Differential growth of seals and sea lions with paedomorphic and peramorphic adult skull morphologies

Links between behavior and skull morphology have been widely demonstrated in carnivorans. The skulls of more‐aggressive species tend to be more peramorphic, with greater crest development for the emplacement of muscles, compared to the more paedomorphic rounded skulls of less‐aggressive species. Are these two endpoints the result of differential growth patterns in dimorphic species? To answer this, we looked at skulls of seals and sea lions ( n = 58, including 22 males, 14 females and 22 unknowns, usually juveniles) across 8 species. We categorized the individuals into ages from immature (teeth erupting, less fused sutures, smaller size), sub‐adult (teeth erupted but not worn, more sutural fusion), and adult (teeth with wear, fully‐fused sutures, and larger size). We compared these individuals by observing the placement of 26 bony landmarks using a geometric morphometric approach. We found that paedomorphic adults have juvenile‐looking skulls, e.g., a short or absent sagittal and nuchal crest, a narrow zygomatic width, and shorter skull length between the braincase and rostrum. Peramorphic adults had more growth resulting in traits including taller sagittal and nuchal crests, a wider zygomatic width, and a longer skull length. The brain case varied little between paedomorphic and peramorphic end points. The increase in skull length happens first through growth, and the width of the zygomatic arch and height of crests increases later, likely in response to the increase of size of the jaw‐closing muscles. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .