PLOS Paleo Top 10 OA Fossil Vertebrates #3: Lunaophis aquaticus

We’ve made it to the top 3 winners of the PLOS Paleo Top 10 Open Access Fossil Vertebrates of the year. And I am very pleased that one of the top 3 is not a dinosaur, but a snake! And an aquatic snake to boot. Lunaophis aquaticus, from the Cretaceous La Luna Formation of Venezuela, was recently described and published in the Open Access Journal PeerJ by authors Adriana Albino, Jorge Carrilo-Briceño, and James Neenan.

The specimen is based on a series of precloacal vertebrae, which may not seem like much for a new species description. However, characteristic features of these vertebrae are enough for the researchers involved in this study to diagnose this new snake, combined with information gleamed from the formation regarding its paleoenvironment and habitat.

Lunaophis is named after the La Luna Formation from which it is recovered, representing a typical marine environment sequence of laminated organic-rich deposits interpreted as a mid-shelf to continental slope under anoxic or poorly oxygenated conditions. Specifically, Lunaophis was found in the Cementos Andinos Quarry in the La Aguada Member of the La Luna Formation. Notably, the La Luna Formation is better known as a large source of petroleum for western Venezuela and eastern Colombia, which can be inferred based on the look on the rich, black color of the formation seen in the photos below.

fig-3-2x
Figure 3: Outcrops of the La Aguada Member in the Cementos Andinos quarry. (A) Fossiliferous strata; (B) Strata with calcareous concretions; (C), (D). Discoidal calcareous concretions. From Albino et al (2016).

Lunaophis co-occurs with other marine organisms, such as sharks and bony fishes, including the large, charismatic Cretaceous fish Xiphactinus audax, as well as other icthyodectiforms and lizardfishes. Sharks are represented in the formation mostly by isolated teeth. Due to the anoxic conditions that likely persisted at the benthic level, few to no invertebrates would have lived in that low-oxygen environment. However, scarce invertebrate remains, such as bivalve molds are found in the limestones, and the authors of this study suggest that these remains might represent better oxygenated conditions, or perhaps a bivalve that was more tolerant of terrible oxygen conditions.

fig-10-2x
The articulated precloacal vertebrae of Lunaophis aquaticus. From Albino et al (2016) For guide to abbreviations, please see the paper.

Independent of the environmental interpretation Lunaophis is found, the vertebrae themselves possess characters that are found in other aquatic snakes, which also led the authors of this study to conclude the aquatic lifestyle of this snake. Based on the shape of each vertebral bone, the shape of Lunaophis‘ body was likely strongly compressed laterally, which would have aided in swimming.

You can play around with a moveable 3-dimensional model of the Lunaophis vertebrate, available at the MorphoMuseum.

Unfortunately, due to the lack of skull information, this study was unable to test a hypothesis of evolutionary relationships to other snake taxa, which is contingent upon more information. However, Lunaophis represents the oldest snake taxon known in northern South America, and the oldest to adopt an aquatic mode of life outside of the African and European Tethyan and Boreal Zones.

Congratulations to the team and to Lunaophis for being voted by the community to #3 in the Top 10 OA Fossil Vertebrates of the Year!

Reference:

Albino et al. (2016), An enigmatic aquatic snake from the Cenomanian of Northern South America. PeerJ 4:e2027; DOI 10.7717/peerj.2027

Featured Image (Top): Reconstruction of Lunaophis aquaticus. Art by Edwin Chavez and Jorge Carillo.

Published by Sarah Z. Gibson

Dr. Sarah Z. Gibson is a paleontologist and science communicator based in Minnesota. Her research focuses on the evolutionary history of ray-finned fishes from the Early Mesozoic. https://orcid.org/0000-0002-6784-3980

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