New paper: pneumatic diverticula and blood vessels in the neural canals of the toothed birds Ichthyornis and Janavis

New paper out this week, open access like usual, go get it for free:

Atterholt, Jessie; Burton, M. Grace; Wedel, Mathew J.; Benito, Juan; Fricano, Ellen; and Field, Daniel J. 2025. Osteological correlates of the respiratory and vascular systems in the neural canals of Mesozoic ornithurines Ichthyornis and Janavis. The Anatomical Record. http://doi.org/10.1002/ar.70070.

If I recall the sequence correctly, Jessie Atterholt met Dan Field at one of the recent Society of Avian Paleontology and Evolution (SAPE) meetings. Between them they spun up the idea of looking for evidence of paramedullary diverticula (PMDs) in the neural canals of some fossil birds that Dan and his collaborators and students had been studying, namely Ichthyornis and Janavis, both toothy ichthyornithines from the Late Cretaceous. This was not long after Jessie and I had our paper on PMDs in extant birds published (Atterholt and Wedel 2022), and we were interested in chasing PMDs down the tree. At the same time, Dan and his former student, Juan Benito, had a big war chest of CT scans of Ichthyornis and Janavis. So the actual work for this project was very similar to the work for Atterholt and Wedel (2022): lots of hours in front of a computer, flipping through stacks of CT slices. But I’m getting ahead of myself.

Ichthyornis you know, it’s one of the toothed birds that O.C. Marsh described in the 1870s, after basically buying the specimen out from under E.D. Cope, one of the many inciting incidents of the Bone Wars. For most of my career I simply could not keep Ichthyornis and Hesperornis straight. It has always been perversely confusing to me that the flightless swimming bird is not named “fish bird”, and the gull-like flying bird is not named for Hesperus, or Venus, a thing actually up in the sky. The “fish bird” was the flyer and the “Venus bird” was the flightless swimmer. It’s just plain backwards. (Before anyone pushes their glasses up their nose in the comments, yes, I know that Hesperornis is intended as “western bird”. Both taxa are from the West. Still confusing.)

Janavis I was not familiar with prior to this project. It’s the sister taxon of Ichthyornis, only named in 2022 by Benito et al. Janavis was big, too, with an estimated wingspan of 5 feet, about the same as the largest extant gulls (or for me, an Oklahoma farmboy, a really big hawk). The vertebrae of Janavis are cuh-ray-zee pneumatic, totally honeycombed inside and fairly Swiss-cheesy in places on the outside, edging up to the frankly unbelievable anatomy of pelicans. Or shoebill storks, about which more in a sec.

Grace Burton, one of Dan’s current PhD students, came over to SoCal last year to do some research at the LACM and work with Jessie and me on the IchyJan project (it only took me about half a dozen emails to realize that I was too lazy to type “Ichthyornis and Janavis” the thousand or so times I’d need to). The three of us had an enjoyable visit to the LACM Ornithology collection to find comparative specimens, some of which we ended up figuring in the new paper. And Jessie and Grace spend a LOT of time looking through CT scans. I got in on some of that, but really, Jessie and Grace did almost all the heavy lifting with both the research and the writing, so it’s only just that they’re the first two authors. This was mostly an Atterholt joint from the get-go anyway. If my interest in weird neural canal anatomy is a roaring bonfire, Jessie’s is more like the Sun.

Of the new coauthors I picked up on this project, one is close to home: Elle Fricano, who works alongside Jessie and me as one of the anatomy faculty at WesternU. We ended up needing to scan some specimens at WesternU with our microCT machine, and Elle did virtually all of the scanning and interp, so we brought her on as an author. Elle’s own research is mostly on the evolution of the cranial base and ear region in humans and other primates, but she’s gotten into pneumaticity with a very nice paper on the human maxillary sinus (Fricano et al. 2025). She also works as a forensic anthropologist, and earlier this year she passed her forensic board exams to became the 176th Diplomate of the American Board of Forensic Anthropology — the 176th ever (full list here) — and one of only 124 active board-certified forensic anthropologists in the world. That is a heck of an achievement for anyone, but especially for someone on the tenure track, with a heavy teaching load, research, committee service, and a family. Am I bragging on my colleague? Heck yes. When a fire burns down a neighborhood out here, Elle is one of the people who goes and sifts bone shards out of the ashes and does her best to give the survivors some closure (not to mention helping investigate other deaths, ones that Nature had less of a hand in). That work is not without its costs, and I’m a little in awe of anyone who chooses to do it.

Anyway: neural canals in fossil birds. We were hunting for hard evidence of pneumatic diverticula inside the neural canal, ideally unambiguous foramina opening into clearly pneumatic spaces in the neural arch or centrum. We found those foramina, and lots of other weird stuff besides. Some of the vertebrae of Ichthyornis and Janavis have bilobed neural canals, and from comparisons with extant birds we’re pretty sure the upper lobe held a big venous sinus. Crocs have one, too, in their bilobed neural canals. Most of the critters that fall evolutionarily between crocs and birds don’t have bilobed neural canals, but they may still have had big venous sinuses that simply failed to leave diagnostic traces — the curse of pneumaticity researchers extended to blood vessels.

Some of our CT scans of extant birds show that upper lobe being shared by both a big venous sinus and pneumatic diverticula, and the upper lobe is sometimes expanded into what Jessie and I nicknamed the “pneumatic attic”: a large space of variable geometry that very often has big pneumatic foramina opening into the transverse processes, postzygapophyseal rami, or neural spines. You can see the “pneumatic attic” with the pneumatic diverticula restored in a vertebra of Ichthyornis in Figure 5, above. Virtually everything we found in Ichthyornis and Janavis could be lined up 1-for-1 with an identical geometry or topology in one or another extant bird, which made us feel better about our interpretations.

One thing that needs more work is the frequent occurrence of small, paired troughs at the ventrolateral corners of the neural canal, not only in Ichthyornis and Janavis but in many extant birds as well. These troughs often bud off little vascular foramina that we can trace down into the centrum, so we’re pretty sure the troughs held blood vessels in life. A lot of vertebrates have a ladder-like arrangement of arteries in their neural canals, which could be the source of these troughs, but they might also have been produced by little basivertebral veins, which birds otherwise seem to lack. Why don’t we we just inject some dead birds, dissect them, and find out, you maybe wondering. Well, we’re gonna, at some point, but that’s at least another whole paper’s worth of work, and possibly several. We’d rather just go look up the answer, but as far as we and our reviewers could tell, no-one has ever written about these troughs and their contents before (if you know otherwise, please sing out in the comments!).

So once again, Jessie and I find ourselves needing to do novel anatomical research on living animals, partly because it’s worth doing in its own right, but also so that we can make progress on the paleontological questions that got us into this in the first place. It’s awfully hard to make informed paleobiological inferences when so much basic anatomy remains to be documented for the first time, even in extant critters. As I keep saying, a lot of this is work that anyone with sufficient time and curiosity could do, much of it inexpensively. So if you find this stuff intriguing, we’d love to have more explorers out here where the pneumatosphere intrudes into the neural-canal-iverse.

As for Jessie and me, this is our fifth neural-canal-related paper (see the evolving list here). We keep kicking them out the rate of one per year, which is nice and sustainable and unlikely to stop anytime soon. According to my to-do list, she and I have at least another 15 collaborative papers planned. Not all of them are about neural canals, but still… I reckon we’d better get to it.

REFERENCES

• Atterholt, Jessie, and Wedel, Mathew J. 2022. A computed tomography-based survey of paramedullary diverticula in extant Aves. The Anatomical Record 306(1): 29-50. https://doi.org/10.1002/ar.24923
• Atterholt, Jessie; Burton, M. Grace; Wedel, Mathew J.; Benito, Juan; Fricano, Ellen; and Field, Daniel J. 2025. Osteological correlates of the respiratory and vascular systems in the neural canals of Mesozoic ornithurines Ichthyornis and Janavis. The Anatomical Record. http://doi.org/10.1002/ar.70070.
• Benito, Juan; Kuo, Pei-Chen; Widrig, Klara E.; Jagt, John W. M.; Field, Daniel J. 2022. Cretaceous ornithurine supports a neognathous crown bird ancestor. Nature. 612 (7938): 100–105. doi:10.1038/s41586-022-05445-y.
• Fricano, Ellen E.I; Nguyen, Joseph; Hallal, Ryan; and Llera Martín, Catherine J. 2025. Under the surface: Correlates with maxillary sinus shape. Journal of Anatomy. https://doi.org/10.1111/joa.14283
• Marsh, O.C. 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office, 201 pp.

Source: https://svpow.com/2025/10/11/new-paper-pneumatic-diverticula-and-blood-vessels-in-the-neural-canals-of-the-toothed-birds-ichthyornis-and-janavis/