Describe the evolution of vertebrates as seen in this tree. Where would you plac

Question

Describe the evolution of vertebrates as seen in this tree. Where would you place an organism such as a platypus? (Describe the interesting characteristics of the platypus and how is makes it hard to place definitively.) What is the purpose of trees like these? Why is creating these trees difficult?

Gnathostomes Tetrapods Amniotes Myxini -- Cephalaspidomorphi Chondrichthyes Actinopterygii Actinistia Dipnoi Amphibia Mammalia Testudines Lepidosauria * Crocodilia v Aves Feathers Osteichthyes (bony fishes) Milk Amniotic egg Legs Lungs or lung derivatives Jaws Two sets of paired appendages Mineralized (ossified) skeletons and teeth Vertebral column Ancestral vertebrate Copyright O Pearson Education, Inc., publishing as Benjamin Cummings.

Explanation / Answer

Vertebrates are characterized by the presence of vertebra.
Jawless fish are the earliest vertebrates which lived during 500-600 million years ago.
The first fish with complete vertebral column evolved 450 mya. They possessed cartilaginous endoskeleton and jaws.
Bony fish first appeared 400 mya. In these fishes, the bony skeleton could support large body. From these, lobe-finned fish and ray fishes evolved.
The first amphibians evolved 365 mya from the lobe-finned ancestor. These organisms are still dependent on water for reproduction.
The first reptiles evolved 300 mya. These organisms are not dependent on water for reproduction. They also contain amniotic eggs and exhibit internal fertilization.
Birds (150 mya) and mammals (200 mya) evolved from reptile-like ancestors.
Before the evolution of birds and mammals, all the existing organisms are ectotherms. Endothermy is present in both birds and mammals.

Ornithorhynchus anatinus (platypus) is an egg-laying semi-aquatic mammal. It shows egg laying character that is seen in reptiles. It shows feeding progeny with milk which is a character of mammals. So, it is placed in Monotremata order.

Phylogenetic trees help us to understand the evolutionary history of organisms. We can use this information to predict how species will change in future.

It is rather difficult to create phylogenetic trees as we have to consider many features while constructing them. Often considering a single factor does not provide an accurate representation of the evolutionary history.

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