# Early Biogeography of Otophysi Points to the Neotropics as the Cradle of Characiphysan Fishes

## TL;DR

This study traces the early evolution of a major group of freshwater fish, finding that the Neotropics were the origin point for a key subgroup.

## Contribution

The study provides a new phylogenetic hypothesis and biogeographic analysis of Otophysi fishes using extensive genomic data.

## Key findings

- The breakup of ancient supercontinents like Laurasia and Gondwana drove divergence in Otophysi fishes.
- The Neotropics are identified as the origin of Characiphysi fishes.
- Transcontinental dispersal during the Upper Cretaceous-Paleocene explains the expansion of Characiphysi.

## Abstract

Freshwaters represent less than 1% of Earth's surface and only 0.02% of the available aquatic habitable volume, yet they host nearly half of the 35,500 known species of bony fishes. Ostariophysan fishes account for 70% of all freshwater fish diversity, comprising approximately 12,000 species across five highly speciose orders. They represent a major evolutionary radiation, the internal phylogenetic relationships of which remain the subject of intense debate. To better understand their early evolutionary history and origin, we reconstructed their phylogeny using dense taxonomic sampling and a combined dataset of complete mitochondrial genomes and sequences from four nuclear genes. Phylogenetic relationships and divergence times were inferred using Bayesian and Maximum Likelihood approaches and molecular dating analyses on a dataset of 687 ostariophysan species, comprising 21,701 aligned positions, including 15,707 variable sites. We also applied model‐based Maximum Likelihood ancestral area reconstruction to investigate the early evolutionary history of Otophysi. Our analyses yielded a highly supported phylogenetic hypothesis for Otophysi, highlighting the role of plate tectonics in driving multiple divergence events, along with subsequent range shifts. These findings are further supported by the contraction of the tropical belt, which began at the end of the Cretaceous and continued throughout the Paleogene. Our results support the divergence of Cypriniformes and Characiphysi as a consequence of the breakup of Laurasia and Gondwana. The origin of Characiphysi is traced to West Gondwana, and the subsequent expansion of the group cannot be explained without invoking transcontinental dispersal during the Upper Cretaceous‐Paleocene.

Otophysan fishes represent 70% of living freshwater fishes with 12,000 species. Relationships among their four orders were explored through a dense taxonomic sampling including 529 complete mitochondrial genomes and 4 nuclear genes for 324 species. The resulting supermatrix including 21,701 base pair for 687 Ostariophysan fishes yielded highly supported relationships and ancestral area reconstructions point to the Neotropics as the craddle of Characiphysan fishes.