Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

ACTA UNIVERSITATIS LATVIENSIS, 2004, Vol. 679, pp. 46-56
New anaspid material from the Late Silurian of
Britain and Estonia
C. GILES MILLER, TIIU MÄRSS, and HENNING BLOM
C. G. Miller, Department of Palaeontology, Natural History Museum, Cromwell Road, London,
SW7 5BD, UK, G.Miller@nhm.ac.uk; T. Märss, Institute of Geology at Tallinn University of
Technology, Estonia Ave 7, Tallinn, 10143, Estonia , marss@gi.ee; H. Blom, Department of
Physiology and Development, Evolutionary Organismal Biology, Norbyvägen 18A , Uppsala,
SE-752 36, Sweden, Henning.Blom@ebc.uu.se
A new birkeniid anaspid Trimpleylepis juncta gen. et sp. nov. is described from the Prídolí, late
Silurian at Man Brook, Welsh Borderland. Trimpleylepis concatenata gen. et sp. nov. is described
from the Ohesaare Borehole, Ludlow, Silurian of Estonia. Histological sections show that
Trimpleylepis has similar features to material previously described from the Family Septentrioniidae
Blom, Märss and Miller, 2002. However, vascular canals have not been seen in sections of either
species, and rare openings of canals have only been seen on one or two specimens of T. concatenata,
so assignment to this family is tentative. Silmalepis cf. erinacea has been identified from Man
Brook and extends the range of the genus into the Prídolí. New anaspid material from the late
Silurian of Gardner’s Bank, Welsh Borderland suggests that anaspids from the Family
Rhyncholepididae Kiær, 1924 were present from the mid Wenlock to the late Prídolí.
Key words: Agnathans, anaspids, Welsh Borderland, East Baltic, late Silurian, Ludlow, Prídolí.
Introduction
The uppermost Silurian of the Welsh Borderland has yielded a rich microvertebrate
fauna. The Man Brook locality is no exception, having produced well-preserved
thelodont scales (Turner 1973, 1984; Vergoossen 1995, 1999; Märss and Miller in
press), acanthodian scales, teeth and fin spines (Vergoosen 1995, 2000), anaspid scales
and platelets (Blom et al. 2002) as well as many osteostracan and heterostracan scale
and shield fragments (collections and documentation at The Natural History Museum).
Anaspids are agnathans with a fusiform head, elongate body, a slanting row of branchial
openings on either side of the body and a strongly hypocercal tail (see Miller et al. in
press for review). Birkeniid anaspids appear in the geological record as disarticulated
phosphatic scales with an external sculpture and a rib on the visceral surface; other
closely related taxa have only spines and dorsal scales (e.g. Lasanius Traquair 1898) or
are naked or with a weakly mineralised exoskeleton (e.g. Jamoytius White 1946). For
the purposes of this article, the general term “anaspid” will be used in place of birkeniid
anaspid. Blom et al. (2002) published a taxonomic scheme combining anaspid body
features and scale morphology with histology. Anaspids were illustrated from Man
Brook (ibid.) but the collection also contained many other fragments of scales, spines
and platelets that were not described or illustrated because the histological structure
was not known from the material available at the time. The external sculpture of these
fragments was consistent with an anaspid affinity, but doubts remained concerning the