Ecological guild evolution and the discovery of the world's smallest vertebrate

Abstract

Living vertebrates vary drastically in body size, yet few taxa reach the extremely minute size of some frogs and teleost fish. Here we describe two new species of diminutive terrestrial frogs from the megadiverse hotspot island of New Guinea, one of which represents the smallest known vertebrate species, attaining an average body size of only 7.7 mm. Both new species are members of the recently described genus Paedophryne, the four species of which are all among the ten smallest known frog species, making Paedophryne the most diminutive genus of anurans. This discovery highlights intriguing ecological similarities among the numerous independent origins of diminutive anurans, suggesting that minute frogs are not mere oddities, but represent a previously unrecognized ecological guild.

Figure 1. Osteological characters of Paedophryne amauensis, P. swiftorum.

A. X-ray of paratype of Paedophryne amauensis (LSUMZ 95002). B. X-ray of paratype of P. swiftorum (BPBM 31886). C,E,G,I. Photos of cleared and double-stained paratype of P. amauensis (LSUMZ 95002). C. Whole body. E. Head. G. Hand. I. Foot. D,F,H,J. Photos of cleared and double-stained paratype of P. swiftorum (BPBM 31886). D. Whole body. F. Head. H. Hand. J. Foot. Skeletal elements labeled as follows: Fp, frontoparietal; Il, illium; Mc1-4, metacarpals 1-4; Mt1-5, metatarsals 1-5; Mx, maxilla; N, nasal; S, Sacrum; Sp, sphenethemoid; Sq, squamosal; U, urostyle; V1, first presacral vertebra; V7, seventh presacral vertebra.

Figure 2. Type localities, call sonograms, and photographs of Paedophryne species.

A. Photograph of paratype of Paedophryne swiftorum in life (BPBM 31880). B. Waveform (upper right), power spectrum (lower left) and spectrogram (lower right) of a single call series consisting of four double notes of the holotype of P. swiftorum (BPBM 31883). C. Type localities of the four species of Paedophryne. Blue: P. swiftorum; red: P. amauensis; yellow: P. kathismaphlox; purple: P. oyatabu. D. Photograph of paratype of P. amanuensis (LSUMZ 95004) on U.S. dime (diameter 17.91 mm). E. Waveform (upper right), power spectrum (lower left) and spectrogram (lower right) of the first four notes of the call of the holotype of P. amauensis (LSUMZ 95000).

Figure 3. Phylogenetic position of Paedophryne and evolution of body size in Asterophryinae.

Maximum likelihood phylogeny of Paedophryne and asterophryine frogs. Colors of branches correspond to maximum male SVL (Paedophryne) or average SVL within each clade on a logarithmic scale (Table 6). Circles above branches correspond to posterior probabilities: black: >0.95; grey: 0.85–0.95; white: 0.5–0.85. Circles below branches correspond to maximum likelihood bootstrap support: black: >95%; grey: 75–95%; white: 50–75%.