Anatomy of the Silurian thelodont Phlebolepis elegans Pander

The Silurian thelodont Phlebolepis elegans Pander from Saaremaa, Estonia, is one of the most-often illustrated early vertebrates, yet its external morphology has remained poorly known and experts seldom agree about its probable body form. We examined hundreds of articulated specimens from the type locality (Himmiste Quarry) to reconstruct its morphological features. We found that a reconstruction published more than four decades ago by A. Ritchie was the best available till now. We disagreed mostly in that the mouth is not terminal, but subterminal, and there is a slight development of a rostrum dorsal to the mouth. The pectoral fin originates close behind the orbits, but is otherwise similar to Ritchie’s reconstruction. We also found the caudal fin to be much larger, more flexible and more symmetrical (though not perfectly symmetrical) than earlier reconstructions, with a large dorsal lobe and an even larger ventral lobe, and a fin web supported by slender ‘ray-like’ scale-covered lobes. The shape, number and location of the branchial openings are notably still not certainly known. Our preferred morphological features are represented by an artist’s restoration. With this revised understanding, future representations of Phlebolepis elegans can be based on more reliable information and its morphology can be compared more accurately with that of other early vertebrates.