Dracopristis

''Dracopristis'' (meaning 'dragon shark') is an extinct genus of ctenacanth (a group of shark-like cartilaginous fish) that lived during the Carboniferous period in North America, around 307 million years ago. The species was discovered in the Kinney Brick Quarry in New Mexico, USA. Like many fossils from the site, the fossils of ''Dracopristis'' are very well-preserved. A single species is known, ''Dracopristis hoffmanorum'', which is named in honor of Ralph and Jeanette Hoffman, the owners of the quarry. Prior to being scientific named, ''D. hoffmanorum'' was informally referred to as the "Godzilla shark".

''Dracopristis'' possessed large dermal denticles along its head, along with rows of short, multi-cusped teeth in its jaws and very large spines on its dorsal fins, the latter of which inspired the name of the genus. The dorsal spines of the type specimen are about in length, while the entire body was approximately in length. Its large spines were likely used for defense against larger fish, while ''Dracopristis'' itself was likely a benthic predator that inhabited shallow, brackish-water environments.

Discovery and naming

The holotype of ''D. hoffmanorum'' was first discovered in May of 2013, when John-Paul Hodnett unearthed the specimen from the late Carboniferous-aged strata of Albuquerque, New Mexico. The fossils were discovered within the Tinajas member of the Atrasado Formation, which, based on index fossils (such as conodonts), has been dated to the Kasimovian stage of the late Pennsylvanian, which is equivalent to the American Missourian. The specific locality which produced the specimen, the Kinney Brick Quarry, is considered a Konservat-Lagerstätten due to the exceptional quality of its fossils.

''Dracopristis'' was formally named, described, and classified by Hodnett and coauthors in 2021. The holotype (catalogued as NMMNH P-68537) is an articulated skeleton, embedded in a matrix of calcareous shale. This specimen belonged to an adult female and represents the most complete ctenacanth fossil so far discovered. Around 87–90% of the cartilaginous skeleton, the animal's coating of tooth-like dermal denticles ,and impressions of its body outline are all preserved. The specimen was studied via CT scanning in 2014, which clarified details of its skeletal anatomy that were otherwise obscured by the matrix. A second assigned specimen (NMMNH P-19181) consists of a neurocranium from a juvenile individual, and was originally misidentified as belonging to '' Orthacanthus huberi.''

The genus name, ''Dracopristis'', is derived from the Latin words , meaning , and , meaning . The dorsal spines, facial denticles, and rows of teeth have been suggested to give the animal a "dragon-like" appearance, and ''-pristis'' is a common suffix given to shark-like fishes. The specific name, ''hoffmanorum'', is in honor of Ralph and Jeanette Hoffman who own the Kinney Brick Quarry and helped conduct research on the taxon. Prior to its scientific description, what is now the holotype of ''Dracopristis hoffmanorum'' was informally referred to as the "Godzilla shark" or, alternatively, the "Manzano ctenacanth" after the Manzano Mountains. The "Godzilla" nickname was inspired by the genus' defining exaggerated back spines and teeth, which are said to resemble the famous movie monster of the same name.

Description

The type specimen of ''Dracopristis hoffmanorum'' is around in length, although some earlier sources erroneously state lengths of up to . Although the specimen is crushed, the skull, gill arches and dorsal fins remain in articulation, and the pelvic girdle and anal fins are particularly well preserved. ''D. hoffmanorum'' had an elongated and dorsoventrally (from top to bottom) flattened body, which is also indicated by the shape of preserved soft tissue impressions and the arrangement of articulated patches of dermal denticles.

Skull and body

The skull of ''Dracopristis'' was broad – nearly as wide as it was long – with eye sockets positioned far forward and a short rostrum. Fenestrae which housed cranial nerves are preserved, but the interior of the skull is too severely crushed for its internal nervous anatomy to be studied, even with the use of CT scans. Compared to other ctenacanths, the jaws were proportionally large and robust. As in living sharks, the rear portions of the palatoquadrates (upper jaws) articulated with the otic processes (equivalent to ear canals). However, unlike living sharks, the forward processes of the palatoquadrates were rigidly connected to the cranium, and additional "anterodorsal processes" anchored the rear portions of the palatoquadrates to the skull, rendering the upper jaws akinetic and inflexible (termed amphistyly). The Meckel's cartilages (lower jaws) articulated with the palatoquadrates. The hyomandibular arch was well-developed, and five gill arches were present which descended in size towards the posterior (back) of the body.

The scapulocoracoids were fused at their coracoidal portions, while the pelvic girdles were unfused. Mineralized neural and haemal arches are preserved along the length of the body, although the vertebral centra are not known. The holotype of ''D. hoffmanorum'' preserves two dorsal fins, an anal fin, pectoral fins, pelvic fins, and most of the heterocercal caudal fin. Both dorsal fins were proportionally large, as were the broad, triangular pectoral fins. The fins were supported by rods of cartilage known as radials and ceratotrichia, with a triangular basal cartilage plate also supporting each of the dorsal fins. While the known individual lacks pelvic claspers, this is attributed to the specimen being female, and males of the species are presumed to have possessed these. The anal fin was supported by a plate of cartilage, and was rounded in shape.

Spines and dermal denticles

Compared to its relatives, ''Dracopristis'' possessed proportionally very large dorsal fin spines.Brett, Carlton & Walker, Sally. (2002). Predators and Predation in Paleozoic Marine Environments. Paleontological Society Papers. 8. 10.1017/S1089332600001078. In the type specimen, the anterior (front) spine is roughly long (about 27% of the length of the body), while the shorter posterior (back) spine is roughly long. Both spines are ornamented with rows of small, rounded denticles along their lateral sides and two rows of larger, recurved denticles along their anterior sides. The first spine is strongly swept backwards, while the second is much straighter. Both dorsal spines articulate with the basal cartilages of the dorsal fins.

The skin was coated in fine dermal denticles, the size and shape of which varied depending on their position on the body. The largest of these were leaf-shaped and distributed along the back of the head, whereas the smaller, shorter denticles were present along the fins and rostrum. The bases of the dermal denticles were wide, and while they were tightly packed, they did not overlap with one another. Denticles up to in diameter were present within the mouth and gill basket.

Teeth

The largest teeth of ''D. hoffmanorum'' could reach up to in width, and were arranged into 12 laterally (towards the outside) positioned rows. Their appearance is similar to those of other ctenacanthiforms such as '' Glikmanius'' and '' Heslerodus'' in sharing a cladodont (multi-cusped) crown morphology and a reniform (d-shaped) root. Unlike other known ctenacanths, however, the cusps on the teeth of ''Dracopristis'' are relatively short, broad, and triangular in shape. The teeth possess five cusps each, with the central cusp being more than twice the height of the outer four. The tooth cusps are ornamented with multiple rows of denticles down their length, the arrangement of which is unique to this species. The dentition is morphologically homodont (teeth do not vary in shape), although the rows of teeth do decrease in size further into the mouth. The teeth on the frontmost row are over twice the crown height of those of the backmost row. In the 2021 description, it is suggested that tooth replacement was very slow.

Classification

''Dracopristis'' was part of the chondrichthyan order Ctenacathiformes, which were likely part of the subclass Elasmobranchii and were thus relatives of living sharks and rays. Despite often being informally called "sharks", ctenacanths were outside of the division Selachii and are not considered "true" sharks. Compared with sharks, the ctenacanths had greatly enlarged ornamented fin spines, proportionally large mouths, and akinetic jaw suspension. Genera such as ''Bandringa'' and ''Sphenacanthus'' (traditionally considered ctenacanthiforms) have been recovered elsewhere within the Euselachii, indicating the group as traditionally defined may not be monophyletic. Rather than being elasmobranchs, it has alternatively been suggested that ctenacanths instead diverged much earlier and were on the stem of Chondrichthyes.

In the 2021 description of ''Dracopristis hoffmanorum'', cladistic analyses were performed which found that the genus was most closely related to the Devonian genus ''Ctenacanthus.'' It was also suggested that ctenacanthiforms are closer to crown group euselachians than to other cladodont chondricthyans such as Symmoriiformes. In a 2024 publication describing the ctenacanths '' Troglocladodus trimblei'' and ''Glikmanius careforum'', Hodnett and coauthors placed ''Dracopristis'' in the newly-erected family Heslerodidae alongside the genera ''Glikmanius'', ''Heslerodus'', '' Avonacanthus'', and '' Kaibabvenator''.

Paleoecology and paleobiology

During the Pennsylvanian, New Mexico was covered by a vast seaway. ''Dracopristis'' would have lived in the shallow coastal waters of this seaway, and probably would have been an ambush predator. It may have hunted small animals such as fish and crustaceans, and its teeth show adaptations for grasping and crushing its prey. As in other ctenacanths, its dorsal fin spines may have served as protection from larger predators. The shape of ''Dracopristis''' pectoral fins suggests it lived a nektobenthic (bottom dwelling) lifestyle, due to similarities to those of living benthic sharks. ''D. hoffmanorum'' may have been a specialist of brackish-water habitats, and its ecology has been compared with that of the bull shark and common sawfish.

During the Carboniferous, the Atrasado Formation consisted of estuarine and lagoonal habitats, evidenced by fish specimens which show adaptations to both freshwater and marine environments. The quality of many of the Kinney Brick Quarry fossils may have been the result of an anoxic zone, which possibly prevented scavengers disturbing them. ''Dracopristis'' shared the estuary with the larger, related ctenacanthiform ''Glikmanius occidentalis'', which may have preyed upon it. The quarry has also yielded numerous specimens of the filter feeding acanthodian ''Acanthodes'', symmoriiforms similar to ''Cobelodus'', hybodonts, holocephalans, ray-finned palaeonisciformes, lungfish, coelacanths, and megalichthyoforms. Rarer genera, such as the large eugeneodont (whorl-tooth shark) '' Campyloprion'' and the aforementioned ''Glikmanius,'' might have only occasionally migrated into the estuary from deeper, marine habitats. In total, more than 31 other distinct fish genera have been identified from the site, and it is considered one of the most diverse and well preserved fossil fish faunas in the Southwestern United States.

Notes

See also

* List of prehistoric cartilaginous fish genera

References

{{Taxonbar, from=Q110223738

Ctenacanthiformes
Prehistoric cartilaginous fish genera
Fossil taxa described in 2021
Fish described in 2021