Calling is postulated to be energetically costly to anurans in general. This morphology demonstrates "Dendrerpeton" having a hearing system that mimics that of anurans. "P. terribilis" is considered to be one of the most intelligent anurans. Both males and females produce calls, which is rare in anurans. The family Centrolenidae is a clade of anurans. Thermal tolerance range in adults is exceptionally low relative to other North American anurans. The ilia of "Gastrophryne" are very distinctive and different from other small anurans. Both anurans and birds use singing in territorial displays to confer aggressive intent. Observations of frequency differentiation among insects, birds, and anurans support the acoustic niche hypothesis. They are therefore among the anurans commonly known as "flying frogs". Decline of anurans and malformations could also suggest increased exposure to ultra-violet light and parasites. Batrachomorpha, containing anurans and their ancestors, and Reptiliomorpha, containing anthracosaurs and amniotes. Like many other anurans, they are often used in laboratory as research subjects. Some anurans will provide parental care towards their tadpoles. In anurans, 70% of polyandrous species exhibit paternal care.