Mammalian Orders

Mammals are commonly classified into a single order of monotremes, 7 orders of marsupials, and about 18 orders of placental mammals. Possible evolutionary relationships between the mammalian orders are shown in Figure 43-10.

Subclass Prototheria



Infraclass Metatheria

Subclass Theria

Infraclass Eutheria figure 43-10

This phylogenetic diagram shows hypotheses of the evolutionary relationships between mammals. Scientists disagree about the details of some of these groupings. Dashed lines indicate relationships that are very uncertain or strongly debated. For updates on phylogenetic information, visit and type in the keyword HM6 Phylo.

Order Monotremata Superorder Marsupialia

Order Xenarthra Order Insectivora Order Chiroptera Order Dermoptera

Order Primates Order Scandentia — Order Macroscelidea Order Lagomorpha

Order Rodentia — Order Pholidota

Order Carnivora Order Cetacea

Order Artiodactyla— «? Order Perissodactyla Order Hyracoidea Order Sirenia — Order Proboscidea Order Tubulidentata - ^1

Copyright © by Holt, Rinehart and Winston. All rights reserved.

(a) Duckbill platypus, Ornithorhynchus anatinus (b) Short-beaked echidna, Tachyglossus aculeatus figure 43-11

Two of the three species of the order Monotremata are shown here: the duckbill platypus (a) and an echidna that is also called a spiny anteater (b).

(a) Duckbill platypus, Ornithorhynchus anatinus (b) Short-beaked echidna, Tachyglossus aculeatus

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