<span>Hyracotherium, Mesohippus, Merychippus, Pliohippus, because over time, the number of toes decreased and body size increased is the right answer</span>
Answer:
The animals present body structure is due to evolution. It is seen in each part including the structure of the heart. The vertebrate heart becomes complex from a simpler form.
Invertebrates, the heart of fishes is two-chambered having one auricle and one ventricle. The deoxygenated blood gets purified in the gills. They are aquatic and no lungs for breathing. The hearts pump a mixture of oxygenated and deoxygenated blood to the body.
The amphibians and reptiles have 3 chambered heart as they lead terrestrial mode of life. The gills modified into the lungs. The left auricle receives pure blood and the right auricle receives deoxygenated blood. The blood purified in the lungs and in the ventricle, both types of blood get a mix. The ventricle pumps the mixed-blood throughout the body.
In the case of birds and mammal, the heart is 4 chambered and the oxygenated and deoxygenated blood are separated. These two are higher vertebrates. No mix of pure and impure blood, the body receives only the oxygenated blood.
This shows to construct the phylogenetic tree of vertebrates - the fishes should be in the bottom, and above it amphibians, reptiles, then, mammals and birds on the top branch of the tree. As the chambers and structure of the hearts modified one after another.
I think the correct answer would be D. In the process of petrification, a tree burning is not included. Petrification is a process that involves organic materials turning into fossils by replacing the original contents of a certain object with minerals.
The increase in the glucagon secreted by the alpha cells of "islets of langerhans" in he pancreas would lead to a rise in the blood sugar level.
The decrease in the secretion of insulin from the beta cells of "islets of langerhans" in the pancreas would also lead to higher blood sugar level
Answer: D. sixty
Explanation: the answer is 60 or sixty
