DOI: 10.5061/dryad.x95x69psc
title: Different selection regimes explain morphological evolution in fossorial lizards

description: Independent origins of similar phenotypes are ubiquitous to the
 evolutionary process and evoke strong and recurrent environmental
 associations. Snakelike lizards evolved multiple times and are often
 portrayed as limb-reduced and body-elongated outcomes from shared
 selection associated with fossoriality. However, a refined
 evaluation including specific head traits and subtle differences in
 subterranean microhabitats unveils some degree of uniqueness even among
 lineages traditionally interpreted as phenotypically similar. Here we
 address regimes of selection in fossorial lizards accounting for
 differences in the burrowing substrate and emphasizing head shape in
 addition to body and limbs. We assembled an ecomorphological
 database comprising 213 species from all major lizard clades, and then
 characterized contemporary morphological diversity and modeled phenotypic
 evolution to test the hypothesis that fossoriality encompasses at least
 two distinct selection regimes. We identified two
 ecomorphological groups within the fossorial lizards: moist-soil fossorial
 and dry-soil fossorial. Both groups evolved towards distinct adaptive
 optima concerning head shape and limb size. Despite some degree of
 uniqueness, these groups also share similar patterns in specific traits.
 Dry-soil fossorial lizards present less morphological variation than
 moist-soil fossorial, possibly due to the combination of distinct sets of
 selective pressures with shared ancestry. Our study provides
 evidence that an often-interpreted general adaptive regime (e.g.,
 fossoriality) may in fact comprise enough ecological and functional
 diversity to elicit several distinct ecomorphological associations despite
 overall convergence among phenotypic traits.
description: We assembled a large morphological database composed of all major
 lizard groups, focusing on snakelike lineages. We modeled phenotypic
 evolution by comparing different hypotheses of selection regimes to
 evaluate if limb reduction, body elongation and head shape evolved towards
 two distinct adaptive optima in fossorial lizards: dry-soil and moist-soil
 fossorial groups. We also characterized current morphological disparity
 within the fossorial lizards, as we predict that the dry-soil fossorial
 group encompasses less morphological diversity than moist-soil fossorial
 lizards, due to unique adaptations involved with headfirst burrowing in
 sand and dry soils. We also evaluated the profiles of morphological
 disparity through time, as we expect that historical processes associated
 with morphological diversity partitioning may reflect different
 combinations of shared ancestry and adaptation in distinct snakelike
 lineages.
description: # Different selection regimes explain morphological evolution in fossorial
 lizards
 [https://doi.org/10.5061/dryad.x95x69psc](https://doi.org/10.5061/dryad.x95x69psc) Here we address regimes of selection in fossorial lizards accounting for differences in the burrowing substrate and emphasizing head shape in addition to body and limbs. We assembled an ecomorphological database comprising 213 species from all major lizard clades, and then characterized contemporary morphological diversity and modeled phenotypic evolution to test the hypothesis that fossoriality encompasses at least two distinct selection regimes. We identified two ecomorphological groups within the fossorial lizards: moist-soil fossorial and dry-soil fossorial. Both groups evolved towards distinct adaptive optima concerning head shape and limb size. Despite some degree of uniqueness, these groups also share similar patterns in specific traits. Dry-soil fossorial lizards present less morphological variation than moist-soil fossorial, possibly due to the combination of distinct sets of selective pressures with shared ancestry. ## Description of the data and file structure We assembled a morphological database comprising 213 species of lizards distributed worldwide, with 1932 specimens sampled (mean of 9 individuals per species) representing all major Squamate clades, except Serpentes. Most preserved animals were measured during visits to herpetological collections or obtained by loans. Both adult males and females were included in our study. Thirteen traits were obtained from direct measurements on preserved specimens by the same researcher using a digital caliper (Mitutoyo Inc., 0 – 200mm, precision 0.01mm). In a few species, metric tape was used to measure very long tails. Damaged or regenerated structures were not considered. Our database focused on functional traits of head shape (9 measurements) and also four post-cranial traits related to locomotion. We modeled phenotypic evolution by comparing different hypotheses of selection regimes to evaluate if limb reduction, body elongation and head shape evolved towards two distinct adaptive optima in fossorial lizards: dry-soil and moist-soil fossorial groups. We also characterized current morphological disparity within the fossorial lizards, as we predict that the dry-soil fossorial group encompasses less morphological diversity than moist-soil fossorial lizards, due to unique adaptations involved with headfirst burrowing in sand and dry soils. We also evaluated the profiles of morphological disparity through time, as we expect that historical processes associated with morphological diversity partitioning may reflect different combinations of shared ancestry and adaptation in distinct snakelike lineages. **List of abbreviations**: N = number of specimens sampled HL = head length HW = head width HH = head height ND = nostril distance NH = nostril height OD = orbital distance SL = snout length LJL = lower jaw length QTL = quadrate-to-tip length TrL = trunk length Tal = tail length FLL = forelimb length HLL = hindlimb length AH = Anthony Herrel's personal herpetological collection MNHN = Muséum national d'Histoire naturelle (Paris, France) MfN = Museum für Naturkund (Berlin, Germany) NHM = Natural History Museum (London, England) MZUSP = Museu de Zoologia da Unidade de São Paulo (São Paulo, Brazil) CHRP = Coleção Herpetológica de Ribeirão Preto - USP (Ribeirão Preto, Brazil) CHUNB = Coleção Herpetológica da Universidade de Brasília (Brasília, Brazil) INPA = Instituto Nacional de Pesquisas da Amazônia (Manaus, Brazil) MNRJ = Museu Nacional do Rio de Janeiro (Rio de Janeiro, Brazil) **Procedures for the morphological measurements were as described**: Head length: caliper tips are positioned at the tip of the snout and the posterior end of the parietal scale, in a dorsal view Head width: caliper is positioned to measure the maximal distance between right and left sides of the head, in a dorsal view Head height: caliper is positioned vertically in a lateral view; one tip of the caliper is on ventral edge of jaw, the other on the heighest point of parietal scale Nasal height: caliper is positioned vertically in a lateral view; one tip at the right nostril opening, the other on the ventral edge of the jaw Nasal distance: caliper is positioned in a dorsal view, one tip in each nostril opening Orbital distance: caliper is positioned in a dorsal view horizontally at mid-eye direction; one tip in each lateral extremity of frontal scale Rostral length: caliper is positioned in a lateral view; one tip at the tip of the rostral, the other at the postocular scale Lower jaw length: caliper is positioned in a lateral view; one tip at the anterior extremity of lower jaw, the other gently positioned at the posterior extremity of the retroarticular process Quadrate-to-tip length: caliper is positioned in a lateral view; one tip at the most anterior tip of the upper jaw, the other at the posterior edge of the quadrate and the squamosal Trunk length: caliper is positioned in a ventral view; one tip at the cloaca, the other in mid-point between the two retroarticular processes, at neck height Tail length: caliper is positioned in a ventral view; one tip at the cloaca, the other at tip of the tail (only intact tails; regenerated tails are not measured) Forelim length: caliper is positioned in a ventral view, one tip at the proximal extremity of forelimb, the other at the tip of the longest forelimb digit; limb is gently stretched Hindlimb length: caliper is positioned in a ventral view, one tip at the proximal extremity of hindlimb, the other at the tip of the longest hindlimb digit; limb is gently stretched