I began with thinking about the similarities between keratin in its hardest form (fingernails, horn sheaths) and the chitin that composes the exoskeletons of some few beetles I've seen in my life. To my eye the two materials seem to have comparable properties. Then I found out that tarantula hair is also made out of chitin, so in more aspects than one it seems that chitin and keratin have convergently evolved.
I understand that chitin is a carbohydrate while keratin is a protein, so there's no commonality regarding the origin of the two, but I am curious as to whether an animal has ever been demonstrated to produce both compounds in some capacity?
