Final answer:
The group with the largest number of bird fossils is the Enantiornithes from the Cretaceous period, not Archaeopteryx from the Jurassic period. Enantiornithes fossils are numerous because these 'opposite birds' were the dominant avian species of the time. Preservation of Cretaceous water birds was also enhanced by their aquatic environment. The answer is option B: cretaceous water birds because that's the best place for preservation early.
Step-by-step explanation:
The largest number of bird fossils come from the Cretaceous period, specifically from a group known as the Enantiornithes or 'opposite birds'. These Enantiornithes had distinctive shoulder bones and retained teeth in their jaws like Archaeopteryx, but they also had a modern trait like a shortened tail with a fan of tail feathers. This group was the dominant avian fauna of the Cretaceous but did not survive past it, unlike the members of the ornithurine lineage that includes all modern birds. As for the preservation of these fossils, it is more likely that Cretaceous water birds were well-preserved due to their aquatic habitats that favored fossilization.
Archaeopteryx, although an important fossil showing reptile-like features and feathers, is from the Jurassic period and is not as numerous as Cretaceous bird fossils. It is particularly well-known due to the excellent condition of the fossils found in the Solnhofen limestone in Germany, which was particularly conducive to the preservation of fine details, like feathers.