| Warkalania | |
|---|---|
 | |
| Live reconstruction ofWarkalania | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Pantestudines |
| Clade: | Testudinata |
| Family: | †Meiolaniidae |
| Genus: | †Warkalania Gaffney, Archer & White, 1992 |
| Type species | |
| †Warkalania carinaminor Gaffney, Archer & White, 1992 | |
Warkalania is anextinctgenus ofAustralianmeiolaniid turtle from theOligocene or earlyMiocene ofRiversleigh,Queensland. While other meiolaniids are known for their elaborate headcrests or long horns,Warkalania only possesses very short horns that form a somewhat continuous ridge across the back of the head. The only known species of this genus,Warkalania carinaminor, is the oldest named meiolaniid turtle of Australia.
Although the presence of meiolaniids in theRiversleigh fauna had been known on the basis of fragmentary remains since at least 1987, the first diagnostic remains were discovered by Neville Pledge in the form of a partialskull from strata dating to the lateOligocene to earlyMiocene. These remains were described byEugene S. Gaffney, Michael Archer and Arthur White as a new genus of meiolaniid turtle they namedWarkalania carinaminor. Theholotype is specimen QMF 22649, a rightsquamosal bone including thetympanic cavity and various scales of that area, and was discovered at the Pancake Site inQueensland. Additional material has also been reported, such as QMF 22650, a left squamosal that may have belonged to the same individual as the type specimen. The other referred specimens include various skull bones including theparietals, aquadrate bone and the squamosal of at least one other turtle.[1][2]
Thegenus nameWarkalania combines the word "Warka" meaning "turtle", which Gaffney and colleagues attribute to a no closer specifiedAustralian Aboriginal language of the Queensland region, and "lania". Thesuffix -lania is a common component in the names of meiolaniid turtles, also used inMeiolania,Gaffneylania andNiolamia. The meaning of the term is however interpreted differently by various authors, partly due to the lack of an etymology given in the description ofMiolania. In the description ofWarkalania, the word is translated as "butcher" from theLatin "lanius", but other researchers point toOwen's description ofMegalania to argue that the suffix is actually derived from the Greek word for "to roam about".[3][4] Thespecies name ofW. carinaminor on the other hand simply translates to "small ridge", a reference to the fact that this genus didn't possess the large horns of other meiolaniids.[1][5]
The skull ofWarkalania is highlyankylosed, entirely obscuring the sutures between the individual skull bones. Consequently, Gaffney and colleagues describe the skull largely on the basis of the contacts between the overlying scutes, which are alphabetically labeled. The individual scale areas are separated by the presence of shallow grooves, similar toNinjemys andNiolamia and different from the raised ridges of some individuals ofMeiolania platyceps. One of the referred specimens preserves scale X, which is located in the central portion of the skull between the scales D and G, likely covering the back of thefrontal bones and the front of theparietal bones. Scale X is of similar size to the same scale inMeiolania platyceps fromLord Howe Island and bears the same kind of conical protrusion on its surface, though smaller than in the later species. While only a single scale X is present, the scales D and G are paired and appear to meet their respective opposite along the midline of the skull.[5] The actual contact between D and G might also be preserved, however it appears much weaker than any other scale contacts in this animal. Much like inMeiolania, scale D lies relatively flat against the skull rather than being notably convex as inNiolamia andNinjemys.[1]
The roof of thecranial cavity appears to be primarily composed of the parietal bones, with some contribution by the supraoccipital bones, and includes the region that would contain the remnants of the synotic tectum. This region however is not well enough preserved to show any differences to other turtles, which are typically rather uniform in the anatomy of this element.[1]
One of the key features that setsWarkalania apart from other meiolaniids is the shape of its horns. Meiolaniids are known for a series of horns located at the side and back of the skull, described as horns or scales A, B and C. Scale or horn A is located the furthest back of the three, while C is closest to the eyes. In other meiolaniid turtles horn C is either conical or, in the case of someMeiolania specimens, flat. InWarkalania meanwhile this element forms a horizontal ridge which continues onto horn B. While this second horn protrudes further to the side than horn C, it is still relatively short and ridge-like. Here the difference to other meiolaniids is very noticeable, as this horn is larger and conical inMeiolania, taking on an appearance similar to that of a cow's horn. There are specimens with small horn cores almost approaching the size seen inWarkalania, but none quite as small.Ninjemys andNiolamia also show very different horn shape. Both share some flattening withWarkalania, though to a lesser degree, but in these two taxa the horn appears much more like a spine that extends far beyond the rest of the head. Horn A is the furthest to the back of the three, but only incompletely known. Preserved elements suggest that it was approximately the size and shape of horn B, with some specimen showing more acute and others showing blunter edges. While only slightly larger than inMeiolania, it stands in stark contrast to the same area inNinjemys andNiolamia. Unlike in more derived forms, these two genera have A horns much more pronounced than any of the preceding scales to the point where they form massive shelves at the back of the head. While the A horns inWarkalania also form somewhat of a shelf, it is not nearly as pronounced as in these other taxa.[1][5] Overall this gives the skull ofWarkalania a less ornate appearance compared to the elaborate crests inNeiolamia andNinjemys or the distinctive bull-like horns ofMeiolania.
Gaffney and colleagues found thatWarkalania shared several features of its horns withMeiolania, including the size of the A horns, the fact that the B horns don't project laterally and the relatively flattened D scales. Considering these characters to besynapomorphies, they concluded thatWarkalania was the closest relative toMeiolaniato the exclusion of bothNinjemys andNiolamia.[1] This was later corroborated by additional studies[5][2] including the phylogenetic tree recovered by Sterliet al. in their description ofGaffneylania. Both results are shown below, with the more recent tree showing the varying positions thatGaffneylania was found in due to its incomplete nature.[4]
Besides the material that formsWarkalania, various other meiolaniid remains are also known from Riversleigh that cannot be confidently assigned to the genus due to the lack of overlapping material.[2] While most of these may or may not belong toWarkalania, at least one fragment of a horn A seems to indicate that a second meiolaniid was also present. It was initially attributed to an indetermined species ofMeiolania[1] and later assigned to Meiolaniidae indet. by Gaffney.[5]Warkalania is the oldest named genus of meiolaniid turtle from Australia, with other Oligocene and older remains being present in the form of isolated bones that are only identifiable as indetermined meiolaniids.[2][6]
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