Hyphalosaurus

Hyphalosaurus; Temporal range: Early Cretaceous, 123–120 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Fossil specimen, on display at the National Museum of Natural Science
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	† Choristodera
Family:	† Hyphalosauridae
Genus:	† Hyphalosaurus ; Gao, Tang & Wang 1999
Type species
	†Hyphalosaurus lingyuanensis; Gao, Tang & Wang, 1999
Species
	†H. lingyuanensisGao et al., 1999; ; †H. baitaigouensisJi et al., 2004;
Synonyms
	SinohydrosaurusLi, Zhang & Li, 1999;

Last updated May 24, 2024

Hyphalosaurus (meaning "submerged lizard") is a genus of freshwater aquatic reptiles, belonging to the extinct order Choristodera. They lived during the early Cretaceous period (late Barremian to early Aptian age), about 123-120 million years ago. The genus contains two species, H. lingyuanensis from the Yixian Formation and H. baitaigouensis from both the Yixian and Jiufotang Formation of Liaoning Province, China.^[1] They are among the best-known animals from the Jehol Biota, with thousands of fossil specimens representing all growth stages in scientific and private collections.

Description and biology

Hyphalosaurus fossils are relatively widespread in the Jehol beds, which represent a series of freshwater lakes. Several specimens of H. lingyuanensis and thousands of H. baitaigouensis specimens are known from the Yixian Formation, including entire growth series from embryos in eggs to fully grown adults.^[2]H. baitaigouensis was originally reported from the younger Jiufotang Formation, though subsequent study showed that the fossil beds it was found in might also belong to the Yixian Formation, specifically from younger rocks and a different region than H. lingyuanensis.^[3] However, a 2024 study confirmed the presence of H. baitaigouensis from the Jiufotang Formation.^[1]H. lingyuanensis and H. baitaigouensis were largely similar in anatomy, both achieved a maximum adult body size of about 0.8 meters. They had small heads with numerous needle-like teeth, and extremely long tails with more than 55 vertebrae. The primary difference between the two species is the number of vertebrae in the neck. H. lingyuanensis had 19 neck vertebrae, while H. baitaigouensis had 26.^[2]

In 2007, the UK Royal Society announced that it had discovered a two-headed fossil of H. lingyuanensis, the first recorded time that such a reptile has been found fossilized and the oldest known case of polycephaly.^[4]

Skin

Several specimens of Hyphalosaurus have been described with clear impressions of the skin. One specimen represents H. lingyuanensis, and another (with clearer impressions) cannot be assigned to a species because part of the neck (the length of which is a key indicator of species) was destroyed when fossil dealers grafted a skull from a different specimen onto the slab. However, both specimens show nearly identical patterns of scales.^[3]

Hyphalosaurus was covered mostly in small, irregularly patterned polygonal scales, though these varied across the body. The scales of the hind legs were smaller, finer and more irregular than those of the torso, while the scales of the tail were nearly square and arranged in more regular rows. In addition to the small scales, two rows of large, round scutes with shallow keels ran along the animals sides. One row ran directly along the flank, with the other either slightly higher or lower and composed of scutes only 1/4 the size of the flank scutes. The flank row of larger scutes extended all the way to the base of the tail, and remained uniform in size across the entire row.^[3]

The tail itself has preserved soft tissue extending well beyond the margins of the skeleton. This, combined with the already flattened appearance of the tail vertebrae, suggests that a ridge of skin may have extended from the top and bottom of the tail creating a small fin. The feet and hands also appear to have been webbed.^[3]

A third specimen, attributable to H. lingyuanensis, was described in 2023, which preserves partial scales from most areas of the body. The preserved portion of the head scales were rhomboid in shape, while those of the neck were rectangular. The webbed nature of the feet was confirmed. The integument was considered comparable to that of crocodilians.^[5]

Reproduction

Numerous embryonic and/or newborn specimens of Hyphalosaurus have been recovered from the Yixian Formation, dating 122 million years ago. ^[4]

In the holotype specimen of H. baitaigouensis, several eggs containing embryos were preserved in and around the body.^[6] These eggs appeared to lack mineralized shells, which Ji and colleagues later interpreted as evidence that Hyphalosaurus gave birth to live young and that egg shells never fully developed inside the body of the mother. However, in 2006, Ji and colleagues re-examined the holotype specimen and noted clearly defined, though thin and leathery, shells. They agreed, however, that these eggs must have developed inside the mother which would later have given live birth (a reproductive method sometimes called ovoviviparity), but were likely expelled from the body when the mother died.^[2] Hou and colleagues (2010) also described several eggs with flexible shells, containing H. baitaigouensis embryos. These shells were soft, and more similar to the eggs of lizards than to those of crocodiles, but nonetheless possessed a thin mineralized shell.^[7]

Another fossil specimen of H. baitaigouensis, described by Ji and colleagues in 2010, appeared to be pregnant, containing 18 fully developed embryos arranged in pairs. One of the rear-most embryos was positioned in a reverse, head-first position, a complication which may have killed the mother. This confirmed that Hyphalosaurus and other choristoderans were viviparous, the only known Mesozoic fresh-water reptiles to give birth to live young.^[8]

Ecology

Both Hyphalosaurus species were aquatic, a lifestyle reflected by their long necks and tails and relatively small limbs. Superficially, they resembled miniature plesiosaurs, though this resemblance arose convergently and does not reflect a close relationship.^[7]Hyphalosaurus was among the most aquatically adapted choristoderans, with smoother, flatter scales than its relatives, a tall and flattened tail for swimming, a long neck and webbed feet. Because the torso was fairly inflexible and the limbs were not particularly adapted for aquatic life, Hyphalosaurus probably swam using mainly its tall, flattened tail. The chest was barrel-shaped and made up of thick, heavy rib bones which would have helped Hyphalosaurus stay submerged.^[3]

Hyphalosaurus appears to have exclusively inhabited deep-water lakes. All specimens are preserved in silt characteristic of the deepest part of the lake environment, and are often preserved alongside deep-water fish and crustaceans. Hyphalosaurus is also conspicuously absent from the aquatic sediments of the Jiufotang Formation, which preserved a more swampy, shallow-water ecosystem.^[3]

Hyphalosaurus is the most abundant tetrapod (four-limbed vertebrate) in the Yixian Formation, and probably played an important role in the aquatic food chain. Its long and highly flexible neck and small, flattened skull indicates that it captured small prey animals like fish or arthropods using a sideways-strike, similar to modern aquatic predators with flattened skulls. Unlike other choristoderans, Hyphalosaurus was likely an active predator, rather than one that used a "sit and wait" ambush strategy. Its fossils are often found preserved alongside the small fish Lycoptera , which may have been a prey item, and at least one specimen preserved fish ribs as stomach contents. However, the lack of preserved stomach contents among the thousands of known specimens may indicate that they ate mainly soft-bodied prey.^[3]

Classification and species

The slab and counterslab of the holotype specimen of H. lingyuanensis were given to different groups of researchers in Beijing, one from the Institute of Vertebrate Paleontology and Paleoanthropology and the other from the Beijing Natural History Museum. Each team described the taxon and published their results independently in January 1999, giving the animal two different names: Hyphalosaurus lingyuanensis and Sinohydrosaurus lingyuanensis. It was quickly recognized that Sinohydrosaurus and Hyphalosaurus were mirror images of one another and in fact represented different halves of the same specimen. The ICZN, which governs the naming of animals, mandates that the older name is valid. However, in June 2001 paleontologists Joshua Smith and Jerry Harris noted that since both were published at almost exactly the same time, a third party needed to select which name would better serve as the objective senior synonym. Smith and Harris took the opportunity to do so, selecting Hyphalosaurus as the senior synonym because the manuscript for its description had apparently been submitted (though not published) earlier. They therefore made Sinohydrosaurus a junior synonym of Hyphalosaurus.^[9]

Hyphalosaurus is related to the large, crocodile-like Champsosaurus and the smaller, lizard-like Monjurosuchus . Its closest relative was the similarly built species, Shokawa ikoi , from the Early Cretaceous of Japan. The choristoderes were a clade of aquatic reptiles that survived the end-Cretaceous extinction along with crocodilians, turtles, lizards and snakes. The choristoderes became extinct by the Miocene.

Phylogeny from the analysis of Dong and colleagues (2020):^[10]

Choristodera

Cteniogenys sp.

Heishanosaurus pygmaeus

Coeruleodraco jurassicus

Neochoristodera

Ikechosaurus pijiagouensis

Ikechosaurus sunailinae

Tchoiria namsari

Tchoiria klauseni

Champsosaurus

	C. gigas

	C. albertensis

Simoedosaurus

	S. lemoinei

	S. dakotensis

"Allochoristodera"

Monjurosuchus splendens

Philydrosaurus

	P. proseilus

	P. proseilus

Lazarussuchus

	L. inexpectatus

	Lazarussuchus sp.

	L. dvoraki

Khurendukhosaurus orlovi

Hyphalosaurus sp.

	Hyphalosaurus lingyuanensis

	Shokawa ikoi

Related Research Articles

The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its exquisitely preserved fossils, and is mainly composed of basalts interspersed with siliciclastic sediments.

Choristodera is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the Miocene. Choristoderes are morphologically diverse, with the best known members being the crocodile-like neochoristoderes such as Champsosaurus. Other choristoderans had lizard-like or long necked morphologies. Choristoderes appear to have been confined to the Northern Hemisphere, having been found in North America, Asia, and Europe, and possibly also North Africa. Choristoderes are generally thought to be derived neodiapsids that are close relatives or members of Sauria.

Simoedosaurus is an extinct reptile known from the Paleocene of North America, Europe and western Asia, and a member of the Choristodera, a group of aquatic reptiles that lived in the Northern Hemisphere from the Jurassic to the early Cenozoic.

Liaoningosaurus is an unusual genus of basal ankylosaurid dinosaur from the Liaoning Province, China that lived during the Early Cretaceous in what is now the Yixian and Jiufotang Formation. The type and only species, Liaoningosaurus paradoxus, is known from more than 20 specimens, with some representing juveniles. It was named in 2001 by Xu, Wang and You.

Shokawa is an extinct genus of choristoderan diapsid reptile, known from the Lower Cretaceous of Japan. It is only known from one species, Shokawa ikoi. The only known remains are a postcranial specimen lacking the skull, discovered at the KO2 locality in sediments belonging to the Okurodani Formation near the village of Shokawa in Gifu Prefecture. Shokawa possessed a long neck with at least 16 cervical vertebrae, and closely resembles and is closely related to the smaller choristoderan, Hyphalosaurus. The generic name refers to the village near where it was found, while the specific name honors the collector of the first specimen, one Mr. Ikoi Shibata.

The Jehol Biota includes all the living organisms – the ecosystem – of northeastern China between 133 and 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation and Jiufotang Formation. These deposits are composed of layers of tephra and sediment. It is also believed to have left fossils in the Sinuiju series of North Korea. The ecosystem in the Lower Cretaceous was dominated by wetlands and numerous lakes. Rainfall was seasonal, alternating between semiarid and mesic conditions. The climate was temperate. The Jehol ecosystem was interrupted periodically by ash eruptions from volcanoes to the west. The word "Jehol" is a historical transcription of the former Rehe Province.

The Jiufotang Formation is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms. It is a member of the Jehol group. The exact age of the Jiufotang has been debated for years, with estimates ranging from the Late Jurassic to the Early Cretaceous. New uranium-lead dates reveal the formation is deposited in the Aptian stage of the Early Cretaceous. Fossils of Microraptor and Jeholornis are from the Jiufotang.

Lazarussuchus is an extinct genus of amphibious reptile, known from the Cenozoic of Europe. It is the youngest known member of Choristodera, an extinct order of aquatic reptiles that first appeared in the Middle Jurassic. Fossils have been found in Late Paleocene, Late Oligocene, Early Miocene and possibly Late Miocene deposits in France, Germany, and the Czech Republic. Two species have been named: the type species L. inexpectatus ("unexpected") from the late Oligocene of France. and L. dvoraki from the early Miocene of the Czech Republic. It was not a large animal; with the total preserved body and tail length of L. inexpectatus being just over 30 centimetres. A complete specimen of Lazarussuchus with preserved soft tissue was found from the Late Paleocene of France, but has not been assigned to a species.

Liaoxisaurus is a genus of choristodere, a type of crocodile-like aquatic reptile. It is known from a partial specimen found in Aptian-age Lower Cretaceous rocks of the Jiufotang Formation, Chaoyang, Liaoning, China. Liaoxisaurus was named in 2005 by Gao Chunling, Lü Junchang, and colleagues. The type species is L. chaoyangensis.

Monjurosuchus is a genus of choristoderan reptile that lived in what is now China and Japan during the Early Cretaceous. It has large eyes, a rounded skull, robust legs with short claws, and a long, thin tail. Fossils have been found that preserve soft tissue, showing that it had soft skin and webbed feet.

Longicrusavis is an extinct genus of basal ornithuromorph bird found only at Dawangzhangzi village in Liaoning Province, China. Longicrusavis was a ground dwelling carnivore, a wader, and part of biological family Hongshanornithidae, considered to have been a dominant species in the Jehol Biota, the prehistoric Chinese ecosystem which supported them. The name Hongshanornithidae represents one of China's oldest recorded cultures in the region, the Hongshan culture.

<i>Khurendukhosaurus</i> Extinct genus of reptiles

Khurendukhosaurus is a genus of choristodere, a type of amphibious reptile. It is known from Lower Cretaceous rocks of Mongolia and Russia. Two species have been named. The type species, K. orlovi, was named in 1984 by Sigogneau–Russell and Efimov for the fragmentary postcranial skeleton PIN 3386/3. This specimen was discovered in the Albian-age Lower Cretaceous Khuren Dukh Formation Formation at Hüren Dukh, central Mongolia. The lake deposits at this site also contain fossils of the choristoderes Irenosaurus and Tchoiria. Other postcranial bones of K. orlovi have been found at this site as well.

Tchoiria () is a genus of neochoristoderan reptile from the Early Cretaceous of Mongolia. The name Tchoiria comes from the city of Choir which is nearby to where the holotype was found. Tchoiria is thought to have a similar diet to another neochoristoderan reptile, Champsosaurus, due to morphology of the skull. It would hunt in freshwater environments, like the living gharials, where it would prey on many different types of fish and turtles.

Neochoristodera is a lineage of specialised crocodile-like fully aquatic choristodere reptiles. Noted for their long jaws and large size, these animals were predominant across the Northern Hemisphere, occurring in freshwater and coastal environments across the Cretaceous and early Cenozoic.

Philydrosaurus is an extinct genus of choristoderan which existed in China during the Early Cretaceous. The type species P. proseilus was named in 2005. Philydrosaurus was found from the Jiufotang Formation and is slightly younger than Monjurosuchus, which was found from the Yixian Formation.

Liushusaurus is an extinct genus of lizard described by Susan E. Evans and Yuan Wang in 2010. The genus has a single species, Liushusaurus acanthocaudata, and is known from eight fossils, several of which preserve soft tissue detail. The specimens were found in the Lower Cretaceous aged Yixian Formation of Northeast China. Liushusaurus is one of eight lizards that are known and have been named from the Yixian Formation, part of the diverse Jehol Biota ecosystem.

Chuanqilong is a monospecific genus of basal ankylosaurid dinosaur from the Liaoning Province, China that lived during the Early Cretaceous in what is now the Jiufotang Formation. The type and only species, Chuanqilong chaoyangensis, is known from a nearly complete skeleton with a skull of a juvenile individual. It was described in 2014 by Fenglu Han, Wenjie Zheng, Dongyu Hu, Xing Xu, and Paul M. Barrett. Chuanqilong shows many similarities with Liaoningosaurus and may represent a later ontogenetic stage of the taxon.

<i>Jeholochelys</i> Extinct genus of turtles

Jeholochelys is an extinct genus of sinemydid turtle that lived during the Early Cretaceous of what is now China. The holotype specimen was discovered in the Jiufotang Formation of Sihedang in Lingyuan, western Liaoning. In 2018, the Chinese palaeontologist Shuai Shao and colleagues named the new genus and species Jeholochelys lingyuanensis based on the specimen. The generic name consists of "Jehol", which refers to the Jehol biota, and "chelys", which is Greek for turtle. The specific name refers to the type locality. Seven skeletons were described in the study, five nearly complete, and two consisting of shells, and hundreds of turtle fossils have been found in the area. The described specimens are kept in the Paleontological Museum of Liaoning.

Heishanosaurus is an extinct genus of choristodere reptile from the Early Cretaceous of China. The type and currently only known species is Heishanosaurus pygmaeus. It is unusual as it is much more primitive than other known choristoderes from the Early Cretaceous of Asia, and retains many plesiomorphic characters.

Brevirostruavis is a genus of Early Cretaceous enenatiornithine bird from the Early Cretaceous Jiufotang Formation of Liaoning, China. The type and only species is Brevirostruavis macrohyoideus.

References

1 2 Zhang, L.-J.; Ji, S.-A.; Zhang, H.-C. (2024). "Discovery of the choristodere Hyphalosaurus baitaigouensis from the Lower Cretaceous Jiufotang Formation of western Liaoning, China and its paleobiogeographic significance". Journal of Palaeogeography. doi:10.1016/j.jop.2024.05.003.
1 2 3 Ji, Q.; Ji, S.; Lü, J.; You, H.; Yuan, C. (2006). "Embryos of Early Cretaceous Choristodera (Reptilia) from the Jehol Biota in western Liaoning, China". Journal of the Paleontological Society of Korea. 22 (1): 111–118.
1 2 3 4 5 6 7 Gao, Ke-Qin; Ksepka, Daniel T. (June 2008). "Osteology and taxonomic revision of Hyphalosaurus (Diapsida: Choristodera) from the Lower Cretaceous of Liaoning, China". Journal of Anatomy. 212 (6): 747–768. doi:10.1111/j.1469-7580.2008.00907.x. ISSN 0021-8782. PMC 2423398 . PMID 18510504.
1 2 Buffetaut, Eric; Li, Jianjun; Tong, Haiyan; Zhang, He (2007-02-22). "A two-headed reptile from the Cretaceous of China". Biology Letters . 3 (1): 80–81. doi:10.1098/rsbl.2006.0580. ISSN 1744-9561. PMC 2373827 . PMID 17443971.
↑ Wang, Miaoyan; Xing, Lida; Niu, Kecheng; Liang, Qingqing; Evans, Susan E. (April 2023). "A new specimen of the Early Cretaceous long-necked choristodere Hyphalosaurus from Liaoning, China with exceptionally-preserved integument". Cretaceous Research. 144: 105451. doi:10.1016/j.cretres.2022.105451.
↑ Ji, Q.; Ji, S.; Cheng, Y.; You, H.; Lu, J.; Yuan, C. (2004). "The first fossil soft-shell eggs with embryos from Late Mesozoic Jehol Biota of western Liaoning, China". Acta Geoscientica Sinica. 25: 275–285.
1 2 Hou, Lian-Hai; Li, Pi-Peng; Ksepka, Daniel T.; Gao, Ke-Qin; Norell, Mark A. (2010-04-22). "Implications of flexible-shelled eggs in a Cretaceous choristoderan reptile". Proceedings of the Royal Society of London B: Biological Sciences. 277 (1685): 1235–1239. doi:10.1098/rspb.2009.2035. ISSN 0962-8452. PMC 2842823 . PMID 20018793.
↑ Ji, Qiang; Wu, Xiao-chun; Cheng, Yen-nien (2010-02-24). "Cretaceous choristoderan reptiles gave birth to live young". Naturwissenschaften. 97 (4): 423–428. Bibcode:2010NW.....97..423J. doi:10.1007/s00114-010-0654-2. ISSN 0028-1042. PMID 20179895. S2CID 8719805.
↑ Smith, J. B.; Harris, J. D. (2001). "A taxonomic problem concerning two diapsid genera from the lower Yixian Formation of Liaoning Province, northeastern China". Journal of Vertebrate Paleontology. 21 (1): 389–391. doi:10.1671/0272-4634(2001)021[0389:ATPCTD]2.0.CO;2.
↑ Dong, Liping; Matsumoto, Ryoko; Kusuhashi, Nao; Wang, Yuanqing; Wang, Yuan; Evans, Susan E. (2020-08-02). "A new choristodere (Reptilia: Choristodera) from an Aptian–Albian coal deposit in China". Journal of Systematic Palaeontology. 18 (15): 1223–1242. doi:10.1080/14772019.2020.1749147. ISSN 1477-2019. S2CID 219047160.

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A fossil unborn or newborn Hyphalosaurus with two heads has been found

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[Jiufotang-1] 1 2 Zhang, L.-J.; Ji, S.-A.; Zhang, H.-C. (2024). "Discovery of the choristodere Hyphalosaurus baitaigouensis from the Lower Cretaceous Jiufotang Formation of western Liaoning, China and its paleobiogeographic significance". Journal of Palaeogeography. doi:10.1016/j.jop.2024.05.003.

[jietal2006-2] 1 2 3 Ji, Q.; Ji, S.; Lü, J.; You, H.; Yuan, C. (2006). "Embryos of Early Cretaceous Choristodera (Reptilia) from the Jehol Biota in western Liaoning, China". Journal of the Paleontological Society of Korea. 22 (1): 111–118.

[gao&Ksepka2008-3] 1 2 3 4 5 6 7 Gao, Ke-Qin; Ksepka, Daniel T. (June 2008). "Osteology and taxonomic revision of Hyphalosaurus (Diapsida: Choristodera) from the Lower Cretaceous of Liaoning, China". Journal of Anatomy. 212 (6): 747–768. doi:10.1111/j.1469-7580.2008.00907.x. ISSN 0021-8782. PMC 2423398 . PMID 18510504.

[Buffetaut-4] 1 2 Buffetaut, Eric; Li, Jianjun; Tong, Haiyan; Zhang, He (2007-02-22). "A two-headed reptile from the Cretaceous of China". Biology Letters . 3 (1): 80–81. doi:10.1098/rsbl.2006.0580. ISSN 1744-9561. PMC 2373827 . PMID 17443971.

[5] Wang, Miaoyan; Xing, Lida; Niu, Kecheng; Liang, Qingqing; Evans, Susan E. (April 2023). "A new specimen of the Early Cretaceous long-necked choristodere Hyphalosaurus from Liaoning, China with exceptionally-preserved integument". Cretaceous Research. 144: 105451. doi:10.1016/j.cretres.2022.105451.

[jietal2004b-6] Ji, Q.; Ji, S.; Cheng, Y.; You, H.; Lu, J.; Yuan, C. (2004). "The first fossil soft-shell eggs with embryos from Late Mesozoic Jehol Biota of western Liaoning, China". Acta Geoscientica Sinica. 25: 275–285.

[houetal2010-7] 1 2 Hou, Lian-Hai; Li, Pi-Peng; Ksepka, Daniel T.; Gao, Ke-Qin; Norell, Mark A. (2010-04-22). "Implications of flexible-shelled eggs in a Cretaceous choristoderan reptile". Proceedings of the Royal Society of London B: Biological Sciences. 277 (1685): 1235–1239. doi:10.1098/rspb.2009.2035. ISSN 0962-8452. PMC 2842823 . PMID 20018793.

[8] Ji, Qiang; Wu, Xiao-chun; Cheng, Yen-nien (2010-02-24). "Cretaceous choristoderan reptiles gave birth to live young". Naturwissenschaften. 97 (4): 423–428. Bibcode:2010NW.....97..423J. doi:10.1007/s00114-010-0654-2. ISSN 0028-1042. PMID 20179895. S2CID 8719805.

[smith-harris2001-9] Smith, J. B.; Harris, J. D. (2001). "A taxonomic problem concerning two diapsid genera from the lower Yixian Formation of Liaoning Province, northeastern China". Journal of Vertebrate Paleontology. 21 (1): 389–391. doi:10.1671/0272-4634(2001)021[0389:ATPCTD]2.0.CO;2.

[:02-10] Dong, Liping; Matsumoto, Ryoko; Kusuhashi, Nao; Wang, Yuanqing; Wang, Yuan; Evans, Susan E. (2020-08-02). "A new choristodere (Reptilia: Choristodera) from an Aptian–Albian coal deposit in China". Journal of Systematic Palaeontology. 18 (15): 1223–1242. doi:10.1080/14772019.2020.1749147. ISSN 1477-2019. S2CID 219047160.

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