Acropora laurae, 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 : 700-702

ACROPORA LAURAE SP. NOV.

FIGURE 9

Diagnosis

Colony probably with determinate growth, digitate or corymbose shape, branches terete. Branch structure axial dominated. Tubular to lipped radial corallites in mixed sizes. Coenosteum costate on corallites and reticulate in between corallites.

Material studied

Holotype. NHMUK PI AZ 8666 , LM-SaQ, 1 specimen, Sanctuary Quarry. Type locality: Sanctuary Quarry , Lower Kinabatangan Area, Sabah, Malaysia,

5°30′40.93″N, 118°16′35.73″E. Oligocene, 27–28 Ma. Collector L. McMonagle, 2007.

Paratype. NHMUK PI AZ 7724 , LM-SaQ, 1 specimen, Sanctuary Quarry. Type locality: Sanctuary Quarry , Lower Kinabatangan Area, Sabah, Malaysia, 5°30′40.93″N, 118°16′35.73″E. Oligocene, 27–28 Ma. Collector L. McMonagle , 2007.

Description of holotype

Corallum . Overall length of specimen 49.5 mm, terete, oval in cross section, basal branch diameter 11.2– 14.35– 17.5 mm, mid branch diameter 9.8–11.8– 13.8 mm, branch tip diameter 6.4 mm.

Corallites. Axial corallite dominates branch structure, visible at the tip of the specimen, not on polished transverse section due to recrystallization; exsert 1 mm, outer diameter 2.5 mm, inner diameter 1.30 mm, wall thickness 0.38 mm, primary and secondary septa present; radial corallites in mixed sizes, larger radials appressed tubular with round calices, profile length 0.39–0.68– 1.15 mm, angle 23.52–29.74–37.57°, outer di- ameter 0.86–1.08– 1.26 mm, inner diameter 0.52–0.64– 0.73 mm, wall thickness 0.14–0.17– 0.21 mm, evenly distributed, not touching, distance between centres 1.32– 2.08– 3.04 mm, primary and secondary septa present. Corallite arrangement sequence 1–6–16–?.

Coenosteum. Evidence of costae on larger radial corallites, reticulate in intercorallite areas.

Description of paratype

Corallum . Overall length of the specimen 71.7 mm, L-shaped, oval in cross section, mid branch diameter 19.09–20.15– 20.65 mm.

Corallites. Axial corallite visible on polished transverse section despite high recrystallization, inner diameter 1.29 mm, primary and secondary septa present; radial corallites in mixed sizes, larger radials short tubular with round calices, inner diameter 0.44–0.72– 1.24 mm, smaller radials subimmersed, evenly distributed, not touching, distance between centres 1.42– 1.97– 2.55 mm, primary and secondary septa present.

Coenosteum. Reticulate in intercorallite areas.

Occurrence

Late Oligocene, 27–28 Ma, Sanctuary Quarry located in the north-east of Sabah, Malaysia.

Palaeoenvironment

The Sanctuary Quarry is the most taxonomically rich outcrop (genus level) of Oligocene age in the Indo- Pacific ( McMonagle, 2012). It has been interpreted as a shallow water environment, in which Acropora laurae sp. nov. co-occurred with abundant branching corals of the genera Actinacis , Porites , Stylophora and some platy colonies of Pachyseris and Cyphastrea .

Remarks

The two specimens studied were collected separately so they cannot be assigned to the same colony. The size and form of the branches suggest a digitate to corymbose growth. Although recrystallization is high, polished surfaces of the branches reveal radial corallites in mixed sizes. These specimens appear to be similar to the extant A. gemmifera ( Wolstenholme et al., 2003) of the humilis species group ( Wallace, 1999), from which they differ in having smaller radial corallites and relatively thinner and less tapering branches. These specimens were interpreted as A. aff. bushyensis by McMonagle (2012); however, the distinctive sturdy nature of the branches, axial-dominated, and dense reticular coenosteum placed this species closer to other species of the humilis group than to the non-axialdominated forms of the lovelli species group, which includes A. bushyensis .

Etymology

This species is named after our friend and colleague Laura McMonagle, collector of the specimens.

Figures

Figure 9. Acropora laurae sp. nov. A–C, holotype, NHMUK PI AZ 8666, Sabah, Malaysia, Oligocene (27.8–28.6 Ma): A, whole specimen. B, detail showing axial corallite. C, detail showing radial corallites and incipient branch. D–F, paratype NHMUK PI AZ 7724, Sabah, Malaysia, Oligocene (27.8–28.6 Ma): D, whole specimen; E, polished cross section showing axial corallite; F, polished lateral surface showing radial corallites in mixed sizes.