Birds closer to crocs or pterosaurs?

Ken Kinman kinman at HOTMAIL.COM
Fri Apr 28 06:11:41 CDT 2000

Dear Colleagues:
     Most would now agree that dinosaurs and birds form a clade, but are
they closer to pterosaurs or crocodiles?  The answer depends on the illusive
ancestry of pterosaurs.  To make all of these interrelationships easier to
understand, I today present a preliminary classification of Order
Thecodontiformes below.  By constrast, if you look at the Arizona Tree of
Life, it has uninformative multiple-polytomies for the diapsid reptile
groupings that are almost worthless (and even worse, they inexplicably place
groups like ichthyosaurs in Archosauromorpha).  I would think all of this
would totally confuse college biology students and even have many professors
scratching their heads.
     Admittedly some groups are "wastebaskets", and as one example, I
dismantled the mammalian "Condylarthra" in my 1994 book (yes, even I dislike
many paraphyletic groups, when they are no longer useful).
     However, I definitely do not think this is the case with the
"Thecodontia", and being really tired of hearing strict cladists badmouthing
this taxon as a worthless "wastebasket", I am here presenting a preliminary
classification of Order Thecodontiformes down to family level.  The Kinman
markers {{in double brackets}} show the cladistic placement of those Orders
which have been paraphyetically removed (or anagenetically upgraded, to put
it another way), including pterosaurs, crocodyliforms, and both orders of
dinosaurs (thence to birds as well).
     This preliminary basic classification does not yet include three
apparently poorly-known families: Doswelliidae, Podopterygidae, and
Elastichosuchidae.  However, if anyone can suggest a preliminary placement
for any of those three families, I would much appreciate that feedback (and
any other feedback about the classification as a whole).  More information
about each family will be added later when the basic phylogeny is
  1  Proterosuchidae
  2  Erythrosuchidae
  3  Proterochampsidae
  4  Euparkeriidae
5A  Scleromochlidae
  ?  {{Order Pterosauriformes}}**(see notes below)
  B  Lagerpetonidae
  C  Lagosuchidae
  D  {{Order Saurischiformes}} (thence to birds,
         although this is disputed by Feduccia
         et al. who apparently believe birds
         evolved from some unknown thecodont stock.
  E  {{Order Ornithischiformes}}
  6  Erpetosuchidae
  ?  Ctenosauriscidae
  7  Ornithosuchidae
  8  Phytosauridae
  9  Prestosuchidae
10  Stagonolepididae (aetosaurs)
11  Rauisuchidae
12  Gracilisuchidae
13  Postosuchidae
14  Poposauridae (usually incl. Postosuchidae)
15  Sphenosuchidae
16  {{Order Crocodyliformes}}
     For those unfamiliar with the Kinman System (1994), the main cladistic
sequence is numbered, and subsidiary sequences are lettered (5A, B, C, D, E,
show the cladistic relationships within the Ornithodira clade).
    **It should be noted that the placement of Pterosauriformes in the
Ornithodira clade is controversial, the major competing theory being that
pterosaurs instead evolved from prolacertiforms.  The prolacertiforms are
not included here because they are generally considered to be part of a
slightly more primitive group of "parathecodonts", but I would certainly be
willing to entertain any suggestions to include some (or all) parathecodont
families at the base of Order Thecodontiformes.  In 1994, I classified the
parathecodonts as three small separate orders (for rhynchosaurs,
protorosaurs, and trilophosaurs) as others had done in the past.
     And anticipating that some strict cladists will complain that
Thecodontiformes sensu stricto (without the markers) doesn't include its
"thecodont" descendants -------well that is the reason the Kinman System
puts in the "cross-referencing" Kinman markers.  If that is not enough for
you, I guess you can always use the name Eothecodontiformes.  Whatever you
call it, this taxon does still serve a useful purpose, and the phylogenetic
uncertainty (and relatively fragmentary fossil record) is such that it will
remain a useful taxon for some time to come.  Unless, of course, one really
prefers the uninformative and confusing type of classification which the
Arizona Tree of Life is providing.
    Strict cladists tend to put either too much or too little information
into their formal classifications (with a never ending proliferation of
taxa).  A more informal and flexible coding for intermediate taxa (which are
often controversial anyway) can pack in just as much information in a more
stable and less confusing manner.  And it also has that add component of
anagenetic information as well.
                         ---------Kenneth E. Kinman
Get Your Private, Free E-mail from MSN Hotmail at

More information about the Taxacom mailing list