Everything about Mammaliaformes totally explained
Mammaliaformes ("mammal-shaped") is a
clade that contains the
mammals and their closest
extinct relatives. The precise
phylogeny is disputed due to the scantness of evidence in the
fossil record. However, it's thought that the Mammaliaformes were of three major groups:
Allotheria, the longest extinct lineage of pre-mammals;
Docodonta, including close relatives such as
Morganucodonta; and
Symmetrodonta, the most
basal of modern mammals. Mammaliaformes
radiated from
Cynodontia.
Probainognathia of the
Eucynodonts probably evolved into the early mammaliaformes, but the branch
Allotheria was so different that they may have come from an entirely different group of cynodonts.
Early mammaliforms were generally
rodent-like in appearance and size, and most of their distinguishing characteristics were internal. In particular, the structure of the mammaliform (and mammal)
jaw and arrangement of
teeth is nearly unique. Instead of having many teeth that are frequently replaced, mammals have one set of baby teeth and later one set of adult teeth which fit together precisely. This is thought to aid in the grinding of food to make it quicker to digest. Being warm-blooded requires more calories than "cold-blooded" animals, so quickening the pace of digestion is a necessity. Early mammaliaformes were probably nocturnal.
Mammaliforms have several common structures. Most importantly, mammaliforms have highly specialized
molars, with
cusps and flat regions for grinding food. This system is also unique to mammals, although it seems to have
evolved convergently in pre-mammals multiple times.
Lactation and
fur, along with other characteristically mammalian features, are also thought to characterize the Mammaliaformes, but these traits are difficult to study in the fossil record. The fossilized remains of
Castorocauda lutrasimilis are a unique exception.
Some non-mammal mammaliformes still retain
reptile-like traits. Some mammaliformes had
reptile-like locomotion. Furthermore, these mammaliformes still had some bones on their lower jaw seen in reptiles.
Taxonomy
Further Information
Get more info on 'Mammaliaformes'.
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