Preadaptive Stage for Flight Origin

Abstract

Pr eadaptive Stage for Flight Origin. Bogdanovich, I. A. -Bipedalism as a preadaptive stage for bird's fl ight is considered. We attribute the formation of full bipedalism in bird ancestors with pelvic limbs transition from segmental to parasagittal position. Th is transition was fast enough. We can assume that the pectoral limbs freed from the support remained while laterally spaced and gave set of transformations with diff erent degrees of reduction. Th us morphologically "winglike" version of the thoracic limbs could appear. Parasagittal pelvic limbs allowed birds ancestors fast and maneuverable running, while the movements of free and highly movable thoracic limbs (feathered unrelated to fl ight) provided dynamic stability of the animal. In addition, their fl uttering movements facilitate hopping from one branch to another and the descent from the trees. On the bottom branches protobirds could jump with perching just by the pelvic anisodactyl limbs, not by thoracic as had supposed earlier. Ac tive interaction of the primary simple feathers with air as well as its protective function could become an impetus for their transformation into diff erentiated structures. Unlike gliding (as preadaptive stage for active fl ight) bipedalism with free feathered forelimbs provides per se parallel development of two autonomous enough locomotor systems of birds (fl ight and terrestrial locomotion) and extensive adaptive radiation of representatives of the class. Key words: bipedalism, fl ight, birds.Despite the long history of the study of the origin of birds and fl ight, the origin and subsequent evolution of feathered wings remains one of the most controversial topics in the vertebrate paleontology (Kaiser, Dyke, 2014). For example, the question of preadaptive stage preceding the fl ight is not entirely unambiguous. As such the terrestrial, through the running and jumping (Dececchi et al., 2016), and arboreal, through gliding (Czercas, Feduccia, 2014) hypotheses are still being discussed.Up to a certain time it was common belief that the way of becoming the birds as a taxon, the transformation of thoracic limbs into wings led to bipedalism (Du Brul, 1962;Ilichyov et al., 1982). Today, the transition to bipedal locomotion with full exemption of thoracic limbs from the support function is considered as a stage that preceded the origin of fl apping fl ight of birds (Long et al., 2003;Kurochkin, Bogdanovich, 2008, 2010. In another point of view the gliding (when in process of air locomotion both fore and hind limbs are involved) is much better suited as a transitional stage to fl apping fl ight than bipedalism, which only leads to reduction of muscles and thoracic limbs as whole (Panyutina et al., 2015). It is impossible not to admit that the exemption of the thoracic limbs from the support-locomotor function was followed by their partial reduction. It is known that reduced organs demonstrate a very large and diverse variability of their parts due to the termination or weakening of natural selection and preservation of indep...

Covariation in Shapes Between the Sternum and Pelvis in Aquatic Birds with Different Locomotor Modes

“…This is most clearly seen in the case of wing-and foot-propelled underwater swimmers. Although both ecological groups share a number of distinctive features, such as posterior position of legs on a long axis of a body (Kurochkin, 1971;Johnsgard, 1987;Ibáñez & Tambussi, 2012), narrow elongated pelvis (Raikow, 1970(Raikow, , 1985Kurochkin, 1971;Bogdanovich, 2003), a great height of the acetabular zone (Ibáñez & Tambussi, 2012;Anten-Houston et al, 2017), low pelvic angles (Anten-Houston et al, 2017) that facilitate their movement under water (Kurochkin, 1971;Ibáñez & Tambussi, 2012), the result of our study showed that covariant changes of the sternum and pelvis in these groups have opposite directions.…”

“…In this study, we tried, fi rst of all, to evaluate the integration between diff erent locomotor modules, which has not previously been the subject of a special study in water birds. Studies of locomotion mechanisms in aquatic birds revealed a signifi cant variation in hindlimb movement patterns even among foot-propelled divers (Johansson & Norberg, 2003;Clift on & Biewener, 2018), which aff ects some structural features of both the pelvis and hind limbs (Kurochkin, 1971;Bogdanovich, 2014). Th ese data extend the understanding of pathways of narrow adaptations in water birds.…”

“…Th ey have a number of morphological features that distinguish them from those swimming on the water surface. Diving birds have narrow pelvic girdles (Kurochkin, 1971;Rainkow, 1985;Bogdanovich, 2003), posteriorly positioned feet (Storer, 1960;Johnsgard, 1987;Ibáñez & Tambussi, 2012), reduced bone pneumaticity (Kurochkin, 1967;Johnsgard, 1987;Llimona & del Hoyo, 1992), high wing loading (Kurochkin, 1971;Livezey & Humphrey, 1986), a number of features in shapes of wing and leg bones (Kurochkin, 1971;Raikow, 1985;Livezey & Humphrey, 1986), pygostyle form (Felice & O'Connor, 2014). Hinić-Frlog & Motani (2010) revealed that measurements of appendicular skeletons successfully separated diving birds from surface swimmers and fl yers.…”

“…Building up muscles of one of the locomotor modules in divers cannot but cause changes in other parts of the body. It is assumed that muscle development of diff erently specialised locomotor modules in birds, like wing and hindlimb, is inversely related: strengthening of one is associated with weakening of the other (Hartman, 1961;Sych, 1992;Bogdanovich, 2014). For example, grebes that use foot-propelled underwater locomotion, have short wings with poorly developed muscles (Johnsgard, 1987).…”

“…For example, grebes that use foot-propelled underwater locomotion, have short wings with poorly developed muscles (Johnsgard, 1987). We can expect that an increase in one of the locomotor modules in divers is correlated with a decrease in the other, which is also accompanied by a change in shape, since the shape of skeletal elements depends on muscles that attach to them (Shmalgauzen, 1982;Bogdanovich, 2014). An example of the relationship between the shape and size of the sternum and pelvis in wing-and foot-propelled divers is shown in fi g. 1.…”