Discussion
"There is a distinct muscle that corresponds topologically, and seems to be homologous, to the pterygialis cranialis of sharks, running (mainly anteriorly, not posteriorly as in sharks, due to the peculiar position of the propterygium of Leucoraja) from the pectoral girdle to the propterygium." \cite{Diogo_2014}
-Interpretation and comparison: this is where you can compare your specimen(s) to more and less closely related species.You describe your specimen with reference to anatomical homologies in those other species.
There are many similarities between the pectoral fins of the Mustelus and the thornback ray: Both have adductors that run from the pectoral girdle.
-Use existing phylogenetic information (where available) to try to explore the question of primitive and derived states in the evolutionary history of this structure.
-Is the structure or system in question relevant to the animal’s ecology? If so, how?Think about feeding, habitat,reproduction.
Fossil evidence of the evolutionary events that would lead to the pectoral fin diversity we see in modern day batoids is difficult to obtain due to their cartilaginous skeleton. Recent dental analysis of extinct neoselachians has suggested the diversification events of the \cite{Guinot2012} The most recent common ancestor of the batoids and the sharks was certainly more shark-like, than batoid like.
-How could you take this project into the future if you had more time/material? What questions have arisen in your work that would make a useful topic of future study?
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