Dr. Andrea Cau 2018 recovers a cladogram of the Theropoda
(Figs. 1-4) focusing on the ultimate appearance of extant birds, represented by Meleagris, the extant turkey (Fig. 4). Many errors accrue in Cau 2018 due to simple taxon exclusion, as you’ll see below. Many clades are not valid when tested in the LRT.
First of all,
Cau 2018 uses the wrong outgroup taxa (taxon exclusion). In the large reptile tree (LRT, 1327 taxa), which tests all of Cau’s outgroup taxa, the outgroup for the Dinosauria is Crocodylomorpha, specifically the basal bipedal crocs, represented by one taxon in Cau 2018, Lewisuchus. Only in the LRT does Archosauria include just Crocodylomorpha and Dinosauria.
- Pan-Aves – all animals more closely related to birds than to crocodiles (traditionally = Avemetatarsalia) includes pterosaurs, so this clade is a junior synonym for Reptilia. In the LRT, Pan-Aves is a junior synonym for Dinosauria.
- Dinosauromorpha – the last common ancestor (LCA) of Lagerpeton, Marasuchus, Pseudolagosuchus and the Dinosauria. In the LRT this is a junior synonym for Archosauriformes –
- Dinosauriformes – Originally: Herrerasaurus + Dinosauria. Currently Marasuchus, Silesauridae and the Dinosauria. Silesaurus is a poposaur, nesting outside the Archosauria. So this is an awkward name that includes Poposauria + Crocodylomorpha + Dinosauria in the LRT.
- Dracohors – Practically: Silesauridae and the Dinosauria. Definition: “Most inclusivemost inclusive clade containing Megalosaurus, but excluding Marasuchus“(Cau 2018). Same issues arise as in Dinosauriformes. Cau did not include basal bipedal crocs (Fig. 1), which clarify basal dinosaur origins and relations in the LRT.
Also unfortunately Cau 2018 excluded several basal theropods.
Segisaurus and Procompsognathus were not included. These taxa attract the traditional stem-dinosaurs Marasuchus and Guaiabasaurus to this clade. Zuolong nests as a relative to the phytodinosaur, Chilesaurus in the Cau cladogram because the LRT sisters to the basal ornithischian, Chilesaurus, were not included. Adding basal phytodinosaurs shifts Chilesaurus out of the Theropoda and shifts Zuolong to the base of the Marasuchus clade. Pisanosaurus and Daemonosaurus also nest within the Ornithischia in the LRT with taxon inclusion.
At the next stage in the Cau 2018 cladogram
(Fig. 2) and in the LRT, Dilophosaurus and Coelophysis nest as basal theropods. Where they differ, Sinocalliopteryx nests at the base of this clade in the LRT, but as the outgroup to the Tyrannoraptora in Cau 2018 (Fig. 3).
- Averostra – Ceratosaurus, Allosaurus , their last common ancestor and all its descendants (Ezcurra and Cuny 2007) is not in the lineage of birds in the LRT.
- Tetanurae – All theropods more closely related to modern birds than to Ceratosaurus. This is a junior synonym of Compsognathidae Cope, 1871 in the LRT. The traditional compsognathids, Sinocalliopteryx, Scipionyx and two Compsognathus taxa nest at basal leaves of several basal theropod clades in the LRT.
At the next stage
(Fig. 3) Cau nests Sinocalliopteryx with the large Compsognathus. By contrast, the LRT nests Sinocalliopteryx basal to Dracoraptor, Zupaysaurus and Megapnosaurus (taxa excluded by Cau) on one branch, Scipionyx (also omitted by Cau) + Ceratorsauria on the other. To shift Sinocalliopteryx to the large Compsognathus adds 24 steps to the MPT.
- Coelurosauria – theropods more closely related to birds than to carnosaurs, includes Aorun, compsognathids, tyrannosaurs, ornithomimosaurs, and maniraptorans. The LRT also recovers this clade.
- Tetanurae – (defined as: theropods more closely related to modern birds than to Ceratosaurus). Cau 2018 wrongly includes the basal ornithischian, Chilesaurus at the base of this clade. Cau 2018 also includes Allosaurus and Eustrespondylus in this clade. These nest with Ceratosaurus in the LRT. In any case, as defined, this is a junior synonym of Coelurosauria.
- Neotetanurae – defined as: containing Allosauroidea and Coelurosauria, and excluding other tetanurans such as megalosauroids, Same problem as Tetanurae.
- Tyrannoraptora – includes tyrannosaurs, ornithomimosaurs, and maniraptorans. In the LRT compsognathids nest at the bases of all these taxa, so this nominal clade is polyphyletic without compsognathids.
At the next stage
(Fig. 4) Cau 2018 xxx
- Averaptora – Paraves sans Troodontidae + Dromaeosauridae (Cau 2018). The LRT validates this clade (Xiaotingia + Anchiornis + birds)
- Maniraptoriformes – Ornithomimus + birds, LCA and all descendants (Holtz 1995). In the LRT this clade is a junior synonym for Compsognathidae.
- Maniraptora – Sans Ornithomimosauria, this clade is also a junior synonym.
- Pennaraptora – The LCA of Oviraptor, Deinonychus and Passer and all descendants. In the LRT this clade is a junior synonym for Compsognathidae.
- Paraves – All theropods more closely related to birds than to oviraptorosaurs. Traditionally this includes Scansoriopterygidae at a basal node. In the LRT the LCA is Mirischia and more complete Ornitholestes. Scansoriopterygidae nests within Aves in the LRT when all the Solnhofen birds are included in the taxon list. Only one, Archaeopteryx, is included in Cau 2018.
- Avialae – Theropods closer to birds than to deinonychosaurs. In Cau 2018 this deletes three scansoriopterygid birds and Xiaotingia. In the LRT Xiaotingia, Ostromia and Eosinopteryx are the proximal outgroup clade to birds.
- Pygostylia – intended to encompass all avialans with a short, stubby tail (Chatterjee 1997), but this is a trait that appears several times by convergence. Late defined as the LCA of Confuciusornis + Neornithes. Both are descendants of Archaeopteryx (Wellnhoferia) grandis, which has a long tail and lacks a pygostyle. This confusion in Cau 2018 (and all other bird workers) comes from the traditional exclusion of other Solnhofen birds from analysis. This is where all Cretaceous bird clades had their radiation documented.
In the final subset of the Cau 2018 cladogram
(Fig. 5) several of the toothed euornithes are wrongly separated from the other toothed Cretaceous birds in figure 4. Patagopteryx nests with missing Struthio in the LRT. Once again, taxon exclusion is the reason for problems in the Cau study.
- Aves – extant birds (includes Cretaceous toothed birds in the LRT)
- Ornithothoraces – (= Enantiornithes + Euornithes) in the LRT these two clades comprise the first split within Aves and both include a specimen of Archaeopteryx at the base. So this is a junior synonym of Aves.
- Ornithuromorpha – (= Euornithes, or the most recent common ancestor of all avialans closer to modern birds than to Sinornis.) Since Sinornis is an enantiornithine, this is also a junior synonym of Aves.
- Carinatae – (= all birds and their extinct relatives to possess a keel, or “carina”, on the underside of the breastbone used to anchor large flight muscles.) Alternatively, as in Cau 2018, Ichthyornis + extant birds. In the LRT Ichthyornis nests within extant birds.
- Ornithurae – (the LCA of Ichthyornis, Hesperornis and extant birds) In the LRT Ichthyornis and Hesperornis and related Cretaceous toothed birds nest within the clade of extant birds.
is indeed key to understanding the assembly of the avian body plan. Taxon inclusion is key to any phylogenetic analysis. Unfortunately for Cau 2018, so many taxa were excluded that Cau recovers a less than optimal origin for the Dinosauria, Theropoda and Aves, along with a series of false positive clades, as explained above.
Cau A 2018. The assembly of the avian body plan: a 160-million-year long process. Bollettino della Società Paleontologica Italiana, 57 (1), 2018, 1-25. Modena