#acanthodian

[kiabugboy]

Inversoceras hides in its shell until the curious Nostolepis gives up and decide to leave it alone

Alt: Inversoceras is a straight slightly curved shelled nautiloid with a narrow opening for its face in front and siphon at the back, here it's being bitten by a Nostolepis, an acanthodian which are the so called spiny sharks even though they're not true sharks. Nostolepis has shark like dorsal and side fins but with spikes at the front

[he-who-needs-to-be-silenced]

Euramerica submission 1

These two goobers are for the rhodophyte forest

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[harpagornis]

Shark Week: Spiny Sharks!

Several acanthodians by Nobu Tamura.

So yeah, shark week! How about we go all the way back into the ancestors of sharks, the Acanthodii, also cleverly known as "spiny sharks"?

Originally thought to be early teleosts, several phylogenetic studies in recent years have firmly placed acanthodians as stem-chondrichthyes*! Some forms like Doliodus are even "missing links", sharing some traits with bony fish latter lost in sharks and rays.

*The ancestors of bony fish, meanwhile, are nested among placoderms or similar forms. Also cool.

Acanthodians were a successful group, having diversified ina menagerie of forms both in salt and fresh water, often resembling modern bony fish in shape. They survived the Devonian extinction, albeit with heavy casualties, and by the mid-Permian they went extinct. Such a bummer!

They are easily my favourite ancient aquatic vertebrates, and though they still live on through their modern cartilaginous descendents, it's neat to imagine a world where their grade survived....

[explosionsoflife]

Pictured is an artist's rendition of an acanthodian, a type of early jawed fish from the Devonian period (400 million years ago). Acanthodians are the earliest known true jawed fishes. They carried less armor than placoderms and are suspected to be the ancestors from which the great diversity of bony-fishes that currently exists evolved from.

(Source)

[explosionsoflife]

Acanthodians, a group of early jawed fishes that were contemporary with placoderms, may have given rise to the great radiation of bony fishes that dominate the waters of the world today.

(Photo source)