Kalthifrons
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''Kalthifrons'' 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 ...
monospecific In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...
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 ...
known from the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Tirari Formation The Dhirari (or Dirari or Tirari) were an indigenous Australian people of the state of South Australia. They are not to be confused with the Diyari people, though the Dirari/Dhirari language (now extinct) was a dialect of the Diyari language. N ...
of
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 ...
. More specifically, ''Kalthifrons'' was recovered from the Mampuwordu Sand Member, which underlies the younger sediments of the Pompapillina Member. This is significant, as the latter preserves some of the earliest records of the genus ''
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 Australia, which would eventually go on to replace mekosuchines. It is currently unclear whether or not the Tirari ''Crocodylus'' directly outcompeted ''Kalthifrons'' or simply moved into the region after the niche was left empty by the extinction of the local mekosuchines. Should the later be the case, then ''Kalthifrons'' may have simply been the victim of
global cooling Global cooling was a conjecture, especially during the 1970s, of imminent cooling of the Earth culminating in a period of extensive glaciation, due to the cooling effects of aerosols or orbital forcing. Some press reports in the 1970s specu ...
and
aridification Aridification is the process of a region becoming increasingly arid, or dry. It refers to long term change, rather than seasonal variation. It is often measured as the reduction of average soil moisture content. It can be caused by reduced preci ...
. A point in favour of the competition hypothesis is that both ''Kalthifrons'' and the Tirari ''Crocodylus'' have broadly similar skull forms, with both being interpreted as generalist semi-aquatic predators much like many of today's crocodiles. Though far from large, ''Kalthifrons'' was nonetheless bigger than many other mekosuchines such as ''
Trilophosuchus ''Trilophosuchus'' ("triple crest crocodile") is an extinct genus of mekosuchine crocodilian from Australia. Its fossils have been found at the Ringtail Site in the Australian Fossil Mammal Sites (Riversleigh), Riversleigh World Heritage Area (no ...
'' and ''
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 ...
''. The genus is
monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...
, meaning it contains only a single species, ''Kalthifrons aurivellensis''.


Discovery and naming

The remains of ''Kalthifrons'' were discovered on the western shores of
Lake Palankarinna __NOTOC__ The Lake Ngapakaldi to Lake Palankarinna Fossil Area is a group of fossil sites located in the Australian state of South Australia within the Tirari Desert in the north-eastern part of the state's Far North region. The group has an ...
in
South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...
's
Lake Eyre Basin The Lake Eyre basin ( ) is a drainage basin that covers just under one-sixth of all Australia. It is the largest endorheic basin in Australia and amongst the largest in the world, covering about , including much of inland Queensland, large port ...
. The
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
(specimen ''SAM P35062''), consisting of a
cranium The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...
and two mandibular rami, was recovered from the Mampuwordu Sand Member of the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Tirari Formation The Dhirari (or Dirari or Tirari) were an indigenous Australian people of the state of South Australia. They are not to be confused with the Diyari people, though the Dirari/Dhirari language (now extinct) was a dialect of the Diyari language. N ...
. The fossil was discovered upside down, causing the area of the
palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sep ...
to be exposed to the elements and thus damaging it significantly. On top of this weathering of the surface, the fossil underwent significant compression during preservation, causing it to appear much flatter than it would have in life. The Golden Fleece Locality, where the fossils were discovered, also yielded a variety of isolated remains, mostly consisting of teeth, osteoderms and vertebrae. While the lack of overlap means that none can be definitely proven to have been those of ''Kalthifrons'', the fact that the locality is thought to have been a mass death site has been used to argue that they likely represent a single species. As a result of this, the material was tentatively referred to ''Kalthifrons''. The generic name derives from the
Dieri The Diyari (), alternatively transcribed as Dieri (), is an Indigenous Australian group of the South Australian desert originating in and around the delta of Cooper Creek to the east of Lake Eyre. Language Diyari is classified as one of the ...
word for "spear" (kalthi) and frons, meaning forehead, a name chosen in reference to the animal's elongated frontal process. The species epithet is a combination of the Latin "aurum" for gold and "vellus" meaning fleece, chosen to reflect the locality where the fossil has been discovered.


Description

''Kalthifrons'' possessed a relatively short and roughly triangular skull that broadly resembles that of today's crocodiles, indicating that it was a generalist predator. Additionally, the snout is described as platyrostral, effectively meaning that it was flattened. However, the precise degree to which this applies is difficult to determine as the holotype skull was badly crushed during preservation, greatly exaggerating its form in profile view. Adam Yates and Neville Pledge speculate that the skull of ''Kalthifrons'' may have been moderately deep, making it similar to that of ''Baru,'' given that the former preserves a distinct swelling above the fifth maxillary tooth that would be absent in an animal with a very deep (altirostral) skull similar to ''
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 ...
''. The tip of the snout appears to have been differently proportioned in ''Kalthifrons'' when compared to other mekosuchines. The
premaxillae The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals has ...
are narrow and the external nares are longer than they are wide, contrasting with those of its closest relatives. The nares themselves are almost entirely surrounded by the premaxillae, save for a small section where the
nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...
s contribute. The region where the premaxilla transitions to the maxilla is marked by a prominent notch where the jaw is constricted to make space for the fourth tooth of the lower jaw, something commonly seen in crocodilians. While this condition can be observed in a variety of mekosuchines, it does help distinguish ''Kalthifrons'' from ''Australosuchus'', as in the latter the fourth dentary tooth slides into a nearly enclosed hole in the bone rather than an open notch. Behind this notch, the maxillae swell laterally, forming a boss around the location where the fifth maxillary tooth would sit. The eyesockets, also known as orbits, are located comparably far towards the front to the skull, at least relative to other crocodilians. This condition is similar to that found in ''Baru darrowi'', and is present due to the fact that the front of the orbits forms a narrow point that extends up until the eleventh tooth of the maxilla. The orbits are also noted for being large, with their individual diameters being much greater than the distance between them. Overall the orbits have an uneven shape, with the anterior segment being pointed, while the main part of the orbits is more circular in shape. This shape is partially caused by how the prefrontals contribute to the orbital margin, as these bones form prominent flanges that extend into the orbits. The
lacrimal bone The lacrimal bones are two small and fragile bones of the facial skeleton; they are roughly the size of the little fingernail and situated at the front part of the medial wall of the orbit. They each have two surfaces and four borders. Several bon ...
s, which are situated before the prefrontals, are elongated and irregularly triangular in shape. Thick ridges extend from the lacrimal's contribution to the orbits until the pointed tip of the bones. These ridges are the result of a distinct change in slope, unlike in the
Saltwater Crocodile The saltwater crocodile (''Crocodylus porosus'') is a crocodilian native to saltwater habitats, brackish wetlands and freshwater rivers from India's east coast across Southeast Asia and the Sundaland to northern Australia and Micronesia. It ha ...
, which has preorbital ridges raised above the rest of the skull. In general, the ridges seen on ''Kalthifrons'' resemble those of ''
Baru wickeni ''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 ...
''. The most characteristic feature of ''Kalthifrons'', and the one it was named for, is its
frontal bone In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...
. As is typical for crocodilians, the frontal is divided into two segments, the posterior one of them is broad and makes up the space between the
eyesocket In anatomy, the orbit is the cavity or socket/hole of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is ...
s and part of the skull table. The anterior process meanwhile is generally long and slender, however, in ''Kalthifrons'' this is taken to an extreme as the anterior process extends much further down the rostrum as is typical, accounting for about 64% of the frontal's entire length. Additionally, the space between the eyes is much wider than in ''Australosuchus,'' owing to the greater width of the posterior section of the frontal. The skull table is flat and trapezoid in shape with elliptical
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 ...
similar to those found in ''
Trilophosuchus ''Trilophosuchus'' ("triple crest crocodile") is an extinct genus of mekosuchine crocodilian from Australia. Its fossils have been found at the Ringtail Site in the Australian Fossil Mammal Sites (Riversleigh), Riversleigh World Heritage Area (no ...
''. The fenestrae are widely spaced, much wider than each fenestra is long, with the interfenestral bar being formed entirely by the parietal. The massive distance between the fenestrae is unusual for mekosuchines and only one other species is noted for having similar proportions, that being an unspecified species of ''Baru'' from the Alcoota fossil site. Though small, the fenestrae are largely unobscured by the surrounding bones overhanging it, with only the parietal slightly overhanging the rear-most corner of the fenestrae. The
supraoccipital The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lobes of the cere ...
, though exposed on the dorsal surface like in the majority of mekosuchines, is narrow, and only makes up a small part of the skull table. The supraoccipital is described as semilunate in shape, whereas it is triangular in most other mekosuchines. Since the mandibular remains found alongside the holotype skull are poorly preserved, little information could be gathered from them. The most notable aspect of the mandible is that the flat underside is offset from the side by a nearly 90° bend. This is most similar to mandibles that have been referred to ''
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 ...
''. Only a handful of postcranial remains have been found, including
vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
that provide no further valuable information. Some
osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of Extant taxon, extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, Temnospondyli, ...
are also known from the Golden Fleece locality, though it is unsure if they belonged to ''Kalthifrons''. They range in shape from square to rectangular, with keels that range from being low to tall. As in other crocodilians, they are ornamented with a series of pits, save for the region where the osteoderms overlap with one another.


Dentition

Given the extensive damage that the underside of the holotype of ''Kalthifrons'' suffered, the exact number of teeth is difficult to determine. Three teeth were preserved in the left premaxilla, with the missing portion before them indicating more were present. However, it remains uncertain whether this region housed one or two teeth, meaning the number of premaxillary teeth could be either four or five. The case of the maxillary teeth is similar, with one side preserving 10 tooth positions with space for more and the other indicating a minimum of 11 teeth. The true number of maxillary teeth was likely higher, but erosion makes it impossible to determine this fact until better material is found. The teeth towards the front of the maxilla are closely spaced, which may suggest that there was too little space for the teeth of the upper and lower jaw to interlock. Again, this may change with the discovery of better material, as the type specimen does not preserve the bone that would be situated between the individual teeth. Regardless of the state of the early maxillary teeth, some degree of interlocking was present in ''Kalthifrons'' based on the presence of a large reception pit located between the sixth and seventh teeth. Even less is known about the tooth crowns, of which only three are known. All were part of the posterior teeth of their respective sections and, accordingly, are short, blunt and broadly rounded. The teeth are compressed side to side and have smooth cutting surfaces. However, there are some better preserved teeth that were collected from the same locality as the holotype. While referral of these teeth remains tentative, Yates and Pledge argue that the nature of the Golden Fleece locality, having been a dried up pool of low-diversity, makes it very likely that they too belonged to ''Kalthifrons''. These teeth correspond well to more anterior dentition, being taller and more pointed, but less compressed, with a gentle inward curvature.


Size

The preserved portions of the skull of ''Kalthifrons'' measure around long from the broken snout tip to the remains of the
quadrate bone The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids ( reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms up ...
. While this is far from the size of larger mekosuchines like ''Baru'' and ''Paludirex'', ''Kalthifrons'' still exceeded the total body length of "dwarf forms" such as ''
Volia ''Volia'' is an extinct monospecific genus of mekosuchine crocodylian closely related to '' Mekosuchus'' and '' Trilophosuchus''. ''Volia'' is known from a collection of largely fragmentary remains including skull bones and limbs recovered fr ...
'', ''
Trilophosuchus ''Trilophosuchus'' ("triple crest crocodile") is an extinct genus of mekosuchine crocodilian from Australia. Its fossils have been found at the Ringtail Site in the Australian Fossil Mammal Sites (Riversleigh), Riversleigh World Heritage Area (no ...
'' and ''
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 ...
''.


Phylogeny

Early research on ''Kalthifrons'' struggled with its relationship to other mekosuchines, though Yates and Pledge ruled out the possibility that ''Kalthifrons'' could belong to any other
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of crocodilian, making a position as a mekosuchine the most probable scenario. In their analysis, ''Kalthifrons position varied greatly between trees, with its uncertain nature creating a large
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 ...
at the base of the group that contains Mekosuchinae minus ''
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 ...
'' (which was recovered as a
sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
to all other taxa). The different positions occupied by ''Kalthifrons'' in their results varied between it being a very basal animal outside of the clade formed by ''Kambara'' and all other mekosuchines to it being a derived member of Mekosuchini, the clade containing ''Quinkana'', ''Baru'' and the dwarf forms. Its shifting position was explained as being the result of the poor preservation, subsequently limited number of usable characters and the incongruent results these characters yielded. However, later studies did recover better resolved trees that somewhat clarified the position of this animal within the family. Lee and Yates (2018) recovered ''Kalthifrons'' as a close relative of ''Pallimnarchus'' and ''Baru'', two other mekosuchines that exhibit a more typical crocodilian morphology. An even more recent paper by Ristevski and colleagues from 2023 proposes a different placement. In their results, ''Kalthifrons'' typically occupies a very basal position within Mekosuchinae alongside ''Australosuchus'' and ''Kambara'', akin to some of the results found by Yates and Pledge. More specifically, one of their results suggested that ''Kalthifrons'' may have been the basalmost member of the group, whereas another saw ''Kalthifrons'' share this placement with ''Kambara''.


Paleobiology

Based on its platyrostral, short and triangular skull, ''Kalthifrons'' was most likely a semi-aquatic generalist predator living in the waterways of what is now South Australia, sharing its habitat with turtles such as '' Elseya sp. (cf. E. lavarockorum)''. The Golden Fleece Locality where ''Kalthifrons'' was discovered is interpreted to have been a watering hole at the time the crocodilian was alive. The scattered and disassociated remains of turtles and crocodiles alike have been interpreted as a single mass death assemblage that may have been formed when the water dried up, leaving its aquatic inhabitants to die. This hypothesis is supported by the presence of a thin layer of
selenite Selenite may refer to: Substances containing selenium *A selenium-containing anion or ionic compound with the SeO32− anion: **Selenite (ion), anion is a selenium oxoanion with the chemical formula SeO32− ***Selenous acid, the conjugate acid, w ...
underlying the sand. A variety of crocodilian remains have been collected from the region that yielded the fossils of ''Kalthifrons'', with the closest geographically being the many isolated teeth and osteoderms that make up a part of the mass death assemblage of the Golden Fleece Locality. Although the fact that they were found in isolation means that they cannot be confidently assigned to the genus, Yates and Pledge nonetheless argue that they are likely to represent ''Kalthifrons'' due to the nature of the site. More anomalous is the discovery of remains of ''
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 ...
'' from other localities within the Mampuwordu Sand Member, which would indicate that this genus survived for an unusually long time. However, today it is generally accepted that these fossils were either reported with faulty provenance or were simply reworked from older layers. Even beyond the scenario that ''Australosuchus'' fossils were wrongfully attributed to the same units as ''Kalthifrons'', Yates and Pledge argue that their overall similar generalist nature means that they would have been unlikely to coexist. The final crocodilian known from the Mampuwordu Sand Member is ''
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 ...
'', which has been identified based on a maxillary fragment discovered in the Woodard Quarry. Though initially identified as a
sebecosuchian Sebecosuchia (meaning "Sobek crocodiles") is an extinct group of mesoeucrocodylian crocodyliforms that includes the families Sebecidae and Baurusuchidae. The group was long thought to have first appeared in the Late Cretaceous with the baurusu ...
, later research has shown that the tall snout and ziphodont teeth are indistinguishable from those of ''Quinkana'' and clearly distinct from those of ''Kalthifrons''. Unlike with ''Australosuchus'', ''Quinkana'' would have clearly occupied a different ecological niche within the Pliocene Lake Eyre Basin and would thus not have been in competition with the semi-aquatic ''Kalthifrons''. Much younger sediments of the
Tirari Formation The Dhirari (or Dirari or Tirari) were an indigenous Australian people of the state of South Australia. They are not to be confused with the Diyari people, though the Dirari/Dhirari language (now extinct) was a dialect of the Diyari language. N ...
, specifically those of the Pompapillina Member, lack remains referable to ''Kalthifrons,'' but do preserve what is generally thought to have been a generalist species of the genus ''
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 ...
''. Based on the dating of this member, the genus entered the Lake Eyre Basin during the middle Pliocene (3.9–3.4 mya), possibly overlapping with the range of ''Kalthifrons''. The appearance of ''Crocodylus'' in Australia, likely arriving after having migrated there via the
Malay Archipelago The Malay Archipelago is the archipelago between Mainland Southeast Asia and Australia, and is also called Insulindia or the Indo-Australian Archipelago. The name was taken from the 19th-century European concept of a Malay race, later based ...
, would have come at a crucial point in the history of mekosuchines. Though highly successful during the
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...
and
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
, the group appears to have experienced a major faunal turnover leading into the Pliocene, with much of the Miocene diversity going extinct after what was likely a brief period of especially intense aridity. While mekosuchines managed to bounce back after conditions briefly became wetter again, the case of the Tirari ''Crocodylus'' represents the first sign of crocodylines replacing mekosuchines in the long run. While this shift is undeniable, the precise reason for the change remains unknown. While it is possible that competition between the two was a factor, given their similar generalist morphology, there is no direct evidence that ''Crocodylus'' drove ''Kalthifrons'' to extinction by outcompeting it. This is further complicated by the fact that ''Paludirex'', another generalist, inhabited Australia until the late Pleistocene, though it is unclear whether or not this genus coexisted with ''Crocodylus''. A second hypothesis is that ''Kalthifrons'' and mekosuchines in general proceeded to suffer from the ongoing
aridification Aridification is the process of a region becoming increasingly arid, or dry. It refers to long term change, rather than seasonal variation. It is often measured as the reduction of average soil moisture content. It can be caused by reduced preci ...
that continued onward throughout the later part of the Neogene and Quaternary. This would suggest that while the group managed to survive the early stages of this change in climate during the Miocene, they failed to adapt to the changing conditions. Following this line of thought, ''Kalthifrons'' could have disappeared before ''Crocodylus'' entered the Lake Eyre Basin, with the latter simply moving into the newly opened niche.


References

{{Taxonbar, from=Q109546662, from2=Q117466787 Mekosuchinae Prehistoric pseudosuchian genera