Lusatia dendroidea Burmann, 1970

Albani, Roberto, Bagnoli, Gabriella, Ribecai, Cristiana & Raevskaya, Elena, 2007, Late Cambrian acritarch Lusatia: Taxonomy, palaeogeography, and biostratigraphic implications, Acta Palaeontologica Polonica 52 (4), pp. 809-818 : 811-814

Lusatia dendroidea Burmann, 1970 emend.

Figs. 4 , 5.

1970 Lusatia dendroidea sp. nov.; Burmann 1970: 296, pl. 6: 1–4.

1976 Multiplicisphaeridium dendroideum ( Burmann, 1970) ; Eisenack et al. 1976: 455–456.

?1978 Lusatia aff. L. dendroidea Burmann ; Dean and Martin 1978: 8, pl. 3: 21.

1990 Lusatia dendroidea Burmann ; Volkova 1990: 71, pl. 21: 1, 2.

1990 Lusatia triangularis (N. Umnova, 1975) comb. nov.; Volkova 1990: 71–72, pl. 21: 5–7.

1990 Lusatia sp. 1 ; Volkova 1990: 72–73, pl. 21: 3, 4.

1993 Lusatia ? sp. 1; Ribecai and Vanguestaine 1993: pl. 1: 11.

2000 Orthosphaeridium ? extensum sp. nov.; Parsons and Anderson 2000: 61–62 (partim), pl. 9: 1, 3, 4, 10, 13 (non 2, 11, 12).

2000 Orthosphaeridium ? triangulare Umnova, 1975, comb. nov.; Parsons and Anderson 2000: 62, pl. 9: 5.

2001 Lusatia dramatica Ribecai and Tongiorgi ; Bogolepova et al. 2001: 83: 6: E, F.

2005 Lusatia dendroidea Burmann ; Ribecai et al. 2005: pl. 1: 5.

2006 Lusatia dendroidea Burmann ; Albani et al. 2006: 49–50, pl. 2: 1–4, 7.

2006 Lusatia dendroidea Burmann ; Raevskaya and Golubkova 2006: pl. 4: 12, pl. 5: figs. 1, 4–6.

2006 Lusatia triangularis (N. Umnova, 1975) ; Raevskaya and Golubkova 2006: pl. 4: 7.

2006 Lusatia sp. ; Raevskaya and Golubkova 2006: pl. 4: 8, 9.

Emended diagnosis.—Vesicle sub−circular to triangular in outline, bearing one to four long processes. Processes simple to branched, freely communicating with the vesicle interiors, thin−walled, psilate. In specimens with more than one process, one process is always simple. Additional thinner and shorter processes or filaments can be present. The process branching originates at a variable distance from vesicle and can attain up to the fourth order. Vesicle thin−walled to thick−walled, smooth to scabrate. Excystment by median split.

Description.—Vesicle outline subcircular, ellipsoidal, or triangular with straight to convex sides. Vesicle wall varies from thin to thick. One to four major processes. Processes hollow, long, thin−walled, well differentiated from the central body, with a subangular to angular basal contact, communicating with vesicle interior.

Processes are simple to branched. One process is always simple in specimens with more than one process. Simple processes conical, tapering gradually to acuminate distal tip which is very flexible, resulting in a distal looping in some specimens ( Figs. 4F , 5D 1 ). Branched processes nearly cylindrical to point of branching, i.e., maintaining near constant width to point of branching. Furcation originates at a variable distance from proximal end of process. Subdivisions in pinnae is highly variable, and up to fourth order. Distal branches of pinnae or pinnulae can be straight or curly (e.g., Figs. 4A , 5D), and in some specimens the high number of subdivisions produces a distal crown. One or two minor, thinner, shorter and simple processes may also be present (e.g., Figs. 4E , 5A, E). Small filaments can be present along the process−stem (e.g., Fig. 5H).

Specimens with three processes have processes originating at the corner of the triangular to subcircular vesicle ( Fig. 4A 1 , D), with the apical process simple. Specimens with two processes have a mostly ellipsoidal vesicle with the processes, one of which is simple, at the opposite poles. Some specimens have only one branched process and an ovoid vesicle. Rare specimens have four processes, with the apical process simple and the other three branched.

Most specimens have three processes; specimens with two processes are common, whereas only a few have one process; specimens with four processes are very rare.

The free communication of processes with the vesicle interior is evident in translucent and thin−walled specimens. Specimens with a dark, thick−walled vesicle and thin−walled processes may simulate a separation between vesicle and processes and give the impression of a bi−layered vesicle. The darker central area may extend shortly into the base of the processes as a spine, or a rod, or simulating a sort of plug with a slight constriction at the base (e.g., Fig. 4C, D ). The vesicle wall and the processes are psilate to scabrate. Excystment by median split (e.g., Fig. 4B ).

Measurements (118 specimens).—Russian material (Moscow syneclise): vesicle length 28 (36.5) 44 ̊m, vesicle width 24 (27.8) 40 ̊m, apical process length 48 (44) 80 ̊m, antapical processes length 48 (60) 76 ̊m, length of branches 8 (26) 40 ̊m.

Russian material (Severnaya Zemlya): vesicle length 20 (27.5) 36 ̊m, vesicle width 16 (21.7) 26 ̊m, apical process length 48 (56) 76 ̊m, antapical processes length 36 (54.5) 76 ̊m, length of branches 16 (27.3) 44 ̊m.

Spanish material (El Fabar tunnel): vesicle length 23.5 (33.2) 40.2 ̊m; vesicle width 18.4 (26) 34.5 ̊m, apical process length 43.7 (69.9) 90.8 ̊m; antapical process length 42.5 (62.7) 88.5 ̊m; length of branches 12.6 (31.1) 49.5 ̊m.

Discussion.— Burmann (1970), in erecting Lusatia and the type species Lusatia dendroidea , included only specimens with three processes. Specimens with one to four processes were mentioned in the original diagnosis of the genus, but were not illustrated, nor included in the variability of the type species. The abundant and well−preserved material from the three different geographical areas allows for more precise evaluation of intraspecific variability of L. dendroidea . Analysis based on more than 1000 specimens indicates intraspecific variation of one to four processes for this species.

Volkova (1990) recorded Lusatia from the Moscow syneclise of the East European Platform and described three species: L. dendroidea Burmann, 1970 , L. triangularis ( Umnova, 1975) Volkova, 1990 , and Lusatia sp. 1 . According to Volkova (1990), L. triangularis differs from L. dendroidea by having processes not communicating with the vesicle interior. She also indicated that L. triangularis could have a double wall, with the processes formed by the outer layer. Incomplete specimens with two processes and a vesicle interpreted as bi−layered were assigned by Volkova (1990) to Lusatia sp. 1 . Based on examination of the specimens from Spain and from the High Arctic of Russia, and reexamination of the Volkova’s collection, the vesicle of Lusatia is considered unilayered, even though with variable thickness (see description). In the material examined in this study, specimens with a thin wall co−occur with specimens with a thicker wall, independent of the number of processes. They are therefore viewed as falling within the range of variation of a single species, L. dendroidea . The different wall thickness could be an artefact of differing preservation or due to different stages in the life cycle of the species.

In her description of L. dendroidea, Volkova (1990) indicated that the termination of the apical process formed a loop. In our material, with hundreds of complete specimens, the terminal loop of the apical process is not a constant feature and therefore is not considered diagnostic.

Parsons and Anderson (2000) transferred Lusatia sp. 1 of Volkova (1990) and L. triangularis of Volkova (1990) to Orthosphaeridium ? due to the presence of an inner body and a median splitting. Our material and a reexamination of Volkova (1990) original collections indicate that these features fall within the variability of L. dendroidea .

We included in our synonymy specimens figured by Parsons and Anderson (2000) that conform well with L. dendroidea , as emended here. We excluded specimens they figured with broader−based processes that merge more gradually with the vesicle ( Parsons and Anderson 2000: pl. 9: 2, 11, 12).

Lusatia dramatica Ribecai and Tongiorgi, 1997 from the upper Cambrian of Sweden differs from L. dendroidea because it has always three processes, all of them ramified, although the apical process displays fewer and less regular branches. This taxon could represent an extreme differentiation, derived from forms of L. dendroidea with three processes.

The younger species Lusatia heteromorpha Vavrdová, 1986 from the lower Llanvirnian (Darriwilian) of Bohemia differs from L. dendroidea in the ornamentation of the vesicle (microgranulate to granulate), in the pattern of branching (processes have shorter, less numerous and more irregular branches) and in the capitate terminations of pinnae.

Figures

Fig. 4. Diacrodian acritarch Lusatia dendroidea Burmann, 1970 emended + herein. Upper Cambrian, El Fabar tunnel, Cantabrian Zone, Spain. All specimens from sample Tun−Filocar. For each illustrated specimen slide number, repository number, and England Finder Graticule are given. All specimens with three processes. A. Stub LU2, MGM−1080K, R42; specimen with subtriangular vesicle (A1), detail of branching of antapical process, with curly terminations (A2). B. Slide ›10/1, MGM−1081K, N36/3, specimen with thick−walled vesicle and excystement by median split. C. Slide II/1, MGM−1082K, P29, specimen showing base of processes slightly constricted simulating a sort of plug. D. Slide ›10/1, MGM−1083K, U44/4, specimen with darker central area extending as a spine into the base of the processes. E. Stub 6, MGM−1084K, O45, specimen with an auxiliary filament. F. Slide ›10/1, MGM−1085K, M28, specimen with a thick−walled vesicle and distal loop of apical process. G. Slide ›10/1, MGM−1086K, E44. H. Slide ›10/3, MGM−1087K, P30/4, specimen with a thick−walled vesicle and excystement by median split.

Fig. 1. A. Map of the Asturian coast showing position of El Fabar fossil locality (star). B. A summary lithological column with stratigraphic position of the acritarch yielding sample (Tun−Filocar, asterisk).