Crikey! It’s World Croc Day!

June 17th is World Crocodile Day! To celebrate, Nilo Mason discusses the anatomy and conservation of their favourite animal: crocodiles. Read on to discover some incredible species highlighted below- one of which could grow to over 11 metres before it went extinct. Crikey!

An Introduction to World Croc Day and Why We Celebrate

Happy World Croc Day! Established in 2017 by Shawn Heflick, Kelly Silvano, and CRC Executive Director Dr. Marisa Tellez, World Croc Day fights to increase visibility and appreciation for all crocodilians.

Of the 26 species within the Crocodylia order, 16 are known as “true” crocodiles - part of the Crocodylidae family. Unfortunately, 9 of the 16 species of true crocodile are classified as threatened (critically endangered, endangered, or vulnerable) by the IUCN Red List, so they need the spotlight more than ever. Five of these species are experiencing a decrease in their global population due to threats such as hybridisation, climate change, and killing for exotic items, including crocodile leather and bush meat.

But why should we care? First of all, crocodiles are amazing predators that maintain balance in their ecosystems. Preying upon injured or slower animals, crocodiles reduce competition for healthy individuals and prevent overpopulation while also removing diseased rotting flesh from the environment via consumption. Furthermore, when digging into riverbanks and building nests, crocodiles alter their surroundings by opening up more space to accommodate nearby animals. Similarly, the Nile crocodile engages in a mutualism with the Egyptian plover bird, allowing it to pick off parasites and clean the crocodile's teeth of leftover debris. Alongside all this, newer anecdotal research suggests that crocodiles may be healthy ecosystem indicators, providing us with another way to monitor wetland environments.

A drawing demonstrating the mutualism between the Nile crocodile and the Egyptian plover. Credit: Biodiversity Heritage Library on Wikimedia Commons.

The Anatomy of Crocodilians

Alongside the Crocodylidae or “true” crocodile family are the Alligatoridae and Gavialidae families, consisting of alligators, caimans, the gharial, and the tomistoma (or false gharial). Fossils suggest that their last common ancestor was around 80-100 million years ago.

An image of a gharial (not a true crocodile) with turtles on its back at Prague Zoo. Credit: Prezmek on Wikimedia Commons.

So what makes a “true” crocodile? Besides seeing you in a while rather than later, there are lots of distinguishing features of crocodiles when compared to the other families. In the state of Florida, American alligators and American crocodiles co-exist, so identification relies more on morphology than location.

A juvenile American alligator laying on a juvenile American crocodile at Gatorama, Florida. Credit: Agsftw on Wikimedia Commons.

Basic traits that can be observed in crocodiles include a V-shaped snout with both the upper and lower teeth protruding when the mouth is shut. Notably, the fourth tooth from the front on either side slots into a groove built into the jaw bone when the mouth is closed. Conversely, alligators and caimans have a more U-shaped snout with only the top set of teeth or neither set showing when the jaws are shut.

A picture of the Nile crocodile, highlighting the fourth tooth’s groove in the upper jaw. Credit: Monika on Pixabay.

Another identifying characteristic of true crocodiles is the presence of sensory pits all along the body, Alligatoroids only harbour these on their head. These pits, known as integumentary multi-sensory organs or dome pressure receptors, detect pressure changes in water to track the movements of other creatures or neighbouring crocodiles.

A close-up shot of a crocodile’s eye, highlighting the black dots on the skin known as ISOs or dome pressure receptors. Credit: Storme on Pixabay.

Moreover, all crocodiles possess lingual salt glands to process and expel excess salt from inhabiting brackish water or even sea water- although some crocodiles such as the freshwater crocodile, prefer no salt at all. These glands are especially pronounced and hyperactive in the saltwater crocodile, allowing them to thrive in higher salinities for longer periods than other crocodiles. Alligatoroids, however, do not have these or have a very reduced version, hence preferring to reside in freshwater such as upstream rivers.

All crocodilians ventilate using a method termed the hepatic-piston pump, in which they move their lungs and liver using their hips and diaphragmaticus muscle to create a vacuum that pulls in or pushes out air. In addition to this, when pulling their lungs and liver back in the water, their centre of buoyancy shifts and allows them to dive, float, or even roll.

These amazing adaptations in their anatomy are highly effective and have persisted unchanged for over 200 million years. Let's hope for 200 million more years of crocodiles!

Spotlighting Some Incredible Species

First up is the dwarf cave crocodile! Discovered in 2010 and first studied in 2016, these dwarf crocodiles live in the Abanda caves of Gabon alongside bats and crickets - their diet of choice. Interestingly, the skin of adult dwarf crocodiles in these caves is bright orange; likely due to bleaching from bat guano (poop) over an extended period. Only three other crocodilians have been documented to utilise caves previously, though these reports are mostly speculative. This cave crocodile is hypothesised to prefer the stable environment of the caves with the abundant food source of the bats (who can cover up to 80% of the cave walls) as opposed to the forests nearby.

A bright orange cave-dwelling dwarf crocodile next to a brown/grey surface-dwelling dwarf crocodile. Credit: Oliver on Wikimedia Commons.

The American crocodile is remarkable due to its ability to parthenogenise. This is the process by which an egg develops into a foetus without the male gamete, similar to cloning. Crocodilians do not have X and Y chromosomes like we do, and so the sex of babies does not depend on genetics, but rather, on temperature. This is known as temperature-dependent sex determination (TSD). American crocodiles use female-male-female TSD: females are born below 30°C and above 33°C, and males are produced between these temperatures. An American crocodile in a study conducted in 2023 produced one female foetus within an egg with no male contact, a discovery never seen before in the Crocodylia lineage.

Finally, estimated to reach over 11 metres long, the Sarcosuchus imperator was a giant prehistoric crocodyliform which lived in Africa during the early Cretaceous. Though this species was not the only large crocodylimorph at the time, what makes Sarcosuchus unique is its dynamic skull shape: its skull broadened drastically with age, something not seen in extant crocodilians. Perhaps this change reflects a diet switch from fish to larger prey as they grew in size. Unfortunately, these huge crocodyliforms went extinct at the early-late Cretaceous boundary, but highly specialised crocodiles then underwent an evolutionary radiation and became much more diverse because of this.

A reconstruction of the skeleton of the Sarcosuchus at the Paris Dinosaur Museum. Credit: Patrick on Wikimedia Commons.

Threats

So what is causing the decline of our current crocodiles? For the critically endangered Cuban crocodile, hybridisation with abundant American crocodiles is reducing the Cuban species’ gene purity. A 2015 study found that an alarming 49.1% of their wild sample were hybrids. As well as their species being watered down by mixed genes, Cuban crocodiles are less likely to get the help they need because the hybrids are misclassified, with up to 57.7% incorrectly identified as pure crocodiles by morphology alone.

Another threat to crocodiles in general is climate change. As mentioned previously, crocodile sex is not determined by genetics, but by temperature of the eggs. Temperature increases of just a few degrees due to global warming could be enough to drive major changes; you might get entirely male or female clutches, throwing imbalance into crocodile populations. Adding to this, warmer water temperatures mean that crocodiles stay submerged for shorter periods of time, putting juveniles at a higher risk of being predated upon. In parallel to these issues, the fact that crocodiles are ectotherms means their body temperature is regulated using the environment around them via basking, entering shade, and submerging in water. If their habitats heat up, they may alter their global distribution, heading further north to achieve their desired temperature range.

Lastly, removing crocodiles from the wild to be put into farms for leather and meat is a real problem. African dwarf crocodiles are captured and sold at roadside to be killed for bush meat and leather. Although these animals make significant contributions to the economy and protein intake of people across their natural range, the demand is not sustainable and could force dwarf crocs into extinction.

Handbag made from West African dwarf crocodile skin at the Natural History Museum, London. Credit: Ian on Wikimedia Commons.

Similarly, critically endangered Siamese crocodiles face being taken from the wild for farming for both their meat and their skins. Between 2010 and 2019, up to 1,430,000 individuals were imported from Thailand for farming. Comparatively, there are only an estimated 200 individuals in the wild. Adding fuel to the fire, the current farmed Siamese crocodiles cannot be released back into the wild as they have been kept with both saltwater crocodiles and Cuban crocodiles, leading to hybrids. These hybrids come with both watered-down genetics and a more aggressive nature than the typical shythe Siamese crocodiles, so they personality of would cause problems if released.

How Can You Help?

Educating yourself on the wonders of crocodiles and what threats they are facing is always a plus. This article should have provided some insight, but don’t stop here! If you are compassionate towards crocodiles or want to protect the planet’s biodiversity, you can try advocacy. Spreading the word and speaking out against harmful practices such as unsustainable farming drive the awareness needed to make large scale changes. Furthermore, signing petitions regarding illegal importing and the exotic wildlife trade can help push for stronger regulations. On a similar note, a good rule of thumb is to not buy crocodile leather or likewise products - you might not be able to guarantee where it came from.

Another tactic for saving crocodilians from the comfort of your own home is zoo adoptions! By giving a donation to support a crocodile within a captive collection, such as Crocodiles of the World UK, you are helping fund their care and associated conservation projects. Alternatively, if you are looking for a more active role in crocodile conservation, consider volunteering with the Crocodile Research Coalition, or taking a crocodile course run by the Crocodilian Academy!

Hopefully, this article has made you aware of how special and important crocodiles are, and encouraged you to partake in their conservation. Happy World Crocodile Day!

About the Author:

Nilo Mason is a passionate Zoology student on placement as a Research Assistant at Dartmoor Zoological Society, deeply committed to wildlife conservation and educating the public about biodiversity. Through their work, they strive to bridge the gap between people and nature, promoting the preservation of our planet's incredible wildlife. You can follow them on LinkedIn: www.linkedin.com/in/nilo-mason