SVP 23 – a new archosaur close to Junggarsuchus

Sullivan et al. 2015
describe a sister of Junggarsuchus sloani (Fig. 1) which is a basal archosaur and a basal dinosauriform, not far from crocs and a sister to Pseudhesperosuchus.

Figure 1. Junggarsuchus colorized. Once thought to be the crocodylomorph closest to crocodylformes, it now nests as a pre-dinosaur.

Figure 1. Junggarsuchus colorized. Once thought to be the crocodylomorph closest to crocodylformes, it now nests as a pre-dinosaur.

From the abstract
“The Middle-Late Jurassic Daohugou (or Yanliao) Biota and Early Cretaceous Jehol Biota are successive assemblages from northeast China. Nno crocodylomorph has been reported from either assemblage. However, a basal (i.e., non-crocodyliform) crocodylomorph was recently recovered from the Daohugou Biota site of Mutoudeng, Hebei Province. The meter-long skeleton shows crocodylomorph synapomorphies, including elongated carpals, and lacks crocodyliform traits such as an expanded coracoid process. The specimen shares key features with the Chinese basal crocodylomorph Junggarsuchus sloani, including vertebral hypapophyses and a slender, rotated metacarpal I. However, the Mutoudeng specimen differs from J. sloani in having shorter distal forelimb segments, and in lacking enlarged anterior maxillary teeth. Phylogenetic analysis recovers this specimen and J. sloani as sister taxa slightly outside Crocodyliformes.

J. sloani is known from one individual lacking the hindquarters, but the Mutoudeng specimen preserves two surprising features in this region: the iliac preacetabular process is very long, and the middle and posterior parts of the tail are entirely sheathed in osteoderms. Such extensive caudal armor is common in basal crocodyliforms but rare in more basal crocodylomorphs. The elongated preacetabular process likely gave parts of the iliotibialis and puboischiofemoralis internus musculature a near-horizontal orientation, allowing them to act as strong femoral protractors. This arguably supports prevailing views of basal crocodylomorphs as terrestrial cursors, but soft tissues preserved with the skeleton unexpectedly challenge the conventional wisdom. Scaly skin is associated with the superimposed feet, and with the right hand, forming sheets of small (< 1 mm) polygons defined by dark lines. In the right hand, patches of skin are visible between digits IV and V, extending distally to the second phalanges of the two digits. The presence of skin in this area implies the hand was webbed, which in turn suggests the Mutoudeng crocodylomorph frequented wet environments and was probably at least semi-aquatic.”

Just a few clues here
as to what will be presented, but more taxa in the ancestry of dinosaurs, or crocs, even if they are not recognized as such by Sullivan et al., are always welcome.

Sullivan C et al. 2015. A new basal crocodylomorph with unexpected skeletal and soft-tisse features from the Middle Late Jurassic Daohugou biota of Northeast China. Journal of Vertebrate Paleontology abstracts.


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