Kambara

K. murgonensis had an overbite, much like modern alligators (top), whereas K. implexidens and K. taraina had interlocking teeth similar to that of a crocodile (bottom).

The toothrow across all four known species of Kambara differs significantly and is used to set them apart. Generally, three different morpholgies 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, tho it is more gentle than in 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.[1]

However, both K. implexidens[2] and K. taraina[5] 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 till 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.[2] 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 characterized by being interlocking.[5]

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.[3]

All teeth are slightly compressed side to side and possess distinct carinae (cutting edges), but are not ziphodont like in some later mekosuchines. Both this compression and the development of the edges is strongest towards the front of the jaw and gradually grows weaker further back in the toothrow, while also becoming more bulbous and peg-like.[2][5] While the number of premaxillary teeth is consistent, the amount of teeth in the maxilla and dentary varies. K. taraina has the lowest number of teeth in the maxillae (and thus throughout the upper jaw) with only 14 teeth on either side.[5] The number is unknown for K. molnari, while both K. implexidens and K. murgonensis possess 16 teeth in either maxilla.[1][2] The lower jaw contains 17 [2][3] to 18 dentary teeth.[5]

Size comparisson of Kambara implexidens

Although a lot of postcranial material of Kambara has been found, most of said material remains undescribed with the exception of the humerus, which had been studied and compared to the equivalent bones in saltwater and freshwater crocodiles. In both of these modern forms, the deltopectoral crest is offset medially from the lateral margin of the shaft. The apex of the crest is also directed medially, which essentially places it just above the midline of the shaft. All in all, the deltapectoral crest sits at a right angle relative to the ventral face of the humeral shaft. However, in Kambara things are notably different. Neither the deltapectoral crest nor its apex are directed medially, with the crest as a whole being just above the lateral margin of the shaft and the apex being directed ventrally. The right angle formed by the crest and shaft however remains. This is associated with the torsion of the shaft. In the modern forms, the humerus is given a sigmoid shape by the fact that the articulating surfaces, the parts of the bone that connect to the joints, are at an angle to another. The humerus of Kambara meanwhile is much straighter, with both surfaces being level to each other. As a consequence, the shaft of the humerus in Kambara is not lengthened as is the case in modern Australian crocodiles.[4]

There are also differences concerning the distal end, the end towards the toes rather than the hip. Here, modern Australian crocodiles have flat medial and lateral surfaces bordering the condyles, which makes the end look somewhat quadratical. In Kambara, the dorsal and ventral faces are compressed, which in turn lengthens the medial and lateral condyles, while also directing these surfaces towards the midline. The profile of the distal end is subsequently hexagonal. Profile and size of the medial and lateral condyles in salties and freshies are nearly identical, but very different in Kambara.[4]

Additional known elements of the postcranial skeleton include shoulder blades, coracoids, bones of the lower arm, finger bone, pelvic bones, hindlimbs as well as multiple parts of the spinal cord, including nearly the entire cervical series, several dorsal and tail vertebrae as well as lumbar vertebrae in articulation. Ribs and chevrons are likewise known. Most of this material however have not seen formal publication and are only described in Buchanan's PhD thesis. Their general proportions seem to resemble modern crocodiles.[6]

Kambara was a medium-sized crocodilian, noted to have been smaller than the more recent mekosuchines Baru and Paludirex.[1] The holotype specimen of K. implexidens, which may be a subadult, has been estimated to have been 2.5 m (8 ft 2 in), while a much larger mandible suggests lengths of up to 3.5 m (11 ft). K. murgonensis is thought to have been of similar size, albeit with a more robust build.[2] The same applies to K. molnari, which was described as reaching lengths from 3–4 m (9.8–13.1 ft).[3]

The skull of an indetermined Kambara species at the Melbourne Museum. It broadly resembles modern crocodiles.

With its appearance generally resembling today's crocodiles, in particular regarding the flat, platyrostral snout, it is generally thought that Kambara was a semi-aquatic generalist.[3][5] One method to determine the details of such a lifestyle may be found in the way the teeth of these crocodilians occlude with another, although the specifics of this are still poorly understood. One hypothesis by Charles C. Mook proposes that an overbite in crocodilians may serve a similar function as the carnassial teeth of mammalian predators, being used to break and slice. The same line of thought would then suggest that interlocking dentition may be better suited when having to restrain large, struggling prey, requiring greater force that would be more evenly spread out across the toothrow.[5]

Following this interpretation, Buchanan speculates on the potential implications for the intermediate dentition seen in Kambara molnari. Buchanan argues that the confluent tooth sockets of K. molnari and their position in the lower jaw may have increased and focused the force of the bite in a smaller area, enhancing their ability to puncture and drawing further parallels to mammalian carnassials.[5]

Another important factor that differentiates the ecology of the various species is the development of the retroarticular process. The retroarticular process serves as an attachment site for important jaw adductor and abductor muscles and is subsequently of great importance in capturing and subduing prey. Among Kambara species, K. taraina stands out as having the most strongly developed processes, which correlates with larger pterygoid muscles and a stronger bite than that of its older relatives. This may suggest that K. taraina was capable of taking on larger, more terrestrial prey items, whereas older species fed on smaller animals. Furthermore, multiple species of Kambara show well defined attachment sites for musculature used to hold and crush prey, an activity the pterygoid would not be involved in. This collaboration between different muscle groups would allow K. taraina to attack large prey, before restraining and crushing it.[5]

A modern Alligator "juggling" a turtle.

Direct evidence for predator prey interaction is rare for Kambara, but does exist. Specifically, Buchanan's thesis figures a chelid turtle from the same locality as Kambara taraina which appears to have been attacked by a crocodile. The fossil, a nearly complete plastron, shows several circular pits arranged in a linear fashion, which is in line with the bite marks left by a crocodilian. The amount of tooth marks present on the plastron indicates that the individual that tried to eat the turtle bit it several times, behavior that would match the "juggling" performed by modern crocodiles. "Juggling" in this case describes the act of repeatedly biting prey like turtles in order to change its orientation, helping to align it either with the teeth or to make it easier to swallow. However, it is believed that in this instance the crocodile was overambitious, as the plastron's width and thickness would be too great for the average Kambara individual to manage. Subsequently, the turtle was let go or escaped the crocodile, allowing the bite to somewhat heal. Despite this however, the turtle later died from infection and necrosis. A costal scute of what is thought to be the same individual has also been recovered, also showing signs of a crocodile bite, some healing and infection. While this suggests that turtles, which were a readily available foodsource, were fed on at least occasionally, it does not necessarily mean that Kambara was specialised for hunting them.[6]

As indicated by aspects of the skull shape, namely the resemblance to modern semi-aquatic ambush hunters, Kambara is typically regarded as just such a semi-aquatic animal, which would be supported by the environment it was found in. While the skull displays no particular adaptations that would suggest any degree of terrestriality, as is for example the case in mekosuchines like Quinkana and Trilophosuchus, some elements of the postcranium suggest a more complex lifestyle.

Most postcranial material remains unpublished, the exception being humerus, which is known from an indetermined species found at the Murgon locality (possibly K. implexidens). Based on the specific anatomy of the deltapectoral crest of Kambara, the upper forelimb may have been able to swing with much greater force, while also providing greater stability against gravity and thus improving the animals ability to perform the crocodilian highwalk, the mode of locomotion during which crocodiles lift their body off the ground. Additionally, these factors may also increase stride-length and walking speed. The change to the deltapectoral crest may also have advantages for swimming, allowing the limbs to better resist the drag during the recovery stroke. Furthermore, the shortening of the humeral shaft may have also come with advantages, although this is less clear due to the fact that no material of the lower forelimb has been described yet, making it ambiguous how the musculature of the lower and upper arm would connect. Regardless, it is possible that the shortening could have brought the musculature into a more proximal position, which would mean that the lower limbs would have exerted less force while walking or swimming, allowing the animal to swing the lower limb faster. The range of motion for the limbs of Kambara is an additional point of consideration. The olecranon fossa and the articular surface of the humerus both suggest a wider range of motion than in saltwater and freshwater crocodiles, but especially the former would require the description of the lower arm to verify this conclusion. The increased range of motion is more certain based on the articular surface, and would suggest that Kambara would have been capable of highwalking at a greater speed than the crocodiles found in Australia now.[4]

An American crocodile performing the highwalk.

Some additional discussion of other postcranial material can be found in Buchanan's PhD thesis, which also contained the later published description of Kambara taraina. Here, Buchanan notes that Kambara does indeed possess some traits associated with terrestrial locomotion, however, they are generally not as well developed as one would expect from a fully terrestrial animal. Among these is the development of the ilium and the astragalus, the later of which only differing slightly from saltwater crocodiles and with only limited mobility of the ankle. The possibility that Kambara possessed a "fibular condyle" similar to Triassic rauisuchians and aetosaurs , which would allow for hinge-like movement of the knee,is mentioned, but cannot be fully confirmed due to the poor preservation of that particular element. Simultaneously, Buchanan notes that the skeletal is not any more specialised in aquatic life than that of modern crocodilians either, suggesting a similarly generalized semi-aquatic mode of life. Finally, it is pointed out that the Kambara taraina bonebed was likely the result of mass death caused by drought, something that would be less likely to affect an animal less dependent on water.[6]

Overall, Kambara seemingly displays a combination of adaptions for both semi-aquatic and somewhat terrestrial life, with the limbs suggesting a superior ability to walk on land relative to modern forms, whereas the shape and form of the skull are indicative of a semi-aquatic ambush hunting lifestyle not unlike the one seen in most extant crocodilians, while certain adaptations of the arm are also adventageous for swimming.[4] Buchanan interprets this to mean that while not being a true terrestrial crocodilian, Kambara may have been much more adapt at leaving the water than members of the genus Crocodylus. However it is also possible that this was no adaption towards movement on land, but rather used for bottom-walking in shallow waters, a habit that could have led to more terrestrial mekosuchines later during the Cenozoic.[6]

One particular question that was raised in the wake of the description of Kambara implexidens was how two rather similar species of the same genus could coexist as closely as it did with Kambara murgonensis. Both species are known from a single fossil site near Murgon, with the remains being intermingled with one another, suggesting they occurred in the same environment at the time of their deaths. Morphologically, both species share a variety of similarities and differences. Both are semi-aquatic animals with platyrostral snouts and both are believed to have reached similar lengths. The two however differ in that K. implexidens was slightly more gracile both in regards to its skull and teeth in addition to the different ways the teeth occluded.[2]

An example for modern sympatric crocodilians includes American alligators and American crocodiles.

In their 1996 description of K. implexidens, Salisburry and Willis argue that the difference in head shape was of little value to their respective ecologies. They suggest that the differences are so minor that they are effectively still the same ecomorph, which they determine may have been similar to that of today's caimans. One possible explanation may be found in taphonomy. Salisburry and Molnar suggest that, if not ecologically different, the two species may have differed in their habitat preferences and possibly wouldn't have crossed paths under normal circumstances. They point out that the fossil site near Murgon shows signs of having undergone both dry and wet periods, with the former greatly reducing the present bodies of water. A drought could have driven one of the species from their natural habitat and forced them to look for sanctuary in water that would otherwise be home to the other form.[2] Somewhat similar circumstances may have led to the creation of the bonebed that preserves the fossils of K. taraina.[6]

It is also possible that the animals were typically kept apart not by preferences unique to the two species but through preferences based on size, age and sex. In modern saltwater crocodiles, the ranges of nesting females and juveniles often overlap upriver or in areas of denser vegetation, whereas large, adult males prefer deeper open waters. This could explain why the Murgon site primarily preserves large individuals alongside some remains of eggs and hatchlings, with only few animals of intermediate size. Such subadults may have lived largely separate from adults in so called "stockyards", as they would pose a threat to small hatchlings while themselves being threatened by cannibalistic adult males. This could explain why the Murgon site primarily preserves large individuals alongside some remains of eggs and hatchlings, with only few animals of intermediate size.[2]

Little has been published on the potential nesting behavior of Kambara other than the fact that the Murgon fossil site preserves not just the remains of large, presumably adult Kambara, but also at least two hatchlings and some fragmentary egg shells. This may suggest that the Murgon site could have been used by Kambara to nest.[2]

Crocodiles will often attack their opponents' limbs during intraspecific combat.

In addition to the many well preserved bones that show no signs of non-taphonomic distortion, there is plentiful material that shows clear signs of injury. This material, covered in Buchanan's thesis, includes a femur that has suffered a comminuted fracture and subsequently formed a callus, a growth of cancellous bone, during healing. Another specimen represents a series of metatarsals, toe bones, which were fractured during the animal's life and then fused into a single element as it healed, with the individual elements roating due to the continued use of the limb. NMV P227802 on the other hand represents a heavily altered humerus, characterized by being swollen and containing numerous sinuses filled with small bone fragments, signs of osteomyelitis. Based on the advanced state of the infection, it is thought to have been chronic and to have been affecting the individual for years. The final pathological specimen noted by Buchanan is a highly deformed fibula, which in some areas is twice as wide as it should be. The reason for the extreme deformation of this particular specimen is not entirely clear, but could have been caused by one of several possible tumorous conditions.[6]

At least some of these pathologies are explainable through intraspecific combat, meaning that individual Kambara attacked members of their own species. Such behavior is commonly seen in extant crocodilians and even recorded in a multitude of fossils. Crocodilians often attack limb bones, which would explain the fractures seen on the pathological humerus and metatarsals. The high number of individuals present at the Kambara taraina bonebed lends itself well to this hypothesis as well, with the crowded nature of the area leading to increased aggression between its residents. In both cases, the injured animal survived and healed. The osteomyelitis of NMV P227802 meanwhile was caused by a bacterial infection causing necrosis and bone death. While it is unclear how the animal was infected, it is possible that the area was exposed by an injury, possibly from the attack of another Kambara.[6]

Both K. murgonensis and K. implexidens were apart of the Tingamarra Fauna, which also included a variety of terrestrial and aquatic animals. Mammals are represented through various marsupials, while the reptile fauna includes softshell turtles, meiolaniid turtles and madtsoiid snakes, which inhabited a lacustrine environment.[1] Fish are also known from this fauna, namely lungfish and teleosts, although none of them were especially large, seemingly maxing out at 100 mm (3.9 in) in length. This would suggest that the waters of this locality were rather shallow, which could indicate that it was a billabong.[4] Furthermore, it is known that the locality was subject to cyclical wet and dry seasons.[2]

The Rundle Formation, which was home to both K. molnari and K. taraina, on the other hand is thought to represent lagoonal mud flats.[3] Unlike with the species of the Tingamarra Fauna, the Rundle species were not sympatric, with K. taraina stemming from the younger deposits of the Kerosene Creek Member instead of the Brick Kiln Seam.[5]

Although so far only known from two sedimentary basins, each preserving two species,[5] Kambara may have been much more widespread than currently known. Holt, Salisbury and Willis propose that Kambara may have been found across many of the inland waterways of Queensland, possibly even all of eastern Australia where temperatures allowed for the presence of crocodilians. If this was the case, then the distribution of Kambara may be similar to how today's freshwater crocodiles inhabit most of northern Australia.[3]