Thursday, July 15, 2021

[PaleoIchthyology • 2021] Choichix alvaradoi • A New Cenomanian Acanthomorph Fish from the El Chango quarry (Chiapas, south-eastern Mexico) and Its Implications for the early Diversification and Evolutionary Trends of Acanthopterygians

Choichix alvaradoi 
Cantalice, Than-Marchese & Villalobos-Segura, 2021

A new Cenomanian spiny-rayed fish from El Chango quarry, Chiapas, south-eastern Mexico is described and included, together with †Zoqueichthys carolinae and †Pepemkay maya, in the most recent phylogenetic analysis of acanthomorph fishes encompassing both extant and extinct taxa. The topologies recovered from the parsimony phylogenetic analysis using both multistate (or composite), and contingent (or reductive), coding are compared, along with a Bayesian estimation. All the analyses corroborate the placement of †Z. carolinae in the Lampripterygii, while both †Choichix alvaradoi gen. et sp. nov. and †P. maya are considered to be incertae sedis members of the Acanthopterygii. Although no apomorphic character states for †C. alvaradoi were found, the unique combination of features supports the description of a new genus and species for the Upper Cretaceous of Mexico. The species herein described is the earliest diverging acanthopterygian lineage. The most outstanding character found is the absence of a true pelvic fin spine, which, together with its placement in the phylogenetic analysis, suggests the independent acquisition of the pelvic fin spine in both paracanthopterygians and acanthopterygians from a segmented first soft ray. This extinct taxon therefore plays an important part in our understanding of both fish diversity through time and the early steps in the diversification of acanthopterygians.

Keywords: Acanthomorpha. acanthopterygian. Cenomanian. Chiapas. Mexico. phylogenetic analysis

Choichix alvaradoi gen. et sp. nov. (IGM 11544).
A, part (mould). B, counterpart.
Scale bars represent 10 mm.

Reconstruction (without scales) of †Choichix alvaradoi gen. et sp. nov. (IGM 11544).  

Systematic palaeontology

Superclass: ACTINOPTERYGII Woodward, 1891
Infraclass: TELEOSTEI Müller, 1845

Subsection: ACANTHOMORPHATA Rosen, 1973
Division: ACANTHOPTERYGII sensu Betancur-R et al. 2017

Genus: †CHOICHIX nov.

Derivation of name: The genus name is the combination of two words in the Tzotzil language: ‘Choy’ (= fish) and ‘Ch'ix’ (= spines), in reference to the number of spines in both dorsal and anal fins.

Type species: IGM 11544, †Choichix alvaradoi gen. et sp. nov.

Choichix alvaradoi sp. nov.

Derivation of name: The species name is a Latinization of the name Alvarado, in honour of Dr Jesús Alvarado Ortega, who devotes most of his life to understanding Mexican palaeodiversity and to teaching students and young researchers. The genus and species names together mean ‘the spiny-finned fish of Alvarado’.

Holotype: IGM 11544, unique specimen preserved in part and counterpart.

Type locality and horizon: El Chango quarry, ..., Ocozocoautla de Espinosa Municipality, Chiapas State, south-eastern Mexico, Cintalapa Formation of Sierra Madre Group (Moreno-Bedmar et al. 2014).

Kleyton Magno Cantalice, Bruno Andrés Than-Marchese and Eduardo Villalobos-Segura. 2021. A New Cenomanian Acanthomorph Fish from the El Chango quarry (Chiapas, south-eastern Mexico) and Its Implications for the early Diversification and Evolutionary Trends of Acanthopterygians. Papers in Palaeontology. DOI: 10.1002/spp2.1359