Frogs have lived on the Earth for more than 200 million years, as long as dinosaurs. Two lineages of frogs among the Neobatrachia have given rise to tree frogs even though they are not closely related to each other. Many millions of years of convergent evolution, resulting in almost identical habitats and ecologies between the two families, have resulted in species that strongly resemble one another. The two groups are the Rhacophoridae or shrub frogs from tropical regions around the Indian Ocean with a few also occurring in East Asia. On our Costa Rica and Panama cruise we encounter the frogs from the second group Hylidae or "true" tree frogs, especially well represented in the New World.
Hylids range from small to large in size and usually have distinct adhesive toe discs which may aid in climbing. Hylidae is one of the largest families of anurans with over 800 species recognized and was recently taxonomically revised by Faivovich in 2005.
One famous member of Phyllomedusinae (highly arboreal leaf frogs) is the waxy-monkey treefrog (Phyllomedusa bicolor) which is adapted for arid regions and avoids desiccation by wiping lipid secretions over its body. Another well-known species of this group is the Central American brightly colored red-eyed treefrog (Agalychnis callidryas). The egg clutches of this and many other tree frogs are attached to leaf surfaces overhanging water. Embryos develop within the eggs and fall into the water when they hatch. Embryos can sense whether different vibration patterns portend immediate predation by wasps or snakes and hatch immediately, or are simply due to rainfall hitting the leaves and so can stay put for a longer development and better chance at survival.
The subfamily Hylinae has the widest global distribution and in the most recent revision has been organized into 4 tribes, nearly 200 species, 45 genera and many of them newly named. One of the most unusual members of this group is the “paradoxical frog” (Pseudis paradoxa), whose tadpoles reach an enormous size of up to 220 mm but subsequently metamorphose into adults ranging from 3 to 4 times smaller.
All tree frogs are suited for life under the canopy of a moist forest, high up in the trees. For this reason they are usually tiny, as their weight has to be carried by the branches and twigs of their habitat; their size varies from 1.5 cm (least tree frog/Hyla ocularis) to 10 cm (Hyla vasta). Most have a typical bright green coloration with white or yellow ventral stripes, which may vary, others are subtly patterned for needed camouflage depending on the particular kind of vegetation they inhabit and the predators they hide from, and their limbs tend to be rather long, resulting in a superior grasping ability allowing them to walk on narrow branches, catch agile prey as well as jump up to 40 times their own length.
Tree frogs do not often descend to the ground, with some exceptions to find mates and spawn. It is during these journeys down into the lower reaches of the rainforest or cloud forests that we stand the best chance of encountering them on our Costa Rica and Panama cruises. However during their adult lives, tree frogs rarely leave the trees at all and usually rest during the day but hunt for food especially during the night, a diet that consists of insects and other small invertebrates such as worms and spiders.
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