Chubutinectes

Chubutinectes (meaning "Chubut swimmer") is an extinct genus of elasmosaurid plesiosaur from the Late Cretaceous La Colonia Formation of Argentina. The genus contains a single species, C. carmeloi, known from a partial skeleton and associated gastroliths.^[1]

Chubutinectes Temporal range: Late Cretaceous (Upper Maastrichtian) PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Order:	†Plesiosauria
Family:	†Elasmosauridae
Clade:	†Weddellonectia
Genus:	†Chubutinectes O'Gorman et al., 2023
Species:	†C. carmeloi
Binomial name
†Chubutinectes carmeloi O'Gorman et al., 2023

Discovery and naming

Photographs from the excavation of the Chubutinectes type specimen

The Chubutinectes holotype specimen, MPEF-PV 5232, was discovered in 2009 within sediments of the La Colonia Formation on the Somún Curá plateau in Chubut Province, Argentina. The disarticulated specimen consists of cervical, pectoral, dorsal, sacral, and caudal vertebral centra and neural arches, various ribs, partial pectoral and pelvic girdles, fore- and hind-limb elements, and about 350 gastroliths.^[1]

In 2023, O'Gorman and colleagues described Chubutinectes carmeloi as a new genus and species of elasmosaurid plesiosaur based on these fossil remains. The generic name, "Chubutinectes", combines a reference to the Argentinean province "Chubut", where the holotype was found, with the Greek word "nectes", meaning "swimmer". The specific name, "carmeloi", honors Carmelo Muñoz, the discoverer of the holotype.^[1]

Description

The holotype of Chubutinectes is an osteologically immature specimen with a dorsal region measuring 1.4 m (4.6 ft) long, indicating that it was larger than an adult Kawanectes from the same formation. This size difference may result from their environmental difference, as Kawanectes lived in estuaries, while Chubutinectes lived in marine habitats.^[1]

Classification

In their phylogenetic analyses, O'Gorman et al. (2023) recovered Chubutinectes as a member of the elasmosaurid clade Weddellonectia, as the sister taxon to the clade containing Aphrosaurus and Hydrotherosaurus.^[1] Nearly identical results were recovered by O'Keefe et al. (2025) in an updated version of this phylogenetic matrix, the results of which are shown in the cladogram below:^[2]

Weddellonectia	Tuarangisaurus Futabasaurus Chubutinectes Aphrosaurus Hydrotherosaurus Morenosaurus Vegasaurus Kawanectes Marambionectes Aristonectinae ⊞ Wunyelfia MLP 99-XII-1-5 (Aristonectinae indet.)[3] Aristonectes parvidens Aristonectes quiriquinensis Kaiwhekea Alexandronectes Morturneria ⊟

Paleoenvironment

Chubutinectes was discovered in layers of the La Colonia Formation, which dates to the upper Maastrichtian. Based on the presence of nanofossils of Micula spp., the rock layers are younger than around 67.3 million years old. The fellow elasmosaurid Kawanectes was also found in this formation, as well as the remains of indeterminate elasmosaurids and the polycotylid Sulcusuchus.^[1][4] Dinosaur fossils, including those of the abelisaurid theropods Carnotaurus and Koleken, titanosaurian sauropod Titanomachya, ankylosaurs, hadrosauroids, and somphospondylans, have also been found.^[5][6][7] Other fossils animals include various species of mammals, turtles and snakes.^[8][9]