Acropora emanuelae, 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 : 736-738

ACROPORA EMANUELAE SP. NOV.

FIGURE 30

Diagnosis

Colonies arborescent or irregular hispidose with indeterminate growth, composed of thick main axis and short or incipient secondary branches. Axial and radials contribute equally to the branch structure. Radial corallites, appressed tubular to immersed at the basal parts of the colony, evenly distributed. Coenosteum composed of short spinules with slightly elaborated tips throughout.

Material studied

Holotype. NHMUK PI AZ 8871 , 23 fragments from the same colony. 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, 30 November 2010.

Paratype. NHM UK PI AZ 8894 , 4 specimens. 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, 30 November 2010 .

Other material studied. East Kalimantan : NHM UK PI AZ 8866 , 23 specimens ; NHM UK PI AZ 8867 , 32 specimens ; NHM UK PI AZ 8868 , 7 specimens NHM UK PI AZ 8870 , 4 specimens ; NHM UK PI AZ 8872 , 1 specimen ; NHM UK PI AZ 8878 , 4 specimens ; NHM UK PI AZ 8879 , 16 specimens ; RGM 791817 , 1 specimen ; RGM 77690, 1 specimen ; RGM 77691, 2 specimens .

Description of the holotype

Corallum . One colony that is arborescent to irregular hispidose composed of 23 broken branches representative of base, main axis and branch tips, overall colony length 21 cm, width 17 cm ( Fig. 30A ); main axis sturdy from which primary branches and secondary branches (branchlets) arise, tapering, branch length 20.21–54.30– 111.68 mm, angle 51.66–59.32–68.96°, basal diameter 18.74–22.74– 29.63 mm, mid branch diameter 10.17–14.79– 17.36 mm, branch tip diameter 5.31– 6.92– 7.99 mm; distance to the nearest primary branches 15.23–20.32– 24.19 mm; secondary branches arise in angles 40.12–45.01–54.53°, secondary branch length 7.85–10.37– 12.02 mm, mid branch diameter 5.91–6.88– 8.29 mm; growth indeterminate.

Corallites. Axial corallite 1.54–2.65– 3.50 mm exsert, outer diameter 1.56–2.10– 2.75 mm, inner diameter 1.02– 1.53– 1.75 mm, wall thickness 0.33–0.37– 0.40 mm, primary septa present, secondary septa visible as points, S1>S2; radial corallites evenly sized and distributed, long tubular appressed towards the branch tips, small round calices, distance between centres 3.88–4.75– 7.10 mm, profile length 2.03–2.35– 2.78 mm, arise in acute angles 13.89–17.56–21.23°, outer diameter 1.08– 1.23– 1.32 mm, inner diameter 0.54–0.68– 0.79 mm, wall thickness 0.28–0.33– 0.42 mm, subimmersed at the basal part of the branches, inner diameter 0.35–0.45– 0.54 mm, distance between centres 2.80–4.23– 5.79 mm, primary septa present. Corallite arrangement sequence 1–3–[3–4]–[4–5]–up to 10 radials at the basal parts of the colony.

Coenosteum. Simple spinules with probably slightly elaborated tips arranged into dense regular pattern throughout. Coenosteum amount 1.82–2.92– 4.26 mm towards the branch tips and 2.71–3.36– 3.95 mm towards the base.

Occurrence

Early Miocene to Early Pliocene. The earliest occurrence of the species is from its type locality TF56, Badak, of Langhian to Burdigalian age, 14.8–17.9 Ma. Specimens from the Naturalis museum are from Ci Angsana, Java, of Tortonian to Serravallian age, 8.5–13.5 Ma, and Gunung Linggapadang of Messinian age, 5.33– 7.25 Ma. The last occurrence is from the outcrop TF518, Bontang, of Early Pliocene to Tortonian age, 5–8 Ma.

Palaeoenvironment

This species was found in beds characterized by grey silt-rich sediments with abundant platy corals of the genera Pachyseris , Astreopora and Porites , as well as digitate Stylophora . Solitary corallites of Paracyathus were observed growing on some branches. These palaeoenvironments have been interpreted as small patch reefs with an influence of siliciclastics in the deltafront of the Mahakam River.

Remarks

This species closely resembles A. kirstyae and thus it is placed in the horrida species group. It differs from the latter in having thicker branches from which shorter branchlets with small radial corallites arise. The skeleton is dense and highly recrystallized, yet the coenosteum and corallites are well preserved. The general hispidose appearance of the colony of A. emanuelae sp. nov. resembles that in the florida species group, but the small tubular appressed corallites are distinctive of A. emanuelae sp. nov. The coenosteum does not show alignment of spinules as is common in the florida group.

Etymology

This species is named after our friend and colleague Emanuela Di Martino, researcher of bryozoans, who was in the field with N.S. at the moment of collection of the type specimen.

Figures

Figure 30. Acropora emanuelae sp. nov. A–C, E and F, holotype, NHMUK PI AZ 8871, TF56, Badak, East Kalimantan, Early to Middle Miocene (14.8–17.9 Ma). D, G and H, paratype, NHMUK PI AZ 8894. TF518, Kampung Narut, East Kalimantan, Late Miocene to Early Pliocene (5–8 Ma). A, aspect of a colony in situ, showing arborescent to hipidose– arborescent corallum, white triangle indicates the figured specimen AZ 8871a. B, AZ 8871a, b, detail of branches showing robust main axis and short branchlets throughout. C, AZ 8871a, detail of branchlet and arrangement of appressed tubular corallites. D, AZ 8894a, electron micrograph showing branchlet variation. E, AZ 8871c, branch tip showing appressed tubular corallites. F, AZ 8871d, basal branch with immersed corallites. G and H, AZ 8894a: G, electron micrograph of immersed corallites; H, electron micrograph of reticulate elaborated spinules on coenosteum.