Muiscasaurus

Muiscasaurus is an extinct genus of ophthalmosaurid ichthyosaur that lived in modern Colombia during the Early Cretaceous. The only known species is the type Muiscasaurus catheti.^[2]

Discovery

The fossils of Muiscasaurus were found in the Paja Formation, whose sediments are exposed near the town of Villa de Leyva in Boyacá Department. These remains were found in 2010 in the middle of a limestone concretion, known as the Arcillolitas abigarradas Member, dating from the Barremian to Aptian epochs of the Lower Cretaceous. Although ammonites were found attached to the fossils, their poor preservation prevented identifying them and thereby establish the stratigraphy and precise age of the specimen. The fossil found, listed as the holotype specimen CIP-FCG-CBP-74, consists of a partial skull and some vertebrae with ribs that were found associated with the skull. These remains were designated in 2015 as the new genus and species Muiscasaurus catheti; the genus name being a reference to the Muisca of central Colombia, with the Latinized Greek word saurus, "reptile". The species name, catheti, means perpendicular and refers to the shape of the nostrils. The remains were prepared for the Centro de Investigaciones Paleontológicas (Paleontological Research Center) in Villa de Leyva.^[2]

Description

The Muiscasaurus fossils corresponds to a juvenile individual, given the incomplete ossification of the vertebrae and the proportions of the skull. This lacks the front of the snout, as well as in the back of the skull, showing some crushing to the right side. The jaw elements are very thin and long, with some teeth preserved, which are relatively small. Muiscasaurus was a relatively large animal: the preserved skull length is 45 centimetres (18 in), and, depending on its exact proportions, could be between 48–65 centimetres (19–26 in) total cranial length.^[2] This individual could reach 3 metres (9 ft 10 in) long and up to 5 metres (16 ft 5 in) long in adults.^[3] Like all advanced ichthyosaurs, Muiscasaurus must had a compact and streamlined body, with a tail shaped like a half moon and all four legs transformed into flippers.^[3]

Muiscasaurus differs from its closest relatives by a combination of features: it had a very thin premaxilla, the nasal aperture is partially divided in two ovals for a spur-shaped nasal process, with the frontal portion in vertical position and the rear one horizontal; in other ophthalmosaurid ichthyosaurs, the aperture was fully open or fully separated into two. The posterior region was narrow and provided with a thin quadratojugal, the teeth were very thin and lacking of the thick enamel and the coarse striations, whereas in similar ichthyosaurs as Pervushovisaurus and Platypterygius had more robust teeth and grooves in the enamel.^[2]

Phylogeny

Muiscasaurus was described based on fossils that were classified as belonging to the Ophthalmosauridae family, which includes most of the ichthyosaurs that lived during the Jurassic and Cretaceous periods. Muiscasaurus seems particularly occupied a very basal position within the family, with respect to the subgroup composed by Platypterygius, Caypullisaurus and Brachypterygius (although the latter two genera were slightly older than Muiscasaurus itself) .^[2]

Cladogram based in the phylogenetic analysis of Maxwell et al., 2015:

The following cladogram shows a possible phylogenetic position of Muiscasaurus in Ophthalmosauridae according to the analysis performed by Zverkov and Jacobs (2020).^[4]

Paleobiology

In addition to Muiscasaurus, in the Paja Formation has been recovered other kind of ichthyosaur, Kyhytysuka sachicarum; it is distinguished of Muiscasaurus for their teeth and cranial features, including thicker, robust teeth with grooved tooth enamel. The analysis could indicate that while P. sachicarum probably had a generalist diet, Muiscasaurus was a much more specialized form, feeding on smaller and softer prey items. This would show that during the Cretaceous period in the neotropics, ichthyosaurs kept some ecological diversity.^[2]

See also

• List of flora and fauna named after the Muisca

References

• v
• t
• e

Paleontology in Colombia

Notable
researchers

After 1900	Brieva Cadena Etayo Hammen Hettner Hoffstetter Jaramillo Páramo De Porta Villarroel
19th century	Cuvier Humboldt

Major
fossiliferous
stratigraphic units

Pleistocene	Sabana Fm. Tibitó Soatá Fm.
Neogene	Barzalosa Fm. Castilletes Fm. Honda Group La Venta Jimol Fm. Uitpa Fm. Ware Fm.
Paleogene	Bogotá Fm. Cerrejón Fm. Cerrejón
Cretaceous	La Frontera Fm. Hiló Fm. Hondita Fm. Oliní Gp. Paja Fm.
Jurassic	Arcabuco Fm. Valle Alto Fm.
Devonian	Cuche Fm. Floresta Fm.

Notable fossils

Pleistocene	Gomphotheres Megatherium
Honda Gp.	Anachlysictis Aramus paludigrus Balanerodus Boreostemma Cebupithecia Colombophis Dracaena colombiana Dukecynus Eunectes stirtoni Galbula hylochoreutes Granastrapotherium Gryposuchus Hilarcotherium Hoazinoides Hondadelphys Huilatherium Lagonimico Langstonia Lycopsis Micodon Miocallicebus Miocochilius Mohanamico Mourasuchus Neotamandua Nuciruptor Patasola Potamosiren Purussaurus Saimiri annectens Saimiri fieldsi Stirtonia Xenastrapotherium
Gualanday Gp.	Colombitherium
Bogotá Fm.	Etayoa
Cerrejón Fm.	Acherontisuchus Anthracosuchus Carbonemys Cerrejonemys Cerrejonisuchus Montrichardia aquatica Puentemys Titanoboa
Oliní Gp.	Eonatator
Hondita Fm.	Pachyrhizodus etayoi Yaguarasaurus
Hiló Fm.	Ammonites
Paja Fm.	Acostasaurus Callawayasaurus Desmatochelys Kronosaurus Leivanectes Leyvachelys Muiscasaurus Padillasaurus Platypterygius Sachicasaurus Stenorhynchosaurus
Arcabuco Fm.	Dinosaur tracks
Valle Alto Fm.	Flora
Cuche Fm.	Antarctilamna Asterolepis Bothriolepis Cheiracanthoides Colombialepis Colombiaspis Florestacanthus Holoptychius Pterygotus Strepsodus
Floresta Fm.	Trilobites

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