Basic Crocodilian Biology

            Crocodilians have evolved for millions of years on this planet and through this period of time, they have adapted themselves well to their role as an apex predator.  Acute hearing, excellent color vision, Integumentary Sense Organs (ISO’s), and a keen sense of smell are just a few of the things that these remarkable animals use to survive in a rather hostile environment on a day to day basis.  In this section, I will attempt to cover basic biology of crocodilians to help give you a better understanding of what you are dealing with as the captive predator the animal is.

Crocodilian Senses:

            The eyes of crocodilians are set high up on their skulls for a reason.  As ambush predators, these animals will many times lower their bodies completely into the water with only their eyes and nostrils showing.  This enables them to move in closer to the potential prey item practically unnoticed.  Most crocodilians are night hunters.  Their eyes have the vertical pupil like what would be seen in cats.  This pupil turns into a thinner slit as more light is available and widens to receive more light when less light is available.

Photos by Chris Law- (1) More light = Less Pupil  (2) Less light = More pupil

            To make the crocodilian a more successful night hunter, there is a wall of cells in the back of the retina which forms the “tapetum lucidum”.  These cells help re-direct light through these specialized eyes to the retina to improve images in the dark.  At the same time, these specialized eyes come to them as a disadvantage at night for croc hunters and poachers.  When a flashlight is shined into their eyes it reflects a very distinctive glow.  This glow typically gives these animals away, and is thus one of the most successful ways of capturing/hunting crocodilians.  Furthermore, crocodilians are able to see in color with these specialized eyes due to the complex set of rods and cones that make up their retina, similar to the human eye.   

            Crocodilians may inhabit many very muddy, bacteria infested, algae overgrown water sources.  In these particular areas, water debris can be very thick and hard on a sensitive part of the body such as the eye.  However, these animals have evolved to cope with this problem as well.  Crocodilians have a transparent nictating membrane which serves as a secondary eyelid.  This inner eyelid moves from the sides while the outer eyelid moves up and down.  When this transparent eye-lid is engaged, it does limit visual ability somewhat, especially in muddy, darker water.  However, it protects the main eye from damage that may be caused by debris in the water (or even during scuffles with fellow crocodilians).  When visual ability is limited, crocodilians have a keen sense of smell to help back them up.

                     Photos Courtesy of : John White- The “Transparent Nictating Membrane”

Hearing:

            Crocodilians, realize it or not, also have relatively excellent hearing ability.  Interestingly, their ears are covered by a flap of tissue on the top of the head, just below the roof of the cranium. This particular flap helps to protect the ear openings while the crocodilian is submerged under water.  Crocodilian’s hearing is very sensitive to a wide range of frequencies.  This is thought to be because it helps enable them to hear distress calls coming from their young while they are still within the egg. 

            An additional sense that is held by crocodilians is the use of sensory nerve fibres, also known as integumentary sense organs.  These organs assist them in catching prey most likely as they are able to sense the slightest disturbances within their watery domain.

The Great Jaws:

            One of the most impressive parts of crocodilians is their powerful jaws.  Crocodilians have a wide variety of shapes in their jaws.  This is typically due to their location, and the mechanical requirements for capturing preferred prey.  As an example, the Indian Gharial has a quite long but very slender snout with long sharp teeth.  These animals typically prey on fish, and small mammals.  The Nile crocodile however, has a much wider, but shorter snout.  The difference is its diet.  Nile Crocodiles hunt larger prey items such as antelope, etc.  Once the prey is captured, their mandibles help to hold their prey until the animal is drowned or is suffocated as its body’s thorax is crushed.  Once the animal is determined to be dead, then usually a group of crocodilians will grab hold of the animal and take turns doing what is referred to as a “death roll”.  During this process, bite sized pieces of meat are ripped off of the body for ease of swallowing.  The Indian Gharial however, doesn’t need to do so much work to eat.  With a quick lateral swipe of its jaws it is capable of capturing fish, then with a couple quick flips of the head to aim the fish’s head straight down, the fish is swallowed whole.

Photo Courtesy of : John White – American Crocodile (Crocodylus Acutus)

Photo Courtesy of : John White – Indian Gharial (Gavialis Gangeticus)

Photo Courtesy of : John White – Spectacled Caiman (Caiman Crocodylus)

Photo Courtesy of : John White – Black Caiman (Melanosuchus Niger)

            The jaws of crocodilians are certainly suited for the environment of where they live.  These animals are certainly well equipped to handle their business.  However, there are a few other interesting facts about these impressive jaws.  Crocodilians have highly impressive closing pressure.  These animals are able to snap their jaws with tremendous power as adults, and you shouldn’t underestimate the bite pressure of a juvenile (don’t let his size fool you).  However, despite their extraordinary closing power, the crocodilian doesn’t have much power for opening.  In fact rubber bands have been used many times to hold larger crocs jaws closed. However, most handlers will use electrical tape for keeping the jaws secure. 

            The teeth in crocodilians are actually replaced throughout the animal’s lifetime unlike most mammals.  As the animals gets older, their teeth replacement process becomes much slower and eventually, once the animal reaches a ripe old age, the teeth gradually stop regenerating in just before death.

Food and Digestion:

            The diet of crocodilians has proven to vary greatly from the egg to adult.  Young crocodilians will typically prey on insects, small fishes and small amphibians.  They are already born with appropriate hunting skills that are passed down the line from generation to generation.  As the animal continues to grow, then its diet will vary.  Juvenile animals will typically prey on smaller mammals (squirrels, birds, etc.), fish, and possibly even appropriately sized turtles.  The diet of the crocodilian varies among species, depending on behavior, morphology (mechanics of the body), geographic location, food availability, nutritional requirements, etc.  Typically, American alligators are not big fans of large prey items.  There have been a number of occurrences where Alligators have taken larger prey however.  Nile Crocodiles, Estuarine Crocodiles, and some others are noted for taking larger prey, and then working together to rip it into appropriately sized pieces for ingestion. 

            When prey is eaten, this includes bone, fur and all.  Turtles are actually taken quite frequently by adult alligators and other crocodilians in which turtle shells take much longer to digest, approximately the same as bone.  However, crocodilians have also devised a way to assist themselves in that aspect as well.  Crocodilians will deliberately seek out stones, referred to as “Gastroliths”.  These Gastroliths act as a grinder in some aspects inside of the crocodilians stomach to assist with the break-down of hard material such as Bone and Turtle Shell. 

            In order for crocodilians to be able to properly digest food, they have to be able to keep there body temperatures at appropriate levels.  American alligators typically like to get their preferred body temperature (PBT) to around 88 Degrees Fahrenheit.  Most crocodilians will average out around that temperature range, while some may like it a tad warmer. Crocodilians like the famous Nile crocodile (Crocodylus Niloticus) would typically have a warmer preferred body temperature. 

Other fascinating body functions....

            As you can see from above, crocodilians have various adaptations that help them to succeed at being the predators that they are.  Below are a couple additional functions that also play an important role in their survival.

The Palatal Valve:

            The palatal valve is a very useful adaptation for crocodilians during times of submersion.  .  Since crocodilians do not have lips and their mouth cannot seal tight, the palatal valve covers the opening to the throat to prevent water rushing into the throat, trachea and the esophagus. The palatal valve enables the crocodilian to make use of its jaws when capturing prey under water.  However, once the prey is captured and drowned, the crocodilian must rise out of the water to swallow the prey.  Otherwise, this could result in a considerable amount of water intake as well.

Photo By: Chris Law (Palatal Valve view)