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As a result, the paraphyletic terms "mammal-like reptile" and "pelycosaur" are seen as outdated and disfavored in technical literature, and the term stem mammal (or sometimes protomammal or paramammal) is used instead. Phylogenetically, it is now understood that synapsids comprise an independent branch of the tree of life. [19]
Mammals and birds filled the empty niches left behind by the reptilian megafauna and, while reptile diversification slowed, bird and mammal diversification took an exponential turn. [44] However, reptiles were still important components of the megafauna, particularly in the form of large and giant tortoises .
Stem mammals therefore include all pelycosaurs, and also all non-mammalian therapsids. Traditionally these were known as "mammal-like reptiles", but this is incorrect; [12] terms such as "stem mammal" are preferred instead, because these synapsids were neither reptiles nor even part of reptile lineage. [11] [12]
The heaviest archeocete, and possibly the heaviest known mammal was Perucetus, with weight estimated at 85–340 t (84–335 long tons; 94–375 short tons), while length is estimated at 17.0–20.1 meters (55.8–65.9 ft), [111] possibly rivaling the Blue Whale in mass. However, Motani and Pyenson in 2024 argued that it is extremely difficult ...
A = Anapsid, B = Synapsid, C = Diapsid. It was traditionally assumed that first reptiles were anapsids, having a solid skull with holes only for the nose, eyes, spinal cord, etc.; [10] the discoveries of synapsid-like openings in the skull roof of the skulls of several members of Parareptilia, including lanthanosuchoids, millerettids, bolosaurids, some nycteroleterids, some procolophonoids and ...
The most popular definition states that Sauropsida is the sibling taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early synapsids have historically been referred to as "mammal-like reptiles", all synapsids are more closely related to mammals than to any modern reptile.
Therapsida [a] is a clade comprising a major group of eupelycosaurian synapsids that includes mammals and their ancestors and close relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more underneath the body, resulting in a more "standing" quadrupedal posture, as opposed to the lower sprawling posture of ...
While these areas lack the characteristic six neocortical layers, birds and reptiles generally possess three layers in the dorsal pallium (the homolog of the mammalian neocortex). [13] [16] The telencephalon of birds and mammals makes neuroanatomical connections with other telecencephalic structures [13] like those made by neocortex. It ...