''Koolasuchus'' is an extinct

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 brachyopoid

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Chigutisauridae. Fossils have been found from Victoria,

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 ...

and date back 125-120 million years ago to

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 125.77 Ma (million years ago) and 121.4 ± 1.0 Ma (Historically, this stage was placed at 129.4 million to approximately 125 million years ago) It is a ...

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

stages of the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

. ''Koolasuchus'' is the youngest known temnospondyl. It is known from several fragments of the skull and other bones such as vertebrae, ribs, and pectoral elements. 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 ...

''Koolasuchus cleelandi'' was named in 1997. ''K. cleelandi'' was adopted as the fossil emblem for the state of Victoria, Australia on 13 January 2022.

History

Between 1978 and 1979, a fossil expedition by the

National Museum of Victoria National may refer to: Common uses * Nation or country ** Nationality – a ''national'' is a person who is subject to a nation, regardless of whether the person has full rights as a citizen Places in the United States * National, Maryland, ...

explored

fossiliferous A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved i ...

outcrops belonging to the Strzelecki Group in Kilcunda,

Victoria, Australia Victoria, commonly abbreviated as Vic, is a state in southeastern Australia. It is the second-smallest state (after Tasmania), with a land area of ; the second-most-populated state (after New South Wales), with a population of over 7 million; ...

. In 1979 during the expedition, a pair of incomplete mandibles (lower jaws) of an unidentified

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

was unearthed from strata deriving from the upper

-aged Wonthaggi Formation at a site dubbed "Rowells Beach". This specimen was then deposited at the National Museum of Victoria under catalog number NMV P186213 along with many other fossils unearthed during the expedition. In 1982, paleontologists Timothy Flannery and Thomas Rich briefly mentioned the discovery in an article where they hypothesized that the mandibles could belong to an ornithischian

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

, a

crocodilian Crocodilia () is an Order (biology), 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 crocodylomorp ...

, or a

labyrinthodont "Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally conside ...

amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

. The uncertainty of this specimen's taxonomy led it to be nicknamed GOK, which stands for "God Only Knows". In 1986, a publication by Anne Warren and R. Jupp described the specimen in more detail where they disproved that it could belong to a crocodilian or an ornithischian. However, they did not definitively identify it as that of a

due to the Cretaceous age of the specimen, one much younger than any other known temnospondyl specimen at the time. In early 1989, Lesley Kool collected a temnospondyl intercentrum (part of the

vertebra 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 spina ...

), NMV-PI86040, from a site known as Potters Hill Road nearby where NMV P186213 was discovered. Another temnospondyl bone, a fragment from the

skull roof The skull roof or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes, including land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In com ...

cataloged under NMV-PI86101, was found by Mike Cleeland on a beach in San Remo. In 1991, these specimens were described by A. A. Warren and colleagues as being unquestionable evidence that temnospondyls were present in the Strzelecki Group. The morphology of the skull roof lead to the authors suggesting that the temnospondyl was either a member of Plagiosauridae or Brachyopoidea. In 1997, Australian paleontologists Anne Warren, Thomas Rich, and

Patricia Vickers-Rich Patricia Arlene Vickers-Rich (born 11 July 1944), also known as Patricia Rich, is an Australian Professor of Palaeontology and Palaeobiology, who researches the environmental changes that have impacted Australia (including the ancient super ...

redescribed all previously mentioned temnospondyl material from the Strzelecki Group along with additional postcranial fossils and jaw fragments. In their redescription, Warren and colleagues described the incomplete mandibles, NMV P186213, as 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 ...

(name-bearing) specimen of a new

and

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of temnospondyl, named ''Koolasuchus cleelandi''. The generic name ''Koolasuchus'' is in honor of Lesley Kool, the discoverer of the intercentrum, and the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

word ''souchos'', meaning "crocodile" in reference to the crocodilian-like body shapes of temnospondyls. The specific name ''cleelandi'' is in honor of Mike Cleeland, the discoverer of a skull roof fragment of ''Koolasuchus''. Several partial skulls have been referred to ''Koolasuchus'' since its

description Description is any type of communication that aims to make vivid a place, object, person, group, or other physical entity. It is one of four rhetorical modes (also known as ''modes of discourse''), along with exposition, argumentation, and narr ...

, however they remain undescribed and are located in the collections of the National Victoria Museum.

Description

''Koolasuchus'' was a large, aquatic temnospondyl, measuring up to in length and weighing up to . Like other chigutisaurids, it had a wide, rounded head and tabular horns projecting from the back of the skull. Although represented by incomplete material, the skull was likely long.

Anatomy

Although more complete skull material has been mentioned in literature, no full-length descriptions of ''Koolasuchus''' skull have been published. However, several tentatively-assigned cranial fragments have been described, including: two pterygoids, a right prefrontal, and an ectopterygoid (a part of the pterygoid that links it to the outer part of the skull). The right prefrontal is incomplete, but bears a significant portion of the orbital margin. It was referred to ''Koolasuchus'' on the basis of its origin and its anatomy, which is similar to that of brachyopoids and plagiosaurs. As for the ectopterygoid, it does not bear characteristics of brachyopids and instead is more similar to those of chigutisaurids and

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 ...

temnospondyls. Four mandibular ramii are known from ''Koolasuchus'' have been unearthed. The postglenoid area, PGA, (where the mandible articulates with the skull) contains extensions of the prearticular and angular bones. The

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

(top) surface of the PGA bears a suture that excludes the articular from being on the dorsal surface of the PGA, a characteristic distinguishing ''Koolasuchus'' from other temnospondyls aside from ''Siderops'' and ''Hadrokkosaurus''. The

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

composes most of the labial (lipped) surface of the anterior mandible. The teeth of ''Koolasuchus'' are sharp, pointed, and serrated, adaptations for a carnivorous lifestyle. The teeth feature lance-shaped tips with keels on their

mesial This is a list of definitions of commonly used terms of location and direction in dentistry. This set of terms provides orientation within the oral cavity, much as anatomical terms of location provide orientation throughout the body. Terms ...

and

distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...

surfaces, a condition similar to that of ''Siderops''. Additionally, the teeth on the mandible are large at the base, proportionately large, and rounded, with 40 teeth present on the mandible. This tooth count is much higher than in other temnospondyls like ''Hadrokkosaurus'' and the indeterminate temnospondyl UCMP 36834. ''Koolasuchus'' is differentiated from ''Siderops'' and ''Hadrokkosaurus'' by its absence of coronoid teeth, teeth present on the coronoid process.

Paleobiology

''Koolasuchus'' inhabited rift valleys in southern Australia during the Early Cretaceous. During this time the area was below the

Antarctic Circle The Antarctic Circle is the most southerly of the five major circles of latitude that mark maps of Earth. The region south of this circle is known as the Antarctic, and the zone immediately to the north is called the Southern Temperate Zone. So ...

, and temperatures were relatively cool for the Mesozoic. Based on the coarse-grained rocks in which remains were found, ''Koolasuchus'' likely lived in fast-moving streams. As a large aquatic predator, it was similar in lifestyle to crocodilians. Although eusuchians and kin were common during the Early Cretaceous, they were absent from southern Australia 120 million years ago, possibly because of the cold climate. By 110 Mya, represented by rocks in the Dinosaur Cove fossil locality, temperatures had warmed and crocodilians had returned to the area. These crocodilians likely displaced ''Koolasuchus'', leading to its disappearance in younger rocks.

References

{{Taxonbar, from=Q132690 Chigutisauridae Prehistoric tetrapod genera Prehistoric vertebrates of Oceania Prehistoric amphibians of Australia Cretaceous temnospondyls Aptian genera Fossil taxa described in 1997 Symbols of Victoria Cretaceous animals of Australia