Synaptichnium and Proterosuchus

Synaptichnium (Nopcsa 1923, Fig. 1) is a fairly large quadrupedal, semi-plantigrade ichnotaxon of the Early to Middle Triassic in which pedal digit 4 remains longer than digit 3, which is atypical for derived archosauriforms. Here (Fig. 1) the pes of Proterosuchus, a basal archosauriform with pedal digit 4 longer than 3, was slightly modified to fit the ichnite. This is appropriate because other less completely known proterosuchids, like Archosaurus and Sarmatosuchus are known. The manus of Proterosuchus is poorly known, but when matched to the impression of Synaptichnium, our guesses become more precise in that now we can model digit 4 shorter than digit 3 despite a lack of bone data. Similar data mining from ichnites occured in Erythrosuchus matched to Isochirotherium ichnites.

Synaptichnium

Figure 1. Synaptichnium compared to a slightly altered pes of Proterosuchus. Note a reduction of one phalanx in pedal digit 4 to match one less pad in the ichnite.

Comparisons to Prolacerta
Prolacerta is a predecessor taxon to Proterosuchus. The manus of Prolacerta is more clompletely known and it has a digit 4 longer than 3. To my knowledge, successor taxa to Proterosuchus do not  preserve a manus until one gets to Ticinosuchus, which also has a manual digit 4 shorter than 3.

Prolacerta.

Figure 2. Prolacerta. Note the relative lengths of the manual and pedal lateral digits. Click for more info.

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
Avanzini M and Mietto P 2008. The occurrence of the vertebrate ichnogenus Synaptichnium in the Anisian (Middle Triassic) of Southern Alps. Studi Trent. Sci. Nat., Acta Geol., 83 (2008): 259-265. online pdf
Broom R. 1903. On a new reptile (Proterosuchus fergusi) from the Karroo beds of Tarkastad, South Africa. Annals of the South African Museum 4: 159–164.
Gower DJ and Sennikov AG 1997. Sarmatosuchus and the Early History of the Archosauria. Journal of Vertebrate Paleontology 17(1):60-73.
Nopcsa F 1923. Die Familien der Reptilien. Fortschritte der Geologie und Paläontologie der Rheinlande und Westfalens. 210 pp.
Sennikov AG 1994. Pervyj srednetriansovyj proteroscchid iz Vostochnoy Evropy. Doklady Akademii Nauk 336:359-661.
Tatarinov LP 1960. Otkrytie pseudozhukhii v verkhnei permi SSSR: Paleontologischeskii Zhurnal, 1960, n. 4, p. 74-80.

wiki/Proterosuchus

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