# Atacamaia

Atacamaia is an extinct genus of coelacanth from the Early Jurassic of Chile. The sole known species, Atacamaia solitaria, was discovered in the Atacama Desert, specifically in the Vaquillas Altas locality, dating to approximately 201 to 174 million years ago. Belonging to the family Whiteiidae, Atacamaia is notable as the first Mesozoic coelacanth found on the Pacific side of Gondwana, offering valuable insights into the distribution and evolution of coelacanths during this period.

## Description

Atacamaia solitaria is represented by a partially three-dimensionally preserved head, exhibiting lateral compression, with dimensions of approximately 80 mm in length and 60 mm in depth. Distinctive cranial features include a broad parietal bone, a series of large supraorbital bones, sclerotic bones, an expanded and angled lachrymojugal, and a metapterygoid with a prominent ventral process. These traits differentiate Atacamaia from other coelacanth genera, particularly in its skull morphology.

## Taxonomy

Atacamaia falls within the Actinistia, the group encompassing coelacanths, and is classified in the family Whiteiidae. Typically associated with Triassic forms, the Whiteiidae family's temporal range is extended into the Early Jurassic by Atacamaia solitaria, marking it as the youngest known member of this lineage. The genus and species were formally described in 2015 by Gloria Arratia and Hans-Peter Schultze, based on the holotype (MNHN SGO.PV 288), which is housed at the Museo Nacional de Historia Natural in Chile.

## Discovery

The holotype of Atacamaia solitaria was unearthed in the Vaquillas Altas locality of the Atacama Desert, Chile, during expeditions in the 1990s. Collected by Kate Shaw in 1994, the specimen originates from Early Jurassic strata, approximately 201 to 174 million years old. The Atacama Desert is renowned for its rich fossil record, including marine vertebrates such as fossilized whales and other significant paleontological discoveries.

## Paleoecology

Atacamaia solitaria inhabited a marine environment during the Early Jurassic, as evidenced by the sedimentary context of the Vaquillas Altas locality. Although the Atacama Desert is now arid, it was once submerged under shallow seas that supported a diverse array of marine life, including coelacanths.

## Phylogeny

Phylogenetic studies place Atacamaia within the Whiteiidae family, alongside genera such as Whiteia and Piveteauia. However, its inclusion in evolutionary trees results in polytomies, indicating unresolved relationships due to its unique combination of cranial features. This complexity suggests that Atacamaia challenges existing frameworks of coelacanth evolution.

## Significance

Atacamaia solitaria holds importance as the first Mesozoic coelacanth identified on the Pacific side of Gondwana, a supercontinent that included South America. Its discovery expands the known geographic and temporal range of the Whiteiidae family into the Early Jurassic. The phylogenetic uncertainties it introduces underscore the need for further investigation into coelacanth evolution during the Mesozoic. Additionally, the Atacama Desert's paleontological richness is underscored by finds such as fossilized whale graveyards and the titanosaur Atacamatitan, reinforcing its status as a key fossil-bearing region.