Lizards ran bipedally 110 million years ago

Area of Science:

• Paleontology
• Ichnology
• Vertebrate Paleontology

Background:

• The fossil record provides insights into the evolutionary history of extinct organisms.
• Lizard trackways (ichnites) offer valuable data on locomotion and behavior.

Purpose of the Study:

• To describe and classify novel heteropod lizard trackways from the Hasandong Formation.
• To determine the locomotion patterns and evolutionary implications of these ancient lizard tracks.

Main Methods:

• Excavation and detailed morphological analysis of fossilized trackways.
• Comparative ichnological analysis with known lizard and non-lizard track assemblages.
• Paleontological dating of the sedimentary formation.

Main Results:

• Discovery of four heteropod lizard trackways assigned to Sauripes hadongensis, n. ichnogen., n. ichnosp.
• Pes tracks (n=25) averaged 22.29 mm long and 12.46 mm wide, exhibiting typical lizard morphology.
• Manus track (19.18 mm long, 19.23 mm wide) showed distinct morphology from pes tracks.
• Predominant pes tracks, long pes stride length, narrow trackway width, digitigrade prints, and specific digit orientation indicated bipedal locomotion.

Conclusions:

• Sauripes hadongensis represents the oldest known lizard tracks globally, dating to the Aptian-early Albian.
• The trackway evidence strongly suggests that early lizards were capable of bipedal running.
• Bipedality may have been an early evolutionary development in lizards, contrary to previous assumptions.