Describe the evolutionary trends regarding jaws and internal

Describe the evolutionary trends regarding jaws and internal support (i.e. skeleton) for the following three groups of fish: hagfish, lamprey, and the other fishes (e.g. bony fish and shark).

Solution

Lampreys are ectoparasites on fish, which uses a circular, sucker-like mouth to clamp onto their hosts. On the flip side, Hagfish, are deep-sea scavengers, which feeds on sunken carcasses. Together these two are known as cyclostomes/jawless vertebrates. Lamprey is closely related to jawed vertebrates in the Clade vertebrata with Hagfish a bit distantly related; all forming Craniata. These fishes were armored in order to help them for self protection.

From these bottom feeding, jawless fish evolved into jawed fish. Jaws evolved only once from gill arches which are the bony parts between gill slits which in turn became fused to its skull. The upper part of the gill support developed into top jaw and the bottom part into bottom jaw. The head of a fish has twenty-four bones that may move together in feeding .The evolution of the jaw led to fish to be able to ingest a wide range of foods and allowed them to become better predators.They were able to reduce their armour due to less vulnerability, and their muscle density also decrease due to more activity.

Reference

1. Shimeld, S, M., & Donoghue, P, C. (2012). Evolutionary crossroads in developmental biology: cyclostomes (lamprey and hagfish).PubMed, 139(12).

2. Serendip. (2008). THE EVOLUTIONARY STEPS OF FISH. Retrieved from http://serendip.brynmawr.edu/exchange/serendipupdate/evolutionary-steps-fish