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Distinguishing The Yellow Face Turtle and the Diamond Head Turtle. - Scott ThomsonEmydura tanybaraga and Emydura subglobosa worrelli Copyright © 2003 World Chelonian Trust. All rights reserved
The two short necked species The Yellow Faced Turtle (Emydura tanybaraga) and the Diamond Head Turtle (Emydura subglobosa worrelli) occur in sympatry in the Daly River of Australia. Bother are now becoming available on the market. They are however extremely difficult to distinguish as when from the Daly both species have yellow stripes and are the same size.
If your Emydura subglobosa is from New Guinea then it is the other subspecies known as the Painted Turtle (Emydura subglobosa subglobosa) and will have a red plastron among other things, easy to distinguish.
In 1996 I published a key to the species of turtles in the Northern Territory of Australia which included these two species. I will use the key here and also include the third species of Emydura of the region that being the Northern Red Face Turtle (Emydura victoriae).
1. Macrocephalic (head large and broadly expanded, too large to fit into carapace and the turtle may have difficulty lifting it off the ground). 4
Not Macrocephalic. 2
2. Triturating surface of upper jaw narrow with little or no medial protrusions of the sheath behind the internal nares; head stripe (if present) yellow to salmon pink or red and often surrounded by a black border, continues anteriorly to the eye down to the snout; prominent leading and trailing eyespots present; snout pointed. E. subglobosa: Diamond-head Turtle
Triturating surface not as above; head stripe (if present) yellow or red without a black border does not continue anteriorly to the eye and down to the snout snout; leading trailing eyespots, if present, not prominent; snout rounded. 3
3. Head stripe (if present) red in colour; triturating surface enlarged and internal nares behind the line joining the corners of the mouth; length of the symphysis of lower jaw equal to the distance between the inner articulatory points of the lower jaw. E. victoriae: Northern Red Faced Turtle.
Head stripe (if present) yellow in colour; triturating surface with prominent medial enlargement behind the internal nares which are level with or in front of the line joining the corners of the mouth; length of the symphysis of jaw half to three quarters of the distance between the inner articulatory points of the lower jaw. E. tanybaraga: Yellow Faced Turtle.
4. Triturating surface enlarged but posterior ends do not make medial contact; internal nares are in front of the line joining the corners of the mouth; gap in triturating surface over the internal nares is triangular in shape; shell appears waxy and bony sutures can be seen through it. E. subglobosa: Diamond-head Turtle.
Triturating surface enlarged and the posterior ends make medial contact; internal nares variable; gap over internal nares is not triangular; shell not waxy often fenestrated, bony sutures not usually visible. 5
5. Medial contact of the triturating surface completely fused with a small opening at the anterior end; internal nares behind the line joining the corners of the mouth; length of the symphysis of lower jaw equal to the distance between the inner articulatory points of the lower jaw. E. victoriae: Northern Red Faced Turtle.
Medial contact of the triturating surface is not fused with the contact between these units visible at all growth stages a small opening at the anterior end; length of the symphysis of jaw half to three quarters of the distance between the inner articulatory points of the lower jaw. E. tanybaraga: Yellow Faced Turtle.
Explanation of the Key
In the past some have argued that I should not write a key that brings each species out twice. I will argue against that by saying that as each of the species has two very distinctive morphotypes (that are a factor of age) that I am not only justified but more correct to allow as many specimens as possible key out.
Macrocephaly is the first issue. This is a response to age and I suspect it is purely a size related response to eating mussels. I have observed captive Emydura victoriae opening mussels with a shell diameter of 15cm. They do this by biting the mussel on the hinge end of the shell, they crush this section causing the muscles of the mollusc to relax and hence the mussel opens. It’s an impressive piece of biting power and certainly explains the massive overgrowth of the temporal muscles. In other words I recommend you don’t get bitten.
Macrocephaly is more developed in the Emydura victoriae and its sister species the Emydura tanybaraga. It is not well developed in the Emydura subglobosa.
As a function of this the triturating plates in the mouth differ between the three species. Emydura subglobosa has an enlarged plate but it is still typical of turtles in that it is restricted to the upper maxillae of the turtle and the internal edges of the plate do not meet or fuse covering the entire palate. The later condition is found in Emydura victoriae. The whole palate is covered by the triturating plate, this forces the opening for the internal nostrils to be well back in the mouth. The Emydura tanybaraga is somewhere in between in that although the left and right sides may meet in the centre they never fuse.
The symphysis of the jaw is where the left and right jaw bones meet (your chin) and in the Emydura subglobosa this is done in typical turtle fashion. In the other two species increased rigidity of the jaws for cracking mussels has expanded the symphysis.
Although colour is a poor character there are several that are reasonable consistent in these species. With the eyes there may or may not be a small black spot in front of and behind the pupil. This is always present in Emydura subglobosa, always absent in Emydura victoriae and a bit variable in Emydura tanybaraga (though generally absent).
The other one is the stipes on the head. In all of these species the colour fades with age so this character is more for identifying younger animals. However the stripe on the head of a Red Face Turtle (E. victoriae) is always red when present. This stripe has no border colour at all. The colour on the Yellow face turtle (E. tanybaraga) is always yellow again with no border colour. The Diamond head turtle (E. subglobosa) is another matter. Whatever colour its stripe is it has a black border, which may be hard to see on the dark grey background colour of the skin but it is there. The strip continues past the eyes down the nose in young animals giving the Diamond Shaped appearance that I name them from. The base colour of the stripe can be cream, yellow or salmon pink and this depends largely on where they are from.
Another feature of the species is the shape of the nose. Its is proble one of the hardest things to explain but Emydura tanybaraga has a shorter face than E. subglobosa. This is best seen in a photo from the side (which I do not have) where you can see a steeper incline from the head in front of the eyes down to the tip of the nose.
These are certainly a pair of species that require a lot of experience to tell apart. Generally six months catching them together on the Daly River helps.
I want to thank John Cann for letting me use the photo’s in the article. I have the express permission of John to use these photo’s and the copywrite of these photo’s belongs to John Cann.
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