Chapter 16 Vertebrata = Craniata Agnatha Gnathostomata Teleostomi Chondrichthyes

Question

Chapter 16 Vertebrata = Craniata Agnatha Gnathostomata Teleostomi Chondrichthyes- -finned Actinistia Dipnoi Tetrapods fishes) (coelocanths) (lungfishes) Actinistia Dipnoi Tetrapods Myxini Petromyzontida (hagfishes) (lampreys) (sharks, skates, Holocephali rays) (chimaeras) (ray Limbs used for terrestrial Placoderms loc Acarthodijt Ostracoderms Loss of scales teeth modified as grinding plates Disk-like buccal fuunnel, long larval stage as ammocoete, vertebrae Unique supportive elements n skeleton of girdle and limbs Placoid scales, claspers Lung or swim bladder derived from gut, endochondral bone Naked skin with slime glands, hearts Bony operculum -Part of second visceral arch modified as supporting element for jaws, teeth with dentine aws frore mendit iar arch, pairs sn circular canals, Teeth formed from keratin Distinct head, tripartite brain, specialized sense orgsne 1 pair semicircular canals, craium, well developed pharyngeal skeleton TExtinct groups figure 16.2

Explanation / Answer

Answer:

There are some basic assumption:
1. Change in characteristics occurs in lineages over time.
e.g. The pleasimorphic state of birds will not have feathers formed.
2. Any group of organisms is related by descent from a common ancestor.
3.There is a bifurcating, or branching, pattern of lineage-splitting.
This assumption suggests that when a lineage splits, it divides into exactly two groups. There are some situations that violate this assumption. For example, many biologists accept the idea that multiple new lineages have arisen from a single originating population at the same time, or near enough in time to be indistinguishable from such an event.

In many cases the original (or plesiomorphic) state of a character is more complex than the changed (or apomorphic state). For example, as they have evolved, many animals have lost complex traits (like vision and limbs). In the case of snakes, the plesiomorphic characteristic is "has legs" and the apomorphic characteristic is doesn't have legs.

Phylogenetic trees could be drawn in different formats, the first diagram is using diagonal lines or the second diagram which is flipped on their sides.In a rooted tree, the branching indicates evolutionary relationships . The point where a split occurs, called a branch point, represents where a single lineage evolved into a distinct new one. A lineage that evolved early from the root and remains unbranched is called basal taxon. When two lineages stem from the same branch point, they are called sister taxa. A branch with more than two lineages is called a polytomy and serves to illustrate where scientists have not definitively determined all of the relationships. It is important to note that although sister taxa and polytomy do share an ancestor, it does not mean that the groups of organisms split or evolved from each other. Organisms in two taxa may have split apart at a specific branch point, but neither taxa gave rise to the other.

All the characteristics stated in the first diagram first one is a common character then the derived chracters are evolved and a new species is formed. E.g. Sharks and chimaeras are evolved from same ancester because they had Placoid scalles and part of the second visceral arch modified as supporting element for jaws teeth with dentine, but later becuse of loss of scales happens to Chimaeras so it is been divided to a separate species.

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