Isopora matahari, Santodomingo & Wallace & Johnson, 2015

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 : 755-758

ISOPORA MATAHARI SP. NOV.

FIGURE 41

Diagnosis

Colonies arborescent with sturdy, thick, straight branches, and sparse incipient secondary branches. Small radial corallites conical to immersed, round calices, evenly distributed. Coenosteum a dense arrangement of elaborated spinules.

Material studied

Holotype. NHMUK PI AZ 7101 , 1 specimen. Type locality: TF56 , Badak , East Kalimantan, 0°19′19.2″S, 117°17′49.2″E, Burdigalian to Langhian age, 14.8– 17.9 Ma. Collector N. Santodomingo, 13 December 2010 . Paratype. NHMUK PI AZ 9118 , 5 specimens. Type locality : TF56 , Badak , East Kalimantan, 0°19′19.2″S, 117°17′49.2″E, Burdigalian to Langhian age, 14.8– 17.9 Ma. Collector N. Santodomingo, 13 December 2010 .

Other studied material. East Kalimantan: NHMUK PI AZ 6683 , 1 specimen ; NHMUK PI AZ 8850 , 1 specimen ; NHMUK PI AZ AZ5088.

Description

Corallum . Sturdy branches. Holotype overall length 110.15 mm, mid branch diameter 16.5 mm, with one primary branch 37 mm long, mid branch diameter 15.7 mm, angle 57°, and one incipient short branch up to 7 mm long. Paratypes, overall branch length 62.72–84.55– 110.05 mm, basal branch diameter 7.54– 13.54–18.48, mid branch diameter 9.69–11.87– 13.88 mm; primary branching indicating arborescent form, probably indeterminate, relatively uniform branchlets in angles 39.05–55.75–76.43°, length 3 to 5 mm.

Corallites. Axial corallite visible in cross section of holotype ( Fig. 41B ) and at some incipient branches, outer diameter 2.30 mm, inner diameter 1.35–1.48– 1.62 mm, primary septa up to three-quarters R, secondary septa up to two-thirds R, arranged as S1>S2; radial corallites evenly sized, evenly distributed, not touching, conical or subimmersed, small round calices, profile length 0.45– 0.58– 0.70 mm, outer diameter 0.54–0.64– 0.70 mm, inner diameter 0.31–0.42– 0.52 mm, wall thickness 0.09– 0.11– 0.13 mm, distance between centres 1.35–2.18– 3.24 mm, primary septa present, secondary septa absent or some visible as points. Corallite arrangement sequence [1-?]–[1–4]–?–[12–16]–[up to 16–24].

Coenosteum. Dense arrangement of elaborated spinules on and between radial corallites. Coenosteum amount 0.72–1.57– 2.64 mm.

Variation of East Kalimantan material

NHMUK PI AZ 6683: one fragment of a branch, oval in cross section, overall length 108 mm, mid branch diameter 13.2–13.4 mm, with two broken branches alternating with a distance of 29 mm, and some incipient branchlets throughout. Small radial corallites evenly sized and evenly distributed. A bivalve cemented on the upper part of the specimen. NHMUK NHMUK PI AZ 8850: the most robust branch of the type series, length 95.7 mm, oval in cross section, branch diameter 19.8–28.6 mm; scar of a secondary branch is diameter 17.4–26.5 mm. Small radial corallites, evenly sized and evenly distributed throughout.

Occurrence

Late to Middle Miocene. Isopora matahari sp. nov. is only known from its type locality TF56, Badak, of Early Langhian to Late Burdigalian age, 14.8–17.9 Ma.

Palaeoenvironment

Fossil specimens of I. matahari were found in the upper bed of the outcrop TF56, Badak, co-occurring with A. kirstyae and a high diversity of coral species including massive forms.

Remarks

The sturdy, cylindrical branches combined with the presence of small conical or subimmersed corallites are characteristics that distinguish I. matahari sp. nov. from all other fossil Acroporidae species studied in Indonesia. The closest related species is the extant Isopora togianensis Wallace, 1997 , but I. matahari sp. nov lacks the tuberculated corallite walls characteristic of I. togianensis . Isopora matahari sp. nov. also resembles the living Papuan species Acropora cylindrica Veron, 2000 , synonymized with I. togianensis by Wallace et al. (2012). Skeletons are highly recrystrallized.

Etymology

The epithet matahari (noun) means sun in Bahasa Indonesian language, and it was given because the type locality Badak was the sunniest place visited during the Throughflow expedition.

Figures

Figure 41. Isopora matahari sp. nov. A, C, D, Holotype, NHMUK PI AZ 7101, TF56, Badak, East Kalimantan, Early to Middle Miocene (14.8–17.9 Ma). B, paratype, NHMUK PI AZ 9118, TF56, Badak, East Kalimantan, Early to Middle Miocene (14.8–17.9 Ma), sturdy cylindrical branches recovered in the same sample with the holotype. A, whole specimen. C, transverse section of primary branch showing axial corallite. D, detail of incipient branchlet. E and F, detail of small conical and subimmersed radial corallites.