Brongniartella (trilobite)

Like other trilobites, Brongniartella is composed of three parts: a cephalon, a multisegmented thorax, and a pygidium. The 13-segmented thorax has a wide but indistinct axis, with extremely shallow axial furrows and the axis and pleurae being almost undistinguishable from the general concavity of the body. The axial furrows of the thorax form a continuous depression, but each axial ring is also independently separated from the corresponding pleura by a shallow, transverse, oblique furrow corresponding to the one crossing the occipital ring from the base of the glabella. The base of each pleura between this transverse furrow and the pleural furrow is slightly swollen, and there is a peg-like interior projection on the posterior margin of each thoracic segment that fits into a corresponding notch of the succeeding thoracic segment. The pygidium is rounded and parabolic with a well-defined axis that ends in front of the posterior margin and a slightly indistinct, narrow posterior border. The pygidial ribs do not extend to the lateral margin of the pygidium. It is composed of 9-12 segments, and some forms bear a postaxial ridge. == Species and interrelationships ==

Brongniartella is traditionally considered to belong to the Eohomalonotinae, though some workers have assigned it to the Homalonotinae. Congreve and Lieberman 2008 performed a cladistic analysis of Ordovician homalonotids and found that Brongniartella was paraphyletic and the basal-most species of Homalonotinae, giving rise to the genera Trimerus and Platycoryphe. They proposed redefining the genus to only include the type species B. bisulcata and moving all other species to the paraphyletic "Brongniartella" group. Parsimony analysis of Congreve and Leiderman 2008: • B. caradociana Dean, 1961 - Caradoc of England • B. edgelli Salter, 1865 - Caradoc of England • B. platynota Dalman, 1828 • B. sp. aff. platynota (Salter, 1865) - Silurian of Jordan • B. trentonensis Simpson, 1890 - Caradoc of Pennsylvania, USA == References ==