Palaeos		Archosauria
Vertebrates		Thecodontia Classification

Archosauria: Thecodontia: Classification

DIAPSIDA
|--LEPIDOSAUROMORPHA
`--ARCHOSAUROMORPHA
   |
   `--ARCHOSAURIA
      |--Proterosuchidae
      `--+--Erythrosuchidae
         `--+--Euparkeriidae
            `--+--Proterochampsidae
               `--Crown Group Archosauria 
                     |--Ornithodira
                     |  |--PTEROSAURIA
                     |  `--DINOSAUROMORPHA
                     `--Crurotarsi
                        |--Phytosauridae
                        `--Rauisuchiformes
                           |--Rauisuchia
                           |  |--Ornithosuchidae 
                           |  `--+--Prestosuchidae
                           |     `--Rauisuchidae
                           `--Suchia 
                              |--Aetosauridae 
                              `--CROCODYLOMORPHA

Order (or Paraorder) Thecodontia

Traditional classification

In applying an Evolutionary-Systematic, rather than a cladistic, classification scheme, Linnean taxonomy is employed. Instead of Basal or Stem Group Archosaur(omorphs), reference can be made to Order Thecodontia, a name that appears in text-books on palaeontology and evolution upto the 1980s, but rarely since.

The Thecodontia were traditionally (up to the 1960s) divided into four suborders, the Proterosuchia, Phytosauria, the Aetosauridae, and the "Pseudosuchia" (more or less equivalent to the Crurotarsi, minus the more derived forms).   The Proterosuchia included various primitive ancestral types, the phytosaurs were crocodile like forms, the aetosaurs specialized armoured creatures, remarkably like the armoured ornithischian dinosaurs, and the Pseudosuchia were a sort of catch-all or "waste-basket" category for everything that didn't fit in any of the other suborders.  This last group was also considered ancestral to dinosaurs, birds, and crocodiles. The Pseudosuchia as an artificial group, having the same "grab-bag" status within the Thecodontia as the Thecodontia have within the Archosauria. Robert Carroll in his book Vertebrate Paleontology and Evolution replaces the Pseudosuchia with the Rauisuchia and the Ornithosuchia, and moves the suborder Sphenosuchia (for small pseudosuchians) to the Crocodilia. The following arrangement relies mainly on Carroll 1988, with a few updates here and there

Infraclass Archosauromorpha Huene, 1946 (cont.)
  Order[1] Thecodontia Owen, 1859 Triassic archosaurs with teeth implanted in sockets
   Suborder Proterosuchia Broom 1906 primitive forms, Late Perm to Late Trias, cosmopolitan
     Family Proterosuchidae Huene, 1914 sprawling lizard or crocodile like, ancestral thecodonts, late Perm to Mid Trias, Cosm
     Family Erythrosuchidae large to huge, semi-sprawlingh terrestrial carnivores, Early to Mid Trias, S Afr, EEur, EAs,
     Family Euparkeriidae small faculatively bipedal types - Early Trias, S Afr, EEur, EAs
     Family Proterochampsidae specialised semi-aquatic types, Mid to Late Trias of SAm
   Suborder Suchia Huxley, 1875 (= Phytosauria Meyer, 1861) crocodile-like forms, L Trias of Eur, N Am, Ind, N Afr
     Family Phytosauridae Jaeger, 1828 (= Suchidae Lydekker, 1885 )
   Suborder Ornithosuchia Huene, 1908 At one time considered ancestral to dinosaurs, now monotypal (Ornithosuchidae only)
     Family Ornithosuchidae Huene, 1908 medium-sized facultively bipedal carnivores, Late Trias of Eur & S Am
   Suborder Rauisuchia Huene, 1942, or Bonaparte, 1982 medium to very large terrestrial preditors, erect mamal, bird and dinosaur like posture, The phylogeny of the group and the status of some of the included families is uncertain. Some specialsied groups became herbivores. Early to Late Trias of Eur, EEur, N Am, Afr, E As
     Family Ctenosauriscidae Kuhn, 1964
     Family Doswelliidae Weems, 1980
     Family Lotosauridae Zhang, 1975
     Family Poposauridae Nopsca, 1928 (Postosuchidae)
     Family Prestosuchidae Romer, 1966
     Family Rauisuchidae Huene, 1936 (= Teratosauridae Cope, 1871)
     Family Shuvosauridae
   Suborder Aetosauria Lydekker, 1889 armoured herbivores, L Trias of Eur, N Am, S Am, N Afr
     Family Stagonolepididae Lydekker, 1887
   Suborder unspecified (proto-crocodylomorphs)
     Family Erpetosuchidae Watson, 1917
     Family Gracilisuchidae
   Suborder unspecified (Ornithodira)
     Family Scleromochlidae Huene, 1914

Hybrid classification

One alternative to the conventional linnaean classification that retains ranks (unlike strict cladistic-based phylogenetic nomenclature) is provided by Olshevsky 1991, who distinguishes between paraphyletic and monophyletic taxa. Whereas Olshevsky only used one prefix, para- in front of the rank of paraphyletic taxa (e.g. parafamily, monophyletic taxa being unmodified), we have used the following:

• para- for a paraphyletic (an ancestral or evolutionary grade defined only by shared primitive features and lack of specialised features) according to consensus opinion
• holo- for holophyletic (=monophyletic)
• ambi- for when different cladistic analyses dissagree as to whether a taxon is paraphyletic or monophyletic
• mono- for a monotypal taxon
• evo- for when a taxon is considered monophyletic according to current consensus cladistic studies, but morphologically and/or stratigraphically intermediate and so considered to have given rise to other taxa according to evolutionary systematics or a general gradistic perspective (which implies reversals (loss of original synapomorphies) and a non-parsimony-based phylogeny)

When no prefix is used, we haven't gotten around to assessing the taxon (or the current page is still under construction)

Hence, under this system, the Thecodontia consitute a Paraorder.

The following hybrid classification is the same as the linnaean one, but with additional suffixes. This system however is probably too complex and confusing to be practical, although we have include dit for the same of interst

Parainfraclass Archosauromorpha Huene, 1946 (cont.)
  Paraorder Thecodontia Owen, 1859 Triassic archosaurs with teeth implanted in sockets
   Parasuborder Proterosuchia Broom 1906 primitive forms, Late Perm to Late Trias, cosmopolitan
     Evofamily Proterosuchidae Huene, 1914 sprawling lizard or crocodile like, ancestral thecodonts, late Perm to Mid Trias, Cosm
     Evofamily Erythrosuchidae large to huge, semi-sprawlingh terrestrial carnivores, Early to Mid Trias, S Afr, EEur, EAs,
     Evofamily Euparkeriidae small faculatively bipedal types - Early Trias, S Afr, EEur, EAs
     Holofamily Proterochampsidae specialised semi-aquatic types, Mid to Late Trias of SAm
   Holosuborder Parasuchia Huxley, 1875 (= Phytosauria Meyer, 1861) crocodile-like forms, L Trias of Eur, N Am, Ind, N Afr
     Holofamily Phytosauridae Jaeger, 1828 (= Parasuchidae Lydekker, 1885 )
   Holosuborder Ornithosuchia Huene, 1908 At one time considered ancestral to dinosaurs, now monotypal (Ornithosuchidae only)
     Holofamily Ornithosuchidae Huene, 1908 medium-sized facultively bipedal carnivores, Late Trias of Eur & S Am
   Ambisuborder Rauisuchia Huene, 1942, or Bonaparte, 1982 medium to very large terrestrial preditors, erect mamal, bird and dinosaur like posture, The phylogeny of the group and the status of some of the included families is uncertain. Some specialsied groups became herbivores. Early to Late Trias of Eur, EEur, N Am, Afr, E As
     Holofamily Ctenosauriscidae Kuhn, 1964
     Monofamily Doswelliidae Weems, 1980
     Monofamily Lotosauridae Zhang, 1975
     Ambifamily Poposauridae Nopsca, 1928 (Postosuchidae)
     Parafamily Prestosuchidae Romer, 1966
     Ambifamily Rauisuchidae Huene, 1936 (= Teratosauridae Cope, 1871)
     Holofamily Shuvosauridae
   Holosuborder Aetosauria Lydekker, 1889 armoured herbivores, L Trias of Eur, N Am, S Am, N Afr
     Holofamily Stagonolepididae Lydekker, 1887
   Parasuborder unspecified (proto-crocodylomorphs)
     Monofamily Erpetosuchidae Watson, 1917
     Monofamily Gracilisuchidae
   Monosuborder unspecified (Ornithodira)
     Monofamily Scleromochlidae Huene, 1914

[1] In the interests of taxonomic continuity (Romer, Colbert, Carroll, etc), we have chosen not to follow Olshevsky (1991) in elavating Thecodontia to Superordinal rank.