Theory #1 -Based on the discovery of a 240-million-year-old fossil archosaur, paleontologists theorize that dinosaurs split off
early from the crocodile family tree. The journal Nature describes Asilisaurus kongwe as a dog-sized, plant-eating dinosaur precursor. Asilisaurus lived during the Triassic period, when crocodile-like beasts ruled the Earth, with dinosaurs becoming dominant some 35 million years later. Theory #2 - Almost 20 years of research on the morphology of birds and dinosaurs support a different theory: that birds may have had an ancient common ancestor with dinosaurs, but they evolved separately on their own path and after millions of years, birds also gave rise to the raptors. Small animals such as velociraptors, that have generally been thought to be dinosaurs, are more likely flightless birds according to this theory.
Compare the two theories regarding the evolution of dinosaurs and then consider the cladogram above. Although the two theories differ on the evolutionary path of dinosaurs, they agree that
A) dinosaurs, reptiles, and birds had a common ancestor.
B) dinosaurs evolved much later than birds or reptiles.
C) the branch containing dinosaurs evolved before either reptiles or birds.
D) dinosaurs should be on the same main branch as snakes, lizards and crocodiles.
I think that since it lives on the ocean floor, at the deepest of the ocean. So anyway, the fin on the Eurypterids is still necessary but not that much, since they live on the ocean floor. Their movements mostly on the ocean floor. So fin would not help them "stick" to the floor. Also there are still gravity acts on the Eurypterids and the feet would help them move faster. Hope this helps.
