Sequential segmental analysis of the crocodilian heart

Area of Science:

• Comparative anatomy
• Cardiovascular research
• Evolutionary biology

Background:

• Standardized terminology for cardiac structure is lacking, hindering comparisons between crocodilian, mammalian, and avian hearts.
• Crocodilians possess a fully septated ventricle, making their hearts more comparable to mammals and birds than other reptiles.
• Understanding crocodilian cardiac anatomy provides insights into vertebrate cardiovascular evolution.

Purpose of the Study:

• To describe the cardiac structure of the crocodile (Crocodylus noliticus) using a standardized segmental approach.
• To compare crocodilian cardiac anatomy with that of human hearts, highlighting shared and divergent features.
• To investigate evolutionary relationships through comparative cardiac morphology.

Main Methods:

• Application of the sequential segmental approach for cardiac analysis.
• Juxtaposition of key views of the crocodilian heart with comparable views of human hearts.
• Detailed examination of atrial and ventricular septa, atrioventricular junctions, and great vessel origins.

Main Results:

• Crocodiles have complete atrial and ventricular septums, but lack the oval fossa found in placental mammals.
• The myocardial component of the ventricular septum is dominant in crocodiles, with a significant proportion of the membranous septum.
• The aortic trunk originates from the left ventricle, and a common atrioventricular junction exists with separate valvar orifices, similar to mammals.

Conclusions:

• Despite evolutionary divergence, crocodilian and human hearts exhibit shared features, such as the offset of atrioventricular valvar orifices.
• The study highlights overlooked commonalities, suggesting shared evolutionary morphogenetic programs between archosaur and synapsid lineages.
• Standardized analysis reveals unexpected similarities, advancing our understanding of vertebrate heart evolution.