By Jennifer Viegas, Discovery News:
May 6, 2009 — Seahorses first stood up sometime after 25 to 20 million years ago, when bodies of open water between Australia and Indonesia changed, leaving these horse-resembling bony fishes with shallow sea grass habitat, according to a new study.
The study, published in the latest Royal Society Biology Letters, explains that an upright stature, shared by humans but which is extremely rare throughout the entire animal kingdom, allowed seahorses to reside in what was essentially a lawn under water.
To this day, seahorses prefer to live in sheltered areas, such as sea grass beds, coral reefs and mangroves.
“Not only can an upright fish maneuver much better in such an environment than a horizontally-swimming one, but the upright sea grass blades would have improved their camouflage,” explained Peter Teske, who co-authored the paper with Luciano Beheregaray.
“Camouflage is of great importance to seahorses, which are poor swimmers,” added Teske, a postdoctoral researcher in Macquarie University’s Molecular Ecology Lab. “It affords them both protection from predators and allows them to sneak up on their prey — including small crustaceans and tiny fish — without being noticed.”
Teske and Beheregaray first took note of pygmy pipehorses, which look like “non-upright proto-seahorses.” They wondered when these two bony fishes diverged, and how this fit into the bigger picture for the Syngnathidae, a family of fish that includes seahorses, pipefishes and both weedy [see also here and here and here] and leafy sea dragons.
To answer these questions, they constructed a family tree using genetic information gathered from the genus Hippocampus, which includes all seahorses, and the genus Idiotropiscis, which contains the very seahorse-resembling southern little pipehorse.
Molecular dating indicates seahorses split from their pygmy pipehorse sister taxon during the Late Oligocene, right when tectonic events in the Indo-West Pacific resulted in the formation of new shallow water sea grass habitats. It appears that seahorses remained mostly isolated in these new regions, allowing them to evolve a number of distinctive features.
Male seahorses like big mates: here.
UK Seahorse tagging project at Studland Bay in Dorset: here.
October 2010: Marine scientist Paul Kay took this picture of pipefish off the Welsh coast. Thought to be a shore or black-striped pipefish, the photograph is so unusual because of where it was taken – such pipefish are normally found only as far north as the Southern Biscay, with the odd one making its way slightly further up the French coast: here.