Early Proetid Trilobites From Northern Europe
2015-07-30T17:10:56Z (GMT) by
All known Lower Palaeozoic proetid trilobites from northern Europe have been examined, and those from the Ordovician of the British Isles and Scandinavia and those from the Silurian of the British Isles and Bohemia are described in detail. Closely related species from other areas are figured for comparison. Members of 23 proetid genera, 8 of which are new, are described and figured. 113 species have been investigated, 36 of which are new. The Lower Palaeozoic proetids have hitherto been poorly understood and neglected, and in this thesis they are comprehensively treated as a group for the first time. With their description and figuring, it is now possible to propose a provisional phylogeny for the earlier Proetidae, and to attempt to seek the origins of many important Devonian genera. Of morphological features, the most useful characters for classification are found in the pygidium. Cephalic characters tend to be less reliable. The rostral plate is always subtriangular or trapezoidal in outline, and in all except one case the connective sutures converge backwards. The preannulus has been found to be restricted to the subfamilies Proetinae and Cornuproetinae. From this study it appears as if at least two main lines of proetid trilobites extend well back into the Ordovician, and there may well be a case in the future for recognising two distinct families. The origin of the Proetidae remains problematical, but they could have their origins in Cambro-Ordovician Hystricurine trilobites, some of which, like the proetids, have a trapezoidal rostral plate.