That we know of, or have fossil records for...
I know it may not be "perfect", but for some reason God had to use the language "birds" and such (and such) to those people back then at that time, to describe some creatures of the sea that might have had some limited ability to "fly" back then...
It is very hard to find a lot of fossil records for that age and era and time, for one thing there just are not very many of them around anymore, for one thing...
Unless it was a very, very common creature, that was very big in numbers, then it's that much harder to have or find any fossils of them around by our period of time since it was so long ago, etc, and a lot geologically has happened to and in the earth since then...
But there could have been, no, more than likely "is or are or were" many, many different kinds of sea creatures back then ("monsters" also) (or pretty monstrous sea creatures) that were more than likely never going to find any fossils of, or fossil record for, ever, (now), (or by now), etc, but that is not to say that those creatures never existed, and there could have been many others we don't know about as well, (and more than likely were), and are never going to ever find out about as well, (such as flying ones, etc), but that is not to say that none like that ever existed back then, etc...
Anyway,
God Bless!