Tuesday, March 21, 2017

London Zoo Part I: Rainforest Life and Nightlife

London Zoo is situated within a large park with abundant opportunities for birding. Here a mute swan browses from a waterside tree.

A European green woodpecker, a lifer for me. This species is ecologically similar to the North American northern flicker, which I'm more familiar with. Both woodpecker species forage mainly for ants on the ground.

I had to restrain myself from spending too much time on birdwatching in the park, but I eventually made it to the zoo.

My first stop was the exhibit closest to the zoo's main entrance, the aquarium. It has a nice collection with many rarely-seen fish species, but it is so dimly-lit that getting any decent photos was a real struggle. My only fish photo taken there that is remotely presentable was of this white-eyed moray.

There is also a poignant display on plastic pollution.

Next, I headed to the Rainforest Life/Nightlife building. Half of this building (the "Rainforest Life" half) is a walkthrough rainforest exhibit where monkeys, sloths, and tamanduas roam freely. Some of the branches in the exhibit are arranged so that the animals can (and do) venture close right overhead or next to the visitors. Here is an emperor tamarin keeping its distance for the time being.

Most surprising to me, however, were the narrow-striped bokies kept in a glass-fronted display on the side of the walkway. Though commonly called the narrow-striped mongoose (including by the exhibit signage), the narrow-striped boky is no longer considered a true mongoose, but a separate radiation of carnivorans endemic to Madagascar. I must have taken around thirty photos of them trying to get a good shot.

The other half of the building (the "Nightlife" half) is a nocturnal exhibit. I'd heard that Panay cloudrunners could be seen here, but, to some slight disappointment, they didn't appear to be on display when I visited.

I did, however, have a great time watching some other rodents present, namely the rakalis. Not only were they a first for me, they are an interesting species in themselves, being the largest Australian rodents. As placentals living in a land of marsupials, rakalis have taken on the role of semi-aquatic predators, a niche that hasn't been exploited by Australian marsupials. They have a decently-sized pool with underwater viewing at the London Zoo, though I didn't see them use it. Regardless, their terrestrial antics were plenty entertaining enough. As is typical of nocturnal houses, my attempted photos turned out less than stellar.

I also received another opportunity to get pictures of Malagasy giant jumping rats. Not there yet...

Say what? It is possible to get halfway decent pictures at nocturnal exhibits? It helps, naturally, when the subject of the photo is one that spends a significant amount of time not moving around much, such as this gray slender loris.

Saturday, March 18, 2017

How Therizinosaurs Nibbled and Munched

That new Anchiornis paper is quite something, isn't it? Everyone else is talking about it, so I don't have to, but check it out if you haven't already.

Instead, I will discuss another recent paper about a different group of maniraptors, the unusual therizinosaurs. Since 2012, a series of publications on the functional biology of therizinosaurs, primarily authored by Stephan Lautenschlager, have contributed greatly to demystifying these bizarre herbivorous theropods. (A selection of these papers are linked in the preceding sentence, but it is by no means an exhaustive list.)

These previous papers have largely focused on the therizinosaur Erlikosaurus from the Late Cretaceous Bayan Shireh Formation in Mongolia, a sensible choice given that this genus has the best-preserved skull material of all known therizinosaurs. The new study, also conducted by Lautenschlager, takes the logical next step by asking: how does Erlikosaurus compare to other therizinosaurs?

Phylogeny of therizinosaurs with digital models of the lower jaws of taxa used in the analysis, from Lautenschlager (in press).

To answer this question, Lautenschlager digitally modeled the lower jaws of other therizinosaur taxa, including Falcarius, Jianchangosaurus, Beipiaosaurus, Alxasaurus, and Segnosaurus, and subjected the models to finite element analysis (FEA). Under FEA, stress (force per unit area) experienced by the jaw under different simulated feeding conditions could be calculated, as could relative bite force. The different feeding scenarios tested were biting using one side of the jaw at different tooth positions, biting using both sides of the jaw at different tooth positions, clipping using the tip of the jaw, pulling an object upwards, pulling an object downwards, and pulling an object sideways.

The results of finite element analysis simulating potential feeding behaviors in different therizinosaur taxa, from Lautenschlager (in press).

It is worthy to note that this study did not calculate the absolute bite force of these therizinosaurs, only their relative bite forces. In other words, instead of estimating how strong a bite the therizinosaurs were actually capable of generating, the study estimated which therizinosaur could generate the highest bite force if all of them exerted the same amount of force with their jaw muscles.

With that in mind, what did the results say? It turns out of the taxa tested, Falcarius and Alxasaurus had, on average, the highest relative bite forces. This is consistent with the idea that Falcarius was more omnivorous than other therizinosaurs and may have still fed on some animal prey. Alxasaurus has also been interpreted as a more generalist forager than other therizinosaurs on the basis of its claw morphology, so having a relatively high bite force may have increased the variety of foodstuffs it could feed on.

On the other hand, the results indicated that Falcarius and Alxasaurus would have experienced greater amounts of stress during feeding than other therizinosaurs, whereas Erlikosaurus and Beipiaosaurus would have experienced the least. Additionally, all therizinosaurs would have experienced less stress while pulling items downwards compared to pulling upwards or sideways, suggesting that they habitually fed at or above head level. However, Erlikosaurus and Segnosaurus were more suited to pulling objects sideways than other therizinosaurs. What appears to have made the difference in this case is that Erlikosaurus and Segnosaurus both had a downturned lower jaw.

This is an interesting result considering that a downturned lower jaw has independently evolved in other herbivorous dinosaurs. The unusual ceratosaur Limusaurus even gained one during growth (in addition to losing its teeth)! This study confirms that such a jaw would have been advantageous for herbivores by helping to mitigate stress while feeding. A similar adaptive benefit has been attributed to the widespread presence of a beak in herbivorous dinosaurs (including therizinosaurids).

Among the taxa studied, Erlikosaurus and Segnosaurus were contemporaneous with one another, suggesting there may have been niche partitioning between them. This is supported by the study: Segnosaurus had relatively higher bite forces (as well as probably higher absolute bite forces, considering its larger size) and may have been able to feed on tougher plants, but Erlikosaurus experienced less stress during feeding and may have been able to use a greater variety of feeding methods. Though not discussed in the paper, one wonders whether the same was true of Jianchangosaurus and Beipiaosaurus, both found in the Yixian Formation. Here, however, the differences are less explicit: Beipiaosaurus experienced lower stresses while feeding, but both had similar relative bite forces.

Reference: Lautenschlager, S. In press. Functional niche partitioning in Therizinosauria provides new insights into the evolution of theropod herbivory. Palaeontology in press. doi: 10.1111/pala.12289

Tuesday, February 28, 2017

Vanolimicola, Rail or Jacana?

Animals that live in or near water usually have an edge when it comes to preserving as fossils. After all, the very habitats they live in are depositional environments. As a result, one might think that we would have an excellent fossil record of the charadriiforms. In addition to living in environments favorable to fossil preservation, charadriiforms are tremendously diverse. True to their common name of "shorebirds", many charadriiforms do forage by walking around on shores (e..g: most plovers), but there are also those that wade into the water (e.g.: avocets), swim on the water surface (e.g.: phalaropes), dive underwater (e.g.: auks), hunt from the air (e.g.: skuas), and even a few that feed on dry land, sometimes far from water (e.g.: buttonquails).

Yet, the early fossil record of charadriiforms is surprisingly sparse. Some bird fossils from near the end of the Cretaceous have been considered charadriiforms, but these specimens are so fragmentary that it is difficult to be certain of their classification. Even if they were charadriiforms, they would have little to tell us about the ancestral morphology of the group. One clade of charadriiforms that has a decent early record, however, are the jacanas.

Comb-crested jacana, photographed by "Djambalawa", licensed.

Extant jacanas live in freshwater lakes, where they use their astonishingly long toes to walk on floating vegetation. (For this reason, they are also known as lily trotters.) In most jacanas, the females are larger than the males, and the latter are in large part responsible for rearing their young. Unlike other living charadriiform groups, jacanas are known from identifiable fossils going back to the Eocene. A recently-described fossil appears to continue this trend... maybe.

The holotype of Vanolimicola, from Mayr (in press).

Vanolimicola longihallucis comes from Messel in Germany, known for being a treasure trove of well-preserved Eocene fossils. The holotype of Vanolimicola is far from the cream of the crop by Messel standards, but it's complete enough to show that it's a small, long-legged bird. (It's rather striking how frequently the description refers to it as being "fragmentary". Had it been discovered almost anywhere else, it likely would have been considered a decent find.) Its sandpiper-like beak and the proportions of its pedal phalanges suggest charadriiform affinities. However, it also has a very long hallux, which would be unusual for most charadriiforms... but is typical in jacanas! Though the feet of Vanolimicola aren't quite as disproportionately large as in modern jacanas, might it represent an early stem-jacana that lacked such specializations?

Perhaps, but the case is far from watertight. Rails are another group of birds that often live and feed on the margins of water bodies. As such, they are superficially similar to shorebirds in many ways, despite being more closely related to cranes. As is well known (at least among paleornithologists), a large diversity of rail-like birds was present in the Eocene, some (such as Songzia from China) being anatomically very similar to Vanolimicola. Proportions of the forelimb bones are a reliable way to distinguish between the skeletons of rails and shorebirds, but unfortunately, the wings of Vanolimicola are poorly-preserved.

Even given these ambiguities, it would have been nice had the description included a phylogenetic analysis to directly test these different possibilities. As of now, the affinities of Vanolimicola remain tantalizing but uncertain. Nonetheless, the fact that it is one of the few semi-aquatic birds known from the Messel makes it a somewhat notable find.

Reference: Mayr, G. In press. A small, "wader-like" bird from the Early Eocene of Messel (Germany). Annales de Paléontologie in press. doi: 10.1016/j.annpal.2017.01.001

Sunday, February 12, 2017

Cruralispennia, the Opposite Opposite Bird

Despite maintaining a continuous list of new maniraptor studies, I have not been very inclined to write entire articles about dinosaur news. After all, everyone else already blogs about them! However, I have come to the conclusion that this assumption is not completely correct. Some of the papers from last year that I found most interesting barely received any popular press. As a result, I have decided that I'm going to start blogging occasionally about maniraptor news, time permitting (but I'm in the middle of working on my Master's, so don't expect too much).

Fossil birds in particular get little attention in the blogosphere (or anywhere else) compared to other dinosaurs, except from Andrea Cau, Mickey Mortimer, and Matt Martyniuk, so it seems appropriate to start with one. I'll discuss one of the first new dinosaurs described this year, the enantiornithine Cruralispennia multidonta.

The name is somewhat clunky; the etymology section in the paper implies that "donta" is Latin for teeth... Even as someone who has never been educated in Latin, that gives me pause. I imagine they had the Latin "dens" or the Greek "odus" or "odon" in mind. Yet behind all that is quite an unusual and fascinating dinosaur.

The holotype of Cruralispennia, from Wang et al. (2017).

Cruralispennia hails from the Early Cretaceous Huajiying Formation in China, the oldest formation from which we have found pygostylian (short-tailed) avialans and home to other spectacularly-preserved early birds such as Eoconfuciusornis, Eopengornis, and Archaeornithura. As its species name suggests, Cruralispennia had a whole lot of teeth, specifically in its lower jaw. As preserved, the holotype preserves at least fourteen lower teeth. Even though most enantiornithines had teeth, this is more than almost all other known enantiornithines except maybe Eopengornis.

Enantiornithes translates to "opposite birds", so called because whereas modern birds have a socket in their coracoid bone where the scapula (shoulder blade) connects to it, most enantiornithines have a socket in their scapula that the coracoid fits into instead. As it happens, Cruralispennia doesn't have this feature, though other details of its anatomy suggest that it is an enantiornithine. However, it has some characteristics that are not only atypical of enantiornithines, but are in fact more similar to those of modern birds, hence the title of this post!

The pygostyle, a fusion of the tail vertebrae at the tip of the tail in short-tailed birds, is short and stubby in Cruralispennia. This is not at all normal for most groups of Mesozoic avialans, which generally have longer, rod-shaped pygostyles, but it is widely found in one specific clade: the euornithines (modern birds and anything more closely related to them than enantiornithines)! In euornithines, the pygostyle supports a mobile fan of tail feathers that functions in steering and braking during flight, and pygostyle shape has been correlated with tail feather structure in modern birds, so one might expect Cruralispennia to have had a (presumably convergent) tail fan as well.

It doesn't. Though the holotype preserves feathers on its tail, it doesn't have large rectrices at all, instead just having short fuzz much like the condition in Eoenantiornis or female(?) Confuciusornis. Perhaps it evolved a blunt pygostyle for a different, undetermined reason from euornithines. Or, speculatively, maybe only some individuals had rectrices? That is the case in Confuciusornis, after all. As is typical in paleontology, we need more specimens!

Photographs and schematics of fossil avialan pygostyles, from Wang et al. (2017). (A) is Cruralispennia, (B) and (C) are other enantiornithines, (D-F) are euornithines, and (G) is Confuciusornis.

Another way in which Cruralispennia is more similar to euornithines than to other enantiornithines is in its growth rate. Modern birds grow unbelievably fast, most reaching adult size in a matter of months or even weeks. This was also the case in some Mesozoic euornithines. Most enantiornithines, on the other hand, took several years. Lines of arrested growth (essentially annual growth rings) are visible when you cut into their limb bones. The describers of Cruralispennia looked at the bone histology of the holotype's humerus, and they found... no growth rings at all, despite the fact that it appeared to have stopped growing. Like most euornithines, Cruralispennia was essentially an adult by the time it celebrated its first birthday.

One last oddity of Cruralispennia that I would like to highlight is its feathers. It is these that its genus name (which translates to "shin feather") refers to. The feathers on its legs and the leading edges of its wings are quite unusual in their structure. Each feather appears to be a narrow, solid sheet for most of its length, but there are short individual filaments that stick out at the tip. The describers gave them another somewhat clunky-sounding name: Proximally Wire-like [feathers] with a Filamentous Distal Tip (PWFDTs). This exact type of feather has not been found in any other kind of dinosaur (living or extinct), though they remind me of the "paintbrush-like" feathers in scansoriopterygids. It's difficult to say what these feathers were used for, but the describers point out that narrow feathers are useful for display without impeding flight too much.

Photographs and schematic of PWFDTs in Cruralispennia, from Wang et al. (2017).

That took longer than I expected. However, Cruralispennia deserved the attention, as I'm certain everyone now agrees.

Reference: Wang, M., J.K. O'Connor, Y. Pan, and Z. Zhou. 2017. A bizarre Early Cretaceous enantiornithine bird with unique crural feathers and an ornithuromorph plough-shaped pygostyle. Nature Communications 8: 14141. doi: 10.1038/ncomms14141

Tuesday, January 10, 2017

Favorite Maniraptor of 2015 Results

My predictions were on the money, as Yi (deservedly) took this one, followed by Dakotaraptor and then Zhenyuanlong. I liked that a Cenozoic maniraptor (Llallawavis) did fairly well for once. Meanwhile, Boreonykus shows that you can gain a decent number of votes as long as you are purportedly a dromaeosaurid, even if you are known from nothing but scrap.

This year's poll looks to be less predictable, as there was no outstanding new maniraptor superstar last year. My guess is that the crown will go to either the enigmatic Fukuivenator or one of the new oviraptorosaurs.

Monday, January 2, 2017

Review of 2016

Despite being one of my busiest years yet, last year was in some ways a success for this blog, as I blogged more in 2016 than in any previous year since 2010 (the year Raptormaniacs was created). If anything, the frequent travel that I did helped me produce more content for the blog: I went to New York to visit a temporary exhibit on bird origins, to South Dakota to attend field camp, to London for TetZooCon, to Utah for SVP, and to Bristol to study. It was not all just filler on here, however, given that I released the longest (and some might say most bizarre) storyline for the Raptormaniacs comic to date. Well, I enjoyed making it. The flip side of all this is that I largely neglected the Tumblr sideblog, but something had to give. Lastly, April Fools' happened, as usual.

Cover image for the "My Little Raptormaniacs" storyline.

Enough about me, you're more likely here for the new maniraptor discoveries. In January, eggshell previously attributed to Genyornis was reinterpreted as belonging to Progura. Quill pits were reported from an Eocene penguin. The genome of the great tit was sequenced. Carotenoid-based feather coloration was found in pink-headed ducks. Great reed warblers were suggested to sing outside of the breeding season to practice their songs. Forty-spotted pardalotes were found to stimulate manna production in eucalyptus trees for feeding. New studies came out on body mass of dodos, the cranial biomechanics of moa, the kicking strike of secretary birds, vocal learning in zebra finches, and the evolution of bill length in 'amakihi, melanin-based coloration system in birds, and chromosomes in white-throated sparrows. Newly-named maniraptors included the non-ornithothoracine avialan Chongmingia zhengi, the Eocene stem-falcon Antarctoboenus carlinii, the enantiornithine Linyiornis amoena, the Cretaceous euornithines Dingavis longimaxilla (which I find suspiciously similar to Juehuaornis) and "Bellulia" rectusunguis (with its genus preoccupied, it would receive a new name later in the year), and the Himalayan forest thrush (Zoothera salimalii).

Mounted specimen of a pink-headed duck, photographed by "Geni", licensed.

In February, duetting in red-backed fairy wrens was found to deter cuckoldry (among themselves, not among their listeners...). Evidence for a theory of mind in common ravens was presented. A specimen of Hesperornis was found with injuries attributed to a plesiosaur attack. New specimens of Archaeorhynchus and Chambicuculus were described. "Furculae" assigned to Dakotaraptor were reinterpreted as turtle entoplastra. New studies came out on the development of fibular reduction in birds, the endocranial anatomy of dodos, the evolution of sexually dimorphic tail feathers, the feather structure of Humboldt penguins, and sound recognition in European starlings. Newly-named maniraptors included the presbyornithid Wilaru prideauxi, the dromornithid Dromornis murrayi, and a bizarre possible maniraptor of uncertain placement, Fukuivenator paradoxus.

Red-backed fairy wren, photographed by Greg Miles, licensed.

In March, brown skuas were reported to be capable of recognizing individual humans. Compositional syntax was found in the calls of great tits. The bill morphology of New Caledonian crows was shown to facilitate tool use. Vocal learning was discovered in red-backed fairy wren embryos. New studies came out on the evolution of color in island birds, the development of feathered feet in domestic chickens and pigeons, the migratory biology of ruby-throated hummingbirds, the vision of small passerines, the morphology of dodos, the mandibular anatomy of Segnosaurus, the tarsometatarsal anatomy of ostriches, the mechanics of sound production in the wings of Smithornis broadbills, and the phylogenetic position of Sylviornis. Newly-named maniraptors included the Cretaceous euornithines Hesperornis lumgairi and Changzuiornis ahgmi, the Eocene apodiform Cypseloramphus dimidius, and an Eocene bird of uncertain placement, Lapillavis incubarens.

Skeletal reconstruction of Sylviornis, from Worthy et al. (2016).

In April, island birds were found to predictably evolve decreased flying ability. Golden-collared manakins and red-capped manakins were discovered to use superfast forelimb muscle contractions during social displays. Vocal mimicry in female superb lyrebirds was reported. The reproductive biology of the sapayoa was described. A new enantiornithine specimen was found to have fish remains as gut contents. New studies came out on the rates of morphological evolution in Early Cretaceous birds, the effect of diet on avian evolution, the taxonomy of geranoidids from the Willwood Formation, the migration strategies of pied flycatchers, brain activity during flight in European starlings, self-regulation in corvids, dental disparity in paravians prior to the K-Pg, the genetic basis for beak size in Darwin's finches, the history of Australian penguins, the biomechanics of courtship displays in Indian peafowl, the evolution of skull shape in raptorial birds, and the ontogeny of limb kinematics in chukars. Newly-named maniraptors included the oviraptorosaur Apatoraptor pennatus and the plotopterids Klallamornis abyssa and Olympidytes thieli.

Red-capped manakin, photographed by Francesco Veronesi, licensed.

In May, the genetic basis for red coloration in birds was described. Research on the phylogeography of the vermilion flycatcher species complex resulted in the recently-extinct San Cristóbal vermilion flycatcher being declared a distinct species. The bill of southern yellow-billed hornbills was found to function in thermoregulation. Hybridization in geese was reviewed. New studies came out on the phylogeny of geese, the structural mechanics of the feather vane, polymorphism in black sparrowhawks, the pelvic limb musculature of ostriches, the evolution of bone-associated genes in birds, duetting displays in magpie larks, and the shape recognition in African gray parrots.

Diagram showing that the enzyme CYP2J19 converts yellow carotenoids to red carotenoids in birds, from Lopes et al. (2016).

In June, wings of juvenile enantiornithines were found preserved in amber. Sexual dimorphism was found in Dromornis stirtoni. Birds were discovered to have higher neuronal density in their forebrains than mammals. Budgerigars and zebra finches were reported to learn grammatical structure in different ways. New studies came out on cognitive development in kaka, the function of nocturnal song in field sparrows, the genetic bases of beards and muffs in chickens, the vascular anatomy of bird heads, the evolution of communal signaling in birds, the chemistry of Troodon tooth enamel, and the osteology of Bathornis. Newly-named maniraptors included the lithornithid Calciavis grandei. "Bellulia" rectusunguis was given the new genus Bellulornis.

Wing of juvenile enantiornithine preserved in amber, from Xing et al. (2016).

In July, great frigatebirds were found to track atmospheric conditions during transoceanic flights. Feather keratin was suggested to be durable enough to be potentially fossilized. The capacity for flapping-based locomotion in Mesozoic paravians was evaluated. New Caledonian crows were reported to use tools for carrying objects. Relational concept learning was demonstrated in ducklings. New studies came out on the consumption of blister beetles by male great bustards, the preservation of avian fossils, visual pigments in emus, interspecies communication between greater honeyguides and humans, visual guidance of flight in hummingbirds, genomic variation in Darwin's finches, and the evolution of ultraviolet vision, closed-mouth vocalizations, skull morphology, and locomotion in birds. Newly-named avialans included the Pleistocene cuckoos Centropus bairdi and Centropus maximus and the Miocene gypaetine vulture Mioneophron longirostris.

Ducklings imprinted on a set of differently-shaped objects (A) prefer a novel set of differently-shaped objects over a novel set of identically-shaped objects (C), whereas ducklings imprinted on a set of identically-colored objects (B) prefer a novel set of identically-colored objects over a novel set of differently-colored objects (E)... though sometimes mistakes are still made (D), from Martinho and Kacelnik (2016).

In August, tool-bending behavior was found to be common in New Caledonian crows. Great frigatebirds were confirmed to sleep in flight. Barbados bullfinches and Carib grackles were discovered to be capable of passing the string-pulling test. The evolution of avian reproduction was reviewed. Zebra finches were found to sing to their unhatched chicks to prepare them for hot weather. New studies came out on the phylogenetic position of the laughing owl, the timing of the crown-penguin radiation, genomic variation in the yellow-rumped warbler species complex, and the diversification of kiwis and passerines. Birds of Stone by Luis Chiappe and Meng Qingjin was published and my review of it can be found here.

Great frigatebird, photographed by "Aviceda", licensed.

In September, pigeons were found to be able to distinguish words from non-words. They were also found to prefer informative over non-informative options and to ignore misinformed leaders. The development of feathers was reviewed. Tool use was reported in Hawaiian crows. Melanin in feathers was elementally characterized. A hard polytomy was argued to be present at the root of Neoaves. Pellets possibly produced by Eocene owls were described. European blackbirds were discovered to switch abruptly to nocturnal flight during migration. New studies came out on the phylogeny of New World vultures, the function of nasal conchae in turkeys, non-vocal signaling during courtship displays in blue-capped cordon bleus, song complexity in pied butcherbirds, the genetic bases for vision in raptorial birds, the morphology of tracheal and esophageal displacement in birds, the development of the grasping foot in birds, and the dentitions of Hesperornis and Ichthyornis. Newly-named maniraptors included the Eocene stem-roller Septencoracias morsensis, the Dahomey forest robin (Stiphrornis dahomeyensis), the Ghana forest robin (Stiphrornis inexpectatus), and the Rudder's forest robin (Stiphrornis rudderi).

Hawaiian crow using stick as probing tool, from Rutz et al. (2016).

In October, red flight feathers in yellow-shafted flickers was found to be caused by diet rather than by hybridization with red-shafted flickers. A preserved syrinx was reported from a specimen of Vegavis. A bonebed of Avimimus was described at last after having been rumored at conferences for many years. Evidence was presented in favor of treating the hen harrier and northern harrier as distinct species. A parrot fossil was reported from the Miocene of Russia. Common swifts were discovered to spend ten months in the air annually. Migratory life histories were found to explain the extreme size dimorphism in Eudyptes penguin eggs. New studies came out on altruism in azure-winged magpies, the relationships between flight style and avian wing aerodynamics, the timing of the columbiform radiation, the mechanics of plunge diving in sulids, and the evolution of the avian bill as a thermoregulatory organ. Newly-named maniraptors included the Pleistocene owl Bubo ibericus, the Eocene owl Eostrix gulottai, and the Eocene albatross Notoleptos giglii. Avian Evolution by Gerald Mayr was published and my review of it can be found here.

Preserved Vegavis syrinx, from Clarke et al. (2016).

In November, an immature enantiornithine specimen was inferred to have had iridescent feathers. Keratin preservation was reported in the claws of Citipati and the feathers of Eoconfuciusornis (alongside melanosomes in the latter case). A new estimate argued that there are around 18,000 species of extant birds. Goffin's cockatoos were reported to be capable of manufacturing tools out of different materials. The microstructure of an isolated feather from the Fur Formation was analyzed. Interhemispheric transfer of imprinting information was found to be absent in the brains of newly-hatched ducklings. New studies came out on the morphology of Chiappeavis, the evolution of avian breeding strategies, and the timing of the origins of avialans and neornithines. Newly-named maniraptors included the enantiornithine Monoenantiornis sihedangia, the oviraptorosaur Tongtianlong limosus, the Miocene galliforms Eurobambusicola turolicus and Mioryaba magyarica, and the zygodactylids Primozygodactylus longibrachium and Primozygodactylus quintus.

Holotype of Tongtianlong limosus, from Lü et al. (2016).

In December, laser fluorescence was used to study the soft tissues of Confuciusornis. A new juvenile specimen of Sapeornis was described, revealing dentary teeth to have been present in this taxon. "Liornis" and Callornis were reevaluated. Complexities in the evolution of avian flight were discussed. New studies came out on the flight parameters of Mesozoic avialans, the histology of cranial joints in mallards, the comparative morphometrics of Darwin's finches and Hawaiian honeycreepers, the evolution of avian genomes and paleognaths, the morphology of the jugal and quadratojugal in maniraptors, the relationships between body feather structure and habitat, and the influence of wing morphology on dispersal in corvoids. Newly-named maniraptors included the Cretaceous euornithine Tingmiatornis arctica.

Confuciusornis specimen photographed under laser fluorescence, from Falk et al. (2016).

Avian Evolution

For all its faults, 2016 was a good year for new science books, and in the comparatively narrow field of paleornithology a whopping number of two major titles were published. I previously reviewed one, Birds of Stone by Luis Chiappe and Meng Qingjin. As promised, here is my review of the other.

Avian Evolution is authored by Gerald Mayr, and I can think of few who are as qualified to cover the subject. Mayr is an incredibly prolific paleontologist known for his research on both Mesozoic and Cenozoic birds, and though I haven't crunched the numbers, he is singlehandedly responsible for a considerable amount of recent paleornithological literature.

Not even close to the entirety of Mayr's output.

After an introduction to avian osteology and relevant geological settings, the first few chapters of Avian Evolution discuss the Mesozoic evolution and diversity of birds, covering the anatomy of Mesozoic avialans and non-avialan pennaraptors, competing hypotheses on the origins of feathers and avian flight, and evolutionary trends leading to neornithines. Though the overview of the Mesozoic is very welcome, the most valuable part of this tome lies in the chapters following it. Whereas information on Mesozoic birds is no longer as difficult to come by as it used to be, there remain very few comprehensive reviews of the Cenozoic bird fossil record. Barring some lone chapters in larger volumes, previous syntheses of the subject have largely been... idiosyncratic in various ways, not to mention increasingly outdated. Mayr's previous work, Paleogene Fossil Birds, is excellent, but only covers Paleogene birds and is extremely expensive. (Avian Evolution is by no means cheap, but is still far more affordable by comparison.)

Given this dreadful situation, the sections on Cenozoic birds in Avian Evolution fill a much needed gap. These chapters are mostly arranged using a phylogenetic framework, insofar as uncertainties in neornithine phylogenetics allow, but a few clades are discussed alongside one another based on ecological similarities rather than close kinship (e.g.: the major groups of hypercarnivorous diurnal birds—accipitrimorphs, falconiforms, and cariamiforms—are covered in one chapter). The final chapter deviates from this structure and instead focuses on the unusual evolutionary trends and unique morphologies of island birds. The book is not confined to fossil taxa clearly closely related to modern forms, nor to the most charismatic extinct clades such as phorusrhacids and teratornithids, but, being a truly comprehensive review, also includes many enigmatic and obscure fossil groups like the eogruids (cursorial birds possibly closely related to cranes), diomedeoidids (procellariiforms convergently similar to oceanitid storm petrels), plotopterids (flightless diving birds of the northern Pacific), and zygodactylids (abundant stem-passerines with zygodactyl feet). For each avian group, the overall anatomy, known fossil record, biogeographic history, and possible paleoecology are all described, with areas in need of future research noted where necessary. One take-home message of this book is that much more work needs to be done on the phylogeny of Cenozoic fossil birds (which will no doubt be facilitated once we have a more stable topology for the extant representatives).

The book is well illustrated with phylogenetic trees, skeletal diagrams, and comparative photographs of specimens. A number of colored plates in the middle of the book display photographs of various spectacular specimens of fossil birds (and some non-avialan dinosaurs). Unlike Birds of Stone, Avian Evolution is not meant to be a pictorial guide and its images are accordingly much smaller, but they are nonetheless of high quality and helpfully supplement the text. Interestingly, a skeletal restoration of Jeholornis by Scott Hartman lacks a retractable second toe, unlike other (and presumably older) versions of this image that I've seen.

In addition to reviewing the primary literature, Mayr provides some observations that are to my knowledge novel or undescribed.
  • Like Chiappe and Meng in Birds of Stone, Mayr supports the proposed synonymy between Iteravis and Gansus zheni. (Unlike Birds of Stone, Mayr directly cites Mortimer for this suggestion.)
  • Alamitornis, originally described as a possible close relative of Patagopteryx, is suggested to be a squamate rather than a bird.
  • In light of the reinterpretation of "Genyornis" eggs as belonging to the megapode Progura, Mayr argues that purported castaway Aepyornis eggs found in Australia should be considered possible candidates for true Genyornis eggs.
  • Neogaeornis, a supposed Cretaceous loon, is considered to share more similarities with grebes.
  • Mayr points out that Paracrax, generally assumed to be a member of the carnivorous Cariamiformes, has a hoatzin-like sternum and may have had a large crop and herbivorous diet similar to that bizarre South American bird.
  • An undescribed London Clay stem-owl specimen, currently held in a private collection, has pieces of the skull indicating that it may have had smaller eyes than extant owls.

Particularly controversial will be Mayr's contention that pennaceous feathers most likely evolved for aerodynamic purposes. This main basis for his argument is that if pennaceous feathers were adaptations for non-aerodynamic functions (such as signaling), it would have been evolutionarily easier to widen the entire shaft rather than forming the complex branching structure of actual pennaceous feathers. Given current knowledge of feather growth, I'm not convinced that it would be developmentally easier to grow a flat sheet rather than adding branches to a feather, despite the structural complexity of pennaceous feathers. Additionally, the argument appears to disregard potential non-aerodynamic benefits of producing branching structures, such as more efficient distribution of material compared to equally-sized continuous sheets. Mayr also suggests that ancestral pennaceous feathers used for display purposes would more likely be sexually dimorphic, which appears to ignore the possible role of mutual sexual selection in ornithodirans (including modern birds).

Mayr points out that pennaceous feathers are generally reduced in flightless birds, attributing the presence of fully formed pennaceous feathers in flightless oviraptorosaurs and dromaeosaurids to potential secondary flightlessness. In particular, he levels the possibility of the small, possibly arboreal scansoriopterygids being close relatives of oviraptorosaurs in support of a volant ancestry for the latter. However, given the many aberrant characteristics of scansoriopterygids, not least of which is the fact that at least some of them appear to have flown or glided using membranes rather than feathers as their primary lift-generating surfaces, I am skeptical that they are particularly informative to oviraptorosaur ancestry even if this phylogenetic hypothesis was correct. In any case, the possibly unusual wing structure of the scansoriopterygids likely makes their relevance to the origin of pennaceous feathers questionable. Though I find it plausible that early pennaceous feathers were used in some form of locomotory behavior (such as increasing maneuverability while running and leaping), I would await more conclusive evidence of secondary flightlessness in non-avialan pennaraptors before declaring aerodynamics to be the most likely explanation for the origin of pennaceous feathers.

I defer to Mayr's knowledge of Cenozoic birds, but I did spot a few minor errors or debatable claims in the Mesozoic chapters besides the discussion of pennaceous feather origins.
  • Avimimus is presented as being of uncertain phylogenetic position, even though it is almost invariably recovered as an oviraptorosaur by recent analyses. (Its position within Oviraptorosauria, on the other hand, is less secure.)
  • A specimen of Baptornis is said to preserve coprolites, but this specimen has been given the new name Fumicollis. (Inexplicably, Fumicollis is mentioned elsewhere in the book.)
  • On a taxonomic note, it is said that affirmation of a close relationship between oviraptorosaurs and scansoriopterygids would make oviraptorosaurs paravians, yet all common definitions of Paraves explicitly exclude oviraptorosaurs. Instead, scansoriopterygids would no longer be considered paravians under such circumstances.
  • Caudipteryx is put forth in support of rectrices being restricted to the tail tip in ancestral pygostylians. Though I concur that it's likely that this was the case for Pygostylia, the presence of rectrices down most of the tail's length in the oviraptorosaur Similicaudipteryx, the dromaeosaurid Zhenyuanlong, the troodont Jinfengopteryx, and the basal avialan or troodont Anchiornis suggests that Caudipteryx may not represent the ancestral condition further down the tree.
  • Lastly and almost inevitably, there are a few typos throughout the text. Most glaringly, a strict consensus tree of neornithine relationships incorrectly shows secretary birds as being more closely related to New World vultures than to accipitrids, likely due to mislabeling of the branches.

Despite these lapses, Avian Evolution is impressively up to date and even cites references from early 2016, including the description of Dingavis and the aforementioned reidentification of "Genyornis" eggs. (However, Chiappeavis is strangely not mentioned as an example of an enantiornithine with a fan-shaped arrangement of tail feathers, even though Feitianius, which was described at around the same time, is.)

This book is part of the Topics in Paleobiology series, a collection of volumes intended to serve as reviews of the primary literature on specific topics in paleobiology for researchers and advanced students. This installment succeeds admirably in my view, being sufficiently technical and comprehensive to synthesize its main topic but helpfully defining specialist terms for those unfamiliar with the specific subject. Think The Complete Dinosaur rather than The Dinosauria in terms of style and level of detail. An extensive bibilography is provided for readers who wish to pursue the discussed topics even further. Avian Evolution is an indispensable review and index to the current literature on fossil birds and I would strongly encourage all academics and well-read laypeople interested in the subject to obtain a copy. Its synthesis of Cenozoic paleornithology alone should secure its place in any paleontological library.

I'm certainly glad that Topics in Paleobiology decided to produce such an essential title. I wonder what else- hold on, what!?

Thanks to this review taking up most of my time, I have not been able to complete my annual retrospective of the previous year's events punctually, but it will be coming up next...