Back
Trinovantedinium boreale
Trinovantedinium boreale Bujak, 1984
Holotype: Bujak, 1984, pl. 4, fig.2
Locus typicus: Aleutian Abyssal Plain, northern North Pacific.
Stratum typicum: Late Eocene
-----------------------------------
Original diagnosis: Bujak, 1984, p. 193
Dorsoventrally compressed cysts with oval to rounded pentagonal outline. Apical horn and left antapical lobe poorly to well developed; right antapical lobe sometimes poorly developed. Solid capitate spines covering most of cyst, and longer hollow spines present on apical and left antapical lobes or horns. Cyst single-walled and pale, sometimes with inner wall present beneath apical and left antapical spines. Cingulum marked by two rows of spines and sometimes by low crests. Sulcus shallow, devoid of spines. Archeopyle intercalary, single plate ?2a.
Dimensions: Cyst length (excluding spines) 45 to 53 µm, breadth (excluding spines) 44 to 50 µm; maximum spine length 4 to 6.5 µm
Original description: Bujak, 1984, p. 193
Variations in morphology of this species include the cyst shape, horn development, and the number of spines present. The cyst shape depends upon the degree to which apical, antapical, and cingular lobes are developed. On specimens with poorly developed lobes or horns, the dorsoventral outline is oval; only the apical and left antapical positions are marked by longer spines. On specimens with well-developed apical, antapical and cingular lobes, the shape of the cyst is rounded pentagonal, but the hypocyst is always asymmetrical in outline because of the poorly developed right antapical lobe. The number of spines varies in this species and on specimens with fewer spines, they are sometimes concentrated on the ambital periphery. Two or more longer, hollow spines are always present on the apical and left antapical horns. Each adcingular border is marked by a row of spines, sometimes arising from a crest. The sulcus is devoid of spines on all examined specimens.
-------------------------------------------
Description: Kurita and Matsuoka 1994, p. 148-151
The chorate cysts are variable in outline from pear-shaped to roundly pentagonal. The cyst wall comprises a thin and laevigate, scabrate or rarely finely reticulate autophragm; however, small cavation is rarely present at the base of the apical and antapical horns. The development of the horns is also variable. Processes are hollow and distally closed, or solid. Process length and shape are variable; usually nontabular, but very rarely incompletely parasutural (Plate I, 16). Process terminations are generally capitate with a dentate margin (Plate I, 19), or acuminate when the processes are short. The density of process distribution is also highly variable. Larger apical and antapical processes, occasionally membranous at proximal base, are distinctive, or sometimes lacking. The paracingulum is basically present and indicated by two parallel rows of processes or by two parallel, low ridges with a dentate margin. The parasulcus is indiscernible or unclearly indicated by a shallow indentation of the phragma or by the absence of processes. The archeopyle is usually not observed, but when visible, it is isodeltaform type I; the operculum is often adnate posteriorly or occasionally detached. The transverse archeopyle index ranges from 0.34 to 0.48 (average 0.43; 8 specimens measured ). Accessory sutures along the paraplate boundaries between 3"/4" and 4"/5" are rarely present. The paratabulation is incompletely indicated by the archeopyle, paracingulum and parasulcus, and rarely by partially parasutural processes.
Morphological variation: Morphological variation of Trinovantedinium boreale was investigated by measuring biometric features of the specimens from the Yubari area. Possible optical error in the measurements is 0.3,µm. First, the length of process was measured on 752 specimens from 37 samples. Since the processes in the apical, antapical and paracingular areas of T. boreale tend to be longer, an "average" process between those areas, which was perpendicular to observation direction, was selected for the measurement on each specimen. Second, the width and length of the cyst body were measured on 70 specimens from 13 samples. The length of the processes was excluded in this measurement. The results are shown in Figs. 5-7.
The measurements revealed that notable variation is present in both process length and cyst ambital shape. These variations occur successively; no distinctive morphotype was therefore recognized within the species. Furthermore, no stratigraphic trend was observed in the variation. The process length distributes in a single cluster with no significant discontinuity ( Fig. 5). Statistics on the measurement are (in µm): arithmetic mean=2.8, range=0.3 7.9, and standard deviation= 1.5. The body length vs. body width (Fig. 6) indicates that the two parameters have only a weak positive relation (regression coefficient r= 0.49), which means that the cyst outline also varies significantly. There is no relation between the process length and the body length (Fig. 7; regression coefficient r=0.013); these two morphological features hence vary independently.
Remarks: Kurita and Matsuoak 1994, p. 149, 151:
Trinovantedinium boreale has been recorded from the Bering Sea ( Matsuoka and Bujak, 1988), northern North Pacific (Bujak, 1984), Hokkaido, northern Honshu (this study) and northern Kyushu (Matsuoka, unpubl. data). Eocene Oligocene assemblages from the East China Sea (Yu, 1989; He and Wang, 1990) and from the Beaufort-Mackenzie area (e.g. Norris, 1986 ) lack the species. The species is therefore distinctive of the middle to high latitudes of the northwestern to northern North Pacific. In spite of the suggestion by Matsuoka and Bujak (1988, pp. 30 31), no evident stratigraphic trend in cyst morphology was found in this study.
Holotype: Bujak, 1984, pl. 4, fig.2
Locus typicus: Aleutian Abyssal Plain, northern North Pacific.
Stratum typicum: Late Eocene
-----------------------------------
Original diagnosis: Bujak, 1984, p. 193
Dorsoventrally compressed cysts with oval to rounded pentagonal outline. Apical horn and left antapical lobe poorly to well developed; right antapical lobe sometimes poorly developed. Solid capitate spines covering most of cyst, and longer hollow spines present on apical and left antapical lobes or horns. Cyst single-walled and pale, sometimes with inner wall present beneath apical and left antapical spines. Cingulum marked by two rows of spines and sometimes by low crests. Sulcus shallow, devoid of spines. Archeopyle intercalary, single plate ?2a.
Dimensions: Cyst length (excluding spines) 45 to 53 µm, breadth (excluding spines) 44 to 50 µm; maximum spine length 4 to 6.5 µm
Original description: Bujak, 1984, p. 193
Variations in morphology of this species include the cyst shape, horn development, and the number of spines present. The cyst shape depends upon the degree to which apical, antapical, and cingular lobes are developed. On specimens with poorly developed lobes or horns, the dorsoventral outline is oval; only the apical and left antapical positions are marked by longer spines. On specimens with well-developed apical, antapical and cingular lobes, the shape of the cyst is rounded pentagonal, but the hypocyst is always asymmetrical in outline because of the poorly developed right antapical lobe. The number of spines varies in this species and on specimens with fewer spines, they are sometimes concentrated on the ambital periphery. Two or more longer, hollow spines are always present on the apical and left antapical horns. Each adcingular border is marked by a row of spines, sometimes arising from a crest. The sulcus is devoid of spines on all examined specimens.
-------------------------------------------
Description: Kurita and Matsuoka 1994, p. 148-151
The chorate cysts are variable in outline from pear-shaped to roundly pentagonal. The cyst wall comprises a thin and laevigate, scabrate or rarely finely reticulate autophragm; however, small cavation is rarely present at the base of the apical and antapical horns. The development of the horns is also variable. Processes are hollow and distally closed, or solid. Process length and shape are variable; usually nontabular, but very rarely incompletely parasutural (Plate I, 16). Process terminations are generally capitate with a dentate margin (Plate I, 19), or acuminate when the processes are short. The density of process distribution is also highly variable. Larger apical and antapical processes, occasionally membranous at proximal base, are distinctive, or sometimes lacking. The paracingulum is basically present and indicated by two parallel rows of processes or by two parallel, low ridges with a dentate margin. The parasulcus is indiscernible or unclearly indicated by a shallow indentation of the phragma or by the absence of processes. The archeopyle is usually not observed, but when visible, it is isodeltaform type I; the operculum is often adnate posteriorly or occasionally detached. The transverse archeopyle index ranges from 0.34 to 0.48 (average 0.43; 8 specimens measured ). Accessory sutures along the paraplate boundaries between 3"/4" and 4"/5" are rarely present. The paratabulation is incompletely indicated by the archeopyle, paracingulum and parasulcus, and rarely by partially parasutural processes.
Morphological variation: Morphological variation of Trinovantedinium boreale was investigated by measuring biometric features of the specimens from the Yubari area. Possible optical error in the measurements is 0.3,µm. First, the length of process was measured on 752 specimens from 37 samples. Since the processes in the apical, antapical and paracingular areas of T. boreale tend to be longer, an "average" process between those areas, which was perpendicular to observation direction, was selected for the measurement on each specimen. Second, the width and length of the cyst body were measured on 70 specimens from 13 samples. The length of the processes was excluded in this measurement. The results are shown in Figs. 5-7.
The measurements revealed that notable variation is present in both process length and cyst ambital shape. These variations occur successively; no distinctive morphotype was therefore recognized within the species. Furthermore, no stratigraphic trend was observed in the variation. The process length distributes in a single cluster with no significant discontinuity ( Fig. 5). Statistics on the measurement are (in µm): arithmetic mean=2.8, range=0.3 7.9, and standard deviation= 1.5. The body length vs. body width (Fig. 6) indicates that the two parameters have only a weak positive relation (regression coefficient r= 0.49), which means that the cyst outline also varies significantly. There is no relation between the process length and the body length (Fig. 7; regression coefficient r=0.013); these two morphological features hence vary independently.
Remarks: Kurita and Matsuoak 1994, p. 149, 151:
Trinovantedinium boreale has been recorded from the Bering Sea ( Matsuoka and Bujak, 1988), northern North Pacific (Bujak, 1984), Hokkaido, northern Honshu (this study) and northern Kyushu (Matsuoka, unpubl. data). Eocene Oligocene assemblages from the East China Sea (Yu, 1989; He and Wang, 1990) and from the Beaufort-Mackenzie area (e.g. Norris, 1986 ) lack the species. The species is therefore distinctive of the middle to high latitudes of the northwestern to northern North Pacific. In spite of the suggestion by Matsuoka and Bujak (1988, pp. 30 31), no evident stratigraphic trend in cyst morphology was found in this study.