Highly aquatic marine stem archosaur with soft tissue preservation

Area of Science:

• Paleontology
• Vertebrate Evolution
• Mesozoic Reptiles

Background:

• Archosauromorpha is a dominant reptile clade, primarily terrestrial.
• Secondary aquatic invasions within Archosauromorpha are poorly understood.
• Early Mesozoic marine reptile evolution is often characterized by exclusively marine forms.

Purpose of the Study:

• To identify the earliest stem-archosaur with clear aquatic specializations.
• To investigate early aquatic diversification within Archosauromorpha.
• To provide evidence for the land-to-sea transition in Triassic reptiles.

Main Methods:

• Analysis of a well-preserved Triassic reptile fossil.
• Identification of anatomical features indicative of aquatic adaptations (hyperphalangy, paddle-like limbs, sacral-pelvic articulation loss).
• Examination of preserved gastrointestinal organs (stomach, liver, intestines).

Main Results:

• Discovery of the earliest stem-archosaur exhibiting advanced aquatic specializations.
• Identification of hyperphalangy, enhanced paddle-like forelimbs, and loss of sacrum-pelvis articulation.
• Oldest known preservation of stomach, liver, and intestinal tracts in a reptile fossil.

Conclusions:

• This fossil represents an advanced aquatic lifestyle in early Archosauromorpha.
• Findings offer insights into Triassic marine ecosystem recovery and reptile diversification.
• Provides unambiguous evidence for both terrestrial and marine forms within a single reptile lineage, supporting the land-to-sea transition hypothesis.