Tag Archives: Lizards

What are komodo dragons, the largest lizards in the world?

An impressive and ruthless predator, Komodo dragons are the largest living lizards on Earth. Their success is based on a very deadly bite, but there’s more than meets the eye to this endagnered, cold-blooded carnivore.

Image via Pixabay.

Reptiles used to rule the Earth, in the form of dinosaurs; today, they’re no longer top dogs. Some of their larger ancestors, such as crocodiles or alligators, bear hints of that fearsome legacy. Of others, such as lizards, for example, we tend to think of more as critters or cutesy pets basking under a heat lamp.

But not all lizards are born equal, and they can be quite fearsome creatures. The Komodo dragon (Varanus komodoensis) is living proof. Not only is it the largest, heaviest lizard on the planet, but the dragon is armed with vicious, shark-like serrated teeth and a potent toxic bite that bleeds its prey dry.

A living dragon

Komodo dragons are one branch of the monitor lizard family that is endemic to a few islands in Indonesia — they get their name from one of these, the island of Komodo, one of their prime habitats. They are the largest living lizards, growing up to 3 meters (10 ft) in length and approximately 70 kilograms (150 lb) of weight. Whichever way you cut it, that’s a lot of lizard. Wild specimens weigh around 70kg (150 lb), but those in captivity can weigh a lot more. The largest specimen officially found in the wild to date was 3.13 m (10.3 ft) long and weighed 166 kg (366lb), although that weight included an undigested meal.

The dragon’s tail is around the same length as its body, and they’re covered in very tough scales. Each scale is reinforced with a tiny bone (these are called osteoderms — ‘bony skins’), meaning that Komodo dragons are, essentially, encased in armor. Although such osteoderms are not unique to the Komodo dragons, they have been studied and described extensively in this species.

Their study was made possible by the Fort Worth Zoo, which housed the longest-living specimens bred in captivity, which lived for 19-and-a-half years. After its death, the zoo donated the body to the University of Texas at Austin, where researchers at the Jackson School of Geosciences examined it with a very powerful CT (computer tomography) device. The animal’s extensive age made for a well-developed, intricate, and striking suit of osteoderm armor.

Osteoderms, colored orange, cover the dragon’s body, as seen by this CT scan of its skull. Image credits The University of Texas at Austin / Jessica A. Maissano et al., (2019), The Anatomical Record.

The study revealed that the osteoderms in Komodo dragons differ in shape and overall coverage from other lizards — they’re more robust and cover more of the animal’s surface. A similar procedure on a baby Komodo dragon found no osteoderms, meaning that this bone skin develops as the animal becomes older.

Diet and behavior

As is befitting of a dragon, these lizards are top predators. They completely dominate their ecosystems, hunting and eating anything and everything from invertebrates to birds or mammals. They will happily eat carrion or other dragons, as well.

Their bite is vicious. Komodo dragons have serrated teeth that are ideal for ripping through flesh and bone. Their lower jaws house glands that secrete an anticoagulant toxin. This makes a bite from such a creature a very dangerous thing. When hunting, Komodo dragons bite down hard and pull back using powerful neck muscles; this tears flesh to shreds. The toxins then kick in to prevent clotting which leads to massive blood loss, sending their unlucky prey into shock.

Komodo dragons are not very active creatures, on account of their slow metabolism (a trait typical of most reptiles), so, most often, these reptiles rely on their camouflage and patience to pounce on unsuspecting prey. Despite their usual lethargy, Komodo dragons are capable of incredibly-fast strikes when hunting. Since they’re not very fast runners, their hunting strategy involves getting one good bite into their target, which virtually always escapes. Then, the dragons will calmly follow their victim, waiting for them to bleed out, using their keen sense of smell to follow the trail of blood. Such a hunt can take them miles away from the place where they delivered the bite.

But when they do happen upon the dead or dying prey, Komodo dragons feast in style. They can eat up to 80% of their body weight in a single feeding. This gluttonous nature, together with their slow metabolism, means that Komodo dragons in the wild typically eat only around once per month.

They are not above eating carrion, which they can detect using their sense of smell as far as six miles away. They are known for digging up graves in search of food. Komodo dragons can attack humans but only do so rarely.

An endangered species

First recorded by Western scientists in 1910, the Komodo dragon has never been an abundant species. Today, they are threatened with extinction as per the IUCN Red List. The main driver of their extinction historically was hunting for sport and trophy, with habitat destruction and climate change being the most pressing issues facing the species in modern times.

Komodo dragons are currently protected under Indonesian law. Authorities have gone so far as to temporarily ban tourist travel to the island of Komodo, and set up the Komodo National Park there in 1980 to aid in conservation efforts.

Such developments are especially surprising since female dragons can reproduce asexually — if no male is present, they can fertilize themselves. However, only males will result from such pregnancies. Combined with the Komodo dragon’s distaste from traveling far from their birthplace, this can quickly lead to inbreeding and collapse of isolated populations. Habitat destruction in the form of forest burning for agriculture leaves the species especially prone to inbreeding.

Vadasaurus herzogi.

Fossilized ancient lizard shows how dinos evolved to live in the oceans

Scientists have discovered a beautifully preserved, almost complete fossil of a new reptile species. Dubbed Vadasaurus herzogi, the discovery offers a snapshot of evolution at work bridging life on land and in the water.

Vadasaurus herzogi.

Image credits Gabriel Bever, Mark Norell, 2017, Nature.

The fossil was recovered from Kimmeridgian-aged (a subdivision of the Late Jurrasic) marine limestones in the Solnhofen municipality of Bavaria, Germany. They belong to an up until now unknown species dubbed Vadasaurus herzogi, and belongs to the Rhynchocephalia lizard order, a close relative of a small group of ancient reptiles called pleourosaurs (genus Pleurosaurus).

Long family history

Calling Rhynchocephalia a modern success story… would be a bit of a stretch. It’s currently represented by a single species, the Tuatara (Sphenodon punctatus,) whose range encompasses 32 islands off the coast of New Zealand. But from an evolutionary point of view, the order has a deep and rich history, spanning over 240 million years and more than 40 known fossil taxa. An evolutionary history that only grows richer with the discovery of this species.

What’s striking about Vadasaurus (latin for “wading lizard”) is that its fossilization captured an ongoing transition from one habitat to another. Its anatomical features aren’t fully tailored to life in the water but were adapted enough to enable an aquatic lifestyle and suggest ongoing adaptation away from life on dry land.

“The early steps in this transition are distributed throughout the skeleton and appear to increase hydrodynamic efficiency for both swimming and aquatic feeding,” the authors note.

For example, the authors report that this 155 million-years-old animal didn’t have the long trunk and short (relative to body size) limbs of later aquatic pleurosaurs. This less-streamlined frame would make it a poorer swimmer compared to latter pleurosaurs, but would give Vadasaurus the upper claw on dry land — longer limbs make for a faster runner, for example. However, it did have features that point to an ongoing adaptation process for life in the water, such as the shape of its skull and nostril position. Its bones were also found to be less mineralized than other land-locked animals. Lower levels of mineralization translate to less weight, an adaptation that could aid buoyancy and reduce energy expenditure needed to stay afloat and breathing.

The skull of Vadasaurus herzogi

Photographs Vadasaurus herzogi’ skull. A) dorsolateral and B) lateral view.
Image credits Gabriel Bever, Mark Norell, 2017, Nature.

All things considered, there are still a lot of things we don’t know about Vadasaurus. However, the species provides a unique opportunity for paleontologists. Comparison of these fossils with earlier (land-dwelling) and later (water-dwelling) pleurosaurs would allow them to trace adaptations to marine life as they were ongoing. It would also provide some insight into how other, separate ancient species (such as ichthyosaurs and mosasaurs) adapted for ocean life.

“The exact degree to which Vadasaurus had adopted an aquatic ecology remains unclear,” the authors add, “but the insight it provides into the origin of the enigmatic pleurosaurs exemplifies the potential of Rhynchocephalia for generating and informing broad-based questions regarding the interplay of development, morphology, ecology and macroevolutionary patterns.”

Ichthyosaurs would conquer the world’s oceans as the dinosaurs trundled around on dry land. Pleurosaurs would join them during the Late Jurassic, and mosasaurs later still, during the Late Cretaceous. Vadasaurus captures the evolutionary processes that led to the pleurosaurs’ relocation to the oceans, slithering snake-like through the waters on long, powerful tails.

The paper “A new rhynchocephalian (Reptilia: Lepidosauria) from the Late Jurassic of Solnhofen (Germany) and the origin of the marine Pleurosauridae” has been published in the journal Nature.