Acropora renemai, 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 : 753

ACROPORA RENEMAI SP. NOV.

FIGURE 39

Diagnosis

Colony probably corymbose; radial corallites immersed, evenly sized, scattered on the branches; coenosteum with densely packed elaborated spinules throughout.

Material studied

Holotype. NHMUK PI AZ 7439 , 1 specimen. Type locality: TF502 , Bontang , East Kalimantan, 0°8′28.68″N, 117°25′51.60″E. Tortonian age, 9.4–9.8 Ma. Collector N. Santodomingo, 2 July 2011.

Paratype. NHMUK PI AZ 9117, 69 fragments recovered together with the holotype, uncertain if all specimens belong to the same colony. Type locality: TF502 , Bontang , East Kalimantan, 0°8′28.68″N, 117°25′51.60″E. Tortonian age, 9.4–9.8 Ma. Collector N. Santodomingo, 2 July 2011 .

Description

Corallum . Cylindrical branches, extending randomly and sparsely from main branches, mostly broken, tapering, branch length 8.73–19.77– 25.42 mm, angle 29.62–37.00–45.12°, basal branch diameter 7.65–8.52– 9.83 mm, middle branch diameter 4.97–6.67– 8.54 mm, branch tip diameter 3.72–4.44– 5.48 mm, some portions of branches lacking radial corallites. Overall length of holotype 15.9 mm, mid branch diameter 5.1 mm.

Corallites. Axial corallites visible at some branch tips, 0.93–1.05– 1.19 mm exsert, outer diameter 1.12–1.32– 1.50 mm, inner diameter 0.52–0.69– 0.79 mm, wall thickness 0.15–0.16– 0.16 mm, primary septa two-thirds R with smooth and straight axial margins, secondary septa up to one-quarter R, S1>>S2; radial corallites dimorphic, tubular appressed towards the branch tips, round to oval calices, profile length 1.18–1.56– 1.78 mm, angle 17.94–29.80–41.82°, outer diameter 0.71–0.80– 0.93 mm, inner diameter 0.34–0.47– 0.56 mm; mostly immersed radials, not touching, sparsely distributed, inner diameter 0.36–0.42– 0.50 mm, angle 35.25–40.69– 46.12°, distance between centres 3.20–4.45–6.00 mm, primary septa up to one-quarter R, secondary septa mostly absent or visible as points. Corallite sequence arrangement 1–[1–3]–[3–6]–?.

Coenosteum. Elaborated spinules evenly and densely distributed both on and between radial corallites. Coenosteum amount 2.54–3.83– 5.89 mm.

Occurrence

Late Miocene. Only known as a fossil from the type locality, outcrop TF502 , Bontang, of Tortonian age, 9.4– 9.8 Ma .

Palaeoenvironment

Acropora renemai sp. nov. was found within a grey silty to sand-rich matrix together with a large phacelloid colony of Caulastraea . Other small massive corals of the genera Dipsastraea , Favites and Platygyra also occur in the same facies. This environment is interpreted as a shallow-water environment with calm waters, probably a lagoon.

Remarks

Branches recovered show only primary branching order, and thus a corymbose or caespito-corymbose form is inferred for this species. We have neither photographic evidence nor field notes to confirm that all recovered fragments belong to the same colony, even though they are from the same sample. For that reason, only one fragment was designated as the holotype (NHMUK PI AZ7439), and the rest of the specimens as paratypes (NHMUK PI AZ9117). Among extant species Acropora renemai sp. nov. closely resembles Acropora squarrosa (Ehrenberg, 1874) from the Red Sea, and therefore it is placed into the loripes species group. Acropora renemai sp. nov. also resembles Acropora maryae Veron, 2000 from the Red Sea synonymized with A. squarrosa by Wallace et al. (2012). According to Wallace (1999), A. squarrosa is restricted to the Red Sea today. Comparisons with the lectotype of A. loripes NHMUK 1892.6.8.219 from the Great Barrier Reef show that corallites in A. renemai sp. nov. are smaller and more scattered, and branches seem to be more delicate. Elaborated spinules of A. renemai sp. nov. are also similar to A. loripes and A. squarrosa . This species represents the earliest occurrence of the loripes group in the fossil record.

Etymology

This species is named after Willem Renema for his contribution to the palaeontological and biological studies of the geology, stratigraphy and ecology of larger benthic foraminifera of Indonesia.

Figures

Figure 39. Acropora renemai sp. nov. Holotype, A, D, H, NHMUK PI AZ 7439, TF502, Bontang, East Kalimantan, Late Miocene (9.4–9.8 Ma). A, whole specimen. B, C, E–G, paratype, NHMUK PI AZ 9117, TF502, Bontang, East Kalimantan, Late Miocene (9.4–9.8 Ma): B, AZ 9117a–d anticlockwise, four specimens showing different parts of a colony. C, AZ 9117b, transverse section of a branch showing axial corallite and cylindrical branches. D, AZ 7439, holotype, electron micrograph of the branch tip showing immersed radial corallites. E, AZ 9117e, branch tip showing appressed tubular radial corallites. F, AZ 9117a, detail of appressed tubular radial corallite. G, AZ 9117c, detail of incipient branch and immersed radial corallites. H, AZ 7439, holotype, electron micrograph of dense reticulate coenosteum formed of elaborated spinules.