Palaeography, Pataeoctimatology, Paiaeoecoiogy,' 13 (1973): 143-156
© Elsevier Scientific Publishing Company, Amsterdam — Printed in The Netherlands

LINGULASMA TENUIGRANULATA — PALAEOECOLOGY OF A LARGE ORDOVICIAN LINGULOID THAT LIVED WITHIN A STROPHOMENID— TRILOBITE COMMUNITY

R. K. PICKERILL

Department of Geology, University of liverpool, Liverpool {Great Britain)
(Accepted for publication December 7, 1972)

ABSTRACT

Pickerill, R. K., 1973. Lingulasma tenuigranulata — Palaeoecology of a large Ordovician linguloid that lived within a strophomenid — trilobite community. Paiaeogeogr., Palaeoclimatol., Paiaeoecoi., 13: 143 — 156.

All the specimens of Lingulasma tenuigranuiata found at two localities in Meifod, Montgomeryshire (North Wales), are in original life position, with the burrow attitudes ranging from vertical, inclined and vertical oblique to inclined oblique. The specimens are all extremely large in size for linguloids (over 3.9 cm in length) and this is attributed essentialiy to an abundant food supply and possibly to vertical phosphate diffusion within the enclosing sediments. The unimodal size-distribution is attributed to an absence of predation and disease and to death by senility. The associated fauna shows that Lingulasrna is part of a strophomenid — trilobite community rather than the normally expected gastropod — bivalve one. The trophic structure of this community is shown to be out of accord with that of recent communities. L. tenuigranuiata represented chance spatfalls in an open sh< lf . nviron- ment which was extremely conducive to its growth and development.

INTRODUCTION

M'Coy's type specimen of Lingu!a tenuigranuittta was collected by Sedgwick from a
now completely overgrown quarry on Gallt-yr-Ancr {U.K. National Grid, Sheet 117 ref. SJ
143132), near Meifod (King, 1928). The specimens discussed here are from two other
localities of the same age in the Meifod district (Fig.l). Many Ordovician species
belonging to the super-family Lingulacea (%aagen, 1885) have been loosely termed
Lingula, but in many cases the internal structure of the valves is unknown and in these
circumstances the generic and even the family assignment is doubtful. However,
because of its large size, its external ornament of fine growth lines and its surface
granulation, Linguta tenuigranulata is considered to belong to the genus Lingulasma
rather than Lingula and from hence forth will be termed Lingu lasma tenuigranulata. The
only record of Lingulasma tenuigranulata outside the Meifod. area is that by Dean {1959),
who notes its occurrence in describing the stratigraphy of the Cross Feil lnlier. However,

R K PICKERILI„