SpecTember 6: Seedworld's Harvest

200 million years have passed since this particular planet was seeded with life by a long-forgotten species. The organisms brought there included a wide variety of plants and invertebrates, a small number of fish, and a single tetrapod-- the American bullfrog. For millions of years afterwards, the frogs had this world all to themselves, and soon evolved into forms unlike any amphibian on Earth. One particular lineage evolved water-tight skin, more efficient lungs, and internal fertilization for its eggs, which now hatched inside them into miniature adults without going through a tadpole stage. In short, they underwent the same transition that the ancestors of reptiles did back on Earth in the Permian period. Now, 200 million years later, these "neo-frogs" are the dominant megafauna of their world, with some groups even achieving endothermy and powered flight. But the largest of all are found in the ocean.
The Bearded Frogwhale (Batrachoposeidon barbatus) is the largest animal in its world, and the largest amphibian to have ever lived. While Earth amphibians have little tolerance for salt water, the watertight skin of these highly derived creatures means they can tolerate it just as reptiles can. The Bearded Frogwhale is a true leviathan, growing up to 65 feet long and weighing nearly 30 tons. An inhabitant of warm tropical seas, it feeds by using its cavernous mouth as a scoop to swallow entire schools of small fish and shrimp, then pressing the excess water out of its mouth by squeezing its flexible throat pouch shut. In this manner, it fills a niche not unlike that of Earth's baleen whales. Both sexes possess a pair of sensory tentacles protruding from their heads; these are filled with nervous tissue and used to navigate. 
Frogwhales fertilize their eggs internally, and give "birth" to one or two relatively large babies, which look like miniature versions of their parents. There is no parental care, however. The babies are fully independent from the moment they leave their mother's brood pouch.