Acropora elenae, 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 : 724-726

ACROPORA ELENAE SP. NOV.

FIGURE 23

Diagnosis

Colonies with thick, short, cylindrical branches; recovered branch tips rounded and apparently terete. Short tubular to subimmersed radial corallites, not touching, sparsely and randomly distributed, large round calices. Reticulo-costate coenosteum throughout with flattened spinules.

Material studied

Holotype. NHUMK AZ 7096 , 16 fragments from the same colony. Type locality: TF508 , Bontang , East Kalimantan, 0°8′56.04″N, 117°25′40.80″E. Tortonian age, 9.4–9.8 Ma. Collector N. Santodomingo, 29 June 2011.

Paratype. NHUMK PI AZ 7444 , 2 fragments from the same colony. TF 508, Bontang , East Kalimantan, 0°8′56.04″N, 117°25′40.80″E. Tortonian age, 9.4–9.8 Ma. Collector N. Santodomingo, 29 June 2011 .

Other material studied. East Kalimantan: NHUMK PI AZ 8815 , 4 specimens ; RGM 790199 , 86 fragments from the same colony.

Description of the holotype

Corallum . Colony probably digitate to small arborescent in situ extends over a surface of 45 cm long and 15 cm wide, preserved into lose silty-rich sediments; cylindrical branches, mostly broken, complete ones with rounded tip giving a cigar-like appearance ( Fig. 23B ); sparse primary branches, arising only from the basal part ( Fig. 23A ), branching angle 42.61–50.99–61.89°, distance between branches 12.65–14.65– 18.66 mm; length 19.30–24.57– 30.19 mm, basal branch diameter 11.54–13.94– 17.02 mm, middle branch diameter 7.27–8.86– 10.37 mm, branch tip diameter 6.97–7.87– 8.57 mm; secondary branchlets sparse, middle branchlet diameter 5.64 mm, branchlet tip diameter 3.46 mm; growth determinate.

Corallites. Axial visible in transverse section and on a few branchlets, low, round calice, 0.11–0.22– 0.39 mm exsert, outer diameter 1.61–1.99– 2.35 mm, inner diameter 1.05–1.24– 1.57 mm, wall thickness 0.22–0.34– 0.41 mm, primary septa up to three-quarters R, secondary septa observed as points and arranged as S1>>S2; radial corallites short tubular to subimmersed, sparse, randomly arranged on axis, round calice, profile length 0.31–0.49– 0.68 mm, angle 45.26–48.19–50.96°, outer diameter 1.38–1.73– 2.07 mm, inner diameter 0.92– 1.34– 1.65 mm, distance between centres 2.9–4.94– 7.14 mm primary septa two-thirds R, secondary septa visible as points, septa S1>>S2. Corallite arrangement sequence 1–[3–5]–[5–6]-up to 10.

Coenosteum. Flattened simple spinules aligned as costae throughout. Coenosteum amount 1.64–3.02– 5.17 mm.

Description of the paratype

Two cylindrical branches, including one robust terete tip, length 24.42 and 54.01 mm, middle branch diameter 9.51–11.41– 15.56 mm, an incipient branch protruding from the upper part of the tipless branch. Axial corallite only visible at transverse cut, even on branch tip that seems to be blind; radial corallites short tubular or subimmersed, profile length 0.31–0.46– 0.59 mm, outer diameter 1.25–1.54– 1.82 mm, inner diameter 0.76– 0.97– 1.07 mm, wall thickness 0.17–0.25– 0.33 mm. Coenosteum costate throughout.

Occurrence

Late Miocene. Acropora elenae is only known for its type locality TF508, Bontang, of Tortonian age.

Palaeoenvironment

The locality TF508 is part of the Bontang gardens outcrops, interpreted as coral carpets deposited in calm shallow waters with high siliciclastic input, probably a lagoon.

Remarks

The presence of branchlets and reticulo-costate coenosteum throughout placed this species as closely related to A. florida and A. bartonensis of the florida species group. Acropora elenae sp. nov. can be recognized based on its large radials being sparse along the branches and cylindrical straight branches. Although the axial corallite is evident in transverse sections of all branches and branchlets, the only complete primary branch appears to be blind, i.e. the axial corallite does not have an open calice at the branch tip; it is difficult to establish if such blind branch tips are the product of secondary calcification processes during deposition of the fossil material.

Etymology

This species is named after Maria Elena Pérez for her contribution to the marine sciences, in particular the ecology of deep-sea benthic foraminifera in highproductivity environments.

Figures

Figure 23. Acropora elenae sp. nov. A, B, D, E, G, holotype NHMUK PI AZ 7096, TF508, Bontang, East Kalimantan, Late Miocene (9.4–9.8 Ma). C, F. NHMUK PI AZ 7444, paratype, TF508, Bontang, East Kalimantan, Late Miocene (9.4– 9.8 Ma). A, AZ 7096a–c, three fragments of the same colony showing basal forked branching (left), and two broken fragments near the branch tip. B, AZ 7096d, branch tip in longitudinal section showing axial corallite and rounded tip. C, AZ 7444a, electron micrograph of a branch showing incipient branchlet and radial corallites. D, AZ 7096b, electron micrograph of an incipient branch from upper view showing large axial corallite and subimmersed radials. E, AZ 7096a, transverse section showing axial corallite. F, AZ 7444a, electron micrograph of subimmersed radial corallite showing septa arrangement. G, AZ 7096b, electron micrograph of costate coenosteum with simple flattened spinules.