Labial cartilage in sharks and kin

Kilmpfinger and Kriwet 2020 composed a ‘brief historical review’:
“The origin and function of LCs (labial cartilages) have been discussed for almost 150 years.
Gegenbauer 1872: vestiges of pre-mandibular visceral arches,
Pollard 1895: remains of skeletal supports of a primitive set of oral cirrhi as in Amphioxus.
Swertzoff 1916: vestiges of two segments of visceral arches
Goodrich 1930: a secondary structure of no great morphological importance
Smith 1937: strengthen and mobilize the mouth corners.
Veran 1995: “without functional utility” and therefore “in decline”
Motta and Wilga 2001: very important to generate suction forces for ingesting prey items.”

Without a valid phylogenetic context,
and a last common ancestor, all hypotheses are likely to end up as wrong guesses, no matter how many µCT scans you use.

Klimpfinger and Kriwet conclude
“It is evident that position and dimension of LCs are connected to the shape of the jaws, forming distinct morphological modules.” That’s pretty generic, something that could have been stated prior to their study. Armed with a valid phylogenetic analysis the authors could have found a last common ancestor and traced the expansion, shrinkage and general evolution of labial cartilages among the various chondrichthyan clades (Fig. 1). Instead the authors, armed with a MSc and a PhD, left those tasks to an amateur blog poster working from data discovered on Google. Focused studies are great, but we still need to understand and confirm the systematics a little better. Taxon exclusion remains the number one problem in paleo.

References
Klimpfinger C and Kriwet J 2020. Comparative morphology of labial cartilages in sharks (Chondrichthyes, Elasmobranchii), The European Zoological Journal, 87:1, 741-753, DOI:
10.1080/24750263.2020.1844323