The assembly of the avian body plan (Cau 2018) pt. 3 of 3

Yesterday and the day before we looked at parts 1 and 2 of the Cau 2018 tree topology of theropods leading to birds (Fig. 3). Today: part 3 of 3.

Node 19. Maniraptora: (Alvarezsauroidea + Pennaraptora) Here’s where the second Compsognathus (CNJ79) would affect the Cau topology. The basal member of Maniraptora in the Cau tree is Jianchangosaurus, which has a toothless premaxillla and nests with therizinosaurs traditionally and in the LRT (Fig. 5). You don’t want a toothless premaxilla at this basal node because most succeeding taxa have premaxillary teeth. In the LRT, Jianchangosaurus is a derived therizinosaur, close to a surprise tiny therizinosaur with long forelimbs and a trenchant pedal digit 2, Rahonavis. That may change or be confirmed with more complete specimens.

The LRT agrees with Cau in nesting Shuvuuia with Haplocheirus.

Node 20. Pennaraptora (Oviraptorosauria + Paraves) The Cau study and the LRT agree that Caudipteryx and Khaan nest together. Lacking from the Cau study, Limusaurus (Fig. 1) nests as a basal oviraptorid in the LRT. In turn the Cau study includes taxa not listed in the LRT.

Node 21. Paraves: Distinct from the Cau tree, the LRT nests Microraptor with Ornitholestes and apart from Deinonychus and Velociraptor. The LRT nests Fukuiraptor with Zhenyuanlong with tyrannosaurs. The Cau study does not include Zhenyuanlong. 

Node 22. Averaptora: In the Cau study Sinovenator nests with Jinfengopteryx and Mei. In the LRT, Jinfengopteryx (Fig. 4) nests as a basal troodontid, derived from a sister to Velociraptor and Haplocheirus. Sinovenator nests closer to birds. Mei nests within birds (Scansoriopterygidae). Yi and Epidexpteryx are also scansoriopterygids. Cau nests them basal to Archaeopteryx.

As we learned
earlier, no two Solnhofen birds are identical. In the LRT they are distinct enough to nest in several basal bird clades. This was completely missed by Cau and most other bird workers.

Missing from the Cau taxon list
are any living birds. In the LRT, the toothed Cretaceous birds nest between paleognaths and neognaths, so that branch was missed.

Sometimes
taxon exclusion adversely affects tree topologies. Start with a wide gamut analysis (Fig. 5) that sets limits on the more focused study that you want to look at.

References
Cau A 2018. The assembly of the avian body plan: a 160-million-year long process. Invited Paper, Bollettino della Societa Paleontologica Italiana 57(1):1–25.