Diversity and function of the fused anuran radioulna

Abstract

Many clades of vertebrates exhibit fusion between elements of the appendicular skeleton. Well-known examples are found in the limbs of modern birds and mammals. These include the tibiotarsus, tarsometatarsus, and carpometacarpus bones in birds, the fused radius and ulna in bats, horses, and artiodactyls (Figure 1d), and the fused tibia and fibula in hedgehogs, sea-lions, coneys, rodents, rabbits, armadillos, aardvarks, and tarsiers (Barnett & Napier, 1953;Sahd et al., 2019;Salami et al., 2011). In extant frogs, the tibia and fibula as well as the radius and ulna are always completely fused in adults (Duellman & Trueb, 1986) and the proximal tarsal bones are fused in some or all species in several families (Centrolenidae, Microhylidae,

Mammalian forelimb evolution is driven by uneven proximal-to-distal morphological diversity

“…fusion and loss of carpal and tarsal bones and alteration of the phalangeal formula; Cooper et al, 2007 ; Hamrick, 2001 ; Holder, 1983 ; Luo et al, 2015 ; Saxena et al, 2017 ). Except for lineages that have undergone complete limb loss such as snakes and caecilians, the meristic composition of proximal segments is much more conserved than that of the autopod, displaying some but less frequent cases of element reduction and partial fusion of the zeugopod bones (observed in anurans, bats, manatees, horses, etc., Holder, 1983 ; Keeffe and Blackburn, 2022 ; Sears et al, 2007 ). Although this meristic information is useful to quantify major evolutionary changes in element composition, most of the morphological variation observed in the limbs results from changes in the shape and relative size of individual elements (i.e.…”

Locomotor, ecological and phylogenetic drivers of skeletal proportions in frogs

“…The history of anuran morphometrics is dominated by a focus on the relationship between limb lengths and jumping performance (Rand, 1952 ; Zug, 1972 ; Dobrowolska, 1973 ; Choi et al, 2003 ; James et al, 2005 ; James et al, 2007 ; James & Wilson, 2008 ; Herrel et al, 2016 ). In contrast, other types of locomotor modes, including walking, hopping, swimming, burrowing and climbing, have received comparatively less attention (Emerson, 1979 ; Wells, 2007 ; Robovska‐Havelkova et al, 2014 ; Vassallo et al, 2021 ), as have regions of the body other than the pelvis and hindlimb such as the forelimb, hands and feet (Manzano et al, 2008 , 2019 ; Keeffe & Blackburn, 2020 , 2022 ; Abdala et al, 2022 ). Despite their relatively conserved body plan (Lires et al, 2016 ), extant anurans show considerable modifications in their skeletal proportions, reflecting their ability to respond to various mechanical challenges and inhabit diverse environments (Citadini et al, 2018 ; Gomes et al, 2009 ; Moen, 2019 ; Moen et al, 2013 ; Simons, 2008 ; Soliz et al, 2017 ; Vidal‐García et al, 2014 ).…”

Modern three-dimensional digital methods for studying locomotor biomechanics in tetrapods

“…FEA involves dividing the object into polygonal elements and assigning material properties to the object to model its physical behaviour ( Richmond et al, 2005 ; Rayfield, 2007 ; Bright, 2014 ; Blasi-Toccacceli et al, 2022 ). Keeffe and Blackburn (2022) used FEA to investigate the mechanical implications of radioulnar fusion in frogs, concluding that the semi-fused condition present in frogs is associated with smaller von Mises stress and higher bending resistance than in unfused or completely fused conditions. FEA of the carpal bones of a chimpanzee revealed that scaphoid–centrale fusion has lower stresses in knuckle walking than lack of fusion, supporting this fusion's role in that behaviour and its evolution ( Püschel et al, 2020 ).…”