What sea-dweller did my hexaped Beast-of-Burdern evolve from?

Disclaimer: This question is the third of a new series of questions of mine about introducing hexapeds to the fauna of my conworld. There are/will be other questions addressing i.a.: characteristics, ecosystems, taxonomy

Setting: In my conworld the world is divided into two humongous continents, each taking up about half of the total landmass of the planet. Each located at the Northern and Southern poles respectively.

1 Equatorial Belt    | Saltwater
2                    | Saltwater
5 Northern Polar Sea | Saltwater
6                    | Sweetwater

Evolution: The Beast-of-Burden (further BOB) has six legs and lives predominantly in the northern part of the continent. Its half-dozen legs have given it an advantage in areas where there's lots of uneven and loose ground, as well as more sole-area which helps it stay aloft in marshland.

It is generally agreed upon that features & traits such as mammary glands and live birth can be attributed to convergent evolution. The same goes for its rather long gestation and its multiple young with each birth.

The BOBs live in comparatively small groups of three dozen individuals at most. There doesn't seem to be a predominant alpha male or female and it has been observed that the whole group cares for young.

They're ruminating herbivores that feed mainly on grasses, mosses, bushes, etc.

Question: What (prehistoric) sea-dwelling creature has the BOB likely evolved from? And how could its evolution have looked like?

This question assumes that the hexaped strain of life coevolved with the quadruped strain; for example on different parts of the continent (e.g. the quadrupeds in the south and the hexapeds in the north).

posted over 7 years ago

dot_Sp0T‭

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