Monophyletic groups

Metabolic studies have also been carried out on hydrogenosomes of rumen ciliates such as Dasytricha, Isotricha, Epidinium and Eudiplodinium. All rumen ciliates form a monophyletic group (Fig. 1 Striider-Kypke et al. 

Class The grade or category of classification which constitutes the largest, definitely determinable, apparently monophyletic group of organisms the category made up of related orders. 

Fig. 1.2. Interrelationships of the major groups of Platyhelminthes based on a consensus of morphological and molecular estimates. Parasitic flatworms, the Neodermata, form a monophyletic group although their interrelationships are estimated differently by different molecular analyses (see Fig. 1.3).

Bacteria do not form a monophyletic group but two distinct kingdoms (eubacteria and archaebacteria). 

Fishes and Amphibians have no neck curvature (character state b), their noses are are just in a dirqct (even) line with their spinal cord, and remain so. In Cows and Humans the neck curvature (b1) appears in stage II and, similarly, the apomorphic state b can be applied to distinguish the monophyletic group Mammals recognized by the development of neck curvature. (Birds have a neck curvature too, but for different reasons this is considered to be a parallel development.)... 

If in a monophyletic group (of 2 or more species) a character occurs with two alternative character states (in different species), then the plesiomorphic character state must be the one also ocurring in the outgroup ("next sistergroup, lower down the cladogram). 

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