Postnatal Development of the Skull of Dinilysia patagonica (Squamata‐Stem Serpentes)

Abstract

The snake skull represents a profound transformation of the ancestral squamate cranium in which dermal skull roof bones were integrated with the braincase, in a manner convergent with that which occurred during the origin of mammals. However, the ontogeny of snake characters at the origin of the clade has until now been inaccessible. Here we describe a postnatal ontogenetic series of the Late Cretaceous stem snake Dinilysia patagonica and compare it to that of extant lizards and snakes. Comparative analysis indicates notable ontogenetic changes, including advanced state of ossification, isometric growth of the otic capsule, fusion of the stylohyal to the quadrate, and great posterior elongation of the supratemporal. Of these transformations, the unfused condition of braincase bones and the retention of a large otic capsule in adults are examples of paedomorphic and peramorphic processes, respectively. Some ontogenetic transformations detected, in particular those present in middle ear, skull roof and suspensorium, are strikingly similar to those present in extant snakes. Nevertheless, Dinilysia retains a lizard-like paroccipital process without an epiphyseal extremity, and a calcified epiphysis that caps the sphenoccipital tubercle. Finally, the integration of the dermal skull roof with the braincase is similar to that seen in mammals with regard to the overall closure of the braincase, but the two evolutionary and developmental modules appear less integrated in snakes in that the parietal bone of the dermal skull roof progressively overlaps the supraoccipital of the chondrocranial braincase.

Patterns of postnatal ontogeny of the skull and lower jaw of snakes as revealed by micro‐CT scan data and three‐dimensional geometric morphometrics

“…Relatively few studies have focused on the postnatal development of the cranial skeleton of snakes (e.g. Rossman, 1980;Young, 1989;Monteiro, 1998;Scanferla & Bhullar, 2014), though these patterns are well-documented in lizards (e.g. Maisano, 2001Maisano, , 2002aBell et al 2003;Torres-Carvajal, 2003;Tarazona et al 2008).…”

Prenatal development of the sound transmitting apparatus in different embryonic stages of Malpolon monsspesulanus (squamata-serpentes)

“…In light of our findings, Wever (1978), Young (2003), Friedel et al (2008), Scanferla and Bhullar (2014) and Dowling (2015) reported that snakes cannot hear. This deduction is supported by the fact that snakes have neither eustachian tube nor tympanum.…”

“…In addition, snakes cannot hear. This presumption is supported by the fact that snakes have neither tympanum nor eustachian tube, and the stapes whose proximal end rests in the vestibular window and its distal end attached to the quadrate bone on which the lower jaw swings (Young, 2003;Friedel et al, 2008;Scanferla and Bhullar, 2014;Dowling, 2015) and that scientific evidence of snakes responding to sound is rare. Snakes do, however, possess an inner ear with a functional cochlea and with poorly developing middle ear components.…”

Hallazgo de restos de la serpiente <em>Dinilysia patagonica</em> Smith-Woodward 1901 en una nueva localidad del Santoniano de Patagonia, Argentina

“…Esta condición per mite inferir que tal variación estaría vinculada a la edad del individuo. Esto es consistente con lo refe rido por Scanferla & Bhullar (2014) respecto que se trataría una variación ontogenética postnatal. De esta manera, los cráneos comparativamente más peque ños, donde el parietal aún tiene participación en el margen del foramen trigémino, corresponderían a individuos jóvenes que aún no han alcanzado su tamaño máximo.…”

“…Restos de este clado son comunes y diversos en depósitos cretácicos de Patagonia, incluyendo algunas de las más primiti vas serpientes terrestres como Najash rionegrina del Cenomaniano-Turoniano (Apesteguía & Zaher, 2006;Zaher et al, 2009;Palci et al, 2013) y Dinilysia patagonica del Santoniano-Campaniano (Smith Woodward, 1901;Estes et al, 1970;Hecht, 1982;Rage & Albino, 1989;Caldwell & Albino, 2002;Scanferla & Canale, 2007;Caldwell & Calvo, 2008;Zaher & Scanferla, 2012, Scanferla & Bhullar, 2014Palci & Caldwell, 2014). Además, varias especies de Madtsoiidae, el "anilioideo" Australophis anilioides y formas inciertas de serpientes se reconocen para el Campaniano-Maastrichtiano (Albino, 1986(Albino, , 1994(Albino, , 2000(Albino, , 2007(Albino, , 2011Martinelli & Forasiepi, 2004;Gómez et al, 2008;Gómez, 2011).…”