Evidence for clinging arboreality in a Middle Jurassic stem lepidosaur

Area of Science:

• Paleontology
• Vertebrate Zoology
• Evolutionary Biology

Background:

• Lepidosaurs, including squamates and the tuatara, comprise over 11,000 species, but early fossil records are sparse.
• Understanding the ecological diversity and evolutionary context of early Lepidosauria is limited due to incomplete fossil specimens.
• Marmoretta oxoniensis, a Middle Jurassic fossil from the UK, is a well-preserved candidate stem lepidosaur.

Purpose of the Study:

• To investigate the paleoecology and habitat of Marmoretta oxoniensis.
• To re-evaluate previous hypotheses suggesting a semi-aquatic lifestyle for Marmoretta.
• To provide insights into the ecological diversity of early lepidosaurs.

Main Methods:

• Analysis of post-cranial anatomy of a partial Marmoretta oxoniensis skeleton using micro-computed tomography (µCT).
• Examination of thoracic zygapophyses, ungual phalanx morphology, and manual phalanges.
• Linear discriminant analysis of the manus (hand) using extant squamate data to infer habitat use.

Main Results:

• Post-cranial anatomy indicates adaptations for climbing, including specific zygapophyseal angles and manual phalangeal morphology.
• Linear discriminant analysis strongly supports clinging arboreality, placing Marmoretta within the scansorial/arboreal iguanians.
• The findings contradict previous semi-aquatic interpretations based on depositional environment.

Conclusions:

• Marmoretta oxoniensis was adapted for an arboreal lifestyle, challenging prior semi-aquatic hypotheses.
• This study provides the first evidence of arboreal habitat use in a stem lepidosaur.
• The arboreality of Marmoretta illuminates the vertical structure of mid-Mesozoic ecological communities.