Kambara
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''Kambara'' is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
mekosuchine Mekosuchinae is an extinct clade of crocodilians from the Cenozoic of Australasia. They represented the dominant group of crocodilians in the region during most of the Cenozoic, first appearing in the fossil record in the Eocene of Australia, and ...
crocodylian Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchian ...
that lived during the
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
epoch in
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
. 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 Murgon () is a rural town and Suburbs and localities (Australia), locality in the South Burnett Region, Queensland, Australia. In the , the locality of Murgon had a population of 2,220 people. Geography Murgon is in the region of Queensland ...
, 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 An alligator, or colloquially gator, is a large reptile in the genus ''Alligator'' of the Family (biology), family Alligatoridae in the Order (biology), order Crocodilia. The two Extant taxon, extant species are the American alligator (''A. mis ...
, both ''K. implexidens'' and ''K. taraina'' had interlocking dentition much more similar to true
crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large, semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term "crocodile" is sometimes used more loosely to include ...
s. ''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 The freshwater crocodile (''Crocodylus johnstoni)'', also known Common name, commonly as the Australian freshwater crocodile, Johnstone's crocodile, and the freshie, is a species of crocodile native to the northern regions of Australia. Unlike ...
. 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 In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
analyses recover it as one of the earliest diverging mekosuchines, but recent studies have commonly found other taxa like ''
Kalthifrons ''Kalthifrons'' is an extinct monospecific genus of mekosuchine crocodylian known from the Pliocene Tirari Formation of Australia. More specifically, ''Kalthifrons'' was recovered from the Mampuwordu Sand Member, which underlies the younger sedim ...
'' or ''
Australosuchus ''Australosuchus'' is an extinct monospecific genus of crocodylian belonging to the subfamily Mekosuchinae. The type species, type and only known species ''Australosuchus clarkae'' lived during the Late Oligocene and the Early Miocene in the Lake ...
'' 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 The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...
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 Murgon () is a rural town and Suburbs and localities (Australia), locality in the South Burnett Region, Queensland, Australia. In the , the locality of Murgon had a population of 2,220 people. Geography Murgon is in the region of Queensland ...
,
Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
. Although known for half a century, the material was first formally described by
Ralph Molnar Ralph E. Molnar is a paleontologist who had been Curator of Mammals at the Queensland Museum and more recently associated with the Museum of Northern Arizona. He is also a research associate at the Texas Natural Science Centre. He co-authored descr ...
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 ''Australosuchus'' is an extinct monospecific genus of crocodylian belonging to the subfamily Mekosuchinae. The type species, type and only known species ''Australosuchus clarkae'' lived during the Late Oligocene and the Early Miocene in the Lake ...
'' (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 In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
, was finally established in 1993 by
Paul Willis Paul Willis (born 1945) is a British social scientist known for his work in sociology and cultural studies. Paul Willis' work is widely read in the fields of sociology, anthropology, and education, his work emphasizing consumer culture, sociali ...
, 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 A thesis (: theses), or dissertation (abbreviated diss.), is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings.International Standard ISO 7144: D ...
, but unlike the cranial material have not been formally published. An exception to this is the
humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...
, 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 In biology, two closely related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter each other. An initially interbreeding population that splits into two or more distinct spe ...
with ''K. molnari'', which stems from older
stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...
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 The Tingamarra Fauna is associated with the early Eocene Murgon fossil site, and contains the earliest known non-flying eutherian, passerine, trionychidae turtles, mekosuchine crocodiles along with frogs, lungfish and teleost fish in Australia. Th ...
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 The Darumbal people, also spelt Darambal and Dharumbal, are the Aboriginal Australian people who have traditionally occupied Central Queensland, speaking dialects of the Darumbal language. and the terms are sometimes used interchangeably. Countr ...
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 Temporal fenestrae are openings in the Temple (anatomy), temporal region of the skull of some Amniote, amniotes, behind the Orbit (anatomy), orbit (eye socket). These openings have historically been used to track the evolution and affinities of re ...
. 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 An alligator, or colloquially gator, is a large reptile in the genus ''Alligator'' of the Family (biology), family Alligatoridae in the Order (biology), order Crocodilia. The two Extant taxon, extant species are the American alligator (''A. mis ...
. 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 ''Crocodylus'' is a genus of true crocodiles in the family Crocodylidae. Taxonomy The Genus, generic name, ''Crocodylus'', was proposed by Josephus Nicolaus Laurenti in 1768. ''Crocodylus'' contains 13–14 extant taxon, extant (living) species ...
''. 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 ''Borealosuchus'' (meaning "northern crocodile") is an extinct genus of crocodyliforms that lived from the Late Cretaceous to the Eocene in North America. It was named by Christopher Brochu in 1997 for several species that had been assigned to ...
'' and ''
Diplocynodon ''Diplocynodon'' is an extinct genus of eusuchian, either an alligatoroid crocodilian or a stem-group crocodilian, that lived during the Paleocene to Middle Miocene in Europe. Some species may have reached lengths of , while others probably did ...
''. 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. 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. The number is unknown for ''K. molnari'', while both ''K. implexidens'' and ''K. murgonensis'' possess 16 teeth in either maxilla. The lower jaw contains 17 or 18 dentary teeth.


Postcrania

Although a lot of postcranial material of ''Kambara'' has been found, most of said material remains undescribed with the exception of the
humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...
, 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. 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 each other. 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. 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
condyle A condyle (;Entry "condyle"
in
s, which makes the end look somewhat quadrilateral. 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 saltwater and freshwater crocodiles are nearly identical, but very different in ''Kambara''. Additional known elements of the postcranial skeleton include
shoulder blade The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...
s,
coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...
s, bones of the lower arm,
finger bone A finger is a prominent digit on the forelimbs of most tetrapod vertebrate animals, especially those with prehensile extremities (i.e. hands) such as humans and other primates. Most tetrapods have five digits (pentadactyly), Chambers 1998 p. 60 ...
,
pelvic bones The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the ilium, isch ...
, hindlimbs as well as multiple parts of the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
, including nearly the entire cervical series, several dorsal and tail vertebrae as well as
lumbar vertebrae The lumbar vertebrae are located between the thoracic vertebrae and pelvis. They form the lower part of the back in humans, and the tail end of the back in quadrupeds. In humans, there are five lumbar vertebrae. The term is used to describe t ...
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 A thesis (: theses), or dissertation (abbreviated diss.), is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings.International Standard ISO 7144: D ...
. Their general proportions seem to resemble modern crocodiles.


Size

''Kambara'' was a medium-sized crocodilian, smaller than the more recent mekosuchines ''
Baru ''Baru'', sometimes referred to as the cleaver-headed crocodile, is an extinct genus of Australian mekosuchine crocodilian. Its fossils have been found from various Late Oligocene and Miocene localities from across the Northern Territory and Que ...
'' and ''
Paludirex ''Paludirex'' (meaning "swamp king") is an extinct genus of mekosuchine crocodylian from the Pliocene and Pleistocene of Australia. A large and robust semi-aquatic ambush hunter capable of attaining lengths of up to , it was likely the top predat ...
''. The holotype specimen of ''K. implexidens'', which may be a subadult, has been estimated to have been , while a much larger mandible suggests lengths of up to . ''K. murgonensis'' is thought to have been of similar size, albeit with a more robust build. The same applies to ''K. molnari'', which was described as reaching lengths from .


Phylogeny

Similarities between a then unnamed ''Kambara'' and other extinct Australian crocodilians were noted since the description of the Murgon mandible in 1982. By the 1993 description, the idea of an endemic Australian crocodilian radiation was better established, at the time including ''Australosuchus'', ''Pallimnarchus'', ''Baru'' and ''
Quinkana ''Quinkana'' is an extinct genus of mekosuchine crocodylians that lived in Australia from about 25 million to about 10,000 years ago, with the majority of fossils having been found in Queensland. Four species are currently recognized, all of whic ...
''. Willis and colleagues took this a step further by including ''
Mekosuchus ''Mekosuchus'' is a genus of extinct Australasian mekosuchine crocodilian. Species of ''Mekosuchus'' were generally small-sized (less than long), terrestrial animals with short, blunt-snouted heads and strong limbs. Four species are currently ...
'' in this group and redefining Mekosuchidae as Mekosuchinae. No detailed phylogenetic analysis was conducted for ''Kambara murgonensis'' in 1993, but it was still recognised as the basalmost member of Mekosuchinae. Subsequent papers largely supported this suggestion, typically recovering ''Kambara'' as one of the earliest branching mekosuchines, although other taxa may be found as slightly more basal or on an even level as part of a
polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...
. For instance, a 2018 study by Lee and Yates, using genetic, morphological and stratigraphic data, found ''Kambara'' to be second only to ''Australosuchus'', whereas Ristevski ''et al.'' alternatively found ''Australosuchus'', ''
Kalthifrons ''Kalthifrons'' is an extinct monospecific genus of mekosuchine crocodylian known from the Pliocene Tirari Formation of Australia. More specifically, ''Kalthifrons'' was recovered from the Mampuwordu Sand Member, which underlies the younger sedim ...
'' or ''Kalthifrons'' and ''Kambara'' to be the basalmost forms. In both cases, ''Kambara'' was found to be a mekosuchine. Although Mekosuchinae as a monophyletic clade became a well established group in the years following ''Kambaras description, it is not without competing ideas. This in particular affects the position of ''Kambara''. In a study dealing exclusively with morphology, ''Kambara'' was still recovered as a mekosuchine, however, the overall make up of the clade was changed significantly. The study found ''Kambara'' in a basal position and including '' "Asiatosuchus" nanlingensis'', a
Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
crocodyloid no longer believed to be related to ''Asiatosuchus''. Additionally, both ''Quinkana'' and ''Australosuchus'' were not found to be mekosuchines in this analysis. Another, much more different placement was also shown in Ristevski ''et al''. In addition to the monophyletic Mekosuchinae recovered by the vast majority of their analysis, two more novel results were also found. These alternative topologies render Mekosuchinae paraphyletic, including the clade
Orientalosuchina Orientalosuchina is an extinct clade of alligatoroid crocodylians from Southeast Asia, Southeast and East Asia that lived between Maastrichtian and Eocene. The clade was named as the result of a 2019 study by Massonne ''et al.'' that included se ...
, but excluding ''Australosuchus'' and ''Kambara''. Instead, these trees recover ''Kambara'' as an early diverging crocodyloid and immediate sister to
Crocodylidae Crocodiles (family Crocodylidae) or true crocodiles are large, semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term "crocodile" is sometimes used more loosely to include all extant membe ...
. However, these results are a minority within the team's analysis and even then nodal support for paraphyletic Mekosuchinae is considered to be poor by the authors. Initially, it was thought that ''Kambara murgonensis'' was the basal most species of the genus, which would have rendered the overbite characteristic for this species the ancestral condition. However, the discovery of ''Kambara molnari'' with its intermediate form, various undetermined crocodilians of the time with interlocking teeth and phylogenetic analysis all seem to suggest that the genus actually began with interlocking dentition, acquiring the overbite later. Recent phylogenies consistently point towards ''K. implexidens'' as the basal most species of ''Kambara'', although ''K. molnari'' is typically removed due to the limited nature of its material.


Paleobiology


Ecology and diet

With its appearance generally resembling today's crocodiles, in particular the flat, platyrostral snout, it is generally thought that ''Kambara'' was a semi-aquatic generalist. 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 proposed that an overbite in crocodilians could serve a similar function as the carnassial teeth of mammalian predators, being used to break and slice. This 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. Buchanan speculated on the potential implications for the intermediate dentition seen in ''Kambara molnari''. Buchanan argued 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. 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. Direct evidence for predator prey interaction is rare for ''Kambara'', but does exist. Specifically, Buchanan's thesis describes 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 The turtle shell is a shield for the ventral and dorsal parts of turtles (the Order (biology), order Testudines), completely enclosing all the turtle's vital organs and in some cases even the head. It is constructed of modified bony elements such ...
, 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, behaviour 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 Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who i ...
. 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 food source, were fed on at least occasionally, it does not necessarily mean that ''Kambara'' was specialised for hunting them.


Locomotion and lifestyle

As indicated by aspects of the skull shape, namely the resemblance to modern semi-aquatic ambush hunters, ''Kambara'' is typically regarded as 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 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 the humerus, which is known from an undetermined 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 high walk, 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 could 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 high walking at a greater speed than the crocodiles found in Australia now. The pelvic bones of ''Kambara'', based on material collected from Tingamarra, were described by Stein and colleagues in 2017 and feature a robust ilium similar to what is seen in modern alligators and gharials, but with notably shallower peduncles (the parts of the ilium that connect to the other bones of the hip). The joint for the femur is shallowly concave and the postacetabular process, the section of the ilium behind this joint, lacks the constriction seen in modern crocodiles. Otherwise the ilium does not differ significantly for what is seen in other Eusuchians. This morphotype is designated "pelvic form one" by Stein and colleagues and differs in its morphology from fossils found in the Rundle Formation that may pertain to another species of ''Kambara'' or possibly a different genus altogether. Assuming the former, the Rundle fossils ("pelvic form two") feature much deeper peduncles which are shared with younger mekosuchines from the Oligocene and Miocene, but lack the specific expansion of the pubic peduncle seen in later taxa. Additionally, "pelvic form two" displays a knob situated atop the postacetabular crest which appears to be convergently developed with the constriction of modern crocodylids. 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 Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...
, 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 The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
rauisuchians "Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilians ...
and
aetosaurs Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...
, which would allow for hinge-like movement of the
knee In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...
, 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. 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 advantageous for swimming. 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.


Sympatry

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. In their 1996 description of ''K. implexidens'', Salisbury 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 A caiman ( (also spelled cayman) from Taíno language, Taíno ''kaiman'') is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within the Alligatoridae family (biology), family, the other being alligators. ...
. One possible explanation may be found in
taphonomy Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek language, Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientis ...
. Salisbury 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. Somewhat similar circumstances may have led to the creation of the bonebed that preserves the fossils of ''K. taraina''. 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.


Nesting

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.


Pathologies

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 rotating due to the continued use of the limb. NMV P227802 on the other hand represents a heavily altered humerus, characterised by being swollen and containing numerous sinuses filled with small bone fragments, signs of
osteomyelitis Osteomyelitis (OM) is the infectious inflammation of bone marrow. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The feet, spine, and hips are the most commonly involved bones in adults. The cause is ...
. 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 The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...
, 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. 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''.


Paleoenvironment

Both ''K. murgonensis'' and ''K. implexidens'' were a part 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 turtle Trionychidae is a family of turtles, commonly known as softshell turtles or simply softshells. The family was described by Leopold Fitzinger in 1826. Softshells include some of the world's largest freshwater turtles, though many can adapt to li ...
s, meiolaniid turtles and madtsoiid snakes, which inhabited a
lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...
environment. Fish are also known from this fauna, namely
lungfish Lungfish are freshwater vertebrates belonging to the class Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, inc ...
and
teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...
s, although none of them were especially large, seemingly maxing out at in length. This would suggest that the waters of this locality were rather shallow, which could indicate that it was a
billabong In Australian English, a billabong ( ) is a small body of water, usually permanent. It is usually an oxbow lake caused by a change in course of a river or creek, but other types of small lakes, ponds or waterholes are also called billabongs ...
. Furthermore, it is known that the locality was subject to cyclical wet and dry seasons. The Rundle Formation, which was home to both ''K. molnari'' and ''K. taraina'', on the other hand is thought to represent lagoonal
mud flats Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal f ...
. 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. Although so far only known from two sedimentary basins, each preserving two species, ''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 crocodile The freshwater crocodile (''Crocodylus johnstoni)'', also known Common name, commonly as the Australian freshwater crocodile, Johnstone's crocodile, and the freshie, is a species of crocodile native to the northern regions of Australia. Unlike ...
s inhabit most of northern Australia.


References

{{Taxonbar, from=Q5230226, from2=Q20718518 Mekosuchinae Eocene crocodylomorphs Crocodiles of Australia Prehistoric pseudosuchian genera