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What features did Pleurocanthodii have that differed from modern sharks?
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chondrichthyan
Southern stingrays (Dasyatis americana or Hypanus americanus) are found in the western Atlantic Ocean.
The order Pleurocanthodii, a group of extinct freshwater sharklike fishes, possessed several distinct anatomical features that differed from modern sharks.
Key differences include:
- Skeletal Structure: Pleurocanthodians featured pectoral and pelvic fins with an archipterygial structure, consisting of a central axis with side branches.1
- Cranial Spine: A long, movable spine made of bone projected backward from the back of their skull.21
- Tail Shape: Unlike the muscular, upturned tail characteristic of modern sharks, the pleurocanthodian tail was nearly symmetrical and only slightly tilted upward.13
- Dentition: Their teeth were unique, featuring two divergent prongs and a central cusp set upon a buttonlike base.1
- Anal Fin: They possessed a two-lobed anal fin, a feature not found in modern sharks.1
While they shared some characteristics with modern chondrichthyans—such as the presence of claspers in males—these specific morphological traits distinguish them from the fusiform body shape and specialized fin structures seen in contemporary shark species.13