Tuesday, November 23, 2010

Recommended definitions for theropod clades Part 1

January 1, 201n is fast approaching along with what will no doubt be a rush to define clades.  The major clades' definitions are already written up for Phylonyms, but there's still hope we can salvage ideal definitions for smaller groups.  It's my hope that authors will use this as a reference to see why certain definitions should and shouldn't be used before they try to register them.

First, some basic rules.
1. If the clade is named after a genus, use the type species of that genus as an internal specifier.  It doesn't matter if it's indeterminate, poorly known or not well nested because it has to belong to the clade in question or else the clade would need a different name.  For example, Sereno defined Alvarezsauridae using Shuvuuia, but if the more poorly known and more basal Alvarezsaurus didn't belong, we couldn't keep calling Shuvuuia's clade Alvarezsauridae anyway.
2. If the clade isn't named after a genus, use the type species of one of the genera originally included by the clade's author as an internal specifier.
3. Whenever possible, use external specifiers that were thought by the clade's author to not belong to it.
4. Strive to make the definition congruent with all suggested topologies, not just your own.  It's naive to think we have the right phylogeny today.
5. If a more than one definition follows the above rules, use the one proposed first.

Herrerasauria Galton, 1985
Definition- (Herrerasaurus ischigualastensis <- Liliensternus liliensterni, Plateosaurus engelhardti) (modified from Langer, 2004)
Comments- No issues, I just added the type species.

Herrerasauridae Benedetto, 1973
Definition- (Herrerasaurus ischigualastensis + Staurikosaurus pricei) (modified from Novas, 1992)
Comments- Sereno (1998) proposed a stem-based definition, but Novas' was first, which follows Galton's (1985) earlier taxonomy of having non-herrerasaurid herrerasaurs.

Avepoda Paul, 2002
Definition- (metatarsal I does not contact distal tarsals homologous with Passer domesticus) (modified from Paul, 2002)
Comments- Paul used "Neotheropoda", so Passer domesticus is used since of the two internal neotheropod specifiers, only it has a preserved first metatarsal.

Averostra Paul, 2002
Definition- (promaxillary fenestra homologous with Dromaeosaurus albertensis) (modified from Paul, 2002)
Comments- Paul's definition used the less specific Dromaeosauridae and did not indicate which accessory maxillary opening should be used.  The promaxillary fenestra is specified, since basal averostrans of Paul only have it, and not a maxillary fenestra.  Ezcurra and Cuny's (2007) node-based definition is not used because it postdates Paul's for a taxon Paul created, and is a junior synonym of Neotheropoda.

Coelophysoidea Nopcsa, 1928 sensu Holtz, 1994
Definition- (Coelophysis bauri <- Ceratosaurus nasicornis, Passer domesticus) (first order revision of Padian et al., 1999)
Comments- Sereno's (1998) definition used Carnotaurus, but abelisaurids have been sometimes seen as carnosaurs (Kurzanov, 1989) and Ceratosaurus has been consistantly used in phylogenies due to its early discovery.  Sereno (online) suggested adding Passer, which is good for phylogenies like Raath's (1984) and early ones where birds derived from Coelurosauria sensu Huene (e.g. Barsbold, 1984).  Is it too much to ask for Podokesauroidea being (Podokesaurus holyokensis <- Ceratosaurus nasicornis, Passer domesticus)?

Dilophosauridae Madsen and Welles, 2000
Definition- (Dilophosaurus wetherilli <- Coelophysis bauri, Allosaurus fragilis) (new)
Comments- This hasn't been defined yet, but besides the obvious Coelophysis, I think Allosaurus is better than Passer since it covers older topologies where Dilophosaurus was carnosaurian AND newer ones where we just need a tetanurine specifier.

Procompsognathidae/inae- Given a definition by Sereno (1998), this seems unwise until more than his studies indicate a need for such a clade, and until Procompsognathus' position even as a theropod is more established.

Coelophysidae Nopcsa, 1928 sensu Welles, 1984
Definition- (Coelophysis bauri + Megapnosaurus rhodesiensis + "Megapnosaurus" kayentakatae) (Holtz, 1994)
Comments- Though Paul (1988) and Novas (1991, 1992) included Dilophosaurus, Welles did not and Coelophysoidea is well established as that larger clade.  Sereno (1998) used Procompsognathus as an internal specifier, but it's been placed outside Coelophysoidea by some authors (Gauthier, 1984; Paul, 1984, 1988; Allen, 2004) so this is not recommended.  Tykoski and Rowe (2004) left out kayentakatae, but Holtz's including it lets us use Coelophysinae for that smaller clade.
Incidentally, if we were allowed to start over, I would use Podokesauridae and define it as (Podokesaurus holyokensis <- Liliensternus liliensterni, Coelurus fragilis, Compsognathus longipes) for this family.  This covers Coelophysis as well, since Podokesaurus shares longer dorsal centra with it than Liliensternus shows.

Segisaurinae Camp, 1936 sensu Kalandadze and Rautian, 1991
Definition- (Segisaurus halli <- Coelophysis bauri) (new)
Comments- Since Segisaurus is always outside (Coelophysis+Megapnosaurus) in phylogenies, this gives some structure to coelophysid relationships and is equivalent to Sereno's Procompsognathinae but uses a more stable genus.

Coelophysinae Nopcsa, 1928
Definition- (Coelophysis bauri <- Segisaurus halli) (new)
Comments- Sereno (1998) used Procompsognathus as the internal specifier as he had it in a clade with Segisaurus outside Coelophysinae.  Thus this definition retains his concept.  None of the taxa used by Nopcsa as non-coelophysine podokesaurids are useful today (Podokesaurus, Procerosaurus, Saltopus, Tanystropheus), and he only included Coelophysis in the subfamily.

Neotheropoda Bakker, 1986
Definition- (Ceratosaurus nasicornis + Passer domesticus) (modified from Padian et al., 1999)
Comments- Sereno (1998) used Coelophysis as an internal specifier, but podokesaurids were specifically excluded by Bakker.  I considered also using Allosaurus, but Ceratosaurus has never been closer to birds than Allosaurus in any topology with coelophysoids outside a Ceratosaurus+Allosaurus clade, and all the authors to use Neotheropoda have theropod birds.  Although the clade now fails under a BAND phylogeny, using Allosaurus instead of Passer would make it fail under the more likely phylogeny where Ceratosaurus is a carnosaur.

Ceratosauria Marsh, 1884
Definition- (Ceratosaurus nasicornis <- Allosaurus fragilis, Passer domesticus) (first order revision of Rowe, 1989)
Comments- Rowe and Gauthier's (1990) definition was node-based and used every ceratosaur they recognized, which is less stable especially since most are coelophysoids.  Sereno's (1998) used Coelophysis, which doesn't work in many phylogenies since it's outside Ceratosaurus+tetanurines.  I think Allosaurus would be a good taxon to add, to account for the many early phylogenies where Ceratosaurus was a carnosaur (e.g. Bonaparte et al., 1990, Currie, 1995) and those where birds aren't dinosaurs.  It also makes sense as a distinctly non-ceratosaurian theropod of both Marsh and Gauthier. 

Neoceratosauria Novas, 1991
Definition- (Ceratosaurus nasicornis + Abelisaurus comahuensis) (modified from Holtz, 1994)
Comments- Padian et al. (1999) used a stem away from Coelophysis, but in most modern topologies that would include tetanurines as well.  There's controversy over using this compared to Ceratosauroidea Bonaparte et al., 1990.  Neoceratosauria is used far more often, was named unofficially before Ceratosauroidea (in Novas' 1989 thesis) and has been given a more useful definition (Ceratosauroidea's is Ceratosaurus<-Coelophysis).

Ceratosauridae Marsh, 1884
Definition- (Ceratosaurus nasicornis <- Abelisaurus comahuensis, Allosaurus fragilis) (first order revision of Rauhut, 2004)
Comments- Allosaurus is added as an external specifier to cover topologies where Ceratosaurus is closer to Tetanurae than abelisaurids (e.g. Rauhut, 1998).

Abelisauroidea Bonaparte and Novas, 1985 sensu Bonaparte, 1991
Definition- (Abelisaurus comahuensis <- Ceratosaurus nasicornis, Allosaurus fragilis) (first order revision of Holtz, 1994)
Comments- Allosaurus is added as an external specifier for topologies where abelisaurids are tetanurines (e.g. Kurzanov, 1989; Forster, 1999).  Wilson et al. (2003) used a stem-based definition which is covered by Abelisauria.

Abelisauria Novas, 1992
Definition- (Abelisaurus comahuensis + Noasaurus leali) (modified from Novas, 1997)
Comments- Both Abelisauroidea and Abelisauria were created for the same purpose- to separate abelisaurids and noasaurids from ceratosaurids.  I suppose ideally, I'd switch their definitions since -ia suggests a more inclusive clade than -oidea.

Noasauridae Bonaparte and Powell, 1980
Definition- (Noasaurus leali <- Carnotaurus sastrei, Compsognathus longipes) (first order revision of Wilson et al., 2003)
Comments- Compsognathus is added to cover the traditional placement in Coelurosauria (Bonaparte and Powell, 1980), as a substitute for Sereno's (online) suggestion of Passer.

Abelisauridae Bonaparte and Novas, 1985
Definition- (Abelisaurus comahuensis <- Noasaurus leali, Ceratosaurus nasicornis, Elaphrosaurus bambergi, Allosaurus fragilis) (new)
Comments- Most definitions have used Carnotaurus as the internal specifier, which is wrong since it isn't the eponymous genus.  The other two are node-based using taxa with uncertain placements, while the above definition is stable and covers all proposed topologies.

Abelisaurinae Bonaparte and Novas, 1985 sensu Paul, 1988
Definition- (Abelisaurus comahuensis <- Carnotaurus sastrei) (modified from Sereno, 1998)

Carnotaurini- I would leave this undefined, since Coria et al.'s original definition could easily be more inclusive than Carnotaurinae, and having Carnotaurus and Aucasaurus as sister taxa isn't supported by recent analyses. 

Carnotaurinae Sereno, 1998
Definition- (Carnotaurus sastrei <- Abelisaurus comahuensis) (Sereno et al., 2004; modified from Sereno, 1998)

Brachyrostra Canale, Scanferla, Agnolin and Novas, 2009
Definition- (Carnotaurus sastrei <- Majungasaurus crenatissimus) (Canale, Scanferla, Agnolin and Novas, 2009)

Continued later with basal tetanurines...


  1. Two years ago, I wrote a post similar to this series. It would be interesting to compare the definitions of the shared taxon names.

  2. My free time is very limited now so I will consider your proposals later but, personally, I would be OK with Carnotaurini being defined. The fact that Carnotaurinae (= C. sastrei <- Ab. comahuensis) would probably be less inclusive than Carnotaurini (= C. sastrei + Au. garridoi) might be a problem to some people but you can solve it by defining Carnotaurini as "C. sastrei + Au. garridoi <- Ab. comahuensis" (node-based; to follow Coria et al.'s original intention), so that Carnotaurini self-destructs if C. sastrei and Au. garridoi don't form a clade excluding Ab. comahuensis. More on the issue later.

  3. That's true about Carnotaurini, though I would also use Majungasaurus and Xenotarsosaurus as external specifiers since they were in Coria et al.'s tree.

  4. "Since Segisaurus is always outside (Coelophysis+Megapnosaurus) in phylogenies,"

    Ahem. Check Yates 2006 (for 2005). I've been looking at coelophysoid phylogeny in some detail (I have some new tiny coelophysoid material from the Aardonyx quarry) and I'm seeing some evidence for a Jurassic coelophysid clade (with the North American kayentakatae and Segisaurus forming a subclade within it). So I wouldn't like this definition to be formalised.

  5. My analysis provisionally finds Procompsognathinae identical to Segisaurinae, and including "S." kayentakatae. In that topology, Adam's hypothesis and Mickey's taxonomy are not in conflict.

  6. Adam- Ah yes, I hadn't noticed that part of your 2005 topology. So your new topology is (bauri(rhodesiensis(kayentakatae,halli)))? That is interesting, and I'd agree argues against formalizing that definition. Maybe paired stem-based definitions for Coelophysinae and Segisaurinae then? (Coelophysis <- Segisaurus) and vice versa.

  7. "So your new topology is (bauri(rhodesiensis(kayentakatae,halli)))?"

    Yes, though nothing is particularly robust. Coelophysids are all so damn similar!

  8. Agreed there! And yet we have so many proposed names for them- Podokesauridae, Procompsognathidae, Coelophysidae, Segisauridae, Syntarsiidae. But for the diverse troodontids, nothing except Troodontidae and Saurornithoididae.

  9. You can't use a bird as an internal specifier for a dinosaur clade -- the PhyloCode even uses this precise manoeuvre as an example of what you shouldn't do. See Recommendation 11A and its accompanying Example 1. http://www.ohio.edu/phylocode/art11.html

  10. Mike- Not precisely correct. You shouldn't use a bird as an internal specifier for Dinosauria itself, because birds weren't recognized as dinosaurs when the group was named. But it's perfectly alright to use birds as internal specifiers for dinosaurian clades that included birds when they were named- Tetanurae, Neotheropoda, Paraves, Avepoda, etc..

  11. hello again, a genus is always named after the first species that was discovered and belonged into it right ??

    Then the Noasaurids should proably be named Compsosuchidae or Laevisuchidae, as those two were found before Noasaurus ( 1933 while Noasaurus was disovered 1980).

    Or is that wrong ??

  12. Nope, that's not how it works. The first-named family-level name based on a genus belonging to the family is the one that's used. Since Laevisuchidae, Laevisuchinae, Laevisuchoidea or the equivalent variations on Compsosuchus have never been proposed, Noasauridae has priority.

    For instance, Aublysodon was named in 1868 and Tyrannosaurus in 1905, but since Aublysodontidae was named in 1928 and Tyrannosauridae in 1906, the latter has priority.

    And yes, part 2 is coming soon.