Burrowing in blindsnakes: A preliminary analysis of burrowing forces and consequences for the evolution of morphology

Abstract

Burrowing is a common behavior in vertebrates. An underground life-style offers many advantages but also poses important challenges including the high energetic cost of burrowing. Scolecophidians are a group of morphologically derived subterranean snakes that show great diversity in form and function.Although it has been suggested that leptotyphlopids and anomalepidids mostly use existing underground passageways, typhlopids are thought to create their own burrows. However, the mechanisms used to create burrows and the associated forces that animals may be able to generate remain unknown. Here, we provide the first data on push forces in scolecophidians and compare them with those in some burrowing alethinophidian snakes. Our results show that typhlopids are capable of generating higher forces for a given size than other snakes. The observed differences are not due to variation in body diameter or length, suggesting fundamental differences in the mechanics of burrowing or the way in which axial muscles are used. Qualitative observations of skull and vertebral shape suggest that the higher forces exerted by typhlopids may have impacted the evolution of their anatomy. Our results provide the basis for future studies exploring the diversity of form and function in this fascinating group of animals. Quantitative comparisons of the cranial and vertebral shape in addition to collecting functional and ecological data on a wider array of species would be particularly important to test the patterns described here.

Endocast, brain, and bones: Correspondences and spatial relationships in squamates

“…Similar levels of resolution were reported in other amphisbaenians (Amphisbaena gonavensis, A. kingii, A. vanzolinii, Allemand, 2017), scolecophidian snakes (Typhlophis squamosus, Rhinotyphlops schlegelii, Allemand et al, 2017;Typhlops jamaicensis, Scanferla, 2022), and alethinophidian snakes (Uropeltis woodmasoni, Olori, 2010; U. pulneyensis, Allemand et al, 2017;Teretrurus sanguineus, Scanferla, 2022). All these taxa being fully fossorial (e.g., Herrel et al, 2021;Kearney, 2003;Navas et al, 2004;Olori & Bell, 2012), this suggests that weak endocranial resolutions for the optic tectum, pituitary and ventral diencephalon are common in burrowing squamates that spend prolonged periods of time underground and are capable of penetrating substrates of higher resistance (Scanferla, 2016). In contrast, these brain regions are distinguishable from the endocast reconstructed here for the cryptozoic lizard Melanoseps, defined as such as it mostly uses the softer top compartment of the soil for burrowing (Malonza & Bwong, 2011;Scanferla, 2016), and similar levels of endocranial resolution were observed in two cryptozoic alethinophidian snakes, Anilius scytale and Atractaspis irregularis (Allemand et al, 2017;Scanferla, 2022).…”

Cranial osteology of Hypoptophis (Aparallactinae: Atractaspididae: Caenophidia), with a discussion on the evolution of its fossorial adaptations

“…Overall, the shape of the premaxilla and its contacts with both the nasals and the maxilla, well‐developed nasofrontal articulation and nasal‐prefrontal contact suggests that Hypoptophis is able to burrow at least through loose substrate. In a recent study by Herrel et al ( 2021 ), it has been demonstrated that scolecophidians mainly use anteriorly directed force during burrowing. Observations of live specimens of Hypoptophis are needed to validate the hypothesis that it is an active burrower, and if so, to study the functional morphological aspects of digging.…”

Burrowing constrains patterns of skull shape evolution in wrasses

“…Relative head width, however, has been shown to constrain burrowing efficiency in terrestrial burrowing vertebrates where diameter scales exponentially with the amount of work required to compress substrate during the burrowing process (Herrel et al, 2021; Navas et al, 2004). Skull diameter then likely functions as a hard constraint among burrowing wrasses and restricts the regions of morphospace that these species can explore and occupy.…”