Bird palates compared

Earlier we looked at updates (= housekeeping) to the bird clade
of the large reptile tree (LRT, 1880+ taxa). Today a selection of bird palates in the LRT are presented in phylogenetic order. Not exactly cherry-picked, those not presented here either do not show the palate, or the palate is obscured along the rim by mandibles in ventral view.

Traditionally
birds are divided into Palaeognathae and Neognathae according to their palates. Palaeognathae include the ratites, “more primitive and reptilian than that in other birds.” According to Wikipedia, “McDowell (1948) asserted that the similarities in the palate anatomy of paleognathes might actually be neoteny, or retained embryonic features. He noted that there were other feature of the skull, such as the retention of sutures into adulthood, that were like those of juvenile birds. Parker (1864) reported the similarities of the palates of the tinamous and ratites, but Huxley (1867) is more widely credited with this insight.”

Cracraft (1974) defined Palaeognathae with five traits
and Feduccia (1980, 1996) defined Neognatha with three traits. In the LRT clades are based on a last common ancestor, not with traits. The short list of traits used by these authors too often converge elsewhere and both precede phylogenetic analysis software.

FIgure 1. Basal bird palates compared. Various sources. DGS colors added here. Based on sister taxa, the premaxilla likely extended back to the medial fenestra in the Pseudocrypturus and Rhynchotus drawings above.

In general, what do we see in basal birds?
in the Solnhofen bird, Jurapteryx (formerly Archaeopteryx, Fig. 1), the premaxillae are large, forming a palate, the maxillae are slender and lateral, the ectopterygoids are comma-shaped, and the rest are struts. That’s our starting point for today’s discussion.

In the basal crown bird and kiwi cousin, Pseudocrypturus
(Fig. 1), enlarging maxillae take the place of shrinking premaxillae. Teeth and ectopterygoids disappear.

In higher basal crown birds, like the ratites
(Fig. 1), the palatines become larger and more robust. Struthio, the ostrich opens up the palate with fenestrae, but other ratites, like Casurarius, don’t.

Ichthyornis
(Fig. 1) and its clade of Cretaceous birds redevelop a full arcade of teeth from Megapodius-like toothless ancestors. Premaxillary teeth are secondarily lost in Ichthyornis and Hesperornis.

In all the more derived extant and extinct birds
(Figs. 1–3) the palatal bones, premaxillae and maxillae assume such a wide variation in morphology based on diet and ancestry that they are best viewed and understood individually and comparatively by the reader, rather than described in detail with patterns and exceptions reported to potential excess in the text.

Figure 2. Palates of crown birds, terresrial clade. Various sources. DGS colors added here.

The greatest variation in palatal patterns
occurs with the relative amount of premaxillae to maxillae in palatal view. In some taxa the premaxillae dominate. In others the maxillae dominate. In a few the premaxillae underlie and laminate to the maxillae. The palatines and pterygoids do not change much. The vomers often disappear, but the large flightless taxa, Aptornis and Dinornis have large vomers. This is likely due to enbryonic retention via neotony (i.e. flightless wings also produce pre-loss vomers).

Figure 3. Palates of crown birds, aquatic clade. Various sources. DGS colors added here.

Adding colors to bones
to ease and speed identification is a method (aka Digital Graphic Segregation, or DGS) first offered in 2003 (e.g. the Jeholopterus skull that appears in the blog masthead above). The DGS method appears to be gaining wide acceptance (or wide convergence) nearly twenty years later for obvious beneficial reasons, whether applied to published µCT scans, traditional photographs or drawings. In the meantime, the switch from expensive 4-color printing press publication to no-cost RGB online publication has no doubt encouraged this transition, though still not universally and still not color-standardized.

References
Cracraft J 1974. Phylogeny and evolution of the ratite birds. IBIS 1116(4): 494–521.
Feduccia A 1980. The age of birds. Harvard University Press, Cambridge (Massachusetts) and London 196pp.
Feduccia A 1996. The origin and evolution of birds. New Haven, CT Yale University Press, 420pp.
Huxley TH 1867. On the classification of birds: and on the taxonomic value of the modifications of certain of the cranial bones observable in that class. Proceedings of the Zoological Society of London 1867:415–472, 36 figure.
McDowell S 1948. The bony palate of birds. Part 1. The Auk 65(4):520–549.
Parker WK 1864. V. On the Osteology of Gallinaceous birds and tinamous. The transactions of the Zoological Society of London 5(3):149–241.

wiki/Palaeognathae
wiki/Neognathae

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