Kambara is an extinct genus of mekosuchine crocodylian that lived during the Eocene epoch in Australia. It is generally thought to have been a semi-aquatic generalist, living a lifestyle similar to many of today's crocodiles. Four species are currently recognised, the sympatric Kambara murgonensis and Kambara implexidens from sediments near Murgon, the poorly preserved Kambara molnari from the Rundle Formation and the youngest of the four, Kambara taraina, also from the Rundle Formation. Kambara were medium-sized crocodilians, with mature specimens generally reaching lengths from .
Species of Kambara are easiest differentiated by the different occlusal patterns of their teeth. While K. murgonensis had an overbite similar to a modern alligator, both K. implexidens and K. taraina had interlocking dentition much more similar to true crocodiles. K. molnari, although incompletely known, seems to represent an intermediate form.
Despite plentiful fossils, the ecology of Kambara is poorly understood. The general shape of the skull, which is flattened, and the environment the fossils were deposited in, all suggest that they were semi-aquatic ambush predators like modern crocodilians. However, subtle differences in the postcranial remains, especially the limb bones, suggest that Kambara may have been better adapted at walking on land than the two crocodile species still inhabiting Australia today, the saltwater and freshwater crocodile. While this could suggest that it was faster on land than living crocodilians, it does not necessarily mean that it was terrestrial like some later mekosuchines are thought to have been. Another question regarding its ecology is posed by the coexistence of K. murgonensis and K. implexidens at Murgon. It is unclear how exactly these two species differed in their niche, but they did differ notably in their anatomy, with the latter being slightly more gracile and with interlocking teeth. It is also possible that the two species didn't coexist at all, but instead were driven together by drought.
As the oldest described and named mekosuchine, Kambara is considered an important piece in understanding the evolutionary history and origin of this group. Phylogenetic analyses recover it as one of the earliest diverging mekosuchines, but recent studies have commonly found other taxa like Kalthifrons or Australosuchus to be the oldest diverging. Other studies suggest that Kambara was no mekosuchine at all, but said results are not supported by all authors.
History and naming Remains of Kambara are exclusively known from the Paleogene of Australia, with the first remains found in rock units of what may be part of the Oakdale Sandstone Formation near the township of Murgon, Queensland. Although known for half a century, the material was first formally described by Ralph Molnar in 1982, who reported a lower jaw bone he believed to belong to a Miocene crocodylid. While noting similarities to other Australian crocodilians, notably Australosuchus (named nine years later), Molnar refrained from naming the material due to the fragmentary nature of the dentary.
The mid 1980s saw the discovery of mammal remains in the area, leading to increased study and revised dating. This new-found attention led to the discovery of several additional crocodilian fossils, including a largely complete skull (QM F21115) collected in 1991. The genus Kambara, with K. murgonensis as the type species, was finally established in 1993 by Paul Willis, Ralph Molnar and John D. Scanlon, who tentatively referred all Murgon crocodile fossils to this taxon. Even at this time it was noted that Kambara seemingly showed a high degree of variation among its fossils, in particular regarding the better preserved lower jaws. For this reason, it was suggested that the fossils could belong to multiple species of a single genus. This was confirmed when a second species, Kambara implexidens, was named three years later on the basis of new material collected from the same locality, with some of the previously recovered fossils now being assigned to this taxon.
A third species was named in 2005 in the form of K. molnari, although it stands out as the species with the least amount of available material. Like with the species before it, K. molnari was known for a while, with the type specimen found in 1991. However the material was not closely examined until the description of K. implexidens.
The most recent addition to this genus was K. taraina, named in 2009 by Lucas A. Buchanan. Although the type description is limited to the skull material (two crania and a lower jaw), which is easily comparable to the previously established species, Buchanan takes note of a "considerable amount" of postcranial remains. These remains were partly described in a thesis, but unlike the cranial material have not been formally published. An exception to this is the humerus, which was covered by Stein et al. and noted to differ greatly from modern forms. K. taraina has been recovered from the Rundle Formation, however, it was not sympatric with K. molnari, which stems from older stratigraphic layers.
In the type description the name Kambara is stated to derive from an Aboriginal word for crocodile, however, it is not specified which language in particular, only that it stems from the Queensland language group.
Species
K. implexidens The fossils of K. implexidens were found alongside those of K. murgonensis in the Boat Mountain area near Murgon, Queensland, indicating that the two species coexisted. Because of this, K. implexidens was not recognised as a distinct species until the discovery of nearly complete skulls in 1993, clearly showing major differences with the type species. Among these differences is the fact that the teeth of K. implexidens interlock, rather than forming an overbite. It is this fact that the species name derives from. Additionally, the skull of this species was relatively more gracile, as are this species' teeth.
K. molnari The third species of Kambara to be described, K. molnari is known from a partial mandible and several isolated remains all collected from the Rundle Formation. It is the least well preserved of all Kambara species, but has enough differences to the other forms to be considered distinct. Most notably, the teeth appear to be intermediate between the overbite of K. murgonensis and the interlocking dentition of K. implexidens and K. taraina. It was named in honour of Ralph Molnar for his consistent contributions to mekosuchine research.
K. murgonensis The type species of the genus, remains of K. murgonensis were part of the Tingamarra Fauna and have been found in areas overlying the Oakdale Sandstone Formation. It was named for Murgon, the closest township to the type locality. It was a moderately robust animal with a skull much wider than that of the contemporary K. implexidens.
K. taraina The youngest species of Kambara, it stems from the Kerosene Creek Member of the Rundle Formation, which means that it did not coexist with K. molnari. Like with K. implexidens, the teeth of K. taraina interlock and thus set it apart from the other known species. The species name derives from the dialect of the Darumbal people and simply means crocodile. This language was chosen as a proxy for that of the Bailai due to the links between the two cultures.
Description The skull of Kambara appears typically crocodilian, being roughly triangular with a rostrum that begins relatively narrow and continues to widen towards the back. The precise degree to which the snout tapers differs between species. K. murgonensis for instance is described as being moderately broad-snouted with a robust build. By comparison, the skull of K. implexidens, although still platyrostral, is notably slender compared to its contemporary relative. Similarly, the teeth are also more slender. The skull table of Kambara was relatively flat, lacking the raised edges seen in today's crocodiles, but instead multiple specimens across species show the presence of well developed pits just before the supratemporal fenestrae.
Ever since the first material of Kambara was described, it was recognised as a highly variable genus, retaining certain key traits but differing notably in others. As noted by Buchanan, the most prominent of these differentiating traits centre around the anatomy of the retroarticular process and the dentition. Regarding the retroarticular process, an important attachment site for the abductor musculature, K. taraina stands out as having a long, high and wide process, offering a greater surface area for the musculature to attach to. By comparison, the retroarticular processes in older species are less well developed, with that of K. molnari being described as long but narrow, while that of K. implexidens was short and low.
Toothrow and dentition
The toothrow across all four known species of Kambara differs significantly and is used to set them apart. Generally, three different morphologies can be observed, with the difference being primarily expressed through how the upper and lower toothrow interact with one another. As in many other crocodilians, the dental margin of Kambara appears wave-like, though it is more gentle than some other mekosuchines.
In K. murgonensis, the teeth of the upper jaw overlap those of the lower jaw, giving it an overbite similar to that of an alligator.
However, both K. implexidens and K. taraina differ significantly, as neither preserve fully overlapping dentition. Instead, distinct occlusal pits reveal that the teeth slid in between each other when the jaw was closed. This means that the teeth of these two species would interlock in a fashion much more similar to what is observed in species of Crocodylus. In K. implexidens, the first teeth of the lower jaw slide into very pronounced pits that pierce the bones of the upper jaw, emerging on its upper surface in front of the nostrils. The remaining premaxillary and maxillary teeth of K. implexidens clearly interlock with each other based on the presence of the aforementioned occlusal pits between the individual tooth sockets up to the ninth tooth of the upper jaw. After this point, the pits are located further medially. This is also confirmed by the pits present in the lower jaw, indicating interlocking teeth in some areas and a slight overlap further back in the jaw. The enlarged fifth tooth of the maxilla does however occupy more space, with its pit being set much further laterally than any of the others. Regardless, this clearly sets not just the skulls but also the dentaries apart from those assigned to K. murgonensis. In K. taraina the teeth clearly interlock in the premaxilla as well, however, while the first pair of dentary teeth also extend into the bone, they do not breach the dorsal surface as in K. implexidens. Regardless, much like those of K. implexidens, the dentition of K. taraina is characterised by being interlocking.
The third type is observed in K. molnari, which shows a somewhat intermediate condition between the overbite of K. murgonensis and the more extensive interlocking dentition of K. implexidens. Around the seventh and eight dentary teeth, as well as from the twelfth to seventeenth, the teeth appear to have interlocked. However, the tenth to twelfth teeth of the dentary are confluent, meaning they are too closely spaced to interlock with those of the upper jaw, necessitating an overbite in this area. This clearly sets it apart from all other species of Kambara and more closely resembles animals such as Borealosuchus and Diplocynodon.