Ticinosuchus and the aetosaurs, redux

Except for
the skull of Ticinosuchus ferox (Krebs 1965; Middle Triassic, ~ 230 mya, ~3 m in length), I have been using the traditional Krebs reconstruction for the post-crania. Here (Fig.1 ) I finally present my own tracing and reconstruction of Ticinosuchus.

Figure 1. Aetosaurus, Stagonlepis and Ticinosuchus shown together to scale. Ticinosuchus is the basalmost taxon in this clade, unrecognized by other cladograms. Perhaps this is due to differences in skull reconstructions. Note the phylogenetic miniaturization at the origin with Aetosaurus.

The morphological differences
between the Krebs and present reconstructions are few. However the posture here (Fig. 1) is a little more sacrum high, based on the long robust hind limbs, as also seen in Stagonolepis (Fig.1). Earlier we looked at the sharp premaxilla in Ticinosuchus that was previously overlooked by all workers. It’s a key trait shared with aetosaurs (Fig. 2).

Figure 2. Aetosaur skulls compared to Ticinosuchus, the long-sought outgroup to this clade.

Historical Notes from Nesbitt 2011
“Krebs (1963, 1965) argued that Ticinosuchus and Rauisuchus were more closely related to crocodylians than to any other group—a view that was opposed by various workers (e.g., Hughes, 1963; Romer, 1966, 1972b; Bonaparte, 1982) who thought that rauisuchids were proterosuchians.”

“Bonaparte (1981, 1984), placed Rauisuchus, Fasolasuchus, Prestosuchus, Saurosuchus, Ticinosuchus and various other fragmentary forms into Rauisuchidae.”

Nesbit 2011
identified the angular premaxilla as a questionable lacrimal. No reconstruction was offered to support this arrangement. He nested Ticinosuchus in a polygamy with a wide range of taxa including Revuletosaurus + Aetosauria, Turfanosuchus, Gracilisuchus, Qianosuchus and Prestosuchus.

Revueltosaurus?
Nesbitt 2011 nested Revueltosaurus at the base of the aetosaurs. The large reptile tree nests Revueltosaurus with Tasmaniosaurus and Fugusuchus (Fig. 3), altogether a sister clade to the Erythrosuchia and not far from Euparkeria. Revueltosaurus has a round premaxilla.

Figure 3. Revueltosaurus compared to its big sister, Fugusuchus, a basal erythrosuchid.

 

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
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

wiki/Ticinosuchus

 

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. 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. 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

The skull of Ticinosuchus. Need confirmation, guys!

The skull of Ticinosuchus (Fig. 1) is a crushed mess. Many have looked at it. Many have shrugged their shoulders. Others have cried.

Ticinosuchus is widely considered an early (Middle Triassic) rauisuchid, smaller than most others.

Figure 1. The skull of Ticinosuchus colorized using DGS. Someone else should either duplicate or invalidate these identities and reconstruction. Let’s figure out this key taxon. Click for more data.

Some elements are easy to identify. Others defy identity.
This is a plea for someone else to identify the ALL the parts present in the skull to see if the second interpretation validates partially or completely the present interpretation.

Figure 2. Colorized elements restored to a best fit reconstruction of the skull of Ticinosuchus. Note the toothless premaxilla. This and dozens of other traits nest Ticinosuchus at the base of the Aetosauria.

The present interpretation demonstrates a close affinity with Aetosauria, a clade that had previously gone unconnected to other reptile groups.

Please submit or publish your own reconstruction and restoration of this enigma. Let’s see what you come up with.

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