Isopora brueggemanni (Brook, 1893)

Santodomingo, Nadiezhda, Wallace, Carden C. & Johnson, Kenneth G., 2015, Fossils reveal a high diversity of the staghorn coral genera Acropora and Isopora (Scleractinia: Acroporidae) in the Neogene of Indonesia, Zoological Journal of the Linnean Society 175 (4), pp. 677-763 : 755

ISOPORA BRUEGGEMANNI ( BROOK, 1893)

FIGURE 40

Madrepora brueggemanni Brook, 1893: 145 , pl. 24, pl. 35 fig. E.

Acropora meridiana Nemenzo, 1971: 146 , pl. 1, fig. 3.

Diagnosis

Colonies arborescent with one and up to three axial corallites, radial corallites tubular appressed with round calices; coenosteum a dense arrangement of meandroid elaborated spinules ( Wallace & Wolstenholme, 1998; Wallace, 1999).

Material studied

East Kalimantan: NHMUK PI AZ 6906 , 1 specimen ; NHMUK PI AZ 8802 , 8 specimens .

Modern comparative material: Lectotype, NHMUK 1878.4 .1.2, Singapore; MTQ G57657, Pulau Redang National Park, Malaysia, 12 m depth; MTQ G61866, Palau; MTQ G48936, Kakaban Island , East Kalimantan, Indonesia.

Skeletal characteristics

Corallum . Two specimens show primary branching indicative of arborescent form, probably indeterminate; branches cylindrical, mostly broken, slightly tapering, length 17.94–26.34– 30.10 mm, angle of 51.20– 64.70–80.36°, basal branch diameter 20.24–23.77– 26.08 mm, mid branch diameter 10.10–13.09– 19.37 mm, branch tip diameter 5.50–7.32– 9.01 mm; secondary branch length 8.20–11.58– 16.30 mm, mid branch diameter 5.50–7.68– 10.11 mm, distance between branches 13.74–13.95– 14.16 mm.

Corallites. Axial corallite visible at some branch tips and on transverse sections, small round calice, 0.88– 0.90– 0.92 mm exsert, outer diameter 2.30–3.53– 4.24 mm, inner diameter 0.90–1.30– 1.88 mm, wall thickness 0.92–1.11–1.32, primary septa developed up to three-quarters R, secondary septa up to one-third R, arranged as S1>>S2; radial corallites gradually sized, evenly distributed, mostly not touching, mainly appressed tubular, rounded tubular or conical, extend- ed in different angles relative to the branch growth axis, small round calices, profile length 1.24–2.70– 7.50 mm, angle 31.59–43.88–58.92°, outer diameter 1.11– 2.20– 3.41 mm, inner diameter 0.50–0.77– 1.25 mm, wall thickness 0.50–0.77– 1.25 mm, primary septa up to two- thirds R, secondary septa up to one-quarter R. Corallite arrangement sequence [1–?2]–[3–8]–[6–8]–up to 10.

Coenosteum. Dense arrangement of meandroid elaborated spinules on and between radial corallites. Coenosteum amount 0.43–1.23– 2.79 mm.

Occurrence

Late Miocene to Recent. The earliest occurrence of the species is from the outcrop TF516, Sangatta, of Tortonian age, 8.9–9.3 Ma. Additional fossils are from the Era Beds, Papua New Guinea, of Late Pliocene to Early Pleistocene age, 2–3 Ma ( Veron & Kelley, 1988). The modern distribution of the species is restricted to the Central Indo-Pacific ( Wallace et al., 2012), and records from Indonesia include several localities in Sumatra, Java, Kalimantan, Sulawesi, Nusa Tenggara, Banda Sea, Halmahera and Irian Jaya ( Table 4).

Palaeoenvironment

Fossil specimens of I. brueggemanni were found together with A. florida in the outcrop TF516, Sangatta, with abundant large massive corals. In modern settings, this species occurs on subtidal reef flats, reef edge and reef slope ( Wallace, 1999).

Remarks

The fossil material recovered from East Kalimantan compares well with Lectotype NHMUK 1878.4 .1.2 from Singapore and modern specimens from Malaysia, Palau and East Kalimantan. Outstanding preservation of the fossil specimens allowed the observation of diagnostic characters of this species, such as thick walls formed by more than three synapticular rings and meandroid elaborated spinules.

Figures

Figure 40. Isopora brueggemanni. A, C, G–I. NHMUK PI AZ 6906. TF516, Sangatta, East Kalimantan, Late Miocene (8.9–9.3 Ma). B, D, F, NHMUK PI AZ 8802, TF516, Sangatta, East Kalimantan, Late Miocene (8.9–9.3 Ma). A, AZ 6906, whole specimen showing branch tip. B, AZ 8802a, b, two specimens showing corallite arrangement and rounded tubular radials. C, AZ 6906, transverse section of a cylindrical branch. D, AZ 8802a, electron micrograph of a branch tip. E, AZ 6906, electron micrograph of a radial corallite showing septa arrangement and more than three synapticular rings. F, AZ 8802a, electron micrograph of axial corallite. G–I AZ 6906: G, electron micrograph of radial corallites; H, electron micrograph of coenosteum showing meandroid spinules; I, detail of meandroid elaborated spinules.