Meeting Abstract

P1.104  Saturday, Jan. 4 15:30  Precocial Development of the Tympanoperiotic Complex in Cetaceans LANCASTER, W/C; ARY, W/J*; CRANFORD, T/W; Sacramento State Univ., Sacramento; San Diego State Univ., San Diego; San Diego State Univ., San Diego tcranfor@mail.sdsu.edu

Cetaceans use acoustic signals to orient and communicate. Light penetrates poorly in aquatic environments, which places a premium on acoustic communication and increases selective pressure to develop a completely functional organ of hearing at or near the time of birth. William F. Perrin found that the tympanoperiotic complex in juveniles in two delphinid species, Stenella longirostris and S. attenuata, were near adult size in spite of smaller skulls and bodies. We gathered data to test whether this feature is common across the Cetacea. We collected homologous measurements from skulls and tympanic bullae of 1 adult and 1 juvenile in 14 species of cetaceans (6 families in Odontoceti and 2 families in Mysticeti). Across all samples, total (body) length (TL) of juvenile specimens ranged from 46-81 % of adult TL, juvenile condylobasal (skull) length (CBL) ranged from 53-93% of adult CBL, and juvenile tympanic bulla length (TBL) ranged from 93-109% of adult TBL. For two species we measured 10 adults and 10 juveniles to assess individual variation. In these samples of Tursiops truncatus and Pontoporia blainvillei, the CBL of juveniles was significantly smaller than adults (Paired Two-sample t-test, P=0.0004 in T. truncatus, P<0.0001 in P. blainvillei), whereas juvenile TBL was not significantly different from that of adults (Paired Two-sample t-test, P=0.0945 in T. truncatus, P=0.4607 in P. blainvillei). Our data demonstrate a pattern of accelerated allometric growth of the tympanic bullae compared to the skulls across a broad range of cetacean taxa. We interpret this as evidence for precocial development of auditory function in the Cetacea.