And since all land vertebrates are descendents of fish, and you can't evolve out of a clade, whales actually are fish.
Ihmes
joined 8 months ago
If you had to choose between being a Tarantula or a Tyrannosaurus Rex for the rest of your life which would you choose and why?
Oxygen levels wouldn't be a factor. The "need high oxygen levels for large size" only applies to invertebrates with very simple breathing systems.
If trex had similar type of lungs as modern birds, they would do just fine. Bird lungs are super efficient (much better than mammals' puny blind sack lungs) that enable them to fly at high altitudes.
Sounds like wolf spiders. They are actually good mammas and they haul their 'lings on their backs until they are old enough to disperse.