought to have been confined to Australia during the early Oligocene. In addition, the halcyornithids, a group of Eocene birds once thought to be most closely related to parrots specifically, were found to be stem-members of Psittacopasserae, the group uniting both parrots and passerines.

The results of the phylogenetic analysis run by Ksepka et al. (in press), from their study. Note that "Afroaves" should be labeled Australaves.

In fact, the phylogeny of psittacopasserans found by this study is strikingly consistent with the results of Mayr (2015), despite the latter having used a much smaller dataset. However, the analysis from the description of Eofringillirostrum still lacks a few more early telluravians that might be interesting to include (such as the possible stem-falcon Masillaraptor and the parrot-like, apparently raptorial Messelastur). I am curious to see this dataset expanded further in the future.

As far as we know, Eofringillirostrum was unique among psittacopedids for its seed-eating adaptations. Other psittacopedids had quite different skulls. Morsoravis had a generalized, thrush-like beak, suggesting a generalist diet of invertebrates and fruit. Psittacopes had a short, slightly downcurved beak, which is found in birds that mainly feed on insects but also eat seeds. Pumiliornis had a long beak and has been found with pollen as gut contents, indicating that it likely fed on nectar. It's often easy to imagine stem-groups as little more than intermediates "on their way" to becoming modern species, but Eofringillirostrum and other psittacopedids show that stem-passerines had their own independent burst of diversification, taking on ecological niches that true passerines wouldn't occupy until millions of years later.

The skulls of stem-passerines (left) compared to those of extant passerines (right) that exhibit similar adaptations, from Ksepka et al. (in press). Morsoravis (A-B) is compared to a hermit thrush (I-J), Eofringillirostrum (C-D) is compared to an American goldfinch (K-L), Pumiliornis (E-F) is compared to a black-throated sunbird (M-N), and Psittacopes (G-H) is compared to a bearded reedling (O-P).

Between Eofringillirostrum, fellow stem-passerine Zygodactylus ochlurus, the stem-hoopoe Laurillardia smoleni, the recently extinct penguin Eudyptes warhami, and the early waterfowl Conflicto, neornithine birds have so far had a strong showing among the new paleontological discoveries of this year. I can only hope that the rest of the year is just as good!

Reference: Ksepka, D.T., L. Grande, and G. Mayr. In press. Oldest finch-beaked birds reveal parallel ecological radiations in the earliest evolution of passerines. Current Biology in press. doi: 10.1016/j.cub.2018.12.040

Monday, February 4, 2019

Conflicto and the Evolution of Waterfowl

Estimating when a specific group of organisms appeared in Earth history is never a simple task. Fossils provide the most direct evidence of when specific organisms were around, but the fossil record is far from complete. As a result, we can't assume that the oldest fossils known from a given clade were the oldest members of that clade to have existed. Fossil taxa can only provide a minimum constraint, telling us that a clade must be at least of a certain age.

If the group we're interested in is still extant (or lived recently enough for genetic material to be recovered), then molecular clocks can help. Molecular clock analyses compare the differences between the molecular sequences of different organisms and use estimated mutation rates to approximate the amount of time that has passed since their lineages diverged. However, when dealing with extremely long timescales (such as tens of millions of years), we usually cannot assume that rates of genetic mutation have remained constant for all that time. As such, most divergence time studies make use of fossils to provide minimum constraints for when specific lineages must have diverged, setting calibrations for their molecular clock. For the results of these studies to be considered reliable though, the fossils used in molecular clock studies need to be well supported as members of the respective lineages they calibrate. After all, using a fossil species to calibrate the age of a certain group does little good if the species is not actually a member of that group.

Neornithine birds are one clade that has been at the center of controversies about the timing of their origin and diversification. However, one conclusion that all divergence time studies on neornithines agree on is that by the end of the Cretaceous, they had diverged into their three major lineages: paleognaths (ostriches, emus, etc.), galloanserans (land- and waterfowl), and neoavians (all other modern birds). This post will focus specifically on the origins of waterfowl.

Modern waterfowl can in turn be split into three main lineages: screamers (an unusual South American group), the magpie goose (a single extant species from Australia), and anatids (the most diverse group, including the ducks and geese we are most familiar with). Compared to other neornithines, the fossil record appears to have been kinder to waterfowl when it comes to preserving traces of their early evolutionary history. Whereas the only potential fossils of Cretaceous paleognaths, landfowl, and neoavians consist of fragmentary specimens of ambiguous affinities, several decently complete skeletons have been posited as strong evidence of waterfowl antiquity.

The phylogenetic relationships among living waterfowl.

The most famous of these ancient purported waterfowl is probably Vegavis, which lived in Antarctica at the very end of the Cretaceous. It is known from two partial skeletons (including one that preserves a syrinx, the vocal organ of modern birds). The original description of Vegavis found it to be more closely related to anatids than to the magpie goose or screamers, which would imply that waterfowl had already diverged into their three modern lineages by the end of the Cretaceous. However, this result has not been replicated by many recent analyses, with some researchers arguing that even galloanseran affinities for Vegavis are not strongly based. A few other Southern Hemisphere birds from around the Cretaceous-Paleogene (K-Pg) boundary have been suggested to be closely related to Vegavis. These include Polarornis from the Late Cretaceous of Antarctica, Neogaeornis from the Late Cretaceous of Chile, and Australornis from the Paleocene of New Zealand. This supposed close relationship has also been questioned though, and in any case these birds are known from far less complete material than Vegavis, limiting their potential in elucidating waterfowl evolution.

Anatalavis is another fossil bird that might provide evidence for an early radiation of modern waterfowl. The type species, A. rex, comes from the North American Hornerstown Formation, which appears to straddle the K-Pg boundary. A. rex is only known from incomplete arm bones, but a second species (A. oxfordi) from the early Eocene of the United Kingdom is known from a partial skeleton. The broad, flattened bill of A. oxfordi is certainly quite duck-like, and its original description suggested that it was a close relative of the magpie goose.

Then there are the presbyornithids, a group of extinct, long-legged waterfowl. Presbyornithids are best known from Paleogene fossils, but a few possible Cretaceous records have been reported, including Teviornis from the Late Cretaceous of Mongolia (known from a partial forelimb). The phylogenetic position of presbyornithids is disputed, but they are often found to be crown-waterfowl (i.e.: nested among the extant waterfowl lineages), usually as close relatives to anatids.

If all of these aforementioned ancient birds were crown-waterfowl as has been suggested, that would indicate that all three extant lineages of waterfowl originated in the Cretaceous and made it through the K-Pg extinction, along with a few extinct waterfowl groups. But were there really modern-type ducks paddling around at the same time that Tyrannosaurus rex was alive? The oldest fossils of unambiguously anatid-like waterfowl are much younger, hailing from the late Eocene, and the oldest unambiguous magpie goose fossil comes from the Oligocene. This by itself does not falsify an early origin of crown-waterfowl; after all, we are familiar with the concept that the fossil record contains many gaps. However, without a better understanding of how the ancient waterfowl relate to extant ones, it is difficult to determine when the lack of fossils reflects true absence and when we're simply looking at a missing record.

A new fossil described by Claudia Tambussi and colleagues might shed light on this question. The fossil comes from the early Paleocene of Antarctica, about 64.5 million years ago, putting it shortly after (by the standards of geologic time) the K-Pg mass extinction of 66 million years ago. Assigned to a new genus and species, Conflicto antarcticus, the specimen is extremely well preserved for a bird fossil. The bones are preserved in three dimensions (instead of being flattened) and represent much of the skeleton, including the skull and most of the major limb bones other than the feet.

The skull of Conflicto, from Tambussi et al. (in press).

Conflicto was about the same size as an extant magpie goose (and thus larger than typical ducks). Its overall anatomy, most prominently its flattened bill, makes it clear that it was a waterfowl, but which modern waterfowl was it most closely related to? To find out, its describers entered it into the phylogenetic dataset used by Worthy et al. (2017), probably the most comprehensive morphological dataset focused on galloanserans so far. When they did so, they found that Conflicto was equally closely related to all extant waterfowl; in other words, it fell outside of the group exclusive to the extant waterfowl lineages. Conflicto was a stem-waterfowl, not a crown-waterfowl.

Possibly even more interesting, however, was what happened to other early waterfowl in this analysis. Anatalavis (also included in this dataset for the first time, as far as I'm aware) was recovered not as a close relative of the magpie goose, but as another stem-waterfowl. In fact, it was found to be the closest known relative to Conflicto, though the authors of the study point out that statistical support for this result is weak. The presbyornithids (formerly recovered as crown-waterfowl by Worthy et al.) turned out to be stem-waterfowl as well. Vegavis was found to be yet another stem-waterfowl, but most curiously it was found to be a close relative of gastornithiforms, which were giant flightless galloanserans so far only known from the Cenozoic Era. It should be noted that the relationship between Vegavis and gastornithiforms is not entirely new, as it was also found by some of the analyses run by Worthy et al. In addition, it does not have strong statistical support.

In any case, the analysis including Conflicto excludes all of these ancient birds from the radiation of modern waterfowl (and that's not to mention the aforementioned skepticism of Vegavis being a galloanseran at all). Thus, they probably should not be used as calibrations for the age of modern waterfowl in future molecular clock studies. If this phylogeny is correct, we have no fossil evidence of modern-type waterfowl from before the K-Pg boundary. Modern waterfowl could well have originated later during the Paleogene, which would be consistent with their known fossil record.

The results of the phylogenetic analysis run by Tambussi et al. (in press), from their study.

In addition to the timing of waterfowl evolution, Conflicto also has implications for the evolution of notable waterfowl features. Among modern waterfowl, the screamers stand out in lacking a flattened beak (along with other strange characteristics), instead having one superficially similar to that of landfowl such as chickens. Given that the magpie goose and anatids are more closely related to each other than to screamers, it might be reasonable to assume that the characteristic flattened bill of these waterfowl originated relatively recently, after their lineage had diverged from that of screamers. However, it has long been noted that screamers have vestigial versions of the filter-feeding plates found inside the mouths of other waterfowl, raising the possibility that the ancestral waterfowl was a flat-beaked filter feeder and that these features were later lost by the screamer lineage.

Conflicto supports this second possibility. With the finding that the flat-billed Conflicto, Anatalavis, and presbyornithids might have been stem- rather than crown-waterfowl, it appears likely that all modern waterfowl (including screamers) descended from a filter-feeding bird with a duck-like bill. Furthermore, Conflicto and presbyornithids both had long hindlimbs, suggesting that this might have been another feature present on the line leading to modern waterfowl.

Skeletal of Conflicto, from Tambussi et al. (in press). Preserved bones are shown in white.

The describers of Conflicto named it for their prediction that its phylogenetic position and evolutionary implications are likely to become the subject of heated debate. They are probably correct. However, for the time being I personally find the results of this study to be very appealing in terms of its congruence with the known fossil record and previous observations regarding extant waterfowl. Let's see what the future brings.

Reference: Tambussi, C.P., F.J. Degrange, R.S. De Mendoza, E. Sferco, and S. Santillana. In press. A stem anseriform from the early Palaeocene of Antarctica provides new key evidence in the early evolution of waterfowl. Zoological Journal of the Linnean Society in press. doi: 10.1093/zoolinnean/zly085

Monday, January 21, 2019

The Raptormaniacs List of Extinct Cenozoic Birds

For almost as long as there has been an online paleontology community, there have been online Lists of Dinosaurs. An entire article could probably be written on the "List of Dinosaurs" phenomenon. To be fair, one can find taxonomic lists of nearly any sufficiently charismatic group of organisms in existence, but the dinosaur enthusiast community appears to be exceptional for the number of times it has independently compiled the "List of Dinosaurs". Examples of some that are still around include George Olshevsky's Dinosaur Genera List, Thomas Holtz's supplement to his dinosaur encyclopedia (last updated in early 2012), and The Compact Thescelosaurus (successor to Thescelosaurus.com). Of course, these lists don't include every dinosaur. They generally only cover non-avialan dinosaurs or, at most, Mesozoic dinosaurs.

A few months after I started this blog in 2010, I wanted in on the fun. I wasn't quite as ambitious as try and make my own version of the List of Every Mesozoic Dinosaur, but I did want to make a list of Mesozoic maniraptors. With all the Lists of Dinosaurs that were already in existence for me to reference, it didn't take long for me to set one up. My list likely doesn't do anything that the other Lists of Dinosaurs don't. It's written for most part in very non-technical language and doesn't cite any technical sources. Its main function over the years has probably been to help myself keep track of Mesozoic maniraptors more than anything else.

However, I am not only interested in Mesozoic maniraptors. Ever since its inception, the heading to my list included the sentence: "I hope to include the Cenozoic taxa someday, but for now I'm focusing on the Mesozoic ones." A comprehensive, up to date list of extinct Cenozoic birds remained an empty niche, but that also made starting one up at all much more challenging. Even Wikipedia doesn't have articles on all Cenozoic extinct birds at the time of writing.

Well, I have now taken the plunge. I have started a separate page on the blog where I've compiled a list of Cenozoic birds.

Before anyone gets too excited, I'd like to make clear that my list does not completely fill the void that is there. At present, the list only includes entirely extinct bird genera, so it does not include extinct species that are classified in the same genera as still-living species. It is possible that I will change that one day. (Will it take another eight years? We'll find out.)

It is very unlikely though that I will ever compile my own list of bird genera known only from extant members. This is due to the immense amount of work that would be required, as well as the fact that several lists of extant birds already exist (a couple of my favorite examples being Taxonomy in Flux and the IOC World Bird List). I suppose if Mesozoic dinosaur fans and Cenozoic dinosaur fans have anything in common beyond liking dinosaurs, it's an inordinate fondness for lists!

My Cenozoic extinct bird list is written in the same non-technical style as my Mesozoic maniraptor list. However, I did have to consult numerous technical publications to compile it. I'd like to highlight in particular Gerald Mayr's Avian Evolution and Paleogene Fossil Birds, Jirí Mlíkovsky's Cenozoic Birds of the World (yes, I am aware of the caveats associated with this work), and Pierce Brodkorb's Catalogue of Fossil Birds. If it weren't for these books, my task would likely have been almost impossible to complete. Some other (less technical) sources of importance were Julian Hume's Extinct Birds and Meig Dickson's A Dinosaur A Day (which, given its coverage of extant birds, is almost certainly the most ambitious List of Dinosaurs of all!).

Given the state of affairs, I would be surprised if I really had managed to include every extinct Cenozoic bird taxon on my first try, so if you spot any errors or omissions, please leave a comment! Keep in mind though that I have excluded certain taxa if they are now considered congeneric with extant taxa or if their genus name is preoccupied and a replacement name has not yet been coined.

Wednesday, January 9, 2019

New (Extinct) Maniraptors of 2018

Now that I can no longer host polls on Blogger, I need a new way to acknowledge the new names in maniraptor paleontology every year (beyond mentioning them in passing during the year end reviews). Why not make myself write a paragraph about each one?

After some thought, I have decided to discuss the new taxa in alphabetical order. That was the way they were listed on the polls, after all. As a bonus, I will now also cover new species of previously-named genera, whereas the polls were focused only on newly-named genera.

Anomalipes zhaoi Yu et al., 2018 (new genus and species)
Meaning of name: Zhao's unusual foot
Location: Wangshi Group, China
Age: Late Cretaceous (Campanian?)

Oviraptorosaurs have generally had a strong showing when it comes to new species lately, often getting two or more new taxa per year, dazzling with spectacularly-preserved holotypes, or both. However, last year gave us just one new species and, truth be told, it's not particularly exciting. Anomalipes is known only from a partial hindlimb. Its describers estimate it to have weighed slightly less than 50 kg, making it larger than average for an oviraptorosaur, but still far from being one of the largest. It was recovered as a caenagnathid in its original description, a result that has been independently corroborated by Andrea Cau.

Archaeopteryx albersdoerferi Kundrát et al., 2018 (new species)
Meaning of name: Albersdörfer's ancient wing
Location: Mörnsheim Formation, Germany
Age: Late Jurassic (Tithonian)

A number of species of Archaeopteryx have been named over the years, but only the type species A. lithographica and sometimes A. siemensii are widely considered to be valid in recent literature. Last year threw a new species into the running. The holotype of A. albersdoerferi has been known to science since the 1990s, nicknamed the eighth or Daiting specimen of Archaeopteryx. However, it had been held in a private collection and was thus unavailable to scientific research until 2009. It comes from slightly younger deposits than the Solnhofen Formation, where the other known specimens of Archaeopteryx were found. Despite being one of the smallest known Archaeopteryx specimens and a late juvenile based on bone histology, the holotype exhibits fusion between some bones of the skull and between the wrist and palm bones, features that aren't seen in other Archaeopteryx specimens. The authors interpret these characteristics as indicators that A. albersdoerferi was more specialized for flight than other Archaeopteryx species.

Ardenna davealleni Tennyson and Mannering, 2018 (new species)
Meaning of name: Dave Allen's shearwater
Location: Ohawe Beach and Waihi Beach, New Zealand
Age: Pliocene (Piacenzian)

The tube-nosed, seafaring petrels are most diverse in the Southern Hemisphere today, but their fossil record in the south is surprisingly scant. The two partial skeletons that have been found of A. davealleni help fill in that void, showing that shearwaters were already present in New Zealand during the Pliocene. A. davealleni is one of the largest shearwaters (comparable to the largest extant species). Anatomically, it resembles the smaller Buller's shearwater, suggesting that it was similarly more specialized for soaring than for underwater flight.

Bannykus wulatensis Xu et al., 2018 (new genus and species)
Meaning of name: Half claw from Wulatehouqi
Location: Bayin-Gobi Formation, China
Age: Early Cretaceous (Aptian)

Bannykus bridges an important gap in our understanding of alvarezsaur evolution, which clearly makes it the most important paleontological discovery in recent history. Not only is it one of the first Early Cretaceous alvarezsaurs to be described, its hands exhibit an intermediate morphology between "typical" theropod hands and the very specialized forelimbs of alvarezsaurids. If I still ran those favorite maniraptor polls, it would be my pick for the best new maniraptor of 2018. I wrote about Bannykus in more detail in a previous blog post.

Skeletal and select elements of Bannykus, from Xu et al. (2018). Preserved bones are shown in gray on the skeletal.

Caihong juji Hu et al., 2018 (new genus and species)
Meaning of name: Big-crested rainbow
Location: Tiaojishan Formation, China
Age: Late Jurassic (Oxfordian)

2018 added another new entry to the persistently increasing list of Anchiornis-like paravians from the Late Jurassic of China. However, the holotype of Caihong is quite spectacular even for a Tiaojishan fossil. It preserves feathers going all the way down to its toes (similar to Anchiornis and Serikornis) and very long tail feathers relative to its body size. Furthermore, analysis of its melanosomes indicates that it had iridescent feathers, especially on its head, neck, and chest. Though not the first Mesozoic maniraptor found to have had iridescent feathers (that honor goes to Microraptor), it is the first known to have the specialized, flattened melanosomes found in some iridescent modern birds. The describers of Caihong also suggest that it had bony crests in front of its eyes, a rarity in paravian theropods. However, some have expressed skepticism of this interpretation, noting that the "crests" might be sideways projections that support a soft tissue brow ridge, which are commonly found in diapsids.

Holotype of Caihong, from Hu et al. (2018).

Chenoanas asiatica Zelenkov et al., 2018 (new species)
Meaning of name: Asiatic duck [named after two extant duck genera, Chenonetta and Anas]
Location: Ööshin Formation, Mongolia and Tunggur Formation, China
Age: Miocene (Serravallian-Tortonian)

Waterfowl appear to have diversified greatly during the Miocene, and last year's findings regarding the genus Chenoanas provided further evidence of that. The recognition of C. asiatica adds a second species of Chenoanas to the Miocene of Central Asia, in addition to the type species C. deserta. The two species differ in details of their humerus (upper arm bone) morphology. The describers of C. asiatica also reassign "Anas" sansaniensis from the Miocene of France and Russia as a third species of Chenoanas, suggesting that this early duck was very geographically widespread. Unlike several other ducks that have been found in the Ööshin Formation, Chenoanas appears to have been more of a dabbler than a diver in its foraging habits.

Cinclosoma elachum Nguyen et al., 2018 (new species)
Meaning of name: Little thrush body
Location: Riversleigh, Australia
Age: Miocene (Burdigalian)

Quail-thrushes are a group of largely terrestrial Australasian passerines. Males are often strikingly colored. Despite their name, they are more closely related to crows than to thrushes. C. elachum is known from various limb bones and represents the oldest known fossil of a quail-thrush. It was smaller than extant quail-thrushes and appears to have lived in a forested environment, supporting previous suggestions that quail-thrushes (which generally live in more open habitats today) had forest-dwelling ancestors.

Ducula tihonireasini Rigal et al., 2018 (new species)
Meaning of name: Tihoni Reasin's imperial pigeon
Location: Gambier Group, French Polynesia (Taravai Island)
Age: Holocene (Meghalayan)

Those who learn of the genus Ducula for the first time are often disappointed to find that the name does not belong to a blood-drinking duck. (Is it strange that I've seen enough people react to the name to be able to comment on how often a specific reaction occurs?) However, the imperial pigeons that actually bear the name are impressive in their own right. These large, tree-dwelling pigeons fly for long distances in search of fruit, making them important seed dispersers in their ecosystems. They are likely responsible for the distribution of many plants on Southeast Asian and Oceanian islands. Large even for an imperial pigeon (though not the largest known species), D. tihonireasini adds further evidence that large body size evolved several times in Ducula. D. tihonireasini may have survived into historic times, given that some 19th Century reports might refer to it.

Eogranivora edentulata Zheng et al., 2018 (new genus and species)
Meaning of name: Toothless early seed-eater
Location: Yixian Formation, China
Age: Early Cretaceous (Barremian-Aptian)

Originally mistaken for a specimen of Hongshanornis, the holotype of Eogranivora turned out to be quite a different theropod with its lack of teeth and stocky hindlimbs. It represents the earliest known euornithine preserved with direct evidence of seed-eating. I wrote about Eogranivora in more detail in a previous blog post.

Holotype of Eogranivora, from Zheng et al., (2018).

Gettyia gloriae (Varricchio and Chiappe, 1995), revised by Atterholt et al., 2018 (new genus)
Meaning of name: Named after Gloria Siebrecht and Mike Getty
Location: Two Medicine Formation, U.S.A.
Age: Late Cretaceous (Campanian)

Previously considered a species of Avisaurus, Gettyia was given its own genus when it was found to be more closely related to the newly-described Mirarce (covered below) than to the type species of Avisaurus (A. archibaldi). Gettyia appears to have been much smaller than the eagle-sized Avisaurus, measuring less than half its size in linear measurements, though both taxa are known only from feet.

Jinguofortis perplexus Wang et al., 2018 (new genus and species)
Meaning of name: Perplexing brave female warrior
Location: Dabeigou Formation, China
Age: Early Cretaceous (Barremian)

Jinguofortis adds to the ever-growing aviary of the Jehol Biota. It had several features indicative of refined flapping ability, including a reduced third finger, a curved third metacarpal (palm bone), and a well-developed ridge on the humerus. The wing feathers of the holotype are well preserved and suggest that it was capable of maneuverable flight. However, it also had characteristics more typical of non-avialan theropods, such as fusion between the scapula and coracoid bones in the shoulder girdle. The phylogenetic analysis in its original description found Jinguofortis to be a close relative of Chongmingia, an enigmatic avialan known from less complete remains. The clade uniting the two (Jinguofortisidae) was in turn found to be fairly closely related to ornithothoracines (enantiornithines and euornithines).

Holotype of Jinguofortis, from Wang et al. (2018).

Kischinskinia scandens Volkova and Zelenkov, 2018 (new genus and species)
Meaning of name: Climbing, named after A. A. Kishchinsky
Location: Olkhon Island, Russia
Age: Miocene (Burdigalian-Langhian)

Despite accounting for about 60% of living bird diversity, passerines are poorly known in the fossil record. As such, we have little fossil evidence of their presumably dramatic evolutionary diversification. Kischinskinia is thus significant in being the oldest known oscine passerine (songbird) from Asia. It is only known from partial hindlimb bones, but enough has been found to suggest that it was a certhioid songbird, making it a close relative of nuthaches, treecreepers, and wrens. Like many living certhioids, it likely foraged by creeping along vertical surfaces. Its early Miocene age is consistent with some recent molecular clock estimates for the divergence times of major songbird lineages and their dispersal out of Australia.

Litorallus livezeyi Mather et al., 2018 (new genus and species)
Meaning of name: Livezey's shore rail
Location: Bannockburn Formation, New Zealand
Age: Miocene (Burdigalian)

Rails are well known (at least in the ornithological community) for their ability to colonize remote islands and tendency to evolve flightlessness. Holocene rails alone are known to have evolved flightlessness over thirty different times. Litorallus (along with Priscaweka, discussed below) shows that this phenomenon has been occurring as far back as the Miocene. This is evidenced by the fact that its lower arm was less than 30% the length of its shin, whereas this value ranges 45-65% in extant flying rails.

Mirarce eatoni Atterholt et al., 2018 (new genus and species)
Meaning of name: Eaton's wonderful winged messenger [named after Arce, winged messenger of the Titans in Greek mythology]
Location: Kaiparowits Formation, U.S.A.
Age: Late Cretaceous (Campanian)

Enantiornithines ("opposite birds") were not recognized as a group until the 1980s, but have since turned out to have been the most diverse lineage of avialans during the Mesozoic. Numerous complete specimens of enantiornithines are now known, the majority coming from the Early Cretaceous Jehol Biota in China. Although these fossils often include stunning preservation of soft tissues such as feathers, they also tend to be preserved as flat slabs, obscuring details of skeletal anatomy. The holotype of Mirarce, on the other hand, is known from bones preserved in three dimensions, and it is the most completely known North American enantiornithine to boot. It appears to have been a close relative of Gettyia (discussed above) and Avisaurus, potentially shedding light on the anatomy of these taxa (which are only known from feet). Mirarce was convergent on modern birds in that it had a narrow wishbone and a deep keel on the breastbone, providing further evidence for parallel evolution of refined flight abilities in avialans. It is also the first enantiornithine found with quill knobs, bony attachment points for wing feathers on the lower arm. Though large for an enantiornithine, Mirarce was not quite as big as Avisaurus.

Skeletal of Mirarce, from Atterholt et al. (2018). Preserved elements are shown in white. Scott Hartman, the illustrator of the skeletal, has noted that the (unknown) skull was depicted as toothless because the describers of Mirarce speculate that toothlessness was common in Late Cretaceous enantiornithines. Personally, I don't think we have enough information to draw that inference.

Muriwaimanu tuatahi (Jones et al. in Slack et al., 2006), revised by Mayr et al., 2018 (new genus)
Meaning of name: First after Waimanu
Location: Waipara Greensand, New Zealand
Age: Paleocene (Selandian)

Muriwaimanu was originally described as a second species of Waimanu, but a study last year noted that a sister group relationship between the two is not strongly supported and gave it its own genus. Only slightly younger than W. manneringi (the type species of Waimanu) in terms of geologic age, Muriwaimanu is among the oldest stem-penguins. Several partial skeletons of this early waterbird have been described, making it one of the most completely known Paleocene penguins.

Orienantius ritteri Li et al., 2018 (new genus and species)
Meaning of name: Ritter's dawn enantiornithine
Location: Huajiying Formation, China
Age: Early Cretaceous (Hauterivian)

Orienantius is the latest in a long list of enantiornithines that have been described from the Jehol Biota (as mentioned under the entry for Mirarce), but the two known specimens are spectacular even for Jehol fossils. They preserve not only feathers, but also the skin membranes surrounding the wings, muscles on the hindlimbs, and pads on the bottoms of their toes. Its wing anatomy suggests that it alternated between flapping and gliding in flight like many small birds today, and was capable of flying with great agility to navigate its forest enivironment.

Holotype of Orienantius, from Li et al. (2018).

Pandion pannonicus Kessler, 2018 (new species)
Meaning of name: From Pannonia, named after Pandion II of Greek mythology
Location: Máriahalom, Hungary
Age: Oligocene (Chattian)

This is one of the oldest known osprey species; the only records that are older come from the early Oligocene of Egypt. P. pannonicus is only known from a claw, but osprey claws are very distinctive. It was smaller than other known ospreys, including the extant species.

Panraogallus hezhengensis Li et al., 2018 (new genus and species)
Meaning of name: Coiling chicken from Hezheng
Location: Liushu Formation, China
Age: Miocene (Tortonian)

This pheasant is known from a well-preserved, nearly complete skeleton. That on its own is a rarity for bird fossils and would have made it a notable discovery. However, its main claim to fame is that it preserves a very elongate windpipe (likely longer than its own body) that would have been coiled up in its chest cavity in life. This unusual feature is also known to have independently evolved in some extant galliforms (including some curassows, guineafowl, and grouse) as well as other birds such as cranes. These birds use their elongate windpipes to produce particularly loud or low-frequency calls, suggesting that Panraogallus did the same.

Holotype of Panraogallus, from Li et al. (2018).

Priscaweka parvales Mather et al., 2018 (new genus and species)
Meaning of name: Small-winged ancient weka
Location: Bannockburn Formation, New Zealand
Age: Miocene (Burdigalian)

Priscaweka was a second flightless rail that lived alongside Litorallus (discussed above). It was smaller (about the size of the recently extinct Chatham rail) and apparently more abundant than Litorallus. Specimens of Priscaweka appear to come in two clusters of size ranges, suggesting sexual dimorphism. If so, it appears that males of this taxon were slightly larger than females, similar to most extant rails.

Proardea(?) deschutteri Mayr et al., 2018 (new species)
Meaning of name: De Schutter's before Ardea
Location: Borgloon Formation, Belgium
Age: Oligocene (Rupelian)

P. deschutteri is only known from a partial foot, but it is notable in that it's one of the earliest known herons. It was a small heron, about the same size as the squacco heron. Its describers note that its assignment to Proardea is tentative.

Qiupanykus zhangi Lü et al., 2018 (new genus and species)
Meaning of name: Zhang's Qiupa claw
Location: Qiupa Formation, China
Age: Late Cretaceous (Maastrichtian?)

2018 was a good year for alvarezsaurs, seeing the description of three new species. Qiupanykus is known from a poorly-preserved partial skeleton that seems pretty anatomically standard for an alvarezsaurid, but it did receive some press for the suggestion that it provided evidence for egg-eating in alvarezsaurs. This would have made it significant for understanding alvarezsaurid paleobiology if true, but unfortunately the evidence is extremely unconvincing (as also noted by Andrea Cau), consisting entirely of the fact that an oviraptorosaur eggshell fragment was preserved near the holotype. That is flimsier reasoning than the assumption that the holotype of Oviraptor was preserved in the middle of raiding a nest; it's at least likely that Oviraptor was interacting with the eggs it was preserved with before it died! Tragically, Qiupanykus was to my knowledge the last maniraptor that Junchang Lü (known for his research on oviraptorosaurs and pterosaurs) described as first author prior to his untimely passing in October 2018.

Rallus gracilipes Takano and Steadman, 2018 (new species)
Meaning of name: Slender-footed rail
Location: Sawmill Sink, the Bahamas (Great Abaco Island)
Age: Pleistocene (Late Pleistocene)

R. gracilipes was another flightless rail species described in 2018, but as a Pleistocene bird it was much younger than Litorallus and Priscaweka (both discussed above). It is known from bones of both the front and hind limbs, and so far is not known to have survived into the Holocene.

Romainvillia kazakhstanensis Zelenkov, 2018 (new species)
Meaning of name: From Kazakhstan, named after Romainville
Location: Kustovskaya Formation, Kazakhstan
Age: Eocene (Priabonian)

Romainvillia is one of the oldest known anseriforms that was likely closely related to anatids (true ducks and geese). Previously known from the Eocene-Oligocene of Europe, R. kazakhstanensis (known from a coracoid) shows that its range extended into Asia as well.

Sequiwaimanu rosieae Mayr et al., 2018 (new genus and species)
Meaning of name: Rosie's following Waimanu
Location: Waipara Greensand, New Zealand
Age: Paleocene (Selandian)

Sequiwaimanu was slightly younger than Muriwaimanu and Waimanu and may have been slightly more closely related to modern penguins, but it is still one of the oldest known stem-penguins. Perhaps more notably, the holotype is the most complete and best-preserved single specimen of any Paleocene penguin found; only its foot remains largely unknown. Like Muriwaimanu, Sequiwaimanu had a spear-like beak and less stiffened flippers compared to extant penguins.

Skull of Sequiwaimanu, from Mayr et al. (2018).

Vanellus liffyae De Pietri et al., 2018 (new species)
Meaning of name: Liffy's lapwing
Location: Tirari Formation, Australia
Age: Pliocene (Piacenzian)

Lapwings are a group of often boldly-colored plovers known for fiercely defending their nests. Facilitating this behavior are the large spurs found on the wrists of many species, including the two that live in Australia today, the banded and masked lapwings. Known from a coracoid, V. liffyae was likely a close relative of these two species, showing that this group of lapwings had colonized Australia by the late Pliocene.

Vorombe titan (Andrews, 1894), revised by Hansford and Turvey, 2018 (new genus)
Meaning of name: Giant big bird
Location: Itampolo, Madagascar
Age: Pleistocene-Holocene (Late Pleistocene-Meghalayan)

The taxonomy of the recently extinct elephant birds from Madagascar have long been controversial. A study last year used a morphometric approach to identify distinct elephant bird species and concluded that only four species were valid: Aepyornis maximus, Aepyornis hildebrandti, Mullerornis modestus, and "Aepyornis" titan (long lumped into A. maximus). The authors consider "A." titan to be distinct enough from Aepyornis to warrant a new genus, Vorombe. Vorombe was the largest elephant bird; the biggest specimens included in the study were estimated at body masses of over 730 kg. An incomplete femur hints that it may have gotten even larger (up to 860 kg). This would make Vorombe the largest paravian known and comparable in size to the smallest adult sauropods (such as Magyarosaurus). Imagine that: the largest known paravian was a recently extinct neornithine bird, a group of theropods notable for their trend in decreasing body size throughout their evolutionary history.

Winnicavis gorskii Bochenski et al., 2018 (new genus and species)
Meaning of name: Górski's Winnica bird
Location: Menilite Formation, Poland
Age: Oligocene (Rupelian)

Another addition to the scant fossil record of passerines, Winnicavis was a small bird (about the size of a great tit) known from articulated wing and leg bones. Several other early passerines have been previously described from the early Oligocene of Europe, but determining their relationships to living passerine groups has proven challenging.

Xiyunykus pengi Xu et al., 2018 (new genus and species)
Meaning of name: Peng's western region claw
Location: Tugulu Group, China
Age: Early Cretaceous (Barremian-Aptian)

The third new alvarezsaur of 2018, Xiyunykus sheds light on the previously unknown Early Cretaceous history of alvarezsaurs along with Bannykus. Unfortunately, a complete forelimb is not known, but what is preserved shows that it likely had an intermediate morphology between Bannykus and "typical" theropods. I wrote about Xiyunykus in more detail in a previous blog post.

Yangavis confucii Wang and Zhou, 2018 (new genus and species)
Meaning of name: Confucius [and] Yang's bird
Location: Jiufotang or Yixian Formation, China
Age: Early Cretaceous (Barremian-Aptian)

Another new species from the Jehol Biota, this confuciusornithiform is known from a nearly complete skeleton, but this time not preserved with any feathers. Yangavis had relatively longer forelimbs and an unreduced claw on the second finger compared to other confuciusornithiforms, though the functional significance of these features has not been rigorously assessed.

Zygodactylus grandei Smith et al., 2018 (new species)
Meaning of name: Grande's paired toes
Location: Green River Formation, U.S.A.
Age: Eocene (Ypresian)

Zygodactylids were a group of small birds from the Eocene-Miocene of Europe and North America. Some authors considered them close relatives of woodpeckers due to their zygodactyl feet (with the first and fourth toes both pointing backward), but more recent studies favor a closer relationship with passerines, which makes sense in light of the fact that molecular evidence indicates that the closest living relatives of passerines are the also zygodactyl parrots. Known from a well-preserved skeleton, Z. grandei is the oldest known species of Zygodactylus and the first to be described from North America. The phylogenetic analysis in its description finds it to be a close relative of Eozygodactylus. Though the authors refrain from making major taxonomic changes to zygodactylids, this opens up the possibility that Eozygodactylus will be considered a species of Zygodactylus in future revisions. Coincidentally, the first new dinosaur of 2019 appears to be another new species of Zygodactylus.

Holotype of Z. grandei, from Smith et al. (2018).

Writing this post turned out to be moderately time consuming, so let me know if you'd be interested in seeing posts like this one in future years. I do have ideas to help reduce the workload should I make it a new annual tradition.