Crocodilian Biology

Erickson 2012 (PLOS ONE) measured bite forces across 83 crocodilians spanning 1–450 kg and fitted log-log regression:

\[ \log_{10} BF \;=\; 1.62 + 0.69\,\log_{10} M_{kg} \]

Saltwater crocodiles (Crocodylus porosus) reach ~16 400 N — the highest bite force ever recorded for any extant animal. Scaling exponent 0.69 > 0.67 implies positive allometry: jaw-adductor cross-sectional area grows faster than body mass. The adductor muscle mass (primarily m. pterygoideus) is offset by the world’s weakest jaw-opening muscles — the jaws can be held closed by a rubber band — a feature exploited by crocodile handlers.

The associated “death roll” (Fish 2007) uses conservation of angular momentum to tear apart prey too large to swallow; the roll rate scales as L^-1/2 with body length.

Crocodilians are the only non-avian reptiles with a fully-septated four-chambered heart. Uniquely, both the left and right systemic arches arise from separate ventricles, connected by the Foramen of Panizza at the base of the aortic trunks. A valve on the right systemic (the cogteeth valve) allows the animal to shunt deoxygenated blood away from the lungs during prolonged dives, conserving O₂ at the working tissues (Axelsson 1996). Under resting aerial conditions the foramen carries a small left-to-right flow and the circulation behaves nearly mammalian.

The shunt is actively controlled by vagal tone and cardiac-output feedback, constituting perhaps the most sophisticated cardiovascular valve system among vertebrates — and providing a comparative model for congenital cardiac shunts (patent ductus, Eisenmenger syndrome) in humans.

Crocodilian jaws are studded with dome pressure receptors (Leitch & Catania 2012) that detect water-surface ripples at nanometre amplitude. Each ISO contains a dense innervation by Merkel-like mechanoreceptors and Krause-type end organs, integrated through the mandibular branch of the trigeminal nerve. Functionally, a lurking crocodile can orient to a prey splash 20 m away in pitch darkness. The same system gates mouth closure during juvenile prey capture, producing the split-second strike.

Female crocodilians build mound or hole nests and guard them through incubation. At hatching, hatchlings emit high-pitched distress calls that elicit maternal excavation; the mother carries the young in a gular pouch to water. Nile crocodiles (Crocodylus niloticus) have been filmed transporting up to 20 hatchlings at once. Extended parental care (months to years) is unusual among non-avian reptiles and is a shared archosaurian trait with birds.

Vocalisation spans subsonic territorial bellows (males) through hatchling distress calls. Saltwater and Nile crocodiles use combined infrasonic calls and water-surface ripples to signal territory.

Crocodilians are polyphyodont: each tooth is replaced ~50 times during a lifetime. Wu 2013 (PNAS) characterised the stem-cell niches at the base of each tooth family. The inspiration has been used in regenerative dental medicine research aiming to reactivate mammalian third-dentition potential. The same biology gives the gharial (Gavialis gangeticus) — with 110 slender, fish-catching teeth — its characteristic dentition.