Because it allowed vertebrates to be free from needing to be near standing bodies of water where they could lay their eggs.
The platypus is in the mammal classification. It is a monotreme, or egg-laying mammal.
Reptiles (I think)
Nothing important
In both an egg cell and a sperm cell, there are 23 chromosomes. The sperm and egg unite (fertilize) to create a zygote (fertilized egg). A zygote has 46 chromosomes. This is important because if a sperm and/or an egg cell have 1 more or 1 less chromosome, a mutation could form in the zygote.
In fact, there are no such things as "evolutionary stages". Evolution, even in the model of punctuated equilibria, is a continuous and gradual process.
Evolution of a Duck Egg - 1912 was released on: USA: 29 July 1912
Egg and sperm
1. An amniotic egg.An amniotic land in an egg that can survive on land. The evolution of the amniotic egg allowed vertebrate land animals to move away from water bodies. They were previously tied to bodies of water because their eggs could not survive on dry land.
Birds are winged, bipedal, warm-blooded, feathered, egg-laying, vertebrate animals.
the chicken
The egg that Riley gives you hatches into a Riolu, the pre-evolution of Lucario.
A bird is a warm-blooded, egg-laying, feathered vertebrate. Penguins are flightless birds.
The platypus is in the mammal classification. It is a monotreme, or egg-laying mammal.
Mammals has these 3 groups .
It is a vertebrate because it has a spinal column in its skeletal system. Also it is a mammal, although it lays eggs, and every mammal (or other warm-blooded creature, like a bird) is a vertebrate.
In this case, the egg came first. The turkey egg existed before the turkey itself evolved into the form we know today.
The bird came first. After a process of long evolution, birds transformed from reptiles to aves. After evolution, the first laid eggs. After that the evolution process started rapidly.