Cann, J. 1997. The Northern Yellow Faced Turtle. Monitor (1997)9(1):24-29; 34-35.
Emydura tanybaraga sp. nov. Holotype A.M.R125498 Collected by A. Georges
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| Carapace differences between E. tanybaraga and
Emydura victoria (with head extended) from the Daly river. |
Description
There is a reasonable morphological variation between forms of this turtle at old age from the
type location and Mitchell River. Large juveniles and medium sized specimens from throughout the
distribution are quite similar. The heads of adult females can grow quite large but not as regularly
or to the extent that megacephaly effects Emydura australis or victoriae. The small
barbells may be present.
A light yellow band of different intensity extends back from the eye to just above the tympanum
which usually fades completely with old age. Young from the Daly may have a band that starts
at the tip of the nose. Another lighter band extends from the angle of the mouth along the
neck. This region also later fades. The top of the head is not a thickly cornified crown but rather
has a light shield, though occasionally this may be absent. Regardless, the crown of the head is
usually mottled with dark patches. Similar coloured patches or spots occur on the fawn to
dark brown-grey carapace. When viewed dorsally, juveniles and young adults are
noticeably pear shaped, and as they age they become more oval in shape. Flaring on the rear
of the carapace is distinctive from M6 back and remains throughout life, but on older turtles
flaring is normally confined to the rear most marginal from M8 back. Viewed from the side,
indications of central ridging is still evident on large juveniles and turtles in early maturity.
Viewed also from the side the apex of the carapace hump in the McKinley and Daly River
turtles is close to the mid line, while in those living in the Walsh River, (at least on the larger
specimens), the apex of the hump is forward, giving a distinctively longer taper to the rear. The
carapace colours are similar and the shields are smooth and slightly waxy, with an indication of
longitudinal sulcations as they begin to age. The bone coloured plastron may occasionally have a
slight indication of pink and is bulged in the centre and both lobes of the plastron turn up,
consequently the turtle appears quite deep in profile. The longest carapace seen in the Daly
was 210 mm, the McKinley 250 mm with a depth of 115 mm, while one from the Finniss River was
285 mm in length with a depth of 120 mm. This latter specimen is almost comparable in size to a
large female collected in the Walsh River, a tributary of the Mitchell. Dorsally the soft parts
are steel grey, below a creamy white, the neck is covered with small smooth tubercles, the barbells
are small or non-existent.
Large female heads from the Walsh River are 'V'-shaped when viewed .dorsally or ventrally. If
this feature occurs in the Daly it is not known.
Although the large females seen from the McKinley River had conventional head shapes.
The red-faced Emydura victoriae hatchlings also have a broad horny sheath inside the upper
mouth, which extends back to about the centre line to form a secondary plate,
though some young may have a division splitting the centre of this sheath which gradually meets.
Hatchling Emydura tanybaraga are not similarly equipped with this strong palate with the exception
of old specimens. Hatchlings of yellow-faced turtles have the palate or sheath which forms a narrow
band along the upper jaw. As these turtles grow, the sheath extends inwards and on old specimens
the roof of the mouth is well protected from possible damage during the feeding process.
The plastron and carapace of hatchling Emydura tanybaraga are distinctively different from the
Emydura victoriae and very similar to other yellow-faced Emydura from the McKinley River.
The front section of the carapace is wider than the rear unlike the Emydura victoriae, and it is
somewhat heart-shaped without the 'V'. There are no serrations on the marginals as there are on
Emydura victoriae, however, what I call serrations is often viewed differently by other turtle
researchers. The centrals are also high ridged, and the shield crinkling is almost restricted to
the central scutes, the others are smooth. The bone coloured plastron can have small dark patches
and has a wider front lobe than the hatchling red-faced turtles, and they are also more tapered
on the rear lobe. ventrally the bone coloured marginals have dark patches at the seams,
with the bone colour slightly extending around on to the upper surface. As they grow
into juveniles, they also grow high ridged, and the marginals flare slightly less than the broader
medium sized red-faced turtles. The edges of the marginals from M3- M6 turn up slightly on both
species. At this stage of growth both red and yellow-faced species look quite similar (like many
turtles across northern Australia) although the crown on the head of the yellow-face only has
dark mottling unlike the normally plain colour of Emydura victoriae or Emydura worrelli. The
attractive iris is similar in colour to Emydura victoriae, but it normally has the dark split or
dots, often in both directions giving the cross effect previously mentioned. The original two I
gave to the Australian Museum were 102 mm and 110 mm long and both showed distinctive annuli.
The skull form of adult Emydura victoriae and Emydura tanybaraga is distinctive. On young
turtles of Emydura tanybaraga, the mandibular symphysis is smaller than the near equal orbit and
tympanic cavities. As the turtle ages the symphysis will become wider than these orifices
but never to the extent of Emydura australis or Emydura victoriae.
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Distribution
Georges and Adams research indicates that Emydura tanybaraga occur in the Daly, South
Alligator and Mitchell Rivers. In the Daly they are known to be found in the general vicinity of
Daly River Mission, up and down stream of Policeman Crossing. The South Alligator River
has some of its headwaters near Coronation Hill, it runs in a general northerly direction, and is fed
by Jim Jim Creek in the flood plains near Nourlangie. Most of this system is in Kakadu
National Park. In this general region of the Northern Territory I would expect that Emydura
tanybaraga will also be in the Reynolds, Adelaide, McKinley, Mary, Howard and East
Alligator Rivers and associated water ways. 1200 km to the east is the Mitchell River. Its
headwaters are within 15 km of the eastern seaboard to the south of Mossman and is the
longest of Cape York water ways. Before entering the Gulf of Carpentaria it is joined by the
Hodgkinson, Palmer, Alice, Lynd and Walsh Rivers. The upper reaches of the Mitchell are not
far from Mount Carbine on the main Peninsula Road. Yellow-faced turtles are reported to the
north of the Mitchell in the Edward and Wenlock Rivers, so at this stage without seeing these
forms, I will still include them in this group. It is unlikely that they will extend into the Jardine
River where Emydura subglobosa occurs.
Type Locality
The type location at Daly River Mission is a typical monsoonal river with the majority of rain
falling during December to April with up to 1200 mm per annum being recorded. Daily
temperatures are approximately 29° - 32°C. During the dry season the river is bordered by
high timbered banks, which accommodate a possible 15m rise during the monsoon. In this
region the river width varies between 30m - 80m and up to 4m deep. There are large bank sand
bars and the vegetation is chiefly pandanus, melaleuca, eucalyptus, casuarina and fig. A
concrete causeway, known as Policeman Crossing, dams back the tidal effect from Anson
Bay, 70 km to the north west. Both fresh and salt water crocodiles are present. The aquatic fauna is
abundant and many salt water fishes intermingle with the fresh. Both grey nurse and black tip reef
sharks are occasionally sighted along with giant mangrove stingray and sawfish.
Breeding Biology
The only published data on this species (at the time considered conspecific with Emydura
victoriae) of turtles' breeding activities was by Smith and Wood in , 1985. They noticed
hatchlings emerging from a nest at 7am on 21st October 1984. The nest site was 3m from and
1.5m above the water level of a billabong associated with the McKinley River. It was
estimated that the nest contained 16 - 17 hardshelled eggs. Of these 10 hatchlings were
retrieved, their dimensions were:
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In addition to this, Legler reports that nesting for this species (as
Emydura australis) occurs between early August to mid-November in this region. On 25th
September 1990 I dived for turtles with Rod Kennett at Girraween Lagoon near Humpty Doo. We collected
23 yellow-faced turtles, many of which were gravid.
Sympatry
Throughout its length the Daly river has six forms of freshwater turtles: Chelodina insculpta,
Chelodina rugosa, Elseya dentata, and three Emydura each of which can have a
different facial colouration. The Alligator River system has an undescribed form of Elseya
dentata, while just below the escarpment a small number of Elseya latisternum are present,
probably swept from the plateau during the wet. The Mitchell also contains Chelodina novaeguineae
sp. and Chelodina rugosa.
Natural History
The habitats of Emydura tanybaraga are extremely diverse, which is not surprising
considering its vast distribution. To what extent the yellow-faced turtles extend upstream from
Policeman Crossing at Daly River Mission is not known. I have caught them as far as Olloo about
80 km upstream, but there has been limited research in this river and the turtles, to my
knowledge, have not entered traps. The original pair I collected in 1971 was by snorkel diving
500m upstream from the crossing. Today diving in this section of the river is out of the question
because of salt water crocodiles. These turtles can be seen by spotlight of a night amongst fallen
timber or the roots of living vegetation. Small juveniles have been noted at night basking amongst debris.