#dermal denticles

The first picture is shark skin under a microscope, the second is a close-up, and the last picture is from further away. They all have dermal denticles, but I chose to show a thresher shark for three reasons, because I think they’re cute, because I felt like it and because I can.

(Sorta)

Click to read all about the Greenland Shark!

This week’s shark feature focuses on a large shark known as the Greenland Shark (Somniosus microcephalus). This shark cruises slowly through the water, earning it the nickname “Sleeper Shark”. Greenland Sharks can be found in the Northern Atlantic and Arctic zones. This shark is typically found in cool water, but during winter will stay near the slightly warmer waters at the surface. To avoid…

 SAWTEETH IN CHONDRICHTHYAN ARENT REAL TEETH

A UK researcher team just figure out that toothlike skin denticles exhibited by many chondrichthyan are not likely related to real teeth.

SHOCKED! 

Chondrichthyans - sharks and rays- are covered of external placoid scales calles skin denticles. Three groups in the class include those with sawlike growths on their heads: Pristiophoridae (sawsharks, Selachii), Pristidae (sawfish, Batoidea) and the extinct Sclerorhynchoidea (Batoidea). 

The skin covering of many in the class are well known, but much less has been learned about the morphological diversity among the group. Researches sought to try to understand if the sawlike growths were related to actual teeth. To find out, they undertook a study of several specimens from embryos to adults. Scanning specimens researchers noted that the sawteeth of Pristiophoridae and Sclerorhynchoidea were morphically similar despite not being very close phylogenetically—in those, the sawteeth develop under the skin in embryos—and in adults are replaced as needed. 

The sawteeth in Pristidae, on the hand, were inserted into sockets in the cartilage and grew continuously and thus never needed replacing. 

Real teeth, in contrast, develop in an ordered sequence governed by genes and those that are lost are replaced by those that have been pre-formed in rows, for just that purpose.

Photo by Marty Snyderman/INNERSPACE VISIONS