TALES OF LONG FACES: PISCIVOROUS ARCHOSAURIFORMS AND THE EVOLUTIONARY WAYS TO FORGE A FISHER

Piscivory refers to a predominantly fish-based diet.This behavior has been inferred for a series of archosauriforms, based on a wide array of morphological features. However, how accurate is the correlation between a strictly piscivorous diet and such purported morphofunctional features? We review such features and their potential correlation to piscivory utilizing the morphological diversity of extant piscivorous archosaurs as a basis. Among these, slender-snouted crocodilians are divided in three categories: (1) narrow-snouted: the proximal portion of the rostrum comprises the largest width and tapers anteriorly until the rostral tip at a constant pace (_Crocodylus_); (2) semi-tubular: the proximal portion of the rostrum comprises the largest width and tapers continuously anteriorly until reaching width stabilization prior to the middle of the rostrum (_Tomistoma_); and (3) tubular: the width difference from the proximal portion with the rest of the rostrum is drastic, with an abrupt, non-continuous thinning by the distal base of the rostrum (_Gavialis_). Concerning piscivorous birds, they fall within one of the two morphotypes described above: (1) narrow-snouted (Ardeidae) and (2) semi-tubular (_Mergus_). Furthermore, we additionally divide piscivorous birds in: (i) brevirostrines (_Fratercula_); (ii) normal (_Larus_); and (iii) longirostrines (_Ardea_). There are several morphological adaptations directly or indirectly related to piscivory, some of which are: (1) longirostry: related to hydrodynamics; (2) external nares position: retracted external nares enable breathing during rostrum submersion and/or carcass feeding; (3) expanded premaxillaries: originally viewed as related to an increase in the capture surface, but extant species do not corroborate this hypothesis; (4) premaxillary/maxillary notch: could increase the capture efficiency, but not exclusively for fishes; (5) teeth number and distribution: high count enables an increase in underwater capture rate; and (6) teeth morphology: the diastemata and the conical, slightly recurved crowns seem to have a direct relation with piscivory. Still, in isolation, those morphological evidences cannot be used as determinant for inferring a piscivorous diet. We propose that inferences on piscivorous diet must rely on a total evidence basis, taking into consideration those multiple lines of evidence as well as other data such as biomechanics, lifestyle and the environment of the taxa in question. [*, CAPES; **, SESu/MEC]