Dino papers: Hopson, 1975, Evolution of Cranial Display Pt. 1

Hopson, J. A. (1975). The evolution of cranial display structures in hadrosaurian dinosaurs. Paleobiology, 1(1), 21-43.

Notes/Summary: This paper was referenced by a few of the Weishampel, so feels like catch-up reading. 

Hopson introduces the idea that the head crests of hadrosaurs were for sexual display -- visual and with the hadrosaur with hollow crests -- audio as well. Crest variations were species and gender-specific and tended to increase (via evolution) with time. Crests varied externally and internally independently of one another and also hadrosaurs had well-developed eyes and ears.  He writes that the hadrosaurs developed diverticula to draw attention to a horn which was used aggressively in mating (he hypothesizes) and then for sexual display (visually) the hollow-crested dinosaurs evolved bone to cover it for acoustic resonation. (all from abstract)

He classifies hadrosaurs into 2 subfamilies (with hollow crests - lambeosaurinae) and without (hadrosaurinae), but in the hadrosaurinae creates 3 subgroups -- kritosaurs, edmontosaurs, saurolophines -- all with non-hollow crests or no bony crests. He believes the ancestral hadrosaurian condition is approximated by kritosaurs -- whilst edmontosaurs are an isolate -- he thinks the deeply excavated narial passages set them apart and all other hadrosaurs have elevated nasal bones in different forms. (including, I assume those that appear earlier in the fossil record).

new term break:

epithelium - The epithelium is a type of body tissue that forms the covering on all internal and external surfaces of your body, lines body cavities and hollow organs and is the major tissue in glands.
https://my.clevelandclinic.org/health/articles/22062-epithelium#:~:text=What%20is%20the%20epithelium%3F,the%20major%20tissue%20in%20glands

In addition to the main olfactory epithelium, the septal organ of Masera (SOM) is another epithelium containing chemosensory neurons. It is located bilaterally on the nasal septum near the entrance of the nasopharynx and is completely encircled by respiratory epithelium (Figure 1). This island of olfactory sensory neurons projects axons to the MOB and targets a subset of glomeruli located in the posterior ventromedial bulb. 
https://www.sciencedirect.com/topics/neuroscience/olfactory-epithelium

**This refers to human olfactory epithelium but helps explicate the term in general.

end.

Questions Hopson poses about previous nasal crest function hypotheses (for -- underwater breathing, olfactory, display and combat organs)
1. Why does selection for above functions (mainly underwater breathing & olfactory) resulted in such diversity of shape among lambeosaurines?

2.  What is the function of the solid crests of the saurolophines?

And relatedly he also asks -- why did lambeosaurines evolve such a complicated way of doing these things that other hadrosaurs presumedly would have also done? In possibly different ways?

Now he argues for social signaling as a function of all crests in hadrosaurs (also after he wrote this note that they found fleshy crests.....). Specifically, he mentioned courtship, mating fights, and sexual selection.  Kritosaurs could have used their crests and humps and horns for combat.

PAUSE pg. 37