Not Studied Much, But Important Nonetheless
The Erythrosuchidae, named for its biggest and most famous member, Erythrosuchus, is both a clade unto itself and forms a transition grade from the primitive proterosuchids, like Proterosuchus, to the derived Rauisuchia and Euparkeria. Among the proterosuchids, Fugusuchus approaches the skull shape of the erythrosuchids. Among the Rauisuchia, Vjushkovia was phylogenetically closest to the erythrosuchids.
Figure 1. The erythrosuchids (in white), the predecessor proterosuchids (in yellow) and the successors Euparkeria and the Rauisuchia (in green).
You Can Almost Skip the Erythrosuchids
Between Proterosuchus and Vjushkovia (essentially skipping all the members of the Erythrosuchidae because successors were derived from basal erythrosuchids), the jaw tip straightened out and increased the depth of the premaxilla, the scapula rotated to the vertical, the femur increased in length and shortened the toes. Dinosaurs, crocs and birds eventually arose from this lineage.
But We’re Here to Talk About the Erythrosuchids
The erythrosuchids increased the size of the skull, decreased the length of the neck, increased the depth of the torso and pelvis and decreased the length of the tail.
Distinct from Proterosuchus, the cervicals were taller and compressed. Tall spines topped the dorsal vertebrae. The torso was deeper due to longer dorsal ribs. The tail was relatively shorter. The scapula had an hour-glass shape, the humerus was more robust. The fingers were shorter. The ilium had a longer posterior process. The pubis and ischium were separate from each other and more ventrally oriented. All the pedal elements were shorter and composed of subequal phalanges.
The Littlest Erythrosuchids
Euparkeria and Osmolskina were two small erythrosuchids that transition into the Rauisuchia and Ornithosuchia. Like Vjushkovia, Euparkeria retained a long neck and long tail. Both Eurparkeria and Osmolskina had an enlarge naris and more gracile skull bones.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
References
Broom R 1905. Notice of some new reptiles from the Karoo Beds of South Africa. Records of the Albany Museum 1: 331–337.
Huene F von. 1911. Über Erythrosuchus, vertreter der neuen reptilordnung Pelycosimia. Geologische und Paläontologische Abhandlungen, N.F. 10: 67–122
Otchev VG 1958. Novye dannye po pseudozukhiyam SSSR: Doklady Akademii Nauk SSR, 123(4):749-751.
Parrish JM 1992. Phylogeny of the Erythrosuchidae. Journal of Vertebrate Paleontology 12:93–102.
Young C-C 1964. The pseudosuchians in China: Palaeontologia Sincia, v. 151, new series C., n. 19, p. 1-205.
The Pterosaur Heresies 