Devonian Harpetidae from the central and eastern Anti–Atlas, Morocco

Abstract

The systematics of 37 new species of Devonian Harpetidae from the central and eastern Anti–Atlas Mountains, Morocco, are described. The new material comes from the Dra—Tafilalet region and the province of Tata. A cladistic study was undertaken involving 138 taxa with the objective of assigning the new taxa to the appropriate genera, which are, as far as possible, monophyletic. In order to identify the widespread homoplasy present amongst harpetid taxa, which has proven so problematical for systematics in the past, many additional morphological characters were coded in the data matrix, totaling 111. In addition to the new material, all those described harpetid species from the Devonian and Silurian in which at least 10% of characters could be reliably coded were included in the study. The parsimony analysis using 20 different seeds identified 636 shortest trees; the consensus tree recognised 10 monophyletic clades to accommodate Devonian species. While the node support was weak the topology of the consensus tree is a substantial improvement on those of previous phylogenetic studies which have tended to be pectinate. The new species were assigned to 10 genera. Four genera (Harpes, Lioharpes, Kielania and Eskoharpes) are redefined and Globoharpes is reduced to a junior synonym of Eskoharpes. Three further genera are recognised, Declivoharpes, Fritchaspis and Helioharpes, which have been misinterpreted in the past and the new genera Maghroharpes, Pinnuloharpes and Stoloharpes established. The new species are assigned as follows:

to Harpes, H. boudibensis, H. lahceni, H. lentigo, H. oudris, H. prescheri, H. sphenocephalus and H. supercilium; to Lioharpes, L. ammari; L. galea, L. morocconensis, L. saredra, and L. scopulum; to Fritchaspis, F. edgecombei; to Helioharpes, H. aougili; to Kielania: K. tumula; to Eskoharpes, E. sicarius; to Maghroharpes, M. azmamarensis, M. forteyi, M. hammii, M. ihmadii, M. laatchanensis, M. minutipunctus, M. oufatenensis, M. terridus, and M. zguidensis; to Pinnuloharpes, P. apteros, P. chaperon, P. hannabouensis, P haustrum, P. igaouii, P. merzaneensis; P. segaouii. and P. torquis; Stoloharpes, S. calceolus, S. capricornus, S. retiarius, and S. rissaniensis.

Decllivoharpes, is also recognised as a genus, although no new species has been assigned to it.

The cladogram produced very few synapomorphies and there are no unique diagnostic characters available to determine genera. To assist in the process of assigning species in the future to the correct genera a working guide using combinations of characters and character states used in the study has been prepared.

The name Helioharpes perradiatus has been widely used with regard to harpetids from the Anti Atlas. This study shows that this has been a ‘portmanteau’ name for at least three distinct species. All are very different from the type material of H. perradiatus, which was recovered from the Western Meseta to the north of the Atlas Mountains, and has not been found to occur in the Anti-Atlas.

The new material figured herein has provided additional information on the eyes of Devonian harpetids of the Anti-Atlas. Typically, each eye lobe has two lenses which vary considerably in shape from species to species and are very different from the symmetrical multi lensed eyes of other Devonian trilobites. Probably in response to environmental changes a small third eye lens appeared for a short time twice, first in the upper Pragian/lower Emsian and then again in the Eifelian. The shape of the Pragian/Emsian lens was circular whereas that of the Eifelian lens was similar to the shape of the two larger accompanying eye lenses.