Thinking about the Crocodylomorpha…

Short one today.
The following GIF animation of 4 frames (5 seconds each) is a subset of the large reptile tree (LRT, 1280 taxa) focusing on the Crocodylomorpha and showing:

  1. Clades within Crocodylomorpha
  2. Extent of bipedality
  3. Extent of dorsal scutes
  4. Extent of elongate ulnare and radiale (synapomorphy of the clade)
FIgure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

FIgure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades. There are more taxa at the origin of this clade, fewer extant taxa here. When traits are unknown (lost due to taphonomy), colors are estimated.

Distinct from all prior smaller studies,
here the Crocodylomorpha is the sister taxon to the Dinosauria. Together these alone comprise the Archosauria. They arise from a sister to the Poposauria and these arise from basalmost Rauisuchia, a sister to Vjushkovia (not Postosuchus). The traditional clade ‘Pseudosuchia‘ is invalid (= not recovered as a monophyletic clade) under this hypothesis/cladogram.

Taxon exclusion
misinformed earlier studies of the Crocodylomorpha. Those earlier studies did not include enough pertinent taxa to recover the present hypothesis of relationships. Most prior studies included irrelevant taxa (members of the Pterosauria), which nest not with archosaurs, but within Lepidosauria.

Figure 2. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocritta. Dorsal scutes are shown above the dorsal vertebrae.

Figure 2. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocritta. Dorsal scutes are shown above the dorsal vertebrae.

Phylogenetic miniaturization
occurred at the origin of the Archosauria, with duck-sized PVL 4597 (Fig. 2) at the origin of the Archosauria. Thereafter dinosaurs lost their dorsal scutes and gained feather placodes.

References
https://en.wikipedia.org/wiki/Crocodylomorpha

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