Strange Snouts in Hadrosauroid Dinosaurs (Glishades ericksoni)

Brief comment to discuss something cool. Yesterday, Zootaxa published on a new hadrosauroid ornithischian dinosaur, Glishades ericksoni. The remarkable thing of note is a peculiar adaptation of the premaxillae, the only known bones preserved (so far). While I am loathe to regard taxa based on such scant material, adapting the principle I derived from TBT, the uniqueness of the material permits a bit of exceptionalism.

In typical hadrosauroids, as in all hadrosaurs, be they “lambeosaurine” or “hadrosaurine”, the premaxillae are elongated, toothless, and are ventrally concave:

Hadrosauroid premaxillae. A, Brachylophosaurus canadensis; B, Maiasaura (=Prosaurolophus) peeblesorum; C, Anatosaurus annectens; D, Prosaurolophus maximus; E, Edmontosaurus regalis; F, Saurolophus osborni.

The ventral morphology of hadrosaur premaxillae is seldom noted, as the discussion typically involves the circumnarial morphology, or data in regards to crests. The ventral margin of the premaxillae are concave, with the lateral edge of the premaxillae forming thin ridges that form a U-shape bound to the anterior ends of each maxilla. Occasionally, as in Anatosaurus annectens, the ventral surface bears longitudinal ridges that form a sort of triturating apparatus, such as occurs in oviraptorid theropods, turtles, and some birds. So while most premaxillae in hadrosaurs are scoop like, in Glishades this condition is inverted:

AMNH 27414, in cranial (A) and ventral (B) views; A’–B’, outline of the oral margin and ventral ridge. Arrows point to the ventral ridge. Premaxilla of Glishades ericksoni Prieto-Marquez. Modified after Prieto-Marquez (2010) .

This ridge is exceptionally sculptured, unlike the dorsal margin of the premaxilla; the dorsal and rostral margins exhibit smooth texture with incised channels, a textural feature noted by Witmer and Holliday Hieronymus et al. [2] to be connected to cornified sheaths (as in ungulate horns and avian and turtle beaks); the irregular ventral surface, however, appears to have characteristics of an irregular cornified pad [2]. As noted by Prieto-Márquez, such a feature is present in Bactosaurus johnstoni, but to a muted degree, and a thickening (without a sulcus) is present in Ouranosaurus nigeriensis.

What this permits us to consider is the morphological aspect of a secondary ventral ridge on the premaxilla; if, as [2] demonstrate, the ridge, despite being denticulate, simply indicates a thickened pad on the ventral surface and that it may not conform to the shape of the cornification. A ridge and sulcus also appears on the palatal surface in some turtles (e.g., Chelonia mydas), and appears to be useful in oral processing.

[1] Prieto-Márquez, A. 2010. Glishades ericksoni, a new hadrosauroid (Dinosauria: Ornithopoda) from the Late Cretaceous of North America. Zootaxa 2452:1-17.
[2] Hieronymus, T. L., Witmer, L. M., Tanke, D. H. & Currie, P. J. 2009. The facial integument of Pachyrhinosaurus (Ceratopsidae: Ornithischia): Morphological and histological correlates of novel skin structures. The Anatomical Record 292:1370-1396.

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5 Responses to Strange Snouts in Hadrosauroid Dinosaurs (Glishades ericksoni)

  1. nick gardner says:

    actually the integument stuff is tobin hieronymous not casey holliday.. you got it right in the lit cited but wrong in the blog post

    good post jaime, ornithischia needs more love

    • qilong says:

      Yes, they need more love. I should have more stuff coming on ornithischians as I work through some of my topics on dentition.

      I’ll fix the post, thanks!

  2. nick gardner says:

    certainly it’s notably interesting that we have a basal hadrosaurOID appearing relatively late in the Americas…. when all other North American hadrosaurOIDs of this time appear to mostly be ‘euhadrosaurs’

  3. nick gardner says:

    for comparison, the only other North American non-‘euhadrosaur’ might be Lophorhothon… hmm

    • qilong says:

      It’d be interesting if we could figure out whether what looks superficially like a “saurolophine” actually was, given that most analyses seem to lump it into a generic “what it isn’t” category.

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