# Fossils indicate marine dispersal in osteoglossid fishes, a classic example of continental vicariance

## TL;DR

Fossils show that bonytongue fishes once lived in the ocean, challenging the idea that their current global spread is due only to ancient continental drift.

## Contribution

New fossil evidence and phylogenetic analysis reveal marine origins and multiple freshwater transitions in bonytongue fishes.

## Key findings

- The last common ancestor of bonytongue fishes was likely marine.
- Freshwater colonization occurred at least four times in the group's history.
- Modern distribution patterns are a result of pseudocongruence, not just continental vicariance.

## Abstract

The separation of closely related terrestrial or freshwater species by vast marine barriers represents a biogeographical riddle. Such cases can provide evidence for vicariance, a process whereby ancient geological events like continental rifting divided ancestral geographical ranges. With an evolutionary history extending tens of millions of years, freshwater ecology, and distribution encompassing widely separated southern landmasses, osteoglossid bonytongue fishes are a textbook case of vicariance attributed to Mesozoic fragmentation of the Gondwanan supercontinent. Largely overlooked fossils complicate the clean narrative invoked for extant species by recording occurrences on additional continents and in marine settings. Here, we present a new total-evidence phylogenetic hypothesis for bonytongue fishes combined with quantitative models of range evolution and show that the last common ancestor of extant osteoglossids was likely marine, and that the group colonized freshwater settings at least four times when both extant and extinct lineages are considered. The correspondence between extant osteoglossid relationships and patterns of continental fragmentation therefore represents a striking example of biogeographical pseudocongruence. Contrary to arguments against vicariance hypotheses that rely only on temporal or phylogenetic evidence, these results provide direct palaeontological support for enhanced dispersal ability early in the history of a group with widely separated distributions in the modern day.