Current vertebrates have following attributes:
1. They have hair on the body.
2. They have mammary organs.
3. They have specific teeth. They have heterodont dentition
4. Three center auto ossicics are available.
5. Stomach is available in them.
6. Their skin has sweat, sebaceous. fragrance organs.
7. Theirheart is four-chambered.
8. They have extensive cerebral cortex.
The zoologists differ on subclass order. Most zoologists consider that mid Cretaceous vertebrates veered to frame two sub-classes. These sub classes were: Prototheria and the Theria.
1. Sub-class Prototheria
The monotremes (the duck-charged platy discharge and the echidna) were prior ordered in the subclass Prototheria. Yet, late fossil proof demonstrates that the monotremes have dentition like subclass theria. In this way monotremes were put in subclass theria. In this way, the Prototheria contains just wiped out structures.
2. Subclass Theria
The subclass Theria separated into three infraclasses in late Cretaceous period. These infraclasses are:
(an) Infra class Ornithodelphia: (ornis, winged animal + delphia, origination). It contains monotremes (mono, one + trema, opening). The monotremes have a cloaca. Monotremes are oviparous. The six types of monotremes are found in Australia and New Guinea.
(b) Infraclass Metatheria: (meta, after) It contains marsupial warm blooded animals. They are viviparous. Be that as it may, they have short incubation periods. They build up a defensive pocket called the marsupium. It covers the female mammary organs. The youthful creep into the marsupium after birth. They bolster in the marsupium and finish their improvement. Around 250 types of marsupials live in the Australian locale and the Americas.
(e) Infraclass Eutheria: (Eu, genuine). It containsJN0-541 placental warm blooded animals. They are conceived at a propelled phase of advancement. The youthful is supported inside the uterus. Theydevelop placenta. The trades amongst maternal and fetal circulatory frameworks happen through placenta. Placenta is made out of both maternal 3101 and fetal tissue.This subclass contains 3,800 species. It has 17 orders.