Fish like reptile (Icthyosaurs). Which go back into water from it's land ancestor evolved before how many years:-

During evolution, first jawless fish probably evolved before how many years ?

Which reptile went back into water to evolve into fish likfe reptile?

Reptiles of different shapes and sizes dominated Earth. Which reptile went back into water to evolve into fish like reptiles 200 mya ?

(Allocation problem) A cooperative society of farmers has 50 hectare of land to grow two crops X and Y. The profit from crops X and Y per hectare are estimated as Rs 10,500 and Rs 9,000 respectively. To control weeds, a liquid herbicide has to be used for crops X and Y at rates of 20 litres and 10 litres per hectare. Further, no more than 800 litres of herbicide should be used in order to protect fish and wild life using a pond which collects drainage from this land. How much land should be allocated to each crop so as to maximise the total profit of the society?

Consider the following three statemetns and select the correct option stating which one is true (T) and which one is false (F). (i) Some land reptiles went back, into water to evolve into fish like reptiles probable 200 mya. (ii) The first mammals were like shrews. (iii) The work of Thomas Maithus on populations influenced Lamarck.

There are 2 gates to enter a school and 3 staircases from first floor to the second floor.How many possible ways are there for a studentto go from outside the school to a classroomon the second floor and come back?

(a) How many million year ago, gigantic reptiles used to dominate on earth ? Give their common name and also mention the period and year in which they were predominanat on earth. (b) Why did these gigantic reptiles disappear from the earth in a short duration ? (c ) Name the most advanced living reptiles. List atleast two characters in which they resemble in mammals.

Land reptiles that went back into water evolve into fish-like reptiles probably 200 mya. Example of such reptile is:

Some of the land reptiles went back into the water to evolve into fish-like reptiles (e.g. ichthyosaurs), probably around