Saturday, January 11, 2020

New (Extinct) Maniraptors of 2019

A longstanding tradition on this blog was to poll readers on their favorite newly-named maniraptors of the previous year. Following the removal of Blogger's poll widget, I was forced to discontinue this tradition. Last year, I tried out a different way of honoring new taxa by writing a paragraph about every extinct maniraptor named in 2018.

I received some positive feedback for this new format, but I'm thinking that I'll change it up again this year. Drafting a paragraph on every new species required me to spend roughly the same amount of time on species known from a single, fairly nondescript bone as those known from essentially complete or particularly bizarre specimens. Although nearly all fossil descriptions have some scientific value, I suspect that isolated coracoids are generally not of as much interest to most of my readers.

This year, I will instead divide this post up into several sections based (approximately) on phylogeny, and briefly discuss each new maniraptor of 2019 under the relevant section. Every new species of extinct maniraptor that was named last year will at least get a mention, but I won't make myself write a full paragraph on each one. This will probably also result in a shorter post that is presumably less daunting to read... though writing about more than forty species produces a sizable post no matter how it's sliced.

Two new theropods were described as alvarezsaurs last year, which is a decent number considering that 2013-2017 went without any new alvarezsaurs being named (with the possible exception of Aorun, which wasn't originally recognized as an alvarezsaur). One of the 2019 alvarezsaurs, Shishugounykus, hails from the Late Jurassic Shishugou Formation of China, making it one of the oldest known alvarezsaurs alongside Haplocheirus and potentially Aorun. Shishugounykus is known from a partial skeleton, including a nearly complete hand, and appears to have been more distantly related to the Late Cretaceous alvarezsaurids than Haplocheirus was. Given the famously bizarre anatomy of alvarezsaurids, any finding that sheds light on their origins is a welcome one.

That's assuming, of course, that Shishugounykus was indeed an alvarezsaur. The phylogenetic analysis in the description of the troodont Hesperornithoides (discussed later in this post) recovered Aorun and Haplocheirus as compsognathids instead of alvarezsaurs, and Shishugounykus reportedly comes out as a compsognathid in that dataset, too. In contrast, a recent unpublished iteration of Andrea Cau's dataset corroborates an alvarezsaur identity for both Haplocheirus and Shishugounykus.

The other new alvarezsaur of 2019 was Nemegtonykus, which was also named after the geologic formation it was found in, the Late Cretaceous Nemegt Formation of Mongolia. Prior to the description of Nemegtonykus, the only alvarezsaur previously known from the Nemegt had been Mononykus. The holotype of Nemegtonykus is a partial skeleton including much of the tail, trunk, and left hindlimb. It exhibits patterns of bone fusion in the hip, shoulder girdle, and feet that are unique among alvarezsaurs.

Skeletal reconstruction of Nemegtonykus showing preserved elements, from Lee et al. (2019).

Therizinosaurs are another group of maniraptors for which new species are described relatively infrequently. Last year gave us Lingyuanosaurus from the Early Cretaceous Jehol Biota of China, known from some vertebrae and partial limbs. The holotype is quite small (coyote-sized), though it probably represents a juvenile. The specimen is incomplete enough that it is unclear whether it really was a therizinosaur; Mickey Mortimer found it as an oviraptorosaur using the Hesperornithoides dataset, but also noted that a therizinosaurian identity was only slightly less parsimonious.

In recent times oviraptorosaurs have usually gotten away with at least one or two new entries every year. Two were described in 2019. One was Xingtianosaurus from the Early Cretaceous Yixian Formation of China, a Caudipteryx-like form known from a partial skeleton with incompletely preserved wing feathers. The other was Gobiraptor from the Nemegt Formation, known from partial remains of the skull, hip, limbs, and tail. Bone histology suggests that the holotype of Gobiraptor was an immature individual, but, at over a meter in length, it was already larger than the adults of many other oviraptorosaurs. Oviraptorosaur researcher Greg Funston has mentioned on social media that unpublished evidence indicates that Gobiraptor is actually the same species as a previously-named oviraptorosaur.

Basal Paravians
2019 was a good year for what Justin Tweet calls "coming attractions" in dinosaur paleontology, which are essentially fossil dinosaurs known to the paleontological community through brief descriptions, conference presentations, and word of mouth, but have yet to receive a formal name. Although not all of them were included in Tweet's list (which was not meant to be exhaustive), I would consider the ornithopod Convolosaurus, the sauropod Wamweracaudia, the allosauroid Asfaltovenator, and the tyrannosauroid Suskityrannus to all qualify as long-standing "coming attractions" that were finally named last year.

Several maniraptoran "coming attractions" came to light in 2019 as well. One of these was the so-called "Naze dromaeosaurid", known from a foot from the Late Cretaceous Snow Hill Island Formation in Antarctica. First mentioned publicly in 2005 and then briefly described in 2007, this dinosaur was formally named Imperobator last year. Despite its original nickname, the describers of Imperobator found its precise phylogenetic position within Paraves difficult to place, and Andrea Cau has argued that it may not even be a maniraptor at all. The title of the paper that named Imperobator called it a "gigantic" paravian, yet its visible dimensions are comparable to those of Deinonychus. That's larger than average for a paravian, but "gigantic" may be overstating it.

One of the most highly anticipated "coming attractions" described last year was Hesperornithoides, a troodont from the Late Jurassic Morrison Formation of the United States. First announced in a conference abstract in 2004, Hesperornithoides (then nicknamed "Lori") was a big deal for several reasons, particularly the fact that Jurassic paravians other than Archaeopteryx were essentially unknown at the time. With the discovery of Anchiornis and its ilk since then, this is no longer the case, but Hesperornithoides remains notable for the three-dimensional preservation of its skeletal elements (as opposed to the flattened state anchiornithids tend to be preserved in) and for being the best-represented Jurassic paravian from North America.

Skeletal reconstruction of Hesperornithoides showing preserved elements, from Hartman et al. (2019).

Hesperornithoides also generated some buzz for the phylogenetic analysis that accompanied its description. The dataset used has greater taxon sampling than any other published analysis of Mesozoic theropods (it includes nearly all Mesozoic maniraptoromorphs known at the time of study and even a handful of Cenozoic birds), and originated from reevaluating the Theropod Working Group phylogenetic dataset, which has been the basis for the majority of Mesozoic theropod analyses. This resulted in several novel findings, such as Haplocheirus as a compsognathid (as mentioned previously) and Pelecanimimus as an alvarezsaur. Time will tell whether these results hold up, but this analysis highlights the importance of independently evaluating phylogenetic datasets, as repeatedly building directly on previous datasets can create an illusion of consensus.

Strangely enough, no new (definite) dromaeosaurids were named in 2019. Someone drew the short end of the stick.

Basal Avialans
In recent times, Archaeopteryx has generally been considered the only known paravian from the Late Jurassic of Germany, but this has started to change in the past few years. In 2017, one supposed Archaeopteryx specimen was reevaluated as an anchiornithid and given the new genus Ostromia. Last year added another new paravian to the lineup, Alcmonavis from the Mörnsheim Formation. Although it is known only from a forelimb, Alcmonavis appears to differ from Archaeopteryx in the robusticity of certain bones as well as the prominence of various muscle attachment sites.

Another exciting find in the Mesozoic avialan department was Fukuipteryx from the Early Cretaceous Kitadani Formation of Japan. Not only is it the first Early Cretaceous avialan to be found in Japan, Fukuipteryx is known from a partial, three-dimensionally preserved skeleton including much of the front and hind limbs. Despite having a short tail with a pygostyle, it was found to have been less closely related to modern birds than the long-tailed Jeholornis was, which may indicate that the pygostyle evolved more than once among avialans, as some other recent studies have suggested.

Skeletal reconstruction of Fukuipteryx showing preserved elements, from Imai et al. (2019).

The "opposite birds" had a good showing last year, and probably the most intriguing new taxon was Elektorornis from the Late Cretaceous of Myanmar, known from hindlimbs and wing feathers preserved in amber. Burmese amber has produced some of the most spectacular fossils of Mesozoic dinosaurs in recent years, including partial specimens of juvenile enantiornitheans and the tail of a non-pygostylian theropod, but Elektorornis is the first of these fossils to be named. It had an unusually long third toe, which the authors suggest may have been used as a probing tool for foraging. It is likely also the smallest known mature Mesozoic dinosaur, the holotype being of comparable size to juvenile enantiornitheans from the same locality despite apparently being an adult or subadult.

Holotype of Elektorornis, from Xing et al. (2019).

Also particularly interesting was Avimaia from the Early Cretaceous Xiagou Formation of China. The holotype is a partial skeleton preserved with an unlaid egg, a first for Mesozoic avialans. Furthermore, histological examination of the egg revealed a double-layered eggshell, indicating that the unfortunate individual had likely died from egg binding (a usually fatal condition in which an unlaid egg is retained for an abnormally long time). A second specimen of Avimaia had been previously described in 2006, but had not been named.

Holotype of Avimaia, from Bailleul et al. (2019). Note the unlaid egg preserved in its body cavity.

As usual, the Jehol Biota did not skimp on enantiornitheans, giving us the relatively large (pigeon-sized) Gretcheniao and the smaller Mirusavis and Shangyang. Mirusavis is noteworthy for preserving medullary bone (produced by female birds before and during egg laying) throughout much of the skeleton, a more extensive distribution of this type of bone than seen in many modern birds.

Although not newly discovered, another Jehol enantiornithean that was given a new name in 2019 was Camptodontornis. It had been originally named "Camptodontus" in 2010, but this genus turned out to be preoccupied by a beetle. It is likely that Camptodontornis is the same as Longipteryx though, as had already been suggested by other studies.

Mesozoic Euornitheans
An unusual euornithean described last year was Mengciusornis from the Early Cretaceous Jiufotang Formation of China. Its teeth were large and curved, but restricted to the tip of the upper jaw. This deviates from the typical pattern in toothed euornitheans, in which the upper jaw tip was usually toothless.

Holotype of Mengciusornis, from Wang et al. (2019).

More closely related to modern birds was Antarcticavis from the Snow Hill Island Formation, known from a partial skeleton, and Kookne from the Late Cretaceous Chorrillo Formation of Argentina, known from a coracoid. The describers of Kookne suggest that it may even be a neognath, as it shares some similarities with waterfowl, but this is naturally difficult to verify with such a fragmentary specimen.

One extinct paleognath was named last year, the emu Dromaius arleyekweke from the Miocene Waite Formation of Australia. Known mainly from hindlimb bones, D. arleyekweke was smaller than modern emus and cassowaries (even the dwarf cassowary). Its feet were proportionately very long, however, indicating that it was probably a fast runner.

Among the galloanserans described last year was what I consider to be one of the most scientifically important new dinosaurs of 2019, the stem-waterfowl Conflicto from the Paleocene López de Bertodano Formation of Antarctica. It is the oldest unequivocal total-group anseriform known from well-represented remains, and may provide evidence that a long-legged, flat-billed body plan was ancestral to all modern waterfowl (including the unusual screamers). I wrote about Conflicto in more detail here. Another Paleocene waterfowl was described last year, the large (swan-sized) Naranbulagornis from Mongolia. It is far less completely known, represented only by a partial carpometacarpus and femur.

Skull of Conflicto, from Tambussi et al. (2019).

On the galliform side of things, 2019 gave us Xorazmortyx from the Eocene of Uzbekistan, which is only known from a partial coracoid. Its describers suggest that it belonged to a group of stem-galliforms called paraortygids, in which case it would be the first paraortygid known from Asia. Better remains are known for a trio of quail from the Macaronesian Islands, Coturnix alabrevis, C. centensis, and C. lignorum. These quail likely went extinct in historic times (within the last 1000 years) due to human activity. Their short wings suggest that they may have been flightless, which would have made them vulnerable to invasive predators.

The early fossil record of pigeons and their kin remains stubbornly sparse, but last year did welcome a new species of recently extinct pigeon, Ducula shutleri from Tonga. Known from sites dated to nearly 3000 years old, D. shutleri was the largest known member of the genus Ducula (the imperial pigeons), probably weighing over 1 kg. Despite its large size, there is no evidence that it had reduced flight capabilities.

Last year we got a new member of the enigmatic Eogruidae, Sinoergilornis from the Miocene Liushu Formation of China. The life appearance of eogruids is mysterious, as they are known mostly from hindlimb bones, and unfortunately Sinoergilornis does not break that curse. Like some other eogruids, Sinoergilornis had only two toes per foot. Although I provisionally treat eogruids as gruiforms here, another study from last year noted that their assignment to Gruiformes is weakly based.

Two species of recently extinct, flightless rails were also described last year, Dryolimnas chekei from Mauritius and the large (chicken-sized) Hypotaenidia vavauensis from Tonga.

Surprisingly, given their diversity and frequent association with aquatic habitats, shorebirds have a relatively poor fossil record, but we did get a new fossil taxon in 2019, Cherevychnavis from the Miocene of Ukraine. Although it is very fragmentary (known only from a coracoid and partial humerus), it is notable for likely being a member of Charadrii (a group that also includes plovers, oystercatchers, etc.), which have a scant fossil record even by shorebird standards.

If any crown-bird group can claim to have a good fossil record, it's the penguins, and last year we gained three new species of extinct penguin, all from New Zealand. Two of these, the giant ?Crossvallia waiparensis from the Waipara Greensand and the smaller Kupoupou from the Takatika Grit, were from the Paleocene, making them some of the oldest known penguins. The third new penguin was Eudyptes warhami, a species of crested penguin that probably went extinct within the last 500 years.

The closest living relatives of penguins, the procellariiforms (petrels, albatrosses, etc.), have a decidedly worse fossil record. As such, the small albatross Aldiomedes from the Pliocene Tangahoe Formation of New Zealand was a pleasant surprise, especially seeing as it is known from a well-preserved skull. Its narrow beak suggests that it may have been more specialized for fish-eating than extant albatrosses (which feed more on squid).

Holotype of Aldiomedes, from Mayr and Tennyson (2019).

Two other waterbirds described last year were the ibis Geronticus thackerayi from the Pliocene-Pleistocene of South Africa, known from numerous (but often fragmentary) bones, and the heron Taphophoyx from the Miocene of the United States, only known from a coracoid and scapula.

The afroavian side of Telluraves only presented one new fossil species last year, but it was a good one: ?Laurillardia smoleni, a small stem-member of Upupides (hoopoes and woodhoopoes) from the Oligocene Tylawa Limestones of Poland. Not only is it known from a nearly complete specimen, the genus Laurillardia had been in severe need of a modern reevaluation.

Holotype of ?Laurillardia smoleni, from Mayr et al. (2019).

Things were more active on the australavian side, with the parrot Heracles from the Miocene Bannockburn Formation of New Zealand receiving substantial press attention. Heracles is known only from partial hindlimb bones, but these are enough to suggest a body mass of around 7 kg, making it the largest known parrot to have ever existed.

2019 was a good year for stem-passerines. The finch-like beaks of the Eocene Eofringillirostrum boudreauxi and E. parvulum showed that stem-passerines had evolved into seed-eating specialists long before true passerines did. E. boudreauxi was found in the Green River Formation of the United States, whereas E. parvulum was found in the Messel Formation of Germany. I wrote about these two species in more detail here. Another new stem-passerine was Zygodactylus ochlurus from the Oligocene Renova Formation of the United States, the youngest known stem-passerine from North America.

Holotype of Eofringillirostrum boudreauxi, from Ksepka et al. (2019).

Among crown-passerines, there was Dasyornis walterbolesi from the Miocene of Australia, the oldest known member of the bristlebirds, a poorly-studied group of Australian songbirds.

The scansoriopterygids from the Late Jurassic of China continue to prove difficult to place phylogenetically. Already considered unusual since their discovery in 2002, scansoriopterygids rocked the paleontological world again in 2015 with the description of Yi, which appeared to preserve membranous wings partly supported by an elongated wrist bone (known as the styliform). Although this seemed to be the most plausible interpretation of the evidence, some researchers were naturally skeptical. 2019 gave us another new scansoriopterygid, Ambopteryx, which also preserves wing membranes and a styliform, providing support for the original interpretation of Yi.

Holotype of Ambopteryx, from Wang et al. (2019).

Another phylogenetically recalcitrant clade of maniraptors is the pelagornithids, a group of seagoing Cenozoic birds with tooth-like projections in their beaks. Protodontopteryx from the Waipara Greensand is the oldest known pelagornithid and is known from much of the skeleton, potentially making it very valuable for understanding the origins of these mystery birds. It would get my vote for the most scientifically important new dinosaur of 2019 (though Conflicto would be a close second). Protodontopteryx was much smaller than later pelagornithids (which include the largest known wingspans of any bird at up to 7 m wide), about the size of a typical gull.

Skull of Protodontopteryx, from Mayr et al. (2019).

Last but not least, Carpathiavis from the Oligocene of Poland is a small (sparrow-sized) bird of unclear affinities. It is known from a nearly complete (but poorly preserved) skeleton with some similarities to rail-like birds.

Wednesday, January 1, 2020

Review of 2019

Last year I didn't quite keep up the "at least one post every month" streak that I managed in 2018, but I did maintain what I think was a somewhat reasonable posting frequency. Furthermore, I made several major overhauls or additions to the blog, namely a list of extinct Cenozoic bird genera and a rewritten "About" page. I even found time to draw a handful of answers for the Raptormaniacs askblog, imagine that. Travel-wise, I attended ProgPal, SVP, and TetZooCon, with SVP being particularly notable in that it allowed me to visit Australia (and the Southern Hemisphere overall) for the first time.

Probably the biggest personal event of last year relevant to the content and themes of this blog was that I got the first part of my PhD research published as a peer-reviewed scientific paper. In this study, my coauthors and I combined genetic and fossil data to investigate the controversial phylogentic relationships of strisorean birds (nightjars, swifts, hummingbirds, etc.). The paper can be read for free here and I also blogged about it here.

My paper on strisorean phylogeny made the journal cover!

Onward to the annual review of new maniraptor research! In January, photoluminescence in the bills of Atlantic puffins was reported. The structure and chemistry of a fossil feather from the Crato Formation was characterized. A feathered enantiornithean foot preserved in amber was described. Conspicuous plumage in fairy wrens was shown not to increase predation risk. New Caledonian crows were found to be able to infer the weight of objects from watching their movements when blown by the wind. New studies came out on the molecular evolution of maniraptor feathers, the cranial anatomy of Beipiaosaurus, and the diversification of trogons. Newly-named maniraptors included the enantiornithean Shangyang graciles, the stem-anseriform Conflicto antarcticus, and the zygodactylid Zygodactylus ochlurus.

Skull of the holotype of Conflicto antarcticus, from Tambussi et al. (2019).

In February, the isolated holotype feather of Archaeopteryx was reevaluated and its assignment to Archaeopteryx was questioned. A thermoregulatory function was documented for cassowary casques. Bill flourescence was reported in rhinoceros auklets. A supposed ibis from the Eocene of Antarctica was reinterpreted as a chimaeroid fish. The pectoral musculature of the European starling was reconstructed in 3D. New studies came out on the evolution of avian cranial morphology, the avian syrinx, and furnariidan plumage brightness, social parasitism in greater anis, the phylogenetic position of adzebills, the Eyles's harrier, and the Haast's eagle, the genomics of raptorial birds, hunting success and flight mechanics in peregrine falcons, metatool problem solving and material selectivity during tool crafting in New Caledonian crows, the rejection of brood parasite eggs by tawny-flanked prinias and chalk-browed mockingbirds, spatial cognition in mountain chickadees, social network position in zebra finches, and the loss of maternal care in icterids. Newly-named maniraptors included the oviraptorosaur Gobiraptor minutus, the Paleocene anseriform Naranbulagornis khun, the recently extinct penguin Eudyptes warhami, the stem-upupidean Laurillardia smoleni, and the stem-passerines Eofringillirostrum boudreauxi and Eofringillirostrum parvulum.

Holotype of Eofringillirostrum boudreauxi, from Ksepka et al. (2019).

In March, preserved feathers were documented in a juvenile enantiornithean specimen from the Calizas de La Huérguina Formation, contrary to previous reports that none had been preserved. New studies came out on bone histology of Yanornis, the distribution of medullary bone in the avian skeleton, the phylogeny of Dendrortyx, Psittacula (sensu lato) and orioles, the taxonomic status of the great white heron, ultraviolet sensitivity in owls, and factors affecting the vocalizations American crows make around food. Newly-named maniraptors included the therizinosaur Lingyuanosaurus sihedangensis, the enantiornithean Avimaia schweitzerae, and the cream-eyed bulbul (Pycnonotus pseudosimplex).

Holotype of Avimaia schweitzerae, from Bailleul et al. (2019). Note the unlaid egg preserved in its body cavity.

In April, amino acids were recovered from Cretaceous and Eocene feathers preserved in amber. Possible flapping adaptations were identified in Archaeopteryx. The taxonomic utility of ancient avian collagen was assessed. Female song in songbirds was reviewed. Memory performance was shown to influence male reproductive success in North Island robins. Plunge-diving was reported as an anti-predator behavior in the white-banded swallow. New studies came out on bone histology of Xixianykus, the scaling of avian osteocyte lacunae, the evolution of feather barbules, avian digestive enzymes, plumage patterns in woodpeckers, color dichromatism in tyrannidans, sex chromosomes in songbirds, and nectarivory in honeyeaters, the phylogeny of paleognaths, passerines, honeyeaters, white-eyes, and West Indian mimids, the convergent loss of flight in paleognaths, the growth of chicken beaks, the dispersal and speciation of tityrines, and convergent plumage evolution in Marquesan reed warblers. Newly-named maniraptors included the oviraptorosaur Xingtianosaurus ganqi, the indeterminate paravian Imperobator antarcticus, the Miocene heron Taphophoyx hodgei, and the Miocene bristlebird Dasyornis walterbolesi.

(Partial) phylogeny of passerines, from Oliveros et al. (2019).

In May, giant oviraptorosaur eggs were described from the Wayan Formation. Mechanisms of auditory species recognition in birds was reviewed. Dryolimnas rails were found to have evolved flightlessness more than once on Aldabra. Food caches were shown to augment song quality in male bull-headed shrikes. New studies came out on the structure of maniraptor eggshells, flapping inducement in Caudipteryx, the correlation of avian neck and leg length, ancient DNA in rhea, the architecture of cancellous bone in moa hindlimbs, the evolution of flightlessness in steamer ducks, drag reduction in kingfishers, and skull shape in parrots, vocal and visual learning in long-billed hermits, locomotion in juvenile hoatzins, the phylogenetic position of adzebills (clashing with the study from earlier in the year), talon shape in raptorial birds, the phylogeny of cuckooshrikes, the taxonomy of the blue-throated flycatcher species complex, and color perception in zebra finches. Newly-named maniraptors included the scansoriopterygid Ambopteryx longibrachium and the basal avialan Alcmonavis poeschli. The new name Camptodontornis was coined as a replacement for the enantiornithean genus "Camptodontus" (preoccupied by a beetle), though it should be noted that previous studies had already considered this genus likely synonymous with Longipteryx.

Falkland steamer ducks, photographed by In Vitrio, under CC BY-SA 4.0.

In June, the plumage coloration of Eocoracias was inferred. The origin of feathers and interspecies hybridization in birds was reviewed. New specimens of Gargantuavis, Pachystruthio (formerly considered synonymous with Struthio), Cayaoa, and Pellornis were described. The cranial anatomy of the rock pigeon was digitally dissected. Nocturnal torpor in superb fairy wrens and novel vocalizations in female cerulean warblers were documented. New studies came out on the development of avian fingers, the influence of climate change on avian distribution through time, the phylogenetic position of Cayaoa and Becassius, the genetic basis of feathered feet in pigeons, the energetic benefits of flocking in pigeons, the function of major call types in common cuckoos, incipient speciation between Kentish and white-faced plovers, acceleration during wing-propelled swimming in auks, forelimb musculature of diurnal raptors, and the phylogeny of weaverbirds. Newly-named maniraptors included the stem-galliform Xorazmortyx turkestanensis, the Miocene shorebird Cherevychnavis umanskae, the whistling long-tailed cuckoo (Cercococcyx lemaireae), and the western yellow-spotted barbet (Buccanodon dowsetti).

Restoration of Eocoracias with inferred plumage coloration, from Babarović et al. (2019).

In July, a sulphur-crested cockatoo was reported to exhibit spontaneous and diverse movement to music. Feathers were suggested to exemplify the generation of novel adaptive structures through sexual selection. The histology of caenagnathid jaws was used to argue that they did not lose teeth through ontogeny, contrary to other recent studies. A new specimen of Phorusrhacos was described, as was a new specimen of Microraptor with a new species of lizard preserved in its body cavity. A supertree of neornitheans was presented. An avian femur from the López de Bertodano Formation, formerly suggested to be a cariamiform, was reevaluated as a large specimen of Vegavis. New studies came out on rates of morphological evolution in Mesozoic avialans, the evolution of brain shape in flying archosaurs (including birds), the homology of avian fingers, the ontogeny of avian femora and ostrich pelvic musculature, the role of wing coloration in avian flight efficiency, the diversification of Amazonian birds, the flight style of Calciavis, differentiation between torrent duck populations, variation in the inner ear labyrinth of wild turkeys, the phylogeny of neoavians, anhingas, Catharus, and open-habitat chats, aerial maneuvering by rosy-faced lovebirds, and parallel adaptation to salt marshes in passerellids. Newly-named maniraptors included the long-awaited troodont Hesperornithoides miessleri, the enantiornithean Elektorornis chenguangi, the recently extinct rail Dryolimnas chekei, and the Pliocene albatross Aldiomedes angustirostris.

Skeletal reconstruction of Hesperornithoides miessleri, from Hartman et al. (2019).

In August, New Caledonian crows were reported to behave more optimistically after tool use. The Canary Islands oystercatcher was suggested to be a subspecies or morph of the Eurasian oystercatcher. Herring gulls were found to respond to human gaze direction. Glaucous-winged gulls were recorded kleptoparasitizing sea otters and sea lions. A large eagle from the Pleistocene-Holocene of the Dominican Republic was described, as was a new specimen of Anthropornis. Chickadees were shown to prefer conspecific odors. New studies came out on nest arrangement in oviraptorids, the function of dromaeosaurid sickle claws, the plumage of juvenile enantiornitheans, the development of avian foot scales, the composition of avian urinary excreta, the evolution of juvenile pheomelanin-based coloration in birds, seasonal plumage coloration in passerines, and female promiscuity in passerideans, trade-offs between locomotion and reproduction in kiwi, the morphology of the hypotarsal in ralloids and toepads in Australian birds, the phylogenetic position of Caracara creightoni, the phylogeny of shrikes, energy conservation in garden warblers, and female song in eastern bluebirds. Newly-named maniraptors included the alvarezsaur Shishugounykus inexpectus, the Paleocene penguin Crossvallia waiparensis, and the large Miocene parrot Heracles inexpectatus. Oh, and my paper on strisorean phylogeny was published, in case you missed that earlier.

Juvenile enantiornithean with close-ups of its plumage, from O'Connor et al. (2019).

In September, the cranial anatomy of a new specimen of Saurornitholestes was described. The genomes of all extant penguins were presented. White plumage was shown to be advantageous for barn owls hunting on moonlit nights. New studies came out on the taphonomy of keratin and melanosomes in feathers, the evolution of the palate in paravians, the relationship between avian foot claws and their keratin sheaths, bone laminarity in emus, adaptations for high-altitude flight in bar-headed geese, the phylogeny of strisoreans and coraciiforms, the taxonomy of the collared owlet species complex, and the correlation between song repertoire and plasticity in songbirds. Newly-named maniraptors included the early pelagornithid Protodontopteryx ruthae and the Pliocene-Pleistocene ibis Geronticus thackerayi. The name Heyuanninae was coined as a replacement for "Ingeniinae".

Skull of the holotype of Protodontopteryx ruthae, from Mayr et al. (2019).

In October, the male white bellbird was reported producing the loudest recorded call of any bird. An enantiornithean foot and tail feather preserved in amber were described. Range of motion in the avian wing was found to correlate with flight style. Darker pigmentation in avian eggshells was suggested to confer a thermoregulatory benefit. Differently sized cuckoos were shown to pose different threats to their hosts. A novel organelle in the retina of Empidonax flycatchers was documented. New studies came out on skull evolution in oviraptorosaurs, the hindlimb morphology of Palaeotis, skeletal development in ducks, the lunar cycle as a driver of migration for European nightjars, the taxonomy of the South American snipe, the thermoregulatory function of tufted puffin bills, food wasting by parrots, the phylogeny of passerines, delayed gratification in New Caledonian crows, breeding behavior in phainopeplas, and memory inception in zebra finches. Newly-named maniraptors included the alvarezsaur Nemegtonykus citus, the enantiornithean Gretcheniao sinensis, the recently extinct quail Coturnix alabrevis, Coturnix centensis, and Coturnix lignorum, the indeterminate Oligocene bird Carpathiavis meniliticus, the Alor myzomela (Myzomela prawiradilagae), and the spectacled flowerpecker (Dicaeum dayakorum).

Male white bellbird calling, from Podos and Cohn-Haft (2019).

In November, evidence of hatching asynchrony in oviraptorid clutches was presented. An assemblage of fossil feathers from the Early Cretaceous of Australia was reported. Vulturine guineafowls were recorded forming multilevel societies. Scavenging behavior in owls was reviewed. Parrots were found to lack aversion to inequity. New studies came out on the structure of flight feathers, the evolution of the avian digestive system, beak preservation in Confuciusornis, the origin of the euornithean predentary, the biogeography of hesperornithiforms, correlation between avian egg and nest characteristics, otic morphology in neognaths, variation in the crest of helmeted guineafowl, nest associations between rough-legged hawks and peregrine falcons, cooperative breeding in chestnut-crested yuhinas, diversification rates in emberizoids, and auditory learning in brown-headed cowbirds. Newly-named maniraptors included the basal avialan Fukuipteryx prima, the Cretaceous euornitheans Mengciusornis dentatus and Antarcticavis capelambensis, the Miocene emu Dromaius arleyekweke, the recently extinct pigeon Ducula shutleri, the recently extinct rail Hypotaenidia vavauensis, and the eogruid Sinoergilornis guangheensis.

Vulturine guineafowl, photographed by Ninara, under CC BY 2.0.

In December, Tereingaornis was reevaluated and considered a dubious taxon. Evidence for mixed-age flocking in avimimids was reported. Rachis-dominated feathers preserved in amber were described. The genomes of the Carolina parakeet and the superb fairy wren were presented. New studies came out on the evolution of feather barb angles and honeyeater beaks, the flight style of Protopteryx, the recovery of ruffled feather vanes in birds, syrinx and hyoid morphology in southern cassowaries, the former population densities of moa, respiration kinematics in wild turkeys, the loss of flight in the Aldabra white-throated rail, the function of juvenile ornamentation in American coots, vision speed in raptorial birds, the phylogeny of owls, the taxonomy of the blue-backed parrot, and begging suppression in young red-winged blackbirds. Newly-named maniraptors included the enantiornithean Mirusavis parvus, the Cretaceous ornithuran Kookne yeutensis, and the Paleocene penguin Kupoupou stilwelli.

American coot with chicks, photographed by Casey Klebba, under CC BY-SA 4.0.

Sunday, December 15, 2019

What Good is Less Than Half a Beak?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Tuesday, November 5, 2019

New "About" Page

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

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

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

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

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