For the purpose of this post (and subsequent related ones), I'm following Turner and Buckley (2008) and Pol et al. (2009) since these are the only large-scale published analyses of crocodyliforms that I'm familiar with. The purpose of this is to try and help familiarize readers with the different clades/grades in this group.

Crocodyliformes are pretty much just crocodylomorphs that are more derived than sphenosuchians. The most basal crocodyliforms are the protosuchids, e.g. Orthosuchus, Protosuchus, Hemiprotosuchus, and the herbivorous Edentosuchus. They span a large geologic range, from the Late Triassic to the Early Cretaceous. Mesoeucrocodylia includes forms that are closer to crocodylians than Protosuchus, such as the gobiosuchids (e.g. Zaraasuchus and Gobiosuchus) which are small Late Cretaceous forms from Mongolia and also more derived forms like Zosuchus and Hsisosuchus.

For now, I'm assuming that the Notosuchia/Ziphosuchia recovered by T&B/Pol et al is "real" (e.g. 'sebecians', 'notosuchians' etc), so this clade plus the Neosuchia are basically Metasuchia (e.g. Notosuchus + Crocodylia). As far as phylogenetic definitions go, basically, all taxa closer to Notosuchus than to crocodylians should be notosuchians, but croc PN (phylogenetic nomenclature) is incredibly FUBAR right now (something to sort out in a later post?), so forgive me if I lapse and mistakenly refer to these as 'ziphosuchians' (or some other name) . Araripesuchus, Mahajangasuchus, peirosaurids (incl. Hamadasuchus), and trematochampsids seem to float around near each other interchangeably, as basal members of either metasuchian clade, I tend to think of these of all these taxa as 'peirosaurs' more or less, they look very similar to each other (except for the bizarre Mahajangasuchus), if I recall right, these are all from the Cretaceous of Gondwana.

Within the Notosuchia, the taxa most people readily think of as 'notosuchians' don't form a clade to the exclusion of 'sebecosuchian'/'sebecians', Simosuchus is apparently the most basal, then candidodontids (e.g. Malawisuchus and Candidodon), notosuchids (Notosuchus, Comahuesuchus and Mariliasuchus), then sphagesaurids (Armadillosuchus, Sphagesaurus, and Adamantinasuchus) and Chimaerasuchus. The sebecosuchians, e.g. taxa like Sebecus and Baurusuchus are closest to the sphagesaurids. Most of the basal notosuchians are from Gondwana, but the sebecosuchians are more globally distributed. As far as I know, these are all from the Cretaceous, with no currently known earlier forms.

Neosuchians are where we first see aquatic forms (Mahajangasuchus is either an aquatic notosuchian or a basal neosuchian...), with the Jurassic thalattosuchians which are apparently closely related to the Cretaceous-Paleogene pholidosaurs. Moving closer to modern crocodilians, you get goniopholids from the Jurassic and Cretaceous around the world, hylaeochampsids (Hylaeochampsa and Iharkutosuchus), atoposaurids, and various eusuchians leading up to the crown clade (e.g. Isisfordia, Rugosuchus, Shamosuchus, Bernissartia). The position of Pristichampsus is variable with respect to whether or not it's within the crown clade (more derived than Gavialis) or outside of it.

More detailed posts to come, count on it.

Related posts

• Iharkutosuchus makadii: an unusual eusuchian crocodyliform
• Shamosuchus redescription available through AMNH
• New unnamed peirosaurid from Argentina
• Armadillosuchus arrudai, just another neglected new non-theropod
• New species of Dakosaurus
• Arquivos do Museu Nacional issue 65-4 open access
• So many new archosaur related papers
• Sphagesaurus just another new weird pan-croc
• Three new crocodylomorphs last week

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