Carrano et al. 2012: Basal Tetanurae interrelations

The classification of theropods
has been going on for a hundred years, spurred every year by the discovery of new taxa. Before computers the main division was based on size. The use of software has clarified that issue.

Several years ago,
Carrano, Benson and Sampson (2010) undertook a large study of theropod dinosaurs, focusing on the basal Tetanurae (closer to birds than to Ceratosaurus), up to and not including Coelurosauria (Compsognathus, Ornitholestes and further derived taxa including birds and kin. The authors note: “Tyrannosauridae is now universally included within Coelurosauria (Novas 1991a; Holtz 1994a), whereas ceratosaurs and coelophysoids are basal to Tetanurae.”

They also note, “The placement of many individual taxa within any of these frameworks also varies. ‘Megalosaurs’ pose an even greater and more complex problem. Many of the taxa that have at one time been referred to Megalosauridae have now been dispersed elsewhere, but a large number of putative megalosaur species remain.”

“In summary, although a great deal of progress has been achieved in recent years (measured mainly by increased consensus), several points of uncertainty remain in tetanuran phylogeny and are therefore of primary interest here. These are: (1) whether spinosauroids (= megalosauroids) and allosauroids form a clade, or are serially arranged outside Coelurosauria; (2) whether ‘megalosaurs’ form a valid clade and, if so, its membership; (3) placement of fragmentary forms of potential geographic and temporal importance; and (4) placement of relatively well known but problematical forms (e.g. Cryolophosaurus, Marshosaurus, Monolophosaurus, Neovenator and Piatnitzkysaurus).”

Their work involved firsthand examination
of hundreds of theropod specimens, but no reconstructions were made. Looking at hundreds of specimens is a very good thing, but reconstructions are the notes that let the reader know how bones were interpreted. Without them one must laboriously go through the raw numbers to check for accuracy. No one wants to do that. Reconstructions are a sort of shorthand enabling one to quickly make comparisons of hundreds of characters.

Zanno and Makovicky (2013) recovered a virtually identical theropod tree topology.

In counterpoint
The large reptile tree (subset: Fig. 1) keeps growing without changing topology. Perhaps it offers some insight into theropod relations. Some of the stability of this tree may be due to the inclusion set. Some taxa are tested together here for the first time. There are fewer theropod taxa here than in the works referenced below, but several theropod taxa are included here that are not included in the referenced works.

Figure 1. Basal theropod subset of the large reptile tree showing troodontids basal to birds and separate from dromaeosaurs.

Figure 1. Basal theropod subset of the large reptile tree showing troodontids basal to birds and separate from dromaeosaurs. See the large reptile tree for included taxa not shown here.

References
Carrano MT, Benson RBJ and Sampson SD 2012. The phylogeny of Tetanurae (Dinosauria: Theropoda). Journal of Systematic Palaeontology 10(2):211–300.
Zanno L and Makovicky PJ 2013. Neovenatorid theropods are apex predators in the Late Cretaceous of North America. Nature Communications | 4:2827 | DOI: 10.1038/ncomms3827 |www.nature.com/naturecommunications

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