Bone indicators of grasping hands in lizards

Area of Science:

• Paleontology
• Evolutionary Biology
• Comparative Anatomy

Background:

• Grasping is a crucial adaptation for arboreal locomotion, yet its manual mechanics in non-mammalian tetrapods remain under-researched.
• Previous studies focused on muscle and tendon structures, with limited exploration of skeletal correlates for grasping in lizards.
• Arboreal niche exploitation is linked to grasping abilities, suggesting significant osteological consequences.

Purpose of the Study:

• To identify morphometric descriptors in the lizard hand skeleton associated with grasping functionality.
• To investigate the skeletal variations that facilitate grasping in squamate reptiles.
• To understand the evolutionary origins and functional morphology of grasping in lizards.

Main Methods:

• Constructed a morphological matrix of 51 variables from 278 lizard specimens across 24 genera and 13 families.
• Utilized Principal Component Analyses (PCAs) on carpal, metacarpal, and phalangeal variables to reduce dataset dimensions.
• Employed Generalized Linear Models to correlate specific skeletal variables with grasping functionality (binary response).

Main Results:

• Identified six significant morphometric variables linked to grasping: two carpal, two metacarpal, and two phalangeal.
• Discovered at least two distinct, independently evolved skeletal combinations enabling grasping in lizards.
• Characterized specific combinations involving the centrale bone, palmar sesamoid presence/absence, metacarpal V, and phalangeal proportions.

Conclusions:

• Lizard grasping involves diverse skeletal configurations, suggesting convergent evolution of this ability.
• Morphological distinctions between graspers and non-graspers indicate a continuum where new abilities emerge.
• Results support the nested origin of grasping within arboreality, potentially enabling functions beyond locomotion, like prey manipulation.