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Lithodinia protothymosa
Lithodinia protothymosa Riding and Helby, 2001d, p.81-83, figs.10A-L.
Taxonomic junior synonyms: Lithodinia australica and Meiourogonyaulax protothymosa (both names not validly published), both according to Riding and Helby (2001d, p.81).
Holotype: Riding and Helby, 2001d, fig.10D.
Age: Callovian.
Original description (Riding and Helby, 2001d)
Description. An ellipsoidal to rounded subrectangular species of Lithodinia. The length and breadth are frequently subequal, especially in specimens where the archaeopyle has operated. Paratabulation indicated by parasutural ridges, crests and processes. Gonal points are marked by relatively prominent short, solid processes which may be distally bifid, buccinate, recurved or subconical. The gonal processes are joined by low, smooth parasutural ridges which may or may not be surmounted by prominent, distally smooth to finely denticulate parsutural crests. Parasutural ridges may be surmounted by short, buccinate or bifid processes. The parasutural crests may also be fenestrate. Intratabular and/or processes may also be present; these are normally nontabular in position. The intratabular ridges are low and smooth and the processes are solid and usually bifid. The paracingulum and parasulcus lack intratabular ornamentation and are not subdivided into paraplates. Autophragm relatively thick, smooth to occasionally microscabrate or microreticulate. Archaeopyle apical, tends to gape; operculum compound with individual paraplates only rarely retained inside the loisthocyst.
Dimensions (µm; n=30): Min. (Mean) Max.
Length of cyst incl. operculum: 74 (87) 96
Length of cyst excl. operculum: 71 (83) 98
Width of cyst: 71 (83) 99
Height of parasutural crests: 2 (7) 15
The measured specimens are form sidewall core samples in Investigator-1 well at 3260.00 m and Tern-2 well at 1459.20m and 1457.30 m.
Comments. This species is characterised by its prominent and variable mixture of parasutural and intratabular ornamentation. It often has relatively large gonal processes, which are connected by parasutural ridges and crests, and a thick, smooth autophragm (fig. 10). It is also significantly larger than most species of Meiourogonyaulax. Individual specimens may have parasutural crests surmounting each parasutural ridge. However, some crests may be reduced or suppressed. In particular, the crest between the 2"' and the 1c paraplates is often reduced or absent. Where the ridges are not surmounted by crests, short processes may be developed, implying that the crests may be the result of coalesed processes. The crests are higher and more consistently developed on the hypocyst, and especially close to the antapical region. These parasutural features are more commonly entire but often fenestrate. They are usually distally smooth, but can be finely denticulate. Intratabular ornamentation is also commonly developed as ridges, which may represent growth structures sensu Gocht (1979; 1984), and/or processes and are nontabular. The ridges may be short, curved or angular and rarely appear to approach a penitabular distribution. The operculum is unequivocally compound (Figs. 10A-F) The opercular pieces are normally and the loisthocysts are usually not longitudinaly elongate; tey may be equant and are frequently wider than long. The autophragm is thick and normally smooth, but is occasionally microscabrate or microreticulate. This species tends to be strongly dorsoventrally flattened.
Comparison. Lithodinia protothymosa is most similar to Lithodinia jurassica Eisenack 1935 subsp. reburrosa Quattrocchio & Sarjeant 1992, which has parasutural processes, the bases of which coalesce to form parasutural ridges, in addition to intratabular processes (Quattrocchio & Sarjeant, 1992). Furthermore, prominent gonal processes, which are distally acuminate to bifurcate, are present. However, this subspecies is smaller than Lithodinia protothymosa and lacks the parasutural crests and intratabular ridges characteristic of this species. It is distinguished from the genotype, Lithodinia jurassica subsp. jurassica by its much larger size and more varied and robust sculptural elements (see Gocht, 1970, pl.35, figs 13-22; Gocht 1975, figs 2-7). Except for the differene in operculum configuration, species of Meiourogonyaulax lack the combination of parasutural and intratabular features seen in L. protothymosa. Meiourogonyaulax penitabulata exhibits penitabular ridges and crests except around the paracingulum and the parasutural ridges in M. viriosa are normally distally smooth. Other species of Meiourogonyaulax which are superficially similar to L. protothymosa include M. valensii Sarjeant 1966 which has high parasutural crests which connect largely gonal processes. The small Meiourogonyaulax rioultii Sarjeant 1965 ex Sarjeant 1968 has distally bifurcate gonal spines but has thin, smooth autophragm and low, smooth parasutural ridges. Meiourogonyailax araneosa Muir & Sarjeant 1978 also has low parasutural crests surmounted by short processes. However, the latter species entirely lacks intratabular ornamentation and is also significantly smaller than L. protothymosa. Irregular process-bearing or trabeculate parasutural ridges characterise M. callomonii Sarjeant 1972, however this species lacks parasutural crests, intratabular ornamentation and gonal processes, Meiourogonyaulax strongyla Sarjeant 1972 has a combination of low, denticulate parasutural ridges and nontabular granules. Thus, it lacks the intratabular features characteristic of L. protothymosa. The nature of the opercula in these taxa is not clear from the original decriptions and illustrations.
Derivation of name. From Meiourogonyaulax? thymosa', a widely used manuscript name of A.D. Partridge, for a Berriasion morphotype and the Greek protos, meaning first.
Holotype and type locality: Figure 10D, CPC 35410, Investigator-1 well, sidewall core sample at 3260.00 m.
Stratigraphical distribution. Litodinia protothymosa has been recorded form the Callovian strata of the Timor Sea region, ranging from the upper Wanaea indotata Zone (7bii) to the lowermost Rigaudella aemula Zone (7aiibii).
Taxonomic junior synonyms: Lithodinia australica and Meiourogonyaulax protothymosa (both names not validly published), both according to Riding and Helby (2001d, p.81).
Holotype: Riding and Helby, 2001d, fig.10D.
Age: Callovian.
Original description (Riding and Helby, 2001d)
Description. An ellipsoidal to rounded subrectangular species of Lithodinia. The length and breadth are frequently subequal, especially in specimens where the archaeopyle has operated. Paratabulation indicated by parasutural ridges, crests and processes. Gonal points are marked by relatively prominent short, solid processes which may be distally bifid, buccinate, recurved or subconical. The gonal processes are joined by low, smooth parasutural ridges which may or may not be surmounted by prominent, distally smooth to finely denticulate parsutural crests. Parasutural ridges may be surmounted by short, buccinate or bifid processes. The parasutural crests may also be fenestrate. Intratabular and/or processes may also be present; these are normally nontabular in position. The intratabular ridges are low and smooth and the processes are solid and usually bifid. The paracingulum and parasulcus lack intratabular ornamentation and are not subdivided into paraplates. Autophragm relatively thick, smooth to occasionally microscabrate or microreticulate. Archaeopyle apical, tends to gape; operculum compound with individual paraplates only rarely retained inside the loisthocyst.
Dimensions (µm; n=30): Min. (Mean) Max.
Length of cyst incl. operculum: 74 (87) 96
Length of cyst excl. operculum: 71 (83) 98
Width of cyst: 71 (83) 99
Height of parasutural crests: 2 (7) 15
The measured specimens are form sidewall core samples in Investigator-1 well at 3260.00 m and Tern-2 well at 1459.20m and 1457.30 m.
Comments. This species is characterised by its prominent and variable mixture of parasutural and intratabular ornamentation. It often has relatively large gonal processes, which are connected by parasutural ridges and crests, and a thick, smooth autophragm (fig. 10). It is also significantly larger than most species of Meiourogonyaulax. Individual specimens may have parasutural crests surmounting each parasutural ridge. However, some crests may be reduced or suppressed. In particular, the crest between the 2"' and the 1c paraplates is often reduced or absent. Where the ridges are not surmounted by crests, short processes may be developed, implying that the crests may be the result of coalesed processes. The crests are higher and more consistently developed on the hypocyst, and especially close to the antapical region. These parasutural features are more commonly entire but often fenestrate. They are usually distally smooth, but can be finely denticulate. Intratabular ornamentation is also commonly developed as ridges, which may represent growth structures sensu Gocht (1979; 1984), and/or processes and are nontabular. The ridges may be short, curved or angular and rarely appear to approach a penitabular distribution. The operculum is unequivocally compound (Figs. 10A-F) The opercular pieces are normally and the loisthocysts are usually not longitudinaly elongate; tey may be equant and are frequently wider than long. The autophragm is thick and normally smooth, but is occasionally microscabrate or microreticulate. This species tends to be strongly dorsoventrally flattened.
Comparison. Lithodinia protothymosa is most similar to Lithodinia jurassica Eisenack 1935 subsp. reburrosa Quattrocchio & Sarjeant 1992, which has parasutural processes, the bases of which coalesce to form parasutural ridges, in addition to intratabular processes (Quattrocchio & Sarjeant, 1992). Furthermore, prominent gonal processes, which are distally acuminate to bifurcate, are present. However, this subspecies is smaller than Lithodinia protothymosa and lacks the parasutural crests and intratabular ridges characteristic of this species. It is distinguished from the genotype, Lithodinia jurassica subsp. jurassica by its much larger size and more varied and robust sculptural elements (see Gocht, 1970, pl.35, figs 13-22; Gocht 1975, figs 2-7). Except for the differene in operculum configuration, species of Meiourogonyaulax lack the combination of parasutural and intratabular features seen in L. protothymosa. Meiourogonyaulax penitabulata exhibits penitabular ridges and crests except around the paracingulum and the parasutural ridges in M. viriosa are normally distally smooth. Other species of Meiourogonyaulax which are superficially similar to L. protothymosa include M. valensii Sarjeant 1966 which has high parasutural crests which connect largely gonal processes. The small Meiourogonyaulax rioultii Sarjeant 1965 ex Sarjeant 1968 has distally bifurcate gonal spines but has thin, smooth autophragm and low, smooth parasutural ridges. Meiourogonyailax araneosa Muir & Sarjeant 1978 also has low parasutural crests surmounted by short processes. However, the latter species entirely lacks intratabular ornamentation and is also significantly smaller than L. protothymosa. Irregular process-bearing or trabeculate parasutural ridges characterise M. callomonii Sarjeant 1972, however this species lacks parasutural crests, intratabular ornamentation and gonal processes, Meiourogonyaulax strongyla Sarjeant 1972 has a combination of low, denticulate parasutural ridges and nontabular granules. Thus, it lacks the intratabular features characteristic of L. protothymosa. The nature of the opercula in these taxa is not clear from the original decriptions and illustrations.
Derivation of name. From Meiourogonyaulax? thymosa', a widely used manuscript name of A.D. Partridge, for a Berriasion morphotype and the Greek protos, meaning first.
Holotype and type locality: Figure 10D, CPC 35410, Investigator-1 well, sidewall core sample at 3260.00 m.
Stratigraphical distribution. Litodinia protothymosa has been recorded form the Callovian strata of the Timor Sea region, ranging from the upper Wanaea indotata Zone (7bii) to the lowermost Rigaudella aemula Zone (7aiibii).