Biology:Muiscasaurus

Short description: Extinct genus of reptiles

Muiscasaurus Temporal range: Barremian-Aptian ~130.0–112.6 Ma PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Subclass:	Diapsida
Order:	†Ichthyosauria
Family:	†Ophthalmosauridae
Genus:	†Muiscasaurus Maxwell et al., 2015
Type species
†Muiscasaurus catheti Maxwell et al., 2015

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.

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.

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. This individual could reach 3 metres (9 ft 10 in) long and up to 5 metres (16 ft 5 in) long in adults. 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.

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.

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) .

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

Ophthalmosauridae	Ophthalmosaurus     Undorosaurus     Acamptonectes       Leninia       Aegirosaurus       Mollesaurus         Muiscasaurus       Brachypterygius       Caypullisaurus     Platypterygius       Platypterygius australis     Simbirskiasaurus     Pervushovisaurus               Sveltonectes     Maiaspondylus       Athabascasaurus       Cryopterygius       Janusaurus       Arthropterygius     Palvennia

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

Ophthalmosauria

Ophthalmosaurinae         Acamptonectes densus       Mollesaurus periallus       Ophthalmosaurus natans     Ophthalmosaurus icenicus                   Gengasaurus nicosiai         Nannopterygius yasykovi       Nannopterygius enthekiodon     Nannopterygius saveljeviensis     Nannopterygius borealis             Arthropterygius volgensis       Arthropterygius lundi     Arthropterygius thalassonotus       Arthropterygius hoybergeti     Arthropterygius chrisorum                   Platypterygiinae     Brachypterygius extremus     Aegirosaurus leptospondylus       Muiscasaurus catheti       Leninia stellans       Sveltonectes insolitus       Athabascasaurus bitumineus       Platypterygius americanus         Acuetzpalin carranzai     Platypterygius sachicarum     Caypullisaurus bonapartei             Grendelius mordax     Grendelius alekseevi     Grendelius pseudoscythicus     Grendelius zhuravlevi             Undorosaurus kielanae       Undorosaurus nessovi     Undorosaurus gorodischensis                 Platypterygius australis       Plutoniosaurus bedengensis     Simbirskiasaurus birjukovi     Platypterygius hercynicus     Sisteronia seeleyi     Platypterygius platydactylus     Maiaspondylus lindoei

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.

See also

• List of flora and fauna named after the Muisca

References

Template:Paleontology in ColombiaTemplate:Ichthyosauria Wikidata ☰ Q21150601 entry