Critical Evaluation of Mode of Life, Ancestry, and Evolution of Pterosaurs - Essay Example

? CRITICAL EVALUATION OF PTEROSAURS Critical evaluation of mode of life, ancestry and evolution of pterosaurs Introduction This paper is a critical evaluation of the evidence for the mode of life, behavior and ancestry of pterosaurs (flying lizards). Researchers’ believe that pterosaurs were the first creatures on the history of creation, to fly. Their evolution approximately matched that of their close relatives, the dinosaurs. They both belonged to the late Triassic period. Even so, the pterosaurs advanced and gave way to bigger forms in the Jurassic and cretaceous. Pterosaurs form the group of the first animals to fly. The winged lizards belonged to the order pterosauria. Their wings stretched from the ankle to a lengthened forth finger. Their bones were hollow, and air filled, like those for birds. They had a keeled breastbone that developed and got attached to flight muscles. Their brain was enlarged hence, showed specialized features associated with flight. Later developments of the species saw their shoulders fused into a structure known as notarium. Its purpose was to conceal the torso during flight and provide a stable support to the shoulder blade. Wilton (2013) research shows that pterosaurs remained conservative for 70 million years after which, they started practicing adaptation with all kinds of new modes of life. Such adaptation lifestyles included change of food and food sources. Pterosaurs are believed to be the ancestors of the modern day birds. However, this is not the truth. They resemble birds in many ways, but they are not close to being birds. There were two major kinds of pterosaurs, the rhamphorhynchoid and pterodactyls. The first consisted of a smaller pterosaur, and the later comprised of large bodied and rare pterosaur (Bennet, 1989). Main features of pterosaurs They belonged to the category of weak flyers. Recent studies implicate that the wings of the pterosaurs were flappers, not gliders. An elongated digit on their claws was attached to them. The flight membrane and muscle attachments connected the digit to the arm, shoulders and chest to enable the creature gain stability during flight (Bennet, 1989). The wings extended up to 40 feet and attached to the hind limbs. The essence was to connect the hands and legs. The bones were hollow (i.e. honeycomb). This made them light for easy flight (Bennet, 1989). The membranes were very complex but very thin for flight purposes. The consistent of the membrane included blood vessels, fibrous tissues and small muscles. The membrane performed cooling functions preventing the body from too much heat (Bennet, 1989). Pterosaurs walked on four legs. This caused constraint to the animal since it could not walk fast with its limbs connected to the wings. These features lead to the conclusion that pterosaurs evolved from tree climbing reptiles. Their claws were curled like those of tree climbing reptiles (Frey et al. 2003). The claws of the hind limbs resembled those of the birds that walked on the ground (Prentice, Ruta & Benton, 2011). Those of the forelimbs resembled those of the perching birds. The adaptability mode for the limbs was to be able to walk on the ground and perch on trees (Bennet, 1989). Scientists critically examine the head of the animals and come up with many physiological and behavioral traits of the animals. The shape of the head acts as an adaptive feature for prey catching. Some pterosaurs had beaks long, to about two feet (Witton, &Naish, 2008). Those that had teeth were very sharp aligned on the side of both jaws. The ones that did not have teeth had very long, pointed and sharp edged bills (Kellner, 2003). The animal had a head that sloped downwards. The floccolus is a lobe in the brain that had connections to the eye and neck muscles (Padian, 1997). The functions of the connection were to stabilize and sharpen view of pray within the eyes. Some pterosaurs had head crests thought to have been used to attract mates or repel rivals and attackers (Prentice, Ruta& Benton, 2008). They had soft tissue head crests that adorned on their skulls. The head crest was estimated to being up to 75% of the skull area (Padian, 1980). This is evidenced by the well-preserved Chinese pterosaur, pterorhynchus that had elaborated color patterning preserved on its head crest. Other pterosaurs had bony head crests that apparently did not have soft-tissue adornment but strikingly colored (Bennet, 1989). Evolution and of pterosaurs Researchers believe that pterosaurs evolved from arboreal reptiles that evolved with growth of skin between their legs so that they could glide from tree to tree (Padian, 1980). Many pterosaurs were very small, but eventually they grew to have wingspans up to twelve meters. The most credible evolutionary trait of the animals was their adaptation to flight. The preservation of their soft tissues such as the soft membrane, the rudder-like tail membrane, formed a major evolution trait. It extended to the formation of web like formation on its toes (Bennet, 1989). In the recent years, many new discoveries have arisen and given a better evolutionary theory of the creatures (Prentice, Ruta & Benton, 2011). It is thought that they are organized into two, the Rhamphorhynchoidea, believed to be the earliest to exist (Witton, & Naish, 2008). They had short metacarpals in the wings and long tails. Evidence from the fossil indicates that they were very primitive (basal). They are said to have existence through the late Triassic period and lasted to the late Jurassic period. The other group is pterdactyloidea. It consists of the pterosaurs with short tails and long wing metacarpals. They developed during the Jurassic period and are said to have lasted through to the cretaceous (Kellner, 2003). Cretaceous is described as the Paleogene, the extinction process that wiped them out at the end of cretaceous. Scientists argue that pterosaurs were a very successful group. Over their existence period, their evolution heightened causing a high increase in their population (Frey et al. 2003: Bennet, 1989). It also caused them to diversify enormously in terms of skull morphology and feeding habits. Even so, they still maintained their characteristics such as four digits in their hands with phalangeal formula and their wing membrane. They also maintained their long necks and fused hipbones (Prentice, Ruta & Benton, 2011). During evolution, the tail grew shorter while the wings grew longer. Their evolution is linked the number and layout of teeth as well as their size. Across the world, the change in size attributes to the increase of oxygen in the atmosphere during the Jurassic and cretaceous periods (Hone & Benton 2007). It allowed a higher rate of respiration that enabled a larger body size (Bennet, 1989). Ancestry of pterosaurs Research has categorized pterosaurs as both bipeds and quadrupeds. The newly discovered tracks of small pterodactyloids thought to have originating from the late Jurassic of France displays quadruped stance (Padian, 1997). The pterodactyloid at crayssac show that the hind limbs were erect and the gait was parasagittal (Bennet, 1989). Researchers have used the Cladistics to determine relationships. It works by assuming that all organisms have a common evolutionary origin (Hone & Benton 2007). If two species were similar, they must have shared close relations. They used the fossils collected thousands of years and determined characteristics of each organism that lived (Bennet, 1989). These fossils give an ancestry history of the pterosaurs. Even so, pterosaurs are deemed very strange (Kellner, 2003). Evolution of flight caused their bones and bodies undergo numerous transformations, therefore, much of the information relevant to place them into groups of their ancestors was lost (Bennet, 1989). Much research indicates that they are diapsid reptiles, evidenced by holes in the skull. The skull is so far the only relevant mode of tying the pterosaurs to the family of reptiles (Witton & Naish, 2008). There are identified characteristics shared by pterosaurs from dinosauromorphs and archosauromorphs. The leg features are common between pterosaurs and dinosauromorphs (Frey et al. 2003). The neck and tails show close ancestry of pterosaurs and archosauromorphs. The same mode of classification is used to characterize families of pterosaurs (Witton & Naish, 2008). There are several families of pterosaurs categorized according to the evidence collected from the fossil. There are those considered more primitive depending on the identified traits such as the anurognathids (Bennet, 1989). Looking at their wings, they share common structures with the bats. An enormously elongated finger supported the distal portion of the wing such that there is a close comparison to the three flight fingers of the bats. If the animal is not flying, the wing is believed to have folded tightly against its body the same way the bats do (Bennet, 1989). The wing membrane is identified to be closely related to the membrane of the bats wings. They also had hair like structures on their wings; however, there are no close connections other than physical characteristics displaying common ancestry between pterosaurs and the bats (Bennet, 1989). The presence of furry, insulating integuments suggests that pterosaurs shared an elevated body temperature with almost all other flying animals (Kellner, 2003). In the year 2003, the pterosaur was classified as the most recent common ancestor of the anurognathidae (preondactylus) and quetzalcoatlus and all their descendants (Hode & Benton 2007). Reproduction and growth There is no valid explanation of how pterosaurs changed during their lifetime. The changes are leant later from fossil such that the juvenile specimens have radically different skeletal structures to those of the adults (Bennet, 1989). There is also a difference in length and proportion of the skull. A trait identified on the juveniles shows that they have shorter jaws and a dental formula adapted to catching insects, whereas the adults have larger and longer jaws with teeth suited for seizing fish (Bennet, 1989). The traits also show that the younger generation of the pterosaurs filled a different ecological niche to that of their parents specifically to avoid direct competition with them. The size of their hips as observed from the fossil remains is taken as a distinctive factor between the male and female ones (Bennet, 1989). The females are thought to have had wider hips, as opposed to the male. This helped them in passing the eggs without struggle (Prentice, Ruta & Benton, 2011). The fossils indicate that the number of females outnumbered the number of male in all taxonomic units of the creatures. It suggests that the male ruled a given territory. Additionally, the creatures lived according to family units. It also means that the males had to defend their territory and only successful males were able to mate (Bennet, 1989). Evidence also indicates that not all pterosaurs had crests; the easy explanation of the crests is to enable two pterosaurs of the same class and family to identify each other and for attraction purposes (Prentice, Ruta & Benton, 2011). Evidence based research indicates that the crest became fully developed only when the male reached reproductive maturity. Research also indicates that females, too, had crests of different lengths though not as developed as the male crests (Padian, 1997). The bright coloration of the crest is attributed to accentuate their presence especially for mating purposes (Bennet, 1989). Some researchers stipulate that the higher and broader crest were used as rudders that helped with steering during flight. For instance, broader head may have been able to catch the wind. This helped the creature reduce the amount of work done to keep itself up on air while flying (Bennet, 1989). Daily life of pterosaurs The study of preserved sclera rings of pterosaurs reveals important insight of the life of these creatures. The rings would show whether the creatures were active by day or during the night. The classification was referred to as niche partitioning (Padian, 1997). It means that a pterosaur that was active during the night would avoid direct competition with another species that would be active during the day (Bennet, 1989). The activity modes at different times are attributed to the availability of food supply. It means that those active during the night had an abundant supply of food during the night and vice versa. It may have also been a survival tactic avoiding predators and enemies. Some were even more complicated as they were only active during the twilight of dusk and dawn to avoid both night and day enemies (Kellner, 2003: Bennet, 1989). Diet The earlier forms of pterosaurs were likely to have been insectivorous (Witton & Naish, 2008). As they continued to evolve, later members started eating fish with other members consuming both fish and insects such as Rhamphorhynchus (Bennet, 1989). A theoretical model stipulates that feeding habits were dependent to age of the pterosaur. Juveniles had short pointed teeth hence, adapted to eating insects (Padian, 1980). Older members had developed beaks that were long and strong hence, could feed on fish. Their teeth were also stronger; hence, they could be able to chew the fish with ease. Fossil evidence points out that pterosaurs beak had small teeth at the edge of their beaks, but the teeth enlarged towards the back (Bennet, 1989). The small teeth are attributed for low resistance as the creature flew on high speed so the lower the resistance in water the better the chances of capturing fish (Bennet, 1989). However, other types of pterosaurs had the opposite dentition. Such types included zhenyuanopterus species. This suggests that they may have focused on small preys and perhaps used a dipping motion to pluck fish out of the water (Bennet, 1989). Other pterosaurs had toothless beaks but still deemed to have been active hunters. An example is the pteranodon species. This species is thought to have the capabilities to land in water or even plunge so that it could scoop fish. Other theories suggest that some pterosaurs were scavengers looking for carrion while on a flight (Kellner, 2003: Bennet, 1989). Predators Any predator that could attack pterosaurs had the capacity to eat them. The dinosaurs were believed to be the biggest predators of pterosaurs. When they went to drink water or search for fish, the crocodiles also fed on them (Frey et al, 2003). At the seas, they had to avoid plesiosaurs and mosasaurs. The sharks in seawaters also proved a problem to them. Their main survival adaptation was the power to fly. If they sensed any danger, they would take off with very high flight speed (Bennet, 1989). Conclusion Pterosaurs evolved from little creatures believed to be reptiles. Researchers’ believe that pterosaurs were the first creatures on the history of creation, to fly. They started evolving so that they could adopt to the persisting adaptation situations. Increment of oxygen during the Jurassic period enabled them to adapt to changing conditions. Most pterosaurs were carnivorous and insectivorous, even though later evolution came with changed feeding habits such as on fruits. Carnivorous mostly fed on fish, but others were better adapted to scavenging. Their activity patterns differed with their protective strategies from predators. Some were active during the day while others during the night. There is a clear explanation about their extinction. Some believe that the birds were adapted to flight hence, causing competition in terms of food. Others believe that climatic changes made them vulnerable to predators hence, their extinction. Reference list Bennett, S.C. (1989) A Pteranodontid Pterosaur from the Early Cretaceous of Peru, with Comments on the Relationships of Cretaceous Pterosaurs. Journal of Paleontology 63 (5), 669- 677. Bennett, S.C. (1996) Year-classes of pterosaurs from the Solnhofen Limestone of Germany: Taxonomic and Systematic Implications. Journal of Vertebrate Paleontology 16 (3): 432–444. Frey, E,. Tischlinger, H.; Buchy, M. & Martill, D. M. (2003) New specimens of Pterosauria (Reptilia) with soft parts with implications for pterosaurian anatomy and locomotion. Geological Society, London, Special Publications 217: 233 Hode, D.W.E. & Benton, M.J. (2007) an evolution of the phylogenetic relationships of pterosaurs to the archosauromorhp reptiles. Journal of systematic paleontology. Kellner, A. W. (2003) Pterosaur phylogeny and comments on the evolutionary history of the group. Geological Society, London, Special Publications, 217(1): 105-137. Padian, K. (1983) A Functional Analysis of Flying and Walking in Pterosaurs. Paleobiology 9 (3): 218–39. Padian, K. (1997) Pterosauromorpha. Pp. 617-618 in Currie, P.J. and Padian, K. The Encyclopedia of Dinosaurs. Academic Press. Prentice, K.C., Ruta, M., & Benton, M.J. (2011) Evolution of morphological disparity in pterosaurs. Journal of Systematic Palaeontology (doi: 10.1080/14772019.2011.56508). Witton, M. (2013) pterosaurs: natural history, evolutionary, anatomy. Princeton university press. Witton, M. P. & Naish, D. (2008) A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE, 3, e2271. Read More