Palæos:		Unit 210: Eureptilia
The Vertebrates		100: Eureptilia

Eureptilia

Captorhinids, Protorothyrids & Araeoscelidans

REPTILOMORPHA
|--SYNAPSIDA
`--+--ANAPSIDA
   |
   Eureptilia
   |--Captorhinidae
   `--+--Protorothyrididae
      `--Diapsida
         |--Araeoscelidans
         `--Neodiapsida
            |--Younginiformes
            `--+--Ichthyosauria
               |  |--Shastasauria
               |  `--Thunnosauria
               `--Sauria
                  |
                  |--LEPIDOSAUROMORPHA
                  `--ARCHOSAUROMORPHA            

1. Araeoscelida X

2. Captorhinidae X

3. Diapsida

4. Eureptilia

5. Protorothyrididae X

The Diapsids

The Eureptilia would have been a footnote in the history of turtles and mammals but for the evolution of the diapsids.  The bulk of reptiles fall into the Diapsida.  The Diapsida ("two arches") are so called because they have two (di-) skull openings on either side of the head, for attachment of temporal muscles (to work the jaw).  However it is now known that some reptiles lost one or even both pairs of openings, so the presence or absence of this characteristic is not a completely reliable guide.

The Diapsida are divided into two important groups, the lepidosaurs (Lepidosauromorpha) and the archosaurs (Archosauromorpha).  There are also a number of different lineages of early, mostly small lizard-like insectivorous forms that lived during the late Carboniferous, Permian, and Triassic periods.  These have been traditionally grouped under the "Eosuchia," but it is now known that this is an artificial taxon, a "waste basket" category for any diapsid that is neither lepidosaur nor archosaur.  Nevertheless the term retains some use as a synonym for "basal diapsid."  MAK991026.

Descriptions

Eureptilia: defined as turtle doves > turtles (diapsids > anapsids)

Range: from the Late Carboniferous

Phylogeny: Reptilia: Anapsida + *: Captorhinidae + (Protorothyrididae + Diapsida). 

Characters: Supratemporal small; parietal & squamosal broadly in contact, so that postorbital does not reach supratemporal; tabular not contact opisthotic; caniniform maxillary tooth. 

Links: link (Tree of Life); Reptile Phylogeny 1; PhyloCode Discussion - Message 2001-06-0004- Re- Nomina Conversa (problem with the definition); Biology 356 (nice discussion); 6SULQJHU (another problem). 

Captorhinidae: Captorhinus. Possible paraphyletic stem group of other amniotes.

Range: Permian of North America, Europe & East Africa. 

Phylogeny: Eureptilia: (Protorothyrididae + Diapsida) + *. 

Characters: Robust skull; flat teeth; most have multiple rows of marginal teeth; ectopterygoid and temporal bones absent; large medial process of the jugal; single (lower) temporal fenestra; supratemporals reduced or absent; $ tabular absent; braincase supported by supraoccipital process; middle ear region open at least laterally and ventrally; possibly stem group of Amniota. 

Links: Phylogeny and Classification of Amniotes; CAPTORHINIDA. 

Image: Captorhinus aguti © 2000 Friends of the Geology Museum (Univ. of Wisconsin -- Madison), reproduced by permission. ATW010208.

Hylonomus lyelli, a protorothyrid from the Late Carboniferous of Nova Scotia.  Image from Cox et al. (1988).

Protorothyrididae: Small, short legged, lizard-like insectivores. Carroll & others place as early amniote stem group. Hylonomus

Range: Middle Carboniferous to Early Permian of North America & ?Europe. 

Phylogeny: Eureptilia:: Diapsida + *.  Unfenestrated skull? 

Links: Protorothyrididae; reptiles; Dinosaurier Album 2 (OK, so the grass is anachronistic.  I still love this page); H- Paleontology and Geology Glossary- H (entry on Hylonomus).  ATW030210. 

Diapsida: 

Range: from the  Late Carboniferous. 

Phylogeny: Eureptilia:: Protorothyrididae + *: Araeoscelidans + Neodiapsida. 

Characters: Upper (triradiate squamosal & triradiate post-orbital) and lower temporal fenstrae; $ suborbital fenestra consisting of a relatively large hole in the palate located between palatine, ectopterygoid, and maxilla [Other taxa may have foramen in this region, but there is usually no fenestra]; ossified sternum; $ (primitively) radius long, measuring 70 - 90% of humerus length; ridge-and-groove ankle joint between tibia and astragalus. 

Links: Temporal Fenestration and the Classification of Amniotes; Introduction to the Diapsids; Reptilian Systematics; Introduction to the Diapsids; Diapsida; Basal Diapsida; Reptiles - Subclass Diapsida.

Note: Domed skull of Amniotes permits muscles to run vertically. Vertical muscles allow strong static pressure when jaws are closed or almost closed. Increase in muscle bulk would strain periosteal covering of bone. Fenestrae may have evolved as unossified attachment points. Later, evolved as openings which "bulging" of these jaw muscles. Note no obvious change in jaw musculature in primitive forms. ATW010731.

Araeoscelida: Petrolacosaurus. Most basal diapsids?

Range: Late Carboniferous to Early Permian.

Phylogeny: Diapsida: Neodiapsida + *.  

Characters: Lizard-like; some euryapsid (upper temporal fenestra only), but jugal still bifurcated; long necks, with great elongation of neck in some; gracile, presumably cursorial, limbs.

Links: DIAPSIDA.  

checked ATW050509