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Re: A couple of questions

Ivan Kwan wrote- 
OK, here's a few short questions for those in the know to answer:

1) Pterosaurs: Ornithodira (& thus the sister group to Dinosauria), or Prolacertiformes? If they are prolacertiformes, would that exclude them from the Archosauria?

If HP David Peters and Dr. Rupert Wild are correct, pterosaurs are derived prolacertiforms, which makes them outside of the Archosauriformes, but in the Archosauromorpha. This will raise two questions of mine later on, but I will continue onward.

Okay, it's impossible for pterosaurs not to be ornithodirans, since Ornithodira is defined as (Neornithes + Pterodactylus + Lagosuchus + Herrerasaurus + Triceratops + Saltasaurus). So if pterosaurs are derived prolacertiforms, Ornithodira just becomes more inclusive. But the Ornithodira is also defined as (Neornithes --> Crocodylia), so in all likelyhood, if pterosaurs were found to derived prolacertiforms, the latter definition would be adopted.

Peters presents the following cladogram on his website, but I don't know if it needs to be updated or not:

--+-- Lepidosauromorpha
 `-- Archosauromorpha
    |-- Rhynchosauria
    `--+--+-- Protorosaurus
       |  |-- Prolacerta
       |  |-- Boreopricea
       |  |-- Jesairosaurus
       |  `-- "Tapinoplatia"
       |     |-- Macrocnemus
       |     `-- "Characiopoda"
       |        |-- Tanystropheidae
       |        `--+-- Langobardisaurus
       |           `-- "Fenestrasauria"
       |              |-- Cosesaurus
       |              |-- Longisquama
       |              `--+-- Sharovipteryx
       |                 `-- Pterosauria
       `-- Archosauriformes
          |-- Proterosuchidae
          `--+-- Erythrosuchidae
             `--+-- Proterochampsidae
                `-- Archosauria
                   |-- Euparkeria
                   `--+-- Parasuchia
                      `--+-- Suchia
                         `--+-- Ornithosuchidae
                            `--+-- Scleromochlus
                               `--+-- Lagosuchus
                                  `-- Dinosauria

Clade "Tapinoplatia"
Diagnosed by:
1. Low scapula grading to posterodorsally oriented and narrow scapula.
2. Short chevrons grading to anteriorly and sagittally oriented.

Clade "Characiopoda"
Diagnosed by:
1. Elongated proximal phalanx of pedal digit V.
2. No more than five tarsals. Distal tarsal III very small.
3. Postcloacal bones on male.

Clade "Fenestrasauria"
Diagnosed by:
1. Proportionately large skull more than half as long as the presacral column (present at least in Longisquama, Sharovipteryx, and Pterosauria).
2. Elongated premaxillary dorsal process contacting the frontals.
3. Ulna and radius straight with little to no spatium interosseum (present in Cosesaurus, Longisquama, and Pterosauria, presumedly reversed in Sharovipteryx).
4. Tibia and fibula straight with little to no spatium interosseum.
5. Procoelous vertebrae.
6. Broad sternal complex formed of paired clavicles and sternal plates and with a cristospine formed of the interclavicle.
7. Strut-shaped coracoid articulating with the cristospine of the sternum.
8. Manual digit V much reduced alongside unreduced digit IV.
9. Metatarsals appressed.
10. Preorbital fenestra (three primatively) closely associated with the naris and without a fossa.
11. Maxilla extensively participating in the border of the external naris.
12. Quadratojugal spur forming the ventral margin of the lower temporal opening.
13. Four sacral vertebrae.
14. Greatly reduced tranverse vertebral processes on caudals.
15. Hemal arches reduced.
16. Tall, narrow scapula oriented posterodorsally.
17. Coracoid grading from elliptical to strut-like.
18. Large postacetabular process of ilium.
19. Large, sharp preacetabular process of ilium.
20. Small overall adult size (14 cm to 25 cm). [Egh, I don't like this character]

If you are reading this HP Peters, could you please post what characters indicate the paraphyly of Pseudosuchia and what permits Ornithosuchidae to be the sistergroup of the clade containing Lagosuchus, Scleromochlus, and Dinosauria. I'm very interested in knowing.

Also, I just found the following post of interest in the DML Archives:
http://www.cmnh.org/dinoarch/1995Jul/msg00083.html


2) Scleromochlus: What is it? Prolacertiform or a basal ornithodiran? (Or a likely pterosaur ancestor)

According to M.J. Benton (1999), it is the outgroup to both Pterosauria and the Dinosauromorpha, or in other words, it's neither, but instead a non-ornithodiran:

-- Archosauria (= Avesuchia)
 |-- Crurotarsi
 `-- Avemetatarsalia
    |-- Scleromochlus
    `-- Ornithodira
       |-- Pterosauria
       `-- Dinosauromorpha

Scleromochlus is united with the Ornithodira by:

1. Forelimb-hindlimb ratio less than 55%.
2. Pubis longer than ischium.
3. Tibia-femur ratio more than 1.0.
4. Distal tarsal IV subequal in transverse width to distal tarsal III.
5. Compact metatarsus with metatarsals I-IV tightly bunched.
6. Metatarsals II-IV more than 50% tibial length.
7. Dorsal body osteoderms absent.

Pterosaurs and Dinosauromorphs are united to the exclusion of Scleromochlus by:

1. Presacral centrum 8 longer than presacral centrum 18.
2. Deltopectoral crest on humerus subrectangular.
3. Fibula tapering and calcaneum reduced in size.
4. Astragalar posterior groove.
5. Calcaneal tuber rudimentary or absent.

David Marjanovic posted on the DML the following message:
http://www.cmnh.org/dinoarch/2001Jul/msg01045.html

He points out the following characters to unite Pterosauria, Sharovipteryx, and Scleromachlus:

1. Skull as least as large as ribcage. (Present in Longisquama [D. Peters, online: "The Origin of the Pterosauria within the Prolacertiformes"])
2. Longer forearms (ulna and radius?) than upper arms (humerus?).
3. Longer humeri than scapulae.
4. Metatarsals I through IV closely bunched together.
5. Hook-shaped metatarsal V. (He admits it is plesimorphic)

Also of interest as far as systematic positions go, this post is rather intriguing about Saltopus:
http://www.cmnh.org/dinoarch/2000Sep/msg00051.html

3) Protarchaeopteryx robusta: primitive oviraptorosaur like Caudipteryx, or still "incertae sedis"?


I believe it is a basal oviraptorosaur, possibly related to Incisivosaurus, with Caudipteryx closer to the other oviraptorosaurs, but this is basaed only on similarities in the dentition of Incisivosaurus and Protarchaeopteryx which have been already discussed on the list by other individuals.


Nick Gardner
Paleoartist
AIM Eoraptor22



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