The wing musculature of the Brown kiwi Apteryx australis mantelli and its bearing on ratite affinities

Abstract

Most previous accounts of the wing muscles of the kiwi have only dealt with the proximal muscles. The few accounts that have treated the distal muscles are incomplete in other respects and sufficient uncertainty exists to warrant the present study. The wing musculature of the kiwi is closely similar to that of other ratites but markedly dissimilar to that of the carinates. In this regard the wing muscles differ from those of the leg. Ratites have far fewer wing muscles than carinates. Significantly, they lack propatagial muscles (and almost certainly propatagia), and neither the M. pectoralis nor the M. supracoracoideus is well developed; in carinates these two flight muscles comprise the bulk of the wing musculature. Furthermore, the insertion tendon of the M. supracoracoideus does not loop through a triosseal canal to effect wing elevation as it does in the carinates. In all of these regards the ratite condition is closer to that of reptiles than of carinates. This raises the question of whether ratites should be regarded as primitive birds, rather than as advanced birds that evolved from carinates. The present skeleto‐muscular data, taken with other evidence, suggests that ratites are primitive birds that evolved from a primitive, volant ancestor. The elements of the pectoral skeleton show a greater degree of individual variation than those of the pelvic skeleton. Aside from its extreme curvature the humerus is the most rudimentary element and few of its features can be compared with those of the carinate humerus. Few of the wing muscles have attachments that can be identified with specific osteological features. Myological data for the kiwi are therefore virtually irretrievable from osteological material, as noted previously for the pelvic muscles. While this might be peculiar to the kiwi (which seems unlikely) the fact should serve as a cautionary note to palaeontologists attempting to reconstruct the muscles of extinct animals.

An exceptionally high density of muscle spindles in a slow‐tonic pigeon muscle

“…coracotriceps may be considered a unique muscle, since the density of the spindles in the muscle of the pigeon was approximately 100 times that of spindle-rich mammalian muscles (Barker, 1974) and about 15 times that of the most spindle-dense avian muscles reported (Maier and Eldred, 1971;Maier, 1983). In addition, muscles composed of entirely tonic extrafusal fibers are extremely rare (Hess, 1970;McGowan, 1982;Maier, 1983). Such a unique muscle, we believe, should be of interest to functional morphologists and neurophysiologists.…”

Comments on the Morphology of Basal Paravian Shoulder Girdle: New Data Based on Unenlagiid Theropods and Paleognath Birds

“…In Rhea, the two bellies of the m. biceps brachii become fused close to the proximal humerus, and have a strong contact with the skin and the crista deltopectoralis. The insertion is double and tendinous into the proximal end of the radius and the ulna, as in most of the neognaths and tinamids (McGowan, 1982;Baumel et al, 1993;Picasso and Mosto, 2018;Lo Coco et al, 2020) but different than Struthio (Jasinoski et al, 2006) and Dromaius (Maxwell and Larsson, 2007).…”

“…One belly is tendinous and originates on the processus acrocoracoideus of the coracoid, while the other belly is fleshy and originates on the lateral edge of the coracoid (Lowe, 1928). In most neognaths the m. biceps brachii also has two bellies with double origins, although in Rhea the double origin is present on the coracoid but not on the proximal end of the humerus, like other extant non-tinamid paleognaths (George and Berger, 1966;McGowan, 1982;Jasinoski et al, 2006).…”

Comparative Three‐Dimensional Moment Arm Analysis of the Sauropod Forelimb: Implications for the Transition to a Wide‐Gauge Stance in Titanosaurs

“…Direct observation of crocodile musculature was conducted on an Australian estuarine crocodile (Crocodylus porosus) (Klinkhamer et al, 2017). Information on bird musculature and additional information on crocodilian musculature was gathered from the literature (Reese, 1915;Hudson and Lanzillotti, 1955;Chiasson, 1962;George and Berger, 1966;McGowan, 1982;Baumel and Witmer, 1993;Meers, 2003;Remes, 2008). Other studies on sauropodomorph forelimb muscles were also consulted (Borsuk-Bialynicka, 1977;Wilhite, 2003;Langer et al, 2007;Remes, 2008;Garcia et al, 2015;Ullmann et al, 2017).…”