''Harpacochampsa'' is a poorly known
Early Miocene
The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages.
The sub-epoch lasted from 23.03 ± 0.05 Ma to 15.97 ± 0.05 Ma (million years ago). It was prece ...
crocodilian
Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest living ...
from the
Bullock Creek lagerstätte
A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These for ...
of the
Northern Territory
The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an states and territories of Australia, Australian territory in the central and central northern regions of Australia. The Northern Territory ...
,
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
. The current specimen consists of a partial skull and fragments of a long, slender snout reminiscent of that of a
false gharial
The false gharial (''Tomistoma schlegelii''), also known by the names Malayan gharial, Sunda gharial and tomistoma is a freshwater crocodilian of the family Gavialidae native to Peninsular Malaysia, Borneo, Sumatra and Java. It is listed as Vu ...
, demonstrating that it was a
piscivore
A piscivore () is a carnivorous animal that eats primarily fish. The name ''piscivore'' is derived . Piscivore is equivalent to the Greek-derived word ichthyophage, both of which mean "fish eater". Fish were the diet of early tetrapod evoluti ...
in life.
It was originally tentatively placed within a group of Australian crocodilians now known as the
Mekosuchinae
Mekosuchinae is an extinct clade of crocodilians from the Cenozoic of Australasia. They first appear in the fossil record in the Eocene in Australia, and survived until the arrival of humans: in the Pleistocene in Australia and within the Holocene ...
, although this has been frequently disputed, with other authors instead suggesting it may have been a more basal
crocodyloid
Crocodyloidea is one of three superfamilies of crocodilians, the other two being Alligatoroidea and Gavialoidea, and it includes the crocodiles. Crocodyloidea may also include the extinct Mekosuchinae, native to Australasia from the Eocene t ...
or a type of
gavialid
Gavialidae is a family of large semiaquatic crocodilians with elongated, narrow snouts. Gavialidae consists of two living species, the gharial (''Gavialis gangeticus'') and the false gharial (''Tomistoma schlegelii''), both occurring in Asia. Man ...
.
History and naming
''Harpacochampsa'' was named on the basis of several bones, primarily of the skull, discovered at the
Bullock Creek fossil site in the
Northern Territory
The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an states and territories of Australia, Australian territory in the central and central northern regions of Australia. The Northern Territory ...
of
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
. The type description lists four specimens, the
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
being formed by the right side of the back of the skull, preserving both the
infratemporal fenestra
An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets ...
and the
supratemporal fenestra. Additional fossils include the tip of the snout preserving most of the premaxillae, a piece of the
mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
and two
osteoderms
Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct ...
.
[
The genus name is a combination of the Greek words "harpaco" (to seize) and "champsos" (crocodile), translating to "seizing crocodile", a nod to the anatomy of the premaxillary teeth and their inferred function. The species name meanwhile alludes to the Camfield Fossil Beds, of which Bullock Creek is a part of.][
]
Description
The tip of the snout in ''Harpacochampsa'' is broadly similar to more slender-snouted species of ''Crocodylus
''Crocodylus'' is a genus of true crocodiles in the family Crocodylidae.
Taxonomy
The generic name, ''Crocodylus'', was proposed by Josephus Nicolaus Laurenti in 1768. ''Crocodylus'' contains 13–14 extant (living) species and 5 extinct species ...
'', with the closest match in terms of robustness being the American crocodile
The American crocodile (''Crocodylus acutus'') is a species of crocodilian found in the Neotropics. It is the most widespread of the four extant species of crocodiles from the Americas, with populations present from South Florida and the coasts ...
. The sutures of the snout also most closely resemble this species, although 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 mammal has b ...
are proportionally narrower. As a whole, the snout tip is relatively deep for its width, the cross-section resembling a flipped D towards the back of the preserved bone with a flat palate and sloping lateral edges. The premaxillae are roughly circular in shape and contain five teeth on each side, separated from the following maxillary teeth by a notch that presumably receives an enlarged dentary tooth, as in many other crocodilians. Notably, the only functional premaxillary tooth (the fifth) preserved in ''Harpacochampsa'' faces slightly outward rather than straight down. The size of the alveoli indicates that the premaxillary teeth differed greatly in size, making the crocodile pseudoheterodont, whereas the maxillary teeth are more uniform. Unlike in other crocodylids, in which the fifth maxillary tooth is the largest, in ''Harpacochampsa'' it is the fourth premaxillary tooth. The nares are slightly longer than wide and set far forward on the snout, almost entirely surrounded by the premaxillae except for a small area to which the nasal bones
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 ...
contribute. Just in front of the nares are two pits that receive the enlarged first dentary teeth, which equal the fourth premaxillary teeth in size. Besides them and the fourth dentary teeth, which are nosted in the notch situated at the premaxillary-maxillary suture, none of the other teeth of the lower jaw appear to pass up the sides of the upper jaw.
The skull table
The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium.
In comparati ...
of ''Harpacochampsa'' is broad and flat with large supratemporal fenestrae, overall resembling a less extreme version of what can be seen in the modern gharial
The gharial (''Gavialis gangeticus''), also known as gavial or fish-eating crocodile, is a crocodilian in the family Gavialidae and among the longest of all living crocodilians. Mature females are long, and males . Adult males have a distinct b ...
. The size of the supratemporal fenestra is most similar to '' Gavialis lewisi''. Several other characters of the skull table are generally similar to gharials as well, such as the relation between fenestra and the surrounding squamosals and parietal bones
The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named ...
and the shape of the orbito-temporal artery. The frontal bone
The frontal bone is a bone in the human skull. The bone consists of two portions.''Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, par ...
does not participate in forming the margins of the fenestra. The sides of the skull table are convex rather than straight or concave, another feature setting apart ''Harpacochampsa'' from modern ''Crocodylus'' species. Following the infratemporal fenestra, the jugal
The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species.
Anatomy ...
is long and slender and the postorbital bar The postorbital bar (or postorbital bone) is a bony arched structure that connects the frontal bone of the skull to the zygomatic arch, which runs laterally around the eye socket. It is a trait that only occurs in mammalian taxa, such as most strep ...
robust, again features shared with gharials. The shape 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 upper ...
is difficult to determine, as the holotype specimen shows signs of having suffered from exostosis
An exostosis, also known as bone spur, is the formation of new bone on the surface of a bone. Exostoses can cause chronic pain ranging from mild to debilitatingly severe, depending on the shape, size, and location of the lesion. It is most commonl ...
, the pathological formation of new bone. The sutures of the sides of the skull table fall into the range observed in extant species, and the exposure of the basisphenoid does not exceed the range of saltwater crocodiles
The saltwater crocodile (''Crocodylus porosus'') is a crocodilian native to saltwater habitats and brackish wetlands from India's east coast across Southeast Asia and the Sundaic region to northern Australia and Micronesia. It has been listed ...
either.[
The two osteoderms known of ''Harpacochampsa'' are generally similar to those of the extant ]freshwater crocodile
The freshwater crocodile (''Crocodylus johnstoni''), also known as the Australian freshwater crocodile, Johnstone's crocodile or the freshie, is a species of crocodile endemic to the northern regions of Australia. Unlike their much larger Austr ...
. The type description estimates that ''Harpacochampsa'' may have reached a length of up to [ based on the proportions of living crocodiles, possibly even as much as .][Willis, P. M. A.,]
Review of Crocodilians of Australasia
" (pdf).
Taxonomy
Although many of ''Harpacochampsa''s gavialoid features were already recognized during the initial description, they were first thought to have been the result of convergent evolution. Instead, it was originally classified as a member of 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 even more loosely to include all extant mem ...
. However, given the sparse material and uncertain internal relationships within Eusuchia
Eusuchia is a clade of crocodylomorphs that first appeared in the Early Cretaceous with '' Hylaeochampsa''. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-T extinction. Since the other two clades ...
, including the position of ''Tomistoma
''Tomistoma'' is a genus of gavialid crocodilians. They are noted for their long narrow snouts used to catch fish, similar to the gharial. ''Tomistoma'' contains one extant (living) member, the false gharial (''Tomistoma schlegelii''), as we ...
'', the authors were hesitant to specify its exact placement with certainty. Two possible hypotheses were suggested, one placing ''Harpacochampsa'' closer to crocodylines and osteolaemines, while the other put forth a possible relationship to a monophyletic grouping of Cenozoic
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
Australian crocodiles, named Mekosuchinae
Mekosuchinae is an extinct clade of crocodilians from the Cenozoic of Australasia. They first appear in the fossil record in the Eocene in Australia, and survived until the arrival of humans: in the Pleistocene in Australia and within the Holocene ...
two years later.[
However the taxon's inclusion within Mekosuchinae has since then been questioned by various authors and its exacact position has become controversial. Works that conclude that ''Harpacochampsa'' was closest to true crocodiles of the subfamily Crocodylinae include papers published by Megirian, Salisbury and Willis, including the type description of '' Kambara implexidens''.] Another publication that recovered ''Harpacochampsa'' as neither being a mekosuchine nor a gavialoid is Ristevski ''et al.'' (2021). This paper described ''Gunggamarandu
''Gunggamarandu'' (meaning "river boss" in Barunggam and Wakka Wakka) is an extinct monospecific genus of tomistomine crocodilian from Pliocene-Pleistocene aged deposits in the Darling Downs (possibly the Riversleigh lagerstätte) of Australi ...
'' from the Pliocene to Pleistocene of Queensland as the first undisputed tomistomine of Australia. Although this confirms the presence of tomistines in Australia, ''Harpacochampsa'' itself was not found to be part of the group and instead recovered as one of the basalmost crocodyloids. Additionally, Ristevski and colleagues did not find tomistomines and gavialoids to form a clade with one another as some other analysis do.
In 2001 Christopher Brochu argued against the work of Megirian et al. (1991) and Salisbury and Willis (1996), finding the taxon's placement within Mekosuchinae likely based on his own examinations of the material. Brochu did however note the unique morphology of ''Harpacochampsa'', which at the time was the only known longirostrine genus in a family of species with either broad and flat or raised skulls. A second longirostrine mekosuchine would eventually be described in 2016 in the form of ''Ultrastenos
''Ultrastenos'' is an extinct genus of Australian mekosuchine crocodilian first described in 2016. The type species ''Ultrastenos willisi'' was discovered at Riversleigh in northwestern Queensland, Australia, and lived during the Late Oligocen ...
'', however phylogenetic analysis conducted at the time found that the inclusion of ''Harpacochampsa'' in the family does cause noise in the resulting phylogeny.
Lastly, although the gavialoid affinities of ''Harpacochampsa'' have traditionally been dismissed, some research still suggest that the taxon is best placed within Gavialoidea alongside tomistomines as a basal grade within the clade. Below is a cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
from a 2018 tip dating Tip dating is a technique used in molecular dating that allows the inference of time-calibrated phylogenetic trees. Its defining feature is that it uses the ages of the samples to provide time information for the analysis, in contrast with traditio ...
study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing
DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...
), and 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: lithostrati ...
(fossil
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 ...
age) data that shows ''Harpacochampsa'' as a gavialid
Gavialidae is a family of large semiaquatic crocodilians with elongated, narrow snouts. Gavialidae consists of two living species, the gharial (''Gavialis gangeticus'') and the false gharial (''Tomistoma schlegelii''), both occurring in Asia. Man ...
:
Paleobiology
The elongated snout of ''Harpacochampsa'' sets it apart clearly from the broad-snouted '' Baru darrowi''. Unlike ''Baru'', which inhabited the shallow streams of what is now Bullock Creek and hunted large mammals, ''Harpacochampsa'' was recovered from sediments that indicate that it inhabited slow moving waters such as billabongs and deep pools of water. Fossils recovered from these sediments confirm the presence of turtles, small fish and lungfish
Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...
up to in length. Accordingly, it is thought that ''Harpacochampsa'' primarily fed on fish and possibly turtles, however given its relatively stout build compared to modern gharials, it is possible that it may have also taken medium-sized mammals as prey. If that is the case, ''Harpacochampsa'' would have likely relied on deeper water to weaken and drown them, while ''Baru'' could rely more on its own strength.[
]
References
{{Taxonbar, from=Q5663052, from2=Q20718388
Crocodilians
Gavialidae
Mekosuchinae
Miocene crocodylomorphs
Crocodiles of Australia
Prehistoric pseudosuchian genera
Fossil taxa described in 1991