Goronyosaurus

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Goronyosaurus
Temporal range: Maastrichtian
Diagram of Goronyosaurus, reconstructed as a mosasaurine, based on known fossils.[1][2]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Clade: †Mosasauria
Superfamily: †Mosasauroidea
Family: †Mosasauridae
Clade: †Russellosaurina
Clade: †Selmasaurini
Genus: †Goronyosaurus
Azzaroli et al., 1972[2]
Species:
†G. nigeriensis
Binomial name
†Goronyosaurus nigeriensis
(Swinton et al., 1930)
Synonyms

Goronyosaurus is an extinct

phylogenetic analyses, although most authors agree that Goronyosaurus belonged to Mosasauridae.[3]

Goronyosaurus possesses unique teeth, which are unlike the teeth of any other mosasaur. Instead of the cutting teeth common among mosasaurs, Goronyosaurus has straight teeth with rounded apices adapted for smashing food.

Discovery and naming

Skull of IGF 14750 at the Florence Museum of Natural History

The

cranium and parts of the mandible. Because of the material being found in the same horizon of the same region of Nigeria, and the similarities in size and anatomy, these new specimens were referred to M. nigeriensis by Augusto Azzarolli and his colleagues.[2]

Description of IGF 14750 demonstrated significant differences of the Nigerian fossils from Mosasaurus. As such, Azzarolli et al. named a new genus Goronyosaurus. The generic name recognizes the

neotype.[2] The specimen was later reassigned as referred material following the reemergence of the original type fossils in literature.[4] A second, unnamed species, from the Farin Doutchi Formation in Niger was reported on by Lingham-Soliar (1991).[3][7][8]

Description

Size of Goronyosaurus compared to a human

Goronyosaurus is a small mosasaur, measuring up to 5.14 m (16.9 ft) long. Previously the body length had been estimated at 7.8 m (26 ft), although Soliar (1988) identified that this length estimate was based on a false skull length to body length ratio (9.1:100). Based on the skull length to body length ratio of Tylosaurus (13.8:100), Soliar (1988) derived a body length estimate of 5.14 m (16.9 ft) from a 0.71 m (2.3 ft) long skull.[4]

Skull

Most of the skull of Goronyosaurus is preserved in the material, although it is heavily crushed and distorted. Overall the skull is long and narrow compared to other mosasaurids, with an estimated complete length of 71 cm (28 in) and a width of only 11.2 cm (4.4 in). Its skull length to skull width ratio (6.31:1) is most similar to

Tylosaurus proriger (5.3:1).[4]

Outdated restored skull based on Azzaroli et al. (1975)[4]

The snout bones of the

foramina are placed close to the dorsal surface of the paired premaxilae. The maxillae bones are unusual for mosasaurids, as they bear teeth which extend posterior to the front of the orbit. It is uncertain exactly how many teeth there were in the maxilla due to breakage, but there is probably around eleven. The nasal bones which project between the external nares are very robust. They are approximately the same width for the entire length, and have a rugged surface, similar to tylosaurines. The nasal openings themselves are relatively small and posterior in Goronyosaurus.[4]

Discussions of the

taphonomic combination of the jugal and coronoid process of the mandible. As such, the true jugal would be only around 19 mm (0.75 in) thick across a majority of its structure, similar in anatomy to Liodon.[4]

Much of the posterior skull has been crushed or broken away from the holotype. The strongly built parietals are very narrow, and are broken, although the articulation with the frontal was probably very intricate. The frontals are triangular, and articulate with the internarial bar strongly. The prefrontals are very crushed and distorted out of their original articulation, but were positioned like Tylosaurus in life. The prefrontals exclude the frontals from participating in the orbit.[4]

Life restoration

The pterygoid bone of the palate is preserved, and bears teeth like in other mosasaurs. The two main processes of the pterygoid are broken, because of their long and slender shape, but it probable looked similar to related taxa. The process of the pterygoid that articulates with the ectopterygoid is similar to Tylosaurus, being flattened vertically and strongly forked.[4]

Generally the

vidian canal is uncovered, probably due to breakage of the thin sheet of bone that normally covers it. These features have been compared favourably to those in Plioplatecarpus, while the elongation and slenderness are similar more so to Tylosaurus.[4]

Dentition

Many isolated teeth found throughout Cretaceous Nigeria can be assigned to Goronyosaurus, because of its unique tooth anatomy. Such isolated teeth display a similar

dentary are slightly more robust than those more posterior, but still curve gently back. Centralized teeth have very blunt cutting edges, with enamel between 150–250 μm that has varying thickness while remaining shallow.[9]

Axial skeleton

Although the first two

centra begin as cylindrical, but become flattened closer to the pelvis. No neural arches are preserved in any dorsal vertebrae. Zygapophyses are weakly present, unlike in the cervical vertebrae, but the inter-arch articulations are still absent. The transverse processes are directed slightly anteriorly and dorsally, and become less pronounced towards the pelvis.[10]

Classification

Due to its unique characteristics and features, Goronyosaurus is notoriously difficult to classify and is left out of most phylogenetic analyses. Goronyosaurus was originally named within its own subfamily, Goronyosaurinae. However, this was based on the characters of the jugal now known to be incorrect. Lingham-Soliar found that Goronyosaurus was within

Prognathodontini and Mosasaurini follow Russell (1967).[12]

Goronyosaurus hunting juvenile plesiosaurs
Mosasauridae

Halisaurinae

Russellosaurina

Plioplatecarpus primaevus

Platecarpus tympaniticus

Tylosaurinae

Lakumasaurus antarcticus

Taniwhasaurus oweni

Tylosaurus proriger

Tylosaurus nepaeolicus

Hainosaurus bernardi

Mosasaurinae
Prognathodontini

Ectenosaurus clidastoides

Goronyosaurus nigeriensis

Plesiotylosaurus crassidens

Prognathodon solvayi

Prognathodon overtoni

Mosasaurini

Clidastes liodontus

Globidens alabamaensis

Mosasaurus hoffmanni

Mosasaurus lemonnieri

Moanasaurus mangahouangae

Plotosaurus bennisoni

Plotosaurus tuckeri

The clade of Goronyosaurus and

glenoid cavity.[11] An earlier version of the 2010 analysis found a more typical phylogeny of mosasaurs, with Goronyosaurus closest to Plotosaurus in derived Mosasaurinae, and the clade Plioplatecarpinae resolved, including Ectenosaurus and Prognathodon (the latter typically a mosasaurine).[13][11] A clade of Goronyosaurus and Plotosaurus was diagnosed by the presence of teeth to the very front of the premaxilla, extension of the tooth row below and behind the orbit, frontally contacting the maxillae, the unforked shape of the contact between skull roof and supratemporal arch bones, location of the vidian canal opening moved posteriorly, absence of zygapophyseal articulations in vertebrae, and complete separation of the deltoid anc pectoral muscle crests on the humerus.[13]

In 2020, Strong et al. assigned Goronyosarus to the Plioplatecarpinae in a clade containing Angolasaurus and Selmasaurus.[14] A plioplatecarpine assignment was also supported by Zietlow, Boyd & van Vranken in their 2023 description of the mosasaurine Jormungandr.[15]

In their 2024 description of the Moroccan plioplatecarpine

Selmasaurini. The results of their analyses are shown in the cladogram below:[16]

Tethysaurus

Plioplatecarpinae

Russellosaurus

Yaguarasaurus columbianus

Carlile Formation
plioplatecarpine

Yaguarasaurus regiomontanus

spp.

Angolasaurus

Plioplatecarpini

Selmasaurini

Selmasaurus johnsoni

Selmasaurus russelli

Gavialimimus

Goronyosaurus

Khinjaria

Paleobiology

Diet

Goronyosaurus has a unique tooth morphology among mosasaurs. Unlike a majority of mosasaurs, which have cutting teeth, Goronyosaurus has straight teeth with a rounded apex designed more for smashing food. This means that it may have competed with mosasaurs with cutting teeth, as well as large predatory

crocodilians and plesiosaurs.[17]

Paleoecology

estuarine (right) environments of the Iullemmeden Basin
.

All known Goronyosaurus fossils come from the Dukamaje and Farin Doutchi Formations of Niger and Nigeria, both of which lie within the

index fossils, but geologists generally agree that the formations are at least Maastrichtian in age based on the occurrence of the ammonite Libycoceras. Some studies suggest the formations can be further constrained to the mid-late Maastrichtian (~70-66 million years ago) based on nannofossil assemblages.[18]

The Iullemmeden Basin was partially submerged under the

Cretaceous–Paleogene extinction.[21]

Notes

  1. lectotype by Soliar (1988).[4] Lingham-Soliar (1991) mistakenly identified IGF 14750 as the holotype.[3]

References

  1. ^ a b c d e Swinton, W. E., Raeburn, C., & Tattam, C. M. (1930). On fossil reptilia from Sokoto Province. Authority of the Federal Government of Nigeria
  2. ^ a b c d e Azzaroli, A.; De Guili, C.; Ficcarelli, G.; Torre, D. (1972). "An aberrant Mosasaur from the Upper Cretaceous of North-Western Nigeria". Atti della Accademia Nazionale dei Lincei. Rendiconti. Classe di Scienze Fisiche, Matematiche e Naturali. Series 8. 52 (3): 398–402.
  3. ^ a b c Lingham-Soliar, T.. (1991). "Mosasaurs from the upper Cretaceous of Niger". Palaeontology. 34: 653–670.
  4. ^ a b c d e f g h i j k Soliar, T. (1988). "The mosasaur Goronyosaurus from the Upper Cretaceous of Sokoto State, Nigeria". Palaeontology. 31 (3): 747–762.
  5. doi:10.2113/gssgfbull.183.6.573
    .
  6. ^ Nopcsa, F. (1925). On Some Reptilian Bones from the Eocene of Sokoto: With 2 Plates and 3 Text-figures. By Francis Baron Nopesa. Nigerian Government.
  7. ^ Moody, R. T. J. and Suttcliffe, P. J. C. (1991). The Cretaceous deposits of the Iullemmeden Basin of Niger, central West Africa. Cretaceous Research 12:137-157
  8. doi:10.5252/geodiversitas2020v42a25
    .
  9. ^ Michaut, M. (2013). Mosasaures du Maastrichtien au sud du Niger (Report). HAL. pp. 1–75.
  10. ^ Azzarolli, A.; De Guili, C.; Ficcarelli, G.; Torre, D. (1975). "Late Cretaceous mosasaurs from the Sokoto District, Nigeria". Atti della Accademia Nazionale dei Lincei. Memorie de la Classe di Scienze Fisiche, Matematiche e Naturali. Sezione 2. Fisica, Chimica Geologia, Paleontologia e Mineralogia. Series 8. 13 (2): 21–34.
  11. ^
    S2CID 84301257
    .
  12. ^ Russell, D.A. (1967). "Systematics and Morphology of American Mosasaurs" (PDF). Bulletin of the Peabody Museum of Natural History. 23: 1–241. Archived from the original (PDF) on 2016-06-24. Retrieved 2017-09-24.
  13. ^
    S2CID 85271610
    .
  14. ISSN 1477-2019
    .
  15. ISSN 0003-0090. Archived
    from the original on 2023-10-30. Retrieved 2023-10-30.
  16. ISSN 0195-6671
    .
  17. S2CID 55363105
    .
  18. doi:10.1006/cres.1998.0135
    .
  19. doi:10.1016/s0195-6671(05)80021-7
    .
  20. doi:10.1016/j.jafrearsci.2023.104878
    .
  21. doi:10.1127/njgpa/213/1999/355
    .

External links
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