J.micropulueontol., 6(2): 89-96, November 1987 Durotrigiu duveyi gen. et sp. nov., an Early Bajocian dinocyst with a variable precingular archaeopyle DAVID BAILEY Stratigraphic Laboratory, B P Petroleum Development Limited. Farburn Industrial Estate, Dyce, Aberdeen AB2 OPR, Scotland ABSTRACT-Durotrigia davryi gen. et 5p. nov. is described from the Inferior Oolite (Early Bajocian) of Dorset, England. It is the earliest distinctly tabulated gonyaulacacean dinocyst with a precingular archaeopyle. The archaeopyle is apparently variable, involving the loss of between 1 and 5 precingular plates. This variability poses some interesting taxonomic problems, particularly the implications to the value of the archaeopyle type as a high-level classification criterion. Some possible causes of archaeopyle variability are discussed. INTRODUCTION In a study of palynological assemblages from the All palynological slides are housed in the Palynolo- Bajocian interval in a borehole in Lyme Bay, Davey (in gical Collections of the British Geological Survey at Penn et al., 1980) observed two previously undescribed Keyworth, Nottingham. All material figures are reg- gonyaulacacean dinocysts from the [ueviuscula and istered in the series MPK 5319 to MPK 5327, MPK sauzei ammonite zones. Davey (up. cit.) noted that one 1186 and MPK 1188. of these forms; Gonyaulacid sp. I “loses more than one Durotrigia daveyi gen. et sp. nov. is the dominant precingular plate in archaeopyle formation”. The other, form in a low diversity assemblage in which other Gonyaulacid sp. 11, apparently had a single plate (3”) marine taxa include Nunnoceratopsis grurilis Alberti, precingular archaeopyle. 1961, Congylodinium erymnoteichos Fenton et a/., During 1984, the author examined Early Bajocian 1980, Escharisphaeridiri pocmki Sarjeant, 1968, material from the Winterborne Kingston borehole in “Tenuu” asymmetrii Fenton et (11.. 1980 and Pareodinia Dorset as part of an M.Sc. research project at the SP. University of Sheffield. Significant numbers of similar forms to those described by Davey (op. cit.) were SYSTEMATIC PALYNOLOGY recorded, and it was noted that the number of Division PYRROPHYTA Pascher 1914 precingular opercular plates varied in otherwise iden- Class DINOPHYCEAE Fritsch 1929 tical forms. Subsequently, the original material of Order PERIDINIALES Haeckel 1894 Davey (op. cit.) was re-examined and a similar Family GONYAULACACEAE Lindemann 1928 variation in archaeopyle structure was observed. It is Genus Durotrigia gen. nov. proposed that Gonyaulacid sp. I and I1 belong to a Diirotrigiu duveyi gen. et sp. nov. single species with variable detachment of precingular (PI. I, figs. 1-5, pl. 2, figs. 1-11; Fig. 2a-d) plates. 1980 Gonyaulacid sp. 1 Davey: pl. 1, figs. 11, 12. In this paper, these forms are formally described and 1980 Gonyaulacid sp. I1 Davey: pl. 1, figs. 15, 16. named in a new genus, Drtrotrigiu, which has a variable Derivation of name. Named after the Durotriges, the (1 P-5P) precingular archaeopyle. ancient Celtic tribe who inhabited Dorset. The specific name is after Roger Davey, who first recorded this MATERIAL form. The material described here is from the lower Diagnosis generico-specifica (ICBN art. 42). Cyst sub- Inferior Oolite (Early Bajocian) ot the Winterborne spherical. proximate or proximochorate. Gonyaulaca- Kingston borehole, Dorset (SY 8470 9790), and BGS cean tabulation: (lacl, lpr, 4‘,2a, 6”, 6c, 6”‘, lp, I””, 5s, borehole 50/03 329 in Lyme Bay (location map, fig. 1). flagellar pore area ). The archaeopyle is formed by the Detailed lithostratigraphy and ammonite dating for loss of 1 to 5 precingular plates (1P-5P). The auto- the Middle Jurassic of the Winterborne Kingston phragm is well tabulated, with distinct sutural ridges borehole is given by Penn (1982). Ammonite control in surmounted by isolated projections and/or crests, the Lyme Bay borehole is from Penn ef ul. (1980). which may be perforate. 89 Bailey 50103 329 0 TERTIARY TRIASSIC 0LATE JURASSIC B LATE CRETACEOUS 1 1 MIDDLE JURASSIC bFi CARBONIFEROUS .. .. , . .. EARLY CRETACEOUS EARLY JURASSIC DEVONIAN I. 0 10 20 Km LOCATION MAP OF WINTERBORNE KINGSTON & BGS 50/03 329 BOREHOLES Fig. 1. Location Map of Winterborne Kingston and BGS 50/03 329 Boreholes 90 Durotrigia diiveyi gen. et sp. nov. Holotype. Slide CSA 145911. MPK 1188, EF reference Occisucysta differs further in being cornucavate andlor H. 3412. suturocavate. Liesbergia Berger, 1986 has a P(3") or Paratype. Slide MPA 2212/2 EF, reference C.33 MPK 2P(3" 4)archaeopyle and has trabeculate parasutural 5326. ornament. Durotrigia gen. nov. also possesses two Type locality. BGS borehole 50/03 329 at 9.5-10.5m. dorsal intercalary plates which do not occur in Dis- Inferior Oolite (sauzei Zone). siliodinium, Occisucysta, Diacanrhirm or Tehamadi- Description niurn. Table 1 summarises the main distinguishing SHAPE. Cyst subspherical. morphological features of Durotrigia and similar WALL RELATIONSHIPS. Autophragm only. genera. WALL FEATURES. Sutural features include low Lingulodinium Wall, 1967 is a skolochorate dinocyst ridges, usually surmounted by isolated projections with a variable precingular archaeopyle, but can also andlor denticulate crests which may be perforate. The develop an epicystal archaeopyle. Ctenidodinium De- spineddenticulations may be distally bifurcate, and flandre, 1938 and related cysts have epicystal tend to be more complex about the cingulum and archaeopyles. antapical pole. Gonal spines are also large. The Diacanthum is originally described with a 2P(3" 4") autophragm has a complex structure (see PI. 1, fig. S), archaeopyle (Habib, 1972). Unfortunately, the holo- appearing scabrate in transmitted light. type for D. hollisteri Habib was lost. However, TABULATION. Indicated by variable, but distinct examination additional material (Habib & Drugg, sutural features. Gonyaulacacean formula: lacl, lpr, 1987) has resulted in an emendation of Diacanthum to 4', 2a, 6", 6c, 6"', Ip, l"", 5s, flagellar pore area. include variability ( 1P-3P) in the archaeopyle. Diacan- ARCHAEOPYLE. Precingular, formed by the loss of thum filapicarirm (Gocht) Stover & Evitt (1978) is up to five precingular plates. Cysts with varying described with a 2P(3" 4'') archaeopyle. Gocht (1970) dehiscence; lP, 2P, 3P, 4P and 5P. The most common noted that one plate often remained behind, and also, type is 4P, with the first and sixth precingulars that "tears (along the cingulum) often extend up to the remaining attached, forming a broad isthmus joining region of the longitudinal furrow". However, he the apical series to the hypocyst. Excystment begins concluded that this was due to mechanical breakage. dorsally at the 3" plate and progresses ventrally in both Dissiliodinium globulum Drugg (1978) is described directions. with a 4P or SP archaeopyle. though it has been CINGULUM. Indicated by six rectangular plates. recorded as varying between 3P and 6P (W. Wille, pers. Cingular sutures often carry complex denticulate crests comm.). Dissiliodinium differs further from Durotrigia which may be perforate and bear bifurcate spines (Fig. in lacking both tabulation and dorsal intercalaries. 2c). Ornamentation is symmetrical about the cingulum. Discussion. Drrrorrigirr drn-eyi gen. et sp. nov. is the SULCUS. Clearly discernible. The innermost part of earliest distinctly tabulated gonyaulacacean dinocyst the sulcus is occupied by a large flagellar pore area with a precingular archaeopyle. The fact that where no detail can be distinguished. Surrounding this archaeopyle variability is described in the generic area are five sulcal plates; as, ras, rs, ps, Is. (Fig. 2d). diagnosis of Durotrigia is contentious. For many years Comparison. Durotrigia gen. nov. differs from all other the archaeopyle in both modern and fossil dinocysts has genera in having a variable (1P-5P) archaeopyle. been considered a high level taxonomic character and Diacanrhirm Habib (Habib & Drugg, 1987) has a Evitt (1967) recommended that forms with different variable ( 1 P-3P) archaeopyle. Dissiliodinium Drugg, archaeopyle structure should be assigned to separate 1978 loses four or five precingulars and is non tabulate. genera. To a large extent this proposal was followed for Occisucystu Gitmez, 1970 and Tehamadiniirin Jan du several years, and Norris (1978) awards the same Chene ('1 d., 19M both have a 2P(2" 3") ;irchacopyle. taxonomic value to the archaeopyle in his supra-generic Table 1. Comparison of morphological features to distinguish Durotrigia gen, nov. from similar genera. Wall Clarity of Dorsal Genus A sclr aeopy le Structure Tabulation lntercalaries DUROTRIGIA IP-5P Autophragm Distinct Present DIACANTHUM 1P-3P Autophragm Distinct Absent OCCISUCYSTA 2P Autophragm Distinct Absent TEHAMADINIUM 2P Cornucavate Distinct Absent DISSILIODINIUM 3-SP Autophragm Absent Absent G 0NG Y L 0 11 IN I U M 2P Autophragm Absent Unknown 91 Bailey 5c C c- SUTURAL CINGULAR lop A. Ventral vlew. 1”’ - B. Dormrl vlew. C. Sutural features. D. Detall of ventral tabulation. 11 = flagellar pore area Fig. 2. Durotrigia daveyi gen. et sp. nov ~ ~ ~~~~~~~~ Explanation of Plate 1 Durotrigia daveyi gen. et sp. nov. Fig. 1. Sample WK 56, stub A, Winterborne Kingston borehole at 918.96m. Ventral View, MPK 5319. Fig. 2. Sample WK 56, stub A, Winterborne Kingston borehole at 918.96m. Dorsal view of specimen showing loss of 2 precingular plates, MPK 5320. Fig. 3. Sample WK 54, stub 1, Winterborne Kingston borehole at 917.56m. Antapical view, MPK 5321. Figs. 4, 5. Sample WK 54, stub 2, Winterborne Kingston borehole