Friday, January 1, 2021

Review of 2020

Wow, a record low in annual post count for this blog. It hasn't been for a lack of topics to write about; I had wanted to blog about estimating neoavian divergence times, the fossil record of shorebirds, the many origins of flightlessness in waterfowl, and more, but I never got around to doing so. Time will tell if I ever do. In part, I've been inactive here because I've been busy. The pandemic hasn't slowed down my academic activities much (for which I'm thankful), so I've still had my hands full working on research projects, reviewing manuscripts, and attending conferences. Those conferences went well for most part, but the switch to online formats meant that I felt less motivated to blog about them, further contributing to the lack of activity here. (Although come to think of it, a post about how online and in-person conference experiences differ might have been interesting...) I also wasn't able to make any new trips to zoos or museums, so there weren't any posts about those either.

My neglect of the blog notwithstanding, I did find the opportunity to work on a few other non-academic projects in 2020. In June, I helped put together the Dino Nerds for Black Lives livestream, and even now I'm flabbergasted that we managed to pull it off. For those who missed or would like to re-experience the livestream, most of the segments have been made available online. In addition to organizing and hosting parts of the event, I also presented a segment on the stream with my longtime friend and collaborator Joan Turmelle, in which we did a one-time revival of our old radio show Incidents and Reflections

Joan and I enjoyed doing the radio show again, so we later started a new podcast, Through Time and Clades. Strictly speaking, our show also includes visual aids, so it's not quite a conventional podcast. We currently operate on a rotating schedule. For the first episode of every month, we discuss a selection of notable new studies on natural history that came out during the previous month. Following that, we switch back and forth each week between two different series until the next month rolls around. One series, led by Joan, discusses human origins, whereas the other series, led by me, discusses the diversity and evolution of crown-group birds (and thus might be of particular interest to readers of this blog).

The title slide for the first episode of "Dinosaurs, the Second Chapter", my podcast series on crown bird evolution.

Possibly the most exciting personal achievement for me in 2020, however, was the fact that I helped name a new dinosaur in Nature! That dinosaur was Asteriornis maastrichtensis, one of the few clear examples of a Cretaceous crown bird, and the holotype includes one of the best-preserved fossil bird skulls yet found. As I wrote about previously, the discovery of this new species was highly serendipitous, and I don't expect that I'll have the chance to take part in such a high-profile study again anytime soon.

Skull of the holotype of Asteriornis maastrichtensis, from Field et al. (2020).

The description of Asteriornis might have been my favorite study from last year (if I may say so myself), but it was far from alone. Despite the state of the world, plenty of new maniraptoran research continued to be published throughout 2020, so let's take a look. As always, my coverage of papers about modern birds is necessarily going to be incomplete, so I put more focus on those that have more direct connections to paleontology, such as studies on anatomy, ontogeny, and higher-order phylogeny.

In January, African gray parrots were reported to voluntarily help members of their own species obtain food rewards. Eggshells from the Late Cretaceous of Europe thought to belong to geckos were reinterpreted as maniraptoran in origin. Avian paleoneurology was reviewed. Seabirds from the Pleistocene of Japan, birds from the Eocene of Antarctica, a partial skeleton of a Paleocene penguin, preserved skin in Palaeeudyptes, and the vocal tract anatomy of king penguins were described. Reversible outer toes were reported in gray-headed and lesser fish eagles. Red-breasted nuthatches were shown to vary their alarm calls according to eavesdropped signals from other birds. New studies came out on how flight feathers stick to one another, the brain structure of extinct avialans, convergent evolution in birds, pelvic ontogeny in greater rheas, life history changes in birds from the La Brea tar pits, the evolution of melanosomes in hummingbirds, evolutionary rates in passeriforms, evolutionary drivers in Acanthiza thornbills, and the phylogeny of Turdus thrushes. Newly-named maniraptors included the microraptorian dromaeosaurid Wulong bohaiensis, the Taliabu myzomela (Myzomela wahe), the Peleng fantail (Rhipidura habibiei), the Taliabu grasshopper warbler (Locustella portenta), the Peleng leaf warbler (Phylloscopus suaramerdu), and the Taliabu leaf warbler (Phylloscopus emilsalimi).

Holotype of Wulong bohaiensis, from Poust et al. (2020).

In February, a horned lark preserved in permafrost was identified. A series of isolated feathers and an avialan wing were reported from Burmese amber. (As I'll mention under March, Burmese amber would become a particularly hot topic later in the year.) A new specimen of Chirostenotes and a paraortygid from the Uinta Formation were described. Evidence of dietary plasticity in passenger pigeons was presented. Convergent evolution between the syrinxes of hummingbirds and songbirds was documented. The vocal sequences of African penguins were suggested to conform to linguistic laws. The nomenclature of Lophorina birds-of-paradise was reexamined. New studies came out on the taphonomy of feathers, inferring lifestyle from paravian claw curvature, locomotion in dromaeosaurids, the diversity of island birds, the origin of complex sociality in birds, introgression in the origin of the domestic chicken, the phylogeny of rails and waxbills, the shape of great auk eggs, the evolution of ornamentation in gulls, hearing in great cormorants, the aerodynamic role of raptor tails, the wing and tail musculature of barn owls, the evolution of plumage coloration in lorikeets and Australasian robins, hybridization among American crow lineages, the processing of encounters with dead conspecifics in American crows, social learning in Eurasian blue tits, and craniofacial integration in Hawaiian honeycreepers and Darwin's finches. Newly-named maniraptors included the Cretaceous euornithean Khinganornis hulunbuirensis, the white-winged tapaculo (Scytalopus krabbei), the jalca tapaculo (Scytalopus frankeae), and the Ampay tapaculo (Scytalopus whitneyi).

Pleistocene horned lark recovered from permafrost, from Dussex et al. (2020).

In March, a special volume on the evolution of feathers was published. A large oviraptorosaur from the Hell Creek Formation was described. The sensory systems of birds were reviewed. The Vaurie's nightjar was reevaluated as possibly belonging to the European nightjar. Evidence for statistical inference in kea was presented. A new classification for fluvicoline tyrant flycatchers was proposed. The supposed Pliocene longspur "Pliocalcarius" was reinterpreted as a species of the lark genus Eremophila. Red-winged blackbirds were shown to eavesdrop on the alarm calls of yellow warblers. New studies came out on snout morphology in dromaeosaurids, the modularity of the avian neck, the phylogeny of junglefowl, trochilin hummingbirds, and Scytalopus tapaculos, lung morphometrics in high-altitude waterfowl, the anatomy of rictal bristles in strisoreans, bill disparity in penguins, the evolution of migratory behavior in tyrant flycatchers, and phylogenetic signal in cowbird skulls. Newly-named maniraptors included the dromaeosaurid Dineobellator notohesperus, the Miocene pheasant Phasianus bulgaricus, the Miocene sandgrouse Linxiavis inaquosus, the Pleistocene owl Asio ecuadoriensis, and... yes, the Cretaceous pan-galloanseran Asteriornis maastrichtensis. Then there was the maniraptor that wasn't: Oculudentavis khaungraae, originally described as an avialan based on a skull preserved in Burmese amber, was quickly met with skepticism regarding its phylogenetic affinities. The paper was retracted in July, and a peer-reviewed study reassessing the specimen as a lizard was later released in October. In addition to the taxonomic controversy, the publicity that Oculudentavis received also sparked discussions about the human rights violations that often underlie the procurement of Burmese amber, resulting in official statements on the subject from scientific journals and organizations like the Society of Vertebrate Paleontology. Having been previously guilty myself of excitedly discussing Burmese amber discoveries without acknowledging the associated ethical issues, it's a topic that I've tried to treat with appropriate circumspection going forward.

Red-winged blackbird, photographed by Walter Siegmund, under CC BY-SA 3.0.

In April, red-billed oxpeckers were shown to warn black rhinos of approaching humans. A new specimen of Longusunguis and an owl from the Jebel Qatrani Formation were described. An enantiornithean foot was reported from, well... Burmese amber. Peramorphic features were identified in avian skulls. New studies came out on the ultramicrostructure of paravian teeth, the evolution of avian brain size, humeral disparity in birds, the genetic basis of avian foot feathering, the development of spinal nerves in avian tails and the olfactory system in chickens, bone histology in elephant birds, the adaptive radiation of neoavians, the phylogeny of turacos and chlorophonias and euphonias, the diversification of babblers, adaptations to migration in the flight feathers of European robins, and speciation rates in tanagers.

Diagram showing black rhinos reacting to approaching humans when warned by red-billed oxpeckers, from Plotz and Linklater (2020).

In May, giant petrels were documented attacking sperm whales. An oviraptorosaur specimen preserved with associated eggs was reported. Evidence of ontogenetic dietary shifts in Deinonychus and iridescent plumage in Calciavis were presented. Avian wing shape was found to correlate with a variety of environmental and ecological factors. A possible case of a common cuckoo being killed by mobbing from a great reed warbler was recorded. New specimens of Anhinga pannonica were described. Avian scavengers were suggested to use auditory cues to help locate food. The classification of xolmiin tyrant flycatchers was revised. Black-capped chickadees were shown to be able to identify female conspecifics by call. New studies came out on pelvic morphology of caenagnathid oviraptorosaurs, the cranial osteology of Sapeornis, the anatomy of Parahesperornis, scaling trends in avian alular feathers, the evolution of avian developmental durations, the development of the avian vertebral column, webbed feet in waterbirds, and flight feather positioning, the genetic basis of reduced lifespans in flightless birds, the phylogeny of kiwi, lorikeets, bowerbirds, and nuthatches, introgression within bean geese, the diversification of frogmouths, and biomechanical diversity in kingfishers. Newly-named maniraptors included the the basal paravian Overoraptor chimentoi, the basal avialan Kompsornis longicaudus, the recently extinct New World vulture Coragyps seductus, the recently extinct accipitrids Gigantohierax itchei, Buteogallus royi, and Buteo sanfelipensis, the recently extinct caracara Milvago diazfrancoi, the Oligocene piciform Jacamatia luberonensis, the Pleistocene troupial Icterus turmalis, and the Pleistocene cowbird Molothrus resinosus.

Northern giant petrel attacking sperm whale, from Towers and Gasco (2020).

In June, the osteology of penguins and plotopterids was compared. The osteology of Rahonavis was described in detail. An ornithuran from the Dinosaur Park Formation, a new specimen of Struthio karatheodoris, and a tyrannidan passeriform from the Oligocene of France were reported. The development of avian flight behaviors and the role of extended parenting in the evolution of corvid cognition were reviewed. Broad-tailed hummingbirds were shown to be able to disciminate non-spectral colors. The endocast of the night parrot was described. New studies came out on chemical preservation in the tail feathers of Anchiornis, the scaling of the avian middle ear, the genetic basis of sexual dichromatism in birds, casque ontogeny in southern cassowaries, the phylogeny of hill partridges, the origin of the domestic chicken, convergent responses to flightlessness in rails, flight efficiency in auks, the mandibulosphenoidal joint in penguins and procellariiforms, inbreeding avoidance in long-tailed tits, and the evolution of Aimophila and Peucaea New World sparrows.

Ontogeny of the casque in the southern cassowary, from Green and Gignac (2020).

In July, high-frequency hearing was documented in Ecuadorian hillstars. Evidence of sequential molting in Microraptor was presented. A juvenile dromaeosaurid from the Prince Creek Formation, a new specimen of Protopteryx, and a crane from the Miocene of Germany were described. Soft tissue analyses were used to support the identification of ovarian follicle preservation in Mesozoic avialans. A partial enantiornithean specimen was reported from (one more time...) Burmese amber. The syrinx of the black jacobin was visualized. A sense of numerical ordinality was found in rufous hummingbirds. Visual adaptations in raptors were reviewed. The classification of lorikeets was revised. The songs of thrush nightingales were found to share categorical rhythms with human music. Birdsong learning was shown to be beneficial to both tutees and tutors in song sparrows. New studies came out on variation in Mesozoic feathers (note: based on Burmese amber specimens), facial pneumaticity in dromaeosaurids, the endocranial anatomy of Velociraptor, sub-surface foot kinematics in birds, the morphology of avian flight feathers, the evolution of ostriches, eggshell coloration in tinamous, flight performance in Andean condors, the phylogeny of Dendrocolaptes ovenbirds, host mimicry in viduids, and cultural evolution in the song of white-throated sparrows. Newly-named maniraptors included the alvarezsaur Trierarchuncus prairiensis, the oviraptorosaur Citipes (a new genus for "Leptorhynchos" elegans), the Pleistocene pheasant Chauvireria bulgarica, the recently extinct pigeon Tongoenas burleyi, the Eocene owl Primoptynx poliotauros, the Ayacucho antpitta (Grallaria ayacuchensis), the Oxapampa antpitta (Grallaria centralis), the Puno antpitta (Grallaria sinaensis), the Chamí antpitta (Grallaria alvarezi), the Graves's antpitta (Grallaria gravesi), and the O'Neill's antpitta (Grallaria oneilli).

Preserved gap in wing feathers of Microraptor, interpreted as indicative of molting pattern, from Kiat et al. (2020).

In August, a special volume on pennaraptoran paleontology was published. The potential for powered flight was assessed in Mesozoic maniraptors. Expanded sternal ribs were documented in Jeholornis. The birds from the Eocene of the Geiseltal and avian macroevolution were reviewed. Large brains were shown to be linked to increased lifespan in birds. Fork-tailed flycatchers were found to produce sounds using their wing feathers. Red-billed queleas were reported to be able to tolerate higher temperatures than any other bird. New studies came out on rates of skull evolution in birds (and other dinosaurs), the correlation of down feather morphology with habitat and temperature, squamosal morphology in birds, the phylogeny of crown birds, pheasants, and elanine kites, the evolution of host use in avian brood parasites and breeding plumages in New World warblers, the flight behavior of Anna's hummingbirds through waterfalls, the diversification of penguins, the genetic basis of nocturnal adaptations in owls, the cranial anatomy of Otus murivorus, and ecosystem engineering by superb lyrebirds. Newly-named maniraptors included the Pleistocene–Holocene coot Fulica montanei, the Pliocene penguin Eudyptes atatu, the Eocene accipitrid Palaeoplancus dammanni, and the Pleistocene barn owl Tyto maniola.

Phylogeny of paravians, with lineages potentially capable of powered flight highlighted, from Pei et al. (2020).

In September, the isolated holotype feather of Archaeopteryx was argued to indeed belong to Archaeopteryx, contrary to a previous study from 2019. A new specimen of Piscivorenantiornis was described. Avian endocasts were shown to be reliable proxies for the sizes of corresponding brain regions. A cortex-like canonical circuit in the avian forebrain was identified and a neural correlate of sensory consciousness was reported in carrion crows. Avian plumage patterns were reviewed. Extreme torpor was documented in Andean hummingbirds. Breeding success was shown to correlate with divorce in plovers. Azure-winged magpies were found to share food with conspecifics depending on availability of food to the recipient. New studies came out on skull modularity in birds (and other archosaurs), hindlimb morphometrics in avialans, beak morphology in Confuciusornis, phylogenetic signal in the lacrimal/ectethmoid of waterfowl, ossification sequences in black-headed gulls and Eurasian reed warblers, vertebral pneumaticity and serial variation in storks, the evolution of growth patterns in passeriforms, and the phylogeny of stipplethroats. Newly-named maniraptors included the Pleistocene–Holocene New World vulture Cathartes emsliei, the Pliocene–Pleistocene owl Glaucidium ireneae, and the Pliocene–Pleistocene corvid Corvus bragai.

Black metaltail, which during torpor attains the lowest body temperature recorded of any bird, photographed by Mickaël Villemagne, under CC BY-NC 4.0.

In October, the aerodynamics of scansoriopterygids were assessed. A shark-bitten hesperornithiform, giant pelagornithids from the Eocene of Antarctica, and large New World vultures from the Pleistocene–Holocene of Uruguay were described. Visual adaptations in birds were shown to correlate with foraging niche in the Peruvian Andes. Differences in visual adaptations between predatory and scavenging raptors was reviewed. Cryptic sexual dimorphism was recorded in Sulawesi babblers. New studies came out on vertebral pneumaticity in Nothronychus, contact incubation in troodontids, plantar adaptations of bird feet, the gust-rejecting mechanism of bird wings, Quaternary avian extinctions in the Bahamas, group organization in foraging phalaropes, the demographic histories of condors, the evolution of communication signals in woodpeckers, and species delimitation in Alaudala larks. Newly-named maniraptors included the oviraptorosaur Oksoko avarsan, the Eocene waterfowl Cousteauvia kustovia, the Eocene possible stem-charadriiform Nahmavis grandei, the plotopterids Empeirodytes okazakii and Stenornis kanmonensis, and the Oligocene accipitrid Aviraptor longicrus. A paper I co-authored also got published this month, in which we proposed a phylogenetic taxonomy of strisoreans.

Holotype of Aviraptor longicrus, from Mayr and Hurum (2020).

In November, the wing musculature of flightless auks was reconstructed. New specimens of Trierarchuncus were described. Feathers preserved in amber were reported... not from Myanmar, but from the Escucha Formation in Spain. Putative ovarian follicle preservation in Mesozoic avialans was again disputed (in response to the earlier paper from July). A large dataset of avian genomes was published. Migratory birds (and mammals) were found to have faster paces of life than non-migratory species. Ecomorphology was shown to correlate with diversity in corvidean passeriforms. New studies came out on group movement and decision-making in vulturine guineafowl, the evolution of the Galápagos rail, the phylogeny of manakins, species delimitation in Calandrella larks, auditory memory in zebra finches, and introgression in Setophaga New World warblers. Newly-named maniraptors included the enantiornithean Falcatakely forsterae (with a highly unusual skull), the gastornithid Gastornis laurenti, the recently extinct sandpiper Prosobonia sauli, the South Georgia gentoo penguin (Pygoscelis poncetii), and the Miocene accipitrid Vinchinavis paka.

Holotype of Falcatakely forsterae, from O'Connor et al. (2020).

In December, evidence of tactile foraging in lithornithids was presented. An oviraptorosaur preserved on top of an embryo-bearing egg clutch, a Saurornitholestes specimen from the Judith River Formation, a new specimen of Macranhinga, and a hornbill from the Miocene of Uganda were described. Interpreting molting patterns from exceptionally-preserved maniraptor fossils appears to be all the rage now, as evidence of sequential molting was also reported in Archaeopteryx. Cartilage preserved on the wishbone of Confuciusornis was documented. Male superb fairywrens were found to maintain vibrant breeding coloration regardless of individual quality. New studies came out on the development of the avian ankle, anthropogenic extinctions of flightless birds, the evolution of paleognath mitogenomes, endocranial ontogeny in ostriches (and alligators), the anatomy of the respiratory system in ostriches (and alligators), the evolutionary history of junglefowl, song frequency in passeriforms, the diversification of suboscines, and the phylogeny of doraditos and white-eyes. Newly-named maniraptors included the Cretaceous euornitheans Abitusavis lii and Similiyanornis brevipectus and the recently extinct owl Ornimegalonyx ewingi.

Oviraptorid preserved on top of egg clutch, from Bi et al. (in press).

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