A new elasmosaurid (Plesiosauria: Sauropterygia) from the López de Bertodano Formation: new data on the evolution of the aristonectine morphology

Abstract

A new elasmosaurid Marambionectes molinai gen. et sp. nov. from the upper Maastrichtian levels of the López de Bertodano Formation is here described. The new taxon is characterized by one autapomorphy: 48 cervical vertebrae with lateral keels in cervicals 5 to 29. The following combination of features also differentiates Marambionectes molinai gen. et sp. nov. from other elasmosaurids: three symphyseal alveoli, symphyseal angle of c. 100°, wide symphyseal sulcus, high and triangular coronoid process, retroarticular process horizontally oriented, circular atlantal cup, low and rounded hypapophyseal keel on atlas-axis complex, cervical centra longer than high (middle cervical with vertebral length index c. 97) and caudal centra without strongly laterally projected parapophyses. The phylogenetic analysis recovers M. molinai gen. et sp. nov. within the Weddellonectia and as a sister group of aristonectines, indicating that the process of decreasing cervical vertebrae numbers, wide symphyseal sulcus and atlas-axis complex with circular atlantal cup and low and rounded hypapophyseal keel started previous to the appearance of aristonectines. In this sense, we suggest that some of the skeletal characteristics of aristonectines were acquired through a process that began in non-aristonectine elasmosaurids, before the appearance of this clade. http://zoobank.org/urn:lsid:zoobank.org:pub:693E0AAA-D03A-42E7-B454-BBA4D481649A

Keywords:

• Plesiosauria
• Elasmosauridae
• Weddellonectia
• López de Bertodano Formation
• Maastrichtian

Acknowledgements

This contribution would not have been possible without logistical support from the Instituto Antártico Argentino and the Fuerza Aérea Argentina (Dotación 50° of Base Marambio). This research was supported by projects PICT 2017-0607 and PICT-2018-02443 and a Fulbright Scholarship (J.P. O'G). The author thanks the staff of the Museo Municipal Ernesto Bachmann for the preparation of the specimens. Thanks to P. Druckenmiller (Museum of the North) for the photos of the holotype of N. bradti and to the curators who allowed the study of material under their care, D.A. Winkler (Shuller Museum), K. Dean (Texas Tech University) and C. Amenabar (IAA). The author thanks M. Paramo (Universidad Nacional de Colombia, Bogotá, Colombia) and the anonymous reviewers for the comments that improve this contribution.

Supplemental material

Supplemental material for this article can be accessed here: https://doi.org/10.1080/14772019.2024.2312302.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Associate Editor: Erin Maxwell