Morganucodonta

Morganucodonta ("Glamorgan teeth") is an extinct order of basal Mammaliaformes, a group including crown-group mammals (Mammalia) and their close relatives. Their remains have been found in Southern Africa, Western Europe, North America, India and China. The morganucodontans were probably insectivorous and nocturnal, though like eutriconodonts some species attained large sizes and were carnivorous. Nocturnality is believed to have evolved in the earliest mammals in the Triassic (called the nocturnal bottleneck) as a specialisation that allowed them to exploit a safer, night-time niche, while most larger predators were likely to have been active during the day (though some dinosaurs, for example, were nocturnal as well).

== Anatomy and biology == left|thumb|Skull of Morganucodon Morganucodontans had a double jaw articulation made up of the dentary-squamosal joint as well as a quadrate-articular one. This implies that they also retained one of their postdentary bones: the articular. There is a trough at the back of the jaw on the inside (lingual) where the postdentary bones sat. The double jaw articulation and retention of the postdentary bones are characteristic of many of the earliest Mammaliaformes, but are absent today in mammals: All crown-group mammals have a lower jaw that is composed of a single bone, and the articular has been incorporated into the middle ear, having become the malleus (while the quadrate has become the incus).thumb|left|Diagram showing characteristic double jaw jointUnlike more basal therapsids such as Sinoconodon, morganucodontan teeth were diphyodont (meaning that they replaced their teeth once, having a 'milk' set and 'adult' set as seen in today's mammals including humans and not polyphyodont (meaning that the teeth are constantly replaced, and the animal and its teeth get larger throughout its lifetime, as in reptiles). Evidence of lactation is present in Wareolestes, via tooth replacement patterns.