Placental mammals were early insectivores and lived along with dinosaurs in the Late cretaceous. During cretaceous mass extinction, dinosaurs became extinct and opened up lots of dietary niches. The ancestral insectivore radiated out into all the niches and had 5 chitinase genes. But those who got adapted for other diets lost their chitinase genes through accumulation of various mutations. These gene remnants passed on to all mammals now exist, as pseudo genes.
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Occassionally, brittle stars are seen in the body of jelly fishes. Interesting fact is the food sources of brittle stars seems to be mesozooplanktons and they were never observed with arms out in water. Then, where do they get their food from? They take food directly from the mouth or the oral arms of the jelly fish. It means, they are stealing food from the jellyfish which are pelagic predators. There are several reports of other brittle stars moving down into the feeding arms or near the mouth and stealing food directly from the host. So these are called as KLEPTOPARASITES.