Myuchelys, Thomson, Scott & Georges, Arthur, 2009

Thomson, Scott & Georges, Arthur, 2009, Myuchelys gen. nov. — a new genus for Elseya latisternum and related forms of Australian freshwater turtle (Testudines: Pleurodira: Chelidae), Zootaxa 2053, pp. 32-42 : 33-34

Myuchelys , gen. nov.

Type species. Elseya latisternum Gray, 1867 designated herein.

Etymology. The name is a combination of a contraction of the Aboriginal word for clear water, Myuna, and the Greek word for tortoises, chelys. It is a generalised reference to the types of habitat often preferred by the species of this genus.

Diagnosis. A member of the short-necked chelid turtles of the Australasian region which, excluding Pseudemydura umbrina ( Siebenrock, 1901) , together form a well-established clade ( Georges & Adams, 1992; Georges, et al., 1998). Differs from other short-necked turtles of the clade in possessing the following combination of characters ( Table 1): Absence of a well-developed alveolar ridge on the triturating surfaces and underlying bones of the jaw ( Fig. 1 B) (present only in the redefined Elseya , Fig. 1 A); parietal arch of skull wide, nearly as wide as tympanum ( Fig. 2 ) (narrower than the tympanum in Elseya and Emydura ); large distinctive head shield, entire, that extends in part down the parietal arch toward the tympanum (absent in Emydura , not extending down the parietal arch in Elseya , Rheodytes and Elusor ); ilium-carapace suture involves pleurals 7–8 and the pygal (as in Elusor but distinct from the condition in Elseya and Emydura ); anterior bridge strut is confluent with the rib-gomphosis of pleural one; no angle of intersection between these two bony units when viewed ventrally (as in Elusor , but unlike Elseya , Emydura and Rheodytes – see Fig. 1 and 2 of Thomson, et al., 1997).

Description. Medium-sized turtles with a broadly oval carapace that is dorso-ventrally flattened and dark brown to black in colour, depending on species. Cervical scute typically present, though present only as a rare variant in most populations of M. latisternum north of the NSW–Queensland border ( Legler & Cann, 1980). Plastron narrow, anterior lobe distinctly wider than posterior lobe. Plastron grey, light cream or yellow often with dark streaking or blotching, especially at the leading growth edge of plastral scutes and ventral surfaces of the marginal scutes. Intergular scute highly variable, but typically as wide as the adjacent gulars. Bridge carapace suture is narrowest medially and at its widest on the peripheral edge of the bridge strut region. Ribgomphosis of pleural five inserts into the centre of peripheral seven; ilium-carapace suture involves pleurals seven, eight and the pygal bone. Parietal arch of skull is wide, nearly as wide as tympanum; crista supraoccipitalis short does not extend past crista paroccipitalis. Lingual ridge small, unmodified.

Species. Myuchelys latisternum ( Gray, 1867) , M. georgesi ( Cann, 1997; Elseya [var. Bellinger] in Georges & Adams, 1992;1996), M. purvisi ( Wells & Wellington, 1985; Elseya [var. Manning] in Georges & Adams, 1992;1996) and M. bellii ( Gray, 1844; Elseya [var. Gwydir] in Georges & Adams, 1992;1996, resurrected by Cann, 1998) are assigned to the new genus. Molecular analyses by Georges and Adams (1992; 1996) verified the validity of each of these as biological species and showed that they formed a distinct clade. Myuchelys purvisi and M. georgesi are cryptic species ( Georges & Adams, 1996; Thomson & Georges, 1996) differing overtly only in intensity of colouration.

Distribution. Species of Myuchelys are found in the coastal rivers of northern New South Wales north to Cape York and west to the Arnhem Land plateau of the Northern Territory ( Georges & Thomson, 2009). Myuchelys bellii is restricted to the tributaries of the Murray-Darling drainage basin that flow west from the Great Dividing Range in northern New South Wales. Myuchelys georgesi and M. purvisi are restricted to the Bellinger and Manning Rivers of coastal New South Wales, respectively. Myuchelys latisternum is the most widespread, ranging from the Richmond River (NSW) in the south to the Jardine River of Cape York in the north (Qld). Its distribution includes also the rivers that flow into the Gulf of Carpentaria and the headwater tributaries that drain the Arnhem Land plateau into the Roper, South Alligator and Daly Rivers of the Northern Territory. An isolated population is known from the headwaters of the Mary River in the Northern Territory in Kakadu National Park.

Habitat. Known from the middle reaches of the rivers they occupy, but greatest abundances for all species of Myuchelys occur in the upper reaches and tributaries of the drainage basins they occupy, often above escarpments that exclude other riverine species.

Relationships. Georges and Adams (1992) established the relationships among the four species of Myuchelys . Despite being a cryptic species pair, Myuchelys georgesi and M. purvisi are not sister species, and indeed their common ancestor has all species of Myuchelys as its descendents. This suggests that many of the characters jointly possessed by these two species are pleisiomorphic for the genus.

Relationships between Myuchelys and the other short-necked genera are less clear, so we undertook a morphological analysis to complement the prior analyses of molecular data ( Georges & Adams, 1992; Georges, et al., 1998). Cladistic analysis of 45 characters (Appendix) from the extant genera of short-necked Australian chelids yielded a phylogeny with strong bootstrap support for all major nodes ( Fig. 2 ). One tree of 69 transitions in length was shorter than all others, with the next shortest trees (n=3) 71 transitions in length. Genera received at least 74% bootstrap support The paraphyly of the genus Elseya , as previously defined, is clearly evident.

Specimens examined. Abbreviations: AM, Australian Museum; NHM, Natural History Museum (BMNH); NTM, Museum and Art Gallery of the Northern Territory; NWC, National Wildlife Collection; QM, Queensland Museum; UC, University of Canberra; UM, University of Michigan Field Series.

Chelodina expansa : UC 2099, Albury (36°05'S, 146°55'E); UC 2074, 2190 -94, Mungabareena Reserve, Albury (36°06'S, 147°00'E). Chelodina longicollis : QM 59266, UC 0199, Hawkesbury River (33°45'S, 150°42'E); QM 59267-68, 59281-2, Jervis Bay (35°08'S, 150°42'E); QM 59274, UC 0134, 0164, 0169, Canberra (35°17'S, 149°08'E); UC 0166, Oasis Creek, Dubbo (32°15'S, 148°36'E); UC 0174, Mumbar, Near Rockhampton (23°23'S, 150°31'E). Chelodina colliei : QM 59272-73, 59283, Perth (31°56'S, 115°50'E); UC 0161-63 Perth, (31°56'S, 115°50'E). Elseya albagula : QM 48012, 48046, Burnett River, near Gayndah (25°37'S, 151°37'E). QM 47987, 47998, 48002, 48010, Dawson River, Theodore (24°57'S, 150°05'E); AM 123067 , Grey's Waterhole, Burnett River (25°32'S, 151°39'E); UC 0305-06 Mary River. Elseya branderhorsti : UC 0334, Maurauke River, Irian Jaya. Elseya dentata : AM 72692-94, 72934-46, 73346, 79160, Bullo River at crossing of Katherine-Kununurra Road (15°42'S, 129°38'E); NTM 17201, 17205-06, 17210, UC 0309-19, 0328, Douglas River (13°47'S, 131°17'E); Elseya dentata [var. South Alligator, sensu Georges & Adams, 1992;1996]: UC 0304, Corroboree Billabong, Mary River; NWC 0531, Deaf Adder Creek (13°04'S, 132°58’); AM 128001 -04, Magela Creek; NTM 13985, Pul Pul Billabong, South Alligator River (13°34'S, 132°35’); NTM 13512, South Alligator River (13°30'S, 132°28’). Elseya dentata [var. Johnstone, sensu Georges & Adams, 1992;1996]: QM 48068, Hartley Creek (15°46'S, 145°19'E); QM 48060, near Cairns (16°55'S, 145°46'E); QM 48059, 48064-65, South Johnstone River (17°38'S, 145°05'E). Elseya irwini NWC 0520, Townsville (19°16'S, 146°49'E); Elseya lavarackorum QM 47908, 47911, 48547, 48564, Elizabeth Gorge, Bowthorn Station (18°13'S, 138°2'E); QM 31939, 31942, 31944, 31946-47, 31949-50, 31952, Gregory River, Riversliegh Station, north of Mt Isa (19°02'S, 138°45'E); UC 0201, QM 48544, Lawn Hill Gorge (18°46'S, 138°25'E); QM 46284 Lawn Hill National Park (18°35'S, 138°35'E). Elseya novaeguineae : AM 42662, 125038, Sepik River, New Guinea (6°47'S, 146°46'E). Elusor macrurus : NHM 1890.2.26.2, UC 170, 184-93, 195-197, 225-229, Mary River, Queensland 26°21'S, 152°41'E. Emydura macquarii : UC 176, Hastings River (31°26'S, 152°28'E); UC 2063-73, Mungabareena Reserve, Albury (36°06'S, 147°00'E). Emydura subglobosa : UC 389, 391, 394-95, Bahunia Springs, Limmen Bight River (16°00'S, 139°05'E); UC 177, Batten Creek, McArthur (15°54'S, 136°40'E); UC 2083-84, Goyder River (12°56'S, 135°01'E); UC 171-72, Gregory River (19°12'S, 137°54'E); UC 2059, 2091, 2095-97, Oolloo Crossing, Daly River (14°04'S, 131°15'E); Emydura tanybaraga : UC 2195, Mareeba Wetlands (17°00'S, 145°26'E); UC 464, 468, 469, Oolloo Crossing, Daly River (14°04'S, 131°15'E); Emydura victoriae : UC 461, 463, 468, 473, 2055-58, Oolloo Crossing, Daly River (14°04'S, 131°15'E); UC 222, Myuchelys bellii : AM 123028 -29, QM 48028, 48038, billabong on Roumalla Creek, 3 km downstream from bridge at Kingston (30°30'S, 150°07'E); Myuchelys georgesi : UM 02016-17, Bellinger River; AM 138387-88, Bellinger River, vicinity of sawmill 1 km from Thora on the Upper Thora Road (30°25'S, 152°46'E); Myuchelys latisternum : AM 123037 , 123039, Lismore Lake, Lismore, Richmond River Drainage (26°50'S, 153°16'E); UC 470, Richmond River, NSW; AM 125474 -75, South Alligator River, Gimbat Station (13°34'S, 132°35'E); QM 48054-55, no data; UC 2094, South Pine River, Bunya crossing (27°21'S, 152°57'E); Myuchelys purvisi : QM 59289-90, Barnard River; AM 123040 , 123042, Barnard River Natmap 1:250000, Hastings SH56-14 488075 (31°44'S, 151°51'E). Phrynops geoffroanus : UC 274, no data, pet trade. Phrynops hilarii : UC 330, 336, no data, pet trade. Phrynops williamsi UC 298-99, 333, no data, pet trade. Phrynops tuberosus UC 328, 332, 337, no data, pet trade. Batrachemys raniceps : UC 2043, no data, pet trade. Pseudemydura umbrina : UC 178, WAM 29348, Twin Swamps Reserve, Perth. Rheodytes leukops : UC 173, 2053, Fitzroy River, Queensland.

Figures

FIGURE 1. Ventral view of the skulls of A. Elseya dentata (UC 0302); B. Myuchelys latisternum (AM 125475) and C. Emydura macquarii (QM 48034). Note the alveolar ridge on the maxillary surface of Elseya dentata.

FIGURE 2. Dorsal and lateral views of the skulls of A. Elseya dentata (UC 0302); B. Myuchelys latisternum (AM 125475) and C. Emydura macquarii (QM 48034).