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1.4.16.14: Evolution and Diversity of Birds - Biology

1.4.16.14: Evolution and Diversity of Birds - Biology


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Learning Objectives

  • Describe the evolutionary history of birds
  • Discuss the diversity of birds

Evolutionary History of Birds

The evolutionary history of birds is still somewhat unclear. Due to the fragility of bird bones, they do not fossilize as well as other vertebrates. Birds are diapsids, meaning they have two fenestrations or openings in their skulls. Birds belong to a group of diapsids called the archosaurs, which also includes crocodiles and dinosaurs. It is commonly accepted that birds evolved from dinosaurs.

Dinosaurs (including birds) are further subdivided into two groups, the Saurischia (“lizard like”) and the Ornithischia (“bird like”). Despite the names of these groups, it was not the bird-like dinosaurs that gave rise to modern birds. Rather, Saurischia diverged into two groups: One included the long-necked herbivorous dinosaurs, such as Apatosaurus. The second group, bipedal predators called theropods, includes birds. This course of evolution is suggested by similarities between theropod fossils and birds, specifically in the structure of the hip and wrist bones, as well as the presence of the wishbone, formed by the fusing of the clavicles.

One important fossil of an animal intermediate to dinosaurs and birds is Archaeopteryx, which is from the Jurassic period (Figure 1). Archaeopteryx is important in establishing the relationship between birds and dinosaurs, because it is an intermediate fossil, meaning it has characteristics of both dinosaurs and birds. Some scientists propose classifying it as a bird, but others prefer to classify it as a dinosaur. The fossilized skeleton of Archaeopteryx looks like that of a dinosaur, and it had teeth whereas birds do not, but it also had feathers modified for flight, a trait associated only with birds among modern animals. Fossils of older feathered dinosaurs exist, but the feathers do not have the characteristics of flight feathers.

It is still unclear exactly how flight evolved in birds. Two main theories exist, the arboreal (“tree”) hypothesis and the terrestrial (“land”) hypothesis. The arboreal hypothesis posits that tree-dwelling precursors to modern birds jumped from branch to branch using their feathers for gliding before becoming fully capable of flapping flight. In contrast to this, the terrestrial hypothesis holds that running was the stimulus for flight, as wings could be used to improve running and then became used for flapping flight. Like the question of how flight evolved, the question of how endothermy evolved in birds still is unanswered. Feathers provide insulation, but this is only beneficial if body heat is being produced internally. Similarly, internal heat production is only viable if insulation is present to retain that heat. It has been suggested that one or the other—feathers or endothermy—evolved in response to some other selective pressure.

During the Cretaceous period, a group known as the Enantiornithes was the dominant bird type (Figure 2). Enantiornithes means “opposite birds,” which refers to the fact that certain bones of the feet are joined differently than the way the bones are joined in modern birds. These birds formed an evolutionary line separate from modern birds, and they did not survive past the Cretaceous. Along with the Enantiornithes, Ornithurae birds (the evolutionary line that includes modern birds) were also present in the Cretaceous. After the extinction of Enantiornithes, modern birds became the dominant bird, with a large radiation occurring during the Cenozoic Era. Referred to as Neornithes (“new birds”), modern birds are now classified into two groups, the Paleognathae (“old jaw”) or ratites, a group of flightless birds including ostriches, emus, rheas, and kiwis, and the Neognathae (“new jaw”), which includes all other birds.

Diversity of Birds

Bird diversity is much greater than that of reptiles, amphibians and mammals respectively. Presently, there are 10,711 extant species and 158 extinct species of birds of the world. The diversity is astounding, with birds existing almost everywhere in the world.

Birds live all over the world. They range in size from the two-inch bee hummingbird to the nine-foot ostrich. More than half of the known birds on earth are perching birds. As we just learned, birds first appeared during the Cretaceous, about 100 million years ago. Birds diversified dramatically round about the time of the Cretaceous–Palaeogene extinction event 66 million years ago, which killed off all the non-avian dinosaur lines. Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world.

Modern birds have wings which are more or less developed depending on the species; the only known groups without wings are the extinct moa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly. Later many groups evolved with reduced wings, such as ratites, penguins, and many island species of birds. The digestive and respiratory systems of birds are also adapted for flight. Some bird species in aquatic environments, particularly seabirds and some waterbirds, have evolved as good swimmers.

Some birds, especially crows and parrots, are among the most intelligent animals. Several bird species make and use tools. Many social species pass on knowledge across generations, a form of culture. Many species annually migrate great distances. Birds are social. They communicate with visual signals, calls, and bird songs. They have social behaviours such as cooperative breeding and hunting, flocking, and mobbing of predators.

Most bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised by sexual reproduction. They are often laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching. Some birds, such as hens, lay eggs even when not fertilised, though unfertilised eggs do not produce offspring.

Try It

Birds are a beautifully diverse class of animal; however, many species are at risk. As of 2009, 1,223 species of birds were marked as endangered by IUCN’s 2009 Red List. In the United States alone, about 74species of birds were at risk.


Epidemiology and evolution of novel deltacoronaviruses in birds in central China

The variety and widespread of coronavirus in natural reservoir animals is likely to cause epidemics via interspecific transmission, which has attracted much attention due to frequent coronavirus epidemics in recent decades. Birds are natural reservoir of various viruses, but the existence of coronaviruses in wild birds in central China has been barely studied. Some bird coronaviruses belong to the genus of Deltacoronavirus. To explore the diversity of bird deltacoronaviruses in central China, we tested faecal samples from 415 wild birds in Hunan Province, China. By RT-PCR detection, we identified eight samples positive for deltacoronaviruses which were all from common magpies, and in four of them, we successfully amplified complete deltacoronavirus genomes distinct from currently known deltacoronavirus, indicating four novel deltacoronavirus stains (HNU1-1, HNU1-2, HNU2 and HNU3). Comparative analysis on the four genomic sequences showed that these novel magpie deltacoronaviruses shared three different S genes among which the S genes of HNU1-1 and HNU1-2 showed 93.8% amino acid (aa) identity to that of thrush coronavirus HKU12, HNU2 S showed 71.9% aa identity to that of White-eye coronavirus HKU16, and HNU3 S showed 72.4% aa identity to that of sparrow coronavirus HKU17. Recombination analysis showed that frequent recombination events of the S genes occurred among these deltacoronavirus strains. Two novel putative cleavage sites separating the non-structural proteins in the HNU coronaviruses were found. Bayesian phylogeographic analysis showed that the south coast of China might be a potential origin of bird deltacoronaviruses existing in inland China. In summary, these results suggest that common magpie in China carries diverse deltacoronaviruses with novel genomic features, indicating an important source of environmental coronaviruses closed to human communities, which may provide key information for prevention and control of future coronavirus epidemics.

Keywords: bird deltacoronavirus common magpie genome recombination spike viral genome.


Animal Ecology

The animal ecology curriculum provides its majors with an understanding of ecological principles and processes and their applications to natural resource management. It is oriented toward students desiring a general and flexible program in environmental biology and for those planning graduate study. Students may select from four options: Fisheries and Aquatic Sciences, Interpretation of Natural Resources, Preveterinary and Wildlife Care, or Wildlife. Graduates find employment as aquaculturists, aquatic ecologists, wildlife biologists, fisheries biologists, resource managers, and ecologists for industry, environmental consulting firms, natural resource and environmental agencies and organizations, zoos, and as educators.

Graduates of the Animal Ecology major understand the basic principles of animal biology, ecology and management, and relevant aspects of scientific communication, basic mathematics and sciences, computing applications, and personal and professional development. Four specific options prepare students for careers in interpretation of natural resources, fisheries and aquatic sciences, pre-veterinary and wildlife care, and wildlife. Each option has specific outcomes expectations that include (1) the scope of the specialization and its relationships to broader aspects of animal ecology, biotic resource management, and other allied scientific disciplines and professions, (2) career opportunities and requirements, and (3) knowledge and skills appropriate for employment at technical and practitioner levels in each discipline. Graduates are able to communicate and work effectively in the multidisciplinary arena of ecology and natural resource management.

All options require three months (400 hours) of relevant work experience or study at a biological station prior to graduation. The latter may be accomplished at the university’s affiliate field stations: Rod and Connie French Conservation Camp in Montana, Iowa Lakeside Laboratory at West Lake Okoboji, and Gulf Coast Research Laboratory at Ocean Springs, Mississippi. Information on these laboratories is available from the department’s Student Services Center.

Preveterinary medicine preparation may be achieved while satisfying degree requirements in animal ecology.

Additional education and training can lead to other opportunities in such areas as research and management, natural resources planning and administration, teaching, and environmental consulting, among others. Graduate training is necessary for many specialized positions within the fields of animal ecology. Students preparing for graduate study should consult with their academic advisor concerning appropriate coursework.

Students wishing to be certified by the American Fisheries Society or The Wildlife Society need to consult with their advisors in selecting required courses in their respective programs. The formal application then needs to be completed and submitted for review by their professional societies. Certification in either society has many professional benefits and may be required or recommended for employment by federal and state agencies and private industry.

Students seeking certification to teach biology in secondary schools must meet requirements of the College of Human Sciences as well as those of the Animal Ecology curriculum. In addition, they must apply formally for admission to the teacher education program (see Teacher Education Program). Students with an interest in careers in outdoor writing are encouraged to obtain a minor or a second major in journalism (see Journalism and Communication, Courses and Programs). Students who wish to pursue a job as a conservation officer may wish to minor in criminal justice (see Criminal Justice).


Origin and Evolution of Birds

Consider for a minute the diversity of birds. There are nearly 10,000 species! Is it possible to trace these birds back to one common ancestor? If so, who is it?

One of the major criticisms of Darwin’s Origin of Species was
the apparent lack of any evidence showing the evolution of birds. Then,
as luck might have it, only two years after he first published his book,
Archaeopteryx appeared in a site in Germany.

Today there are 8 preserved fossils of Archaeopteryx in various
museums of the world. What an amazing find for science because it stirred
scientists to try to figure out how birds were related to other creatures.

Archaeopteryx
was amazing for a few reasons. First it superficially resembled both a
bird and a reptile. In fact, except for the feathers, the
bird-like feet
, and the fact that it had a wishbone
(furcula) it didn’t really look like a bird. The jaws
had teeth
in them, of which no bird today has teeth. It also
had the ankle bone fused to the shinbone. Clearly this
bird had features of dinosaurs AND birds. So where did birds evolve?

Three hypothesis on origin of birds finally arose:

  1. Therapod dinosaur hypothesis: The first was a hypothesis
    that they came from the therapod dinosaurs. Therapods are meat eating
    dinosaurs such as Allosaurus.
  2. Crocodiles – the second hypothesis was that they
    came from crocodiles because they had an endolymphatic duct. Yet, as
    more research was conducted, they discovered that there was a tremendous
    amount of variation in this duct even among the lizards and other reptiles.
    Not many people today give much attention to this hypothesis
  3. Neither crocodiles or dinosaurs:Neither on the dinosaur
    line or the crocodile line. Reasoning because several dinosaurs were
    very specialized already.

Today we can show that birds are related in many ways to Dinosaurs. By
using key characters we can use cladistics to understand better the relationships.
For instance we can look at features they share in common with animals
such as reptiles, and ancient dinosaurs in order to figure out where they
may have evolved. They can thus, be linked generally to Ornithodira
and more specifically to Manirapterans.

If you look at a cladogram
of Diapsids which includes snakes, lizards, crocodiles (archosaurs),
and dinosaurs and birds, you can get a better picture as to where birds
fit in.

Looking in particular at the Ornithodira, Dinosaurs, Saurischian
dinosaurs, Therapods, Tetanurae, Coelesaurs, Manirapterans
. (list
heirchial)

Summarization of the set of derived characters that link them
to the dinosaurs:

Once the idea that birds came from dinosaurs began, there was a scurry
to find fossil evidence that could link birds back to their dino-roots.
Several different dino-birds arose in the last century. One was Caudipteryx

In China a fossil
was found that was dinosaur-like but had feathers. It seems that the wings
would have been too small to allow it to fly, but, the fact that it had
wings made it big news! Thus, the idea was that the initial evolution
of feathers may not have been for powered flight. In fact, if you look
at the tail feathers, it looks as though they are symmetrical around the
shaft. This finding forced a reconfiguration of the systematics of the
group.

Another fossil was found that, although it was not a fossil with wings,
it was a closely related dinosaur to birds that was very small and appeared
to be arboreal. This tiny fossil is only about 10 cm long and if it lived
in the trees could have glided from tree to tree.

For almost a century scientists have been debating this issue. The common
belief was that flight must have evolved from the trees down. This is
because every known modern semi-airborn animal (glider), seems to be arboreal.
Yet, another competing theory is that the wings are used to catch insects
and thus evolved from the ground up.

One set of reasoning for the ‘ground-up‘ hypothesis is that dinosaurs
could have been leaping to catch insects and wings allowed them to come
down in one piece. Part of the evidence is that the capturing of prey
was the same movement for flight.

Wing-Assisted Incline running. (copy
of the study).

In a 2003 article in science, Kenneth Dial proposed his theory of ‘wing-assisted
incline running’ as a way for wings to evolve. In the study he used chucker
partridges and had them run up grades from 0 to 90 degrees. From 0 to
45 degrees, they just used their legs, but greater than 45 they used their
wings too. When they flap their wings, they put traction on the surface
and thus, increase their ability to run up the incline


Watch the video: BOC; Prof. Jon Fjeldså The Evolution of Passerine Birds Explained (October 2022).