Bent Back Ribs

The anterior caudal ribs (aka: transverse processes) of basal tetrapods
are bent back. Their tips point to the end of the tail.

The anterior caudal ribs of derived tetrapods are transverse.
They stick straight out to the sides.

There are exceptions and transitions
(based on taxa recovered in the large reptile tree).

Among the Lepidosauromorpha –

  1. Eunotosaurus (alone, but many sisters are skull-only taxa)
  2. Pareiasaurs + Turtles
  3. Lepidosauriformes – (except Rhyncosaurs as a reversal with curved back ribs)

Among the Archosauromorpha –

  1. Therapsida
  2. Mesenosaurus (alone, so far)
  3. Broomia (alone, so far)
  4. Marine and Terrestrial Younginiformes (beginning with Galesphyrus) This clade includes all enaliosaurs and archosauriformes.

So what’s going on here?
I don’t know. It’s just important to note the patterns and exceptions. Straight out anterior caudal ribs are shown to be a convergent trait several times over. So are bent back ribs.

 

 

 

Advertisements

One thought on “Bent Back Ribs

  1. At a guess — backswept is heritage of fish–lateral undulation through trunk and tail, and likely continued as simple unmodified metameric pattern. Transverse in cases you show, probably modifications of femoral muscles [with relative immobility of tail base.]

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 )

Twitter picture

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

Facebook photo

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

Google+ photo

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

Connecting to %s