Prehistoric Planet Season 2

To the delight of many, Prehistoric Planet came back this year for a second season. Much of the praise that was lavished on the first season is equally applicable to this one, so I think it's fair to cut to the chase and dive into the specifics of its maniraptoran portrayals. Season 2 follows its predecessor in focusing on life during the Maastrichtian Age of the Late Cretaceous, and with this setting comes a whole cast of both new and returning maniraptoran taxa.

One of these returning maniraptorans is the oviraptorosaur Corythoraptor from the Nanxiong Formation of China, this time shown in a nesting colony. From an aesthetic standpoint, I'm very much a fan of the Corythoraptor model in this series, so it was fantastic to see it get some airtime besides becoming tyrannosaurid chow. This segment was also a great opportunity to showcase the relatively large amount of data we have on oviraptorid reproduction. Sharp-eyed viewers might notice that the Corythoraptor eggs have a rough surface texture composed of numerous tubercles and are arranged in multiple superimposed, partially buried rings with their narrower ends pointing outward and inclined downward, all of which are traits that have been observed in preserved oviraptorid nests. The narration informs us that male Corythoraptor are responsible for tending to the nests, a behavior that has been suggested for oviraptorids based on several lines of evidence. The posture of the nesting Corythoraptor and the presence of a central opening in the nest for them to sit in are also inspired by known oviraptorid specimens.

A Corythoraptor inspects its nest.

There are a few details in this depiction that may be controversial. One scene shows a Corythoraptor moving one of its eggs to a different spot in the nest, but it has been argued that most Mesozoic pennaraptorans likely did not manipulate their eggs after they were laid. In fact, a few studies have disputed the popular idea that oviraptorids incubated their own eggs at all, primarily on the basis of their nest architecture, though recent experimental evidence indicating that such eggs would have still benefited from the body heat of a parent and the absence of any obvious alternative means of incubation currently suggests to me that some level of contact incubation in these dinosaurs is more plausible. I was surprised that the Corythoraptor eggs were not colored blue-green following the inference of such coloration in eggs referred to Heyuannia. This is not a demonstrable inaccuracy (as egg coloration can be highly variable in closely related modern birds), but it seems like the type of scientific detail that Prehistoric Planet has otherwise fallen over itself to include.

Like nest-guarding animals of today, the Corythoraptor in the show have to contend with potential nest raiders. There is an irony to oviraptorids (once interpreted as specialist "egg thieves") being shown suffering from egg predation themselves. In this case, the main threat that appears is the dromaeosaurid Kuru, an unexpected choice given that this dinosaur was named in 2021 (almost certainly well into the production of the series) and is not known to have occurred at the same locality as Corythoraptor, instead having been discovered in the Barun Goyot Formation of Mongolia. I wasn't particularly bothered by this—if these taxa overlapped in time (which is a possibility given that the ages of many Upper Cretaceous fossil-bearing rock units in Asia are far from well constrained), it's entirely plausible that they had geographic ranges larger than their current fossil record would suggest. The Kuru is depicted using the cover of darkness to target the Corythoraptor nests, likely based on evidence from scleral ring anatomy that some dromaeosaurids, including the closely related Velociraptor, may have been primarily nocturnal. 

Speaking of Velociraptor, it is another returning face from the first season. In this season's outing, a family of Velociraptor are portrayed using steep terrain to their advantage while hunting the pachycephalosaur Prenocephale. It's a nice sequence that further showcases the potential diversity of hunting strategies in dromaeosaurids, and includes some cute baby Velociraptor to boot. New to the series (and to paleontology documentaries in general, as far as I'm aware) is the bizarre giant unenlagiine dromaeosaurid Austroraptor from the Allen Formation of Argentina, which is shown preying on fish, as has been hypothesized based on its long snout containing numerous conical teeth.

An Austroraptor dismembers a gar.

The final dromaeosaurid genus to appear in this season is Pyroraptor from southeastern France, with a few juveniles briefly showing up on a shoreline to eat some stranded ammonoid larvae. I'll admit, it did enter my head that Asteriornis* would have been an excellent fit for the geographic location and ecological role demanded by this scene, but I understand that reusing the existing juvenile dromaeosaurid model was undoubtedly much easier for the filmmakers than designing an entirely new animal for such a minor part.

*I'd originally assumed that Asteriornis, having been described in 2020, did not have a chance of being included in either season of Prehistoric Planet. However, the second season does extensively feature the Malagasy mammaliaform Adalatherium, which was described about a month after Asteriornis was.

Moving away from dromaeosaurids (probably), this season also depicts Imperobator from the Snow Hill Island Formation of Antarctica. Imperobator was a large paravian of unclear affinities, and unlike dromaeosaurids, its second toe on each foot was not specialized for being raised off the ground, which Prehistoric Planet portrays correctly. In one scene, several Imperobator are shown as though they were filmed using a thermal imaging camera, and later on, the group attempts to hunt the ornithopod Morrosaurus. Coincidentally, the events in this segment bear some resemblance those of to a fan-made storyboard sequence by Denver Humphries and Ilari Pätilä.

A pair of Imperobator catch their breath on the surface of a frozen lake.

Troodontids are represented in a couple of scenes. Several individuals investigate a fresh Alamosaurus carcass, but, consistent with studies on the structure and wear patterns of troodontid teeth, they are unable to penetrate its thick hide until a Tyrannosaurus opens it up. That troodontids coexisted with these larger dinosaurs is not in doubt, given that their teeth have been found in the Ojo Alamo Formation (or Kirtland Formation, depending on your terminology) of the southwestern United States. Pectinodon from the Lance and Hell Creek Formations further north appears in a separate segment, in which a group visits an alkaline lake to feed on swarms of brine flies, a behavior probably inspired by some extant gulls. The Pectinodon family here consists of a male and its offspring, reflecting the fact that male parental care has been inferred in troodontids for the same reasons that it has in oviraptorids.

Not content with only the flies as a food source, the adult Pectinodon is shown preying on some other paravians that have gathered at the lake, a flock of presbyornithids. An unusual decision was made here to refer to the presbyornithids by a name that has yet to be formally published, originally used for some undescribed pectoral girdle bones from the Hell Creek Formation. Regardless, the anatomy of the presbyornithids, like that of essentially all the other prehistoric animals in the show, is depicted very solidly. Details such as the webbed feet and the flattened, hook-tipped bill lined with keratinous plates for filter feeding were evidently referenced from more completely known Cenozoic presbyornithid fossils. In the interest of full disclosure, I should mention that conversations I've had with Darren Naish, the main scientific consultant on the series, were used to inform these presbyornithid restorations. So that's my informal and infinitesimally minuscule contribution to Prehistoric Planet, and I'm relieved that I no longer have to keep the existence of Season 2 a secret!

The flamingo-duck's smile.

Having said that, my most severe criticism of this season concerns this segment. After the presbyornithids are introduced, the narration follows up with, "Dinosaurs, are here, too" as an segue to the arrival of the Pectinodon, thus implying that the presbyornithids are not also dinosaurs! This is not only flat-out inaccurate, but not mentioning that birds are themselves a group of dinosaurs seems like a major missed educational opportunity, especially considering that Prehistoric Planet has not shied away from showing non-avialan dinosaurs with bird-like appearances and behaviors (including in this very same segment). Darren has hinted that wording more explicitly recognizing the dinosaurian nature of birds was met with pushback from other forces during show production, which I think is incredibly unfortunate given that Walking with Dinosaurs had no issue with referring to avialans as "flying dinosaurs" in 1999.

That's not to end on a dour note, however. There is one more maniraptoran featured in the series left to discuss: the flightless marine euornithean Hesperornis, probably one of the most aquatically-adapted dinosaurs ever to have lived. The best known fossils of Hesperornis are between Coniacian–Campanian in age, but undescribed specimens from the Hell Creek Formation have been mentioned in scientific literature. Having been named in 1872, Hesperornis is no stranger to science, nor to appearances in popular media. However, I feel reasonably secure in saying that the Hesperornis in this series is the most scientifically rigorous depiction of this taxon ever animated in a work of this genre. In Prehistoric Planet, Hesperornis has a beak occupying distinct parts of its jaws from its teeth (despite the narration incorrectly stating that it had a "beak full of [...] teeth"), sprawling hindlimbs with the shins held close to the body, and a rudder-like tail fan (suggested by its broad, flat tail vertebrae), all features that are commonly overlooked in artistic restorations.

A Hesperornis terrorizes a school of fish.

Last but not least, it should be said that Prehistoric Planet Season 2 goes a long way towards addressing both of my main concerns about the first season: the near-absence of tetrapods that weren't non-avialan dinosaurs, pterosaurs, or large marine reptiles, and the limited disclosure about the science behind creative decisions made for the show. This season not only includes two avialan species (the presbyornithids and Hesperornis), but also the crocodylomorphs Simosuchus and Shamosuchus, the snake Madtsoia, the mammaliaform Adalatherium, and (returning from the previous season) the large frog Beelzebufo in prominent roles. On a related note, though ammonoids were not tetrapods, Prehistoric Planet must also be commended again for highlighting the diversity and life history of these key players in Mesozoic marine ecosystems, in a way that no other paleontology documentary has done before.

As for scientific content, twice as many "Uncovered" videos explaining the scientific backing behind the series were produced for this season compared to the last. Half of these segments are also directly attached to the main series episodes (instead of only being available as separate videos), likely allowing them to reach a wider audience. Furthermore, a Prehistoric Planet podcast was released, explaining additional details about the show's creative process. These are welcome additions to the lineup of official Prehistoric Planet media, but they probably still just barely unveil the curtain on the substantial effort and decision-making that assuredly went into the series. I for one would be eager to see even more behind-the-scenes material.

Whether there's more in store from Prehistoric Planet, only time will tell. However, for now I wouldn't be too upset if this were all we ever got. The two seasons of this show have been a veritable triumph, representing by far the most scientifically grounded and up to date portrayal of life in the latest Cretaceous that's currently available as a documentary series.

Alvarezsaurid Paleobiology, an Update

It's been a few years since I wrote a post about alvarezsaurids on this blog, in which I discussed the interpretation of these dinosaurs as specialized insectivores that used their unusual forelimbs to dig for social insects, and why I happened to think that that was the most convincing model for their lifestyle and ecology. Back then, I had little expectation that there would be much alvarezsaurid news in the immediate future, so it was a pleasant surprise to see an alvarezsaurid featured prominently and portrayed as a termite-eating specialist in the high-profile documentary series Prehistoric Planet last year. Not only that, but many studies on alvarezsaurids have been published in the intervening time. Has this newfound information updated and modified my thoughts on how alvarezsaurids lived? Let's take a look.

The New Alvarezsaurs on the Block
To start off, several new alvarezsaurid taxa were named in recent years, including Trierarchuncus from the Hell Creek Formation of the western United States (Fowler et al., 2020; Freimuth and Wilson, 2021), Dzharaonyx from the Bissekty Formation of Uzbekistan (Averianov and Sues, 2021), and Khulsanurus and Ondogurvel from the Barun Goyot Formation of Mongolia (Averianov and Lopatin, 2022a; Averianov and Lopatin, 2022b). The braincase of an indeterminate alvarezsaurid from the Qiupa Formation of China was also described (Agnolín et al., 2022), and the anatomy of Parvicursor was reevaluated in detail (Averianov and Lopatin, 2021).

Nearly complete thumb claw of Trierarchuncus, from Fowler et al. (2020).

In general, most of these new findings don't substantially change what I previously talked about, but it's great to have more alvarezsaur anatomy to work with. Trierarchuncus deserves mention, however, in that one of the specimens referred to it represents the most completely preserved alvarezsaurid thumb claw to date. I noted in my previous post on alvarezsaurs that complete alvarezsaurid thumb claws are hard to come by, making it difficult to compare their shape to the claws of modern animals. This Trierarchuncus specimen reveals that at least some alvarezsaurid thumb claws were much more sharply curved than formerly expected, in line with their hypothesized function in hook-and-pull digging.

Reconstructed curvature of the thumb claw of Mononykus based on that of Trierarchuncus, from Fowler et al. (2020).

In addition, comparing the claws of differently sized Trierarchuncus individuals suggests that as alvarezsaurids aged, the bony core of their thumb claws became wider and gained a roughened texture (possibly induced by stress) near where the claw attached to the rest of the thumb, consistent with the use of the claws in strenuous activity (Fowler et al., 2020; Freimuth and Wilson, 2021).

Turning Tail
As I mentioned in my previous post, a long tail for balance can be a helpful adaptation to a hook-and-pull digger. Although alvarezsaurids were long tailed, however, a long tail is typical of diapsid reptiles, so this in itself was not necessarily a specific adaptation to digging in alvarezsaurids. That being said, alvarezsaurids did have a few unusual features of the tail that may shed light on their lifestyle, and Meso et al. (2021) provided a detailed description and functional interpretation of alvarezsaurid tail anatomy.

For one, alvarezsaurids were long-tailed even for theropods; relative to their body size, they probably had among the longest tails of any maniraptoran. For another, many features of their tail vertebrae suggest that their tails were more flexible from side to side than those of most other theropods. Probably to compensate for this increase in length and mobility, the muscles along the top of the tail that would have helped hold it aloft appear to have been well developed in alvarezsaurids. Also abnormal among theropods is the fact that alvarezsaurid tail vertebrae were procoelous: the back end of each vertebra fit into a socket in the front end of the vertebra behind it. (In typical theropods, the joint surfaces of the tail vertebrae tend to be flat or nearly so.) This may have been another way of reinforcing the tail, giving it further mobility without a correspondingly high risk of dislocating the vertebrae.

Reconstructed tail musculature of an early alvarezsaur (A), a patagonykine alvarezsaurid (B), and a parvicursorine alvarezsaurid (C), from Meso et al. (2021).

Meso et al. note that overall configuration of the alvarezsaurid tail exhibits similarities to that of the extant aardvark (Orycteropus afer), which also has large muscles running along the top of a long (by mammal standards), strong, and flexible tail. In aardvarks, the tail probably serves an important role as a brace while digging (Endo et al., 2013). This could have also been the case in alvarezsaurids, but Meso et al. suggest that their characteristic tail morphology might have provided another adaptive benefit. As I discussed previously, one of the many strange features seen in alvarezsaurids is their apparent specialization towards running, and it is likely that they relied on this as a means to escape predation. Meso et al. posit that their increased tail flexibility gave alvarezsaurids a smaller turning radius, granting them a further advantage in avoiding pursuers.

Diagram showing how the flexible tail of alvarezsaurids might have helped them avoid predators (with a successful escape making use of a reduced turning radius shown in B), from Meso et al. (2021).

Creatures of the Night
How an animal perceives the world naturally has a major influence on how it interacts with its environment and the other organisms in it, and Choiniere et al. (2021) offered some considerable insight into this aspect of alvarezsaurid biology. Their study was not focused solely on alvarezsaurs, but compared the proportions of the scleral ring (a bony ring embedded in the eyeball of many vertebrates, though not in mammals) and the anatomy of the inner ear in a wide variety of Mesozoic dinosaurs to those of extant birds and other reptiles. However, the results they found for the alvarezsaurid Shuvuuia (one of the few alvarezsaurs in which both of these elements are well preserved) were especially intriguing.

The anatomy of both the scleral ring and inner ear in Shuvuuia strongly suggests that it was primarily active at night. What's more, its inner ear exhibits an extreme morphology similar to that of the extant western barn owl (Tyto alba), a nocturnal predator that famously uses sensitive hearing to detect prey. It's important to emphasize here (as I've seen some popular retellings of this study misunderstand this) that the observed similarities between the inner ear of Shuvuuia and barn owls are due to the structure of the ear itself, not related to ear asymmetry.

Barn owls and their close relatives in the group Tytonidae are one lineage of owls that have evolved asymmetrical ears, which help them pinpoint the location of their prey. Ear asymmetry in owls can take several different forms, but in tytonids, the left ear opening is generally positioned higher than the right. However, this asymmetry is not reflected in their skull (Norberg, 2002). There are owls (such as those in the genus Aegolius) that do have asymmetrical skulls, but tytonids are not among them. Choiniere et al. also found no evidence of skull asymmetry in Shuvuuia. Might alvarezsaurids have instead had asymmetry in the soft tissue morphology of their ears, like barn owls? That seems like a possibility, but we may not be able to determine one way or another from their bony anatomy.

The back of the skull and inner ear of Shuvuuia (A–C) compared to that of a western barn owl (D–F), from Choiniere et al. (2021).

As noted by Choiniere et al., a combination of a nocturnal lifestyle with specialized hearing is widespread in tetrapods, especially in mammals, so the fact that Shuvuuia exhibits evidence of these traits does not by itself indicate that alvarezsaurids were myrmecophagous (feeding mostly on social insects). However, there is indeed an extant myrmecophage that often forages at night primarily by acoustic cues, the bat-eared fox (Otocyon megalotis) (Renda and le Roux, 2017). Therefore, I consider these new findings on alvarezsaurid sensory biology very much compatible with the hypothesis that they were myrmecophages. (In fact, I was aware of Choiniere et al.'s research before its formal publication, and deliberately inserted a reference to the bat-eared fox into my last alvarezsaur post as oblique foreshadowing.)

A bat-eared fox, photographed by Yathin S Krishnappa, under CC BY-SA 3.0. This species feeds mainly on termites, which it locates using its sensitive hearing. Perhaps alvarezsaurids did the same?

The Incredible Shrinking Alvarezsaurs
My previous post also mentioned small body size as as a curious evolutionary trend in later alvarezsaurids, and Qin et al. (2021) investigated this phenomenon in more detail. First of all, by inferring growth patterns based on the bone microstructure of individual alvarezsaur specimens, they confirmed that some alvarezsaurids, such as Albinykus and Xixianykus, had adult body masses of only about 1 kg or less. (It's worth noting though that one of the smallest known alvarezsaurids, the type specimen of Parvicursor, was subsequently reinterpreted as a juvenile instead of an adult by Averianov and Lopatin, 2021.)

Interestingly, Qin et al. indicated that Albinykus and Xixianykus had very different growth strategies from one another despite being of similar sizes. Whereas the type specimen of Albinykus had essentially stopped growing by the time it was three years old, the type specimen of Xixianykus grew more slowly but across a longer period of time, living for over a decade. This diversity in alvarezsaurid growth patterns was also observed more recently by D'Emic et al. (2023).

When Qin et al. plotted alvarezsaur body size across the evolutionary history of these dinosaurs, they found that not only were later alvarezsaurids smaller overall than their ancestors, but their small body size evolved very quickly in the early Late Cretaceous, about 90 million years ago. What may have caused this sudden miniaturization? Qin et al. point out that this event would have shortly followed the estimated diversification of both ants and termites during the Cretaceous, which may have created the opportunity for dedicated myrmecophagy to evolve in alvarezsaurs. Specialized insectivory as a driver of alvarezsaurid size reduction would also align with the median body size of insectivorous land vertebrates being consistently smaller than those with other dietary habits, a pattern that has been shown to hold true across different groups and biomes (Cooke et al., 2022).

Evolution of alvarezsaur body size over time, from Qin et al. (2021).

When All You Have is a Pick...
As I hope I reviewed thoroughly in my last alvarezsaur post, there are many features of alvarezsaurid forelimbs that suggest they functioned in digging. However, just how effective their claws would have been at this task had not been quantitatively tested until recently. Qin et al. (2023) applied finite element analysis (FEA) to alvarezsaur hand claws to compare how they performed under different scenarios. (This study also looked at the claws of therizinosaurs, but this post is not about them.) 

For each claw studied, three scenarios were tested: piercing (puncturing a substrate), pulling (using the underside of the claw to pull an object downward), and scratching (dragging the tip of the claw through a substrate), with the last being considered analogous to digging. When compared to a variety of mammals representing a range of claw morphologies and functions, the claws of alvarezsaurids were found to behave akin to those of pangolins: experiencing relatively low stress and similar stress distributions across all three scenarios. On the surface, it may sound surprising that such seemingly specialized claws would be well suited to multiple tasks in this way, but as Qin et al. point out, this makes a lot of sense if alvarezsaurids were diggers. Hook-and-pull digging in particular requires piercing, pulling, and scratching motions, so it would be potentially advantageous for animals adapted for this behavior to excel at all three.

Furthermore, Qin et al. found that the claws of alvarezsaurids performed better at scratching than those of earlier, non-alvarezsaurid alvarezsaurs, which had hands more broadly similar to those of typical theropods. This may suggest that increased digging specializations were specifically being selected for during alvarezsaur evolution.

Claw performance under different simulated scenarios in a selection of mammals (a), non-alvarezsaurian theropods (b), and alvarezsaurs (c), from Qin et al. (2023). What surprises me the most is that the fields for the pangolin and the tamandua plot so far apart, especially considering that, according to the supplementary material, the pangolin species studied was the tree pangolin (Phataginus ["Manis"] tricuspis), which, like tamanduas, spends a lot of time in trees. Maybe there is more functional variation among these superficially similar myrmecophages than commonly appreciated.

It makes me happy to see so much new alvarezsaur research being done lately, and new advances have been made in understanding the digging abilities of extinct mammals as well (Nakai and Fujiwara, 2023), which could perhaps be applied to alvarezsaurs in the future. I'm certainly pleased that essentially all of these new alvarezsaur studies either reinforce or are consistent with the hypothesis that alvarezsaurids were myrmecophages. However, what excites me most of all is that I might have had a very small hand in bringing some of this science to fruition. I have it on good authority from Qin Zichuan that he and his colleagues' study on alvarezsaurid claw biomechanics was directly inspired by my previous alvarezsaur post, in which I idly suggested some potential directions for future investigations into alvarezsaurid ecology. For my humble blog post, having stimulated actual scientific research on these remarkable dinosaurs is just about the highest honor that I can conceive of.

Excerpt from the acknowledgements of Qin et al. (2023).

References

• Agnolín, F.L., J.-C. Lu, M. Kundrát, and L. Xu. 2022. Alvarezsaurid osteology: new data on cranial anatomy. Historical Biology 34: 443–452. doi: 10.1080/08912963.2021.1929203
  
• Averianov, A.O. and A.V. Lopatin. 2021. A re-appraisal of Parvicursor remotus from the Late Cretaceous of Mongolia: implications for the phylogeny and taxonomy of alvarezsaurid theropod dinosaurs. Journal of Systematic Palaeontology 19: 1097–1128. doi: 10.1080/14772019.2021.2013965
  
• Averianov, A.O. and A.V. Lopatin. 2022a. The second taxon of alvarezsaurid theropod dinosaurs from the Late Cretaceous Khulsan locality in Gobi Desert, Mongolia. Historical Biology 34: 2125–2136. doi: 10.1080/08912963.2021.2000976
• Averianov, A.O. and A.V. Lopatin. 2022b. A new alvarezsaurid theropod dinosaur from the Upper Cretaceous of Gobi Desert, Mongolia. Cretaceous Research 135: 105168. doi: 10.1016/j.cretres.2022.105168
  
• Averianov, A.O. and H.-D. Sues. 2021. New material and diagnosis of a new taxon of alvarezsaurid (Dinosauria, Theropoda) from the Upper Cretaceous Bissekty Formation of Uzbekistan. Journal of Vertebrate Paleontology 41: e2036174. doi: 10.1080/02724634.2021.2036174
• Choiniere, J.N., J.M. Neenan, L. Schmitz, D.P. Ford, K.E.J. Chapelle, A.M. Balanoff, J.S. Sipla, J.A. Georgi, S.A. Walsh, M.A. Norell, X. Xu, J.M. Clark, and R.B.J. Benson. 2021. Evolution of vision and hearing modalities in theropod dinosaurs. Science 372: 610–613. doi: 10.1126/science.abe7941
• Cooke, R., W. Gearty, A.S.A. Chapman, J. Dunic, G.J. Edgar, J.S. Lefcheck, G. Rilov, C.R. McClain, R.D. Stuart-Smith, S.K. Lyons, and A.E. Bates. 2022. Anthropogenic disruptions to longstanding patterns of trophic-size structure in vertebrates. Nature Ecology and Evolution 6: 684–692. doi: 10.1038/s41559-022-01726-x
  
• D'Emic, M.D., P.M. O'Connor, R.S. Sombathy, I. Cerda, T.R. Pascucci, D. Varricchio, D. Pol, A. Dave, R.A. Coria, and K.A. Curry Rogers. 2023. Developmental strategies underlying gigantism and miniaturization in non-avialan theropod dinosaurs. Science 379: 811–814. doi: 10.1126/science.adc8714
• Endo, H., K. Mori, D. Koyabu, S. Kawada, T. Komiya, T. Itou, H. Koie, M. Kitagawa, and T. Sakai. 2013. Functional morphology of the aardvark tail. Anatomia, Histologia, Embryologia 42: 90–98. doi: 10.1111/j.1439-0264.2012.01169.x
  
• Fowler, D.W., J.P. Wilson, E.A. Freedman Fowler, C.R. Noto, D. Anduza, and J.R. Horner. 2020. Trierarchuncus prairiensis gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana. Cretaceous Research 116: 104560. doi: 10.1016/j.cretres.2020.104560
  
• Freimuth, W.J. and J.P. Wilson. 2021. New manual unguals of Trierarchuncus prairiensis from the Hell Creek Formation, Montana, and the ontogenetic development of the functional alvarezsaurid hand claw. Cretaceous Research 119: 104698. doi: 10.1016/j.cretres.2020.104698
• Meso, J.G., Z. Qin, M. Pittman, J.I. Canale, L. Salgado, and V. Díez Díaz. 2021. Tail anatomy of the Alvarezsauria (Theropoda, Coelurosauria), and its functional and behavioural implications. Cretaceous Research 124: 104830. doi: 10.1016/j.cretres.2021.104830
  
• Nakai, D. and S. Fujiwara. 2023. Fossorial mammals emphasise the forelimb muscle moment arms used for digging: new indices for reconstruction of the digging ability and behaviours in extinct taxa. Journal of Anatomy 242: 846–861. doi: 10.1111/joa.13815
  
• Norberg, R.Å. 2002. Independent evolution of outer ear asymmetry among five owl lineages; morphology, function and selection. Pp. 329–342, in I. Newton, R. Kavanagh, J. Olsen, and I. Taylor (eds.), Ecology and Conservation of Owls. CSIRO Publishing, Clayton. 
• Qin, Z., Q. Zhao, J.N. Choiniere, J.M. Clark, M.J. Benton, and X. Xu. 2021. Growth and miniaturization among alvarezsauroid dinosaurs. Current Biology 31: 3687–3693. doi: 10.1016/j.cub.2021.06.013
• Qin, Z., C.-C. Liao, M.J. Benton, and E.J. Rayfield. 2023. Functional space analyses reveal the function and evolution of the most bizarre theropod manual unguals. Communications Biology 6: 181. doi: 10.1038/s42003-023-04552-4
• Renda, S. and A. le Roux. 2017. The sensory ecology of prey detection in the bat-eared fox (Otocyon megalotis). Behaviour 154: 227–240. doi: 10.1163/1568539X-00003419
  

SAPE 2023

I'd never been to a SAPE (Society of Avian Paleontology and Evolution) conference before, partly because one hadn't happened for years. This year's meeting in Málaga had originally been scheduled for 2020, which would have been while I was studying for my PhD. The COVID-19 pandemic, however, had other plans, and ended up delaying the conference for three years.

This was not only my first SAPE, but also my first time in Spain, so I wasn't quite sure what to expect. However, almost everything went reasonably smoothly for me, other than the fact that I am still recovering from a post-conference ailment—that's one thing I didn't miss about in-person meetings! As far as the conference itself was concerned, I found it very well organized, with a variety of planned activities and enough downtime in between to make it eventful without being hectic. It probably helped that it was a fairly small conference, allowing the talks to be spread out enough that one could attend all of them without feeling overwhelmed.

It was also nice to see this familiar face on Spanish television.

Speaking of talks, I gave another version of my presentation from last year's SVP, summarizing the results of my PhD research. Even more so than SVP last year, my labmates represented a large contingent among the attendees. In fact, the session I spoke in consisted almost exclusively of presentations by members of my supervisor's lab group! Many jokes were made about how we were essentially holding our weekly lab meeting at SAPE. Outside of my labmates' work though, some presentations I especially enjoyed included Phoebe McInerney's talk on dromornithid cranial anatomy, Jacob Blokland's talk on the phylogeny of Australian fossil ralloids, and Anaïs Duhamel's talk on studying the migratory behavior of fossil birds.

To me, one of the perks of traveling someplace new is of course the opportunity to see birds and other wildlife that I haven't seen before. The rich biodiversity of Spain was promising in this regard, and the organizers of SAPE this year did very well to capitalize on it by arranging two field trips with ample birding opportunities. First, there was a half-day excursion to Desembocadura del Guadalhorce, a nature reserve dedicated to conserving the estuary of the Guadalhorce river. The other spanned a full day, visiting El Caminito del Rey (a hiking trail along the side of a narrow gorge) in the morning and, after a surprisingly lengthy lunch, Laguna de Fuente de Piedra (a large saline lagoon) in the evening. In total, I saw over 70 species of birds in Spain, more than 30 of which I'd not seen in the wild previously. A few of my favorite sightings included greater flamingos, Eurasian griffon vultures, and endangered white-headed ducks.

Most of these birds were seen from a fair distance, so I didn't take many bird photos. However, here is a pair of Kentish plovers we spotted on the beach at Desembocadura del Guadalhorce.

Rock pigeons along El Caminito del Rey. It almost felt strange to encounter this species in such a naturalistic setting, but their mastery of this environment was immediately evident. You haven't truly seen rock pigeons unless you've seen them acrobatically catching updrafts along sheer cliffs like these.

A non-avian resident of the gorge, an Iberian ibex.

A distant view of Laguna de Fuente de Piedra. At the time of our visit, most of the water had dried up (as it does every so often), concentrating a decent number of flamingos, waterfowl, and shorebirds.

Review of 2022

Well, I succeeded in posting more last year than I did in 2021, at least. However, most of the posts I made were not research-heavy informational articles about maniraptors, as I've intended this blog to focus on. Instead, I was motivated to write by the release of Prehistoric Planet, the return of in-person conferences, and a sudden urge to talk about a childhood icon.

If my relative silence on here reflects anything, it's probably that 2022 was a big year for me. Most conspicuously, I graduated with my PhD from the University of Bath and started a postdoctoral position at the University of Cambridge. In addition, a paper I co-authored was published: spearheaded by my labmate Juan Benito Moreno, we described the postcranial anatomy of Ichthyornis based on 40 new specimens. I also finished drawing an infographic on bird phylogeny, on which I'd been working intermittently for about two years (and planning for even longer than that), and was fortunate enough to be invited for an interview about my research and outreach by science communicator Jon Perry. Miraculously, I was able to continue updating New Dinosaur Alert and Through Time and Clades fairly consistently. Between research, peer reviewing, networking, and a well of other personal projects either in progress or on the horizon, I'm fully expecting activity on this blog to remain low in the foreseeable future. There are still elements of blogging I enjoy, however, so I certainly don't intend to stop posting entirely.

My infographic on bird phylogeny, which can be viewed in detail here.

I will be making a few changes to this year's review of new maniraptoran research. First of all, I will not be writing a separate post going over new species in detail, as I think the time and effort spent on that would be largely redundant with respect to my work on New Dinosaur Alert. Secondly, though listing studies by publication month has been convenient for me in previous years, I suspect that that format is not particularly useful to most readers. Instead, I will try out a rough phylogenetic organization of the stories here. 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.

General and non-paravian maniraptors

• Environmental factors affecting feather taphonomy
• New alvarezsaurs Dzharaonyx eski and Ondogurvel alifanovi
• Redescription of Parvicursor
• New therizinosaur Paralitherizinosaurus japonicus
• Cranial biomechanics of oviraptorosaurs
• Reproductive biology of oviraptorosaurs
• Flapping mechanics of Caudipteryx
• Caenagnathids from the Cerro del Pueblo Formation
• Subadult specimen of Yulong
  
• Tracks from the Late Cretaceous of Italy identified as likely belonging to oviraptorosaurs

Estimated gape limits in oviraptorosaurs, from Meade and Ma (2022).

General and non-neornithean paravians

• Comment and response on the role of wing-assisted incline running (WAIR) in the origin of avian flight
  
• Skull morphometrics of Mesozoic paravians
• Body profiles of Mesozoic paravians based on soft tissues
• Soft tissues of the feet in Mesozoic paravians
• New dromaeosaurids Natovenator polydontus and Daurlong wangi
• Microraptor ate mammals
• Maxillary evolution in eudromaeosaurs
• Giant dromaeosaurid from the Bissekty Formation
• Osteology of Dineobellator
  

Holotype of Daurlong wangi, from Wang et al. (2022).

• Troodontid hand from the Yixian Formation
• Birds of the Mesozoic by Juan Benito Moreno and illustrated by Roc Olivé Pous published (I may have had a hand in this one)
  
• Evidence of frugivory in and cranial osteology of Jeholornis
• Pectoral girdle morphology of Sapeornis and Piscivorenantiornis
  
• New confuciusornithiform Confuciusornis shifan
  
• Taphonomy of a claw sheath in Confuciusornis
• Ontogenetic niche shifts in Confuciusornis
  
• New enantiornitheans Beiguornis khinganensis, Musivavis amabilis, and Yatenavis ieujensis
• Cranial anatomy of Yuanchuavis
  
• Diet of longipterygids
  
• Enantiornithean braincase from the Adamantina Formation
• Scales of Gansus
• New ichthyornithean Janavis finalidens
• Postcranial anatomy of Ichthyornis
  
• Connectivity patterns of the hindlimb musculoskeletal system in diving avialans
  
• Review of hesperornithiform diversity

Schematic skeletal of Janavis finalidens with preserved bones shown, from Benito et al. (2022).

General crown birds 

• Second edition of Paleogene Fossil Birds by Gerald Mayr published
• Catalogue of fossil birds of Cuba
• Survey of the avian uncinate bone
• Variation in avian sternal keel shape
  
• Functional morphology of the avian pelvis
• Ossification of the avian vertebral column
• Identification of skeletal maturity in birds
• Bone histology of large flightless birds
• Scaling of avian ear morphology
• Survey of avian paramedullary diverticula
  
• Development of the avian pelvis parallels its evolutionary history
• Diversification of avian limb morphology
• Environmental signal in the diversification of avian skeletons

Developmental history of the avian pelvis compared to its evolutionary history, from Griffin et al. (2022).

• Special issue on avian functional traits
• Interrelationships among body mass, jaw musculature, and bite force in birds
• Avian coracoid strength as an indicator of wing-beat propulsion
• Possible link between avian brain size and flight mode
• Flying birds transition between stable and unstable states via wing morphing
• Role of wingbeat frequency and amplitude in avian flight power
• Role of tail in stability and energetic cost of avian flapping flight
• Soaring performance of giant birds (and pterosaurs)
• Correlation between high wing loading and avian dive performance
  
• Diversity of avian eggshell thickness indices
• Review of feather function in birds
• Evolution of avian facial bristles
• Review of thermal effects of plumage coloration
• Contrastingly-colored ventral wings as visual collision avoidance signals in birds
  
• Ornaments are equally informative in male and female birds

Associations between ornament elaboration and body condition or fitness in mutually ornamented bird species, from Nolazco et al. (2022).

• Correlation between avian neuron numbers and innovativeness
• Problems with using comparative analyses of avian brain size to test hypotheses of cognitive evolution
• Adaptive variation in the upper limits of avian body temperature
• Genomic basis for avian tactile foraging
• Review of genomic bases for adaptation in birds
• Evolution of the broken-wing display in birds
• Aggressive signaling among competing bird species
• Complexity of avian brood parasite–host relationships
• Effect of flight efficiency on gap-crossing ability in birds from the Amazon
• Riverine barriers as obstacles to dispersal in birds from the Amazon
• Interspecific competition limits avian species ranges in tropical mountains
• Seasonal avian species richness on islands
  
• Biome conservatism in galliforms and falcons
  
• Macroevolutionary dynamics of avian climatic niche space
  
• Changes in avian range size from Pleistocene climatic oscillations
  
• Post-settlement extinction rates for New Zealand birds
• Phylogenetic nomenclature of avian clades, including new names for the moa–tinamou clade (Dinocrypturi), the mesite–sandgrouse clade (Pteroclimesites), the putative turaco–bustard clade (Musophagotides), the phaethontimorph–aequornithean clade (Phaethoquornithes), and the suliform–pelecaniform clade (Pelecanes)
• Bird from the Na Duong Formation
• Conflicting signals in neoavian phylogenetics
• Phylogeny of neoavians based on retroelements
• Rate of mutation accumulation in neoavians
  
• Evolution of diving in neoavians
  
• Review of convergence across nectarivorous birds
• Coevolution between channel-billed cuckoos and pied currawongs

Distribution of diving behavior in aquatic neoavians, from Tyler and Younger (2022).

 Paleognaths

• Review of the paleognath fossil record
• Review of putative paleognath fossils from South America and Antarctica
• Bone histology of paleognaths
• Stratigraphic distribution of the egg taxon Psammornis
  
• Reevaluation of Struthio asiaticus
• Preserved peptides in ostrich eggshell from the Liushu Formation
• Trade-offs between heat and cold tolerance in common ostriches
• Divergent benefits of cooperative breeding for male and female common ostriches
• Diogenornis-like fossils from Argentina reinterpreted as remains of an indeterminate paleognath and a stem-penguin
• Wing anatomy of the greater rhea
• Intraspecific variation in the casque of southern cassowaries
• Phylogeny of kiwi
• Population genetic structure of North Island brown kiwi
• Genetic evidence for a post-glacial population expansion in eastern moa
• "Tinamou egg" from the Dolores Formation reinterpreted as a mammal intestinal stone

Variation in the casque of southern cassowaries, from Green et al. (2022).

Galloanserans

• Evidence from ancient protein sequences presented in favor of a dromornithid (instead of megapode) identity for putative Genyornis eggshells
• Bone histology of Dromornis
• Ecomorphology of the anseriform tarsometatarsus
  
• New Miocene anatid Allgoviachen tortonica
• New Miocene anatid Notochen bannockburnensis
• New Miocene filter-feeding, flightless swans Annakacygna hajimei and Annakacygna yoshiiensis (memorably deemed the "ultimate bird[s]" to ever exist by their describers)
• Development of denticulations in domestic geese
• New Miocene shelduck Miotadorna catrionae (argued to be synonymous with Miotadorna sanctibathansi by a later study)
• Use of wings by common mergansers while diving
• New Pleistocene duck Spatula praeclypeata

Skeletal reconstruction of Annakacygna hajimei, from Matsuoka and Hasegawa (2022).

• Endocast of Sylviornis
• Evolution of courtship displays in galliforms
• Ecosystem engineering by mound-building malleefowl
• Thermoregulatory function of the throat sack in helmeted guineafowl
• Phylogeny of American quails
• Generation of a three-dimensional illusion and a novel form of blue structural color in feathers of great argus
• New Pliocene phasianid "Pliogallus" csarnotanus ("Pliogallus" is almost certainly synonymous with the extant Gallus)
• The origin of domestic chickens (a comment and response to this study was published later in the year)
• Development of ribs and intercostal muscles in chickens
• Kinematics of walking up and down steps in common quails
• New Miocene phasianid Centuriavis lioae

Holotype of Centuriavis lioae, from Ksepka et al. (2022).

Miscellaneous neoavians

• Flamingo from the Kramer Beds
• Phylogeny of flamingos
• Limited domestic introgression in rock pigeons of the Outer Hebrides
• Neurons of rock pigeons consume less glucose than those of mammals
• Taxonomy of the brush cuckoo species complex

Strisoreans

• Taxonomy of eared nightjars
• Craniomandibular simplicity in the band-winged nightjar
• New Miocene owlet-nightjar Aegotheles zealandivetus
• Moonlight drives nocturnal vertical flight dynamics in black swifts
• Torpor in common swifts
• Model of the musculoskeletal system of hummingbird wings
• Evolution of sexually dimorphic traits in hummingbirds
• Plumage color diversity of hummingbirds
• Heterothermic spectrum in hummingbirds
• Review of vocal communication in hummingbirds
• Intersexual social dominance mimicry drives female polymorphism in white-necked jacobins
• Sexual selection for flight performance in mellisugin hummingbirds

Plumage color diversity in hummingbirds, from Venable et al. (2022).

Gruiforms and charadriiforms

• Relationship between flightlessness and brain morphology in rails
• Phylogenetic position of the Zapata rail
• Divergence times of shorebirds
• Buttonquails from the Oligocene–Miocene of France
• Phylogeny of skuas
• Flightless molt strategies of Atlantic puffins
• Dark wing pigmentation improves flight efficiency in gulls

Time-scaled phylogeny of shorebirds, from Černý and Natale (2022).

Phaethoquornitheans

• New stem-loon Nasidytes ypresianus
• Review of the evolutionary and biogeographical history of penguins
• Comparative anatomy of the synsacral canal in penguins
  
• Illustration of penguin head anatomy
• Genomic insights into penguin evolution
• Breeding biology of erect-crested penguins
• Comparative anatomy of the compound rhamphotheca in procellariiforms
• Historical genetic structure of short-tailed albatrosses
• Deep diving in black-browed albatrosses
• Phylogeny of the fairy prion and the fulmar prion
• Response of streaked shearwaters to cyclones
• Species delimitation in Puffinus shearwaters
• New specimens of Leptoptilos robustus
• Phylogeography of frigatebirds
• Diversification of blue-eyed shags
• Comparative morphology of the remote-touch bill-tip organ in ibises

Holotype of Nasidytes ypresianus, from Mayr and Kitchener (2022).

Telluravians

• New Miocene telluravian-like bird Zealandornis relictus
• Formation of Indo-Pacific bird diversity across barriers and along elevational gradients
• River network rearrangements promote speciation in lowland Amazonian birds
• Myological variation in raptors
• Postcranial skeletal pneumaticity in accipitrimorphs
• Humeral morphometrics in vultures
• Large condor from the Luján Formation
• New Miocene cathartid vulture Dryornis hatcheri
• Coloration mechanisms of bare skin on the heads of American vultures
• Paleogenomics of Coragyps occidentalis
  
• Orbit and endocranial morphology of the letter-winged kite
• New Miocene gypaetine vultures Gypaetus georgii and Neophron lolis
• New genus Cryptogyps for "Taphaetus" lacertosus, identified as an aegypiine vulture
• Optimization of perching maneuvers by Harris's hawks
• Buteo hawk from the Miocene of Italy
• Avoidance of the confusion effect by Swainson's hawks while hunting Mexican free-tailed bats

Skull and endocast of the letter-winged kite, from Keirnan et al. (2022).

• New stem-owl Ypresiglaux michaeldanielsi
• Giant barn owl from the Holocene of Guadeloupe
• Role of the tail in drag minimization in gliding barn owls
• Genomic basis of insularity and ecological divergence in barn owls of the Canary Islands
• Phylogenetic position of the forest owlet
• New Miocene owl Miosurnia diurna
• New extant owl, the Príncipe scops-owl (Otus bikegila)
• Reevaluation of a putative Holocene record of the Eurasian eagle owl from Britain
• Great gray owls hover to defeat an acoustic mirage while hunting

Holotype of Miosurnia diurna, from Li et al. (2022).

• New indeterminate telluravian Lutavis platypelvis and possible stem-courols Plesiocathartes insolitipes, Waltonavis paraleptosomus, and Waltonavis danielsi
• Social diffusion of foraging techniques in southern ground hornbills
• Woodpeckers minimize cranial shock absorption
• Evolution of drumming in woodpeckers
• Correlated evolution between color conspicuousness and drum speed in woodpeckers
  
• Evolution of sweet taste perception in woodpeckers
• Role of cranial kinesis in retracting stuck beaks of black woodpeckers during pecking
• Brain regions of downy woodpeckers linked to drumming displays
• New stem-falcon Danielsraptor phorusrhacoides
  

Skull of the holotype of Danielsraptor phorusrhacoides, from Mayr and Kitchener (2021). (The print version of the journal retroactively dates the paper to 2021, but really, the paper was first released in 2022.)

• Biogeography of psittacopassereans
• Phylogeny of parrots
• Coevolution of brain size and life expectancy in parrots
• Past trophic ecology of kea
• Origin of tool use in Tanimbar corellas
  
• Composite tool use by Tanimbar corellas
• Potential case of an innovation arms race between sulfur-crested cockatoos and humans
• Climbing mechanics of green-cheeked conures
• Tripedal locomotion in rosy-faced lovebirds

Experimental setup for studying composite tool use in Tanimbar corellas, from Osuna-Mascaró et al. (2022).

• New stem-passeriforms Minutornis primoscenoides, Psittacomimus eos, ?Psittacopes occidentalis, and Primoscens carolinae
• Comparative anatomy of the carpometacarpus in passeriforms
• Evolution of carotenoid-based plumage coloration in passeriforms
  
• Patterns of ultraviolet reflectance evolution in passeriforms
• Latitudinal gradients in passeriform colorfulness
• Correlates of aerial displays in passeriforms
• Drivers of variation in cup nest size in passeriforms
• Macroevolutionary consequences of nest type in passeriforms
• Faster evolution of song discrimination not associated with faster speciation rates in passeriforms
• Evolution of mimicry in juvenile tyrannidans
• Dancing drives sexual size dimorphism in manakins
• Evolution of gene expression underlying superfast muscles of manakins
• Conflicting signals in manakin phylogenetics
• Phylogeny of Lepidothrix manakins
• Speciation in Pipra manakins
• The black-and-white becard actually consists of two distantly related species
• Evolution of exaggerated sexual traits in kingbirds
• Population dynamics of antbirds
• Diversification of Willisornis antbirds 
• Diversification of bare-eyes
• Adaptations to climbing in the feet of ovenbirds
• Correlates of molecular evolutionary rates in ovenbirds
• New extant ovenbird, the subantarctic rayadito (Aphrastura subantarctica)

Distribution of mimetic traits in juvenile tyrannidans, from Londoño et al. (2022).

• Nest architecture linked with ecological success in songbirds
• Feather growth rate in songbirds explained by breeding latitude
• Post-copulatory multimodal display performed by male superb lyrebirds
• Emergence of multilevel societies in superb fairy-wrens
• Evolutionary history of female ornamentation in white-shouldered fairy-wrens
• Relationship between geographic range size and speciation in honeyeaters
• New genus Eugymnomyza for the crow honeyeater ("Gymnomyza" aubryana)
• Diversification of corvideans
• The phylogeny of the maroon oriole species complex
• Australian magpies cooperatively remove tracking devices from each other
• Phylogeography of Paradisaea birds-of-paradise
• Diversification of corvids
• High associative neuron numbers in corvids
• Speciation in scrub-jays
• Delay of gratification in Eurasian jays
• Diversification of nutcrackers
• How consensus in Eurasian jackdaws governs mass departures from their roosts
• Brain atlas of the carrion crow
• Recursive sequence generation in carrion crows
• Review of tool use in common ravens

Phylogeny of corvideans, from McCullough et al. (2022).

• Phylogeny and phylogeography of New Zealand wattlebirds
• Migratory route of the Arctic warbler
  
• New extant white eyes, the Meratus white-eye (Zosterops meratusensis) and the Wangi-wangi white-eye (Zosterops paruhbesar)
• Effectiveness of camouflage in Eurasian treecreepers
• New recently extinct thrush Geokichla longitarsus
• Pressure for rapid mate recognition promotes plumage sexual dichromatism in Turdus thrushes
• Phylogeny of Afro-Eurasian flycatchers
• Extinction risk of shamas
  
• New extant Afro-Eurasian flycatcher, the Meratus jungle flycatcher (Cyornis kadayangensis)
• Polymorphism and hybridization in Cyornis flycatchers
• Taxonomy of Erithacus robins
• Taxonomy of bush robins
• Convergence in open-habitat chats
• Phylogeography of the black sunbird and the olive-backed sunbird
• Convergent evolution of pendent nests in weaverbirds and American blackbirds
• Effect of genetic architecture on adaptation for host mimicry by cuckoo-finches
• Social role of song in zebra finches
• Mitogenomics of wagtails
• Hand-wing index as a proxy for dispersal ability in emberizoids
• Biogeography of Arremon passerellid sparrows
• Niche construction by brown-headed cowbirds through altering host brood size
• Hybrid between a rose-breasted grosbeak and a scarlet tanager
• Feather coloration mechanisms of male painted buntings
• Morphological convergence in tanagers
• Evolution of plumage coloration in tanagers
• Phylogeny of Thraupis tanagers
• Comparative genomics of Darwin's finches
• Diversification of the variable seedeater species complex

Hybrid between rose-breasted grosbeak and scarlet tanager, from Toews et al. (2022).