Miocene brachyuran Crustacea from Konar-Takhteh and Ahram sections, southwestern Iran

Crustáceos braquiuros del Mioceno de las secciones Konar-Takteh y Ahram, Irán suroccidental

Mehdi Yazdi¹, Ali Bahrami¹, Peyman Abbasi¹, Reza Sadeghi², Francisco J. Vega^3,*

¹ Department of Geology, University of Isfahan, POB. 81746-73441, Isfahan, I.R. Iran.

³ Instituto de Geología, UNAM, Ciudad Universitaria, Coyoacán, México, D.F., 04510, México. *vegver@unam.mx

Manuscript received: February 21, 2013.
Corrected manuscript received: March 20, 2013.
Manuscript accepted: March 21, 2013.

Abstract

Five species of brachyuran Crustacea from the Middle Miocene are described from the Guri Member of the Mishan Formation in southwestern Iran. The species include the leucosioids Leucosia persica; Seulosia sp. cf. S. rhomboidalis; Myra sp.; the portunoid Portunus withersi and the xanthid Demania ahramensis n. sp. The paleobiogeographic affinities of these genera reinforce previous interpretations of a wide distribution between the Persian Gulf and the Indopacific regions.

Keywords: Crustacea, Decapoda, Brachyura, Miocene, southwestern Iran.

Resumen

Se describen cinco especies de crustáceos braquiuros del Mioceno Medio del Miembro Guri de la Formación Mishan en el suroeste de Irán. Las especies incluyen a los leucosioideos Leucosia persica; Seulosia sp. cf. S. rhomboidalis; Myra sp.; el portunoideo Portunus withersi y el xántido Demania ahramensis n. sp. Las afinidades paleobiogeográficas de éstos géneros refuerzan las interpretaciones previas sobre una amplia distribución entre las regiones del Golfo Pérsico y el Indopacífico.

Palabras clave: Crustacea, Decapoda, Brachyura, Mioceno, suroeste de Irán.

1. Introduction

After the Burdigalian (Early Miocene) lake depositional system of Gachsaran Formation (on the depression of areas between Fars platform and Dezful expression), marine environments expanded and the Gachsaran Formation was covered by a transgressive and shallow marine sequence (the Mishan Formation). The Mishan Formation contains about 943 m of green to grey marl and clay-limestone with rich fossil content. The lower 60 m of this formation consist of burrowed limestone, which is replaced by reef limestone, called the "Guri member" of Mishan Formation (Fig. 1). In the type section (Gachsaran oil field), its name is derived from a village (Mishan village) located in 50 km south – southeast of Gachsaran city at Southwestern Iran (Figs. 2, 3). The Mishan Formation is mainly sandy at the type section area and changes laterally to siltstone facies at inner Fars and Bandar Abbas regions.

In other regions, except for inner Fars in which Mishan Formation is located over the Razak Formation, the Mishan Formation overlies the Gachsaran Formation and is overlaid by the Aghajari Formation. The lower boundary is sharp and the upper boundary transitional. Reef limestone from Guri Member of Mishan Formation is an index due to its large content of Operculina and other micofossils. In addition to plankton foraminifera, bivalves, gastropods, echinoids and crustaceans, it suggest an early to Middle Miocene age for this formation. Two sandy limestone horizons at the upper part of Mishan Formation (studied in Konar-Takhteh and Ahram sections) bear rich and diverse crustaceans fossils (Fig. 3).

All the studied specimens are housed at the University of Isfahan, Department of Geology under acronym EUIC. The museum number of each specimen is given at the figure caption.

The Miocene deposits of southwestern Iran are rich in crustacean remains. Vega et al. (2012) listed 13 species, most of them belonging to extant genera which are mainly distributed today in the Indopacific region. The paleobiogeographic affinities of the Miocene brachyuran fauna from Iran with the Indopacific region were mentioned by Glaessner (1933), Vega et al. (2010, 2012) and Heidari et al. (2012). The Guri Member of the Mishan Formation is probably one of the most productive lithostratigraphic units in terms of diversity and abundance of Miocene crustaceans. Future collects will surely reveal that the Mishan Formation has a fossil crustacean diversity as high as that reported from Miocene to Pleistocene lithostratigraphic units of the Indopacific region (see Karasawa et al., 2008 for examples and references).

2. Geological setting

The studied sections are part of Iranian oilfields at the Southwestern portion of the country. Konar-Takhteh section (Fig. 3) is located 10 km from Konar-Takhteh city, 35 km southeast of Kazerun, before (Tunnel 2 Pisa) underground highway at coordinates: Base N 29º 34' 9" E 51º 28' 57" (Fig. 2).

Ahram section is located 15 km east of Ahram city, close to the Beniun village, 175 km southeast of Kazerun, with coordinates: Base N 28º 47' 48" E 51º 23' 32" (Fig. 2)

The main lithology of the Mishan Formation in the studied section consists of reef limestones of the Guri Member at the base of the formation and green to grey marls with several sandy limestones, thin layers of gypsum and sub minors of sandstone. Because of the similar lithology and fossil contents between the two studied sections, only one section is here described.

The detailed measured sequence and lithologic features (top to base) of the Mishan Formation at Konar-Takhteh section is as it follows:

- Top: Alternation of fine grained micro-conglomerate, gray marl, sandstone, sandy limestones, anhydrite and halite with bituminous shales, (Aghajari Formation) - 500 m.

- Green marl with thin sandstone layers, sandy limestones intercalations and thin bedded gypsum layers - 100 m.

- Yellow to grey sandy limestones layers rich in gastropods, bivalves and crustaceans (Crab bearing beds) - 20 m.

- Olive to greenish marls with gypsum layers - 80 m.

- Platy green marl and sandy brown limestones - 260 m.

- Grey to white thin bedded sandy limestones with bivalves, gastropods and bryozoans - 50 m.

- Olive to green marl with thin bituminous shale layers - 315 m.

- Green marls - 150 m.

- Green to grey marls with sandy brownish limestones and gypsum intercalations – 20 m.

- Base: Red to brown thick bedded gypsum, halite and grey to brown shale (Gachsaran Formation).

3. Systematic palaeontology

Infraorder Brachyura Latreille, 1802 ]]> Section Eubrachyura de Saint-Laurent, 1980
Superfamily Leucosioidea Samouelle, 1819
Family Leucosiidae Samouelle, 1819
Subfamily Leucosiinae Samouelle, 1819
Genus Leucosia Weber, 1795

Type species: Cancer craniolaris Linnaeus, 1758, by subsequent designation of Holthuis (1959).

Leucosia persica Vega, Gholamalian and Bahrami, 2010
Fig. 4.1 – 4.11

Leucosia persica Vega, Gholamalian and Bahrami, 2010, p. 486, fig. 5 a-p.

Description: see Vega et al. (2010, p. 487).

Measurements: EUIC 503, carapace length = 24 mm, width = 20mm, height = 6 mm; EUIC 504, carapace length = 28 mm, width = 22 mm, height = 6 mm; EUIC 505, carapace length = 24 mm, width = 25 mm, height = 5 mm; EUIC 506, carapace length = 24 mm, width = 23 mm, height = 6 mm; EUIC 507, carapace length = 27 mm, width = 26 mm, height = 8 mm; EUIC 508, carapace length = 22 mm, width = 17 mm, height 7 = mm; EUIC 509, carapace length = 20mm, width = 21 mm, height = 6 mm.

Discussion: The species was described from the Middle Miocene Mishan Formation of the Hormozgan Province, southern Iran (Vega et al., 2010).

Genus Seulocia Galil, 2005

Type species: Leucosia rhomboidalis de Haan, 1841, by subsequent designation of Galil (2005).

Seulosia sp. cf. S. rhomboidalis (de Haan, 1841)
Fig. 4.12, 4.13

Description: Subrhomboidal carapace, constricted front, widest at midlength; anterolateral margin one-third the total carapace length; rimmed posterolateral margin; rounded posterior margin; elongate sternum; subquadrate, fused sternites 3 and 4; sternites 5 constricted on median portion; subovate sternites 6, postero-laterally inclined; subovate sternites 7 and 8 similar.

Material: One incomplete carapace, EUIC 510, Ahram section, Middle Miocene Mishan Formation, Iran.

Discussion: Seulocia rhomboidalis is an extant species, with a fossil record from the Pliocene-Pleistocene of Taiwan (Hu and Tao, 1996). The single Iranian specimen is similar to this species, but more complete specimens are needed to confirm the specific identity.

Subfamily Ebaliinae Stimpson, 1871
Genus Myra Leach, 1817

Type species: Leucosia fugax Fabricius, 1798, by monotypy.

Myra sp.
Fig. 4.14 – 4.16

Description: Subovate carapace, constricted anteriorly, wider at anterior third, surface covered by fine granules; narrow anterior margin; sinuous anterolateral margin; posterolateral margin broadly curved; narrow posterior margin, about one-fourth the maximum carapace level, with short, rounded posterolateral tubercles; posterior spine relatively short, twice the length of anterolateral tubercles; sternum subovate longitudinally; subtrapezoidal, fused sternites 3 and 4; sinuous sternites 5 to 7, decreasing progressively in size towards posterior portion.

Material: Two incomplete carapaces, EUIC 511 and EUIC 518, Konar-Takhteh section, Middle Miocene Mishan Formation, Iran.

Measurements: EUIC 511, carapace length = 15mm, width = 14 mm, height = 6 mm; EUIC 518, carapace length = 13mm, width = 12 mm, height = 5 mm.

Superfamily Portunoidea Rafinesque, 1815
Family Portunidae Rafinesque, 1815
Genus Portunus Weber, 1795

Type species: Cancer pelagicus Linnaeus, 1758, by subsequent designation of Rathbun (1926).

Portunus withersi (Glaessner, 1933)
Fig. 5.1 – 5.4

Neptunus (Achelous) withersi Glaessner, 1933, p. 8, pl. 2, figs. 1–3.

Portunus (Achelous) withersi (Glaessner, 1933); Glaessner, 1969, p. R510, fig. 319.2.

Portunus withersi (Glaessner, 1933); Karasawa et al., 2008, p. 127.

Description: Carapace one-third wider than long; curved anterolateral margin, with at least five antero-lateral spines of uniform size; slightly curved posterolateral margin, smooth, about two-thirds the total carapace length; posterior margin nearly straight, smooth, half the maximum carapace width; dorsal carapace regions not clearly marked; broad branchial areas; relatively deep cervical groove; distinct gastrocardiac and lateral cardiac grooves; relatively wide third maxillipeds, with median longitudinal groove; elongate sternum, fused, triangular sternites 1 and 2, inverted triangular sternite 3, inverted subtrapezoidal sternite 4, with median longitudinal deep groove and lateral process, subrectangular sternites 5, with rounded outer margins, two-thirds the length of sternite 4, sternites 6 nearly identical to sternites 5, sternites 7 one-third longer than sternites 6, sternites 8 small, subtriangular, one-third shorter and narrower than sternites 7; triangular male pleon, triangular telson, one-third longer than sternites 5, subtrapezoidal, fused somites 5-6, one-third shorter than length of sternites 6 and 7 together, trapezoidal, fused somites 3-4, base nearly as wide as posterior margin, one-third longer than somite 6; wide third maxillipeds with median longitudinal groove.

Material: Three incomplete carapaces, EUIC 512 and EUIC 513, Konar-Takhteh section, Middle Miocene Mishan Formation, Iran.

Measurements: EUIC 512, carapace length = 53 mm, width = 64 mm, height = 12 mm; EUIC 513, carapace length = 55 mm, width = 67 mm, height = 12 mm; EUIC 519, carapace length = 50 mm, width = 61 mm, height = 11 mm.

Discussion: The species has been reported from the Lower Miocene of Iran by Glaessner (1933), from the Fars Group near Sulabadar and the Guri Member of the Mishan Formation at Hormozgan, Southern Iran (Heidari et al., 2012). This report extends the biostratigraphic record of the species to the Middle Miocene.

Family Xanthidae MacLeay, 1838, sensu Karasawa and Schweitzer, 2006
Subfamily Xanthinae MacLeay, 1838
Genus Demania Laurie, 1906

Type species: Demania splendida Laurie, 1906, by original designation.

Demania ahramensis n. sp. ]]> Fig. 5.5 – 5.10

Diagnosis: Subhexagonal carapace, widest at mid-length; fronto-orbital margin half the maximum carapace width; narrow orbits, with two notches on dorsal surface; anterolateral margin with three lobes; strongest lobe at mid-length; smooth posterolateral margin; straight posterior margin; dorsal carapace regions and cervical groove well defined; elongate sternum; triangular male pleon; chelipeds relatively massive, equal; elongate, slender P2-P4.

Description: Subhexagonal carapace, one-third wider than long, widest at mid-length; fronto-orbital margin half the maximum carapace width; anteriorly protruded front, bilobed; narrow orbits, with two notches on dorsal surface; convex anterolateral margin, with three lobes that become stronger towards posterior portion; strongest lobe at mid-length; convex posterolateral margin, nearly as long as anterolateral margin, without lobes; straight posterior margin, half the maximum carapace width; well defined dorsal carapace regions; inverted subtriangular potogastric lobes; clearly marked mesogastric process, extends to level of orbits; subpentagonal mesogastric region; subquadrate cardiac region; depressed intestinal region; transversely ovate hepatic lobes; transversely subovate, elevated mesobranchial regions; flat metabranchial regions; elongate sternum; transversely subovate sternite 3; inverted subtrapezoidal sternite 4, with lateral process; subrectangular sternites 5, as wide but one-third shorter than sternite 4, with lateral process; subquadrate sternites 6, one-third longer than sternites 5, with lateral process; sternites 7 subquadrate, as long but half the width of sternites 6; triangular male pleon, triangular telson, one-third longer than sternites 5, subtrapezoidal; somite 6, one-third shorter than length of sternites 6 and 7 together; subrectangular somite 5, half the length of somite 6; rectangular somite 4, one third wider but slightly shorter than somite 5; equal, massive chelipeds; subrectangular coxa of right cheliped, two-thirds the length of sternite 4; small basis, subtriangular; subrectangular ischium, one-third wider than coxa; subrectangular merus, massive, three times the length of ischium; massive carpus, subquadrate, half the length of merus; subrectangular palm, with a row of three tubercles on dorsal surface; articles of left cheliped nearly identical to those of right cheliped, except for merus that is more massive; subrectangular coxae of P2-P4; basis small; subquadrate ischia; elongate, subrectangular meri.

Etymology: The specific name is derived from the Ahram section, Southern Iran.

Material: Four carapaces, two of them nearly complete, EUIC 514 – EUIC 517, Konar-Takhteh section, Middle Miocene Mishan Formation, Iran.

Measurements: Holotype EUIC 514, carapace length = 30 mm, width = 44 mm, height = 15 mm; paratype EUIC 515, carapace length = 30 mm, width = 42 mm, height = 15 mm; paratype EUIC 516, carapace length = 28 mm, width = 30 mm, height = 18 mm; paratype EUIC 517, carapace length = 40 mm, width = 45 mm, height = 18 mm.

Discussion: The fossil record of the extant genus Demania includes Demania caltripes (Alcock, 1898) from the Pliocene-Pleistocene of Taiwan (Hu and Tao, 1996); D. chayiensis (Hu, 1981) from the Late Miocene to Early Pliocene of Taiwan (Hu, 1981; Hu and Tao,1996); D. pilipinas Karasawa and Kato, 2008 (in Karasawa et al., 2008) from the Early Pleistocene of the Mandog Formation, Phillipines (Karasawa et al., 2008); D. reynaudi (H. Milne Edwards, 1834) from the Pliocene-Pleistocene of Taiwan (Hu and Tao, 1996); D. scamberrima (Walker, 1887) from the Pliocene of Java (Van Straelen, 1938); D. wardi Garth and Ng, 1985, from the Pleistocene of New Hebrides (Garth and Ng, 1985) and Demania sp. from the Early Pleistocene of the Mandog Formation, Phillipines (Karasawa et al., 2008).

The new species differs from the other fossil species of Demania in having a smooth dorsal carapace surface, while the previously known fossil species have tubercular or granular surfaces. The Iranian species extends the biostratigraphic and paleogeographic range for the genus to the Middle Miocene of the eastern Tethys.

Acknowledgements

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