Mammal taxa: origin times

A few days ago, we looked at a revised and expanded cladogram of the Mammalia based on skeletal traits (distinct from and contra to a cladogram based on DNA). Today we add chronology to the cladogram to indicate the first appearance of various mammals and estimate the origin of the various clades (Fig. 1).

Note that derived taxa
that chronologically precede more primitive taxa indicate that primitive taxa had their genesis and radiation earlier than the first appearance of fossil specimens, which always represent rare findings usually during wide radiations that increase the chance the specimen will fossilize in the past and be found in the present day.

Looking at time of mammal taxa origin categories:

Figure 1. Cladogram with time notes for the Mammalia (subset of the LRT).

Figure 1. Cladogram with time notes for the Mammalia (subset of the LRT).

Some notes:

  1. Both prototheres and basal therians were present (and probably widespread) in the Late Triassic.
  2. Derived prototheres appear in the Late Triassic, suggesting an earlier (Middle Triassic?) origin for Mammalia and an earlier (Middle Triassic?) split between Prototheria and Theria.
  3. Both fossorial metatherians and basal arboreal eutherians were present (and probably widespread) in the Late Jurassic. These were small taxa, out of the gaze of ruling dinosaurs.
  4. Large derived eutherians eolved immediately following the K-T boundary in the Paleocene and radiated throughout the Tertiary.
  5. A large fraction of prototherians, metatherians and eutherians are known only from extant taxa, some of which are rare and restricted, not widespread.
  6. Multituberculates and kin are derived placentals close to rodents by homology, not convergence.

 

2 thoughts on “Mammal taxa: origin times

  1. Burrowing Jurassic taxon nests with golden moles, and Jurassic rodent-toothed allotheres are grouping with rodents. The Jurassic taxa all have primitive postcrania involving characters your analysis doesn’t use, since it’s based on generalized amniote characters. That’s about as obvious a case of convergence that I’ve seen in phylogenetics.

    Stratigraphy and geography are independent tests from morphological analyses, and this is one of multiple examples showing your analysis failing. Another is all of your non-Gondwanan marsupials. These should all be red flags.

    • Opposites may attract in love. Similars attract in the LRT. A gradual accumulation of traits is all I’m looking for…and you see these as red flags. Yours is a topsy-turvy world. It’s a common and recognized syndrome in paleo shared by you and those who think turtles and pterosaurs are archosaurs, yada yada.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.