Reconstructing the hand of Ticinosuchus

Sometimes fossils are wonderfully preserved
and fully articulated. Sometimes they are wonderfully preserved but woefully disarticulated. At such times, most of the bones can be fit together with ease, but the bones of the fingers and toes can be vexing.

Figure 1. Ticinosuchus forelimbs. Note the scattered manual elements here reconstructed to create PILs and match sister taxa patterns.

Figure 1. Ticinosuchus forelimbs. Note the scattered manual elements here reconstructed to create PILs and match sister taxa patterns. Yellow is the radius. Pink is the ulna. Metatarsal 3 is the most robust based on sister taxa. The phalangeal pattern is 2-3-4-5-4.

Case in point: Ticinosuchus
An important taxon in the evolution of crocs and dinosaurs and other Triassic oddities is the basal rauisuchian, Ticinosuchus. It had departed from the rauisuchian ancestors so much that it is basal to the armored herbivorous aetosaurs of the Late Triassic. Most of the elements of both manus of the Ticinosuchus are present, but scattered. That doesn’t mean they’re impossible to put back together again.

Trace the parts.
Move the parts into a logical pattern (thick with thick, thin with thin, gradually tapering digits, phylogenetic bracketing patterns) then test your results to see if PILs (parallel interphalangeal lines) are produced. When all that happens, you can have high confidence in a correct solution.

Figure 2. Ticinosuchus overall, hand, foot and skull.

Figure 2. Ticinosuchus overall, hand, foot and skull. The hand is presented as originally interpreted by Krebs and by a new reconstruction based on the tracing in figure 1 and phylogenetic bracketing.

This is a long-armed quadrupedal taxon with long (longer than each metacarpal). Metacarpal 3 was the most robust. Metacarpal 5 was extremely short. Digits 3 and 4 were subequal. Digit 1 was the shortest digit, but digit 5 had smaller phalanges. Where known, sister taxa share most of these traits.

Earlier here, here and here we put the manus of an early archosauriform together.

References
Krebs B 1965. Ticinosuchus ferox nov. gen. nov. sp. Ein neuer Pseudosuchier aus der Trias des Monte San Giorgio. Schweizerische Palaontologische Abhandlungen 81:1-140.
Lautenschlager S and Desojo JB 2011. Reassessment of the Middle Triassic rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus. Paläontologische Zeitschrift Online First DOI: 10.1007/s12542-011-0105-1

wiki/Ticinosuchus

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