Functional morphology of the forelimb of Tupaiids (Mammalia, Scandentia) and its phylogenetic implications

Abstract

In this study, the forelimb of 12 species of tupaiids was analyzed functionally and compared to that of other archontan mammals. Several differences that relate to differential substrate use were found in the forelimb morphology of tupaiids. These differences included shape of the scapula, length and orientation of the coracoid process, size of the lesser tuberosity, shape of the capitulum, length of the olecranon process, and shape of the radial head and central fossa. The forelimb of the arboreal Ptilocercus lowii, the only ptilocercine, is better adapted for arboreal locomotion, while that of tupaiines is better adapted for terrestrial (or scansorial) locomotion. While the forelimb of the arboreal Ptilocercus appears to be habitually flexed and exhibits more mobility in its joints, a necessity for movement on uneven, discontinuous arboreal supports, all tupaiines are characterized by more extended forelimbs and less mobility in their joints. These restricted joints limit movements more to the parasagittal plane, which increases the efficiency of locomotion on a more even and continuous surface like the ground. Even the most arboreal tupaiines remain similar to their terrestrial relatives in their forelimb morphology, which probably reflects the terrestrial ancestry of Tupaiinae (but not Tupaiidae). The forelimb of Urogale everetti is unique among tupaiines in that it exhibits adaptations for scratch-digging. Several features of the tupaiid forelimb reflect the arboreal ancestry of Tupaiidae and it is proposed that the ancestral tupaiid was arboreal like Ptilocercus. Also, compared to the forelimb character states of tupaiines, those of Ptilocercus are more similar to those of other archontans and it is proposed that the attributes of the forelimb of Ptilocercus are primitive for the Tupaiidae. Hence, Ptilocercus should be considered in any phylogenetic analysis that includes Scandentia.

A new species of small-eared shrew in the Cryptotis thomasi species group from Costa Rica (Mammalia: Eulipotyphla: Soricidae)

“…Specifically, we calculated five indices of relative fossoriality from seven measurements taken from the humerus and compared them with mean indices from 17 other species of Cryptotis in Woodman and Gaffney (2014). All five indices are expected to increase with increasing fossoriality (Sargis 2002;Samuels and Van Valkenburgh 2008;Woodman and Gaffney 2014;Woodman and Stabile 2015):…”

Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (Xenarthra, Folivora) of Patagonia

“…These inferences were based on previous works on extant Pilosa (Taylor, 1978(Taylor, , 1985Mendel, 1979Mendel, , 1981Mendel, , 1985Nyakatura et al, 2010) and other mammals (Argot, 2001;Szalay and Sargis, 2001;Sargis, 2002;Candela and Picasso, 2008), and mechanical analogues when needed. The interface between function and biological role was the averaged biomechanical situation (Oxnard, 1984), which integrates functional information of each feature and element in a mechanical profile.…”

“…serratus and rhomboideus require increased mechanical advantage because they must resist the rotation of the scapula during climbing. Additionally, Sargis (2002) linked locomotion on arboreal substrates with high demands on the mm. supraspinatus and deltoideus.…”

“…The combination of these functional features resembles the condition in Santacrucian sloths, but also of other xenarthrans analyzed here (e.g., Tamandua and Myrmecophaga). In contrast, stabilization of the elbow joint and increased extension of the antebrachium are linked by Argot (2001), Sargis (2002) and Candela and Picasso (2008) to terrestrial forms with cursorial locomotor styles.…”

New partial skeletons of Palaeocene Nyctitheriidae and evaluation of proposed euarchontan affinities

“…The humeral morphology (electronic supplementary material, figure SI5-1) indicates that nyctitheriids had considerably mobile shoulder and elbow joints [20]. Two characteristics, a medially protruding lesser tuberosity on which powerful medial rotators of the arm insert and a spherical capitulum that allows considerable rotation of the radius in pronation and supination of the forearm, are proposed synapomorphies for Euarchonta [1].…”