Question

30. How are mass extinction events distinguished from background extinction rates? Which common environmental factor associated appears to be associated with all past and even current mass extinction events? What are some of the global consequences caused by this common environmental factor that lead to mass extinctions?

31. According to the traditional classification of vertebrates, class Reptilia is a paraphyletic group because it does not include all descendants of a common ancestor. Which group has been left out of the classification but is really part of the reptile clade?

32. Why was the Cambrian era most unique among the fossil record of animal evolution? How did all those different animal body plans arise so quickly?

Answer 1

30. The difference between a background extinction and mass extinction is that the species are not able to adapt the gradual changes in the environment and eventually extinct are called background extinction while mass extinctions is wiping out entire species, general or even families due to harsh conditions of environment in a short period of time. Total five major mass extinction events has occured

The common environmental factors are like asteroid or comet impact, climate change,drop in sea level, earthquakes, volcanoes, gamma ray burst, plate tetonics, global warming etc

Due to extensive urbanisation, deforestation, and destruction of natural environment is leading to global warming which turn is leading to the gradual extinction of many species of flora and fauna. Further global warming has led in snow melting which resulted in increase in volume of the water cycle hence rise in sea level ; extreme weather, ozone layer depletion etc.

31. Birds is the group which has been left out but is actually part of the reptile clade. Birds share an ancestory with dinosaurs, i.e. they have descended from dinosaurs and dinosaurs are reptiles hence, which makes birds come under the classification of reptile or in other words birds are reptiles.

32, Before Cambrian time, life was simple. It is in the Cambrian period, that most of the animals fossils were appeared.This is also known as Cambrian explosion. It is unique in the sense that incredible diversity of life emerge, including the chordates.

It us unique because of very high proportion of lagerstätte sedimentary deposits. (it is a sedimentary deposit where not only the hard body preserved but also "soft" parts of organisms are preserved) and that is also why they were easily fossilized like ancestors of arthropods (trilobites) etc.