Isochirotherium Haubold 1971

JUNIOR SYNONYM(S): N/A

DESCRIPTION: Manus - Manus tracks are pentadactyl and digitigrade, with digit I often poorly preserved or absent. There is little difference in the lengths of digits II and III, which are both longer than digits I and IV. Digit V is situated proximally below digit IV. It is divergent (from the long axis through digit III) and separated from the other digits. Digits II, III and IV fuse at their proximal ends into metatarsal-phalangeal pads. At least four of the digits (I-IV) are probably terminated by small triangular claws, although these are not as prominent as those on the pes. The manus is relatively small compared to the pes. The manus to pes length ratio is 0.35 : 1. Pes – Pes length range ca. 142 mm – 174 mm. The pes is pentadactyl and digitigrade-plantigrade (sometimes a long slender impression or cast of the tarsus is preserved). Digit II is always longer than digit IV and may be as long as digit III. Digit III may be slightly longer than digit II or the same length. The length of digit I can vary, but it is always shorter than digits II or III. Digit I can be shorter than digit IV, approximately the same length, or even longer. Digits II and III are usually thicker/wider than digits I and IV. Digit V is recurved and situated proximally below digit IV. When compared with a Chirotherium form of similar size, an Isochirotherium digit V is usually more slender and slightly less recurved. Claws are prominent on digits I–IV, but there is no evidence for a claw on digit V. Phalangeal pads are prominent. Trackway - The trackway shows a pronounced outward rotation from the midline. The average rotation is 20◦ –30◦ . The positioning of the manus is variable. It may be situated either: (a) immediately in front of pes digits II or III; (b) on the outside of the trackway, parallel with the pes and almost level with the distal ends of pes digits II and III; (c) to the outside of the trackway and just in front of the pes.

BEHAVIOR(S): Repichnia

ENVIRONMENTAL SETTINGS: Continental; terrestrial

POSSIBLE TRACEMAKERS: Archosaurs

GEOLOGIC RANGE: Middle Triassic

ADDITIONAL REFERENCES: Emended by King et al., 2005.

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