Qianshanosuchus

To determine the relationship between Qianshanosuchus and other crocodylians, two different datasets had been used by Boerman and colleagues. The matrix of Shan et al. (2021) was chosen as the first dataset due to its extensive coverage of Asian crocodylians. The second matrix on the other hand, Rio and Mannion (2021), offers a series of additional advantages and disadvantages compared to Shan's dataset. Rio and Mannion included several additional characters with more reductive coding and more objective wording. However, unlike the former, this dataset did not include a large amount of basal crocodyloids or most orientalosuchines. The two matrices subsequently differ notably in how they recover the internal relationships of Crocodylia. Shan et al. recovers Tomistominae as an independent group more closely related to Crocodylidae than to the basal Gavialoidea, while the other dataset shows tomistomines and gavialines as forming a clade more derived than Alligatoridae.^[1]

As the material of Qianshanosuchus is thought to have belonged to a juvenile, both matrices were used multiple times under changed circumstances to account for any features that would change with age. Initial analysis took the datasets as they were while additional tests either removed any juvenile characters from Qianshanosuchus or included data for juvenile specimens of the American alligator and Nile crocodile. Using the matrix of Shan et al. consistently recovered Qianshanosuchus as a basal member of Crocodyloidea, less derived than the various species of Asiatosuchus. This outcome remained unchanged regardless of the inclusion of juvenile characters. Likewise, the results formed by the Rio and Mannion matrix showed little impact of the juvenile characters on the general placement of Qianshanosuchus. Unlike in the former tests, here the taxon was placed outside of Crocodyloidea and even Longirostres (a clade formed by crocodyloids and gavialoids). This dataset found it to consistently align itself with Asiatosuchus, although the exact relations of the formed clade varied slightly across the analysis.^[1]

Boerman and colleagues conclude that, although the precise topology of the different crocodilian clades differ between analysis and matrices, Qianshanosuchus consistently shows affinities with taxa typically considered to be basal crocodyloids. They argue that the different results stemming from the Rio and Mannion matrix may partially be caused by their relative recency and tentatively assign Qianshanosuchus to the Crocodyloidea. The two phylogenetic trees below show Qianshanosuchus' position as recovered with the matrix of Shan et al. (left) and Rio & Mannion (right) respectively without changes to the dataset to account for juvenile traits.^[1]

Qianshanosuchus represents the first basal crocodyloid known from the Paleocene of China, with the previously oldest member of this clade being Asiatosuchus grangeri from the middle Eocene, approximately 15 to 20 million years later. Phylogenetic analysis following the matrix of Shan et al. suggests that Qianshanosuchus would be immediately basal to Prodiplocynodon and Albertosuchus, two taxa from the late Cretaceous of North America. Following these results, this would require the Asian Qianshanosuchus to have diverged from its North American relatives at some point during the Maastrichtian, a hypothesis which could be corroborated by Jiangxisuchus from the Cretaceous of China. Previous analysis have placed it as a basal crocodyloid, however during the description of Qianshanosuchus it was recovered as an alligatoroid instead. Regardless, this dispersal may have occurred through the Bering land bridge, which would have been exposed during the Maastrichtian. Although alligatoroids were suggested to have also dispersed from North America to Europe prior to the Eocene, the lack of crocodyloids in Cretaceous Europe suggests that the ancestors of Qianshanosuchus likely did not arrive in China over this western route. Additionally, the recovered relationship to "Asiatosuchus" depressifrons and "Asiatosuchus" germanicus from France and Germany would lend support to the further dispersals of crocodyloids from Asia onwards to Europe, at least following the results using the Shan et al. matrix. It is also possible that crocodyloids dispersed into Europe more than once, as "Asiatosuchus" depressifrons was found to be more closely related to Asiatosuchus species from Asia and North America than to the other European species.^[1]