Wikipedia

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, US, and like many fossils from the site, is 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
Temporal range: Carboniferous (Kasimovian), 307–303.7 Ma
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An illustration of D. hoffmanorum
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: †Ctenacanthiformes
Family: †Heslerodidae
Genus: †Dracopristis
Hodnett et al. 2021
Species:
†D. hoffmanorum
Binomial name
†Dracopristis hoffmanorum
Hodnett et al. 2021

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, features which inspired the name of the genus. The dorsal spines of the type specimen are about 0.57 m (1 ft 10 in) in length, while the entire body was approximately 2 m (6 ft 7 in) in length. Its large spines were likely used for defence against larger fish, while Dracopristis itself was likely a benthic predator that inhabited shallow, brackish-water environments.

Discovery and naming

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An exposure of limestone belonging to the Atrasado Formation, photographed along a roadcut near Jemez Springs, New Mexico

The holotype of D. hoffmanorum was first discovered in May of 2013,[1][2] when John-Paul Hodnett unearthed the specimen in the late Carboniferous-aged strata of Albuquerque, New Mexico.[2][3][4] 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 (equivalent to the American Missourian) stage of the late Pennsylvanian.[1][5] The specific locality which produced the specimen, the Kinney Brick Quarry, and has been deemed a Konservat-Lagerstätten due to the exceptional quality of its fossils.[5]

Dracopristis was formally named, described, and classified by Hodnett and coauthors in 2021.[4][5] The holotype specimen (catalogued as NMMNH P-68537) is an articulated skeleton, embedded in a matrix of calcareous shale,[5] which belonged to an adult female and which represents the most complete ctenacanth fossil so far discovered.[5][6] Around 87–90% of the cartilaginous skeleton is preserved, as well as the animal's coating of tooth-like dermal denticles and impressions of its body outline.[4][5] The specimen was studied via CT scanning in 2014, which clarified details of its skeletal anatomy which were otherwise inaccessible to researchers.[6] A second assigned specimen (NMMNH P-19181) consists of a neurocranium from a juvenile individual, and was originally misidentified as belonging to Orthacanthus huberi.[5][7]

The genus name, Dracopristis, is derived from the Latin words draco, meaning 'dragon', and pristis, meaning 'shark'.[5] The dorsal spines, facial denticles, and rows of teeth give the animal a "dragon-like" appearance,[2][3][5] while -pristis is a suffix used to denote shark-like fishes.[2][5][8][note 1] 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.[5] Prior to its scientific description, what is now the holotype of Dracopristis hoffmanorum was informally referred to as the "Godzilla shark" or,[4][12] alternatively, the "Manzano ctenacanth" after the Manzano Mountains.[1][13] The "Godzilla" nickname was inspired by the genus' defining exaggerated back spines and teeth, which give a vague resemblance to the character.[3][4]

Description

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The type specimen of Dracopristis hoffmanorum has been confidently measured at 2.06 m (6 ft 9 in) in length,[5] although some earlier sources erroneously state lengths of up to 2.5 m (8 ft 2 in).[1][6] While 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.[1] 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.[5]

Skull and body

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The teeth and disarticulated skull of Glikmanius careforum, a potential close relative of Dracopristis

The skull of Dracopristis was broad, being nearly as wide as it was long, with eye sockets positioned far forward and a short rostrum. Fenestrae which housed cranial nerves are preserved; however, the interior of the skull is too severely crushed for its internal nervous anatomy to be studied, even via CT scanning. 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.[5]

The scapulocoracoids (pectoral girdle) 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,[5] as were the broad, triangular pectoral fins.[2] 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 likely possessed these. The anal fin was supported by a plate of cartilage, and was rounded in shape.[5]

Spines and dermal denticles

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Compared to its relatives, Dracopristis possessed proportionally very large dorsal fin spines.[1][14] In the type specimen, the anterior (front) spine has been measured at roughly 57 cm (22 in) long (about 27% of the length of the body), while the shorter posterior (back) spine was roughly 40 cm (16 in) long. Both spines were 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.[5]

The skin was coated in fine dermal denticles, the size and shape of which varied depending on the position on the body. The largest of these were leaf-shaped and distributed along the back of the head, while 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 one another. Mucous membrane denticles up to 5 mm (0.20 in) in diameter were present within the mouth and gill basket.[5]

Teeth

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The largest teeth of D. hoffmanorum could reach up to 2 cm (0.79 in) in width, and were arranged into 12 laterally (towards the outside) positioned rows.[1][4] 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.[1] Unlike other known ctenacanths, however, the cusps on the teeth of Dracopristis are noticeably shorter, broader, and more triangular in shape than those of its relatives.[1][5] The teeth possess five cusps each, with the central cusp being more than twice the height of the other 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; those of 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.[5]

Classification

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Elasmobranchii
Phylogenetic position of D. hoffmanorum as reconstructed by Hodnett and colleagues in 2021.[5]
 
Large, ornamented dorsal spines of ctenacanths, such as Ctenacanthus (pictured) and Dracopristis, are a defining feature of the group

Dracopristis was part of the chondrichthyan order Ctenacathiformes,[5] which were likely part of the subclass Elasmobranchii and were thus relatives of living sharks and rays.[5][15] Despite often being referred to informally as sharks,[5][12][16] however, ctenacanths were outside of the clade Selachimorpha and are not considered "true" sharks.[17] Compared with selachimorph sharks, the ctenacanths are differentiated by their greatly enlarged ornamented fin spines, their proportionally large mouths and their akinetic jaw suspension.[4][5] Genera such as Bandringa and Sphenacanthus (traditionally considered ctenacanthiforms)[18][19] have been recovered elsewhere within the Euselachii, indicating the group as traditionally defined may not be monophyletic.[5][15] Rather than being elasmobranchs, it has alternatively been suggested that ctenacanths instead diverged much earlier and were on the stem of Chondrichthyes.[20]

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.[5] It was also suggested that ctenacanthiforms are closer to crown group euselachians than to other cladodont chondricthyans such as Symmoriiformes.[5] 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.[16]

Paleoecology and paleobiology

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The modern bull shark (Carcharhinus leucas) has been proposed to be a close ecological analogue to Dracopristis

During the Pennsylvanian, New Mexico was covered by a vast seaway;[4] Dracopristis would have lived in the shallow coastal waters of this seaway, and probably would have been an ambush predator.[2] It may have hunted small animals such as fish and crustaceans,[21] and its teeth show adaptations for grasping and crushing its prey.[2][4] As in other ctenacanths, its dorsal fin spines may have served as protection from larger predators.[4][14] Unlike other members of its order, however, the shape of Dracopristis' pectoral fins suggests it lived a nektobenthic (bottom dwelling) lifestyle, due to similarities to those of living benthic sharks.[2] 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.[2][5]

 
The articulated remains of a large symmoriiform similar to Cobelodus, discovered at the Kinney Brick Quarry[1]

During the Carboniferous, the Atrasado Formation consisted of estuarine and lagoonal habitats,[1] evidenced by fish specimens which show adaptations to both freshwater and marine environments.[21] There may have been an anoxic zone, which allowed fossils to be preserved without scavengers disturbing them and explains the level of quality many of the Kinney Brick Quarry fossils show.[21] Dracopristis shared the estuary with the larger, related ctenacanthiform Glikmanius occidentalis,[5] which may have been one of its predators.[2][21] The quarry has also yielded numerous exceptionally preserved specimens of the filter feeding acanthodian Acanthodes, articulated skeletons belonging to symmoriiforms similar to Cobelodus,[1] remains of hybodonts, holocephalans, ray-finned palaeonisciformes and lobe-finned lungfish, coelacanths and megalichthyoforms.[1][21] 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.[5][21] In total, more than 31 other distinct fish genera have been identified from the site,[21][22] and it is considered one of the most diverse and well preserved fossil fish faunas in the Southwestern United States.[1]

See also

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Notes

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  1. ^ The root -pristis is traditionally recognized to translate as "sawfish" and is derived from the Ancient Greek name of the animal, πρίστις or prístēs.[9][10] A literal English translation of πρίστις would be "sawyer or "a saw".[10][11]

References

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  1. ^ a b c d e f g h i j k l m n Hodnett, John-Paul M.; Lucas, Spencer G. (2015). "Paleozoic Fishes of New Mexico: A review". New Mexico Museum of Natural History and Science (68): 51–64 – via Google Books.
  2. ^ a b c d e f g h i j Long, John A. (2024). The secret history of sharks: the rise of the ocean's most fearsome predators. New York: Ballantine Books. pp. 282–285. ISBN 978-0-593-59808-5.
  3. ^ a b c Spry, Jeff (April 23, 2021). "This new species of 300-million-year-old "Godzilla shark" was king of the lagoon". syfy.com. Retrieved November 4, 2024.
  4. ^ a b c d e f g h i j "New Mexico's 'Godzilla' Shark Fossil Gets an Official Name". smithsonianmag.com. Archived from the original on April 26, 2021.
  5. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae Hodnett, J-.P. M; Grogan, E. D.; Lund, R.; Lucas, S. G.; Suazo, T.; Elliott, D. K.; Pruitt, J. (2021). "Ctenacanthiform sharks from the late Pennsylvanian (Missourian) Tinajas Member of the Atrasado Formation, Central New Mexico". New Mexico Museum of Natural History and Science Bulletin. 84: 391–424.
  6. ^ a b c Domenici, Donna (May 8, 2014). "Ancient Shark Fossil Admitted to Presbyterian Rust Medical Center for CT Scan". New Mexico Museum of Natural History and Science. Retrieved October 31, 2024.
  7. ^ Zidek, J. (1992). "Late Pennsylvanian Chondrichthyes, Acanthodii, and deep−bodied Actinopterygii from the Kinney Quarry, Manzanita Mountains, New Mexico". shark references.
  8. ^ "A Dictionary of the Latin Language". The Latin Lexicon. Retrieved November 6, 2024.
  9. ^ "Henry George Liddell, Robert Scott, A Greek-English Lexicon, πρίστις". Perseus Digital Library (in Greek). Retrieved November 5, 2024.
  10. ^ a b "Family PRISTIDAE Bonaparte 1835 (Sawfishes)". The ETYFish Project. March 31, 2023. Retrieved November 6, 2024.
  11. ^ "Pristiophorus cirratus, Common Sawshark". FishBase. Retrieved November 5, 2024.
  12. ^ a b "Dracopristis hoffmanorum: 'Godzilla' shark discovered in New Mexico gets formal name". Firstpost. April 17, 2021. Retrieved December 15, 2021.
  13. ^ Wilk, Olga; Olive, Sebastien; Pradel, Alan; Den Blaauwen, Jan L.; Szrek, Piotr (May 4, 2021). "The first lower jaw of a ctenacanthid shark from the Late Devonian (Famennian) of Belgium". Journal of Vertebrate Paleontology. 41 (3). doi:10.1080/02724634.2021.1960537. ISSN 0272-4634.
  14. ^ a b Brett, Carlton & Walker, Sally. (2002). Predators and Predation in Paleozoic Marine Environments. Paleontological Society Papers. 8. 10.1017/S1089332600001078.
  15. ^ a b Ginter, Michał; Hampe, Oliver; Duffin, Christopher J. (2010). Handbook of paleoichthyology: teeth. München: F. Pfeil. ISBN 978-3-89937-116-1.
  16. ^ a b Hodnett, John-Paul M.; Toomey, Rickard; Egli, H. Chase; Ward, Gabe; Wood, John R.; Olson, Rickard; Tolleson, Kelli; Tweet, Justin S.; Santucci, Vincent L. (February 2024). "New ctenacanth sharks (Chondrichthyes; Elasmobranchii; Ctenacanthiformes) from the Middle to Late Mississippian of Kentucky and Alabama". Journal of Vertebrate Paleontology. doi:10.1080/02724634.2023.2292599. ISSN 0272-4634.
  17. ^ Ebert, David A.; Fowler, Sarah; Dando, Marc (2021). Sharks of the World: A Complete Guide. Princeton: Princeton University Press. ISBN 978-0-691-20599-1.
  18. ^ Zangerl, Rainer (1969). "Bandringa rayi: A New Ctenacanthoid Shark form the Pennsylvanian Essex Fauna of Illinois". Fieldiana Geology. 12: 157–169.
  19. ^ Case, Gerard Ramon (1992). A pictorial guide to fossils (2nd ed.). Malabar, Fla: Krieger Pub. ISBN 978-0-89464-678-2.
  20. ^ Bronson, Allison W.; Pradel, Alan; Denton, John S. S.; Maisey, John G. (March 7, 2024). "A new operculate symmoriiform chondrichthyan from the Late Mississippian Fayetteville Shale (Arkansas, United States)". Geodiversitas. 46 (4). doi:10.5252/geodiversitas2024v46a4. ISSN 1280-9659.
  21. ^ a b c d e f g M. Hodnett, John-Paul; Lucas, Spencer G. (2021). "Review Of The Late Pennsylvanian Fish Assemblage From The Kinney Brick Quarry, New Mexico". New Mexico Museum of Natural History and Science Bulletin. 84: 359–390.
  22. ^ "Dracopristis hoffmanorum". sharkreferences.com. Archived from the original on August 8, 2021.
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