Anatomy of the forelimb musculature and ligaments ofPsittacus erithacus(Aves: Psittaciformes)

Abstract

Parrots (order Psittaciformes) are a rather homogeneous group of birds that can be easily distinguished by the notably modified morphology of the skull and hindlimb. Detailed description of the forelimb morphology in these birds has never been provided, though parrots are often used as model objects in flight studies. Parrots are also considered the closest living relatives of the perching birds (Passeriformes), and thus knowledge of the wing morphology in Psittaciformes is important for understanding the evolution of the locomotor apparatus on the way to the most speciose group of birds. Here we provide a comprehensive illustrated description of the wing morphology (musculature and ligaments) of the African grey parrot (Psittacus erithacus) and compare it with several closely related taxa of the high clade Eufalconimorphae and more distantly related outgroups (based on personal dissections and literature data). We note a general similarity of the wing musculature between P. erithacus and Falconidae. A number of features common with the outgroup Columbidae supports a generally plesiomorphic structure of the forelimb in parrots as compared with the Passeriformes. Nevertheless, the wing of the Psittaciformes displays a series of structural (likely autapomorphic) modifications, which can be explained in terms of adaptations for flight with vertical body. An analysis of the anatomical data for parrots (ratio of wing elevators and highly unusual development of the M. supracoracoideus), which is based on the current experiment-based knowledge of the flapping flight in birds, allows us to hypothesize that parrots are able to produce useful aerodynamic force during the upstroke, which is also known for pigeons and hummingbirds. This supposed ability of vertical flight and the zygodactyl foot together link the origin of parrots with the dense (likely tropical) forests.

Shifts in eggshell thickness are related to changes in locomotor ecology in dinosaurs

“…While an eggshell microstructure or egg morphology specific to eufalconimorphs has yet to be discovered, it is interesting to note that many myological similarities have been described in the forelimb of parrots and falcons (and passerines to a lesser extent), and might be associated with a flight strategy ancestral to the whole clade (Razmadze et al. 2018). Further functional studies on the flight and reproduction of eufalconimorphs are required to establish a potential link between these hypothetical flight‐related traits and an ancestral increase in eggshell thickness.…”

Embryonic Development of the Avian Sternum and Its Morphological Adaptations for Optimizing Locomotion

“…To provide the necessary attachment site for these two flight muscles, the sternal keel in the hummingbird is greatly extended (Figure 2G-I) compared to thorax length. Similarly to the hummingbird, the parrot has adapted large wing elevator muscles to support upward aerodynamic forces during upstroke to support vertical locomotion in forest habitats [42]. Strikingly, a sternal keel is present in some aerially flightless birds, such as penguins and the flightless auk (Figure 2J-M).…”

Enthesis strength, toughness and stiffness: an image-based model comparing tendon insertions with varying bony attachment geometries

“…Flattening of this ridge (reduction of B 0 /A 0 ), as seen at the patellar tendon insertion of the knee, contributed to the maintenance of strength over 43% of the ROM, which may assist the patellar tendon in high-stress activities such as running, jumping, and kicking over a significant range of orientations [51,54]. This feature can be seen in tendons across other species that serve a predominantly energy-storing role, such as the insertion of the supracoracoideus tendon into the dorsocaudal surface of the humerus, just distal to the tuberculum dorsale [55], at the wings of birds, which may achieve the effect of bone ridge flattening to optimize strength over powered wing flapping [56].…”