Mackinneyella obesa ( Crockford, 1957 )

Ernst, Andrej, 2016, Bryozoan fauna from the Permian (Artinskian-Kungurian) Zhongba Formation of southwestern Tibet, Palaeontologia Electronica (1946) 51 (9), pp. 1-59 : 44-46

Mackinneyella obesa ( Crockford, 1957)

Figures 19.7-8 , 20.1-4 ; Table 27

1957 Polypora obesa Crockford , p. 67, pl. 19, fig. 4.

Material. SMF 23.188– SMF 23.194.

Exterior description. Robust reticulate colony with straight branches joined by wide dissepiments. Bifurcation common. Regular branches 1.7–2.1 mm wide, widening before bifurcation to 2.4–2.6 and narrowing after the bifurcation to 1.2– 1.5 mm. Autozooecia arranged in 5–9 alternating rows on branches. Apertures circular, arranged in regular alternating rows, 6–8 spaced per fenestrule length. Fenestrules medium in size, elongate, sub-rectangular. Keels absent; nodes on the obverse side present, arranged irregularly between autozooecial apertures; large nodes on the reverse side present. Internal granular skeleton thick, well-developed, continuous in microstyles. Outer lamellar skeleton moderately thick. Large nodes on the reverse colony surface present.

Interior description. Autozooecia rhombic in mid-tangential section; with well-developed vestibule protruding highly above the colony surface; elongate to branch length; aperture positioned at distal end of chamber. Hemisepta absent. Heteromorphs absent.

Remarks. Mackinneyella obesa ( Crockford, 1957) differs from M. ovalifenestrata Sakagami, 1964 from the Lower Permian of Japan by having wider branches (1.7–2.1 mm vs. 1.2–1.4 mm in M. ovalifenestrata ). Mackinneyella obesa differs from M. granulosa Reid, 2003 by also having wider branches (average branch width 1.84 mm vs. 1.46 mm in M. granulosa ). Mackinneyella obesa differs from M. brevicellata Baranova, 1960b from the Lower Permian of Russia by having wider branches (1.7–2.1 mm vs. 0.52–0.95 mm in M. brevicellata ) and larger fenestrules (fenestrule width 0.55–1.20 mm vs. 0.47–0.72 mm in M. brevicellata ; fenestrule length 1.50–2.30 mm vs. 1.66– 2.10 mm in M. brevicellata ).

Occurrence. Noonkanbah Formation, Lower Permian (upper Artinskian –Kungurian); Western Australia. Zhongba Formation, Permian ( upper Cisuralian –Guadalupian); Zhongba area of southwestern Tibet .

Genus PROTORETEPORA de Koninck, 1878

Type species. Protoretepora crockfordae Wyse Jackson, Reid and McKinney, 2011 (revised by Wyse Jackson, Reid and McKinney, 2012). Cascades Group, Lower Permian (late Artinskian–early Kungurian); Tasmania.

Diagnosis. Colony fan-shaped to conical, longitudinally pleated; branches broad, linear, essentially parallel, closely spaced, dichotomously dividing; regularly placed lateral expansions of branches fuse with those developed from adjacent branches to form circular to oval-shaped intermediate-sized fenestrules; additional extrazooecial skeleton may be present between autozooecial apertures at fusion points; lateral expansions depressed relative to main branch obverse and reverse surface; typically 5–6 rows of autozooecia per branch with fewer on lateral branch expansions; zooecial apertures circular, lacking peristomes, aligned longitudinally and diagonally in alternating rows; keels and large obverse styles absent, small styles common in interapertural skeleton; autozooecial chambers tubular, diverging from budding plate at an angle of 50–60°, with long axis directed toward obverse surface, laterally placed chambers inclined disto-laterally at acute or obtuse angle; zooecial chamber cross-sections polygonal or hexagonal in deep section parallel to base; rounded-polygonal in shallow section; hemisepta and diaphragms absent; large diameter distal tube short; reverse axial wall of varying thickness, granular skeleton present in basal plate and axial wall, basal plate with closely spaced fine ridges on reverse side; extrazooecial skeleton laminated, traversed by abundant, typically small styles closely spaced; heteromorphs not known (modified after Wyse Jackson et al., 2011).

Remarks. Proteretepora de Koninck, 1878 differs from Anastomopora Simpson, 1897 in the absence of exozonal tubes in autozooecia. Furthermore, Anastomopora shows a skeletal microstructure which implies an original aragonitic skeleton, whereas Protoretepora has a typical low-Mg calcite laminated skeleton.

Occurrence. Permian (Artinskian–Ufimian); Australia, Tasmania, Indonesia, Mongolia, Thailand.

Figures

FIGURE 19. Thin section photographs of Polypora aff. voluminosa Trizna and Klautzan, 1961, SMF 23.187 (1–3, and 5) and SMF 23.185 (4 and 6); and Mackinneyella obesa (Crockford, 1957), SMF 23.191 (7) and SMF 23.192 (8). 1 and 2, tangential section branches and fenestrules; 3, tangential section of the reverse side showing nodes; 4, tangential section showing autozooecial apertures and chambers with hemisepta (arrow); 5, tangential section showing autozooecial apertures, chambers and heteromorph (arrow); 6, tangential section showing autozooecial apertures and nodes; and 7 and 8, tangential section showing autozooecial apertures and chambers.

FIGURE 20. Thin section photographs of Mackinneyella obesa (Crockford, 1957), SMF 23.194 (1, 3), SMF 23.191 (2), and SMF 23.189 (4); and Protoretepora irregularis n. sp., paratype SMF 23.198 (5), SMF 23.268 (6), and SMF 23.195 (7). 1–3, and 7, tangential section showing autozooecial chambers; 4, branch transverse section; 5, branch longitudinal section; and 6, external view of the reverse side of the colony.