Recent fossil evidence for supraorbital salt glands in early birds: did other early birds and dinosaurs also have salt glands?

The skulls of marine or estuarine birds often show a depression above the orbit. Instantly, it is possible to recognise where a supraorbital nasal salt gland was present on each side in life. The glands secrete a concentrated salt solution and thus enabled the bird to drink sea or estuarine water and/or to eat salt-rich invertebrate prey.

Even before the function of the nasal glands was discovered by Knut Schmidt-Nielsen in the late 1950s, the comparative anatomists and palaeontologists had been at work. Brian John Marples (1907-1997) in 1932 examined the skulls of the extinct birds Hesperornis and Ichthyornis. He found large depressions above the eye indicating the presence of supraorbital nasal glands. Hesperornis was a large flightless bird that lived in a marine environment; Ichthyornis was also a sea bird about the size of a pigeon*. Both are from the Late Cretaceous (63.5-78 million years ago).

A very recent paper from workers in China and the USA describes the finding of supraorbital depressions in the skull of Iteravis, a bird from the 40 million years earlier, i.e of the Early Cretaceous. The fossil is from Liaoning in north-eastern China.

From Wang et al. 2018

The authors studied even earlier fossils than Iteravis on the dinosaur-bird line and could find no evidence for the presence of supraorbital glands. However, I cannot agree with the authors in accepting the lack of supraorbital glands as evidence for the absence of salt glands in very early birds, their dinosaurs ancestors or other contemporary early birds. Yes, many modern birds with salt glands have them in the supraorbital position: but many do not.

Gerhard Technau in Berlin made an extensive comparative study of the nasal glands of birds. His paper, published in 1936, is over 100 pages long. When, in 1975, we compared Technau’s findings with a list of birds known to have functional salt glands, we found that salt glands are not always in the supraorbital position. These early studies have been confirmed more recently. The salt gland in gannets, boobies, cormorants, shags, and pelicans, for example, are situated within the roof of the orbit; depressions in the bone are found there.

We used Technau's diagram for our book in 1975. We stuck with Technau's
nomenclature but the sharp-eyed will notice his terminology is incorrect.
His 'interorbital' (i.e. between the orbits) should be 'intraorbital' (within
the orbit).

Thus it is entirely possible that other early birds, as well as their dinosaur ancestors, had salt glands as well as those leaving evidence of supraorbital nasal glands in their fossilised remains.

The new paper is:

Wang X, Huang J, Hu Y,  Liu X, Peteya J, Clarke JA. 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. Note - two - and I have only checked two - of the references given in this paper are incorrect.

Other references

Technau G. 1936. Die Nasendrüse der Vögel. Zugleich ein Beitrag zur Morphologie der Nasenhöhle. Journal für Ornithologie 84, 511-617.
( I have been able to find nothing about Technau nor his other work.)

Siegel-Causey D. 1990. Phylogenetic patterns of size and shape of the nasal gland depression in Phalacrocoridae. The Auk 107, 110-118.

Marples BJ. Structure and development of nasal glands in birds. Proceedings of the Zoological Society of London (1932), 829-844.

Peaker M, Linzell JL. 1975. Salt Glands in Birds and Reptiles. Cambridge: Cambridge University Press.

*Relevant here is the recent work on using knowledge of the structure of nasal salt glands to infer what was happening in extinct birds has appeared so far only as an abstract:
Caggiano EG, Cerio D, Porter R, Ridgely RC, Witmer LM. 2017. The nasal salt gland of extant birds: anatomical structure and its relevance for inferring the behavior and habitat preferences of extinct birds. FASEB Journal 81, Abstract 579.5. 

Who was Marples, B.J. (1932)?

Twenty-five years before Knut Schmidt-Nielsen discovered salt glands in birds, the structure and development of the nasal or supraorbital glands – that turned out to be the salt glands – were studied by B.J. Marples at the University of  Manchester¹. The late Jim Linzell and I quoted his work in our monograph on salt glands². However, his name was unfamiliar to us and we had no idea what had become of him. I always wanted to ask Marples why had worked on the nasal glands. Nothing of their remarkable function was known and the only function anybody could think of was to wash seawater out of the nostrils. Wrong!

Only when reading Whose Bird?³ last year did I find the answer. Brian John Marples (1907-1997) was, from 1937 until 1966, Professor of Zoology at Otago University in New Zealand. Like so many zoologists of that era, his interests were wide-ranging, if firmly grounded in the Oxford school of comparative anatomy of Goodrich and de Beer. An obituary in the Yearbook of the Royal Society of New Zealand⁴ provides an excellent account of his interests and achievements in ornithology, arachnology and vertebrate palaeontology (particularly the fossil penguins of the Oligocene).

Marples’ (Marples’s when I did O-level English) Penguin (Palaeeudyptes marplesi Brodkorb, 1963) from the Late Eocene was named in his honour. The extinct birds in this genus start at the size of the Emperor Penguin⁵.

Again, like so many of his British contemporaries, it is reported that his lecture delivery was in the languid style with diagrams drawn on the blackboard. It seems that he retired early because the university thought his department needed an infusion of experimental biology. He returned to Woodstock, near Oxford.

So, while we were writing the monograph, Marples was living near Oxford and, had we known that, I could have asked him how he came to work on nasal glands and whether or not he had an inkling that they could prove to be more important than was thought at the time.

¹Marples, B. J. 1932. The structure and development of the nasal glands of birds. Proceedings of the Zoological Society of London 102, 829 – 844.

²Peaker, M. & Linzell, J.L. 1975. Salt Glands in Birds and Reptiles. Cambridge University Press (ISBN 0 521 20629 4).

³Beolens, B. & Watkins, M. 2003. Whose Bird? London: Christopher Helm (ISBN 0-300-10359-X)

^{4 http://www.royalsociety.org.nz/publications/reports/yearbooks/year2000/obituaries/brian-marples/
5 http://nzbirdsonline.org.nz/species/marples-penguin}