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: 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.

Tuesday, January 1, 2019

Review of 2018

I made fewer than 20 posts on this blog last year, a foreseeable consequence of continuing work on my PhD. However, I'd like to draw attention to the fact that I wrote at least one post for every month of the year, a first in the history of Raptormaniacs! These posts included summaries of recent scientific discoveries about maniraptors (some of which have ended up being among the most popular posts on this blog) as well as the usual conference and trip reports. Last year, I attended ProgPal, IPC, SVP, and PalAss, presenting my ongoing research at each one. A personal highlight of 2018 was the fact that I got to speak at TetZooCon. I also enjoyed visiting Dinosaurs in the Wild and the French National Museum of Natural History.

I said last year that I would at least try to update the Raptormaniacs askblog more often in 2018, which... uh, didn't happen. This was, in part, the fault of Tumblr for flagging the askblog as explicit without notifying me, but I didn't exactly follow through once the issue had been cleared up either. Mark my words though: as long as nothing happens to me, there will eventually be a proper conclusion to the Raptormaniacs comic. It might take months or (more realistically?) years before I get to work on it, but it will be done. I am all too familiar with the frustration of following an enjoyable web series that fades away without notice to let that be the eternal fate of one of my own major works.

Speaking of how web series end, last year my friend Joan Turmelle and I made the difficult decision to officially cancel one of our longstanding and very popular collaborations, the webcomic TetZoo Time. However, in its place we have started a new paleontology-themed comic, Chile & Yi, which can be followed on DeviantArt and Tumblr. I consider Chile & Yi in some ways to be a spiritual successor to both TetZoo Time and Raptormaniacs, so if anyone is somehow starved for the very niche genre of "paleontology webcomics I am involved with", I encourage them to check it out.

The first comic we made for Chile & Yi.

I made a few significant changes to this blog proper as well, namely retiring two of my few annual Raptormaniacs traditions: the April Fools' posts (by choice) and the favorite new maniraptor polls (by necessity). Dispensing with the April Fools' posts in particular was another tough choice to make and I share the disappointment that some of my friends and readers have expressed in response, but I do think it was the right decision in the end. I have been considering alternative ways of celebrating the occasion in coming years though, so stay tuned! On the whole, it can be said that 2018 was a time of change for Raptormaniacs, despite the reduced posting frequency.

National Geographic called 2018 the Year of the Bird, and as usual scientific advances in our understanding of maniraptors continued unabated. In January, the structure of super-black bird-of-paradise feathers was described. Emperor penguins were reported feeding at night during breeding period. Structures in the lower jaw of caenagnathids were interpreted as vestigial tooth sockets. Stress in female yellow-legged gulls was found to prime their young for quicker antipredator behavior. Alarm calls were shown to evoke a visual search image for predators in Japanese tits. A new specimen of Archaeopteryx and an amber-trapped juvenile enantiornithine were described. New studies came out on the morphometrics of hesperornithines in comparison to extant diving birds, the kinematics of avian take-off, variation in growth patterns of basal paravians, the evolution of song in ovenbirds, the development of flight feathers, the diversification of fluvicoline flycatchers, the benefits of tool use in New Caledonian crows, the anatomy of finger joints in ostriches, and the importance of spatial memory for long-billed hermits. Newly-named maniraptors included the anchiornithid Caihong juji, the Miocene passerine Kischinskinia scandens, and the Cretaceous euornithine Eogranivora edentulata.

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

In February, a three-legged African penguin was reported. Tau accumulations (usually indicative of brain damage in humans) were documented in woodpeckers. New specimens of Anchiornis were described. Cognitive performance was shown to be linked to group size in Australian magpies. The ecology of New Zealand birds was inferred from coprolites. Yellow-billed oxpeckers were observed roosting on their mammalian hosts. It was argued that pelvic morphology prevented most Mesozoic avialans from sitting directly on their eggs. New studies came out on the adjustment of heart rate and body temperature in greylag geese, maneuverability in hummingbirds, thermoregulation in parrots, the distribution of medullary bone in birds, mimicry of hairy woodpeckers by downy woodpeckers, the evolution of drumming in woodpeckers, the biomechanics of terrestrial locomotion in birds, the taxonomic composition of vegaviids, the flight style of Concornis and Eoalulavis, the correlation between curvature and keratin sheath extent in beaks, the phylogenetic position of the Cuban macaw, and phalangeal joint kinematics of ostriches running on sand. Newly-named maniraptors included the Paleocene penguins Sequiwaimanu rosieae and Muriwaimanu tuatahi (formerly a species of Waimanu), the Miocene rails Litorallus livezeyi and Priscaweka parvales, the Miocene duck Chenoanas asiatica, and the southern dark newtonia (Newtonia lavarambo).

Downy woodpecker, photographed by Wolfgang Wander, under CC BY-SA 3.0.

In March, evidence of salt glands was reported in Iteravis. Black jacobins were found to vocalize above the known hearing range of birds. Genomic evidence of speciation reversal was documented in common ravens. A juvenile enantiornithine specimen was described. The diet of Mesozoic avialans was reviewed. Wing bone geometry in Archaeopteryx was put forth as evidence that it performed powered flight. The white-chested tinkerbird was shown to have been based on an individual of the yellow‐rumped tinkerbird. New studies came out on variation in avian egg shape and nest structure, the phylogeny of tytonid owls, call recognition in common cuckoos, the postcranial skeletal anatomy of Buitreraptor, cognitive deficiencies in hybrid chickadees, and the nanostructure of the avian eggshell. Newly-named maniraptors included the alvarezsaur Qiupanykus zhangi, the oviraptorosaur Anomalipes zhaoi, and the Oligocene heron Proardea deschutteri.

The skull of Iteravis, with a close-up highlighting the depressions that would have made space for salt glands, from Wang et al. (2018).

In April, the courtship display of the Vogelkop superb bird-of-paradise was released on film for the first time. The cranial anatomy of Confuciusornis was reevaluated. Teeth were found to represent a negligible proportion of body mass in avialans. Multiple parallel deinonychosaur trackways from the Tianjialou Formation and a new specimen of Citipati were described. Cowbird eggshells were shown to be more resistant to cracking than those of their hosts. Moa were discovered to not have dispersed large seeds. Madrynornis was redescribed. New studies came out on color polymorphism in owls, the phylogeny of neoavians, drivers of dwarfism in emus, the diversification of ovenbirds, the evolution of display complexity in birds-of-paradise, the benefits of high-speed stooping in peregrine falcons, the courtship display of Costa's hummingbirds, host suitability for common cuckoos, the morphometrics of accipitrid skull shape, the feeding mechanics of paravians (and other theropods), and the genome of the common loon. Newly-named maniraptors included the Pleistocene rail Rallus gracilipes.

The courtship display of the greater superb bird-of-paradise (A) compared to that of the Vogelkop superb bird-of-paradise (B), from Scholes and Laman (2018).

In May, deforestation was suggested to have contributed to differential survival in avialans during the K-Pg. A complete skull of Ichthyornis was described. Caller characteristics were found to influence recruitment to jackdaw mobs. Oviraptorosaurs were shown to have constructed their nests so that they could brood their eggs without crushing them. Incipient speciation and bony head protrusions in birds were reviewed. Hulsanpes was redescribed. The taxonomy of confuciusornithiforms was revised. New studies came out on migration to molting grounds in North American birds, the evolutionary assembly of the avian body plan, the biogeographic origins of Darwin's finches, the evolution of nesting characteristics in birds, visual fields in raptorial birds, the scaling of avian bipedal locomotion, feather development in ducks, skin ultrastructure of maniraptors, and the correlation between drumming behavior and genes that encode calcium-handling proteins in woodpeckers. Newly-named maniraptors included the Pliocene plover Vanellus liffyae and the Miocene galliform Panraogallus hezhengensis. The Ascent of Birds by John Reilly was published and my review of it can be found here.

Reconstructed skull of Ichthyornis, from Field et al. (2018).

In June, the evolution of tongue mobility in avialans (and other ornithodirans) was investigated. Cultural evolution in birds was reviewed. Age at fledging is found to be a cause and consequence of predation risk in passerines. Great tits were shown to have a high level of self control. New studies came out on high altitude colonization in ruddy ducks, nestling recognition in large-billed gerygones, genomic differentiation between northern flicker taxa, the taphonomy of submerged avian carcasses, the phylogeny of Antilophia and Chiroxiphia manakins, the ontogeny of the avian tail, the cranial morphology of Sinovenator, the evolution of vocal mimicry in songbirds, the phylogenetic position of Foro, and cultural transmission in New Caledonian crows. Newly-named maniraptors included the zygodactylid Zygodactylus grandei, the western square-tailed drongo (Dicrurus occidentalis), and the Whenua Hou diving petrel (Pelecanoides whenuahouensis).

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

In July, the spectacled cormorant was shown to have formerly lived in Japan. Coordinated misdirection was reported to be a widespread anti-predator behavior in Neotropical birds. Preserved eggshell cuticle in Cretaceous maniraptors was examined. Tactile interactions between American crows and dead conspecifics were documented. The development of avian digits was reviewed. New studies came out on the structure of parrot brains, egg size in Oriental cuckoos, aggressive interactions between crows and ravens, the phylogeny of Chaetura swifts, the agility of running birds, the visual displays of Costa's hummingbirds, the morphology of avian maxillae, the forelimb musculature of African gray parrots, the middle ear vasculature of passerines, the relationship between avian egg shape and rolling dynamics, the dynamics of take-off and landing in diamond doves, and the basicranial soft tissues of Nothronychus. Newly-named maniraptors included the Miocene passerine Cinclosoma elachum and the Oligocene osprey Pandion pannonicus.

Schematic of coordinated misdirection performed by a pair of yellow-throated euphonias, showing the female discreetly entering their nest as the male continues to fly onward, diverting the attention of observers away from the location of the nest, from Gulson-Castillo et al. (2018).

In August, the genome of the ʻalalā was assembled. Categorical perception of color was reported in zebra finches. Economic decision-making was found in parrots. New studies came out on heterospecific alarm call recognition in superb fairy-wrens, signatures of human commensalism in the house sparrow genome, the endocranial anatomy of oviraptorosaurs, the evolution of egg shape in birds, swimming kinematics in common loons, the incubation period of troodonts, facial display in blue-and-yellow macaws, the development of pelagornithid pseudoteeth, long-range dispersal in tawaki, color vision in Harris's hawks, and colonization of habitat patches by willow warblers. Newly-named maniraptors included the confuciusornithiform Yangavis confucii, the Oligocene passerine Winnicavis gorskii, and the alvarezsaurs Bannykus wulatensis and Xiyunykus pengi.

Select bones and reconstructed skeletal of Bannykus wulatensis, from Xu et al. (2018).

In September, preserved pellets were described in Anchiornis. Reflection of near-infrared light was found to be a thermoregulatory strategy used by birds. Ejecting parasitic cowbird eggs was shown to be costly for dickcissels. New studies came out on the killing kinematics of loggerhead shrikes, the visual attention of pigeons, genomic differentiation in recently-diverged avian species, molting patterns in gruiforms, the evolution of parental activity at the nest in birds, the preservation of Shuvuuia feathers, the abundance and survival of migratory birds in North America, the development of striped feathers in galliforms, and adaptations for having proportionately large brains in hummingbirds. Newly-named maniraptors included the basal pygostylian Jinguofortis perplexus, the elephant bird Vorombe titan, and the blue-throated hillstar (Oreotrochilus cyanolaemus).

Anchiornis specimen preserved with pellet, from Zheng et al. (2018).

In October, pigmented dinosaur eggshells were found to likely have originated among maniraptors. Patterns of diversification in the avian limb skeleton were shown to be correlated with clade-specific ontogenetic trajectories. A new specimen of Archaeorhynchus with preserved lungs was described. New Caledonian crows were reported to be capable of constructing compound tools. Rapid speciation in manakins was suggested to be linked to acrobatic courtship behavior. The sensory ecology of elephant birds was investigated based on endocranial anatomy, though inferences of nocturnality are likely premature. New studies came out on pair bonding in great tits, the courtship display of blue-capped cordon-bleus, the genetic basis for color polymorphism in Gouldian finches, song learning in savannah sparrows, the evolution of iris color in owls and signal modality in birds, the mitochondrial genomes of parrots, the phylogenetic position of Mascarene owls, the phylogeny of babblers, the origin of the Inaccessible Island rail, the diversification of Todiramphus kingfishers, near-ground soaring in Gyps vultures, heat-conservation behaviors in birds, the correlation between avian pelvis and egg size, the ontogeny of wing-assisted incline running, the senses used by scavenging birds, the taxonomy of the white-browed shortwing, and stability during avian take-off. Newly-named maniraptors included the basal avialan Archaeopteryx albersdoerferi, the enantiornithine Orienantius ritteri, and the Rote leaf warbler (Phylloscopus rotiensis).

The evolution of eggshell pigmentation mapped onto archosaur phylogeny, from Wiemann et al. (2018).

In November, the crest feathers of peafowl were shown to be attuned to frequencies generated by their courtship displays. A three-species hybrid wood-warbler was reported. The textbook wisdom that the black bib of house sparrows signals dominance was questioned. The molecular and cellular profiles of avian scales were shown to be distinct from those of crocodylian scales. The smallest known dromaeosaurid tracks were described. New studies came out on plumage patterns of Confuciusornis, tool making in Goffin's cockatoos, gliding strategies in Gyps vultures, the evolution of iridescent plumage, fuel load in birds, the biomechanics of foraging flight in common swifts, the genetic basis for bill size in black-bellied seedcrackers, correlated complexity in the displays of birds-of-paradise, and the phylogeny of Hylopezus and Myrmothera antpittas. Newly-named maniraptors included the enantiornithines Mirarce eatoni and Gettyia gloriae (formerly a species of Avisaurus).

The suggested formation of a three-species hybrid wood-warbler (pictured in C), from Toews et al. (2018).

In December, amber-trapped specimens of rachis-dominated feathers were described. Medullary bone was reported in an enantiornithine. Hybrid speciation in birds was reviewed. A nesting rufous-tailed hummingbird was documented mistakenly attacking a snake-mimicking caterpillar. Secondary flightlessness was shown not to correlate with brain morphology in neornithines. Aerodynamic forces produced by the wings of Caudipteryx were found to have been limited. New studies came out on different rates of ageing between different white-throated sparrow morphs, the genomic basis for increased cognition and longevity in parrots, the structure of primary feathers, the evolutionary links between different signaling traits in hummingbirds, the relationship between beak shape and feeding ecology in birds, population differentiation in northern cardinals, the development of avian forelimb position, the courtship display of broad-tailed hummingbirds, and the phylogenetic affinities of Calcardea. Newly-named maniraptors included the recently extinct pigeon Ducula tihonireasini.

Rachis-dominated feathers preserved in amber, from Xing et al. (2018).