Which organism would you expect to have evolved first, a spider or a lizard? Why?

Answer 1

I wouldn't go by my expectations, I would go by what the physical evidence shows.

The earliest known spider is Attercopus fimbriungis, found in sediments dated to at least 380 million years ago. It was much thicker in body than modern spiders, with spinnerets on the underside of the abdomen (not the tip, as in modern spiders), but had the familiar eight legs and fangs of a spider.

The earliest known Diapsid reptile was Petrolacosaurus, which was very similar to a lizard, and gave rise to both the Lepidosaur lineage that became lizards, snakes and mosasaurs, and the Archosaur lineage that became crocodiles, dinosaurs and birds.

Petrolacosaurus lived in the Late Carboniferous, about 300 million years ago. It lived at a time when there were numerous invertebrates alive much larger than it, including the giant dragonfly Meganuron and gigantic spiders.

So, spiders definitely evolved first.

Answer 2

If I were an evolutionist, I'd say spiders, since arthropods in general were around a long time before vertebrates.

Answer 3

spiders and lizards are not "organisms" they are living species. the first "organism" would have been the very first replicating single cell. By the sheer logic of the passage of aeons of time, and the permutation of probabilities, it would have been impossible for it NOT to have happened eventually, that a particle of matter would have suddenly become self replicating, and the very first simple single-cell organism to have thus come into existence.

Answer 4

A spider.
Because they did evolve first.