Labascicorona: Triassic shark scales, not a complete fish

Labascicorona is a formal form genus for microscopic placoid scales attributed to elasmobranch fishes in Middle and Late Triassic rocks. It is not a Jurassic shark genus founded on teeth: the isolated scales do not establish one biological species or a complete body. Their repeated crown and base shapes are useful for comparing marine strata in northeastern British Columbia. The evidence belongs in the ancient fish catalogue, with the limits of a scale-based name kept clear.

Quick facts

A scale-form name from Triassic microfossils

M. J. Johns introduced Labascicorona in a 1997 Geological Survey of Canada monograph on Middle and Late Triassic elasmobranch ichthyoliths from the Peace River–Williston Lake region of northeastern British Columbia. The study examined tiny phosphatic fossils recovered from carbonate rocks. It treated the material within a system of form taxa: the names classify recurring isolated elements, rather than asserting that each name represents a complete biological animal.

Within Labascicorona, the authors named several scale forms, including L. alata, L. longifossae, L. mediflexura, L. nitidifastigia and L. trifastigia. The suffix “s.f.” means scale form. It matters because a fossil scale can be described and compared even when it cannot be confidently associated with a named shark skeleton.

What a placoid scale preserves

Placoid scales are small dermal structures of elasmobranch fishes. In the fossil material, a scale can preserve a crown and a basal attachment structure, with margins, ridges or other surface features that help distinguish one form from another. A microscope reveals details that would be invisible in a body fossil collected by ordinary field methods.

Those details support classification of the scales and comparisons among fossil assemblages. They do not preserve the jaws, vertebral column, fins or proportions of the fish that carried them. Nor does a collection of several scale forms automatically belong to a single individual. The surrounding sediment may combine elements shed or transported from different animals.

Why the forms help correlate rocks

At Black Bear Ridge, L. mediflexura is reported as common or abundant in parts of the upper Carnian to lower Norian succession. It occurs among other elasmobranch scales and teeth and the remains of ray-finned fishes. Changes in these tiny assemblages can be compared with independent indicators such as conodont and ammonoid zones.

That makes the microfossils useful to stratigraphy: they help researchers compare layers where larger fossils may be scarce. Their value depends on recognising a repeatable form and documenting where it occurs. The distribution does not imply that a named scale form identifies a single shark species across every locality or that every bed with the form has the same age at fine resolution.

Where reconstruction must stop

Because Labascicorona is defined from scales, there is no secure basis here for assigning one full body shape, length, diet or behaviour. A reconstruction may depict a plausible Triassic elasmobranch as an artistic scene, but it cannot be presented as the anatomy of Labascicorona. The supported statement is narrower and more useful: these scale forms record elasmobranch presence and help compare Middle and Late Triassic marine deposits.

The distinction also prevents an old headline or a visual from being mistaken for the scientific classification. A scale-form genus is not equivalent to a skeletal genus. The fossil is small, but it still provides a concrete record when its limits are stated alongside its stratigraphic value.

Explore related evidence in the ancient fish catalogue.