Synapsid evolution – then and now

With the addition of more taxa,
the lineage of synapsids (including mammals) is filling up nicely — and a little differently than what was once thought. In 1982 TS Kemp produced this image (Fig. 1).

Figure 1. Synapsid evolution according to TS Kemp 1982.

Figure 1. Synapsid evolution according to TS Kemp 1982.

The large reptile tree confirms many of these nestings, adds a few taxa, and subtracts Casea, which now nests with Milleretta and kin (Fig. 2).

Figure 2. The TS Kemp figure modified to reflect changes recovered by the large reptile tree. Casea is removed. It is not related to the rest of these taxa but nests with Milleretta. Therapsids appeared near the Haptodus node with Cutleria. Therapsids thereafter split into anomodonts and the rest of the clade.

Figure 2. The TS Kemp figure modified to reflect changes recovered by the large reptile tree. Casea is removed. It is not related to the rest of these taxa but nests with Milleretta. Therapsids appeared near the Haptodus node with Cutleria. Therapsids thereafter split into anomodonts and the rest of the clade.

Every cladogram
is built, more or less, from past efforts. Sometimes this can be a problem when the root cladogram has unrecognized problems.

Kemp (1982) produced his family tree (Fig. 1) without the aid of phylogenetic software and prior to the discovery of several key taxa.  He was building on past work by Romer and Price (1940) and others before them. The large reptile tree also builds upon early work.

More links for synapsid family trees at reptileevolution.com here, here, and here.

References
Kemp TS 1982. Mammal-Like Reptiles and the Origin of Mammals.  Academic Press: London. 363 pp.
Romer AS and Price LW 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.

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