Back
Wrevittia cretacea
Originally Gonyaulax, subsequently (and now) Gonyaulacysta. This combination was not validly published in Sarjeant, 1966, since that author did not fully reference the basionym.
Holotype: Neale and Sarjeant, 1962, pl.19, fig.1-2; text-fig.2
Locus typicus: Speeton Clay, Speeton, Yorkshire
Stratum typicum: Hauterivian
Original description: Neale and Sarjeant, 1962, p. 441-443: Gonyaulax cretacea
Diagnosis: A species of fossil Gonyaulax of small size having a polygonal theca, with strongly developed apical horn and with antapex flat. Tabulation 5', 6", 6''', 1p, 1pv, 1''''; in addition, a small oval plate is present at the junction of plate 1''' with the transverse and longitudinal furrows and two small plates separate the longitudinal furrow from the posterior end of the transverse furrow and from plate 6""". Transverse furrow strongly spiral, laevo-rotatory, divided into sections (?5) by low ridges; longitudinal furrow broad and sigmoidal. Crests on plate and furrow loundaries of moderate height, irregularly perforate and with deinticulate edges, the height of the denticulations being very variable; spines are sometimes present at crest junctions.
Dimensions: Holotype: overall length, 46.5 µm, shell length 35 µm, breadth 30 µm. Range: overall lengths c. 35-50 µm (14 specimens).
Description (annotated): Theca of chestnut brown colour, without or with minute granulation. Structure of the apex not clear; five apical plates appear to be present, with plate 1" elongate and forming the forward prologation of the longitudinal furrow. Six well-developed pre-equatorial plates, plate 3'' being lost in pylome formation. The transverse furrow is broad and in the form of a laevo- rotatory spiral whose two ends differ in anteroposterior position by more than twice the furrow"s breadth; since the longitudinal furrow is sigmoidal, the two ends of the transverse furrow both intersect the median dorso-ventral plane through the shell. The posterior end is separated from the longitudinal furrow by a crescentic plate. A small oval plate, which was perhaps the point of origin of the transverse flagellum, lies between the anterior end and plate 1'''. A third small plate, roughly pear-shaped, separates plate 6''' from the longitudinal furrow. The boundaries of these plates with furrows do not bear crests. Six post-equatorial plates are present, with plate 1''' reduced and elongate. A posterior intercalary plate is present: it is of pentagonal shape and separates plate 6''' from the antapex. A quadrilateral posterior ventral plate separates the longitudinal furrow and plate 6''' from the antapex: the latter is occupied by a single pentagonal antapical plate. The crests bounding plates are of variable height, being very reduced or absent on parts of the margins of the longitudinal furrows. The degree of denticulation is very variable, both between individuals and on each theca: the denticles are sometimes truncated. The crests are yellowish brown in colour: they are frequently perforate, but the perforations are not of constant size and show no arrangement. Spines are present at some crest junctions, functioning presumably as strengthening structures: they are frequently perforate, but the perforations are not of constant size and show no arrangement. Spines are present at some crest junctions, functioning presumably as strengthening structures: they are most strongly developed on the corners of the antapical plate and at the junctions of crests with the transverse furrows.
Affinities:
Neale and Sarjeant, 1962, p. 443
Remarks: The general appearance of this species is strikingly similar to that of G. jurassica Deflandre, 1938: however, G. cretacea differs from the latter species in its sigmoidal longitudinal furrow and the detail of the tabulation of the ventral surface. It is probable nonetheless that G. cretacea may have evolved from G. jurassica by a process of modification of ventral structure.
--------------------------------------------------------------------------------------------------------------------------------
Remarks Duxbury, 2023:
Remarks: This species has been transferred to Wrevittia here, being considered essentially similar to Wrevittia helicoidea (Eisenack and Cookson 1960) Helenes and Lucas-Clark 1997 but lacking the prominent surface ornament of the latter (see Plate 20, Figs. 13, 17 and Plate 21, Fig. 15), a distinction highlighted by Sarjeant (1966b, p. 117) and repeated by McIntyre and Brideaux (1980, p. 13).
Helenes and Lucas-Clark (1997, p. 186) provisionally included this species in Stanfordella, “pending clarification of its paratabular characteristics” and citing conflicting data from Neale and Sarjeant (1962), McIntyre and Brideaux (1980) and Below (1981). Their conclusions from the first two cited references are, however, based on poor original illustrations, but their reference to Below (1981) appears to be more reliable, being based on the last author’s clear SEM work. They stated, “Below’s (1981, pl. 15, fig. 6) specimens from the Early Cretaceous of Morocco, show an A/ai ventral arrangement that precludes assignment to Stanfordella. These specimens probably have a paratabulation pattern similar to the one shown here in Wrevittia helicoidea comb. nov”.
This species was first described by Neale and Sarjeant (1962, p. 19) from the Shell West Heslerton No. 1 Borehole, at 99.25 m (325 ft 7"); the age of this sample was subsequently listed in Sarjeant (1966a, p. 19) as “Middle Hauterivian” (quoted as 99.25/50 m). In the same volume, Sarjeant (1966c, p. 214) tabulated that sample, but as “Upper Hauterivian”, together with four other samples from the Shell West Heslerton No. 1 Borehole, between 103.25 m (338 ft 9" - Middle Hauterivian) and 19.25 m (63 ft 2" - Upper Barremian).
Sarjeant (1966c, p. 214) did not include Wrevittia cretacea in his stratigraphical distribution chart but, in earlier comments on Wrevittia helicoidea (Sarjeant 1966b, p. 117) he stated, “Gonyaulacysta cretacea (Neale and Sarjeant 1962) is present in somewhat earlier horizons (99.25 m - Hauterivian)”, and “It seems probable G. cretacea is ancestral to G. helicoidea”. Sarjeant (1966c, p. 214) illustrated Wrevittia helicoidea (as G. helicoidea) as occurring only in the 42.5 m and 39.0 m samples (early to middle Barremian).
In the present study, both Wrevittia cretacea and W. helicoidea were long-ranging; the first was recorded between Beds D2A and LB2D at Speeton and W. helicoidea ranged througout (i.e., both ranged between the amblygonium and fissicostatum ammonite Zones). There is no evidence that W. cretacea is ancestral to W. helicoidea.
Holotype: Neale and Sarjeant, 1962, pl.19, fig.1-2; text-fig.2
Locus typicus: Speeton Clay, Speeton, Yorkshire
Stratum typicum: Hauterivian
Original description: Neale and Sarjeant, 1962, p. 441-443: Gonyaulax cretacea
Diagnosis: A species of fossil Gonyaulax of small size having a polygonal theca, with strongly developed apical horn and with antapex flat. Tabulation 5', 6", 6''', 1p, 1pv, 1''''; in addition, a small oval plate is present at the junction of plate 1''' with the transverse and longitudinal furrows and two small plates separate the longitudinal furrow from the posterior end of the transverse furrow and from plate 6""". Transverse furrow strongly spiral, laevo-rotatory, divided into sections (?5) by low ridges; longitudinal furrow broad and sigmoidal. Crests on plate and furrow loundaries of moderate height, irregularly perforate and with deinticulate edges, the height of the denticulations being very variable; spines are sometimes present at crest junctions.
Dimensions: Holotype: overall length, 46.5 µm, shell length 35 µm, breadth 30 µm. Range: overall lengths c. 35-50 µm (14 specimens).
Description (annotated): Theca of chestnut brown colour, without or with minute granulation. Structure of the apex not clear; five apical plates appear to be present, with plate 1" elongate and forming the forward prologation of the longitudinal furrow. Six well-developed pre-equatorial plates, plate 3'' being lost in pylome formation. The transverse furrow is broad and in the form of a laevo- rotatory spiral whose two ends differ in anteroposterior position by more than twice the furrow"s breadth; since the longitudinal furrow is sigmoidal, the two ends of the transverse furrow both intersect the median dorso-ventral plane through the shell. The posterior end is separated from the longitudinal furrow by a crescentic plate. A small oval plate, which was perhaps the point of origin of the transverse flagellum, lies between the anterior end and plate 1'''. A third small plate, roughly pear-shaped, separates plate 6''' from the longitudinal furrow. The boundaries of these plates with furrows do not bear crests. Six post-equatorial plates are present, with plate 1''' reduced and elongate. A posterior intercalary plate is present: it is of pentagonal shape and separates plate 6''' from the antapex. A quadrilateral posterior ventral plate separates the longitudinal furrow and plate 6''' from the antapex: the latter is occupied by a single pentagonal antapical plate. The crests bounding plates are of variable height, being very reduced or absent on parts of the margins of the longitudinal furrows. The degree of denticulation is very variable, both between individuals and on each theca: the denticles are sometimes truncated. The crests are yellowish brown in colour: they are frequently perforate, but the perforations are not of constant size and show no arrangement. Spines are present at some crest junctions, functioning presumably as strengthening structures: they are frequently perforate, but the perforations are not of constant size and show no arrangement. Spines are present at some crest junctions, functioning presumably as strengthening structures: they are most strongly developed on the corners of the antapical plate and at the junctions of crests with the transverse furrows.
Affinities:
Neale and Sarjeant, 1962, p. 443
Remarks: The general appearance of this species is strikingly similar to that of G. jurassica Deflandre, 1938: however, G. cretacea differs from the latter species in its sigmoidal longitudinal furrow and the detail of the tabulation of the ventral surface. It is probable nonetheless that G. cretacea may have evolved from G. jurassica by a process of modification of ventral structure.
--------------------------------------------------------------------------------------------------------------------------------
Remarks Duxbury, 2023:
Remarks: This species has been transferred to Wrevittia here, being considered essentially similar to Wrevittia helicoidea (Eisenack and Cookson 1960) Helenes and Lucas-Clark 1997 but lacking the prominent surface ornament of the latter (see Plate 20, Figs. 13, 17 and Plate 21, Fig. 15), a distinction highlighted by Sarjeant (1966b, p. 117) and repeated by McIntyre and Brideaux (1980, p. 13).
Helenes and Lucas-Clark (1997, p. 186) provisionally included this species in Stanfordella, “pending clarification of its paratabular characteristics” and citing conflicting data from Neale and Sarjeant (1962), McIntyre and Brideaux (1980) and Below (1981). Their conclusions from the first two cited references are, however, based on poor original illustrations, but their reference to Below (1981) appears to be more reliable, being based on the last author’s clear SEM work. They stated, “Below’s (1981, pl. 15, fig. 6) specimens from the Early Cretaceous of Morocco, show an A/ai ventral arrangement that precludes assignment to Stanfordella. These specimens probably have a paratabulation pattern similar to the one shown here in Wrevittia helicoidea comb. nov”.
This species was first described by Neale and Sarjeant (1962, p. 19) from the Shell West Heslerton No. 1 Borehole, at 99.25 m (325 ft 7"); the age of this sample was subsequently listed in Sarjeant (1966a, p. 19) as “Middle Hauterivian” (quoted as 99.25/50 m). In the same volume, Sarjeant (1966c, p. 214) tabulated that sample, but as “Upper Hauterivian”, together with four other samples from the Shell West Heslerton No. 1 Borehole, between 103.25 m (338 ft 9" - Middle Hauterivian) and 19.25 m (63 ft 2" - Upper Barremian).
Sarjeant (1966c, p. 214) did not include Wrevittia cretacea in his stratigraphical distribution chart but, in earlier comments on Wrevittia helicoidea (Sarjeant 1966b, p. 117) he stated, “Gonyaulacysta cretacea (Neale and Sarjeant 1962) is present in somewhat earlier horizons (99.25 m - Hauterivian)”, and “It seems probable G. cretacea is ancestral to G. helicoidea”. Sarjeant (1966c, p. 214) illustrated Wrevittia helicoidea (as G. helicoidea) as occurring only in the 42.5 m and 39.0 m samples (early to middle Barremian).
In the present study, both Wrevittia cretacea and W. helicoidea were long-ranging; the first was recorded between Beds D2A and LB2D at Speeton and W. helicoidea ranged througout (i.e., both ranged between the amblygonium and fissicostatum ammonite Zones). There is no evidence that W. cretacea is ancestral to W. helicoidea.