A new species of Embsaygnathus (Conodonta) from the Arundian (Carboniferous) of Co. Dublin, Ireland

Embsaygnathus crosbiei sp. nov. Jones is recorded from Arundian limestones at Newcastle, Co. Dublin, Ireland. It is suggested that E. crosbiei and Embsaygnathus asymmetricus Metcalfe were derived from the Geniculatus claviger Roundy — Geniculatus glottoides Vosges lineage.


INTRODUCTION
Investigation for Chevron Mineral Corporation of Ireland, of the 130m deep borehole CN/NC-18 (Grid ref. N 998 286), at Newcastle, 17km east-south-east of Dublin, produced a conodont fauna at 4.0m depth, including Embsaygnathus crosbiei sp. nov. described here. Foraminifera from the same level confirmed the Arundian age. Processing of further intervals from the drill core failed to produce any more examples of this species, but a specimen of Embsaygnathus asymmetricus Metcalfe 198 1 and several specimens of Geniculatus claviger Roundy 1926 emended Hass 1953 were recovered. It is considered that this new species may be an intermediate form on the evolutionary pathway from Ge. claviger to E . asymmetricus (see Fig. 1). Examples of recurved or geniculate platform conodonts are rare in the Dinantian. It is unusual to erect a new species on the strength of one specimen, but occurrences of the genus are rare and it is thought unlikely that further examples will be recovered for some time. Enquiries from other workers in this area and processing of available material have failed to produce any more examples. Since it is considered to be an important link in the evolutionary story of rare recurved and geniculate platform conodont elements, it was considered worthwhile publishing.
The rarity of this conodont animal also means that only the Paelement is described here, the determination of the rest of the apparatus must wait until more evidence has been gathered.
The holotype and other figured specimens are presently stored in the micropalaeontology collection of Conodate International Ltd. They will eventually be reposited in the collection of the National Museum of Ireland numbers NMING: F20941-7.

MICROPAL AEONTOLOGY
from the Craven lowlands of nothem England. He recovered three specimens from the G. homopunctatus Biozone (Chadian and Arundian) of the Metcalfe (1981) first described E. asymmetricus Embasy Limestone of Embasy Bank, Skipton, Yorkshire. Since then a few further individuals have been recorded, making a total of eight. Swift recovered a single specimen from the commutata Zone (Arundian -?lower) of the Isle of Man, Ronaldsway Member, Derbyhaven Formation (Varker & Sevastopulo 1985, P1. 5.6, Figs 11 & 16), Reynolds found the species in the Visean Limestones of theEshton andRylston areas of the Craven Basin (in Metcalfe 1980 1987) it is likely that the range of E. asymmetricus is also restricted to the Arundian. The other genus discussed here is Geniculatus Hass 1953. Examples of Ge. Claviger are not uncommon and range throughout the Dinantian, but the species Ge. glotroides Vosges 1959 is rare. Previously recorded specimens of Ge. glotfoides include one from the L. commutata Zone (Arundian) at Reenydonagen, Co. Cork, (Varker and Sevastopulo 1985, P1. 5.6, figs 5 , 6) whilst Voges' (1959) twenty specimens were recorded from the junction of the "Liegende Alaunschiefer"the predominantly Hydrite horizon (cuII/unchorulis Zone) of Bomighausen, W. Germany. Groessens found a single reworked specimen in V3byChert Limestones in the Houthem borehole DB 105 in Holland (in Bless e f ul. 1976), the only recorded specimen of this age, but probably derived from older rocks.
This paper reports two specimens from the Dublin Basin.

SYSTEMATICS Order Conodontophorida Eichenberg 1930
Genus Embsaygnathus Metcalfe 198 1 Type species Embsaygnathus asymmetricus Metcalfe 198 1 The orientation of the element has been inverted from Metacalfe's description, so that anterior and posterior are reversed, i.e. It is the anterior bar that is strongly recurved, and the platform continues with a posterior bar.

Derivation of name. This species is named in honour of the late Dr
Crosbie Matthews of Bristol University, and in memory of his strong associations with Ireland. Range. Since only one specimen of E. crosbiei has so far been recorded, it is not possible to define a range. However its recovery Embsaygnathus crosbiei sp. nov. from mid Arundian limestones is within the established range of Embsuygnathus, which runs from late Chadian to Arundian (Metcalfe 1981).

Diagnosis. A species, of
Description. E. crosbiei is strongly recurved and possesses a narrow platform with restricted ornament. The anterior bar extension curves outwards and then to the posterior through a total of 160O. The small basal cavity is subcircular and located at the junction of the platform and the anterior bar which are both keeled. Remarks. E. crosbiei differs from E . asymmetricus in the following features. The platform is narrow and symmetrical but bears only two to four low nodes on the edges, whereas there are eight to ten transverse ridges on the wide platform of E. asymmetricus. In lateral view it is straight without the arch seen in E. asymmetricus. The sharp carina develops only four blunt fused nodes posteriorly instead of thirteen to fourteen. There is a shallow trough on each side of the carina. E. asymmetricus carries no main cusp which is a feature of Geniculatus, but E. crosbiei does bear a strong denticle at the start of the anterior blade. Metcalfe (1981) describes therecurved blade of E. asymmetricus as being a posterior bar, but it is considered here that it is the anterior bar which is recurved and compares with the geniculate anterior bar of Geniculatus ( Fig. 1 and Table 1). In E. asymmetricus the anterior blade curving outwards and posteriorly through a total of 170°, carries ten denticles which slope towards the anterior. In E. crosbiei the carina continues towards the anterior into a strong blade, with ten sharp denticles, which curves to the posterior through 160' (Table 2).

ASSOCIATED FAUNA
In both species of Embsaygnathus the arboral surface is strongly keeled, as opposed to that of Geniculatus which is grooved ( Table 2). In E. asymmetricus the anterior keel diverges from the cavity at 110' whilst in E. crosbiei it diverges at 1 00'. In E. crosbiei the basal cavity is also found at the anterior end at the junction of the platform and blade, it is small subcircular and flared, and slightly pointed to the posterior. This new species clearly falls within Embsaygnathus although it does bear similarities to Geniculatus (Tables 1 and 2).

PHYLOGENY
Examination of a number of specimens of Ge. claviger revealed a variation in the width of the posterior bar. An example found at 20.7-25.4m from CN/NC-18 (PI. 1 and Fig. 1) cames a flange which is broadest at the anterior and tapers posteriorly. Thornbury (1985) figured a specimen with a broad flange from the D . latus Subbiozone of the S. anchoralis Biozone (late Courceyan), at Ballygarvan, Co.
Cork. This form appears to be a morphological intermediate between Ge. claviger sensu strict0 and Ge. glottoides, and it is likely that it is from such a variant that E. crosbiei is derived (Fig. 1). It is envisaged that the broad flange enlarged into the somewhat plain platform of E. crosbiei which then went on to develop into the well ribbed platform o f E. asymmetricus. Evidence for the transition of the anterior bar from the stubby geniculate form of Geniculatus, to the strongly recurved form ofErnbsuygnathus has not yet been seen. Morphological comparisons of these forms are seen in Tables 1 & 2. The combination of all the features described and illustrated in Table 2 excludes the possibility that E. crosbiei is an aberrant form of E. asymmetricus.
It is interesting to speculate from the form similarities, that the lineage may have had its origins in the Devonian from Palmatolepis (Tripodellus) gracilis, and may have given rise in the Silesian to Neogondolella.
Embsuygnathus from the Carboniferous of Ireland Geniculatus Hass 1953 Embsaygnathus Metcalfe 198 1 Type species Ge. claviger Roundy 1926 E . asymmetricus Metcalfe 1981 Outline geniculate recurved. row of nodes or denticles at right angles to carina develop outwards into an anterior bar with 10 denticles sloping towards the anterior. It then curves towards the posterior through (a further 800).

Posterior
strongly keeled the anterior keel diverges from the cavity at 110' .
at the anterior end at the junction of the platform and anterior bar. It is small, subcircular, strongly flared with extended lips. It is slightly pointed towards the posterior and extends along platform and anterior bar as grooves.

E. crosbiei Jones 1991
May have been broken off narrow and symmetrical, 2-4 nodes on edges, sharp carina develops 4 blunt fused nodes towards the posterior trough on each side of carina.
start of anterior blade bears a strong denticle.
carina continues anteriorly into a strong blade with 10 sharp denticles which curves posteriorly through 160'. strongly keeled, the anterior keel diverges from the cavity at looo.
at the anterior end at the junction of the platform and blade. It is small, subcircular flared. It is slightly pointed towards the posterior.