An Investigation of the Scientific Hierarchy of Classification in the Sub-phylum Vertebrata




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Extended Essay
An Investigation of the Scientific Hierarchy of Classification in the Sub-phylum Vertebrata

Eric Sutter

Candidate Session Number:

February 2008

Subject Area: Biology

Number of Words: 2551

Abstract

The research question to be investigated is: What are the subdivisions of the sub-phylum Vertebrata of the phylum chordata and what defines these subdivisions?


The investigation analyzes the classes in which organisms are divided into the sub-phylum Vertebrata in the phylum chordata. The information found in this investigation will provide insight into the working of taxonomy provide information on qualification for organisms to fit into these classes. Biological classification has changed greatly throughout history, this investigation analyzes some specific changes relating to vertebrate classification.

Table of Contents


Abstract ...............................................................................................p.2

Diagram of the hierarchy of scientific classification.............................p.4

Taxonomic Ranks................................................................................p.5

Phylum Chordata.................................................................................p.7

Sub-phylum Vertebrata........................................................................p.8

Class Agnatha.....................................................................................p.9

Agnatha radula diagram......................................................................p.10

Class Placodermi................................................................................p.11

Class Chondrichthyes.........................................................................p.12

Class Osteichthyes.............................................................................p.13

Class Amphibia...................................................................................p.14

Dendrobates Azureus Photograph.....................................................p.15

Class Reptilia.....................................................................................p.16

Class Aves.........................................................................................p.17

Class Mammalia................................................................................p.18

Conclusions.......................................................................................p.19

List of References.............................................................................p.20

Diagram of the modern hierarchy of scientific classification:




Taxonomic Ranks

As seen in the diagram on the previous page. There are eight ranks in which all life is put through in modern taxonomy. Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species, are the eight ranks in order from highest to lowest. These ranks were developed to provide grouping for selections of species enabling easier discussion of related organisms. This modern hierarchy of classification makes use of DNA sequencing to find relationships between species and apply them to the appropriate groups. There have been many reorganizations of species within this tree, with each reorganization attempting to increase accuracy of suspected related species.
Domain is the highest rank and divides into only 3 categories, Archaea, Eubacteria, and Eukaryota. In this investigation will be in the Eukaryota domain.
The next highest rank is Kingdom, in this rank there are six categories, Animalia, Plantae, Fungi, Protista, and Prokaryota or Monera. This investigation is in the Animalia kingdom.
Phylum is the next highest rank. There are approximately thirty-five phyla total, this investigation will be looking at only the Chordata phylum. Phylum Chordata covers an immense number of organisms and this investigation will only focus on the sub-phylum Vertebrata.
Class is the next highest rank under phylum and sub-phylum. In this investigation all of the classes in the sub-phylum Vertebrata will be examined.
Order, the next highest rank divides the classes into more categories. Specific orders will not be examined beyond a few specific organisms in this investigation.
Family the third lowest rank describes a series of organisms that at this point show many obvious shared traits. No specific Families will be looked at in this investigation.
Genus, the second to lowest classification is used in describing specific organisms in binomial nomenclature. Using this system the first name of the binomial nomenclature is the genus. For example in the binomial nomenclature of the organism Dendrobates Azureus the name Dendrobates is the genus.
Species, is the lowest rank of the hierarchy of classification. Organisms are often defined by species depending on if they are capable of interbreeding. In the binomial nomenclature system it is the second name after Genus. In Dendrobates Azureus the name Azureus is the specific species of organism.

Phylum Chordata

The phylum Chordata contains animals in which have a notochord: a rod shaped supporting axis or backbone.1 These organisms fall into the kingdom Animalia and can be subdivided into several sub-phylums, the focus of which will be on the sub-phylum Vertebrata.

Phylum Chordata however can also contain invertebrates which can have a boneless spinal chord in the beginning stages of life. Features of Chordates include bilateral symmetry, a complete digestive system, bone or cartilage endoskeleton, and segmented body.2 The oldest fossil records of chordates date back to the Cambrian age, around 525 million years ago.3

Sub-phylum Vertebrata

Organisms in the sub-phylum Vertebrata are vertebrates and subsequently contain a backbone and spinal column as well as a variation of other bones depending on the organism. About 57,739 species of Vertebrates have been described.4


The use of use of a back bone as well as other bones provides the organisms in this sub-phylum protection of vital organs as well as an appropriate attachment site for muscles. Many organisms have cartilaginous features which were at one point thought to be the predecessors of bony structures, but it now thought to be the opposite.5

There are eight classes in which vertebrates are categorized as, four which are aquatic and four which are terrestrial. The aquatic classes are Agnatha, Placodermi, Chondrichthyes and Osteichthyes and the terrestrial classes are Amphibia, Reptilia, Aves and Mammalia.


Class Agnatha

The class Agnatha is constituted of fish without jaws and are the oldest known vertebrates. Modern fish which are classified as Agnathas are the hag fish, and lampreys. These fishes have a radula, a sort of tongue lined with teeth, and elongated necks. The use of the radula and lack of jaw is for parasitic purposes. The lack of jaw and sharp teeth enable lamprey to latch onto other fish to drink the blood of the animal.6

Diagram of an organism in the class Agnatha, radula lined with teeth is demonstrated in this image.





Class Placodermi

Placoderms are an extinct class of armored fish. Although extinct now, they were extremely common during the Devonian period, based on fossil evidence. These fish had paired fins and a heterocercal tail. This particular type of tail fin is identified by it extending vertically past the dorsal fin. Placoderms are thought to have been very efficient swimmers because of these fin configurations.7 A defining feature of the Placoderms was that they did not have teeth but instead had bony plate structures which fit the same function. Placoderms were some of the first fish to inhabit both freshwater and saltwater environments.8

Class Chondrichthyes

In almost complete opposition to the class Placodermi, the Chondrichthyes are defined by their lack of bones. Instead of calcified bone structures members of the Chondrichthyes class would primarily be cartilaginous, in which they would have cartilage rather than calcified true bone. Some organisms in this class would have calcified bones for their teeth and spine, but would otherwise be cartilaginous. Organisms in this category are still in existence today in the form of sharks, rays, skates and chimeras, but have also been on earth for almost 450 million years from fossil evidence.9
An interesting characteristic which can separate members of the class Chondrichthyes from other common fish is their lack of a swim bladder. Sharks in this class are required to be in constant motion to prevent themselves from sinking to the bottom of the ocean. Skates and rays are often found resting on the bottom of the ocean, as they too sink when not in motion. Many organisms in this class show a characteristic of countershading, in which they are dark on the upper half of their body and light on the lower half. This enables them to blend in with the environment to predators and prey above and below them.10

Class Osteichthyes

This class is made of bony fish, which have skeletons reinforced by calcium. Like the Agnathas, Placoderms and Chondrichthyes, these fish have paired fins, which enable balanced swimming. These paired fins are pectoral fins and pelvic fins. Unlike the Agnathas these fish had jaws and could have either many teeth or none at all. Some organisms in the Osteichthyes class feature a special bone called the operculum which, by moving back and forth, enables the fish to respire using their gills without being forced to swim. The strength added by having calcified bones does not come without it's faults however. In order to counter the weight of the calcified bone structures in these fish, they have an organ called a swim bladder.8 This organ enables the fish to control their own buoyancy and counter the weight of their calcified bones. The swim bladder can also function as a sound production device as well as detecting vibrations.11 Members of this class also feature mucus glands in their skin and scales which can provide a protection from parasites and disease. They differed greatly from the Placodermi class because their tails are primarily homocercal and never have placoid scales, some fish in this class do not even have any scales at all.12

Class Amphibia

The class Amphibia features common organisms such as frogs, salamanders, newts, and toads, as well as less commonly known burrowing caecilians.13 Amphibians are typically born underwater but often live most of their adult life out of water although in moist environments. They usually return the water to lay their eggs which are fertilized by a male externally, although some creatures of this class carry their eggs until birth and are thus fertilized internally. The larvae are born with many features similar to fish such as gills and tails, however through the process of metamorphosis, neoteny occurs and they lose these features as they mature. Another remarkable feature of this class is that many creatures in it are capable of absorbing oxygen and water directly through their skin. This enables them to passively take care of physical needs of their body, however it also leaves them susceptible to pollution in their environment causing great damage to themselves. Fossil record of the class dates back to the Jurassic period, 206 to 144 million years ago, and some frogs even date back to the Devonian period, 417 to 354 million years ago .14

Photograph of a Dendrobates Azureus, a member of the Amphibia class.




Class Reptilia

The class Reptilia is composed of such animals as turtles, snakes, lizards and crocodiles. Defining features of reptiles is that they have fully ossified bones, in that they are completely composed of calcium and are not cartilaginous.15 They are ecothermic creatures or more commonly referred to as cold blooded. This means that rather being endothermic, in that they would create their own heat, they are forced to position themselves in the environment appropriately to obtain the heat they need. For example a tortoise may choose to move it self into the sunlight to raise it's body temperature rather than their body raising it automatically through homeostasis.16 All reptiles are not only ecothermic but they all have paired limbs with five toes, lungs, and a three or four chambered heart. Their eggs feature an extra membrane called the amnion which provides protection from the environment. Based on fossil evidence there is some debate as to if birds had at once point been part of the Reptilia class. Because of this debate some consider the class Aves to be a subgroup of the class Reptilia.

Class Aves

Considered to be descendants of the dinosaurs and possibly a subgroup the class Reptilia, members of the Class Aves, feature many characteristics which are similar to reptiles.17 Similar to reptiles birds lay eggs, and have strong bones. The eggs which reptiles lay are much more leathery and somewhat soft while birds lay smooth hard-shelled eggs. The bone structure of birds is somewhat different than reptiles in that while they are both strong and fully ossified, the birds bones are much more porous making the very light, which is a requirement for flight. A bone called the furcula or commonly known as the “wish bone” enables birds to beat their wings rapidly without deflating their chest in mid-flight.17 In contrast to reptiles, birds also feature feathers, which provide insulation of heat, since birds are endothermic, and enable some birds to fly. Rather than teeth or jaw bones, birds have bills, strong pointed structures coated in keratin which enable them to be precise in picking up food or nesting material off the of ground as well as being strong enough to crack seeds open. Unlike many other organisms birds have an amazing vocal range only challenged by that of the class Mammalia.19

Class Mammalia

The class Mammalia is classified by it's endothermic animals which contain mammary glands in the female, three middle ear bones, and hair.20 Mammals are subdivided into twenty-one orders based on specific features of the particular mammal. The malleus, incus, and stapes are the three middle ear bones which make Mammals unique. These bones work as receptors for sound vibrations and which are translated into neural impulses. In addition to these bones, Mammals have a diaphragm, sweat glands, large cerebral cortex and a four chambered heart.21 Animals in the class Mammalia have hard ossified bones but can also have cartilaginous features. Similar to birds, the hair on Mammals is used as insulation and made of keratin, however it is thought that the keratin was developed independently of reptiles and birds.
Of the class Mammalia there exists 3 major groups which mammals can be divided into. The Placental Mammals, which are raised with a placenta inside the uterus of a female. The marsupials, which contain a pouch in which to carry their young and give birth from, and finally the Monotremes, which lay eggs and do not contain true mammary glands but do provide milk for their offspring.

Conclusions

The use of the scientific classification provides us with a way to relate animals to one another. We are able to differentiate living organisms from one another and where what features they might have. By knowing the classification of an organism one could determine what possible features it might have, or using the features of an organism determine what category is belongs to within the hierarchy of classification.

Using these systems we are able to relate species to one another and discover how they may have evolved over time providing us with insights into the history of life so we can better understand the workings of life today. There is tremendous need for understanding of ecosystems in order to maintain them in their balanced state and by better understanding the role of organisms within them we can try to preserve them.



List of References

  1. http://museum.nhm.uga.edu/gawildlife/glossary/gawwglossary.html

  2. http://animaldiversity.ummz.umich.edu/site/accounts/information/Chordata.html

  3. http://www.tolweb.org/Chordata

  4. Jonathan E.M. Baillie, et al. (2004). A Global Species Assessment. World Conservation Union.

  5. http://www.infoplease.com/ce6/sci/A0857332.html

  6. William Wirt Calkins. The Chicago Academy of Sciences: The Lichen-Flora of Chicago and Vicinity. 1896

  7. http://www-biol.paisley.ac.uk/Courses/Tatner/biomedia/units/fish4.htm

  8. http://www.ucmp.berkeley.edu/vertebrates/basalfish/placodermi.html

  9. http://www.ucmp.berkeley.edu/vertebrates/basalfish/chondrintro.html

  10. http://www.cyhaus.com/marine/sharks.htm

  11. http://fsc.fernbank.edu/STT/VertBio/pages/Osteichthyes/osteichthyes.htm

  12. http://school.discoveryeducation.com/curriculumcenter/oceans/glossary.html

  13. http://www.ucmp.berkeley.edu/vertebrates/tetrapods/amphibintro.html

  14. http://www.ucmp.berkeley.edu/vertebrates/tetrapods/amphibfr.html

  15. http://animaldiversity.ummz.umich.edu/site/accounts/information/Reptilia.html

  16. http://reptilis.net/cold-blood.html

  17. http://www.ucmp.berkeley.edu/diapsids/birds/birdlh.html

  18. http://animaldiversity.ummz.umich.edu/site/accounts/information/Aves.html

  19. http://animals.about.com/od/birds/p/aves.htm

  20. Charles Robert Darwin (1809–1882).  Origin of Species.
    The Harvard Classics.  1909–14.

  21. http://animals.about.com/od/mammals/p/mammals.htm


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