Monday, June 11, 2018

ProgPal 2018

I said last year that I intended to attend ProgPal again, and I did. This year the conference was held in Manchester and the icebreaker took place at the Manchester Museum. Here is their cast of the Tyrannosaurus specimen "Stan".


Though I would have liked to explore the museum more than I did, the fact that my digital camera happened to be under repair made me less inclined to take photos than usual. In addition, I ended up being too caught up in conversation to check out most of the exhibits. Thanks to Callum McLean for ensuring that I didn't miss the museum's maniraptor specimens such as this Confuciusornis!


There were also casts of several bones from Hesperornis.


Being more familiar with the conference logistics and knowing more people this time around, the whole conference honestly feels like a blur. (Given that ProgPal lasts for only three days with the main bulk of events packed into a single day, this may well be the way it's supposed to feel!) I still had lots of fun and got to meet many new faces.

The newly expanded University of Bath paleo-contingent was well represented, with nearly all other paleontology grad students in my year not only attending the conference but also presenting their research. Unlike last year, I gave a talk of my own about my ongoing work. I won't say much about it here until it's published, but responses were, dare I say, overwhelmingly positive.

My title slide.

Institutional loyalties aside, a selection of presentations that I thought were highlights include:
  • Orla Bath Enright's talk on Burgess Shale taphonomy
  • Robert Brocklehurst's talk on convergence between afrosoricidans and lipotyphlans
  • Alessandro Chiarenza's talk on dinosaur diversity prior to the K-Pg
  • Christopher Stockey's talk on an assemblage-level reconstruction of color patterns in fish from the Bolca Lagerstätte
  • Nuria Melisa Morales Garcia's poster on a new approach to studying Triassic mammaliaform jaw biomechanics

ProgPal remains a fantastic opportunity for paleontology students to hone their skills and network with future colleagues.

Wednesday, May 9, 2018

Did Confuciusornis Really Eat Fish? The Mysteries of Mesozoic Bird Diets

Without a doubt, the Jehol Biota dating to the Early Cretaceous of northeastern China has been one of the greatest contributors to the exponential increase in our understanding of Mesozoic bird biology and evolution in recent years. Hundreds of complete dinosaur skeletons have been recovered from the Jehol, often preserved with soft tissue structures such as feathers and scales. These fossils have shed much light on the anatomy and life appearance of Mesozoic birds and other feathered dinosaurs. Naturally, such complete specimens sometimes also preserve gut contents, providing us with information about the feeding habits of these dinosaurs.

A recent paper by Jingmai O'Connor, a leading expert on Jehol fossil birds, reviews our current knowledge of Mesozoic bird diets. I was reminded of Darren Naish's 2014 review paper on evidence of avian behavior (including feeding) preserved in the fossil record... which isn't cited by this new paper. Hmm.

Nonetheless, the detailed overview and evaluation of previous claims makes O'Connor's paper an important publication on the topic of Mesozoic bird biology. As expected, Jehol specimens have contributed the most direct evidence on this subject: fish have been preserved as gut contents or pellets in the euornithines Piscivoravis and Yanornis, whereas seeds have been preserved as gut contents in the long-tailed avialan Jeholornis, the basal short-tailed avialan Sapeornis, and the euornithine Eogranivora. A few Mesozoic birds outside of the Jehol have also been reported with gut contents: the enantiornithine Eoalulavis from Spain was preserved with crustacean exoskeletons and the hesperornithine Fumicollis (not mentioned in O'Connor's paper) from the United States was preserved with fish remains.

Seeds preserved in the gut of Jeholornis, from O'Connor (in press). Insets show the skull and teeth of Jeholornis.

In addition, a large number of Jehol birds have been preserved with gastroliths (gizzard stones). These include specimens of Jeholornis, Sapeornis, Archaeorhynchus, Bellulornis, Changzuiornis, Dingavis, Eogranivora, Gansus, Iteravis*, and Hongshanornis. Gastroliths are also known in some non-avian theropods (such as Caudipteryx), but it appears that not all Mesozoic theropods used gastroliths given that some have never been preserved with them despite being known from numerous specimens. It's likely that a muscular gizzard was widespread in theropods, yet only some lineages independently evolved the habit of swallowing stones as digestive aids.

*This paper is yet another recent publication that accepts the synonymy of Iteravis and "Gansus" zheni (even though they're still listed separately in the table listing preserved gut contents in Mesozoic birds). Looks like this taxonomic revision can now be comfortably considered the general consensus.

Cretaceous euornithines that preserve gastroliths, from O'Connor (in press). (A) is Dingavis, (B) is Archaeorhynchus, (C) is Eogranivora, (D) is Hongshanornis, and (E) is Gansus.

The positioning of gut contents preserved in the specimens can sometimes provide evidence for the anatomy of their digestive system. Ingested food in both Sapeornis and Yanornis have been found clustered near the base of the neck, suggesting that these birds had a crop, an expansion at the base of the esophagus that is used to temporarily store food.

Despite the wealth of information they contain, however, interpreting Jehol fossils is not always straightforward. They are generally preserved as crushed slabs, which can distort anatomical information in spite of the completeness of the specimens. When it comes to inferring diet of fossil taxa, chance associations between the specimens and external objects can also mislead. O'Connor identifies several instances of purported gut contents in Jehol birds that are not as convincing as the previous examples.

Fish remains associated with the euornithine Jianchangornis** and the enantiornithine Piscivorenantiornis, for example, are not located directly within their body cavity and cannot be definitively considered evidence for diet, contrary to previous interpretations. In fact, the mass of fish bones preserved near Piscivorenantiornis (originally interpreted as a pellet) more strongly resembles the fossilized droppings of carnivorous fish or aquatic reptiles that have previously been found in the Jehol. This renders the name of this bird (meaning "fish-eating opposite bird") particularly awkward.

**An additional tidbit provided in the paper is that the skull of the only known specimen of Jianchangornis is a composite constructed from several different animals, not all of which may even be birds! Given that features of its teeth were claimed to be one of its distinguishing features in its original description, a restudy of the specimen may be in order.

Another enantiornithine, Bohaiornis, has been suggested to have been a carnivorous, raptorial bird, based primarily on the fact that one specimen was preserved with a few small gastroliths. Raptorial birds today are known to consume small numbers of stones to aid in cleansing their digestive system, and it was thought that this represented evidence of Bohaiornis having done the same. (In contrast, the gastroliths of herbivorous birds tend to be more numerous and are used to help grind up food.) However, based on personal examination of the specimen, O'Connor concludes that the supposed gastroliths are more likely to be precipitated minerals.

Enantiornithines purportedly preserved with gut contents, from O'Connor (in press). (A) is Bohaiornis, (B) shows its supposed gastroliths, and (C) is Piscivorenantiornis.

Outside of China, the enantiornithine Enantiophoenix from Lebanon has been interpreted as a sap eater based on globs of amber associated with the holotype, but the specimen is highly disarticulated and as such the amber cannot be confirmed as gut contents. With these reevaluations, the only direct evidence of diet in enantiornithines is found in the aforementioned Eoalulavis. Enantiornithines likely exhibited a variety of specialized feeding strategies given the diversity of their tooth and skull shapes, but it appears that they mainly fed on foods that would not preserve easily as fossils.

One Jehol bird in which the absence of preserved gut contents has been especially perplexing is Confuciusornis. Known from hundreds of specimens, more specimens of Confuciusornis have been collected than likely any other Mesozoic dinosaur. Despite this, no specimens that preserve definite gut contents have been identified. One individual was thought to preserve fish remains in a crop. However, this association is by no means unequivocal, especially given that it has only been reported in one out of hundreds of Confuciusornis specimens. O'Connor points out that, in contrast, about half of all known Yanornis specimens preserve fish in their gut. Regardless of whether the fish associated with that one specimen represents ingested material, evidence for fish being the main diet of Confuciusornis is lacking.

One of the many, many, many known specimens of Confuciusornis, photographed by Tommy from Arad, under CC BY 2.0.

Even without direct evidence from gut contents, one might think it wouldn't be so hard to get at least a general idea of what Confuciusornis ate. Inferring diet in many Mesozoic birds can be tricky because they had teeth, which makes it difficult to compare them to modern birds (all of which are toothless). Confuciusornis, however, had a beak instead of teeth, convergent with modern birds. Despite this, no living bird has a beak that closely resembles that of Confuciusornis, setting us back to square one.

Not that paleontologists haven't tried drawing conclusions from the beak morphology of Confuciusornis. A common interpretation is that Confuciusornis ate seeds, which on the surface seems reasonable. Its beak was quite robust and tooth loss is commonly associated with herbivory in other theropods. However, this runs into the same problem as the suggestion that it fed mainly on fish: definite seed-eating birds found in the Jehol regularly preserve gut contents, yet the same cannot be said of Confuciusornis.

Another recent study may shed light on this problem. Andrzej Elżanowski and colleagues have redescribed the skull anatomy of Confuciusornis based on detailed examination of multiple specimens and comparison with modern birds. As mentioned previously, the anatomical features of Jehol fossils aren't always easy to interpret, and the reconstruction presented in this new paper differs from those of previous authors in some notable ways. It's probably no coincidence that one of the authors on the paper is Gerald Mayr, known for his research on similarly crushed bird fossils of the Eocene Messel Shale.

Reconstructed skull of Confuciusornis, from Elżanowski et al. (2018).

One of the most surprising discoveries made by the researchers was that, despite not being particularly closely related to modern birds among Mesozoic avialans, Confuciusornis resembled certain living birds in more than just its lack of teeth. In their new interpretation, Confuciusornis had a bony rim behind its eye socket, and this rim was connected to the back of the skull by a bony bridge. Among modern birds, the prominent rim behind the eye is also found in the tawny frogmouth, the courol, puffbirds, some rollers, and some kingfishers. In addition, the tawny frogmouth also has a bony connection between the rim and the back of the skull.

All of these modern birds feed in a similar manner: watching from a perch before flying forth to grab their prey (often insects) in their jaws. This method of hunting is called sally-striking. The bony expansions of the skull behind their eyes likely provide room to attach larger jaw-closing muscles, increasing the grip strength of their beak.

Some modern sally-striking birds, including a tawny frogmouth (top left), white-whiskered puffbird (top right), Indian roller (lower left), and brown-headed paradise kingfisher (lower right), composited from photographs by JJ Harrison, Len Blumin, Shantanu Kuveskar, and "markaharper1", under CC BY-SA 3.0.

Is a sally-striking lifestyle consistent with the rest of Confuciusornis anatomy? Probably! Like modern sally-strikers, its beak was relatively large and deep. A close relative of Confuciusornis, Changchengornis, even had a slightly hooked bill like many modern sally-strikers do. The foot anatomy of Confuciusornis suggests that it was capable of perching, and its wing shape would have allowed it to maneuver well in its forest environment while making its prey-catching flights. Confuciusornis was also about the same size as some of the larger sally-striking birds today (such as the tawny frogmouth). And if Confuciusornis mainly fed on invertebrates whose remains might not have survived for long in the digestive system, that would explain why its gut contents are so rarely preserved.

Sally-strikers may snatch their quarry from the ground, from vegetation, or in mid-air. Though Confuciusornis could probably perch, some of its limb proportions have been likened to birds that spend part of their time on the ground. And while it may have had relatively maneuverable flight, it still lacked many of the flying specializations that modern birds possess, so it may not have been quite as acrobatic as some living sally-strikers. Perhaps it primarily apprehended prey on the ground, which might also explain how two individuals ended up as gut contents of the terrestrial theropod Sinocalliopteryx!

On the whole, the suggestion that Confuciusornis was a sally-striker appears plausible in light of what was previously inferred about its biology. Given this model, I do wonder if we'll ever find direct evidence of Confuciusornis feeding on vertebrates. Many modern sally-strikers also readily prey on smaller vertebrates in addition to insects, and Confuciusornis certainly was large enough to have done so. Even if vertebrates did not account for a large proportion of its diet, it is perhaps not a huge stretch to predict that such a discovery will one day be found.

References

Sunday, April 1, 2018

The End of a Tradition

Given that this blog has always been a side project that I work on when I happen to have the drive and opportunity, I have not beholden myself to a regular posting schedule here. Nonetheless, a few annual traditions have arisen. At the beginning of the year, I always write up an overview of the past year's scientific discoveries on maniraptors, shortly followed by the results of my annual poll on my readership's favorite newly-named maniraptor genera. Then on April 1st, I always make an April Fools' post, usually on a blatantly fake scientific discovery, but sometimes on a dramatically different creative direction for the blog. Starting this year, however, I will be scrapping that last tradition.

Didn't see that coming, eh?

My decision was prompted by a Twitter thread by biologist David Steen, in which he argues against the use of "April Fools' articles" by scientists and science communicators. To summarize his points: first of all, misleading the audience when one has built themselves up as a credible source is counterproductive. Secondly, not everyone will get that such articles are jokes. Lastly, the articles will not be read only on April Fools', nor will everyone who did read them on April Fools' remember when they did so.

This is not by any means the first time I've encountered similar sentiments. They are legitimate concerns, I've thought to myself in self-consolation. But my April Fools' jokes have never been intended to "fool" anyone. If anything, I aim to get a laugh out of my audience rather than a laugh at their expense. My posts are slathered so thickly in absurdity and sarcasm that the jig is obvious. In fact, they could even be considered a creative brand of science communication, considering that I often use them as an opportunity to point out the flawed logic of real pseudoscience. No one would ever misinterpret my April Fools' posts as seriously championing the outlandish claims they contain.

Unfortunately, it has dawned on me that the last point up there isn't true. Regardless of my intent, it's likely that some readers will be (and probably have been) misled. Though I don't remember anyone ever claiming to have taken the April Fools' jokes on Raptormaniacs seriously, I should've known better from experience with my earlier attempts at satire, such as the time I pretended to justify depicting phorusrhacids without feathers using the same flawed arguments that I've seen applied to dromaeosaurids*. Even with excessive use of exclamation marks, even with blatant self-contradictions, even with my explicitly pointing out the fact that there were self-contradictions, more than a few commenters confessed that they'd thought (if only momentarily in some cases) that I'd been serious. Naturally, I'd feel a twinge of frustration whenever someone didn't get the joke, but ultimately I can't blame the audience. Some pseudoscience really is that outlandish, that illogical, and that poorly-presented.

*Such arguments don't appear to be nearly as common anymore. Things do change...

Aren't unfeathered terror birds ridiculous? No one will ever think that I think terror birds were unfeathered if I drew a satirical picture of one without feathers! Actually, some will.

I've had fun coming up with my April Fools' articles and (I think) some of my readers have had fun reading them as well. I myself have enjoyed reading the fake articles written by other science bloggers such as Darren Naish (who has also announced that he will be dropping the tradition this year). However, having fun is not worth adding to the mountains of misinformation that already exist.

I don't want to come across as anti-fun. I am a staunch supporter of using humor and levity in science communication. But humor can be employed in many ways that don't involve creating misinformation. By abandoning this yearly tradition, I hope to remind myself to apply my sense of humor in a more productive fashion.

Another old work of mine (and a Raptormaniacs comic to boot) that (I think) uses humor while communicating science more effectively than a fake scientific article.

(If anyone has read to the end expecting me to pull a double fake-out: no, this post is not a joke.)

Monday, March 19, 2018

The Salt Glands of Iteravis

Many birds have salt glands that function in removing excess salt from their bodies. These glands are typically located above the eyes, and the salty fluid they secrete is eliminated via the nostrils. As one might expect, seabirds have some of the best-developed salt glands among birds, given that they can't help ingesting large quantities of salt. However, well-developed salt glands can also be found in birds that are terrestrial carnivores, live in deserts, or forage for freshwater invertebrates.

To accommodate their well-developed salt glands, these birds often have visible depressions in their skull. As such, the existence of well-developed salt glands in fossil birds can be inferred from the presence of such depressions. Until recently, these depressions had only been identified in Ichthyornis, Hesperornis, and Parahesperornis among Mesozoic dinosaurs. All three of these taxa were seagoing birds from the Late Cretaceous. A new paper, however, reports evidence of salt glands in Iteravis, a euornithine (i.e.: a closer relative of modern birds than enantiornithines were) from the Early Cretaceous of China. This represents the oldest clear evidence of salt glands in dinosaurs to date.

One of the specimens of Iteravis described in this paper, from Wang et al. (2018).

Iteravis is known from many specimens (several of which are described in the new paper), all of them found at the same locality. Their fossils, however, formed in lakes (typical of similar Early Cretaceous deposits in China) rather than in the ocean. Why did Iteravis have well-developed salt glands? One possibility the authors raise is that the lake Iteravis was found in may have been meromictic, composed of several layers of water that did not intermix. Such lakes often have bottom waters that are much saltier than the water at the surface. It is worth noting though that none of the other birds from the same locality possess evidence of well-developed salt glands. The authors also point out that freshwater birds with large salt glands tend to feed on invertebrates, so it may have been that Iteravis did the same. Another possibility is that Iteravis migrated to the sea on a seasonal basis, which many modern waterbirds do.

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

Besides identifying evidence for salt glands, this study contributes to our knowledge of Iteravis biology in a couple of other ways. First of all, the authors sampled melanosomes (organelles containing melanin pigment) preserved in the wing and body feathers of Iteravis and found them to be characteristic of melanosomes found in black feathers. Secondly, one of the newly-described Iteravis specimens preserves soft tissues surrounding the feet. These soft tissues are said to be similar to those preserved in Yanornis (another Early Cretaceous euornithine), which have previously been interpreted as evidence for partially webbed feet. The authors of the new paper, however, interpret them as representing lobed toes similar to those of grebes and coots. (Funnily enough, such toes have also been inferred but recently questioned in hesperornithines.)

My amateur restoration of Iteravis incorporating new information about its life appearance described by Wang et al. (2018), including black plumage and lobed toes.

This paper is additionally notable in that it considers "Gansus" zheni (a euornithine found at the same locality) to be the same as Iteravis. In fact, the authors found that the holotype of "Gansus" zheni also preserves the same skull depressions for salt glands. The idea that the two taxa are synonymous was first suggested online by Mickey Mortimer, and has subsequently been supported by two recent books on fossil birds, but this is the first time that it has been put forth in peer-reviewed literature.

Intriguingly, there is still no good evidence for well-developed salt glands in any non-euornithine dinosaurs, even those that likely had ecologies that would have benefited from such organs. The authors suggest that perhaps other dinosaurs were able to rely more on their kidneys for maintaining salt balance, or had salt glands situated in other parts of the body where they wouldn't have led to the evolution of the characteristic skull depressions.

This is an interesting paper that both increases our understanding of a Mesozoic bird and raises thought-provoking questions about the evolution of other dinosaurs. I was, however, a little surprised to see it repeating the obsolete interpretation that Hongshanornis was toothless.

Reference: Wang, X., J. Huang, Y. Hu, X. Liu, J. Peteya, and J.A. Clarke. 2018. The earliest evidence for a supraorbital salt gland in dinosaurs in new Early Cretaceous ornithurines. Scientific Reports 8: 3969. doi: 10.1038/s41598-018-22412-8

Wednesday, February 7, 2018

Who Ate Those Seeds? Not Hongshanornis!

In 2011, a study found clusters of seeds preserved in the body cavity of several Cretaceous birds. This shed light not only on the dietary habits of these birds, but also on their digestive anatomy, as the clustering of the seeds suggested the presence of a crop, which is a pouch at the end of the esophagus that serves as a temporary food store in many modern birds. Most of the Cretaceous specimens were identified as Sapeornis, a bizarre basal avialan that I've previously written about. One of them, however, was assigned to Hongshanornis, a smaller avialan more closely related to modern birds.

Some things about this supposed Hongshanornis did not add up though. Hongshanornis had slender hindlimbs and long toes, which have been suggested as evidence that it foraged on the margins of water, similar to plovers and sandpipers today. Though it is perhaps not inconceivable that Hongshanornis ate seeds occasionally, its apparent wading habits are not generally characteristic of seed-eating birds.

A new study reevaluates the specimen and confirms that it's not a specimen of Hongshanornis at all. The authors assign it to a new species, Eogranivora edentulata, which translates appropriately to "toothless dawn seed-eater". Like Hongshanornis, Eogranivora was a euornithine, the broad group including modern birds and all other avialans more closely related to them than to the enantiornithines or "opposite birds". However, Eogranivora differed from Hongshanornis in several significant ways.

The holotype of Eogranivora, from Zheng et al. (2018).

To start off, Eogranivora didn't have any teeth, as suggested by its species name, whereas Hongshanornis, like most other non-neornithine theropods, did. One might wonder how the authors of the 2011 paper managed to mistake a toothless specimen for a toothed taxon in the first place. This is almost certainly because the teeth of Hongshanornis were minuscule, to the point where Hongshanornis was initially thought to have been truly toothless. Only detailed reexamination of its holotype revealed that Hongshanornis did have tooth sockets, and it took an entirely new specimen for preserved teeth to be found at all. Indeed, the 2011 paper outright follows the original claim that Hongshanornis was toothless, despite having been submitted for review after the paper identifying tooth sockets in Hongshanornis was published...

There are some more obvious discrepancies between Eogranivora and Hongshanornis, such as the fact that Eogranivora did not have the slim hindlimbs of Hongshanornis. On the contrary, the feet of Eogranivora were relatively short and stocky, with stubby toes. Whatever it was doing, it almost certainly wasn't wading like Hongshanornis may have been. Each of its feet also lacked a hallux, the typically backward-pointing "perching toe" of most short-tailed avialans.

Photograph and schematic of the foot of Eogranivora, from Zheng et al. (2018)

The absence of halluces in Eogranivora is notable because this is a common feature of modern birds that spend much of their time on the ground. Unlike many ground-dwelling birds, however, the short feet of Eogranivora don't look particularly suited to fast running. Its wings, on the other hand, were still fairly well-developed. I am reminded of the Pallas's sandgrouse, a modern bird that has lost its halluces and primarily forages for seeds on the ground, but is still a powerful flier and not a specialized runner.

Eogranivora and Hongshanornis drawn to scale. The approximate lengths of the flight feathers are known in both taxa. I've been attempting actual measurement-based restorations of fossil birds lately, and though I may be no Emily Willoughby or Matt Martyniuk, I find that these drawings do help give me a better sense of the proportions and possible life appearance of these animals, especially regarding species that have rarely or never been properly restored by others in the past.

Eogranivora represents the first direct evidence of herbivory in a Mesozoic euornithine. It also lends support to the hypothesis that tooth loss was correlated with herbivorous diets in Mesozoic avialans (and perhaps theropods more generally), including the ancestors of modern birds. Granted, other Mesozoic avialans that preserve direct evidence of seed-eating (Jeholornis and Sapeornis) had teeth, but they did exhibit partial tooth loss. (Jeholornis lacked teeth in at least the front of the upper jaw, whereas Sapeornis lacked teeth in the lower jaw as an adult.)

Welcome to our ever-growing roster of Mesozoic birds, Eogranivora. You may not be Hongshanornis, but being a toothless, seed-eating, ground-dwelling Mesozoic euornithine that is not a runner is still pretty cool in my book.

Reference: Zheng, X., J.K. O'Connor, X. Wang, Y. Wang, and Z. Zhou. 2018. Reinterpretation of a previously described Jehol bird clarifies early trophic evolution in the Ornithuromorpha. Proceedings of the Royal Society B 285: 20172494. doi: 10.1098/rspb.2017.2494

Monday, January 15, 2018

Hesperornithines: Super-Loons No More?

Among the most remarkable of Mesozoic birds—nay, among the most remarkable of all Mesozoic theropods—were the hesperornithines. These diving birds from the Cretaceous are known to have lived in both freshwater and marine habitats, and the largest could attain body masses comparable to that of a wolf. They swam with strokes from their feet; in fact, the most specialized (and best known) forms had highly reduced forelimbs and were certainly flightless. Even with the great diversity of waterbirds today, and even with new evidence of semi-aquatic specializations in a few non-avialan dinosaurs like Spinosaurus and Halszkaraptor, hesperornithines remain prime candidates for being the most aquatically-adapted dinosaurs known.

Furthermore, unlike many other maniraptoran oddballs (such as the aforementioned Halszkaraptor), hesperornithines are no newcomers to the scientific spotlight, having been known to paleontologists since the 1870s. Together with Archaeopteryx and Ichthyornis, Hesperornis is a member of the "classic trio" that always represents Mesozoic avialans in popular books about paleontology.

Mounted skeleton of Hesperornis, photographed by "Quadell", under CC BY-SA 3.0.

Given the long period of time that we've been aware of their existence, it's not surprising that a good deal has been written about hesperornithines. Naturally, much of this literature has been spent drawing parallels between hesperornithines and extant birds, and two modern groups in particular are widely considered the best functional analogues for hesperornithines: loons (divers) and grebes. Indeed, when paleoartist Matt Martyniuk combed through the literature for hints on how to most plausibly restore Hesperornis, he concluded that hesperornithines could be thought of as "super-loons with grebe feet".

Like hesperornithines, loons and grebes are foot-propelled diving birds. However, they are not the only modern birds that use this method of underwater locomotion; cormorants and some ducks do so, too. Despite the long history of loons and grebes being considered ideal analogues for hesperornithines, this assumption has largely been based on perceived similarity instead of quantitative analysis, with little consideration given to comparison with other diving birds.

In a newly-published study, Alyssa Bell and colleagues performed the first quantitative comparison between hesperornithines and extant diving birds by using morphometrics. The authors took measurements that characterized the shape of the hindlimb bones in a variety of diving birds, including hesperornithines, loons, grebes, cormorants, and diving ducks. They then plotted these measurements against each other (after removing the influence of body size), which allowed them to assess the geometric similarity between each bone in different bird species.

As it turns out, though hesperornithines did overlap with loons or grebes on some measurements, they were generally more similar to diving ducks and especially cormorants! (It's perhaps also worth noting that, despite being frequently discussed in conjunction with one another, loons and grebes often occupied separate regions of the plots in this study.)

Flightless cormorant swimming, photographed by "putneymark", under CC BY-SA 2.0. Better than loons as a functional analogue for hesperornithines?

What does this mean for our understanding of how hesperornithines lived and functioned? It's hard to say. The authors point out that the influence of hindlimb bone shape on locomotion in diving birds has not been well studied, though their findings do suggest that future studies on hesperornithine biomechanics should probably look to cormorants as modern functional analogues instead of (or at least in addition to) loons or grebes.

Bell et al. also investigated the popular inference that hesperornithines had grebe-like lobed toes, instead of the webbed feet common in other diving birds. This idea was first suggested in the 1930s because similarities were observed between grebes and Hesperornis in the shape of the joint surfaces between their feet and their fourth toes. However, Bell et al. found that the same joint morphology is also present in some diving birds that have webbed feet, such as the flightless cormorant. Conversely, grebe-like joint morphology is not found in coots (which have lobed toes).

This does not mean that it is now incorrect to depict hesperornithines with lobed feet, but it does indicate that there is no compelling reason to think that their feet were lobed rather than webbed. Furthermore, the authors point out that the grebe-like joints are really only observed in the most specialized hesperornithines (such as Hesperornis and Parahesperornis), so even if joint morphology correlated with the soft tissues of the toes, lobed toes would have only been present in these later forms (which is consistent with the conclusions of some other recent research).

Western grebe showing off its lobed (not webbed) toes, photographed by Britta Heise, under CC BY 2.0. Hesperornithines have commonly been depicted with similar toes, but the evidence for this may be weaker than previously thought.

What about terrestrial locomotion? Hesperornithines have also been widely considered to have been similar to loons and grebes in how they would have gotten around on land; in other words, it's assumed that they wouldn't have gotten around well at all. Though grebes and the red-throated loon are capable of walking for short distances, it is very energetically costly for them to do so, and other loon species can't walk upright at all, instead having to awkwardly shuffle on their bellies. Cormorants, on the other hand, have no trouble with standing and walking upright on land, even if they won't be running marathons anytime soon. Do the findings of the new paper suggest that we need to rethink this aspect of hesperornithine biology as well?

Bell et al. briefly address this question. Unlike in typical dinosaurs, the hindlimbs of foot-propelled diving birds are often held splayed out to their sides. As such, it is advantageous for diving birds to have a very short femur (thigh bone), because this would allow them to place their feet directly behind their bodies, increasing the efficiency of the kicking strokes that they use for swimming. A possible trade-off of this is that if the femur is dramatically reduced in length compared to the rest of the hindlimb, this may impede the ability of a diving bird to balance upright on land. Indeed, loons have the shortest femora relative to their other hindlimb bones out of all the extant diving birds examined in the study, with grebes (especially the large-bodied western and Clark's grebes) coming in second.

As for hesperornithines, in the smaller and less specialized Baptornis and Brodavis, femur length relative to the foot is most similar to that of cormorants, but femur length relative to the lower leg is closest to that of the grebe genus Podiceps. In contrast, the larger Hesperornis and Parahesperornis had femoral proportions (especially relative to the lower leg) that most closely match those of loons. So if I had to guess, most hesperornithines probably could exhibit at least grebe-like if not cormorant-like gaits on land, but it appears plausible that the very specialized hesperornithids (Hesperornis and Parahesperornis) really were confined to loon-like shuffling.

Western grebe walking on land, photographed by Kevin Cole, under CC BY 2.0. This type of locomotion is very tiring for these specialized diving birds and cannot be sustained for long. Based on evidence from relative proportions of the hindlimb bones, some hesperornithines such Brodavis and Baptornis may have been able to achieve at least this level of terrestrial competence.

The upshot of this paper is that perhaps we should start thinking of hesperornithines as super-cormorants rather than super-loons, and we can no longer assume that they had grebe-like feet. Nonetheless, the most specialized hesperornithines may have been loon-like in their compromised ability to move on land. Of course, it's to be expected that no single group of modern birds serves as a perfect hesperornithine analogue; after all, the later hesperornithines evolved specializations for swimming and diving more extreme than those of any foot-propelled diving bird today. Most of all, this study highlights the need for us to test long-held assumptions using hard data instead of first impressions, or else we risk pigeonholing ourselves in nooks that may not, in fact, provide the best fit.

Reference: Bell, A., Y.-H. Wu, and L.M. Chiappe. In press. Morphometric comparison of the Hesperornithiformes and modern diving birds. Palaeogeography, Palaeoclimatology, Palaeoecology in press. doi: 10.1016/j.palaeo.2017.12.010

Friday, January 5, 2018

Favorite Maniraptor of 2016 Results


Last year was a close race, but the unusual Fukuivenator narrowly won against Tongtianlong, an oviraptorosaur known from a nearly complete skeleton preserved in three dimensions. Coming in third place was Apatoraptor, one of the most completely known caenagnathid oviraptorosaurs.

These polls are inevitably biased in favor of taxa that receive more press. Though a truly level playing field is impossible to achieve, I will try something new this year by providing a concise blurb for each contestant and links to their original description papers. This way at least, none of the taxa will be complete unknowns. That being said, I suspect one particular genus already has this year in the bag...

  • Albertavenator: A troodont from the Late Cretaceous of Canada. Known from a single bone in the skull.
  • Almas: A small troodont from the Late Cretaceous of Mongolia. Known from a partial skeleton including a nearly complete skull. It has been included in several phylogenetic analyses in the past, but wasn't named until last year.
  • Aprosdokitos: A small penguin from the Eocene of Antarctica. Known from a single upper arm bone.
  • Beibeilong: An oviraptorosaur from the Late Cretaceous of China. Known from an embryo long nicknamed "Baby Louie" as well as several eggs. Its adult size would have been comparable to that of Gigantoraptor, the largest known oviraptorosaur.
  • Chupkaornis: A hesperornithine from the Late Cretaceous of Japan. Known from a partial skeleton including parts of the vertebral column and hind limbs. It is the most completely known Asian hesperornithine.
  • Corythoraptor: An oviraptorosaur from the Late Cretaceous of China, one of many recently named from the Nanxiong Formation. Known from a nearly complete skeleton. It had a particularly tall crest on its head.
  • Crexica: A rail from the Miocene of Russia. Known from partial limb bones.
  • Cruralispennia: An enantiornithine from the Early Cretaceous of China. Known from a mostly complete skeleton with preserved feathers. It had several features unusual for an enantiornithine, including strap-like feathers on its legs and wings as well as a rapid growth rate.
  • Daliansaurus: A troodont from the Early Cretaceous of China. Known from a nearly complete skeleton.
  • Diomedavus: A small albatross from the Oligocene of the USA. Known from parts of the limbs and hip as well as a single neck vertebra.
  • Garrdimalga: A large megapode from the Pleistocene of Australia. Known from parts of the limbs and skull.
  • Halszkaraptor: A small dromaeosaurid from the Late Cretaceous of Mongolia. Known from a nearly complete skeleton. It had some unusual anatomical features suggesting that it foraged in the water, including numerous teeth, a long neck, and paddle-like forelimbs.
  • Jianianhualong: A troodont from the Early Cretaceous of China. Known from a nearly complete skeleton with preserved feathers.
  • Junornis: An enantiornithine from the Early Cretaceous of China. Known from a mostly complete skeleton with preserved feathers. The size and shape of its wings suggest that it used bounding flight, similar to many small extant birds.
  • Kumimanu: A large penguin from the Paleocene of New Zealand. Known from a partial skeleton including parts of the limbs, hip, and vertebral column. Among the most completely known giant penguins.
  • Latagallina: A large megapode from the Pleistocene of Australia. Known from several specimens, including one that is nearly complete. The type species was formerly considered a species of Progura.
  • Latenivenatrix: A large troodont from the Late Cretaceous of Canada. Known from several specimens, including a partial skeleton. Many of these were formerly considered specimens of Troodon. The largest troodont known, estimated at over 3 m long.
  • Liaoningvenator: Yet another troodont from the Early Cretaceous of China. Known from a nearly complete skeleton.
  • Maaqwi: A euornithine from the Late Cretaceous of Canada. Known from parts of a forelimb. Its thickened bone walls suggest that it was a diving seabird.
  • Miohypotaenidia: A rail from the Miocene of Russia. Known from partial limb bones.
  • Ostromia: A basal paravian from the Late Jurassic of Germany. Known from a partial skeleton including parts of the limbs and faintly-preserved wing feathers. The holotype has had a convoluted taxonomic history, having been mistaken for a pterosaur and later considered a specimen of Archaeopteryx.
  • Piscivorenantiornis: An enantiornithine from the Early Cretaceous of China. Known from a partial skeleton along with a possible pellet containing fish bones.
  • Serikornis: A basal paravian from the Late Jurassic of China. Known from a complete skeleton with "silky" feathers preserved all over its body.
  • Tsidiiyazhi: A stem-mousebird from the Paleocene of the USA. Known from a partial skeleton. The oldest known member of the "core landbird" clade Telluraves.
  • Vanolimicola: A shorebird-like bird from the Eocene of Germany. Known from a partial skeleton.
  • Zhongjianosaurus: A small dromaeosaurid from the Early Cretaceous of China. Known from a partial skeleton. One of the smallest dromaeosaurids known.