Tales of the Continental Divide: The Adventures of Mesosaurus

Mesosaurus was an unusual reptile. It looked kind of like crocodiles do today, with a long, thin body, eyes located on top of the skull, webbed feet, and an average length of about 16 inches. It also lived kind of like many crocodiles do today, in freshwater environments. Possibly one of the weirdest things about mesosaurus is that it did all of these things during the Permian period, 320-280 million years ago. That’s 130 million years before crocodiles (and dinosaurs as well) even existed!



Mesosaurus, next to an Ichthyasaur of a much later age, photo courtesy in the Internet Archive Book Images


                In fact, Mesosaurus is was one of the earliest reptiles discovered to have made the transition back into a marine environment. The earliest reptiles appear in the fossil record around 340 million years ago, so it seems that after a mere 20 million years, this retile was done with terra firma. In fact, one of the mesosaurus skeletons that have been discovered is the earliest reptile found with amniote embryos fossilized with it, meaning these are one of the ealiest animals known to have laid hard-shelled eggs. So we’re talking about the early history of reptiles here.


Lower Permian

Lower Permian Mesosaurus, photo courtesy of elrina 753


But speaking of reptiles, it should be pointed out that mesosaurus is not like most of the reptiles we see today. Ancient reptiles can be divided into different categories, based partly on the number of holes they have on either side of their skull. Snakes and lizards are diapsids, defined by two particular holes on either side of their skull, but mesosaurus was an anapsid, which means that it lacks these holes. Anapsids are very primitive reptiles, and in fact some scholars classify them as “parareptiles”. The only species of anapsids living today are turtles and tortoises, who have a fascinating history of their own.



Mesocaurus in matrix, photo courtesy of Museo Civico di  Historico Naturale Milano


The most common type of large reptiles found in the Permian were synapsids, like the dimetrodon in the Permian section of our Hall of Paleontology, and the Edaphasaurus in the great mural featured in that hall. The only synapsids that exist today are, well, all mammals. That’s right, that big, fin-backed lizard in our hall is more closely related to us than to a dinosaur. But of course he’s still a distant relative, like an old uncle.



Recreation of a Dimetrodon, photo courtesy of Rick Hebenstreit


But back to Mesosaurus… There’s another reason that this animal is notable, and that’s the 7,772 mile journey some of its fossils made after their deposition! During the Permian, when mesosaurus was doing its thing, Pangea, the ancient Super Continent, was still forming. Pangea formed around 270 million years ago, ushering in the end of the Permian Period and the extinction of the great synapsids, and making way for the reign of the dinosaurs. It was actually the formation of Pangea and the resulting environmental changes (helped by volcanic activity and climate change) that caused this extinction, which was the worst extinction event in Earth’s history.


Photo Courtesy of David Smith


Around 200 million years ago, Pangea began to break apart. The continents that are now called Africa and South America separated, drifting away from each other and carrying the already fossilized bones of Mesosaurus with them. In the early 20th century, Continental Drift was a hotly debated topic, and it was the fossils of mesosaurus that helped to validate the theory. The remains of this fresh water-dwelling reptile, can be found in Eastern South America and Western Africa, separated be 7,000 miles of ocean. We are sure mesosaurus lived in fresh water, because the rock that its fossils have been discovered in specifically forms in that environment. So, either some of these little guys hopped a tramp steamer, or they were dragged with their respective continents. This, along with numerous other bits of evidence, like the mid-Atlantic Ridge, have helped to validate the theory of Continental Drift.


HMNS Unveils Ground-breaking Discovery: Soft Tissue from the Dinosaur Age!

Well, the news is out, and here’s the scoop. The Houston Museum of Natural Science is involved in the next great discovery in the world of paleontology. In the forests of Myanmar, scientists have unearthed several pieces of 99-million-year-old amber that contain some of the best-preserved prehistoric lizards ever found. These little creatures walked alongside Tyrannosaurus rex, but encased in fossilized tree resin, they seem perhaps days old. The skin and soft tissues, the color of their scales and even their tongues have all survived millions of years of geologic time.


HMNS unveiled these specimens the morning of Wednesday, March 30, as part of our newest exhibit, Amber Secrets: Feathers from the Age of Dinosaurs. This announcement follows a social media buzz created by a paper published in Science Advances, written by Dr. Juan D. Daza of Sam Houston State University and co-authored by Dr. David Grimaldi of the American Museum of Natural History, curator of the Amber Secrets exhibit. The paper outlines the significance of this incredible discovery, crucial to a deeper understanding of the ecosystems of the mid-Cretaceous.


Unlike most fossils important to paleontology that amount to little more than mineralized skeletons, these lizard specimens, measuring a half-inch to almost two and a half inches, offer tissue samples allowing scientists to get an intimate look at these extinct reptiles down to the cellular level. Using CT scanners and 3D printers, paleontologists can zoom in and reconstruct these specimens in high detail, creating fully articulated copies of these ancient animals for research.

The favorite of the collection is an ancestor of the modern chameleon. A curling tail and features of its skull suggest it may have fed and moved similarly, but were it preserved in rock, these details would have been lost. Through the golden lens of amber, this lizard, like the others, looks out at us from across the expanse of time.

These lizards aren’t the only rock stars of this exquisite collection of Burmese amber, also called Burmite. The collection opened Feb. 19 showcasing more than 100 specimens containing feathers, invertebrates, fungi and flora preserved with incredible detail. Using modern technology, paleontologists are learning more about the ecosystems in this cross-section of time than ever before. These faithfully-preserved samples of ancient life allow us to peer across deep time and discover proof that feathered creatures lived alongside Tyrannosaurus rex and Triceratops, and evidence that could explain the development of the relationship between angiosperms and pollinators. The solutions to scientific puzzles like whether dinosaurs had feathers and the exact era in which plant life began to develop flowers could be contained inside these beautiful gold-glowing fossils.


Don’t just read about these amazing discoveries online; come meet these time-travelers for yourself, and learn the secrets they have to tell in Amber Secrets: Feathers from the Age of Dinosaurs while there’s still time. Open now through March 26, 2017.

Calling all Scouts with a curiosity for the slick and slithering: Register now for our spring Herpetology Workshop!

Your old favorite is back — our spring Herpetology Workshop on April 20! This course helps Scouts earn the Reptile and Amphibian study merit badge by completing eight of the badge’s 10 requirements in a single five-hour course.

Reptiles and Amphibians meet the masses!

Student Scouts will convene from 9:30 a.m. to 2:30 p.m. and learn the identifying characteristics of reptile and amphibian species, important components of various species’ natural environments, reproductive processes, movement and behavior, and even explore some long-held superstitions about creepy crawlers.

Reptiles and Amphibians meet the masses!

HMNS Scouts courses are offered throughout the spring, with many allowing campers to earn multiple merit badges in a single day. For more information on all things Scouts, including class schedules, class requirements and registration, click here or email scouts@hmns.org.

Reptiles and Amphibians meet the masses!

To request to be added to our dedicated Scouts mailing list, click here.

Meet Charro, our new resident iguana!

The Butterfly Center recently acquired a new iguana.  His name is Charro (which means “cowboy” – as in “charro beans”) and we believe he is between 5 and 10 years old.  For the time being, he is housed in a cage in the rainforest area.  We may eventually let him loose to wander freely in the Center, once he is thoroughly acclimated – but for now, he seems to be content (and is particularly visible to patrons) in his cage.  Keeping him confined does allow us to find him easily in order to take him outside for some exercise and sunshine on a daily basis. 

We’ve had several free-ranging iguanas in the Center over the years.  It is a perfect place for them – much better than the situations in which pet iguanas are typically found.  Indeed, all of our resident iguanas have been pets that outgrew the space and/or time their owners could provide them.  I think it is unfortunate that these creatures continue to be sold as pets:  what starts as a cute little green lizard ends up as a small dinosaur – and most people are not prepared to handle the latter.

But as a result of all the iguanas we’ve had, I’ve learned more about them than I ever expected to know.  They are actually very interesting and personable creatures!  If you’d like to learn more yourself, read on – or check out the excellent information at the website of the Green Iguana Society.

iguana of sea
Galapagos Island Iguana
Creative Commons License photo credit: Ansgar Berhorn

Iguanas are in the same family (Iguanidae) as the little green or brown anole lizards we see in our gardens here in the southern USA.  The most common species available through the pet trade is the common or green iguana.  Green iguanas (the scientific name is Iguana iguana) are common in tropical areas from Mexico to South America.  In their native habitat, they often sit sunning themselves high up in trees, especially along rivers.  If a hawk or eagle flies over (both are major predators of iguanas) they will fling themselves into the river below.  They are excellent swimmers!   There are several other species of iguana, including the spiny or black iguana (also common in Central America, especially near the coast), and of course the famous marine iguanas and land iguanas of the Galapagos Islands (both species believed to have evolved from green iguanas). 

summer-09-042Baby iguanas are about 8 inches or so long and bright green.  But they soon get much larger, some growing to over 6 feet long.  As they mature, they lose their bright green color, and males in particular gain “secondary sexual characteristics.”  People often ask about Charro’s large jowls (the big lumps on either side of his head).  We like to say that they are like biceps on men – enticing to females and intimidating to other males!  The jowls, large dewlap (flap of skin below the chin), and the orangish skin color are all characters seen in mature male iguanas.  Male iguanas also develop fatty deposits on top of their head.  Mature females are slimmer and duller colored, with smaller jowls and dewlap and no head lumps. 

Although much less colorful than the babies, adult iguanas can change color up to a point.  We’ve noticed that Charro gets darker when he is taken out into the sunshine, and lighter when he’s back in his cage.  Iguanas use their color to regulate their body temperature – they darken up to absorb more heat.  An iguana’s color can also indicate its mood or stress levels (sometimes their colors become more contrasting when threatened or frightened).  Male iguanas in particular become more colorful when they are in their breeding season.  The orange becomes brighter, and the black stripes on the tail, etc., more pronounced.

Iguanas apparently have excellent vision, and can see colors as well as we do.  They also have a “third eye” (called the parietal eye), a clear scale on the top of their head.  This organ senses light and dark, and alerts them to aerial predators.  

Male iguanas in particular develop pointed “tubercular scales” on the back of the neck, and have a ridge of flexible spines along the back.  I have not been able to find any known function for these, beyond ornament.  Quite a few of Charro’s ridge spines have been broken off, and we are not sure whether they will grow back.  Iguanas do molt their skin periodically – unlike snakes, which shed their entire skin at once, iguanas lose theirs in patches over several weeks. 

Iguanas can live for over 15 years, but usually don’t make it that long in the wild because other animals (including humans) love to eat them!  In fact, they are sometimes called “chicken of the trees” or “bamboo chicken.” Their eggs are also eaten, and their skin is sometimes used for belts or boots, etc.

summer-09-040Iguanas themselves are strict vegetarians, which is rather unusual among lizards (most eat insects or other small animals).  For us, of course, it is fortunate that iguanas have no interest in eating butterflies!  We feed Charro healthy salads of vegetables and fruits.  Greeny leafy vegetables such as collard greens are especially good for him.   According to the Green Iguana Society website, although iguanas will eat almost anything you offer them, they should not be given any animal protein!

Because iguanas, especially the males, are quite territorial, we have been advised (by none less than the director of the Houston Zoo) to keep only one iguana at a time.  Indeed, many years ago when we had a male and female, they had a tremendous battle and the male was badly injured.  Although in nature you may see several iguanas in close proximity, they are not social creatures and really only get together to mate. 

Long-time patrons of the Butterfly Center will remember some of our previous iguanas.  Sidney died in 2004 at the age of 14, after more than three years in the Center.  A large, stocky and colorful iguana, he acted more like a dog than a lizard; he was so friendly that he would crawl into people’s laps to be petted.  When Sidney died, we had an autopsy done; the vet told us he died of a heart attack (apparently a common cause of death in older, captive, male iguanas!) 

Gandalf was not quite as friendly as Sidney, but was a truly magnificent specimen.  Unlike Sidney and Charro, he had a complete, unbroken tail that was exceedingly long (Gandalf was about 6 feet long including the tail.)  Unfortunately, after several years of climbing all over the Center, he made an unfortunate misstep.  We believe he slipped off one of the planters on the second floor and crashed onto the cement floor around the cenote.   This undoubtedly happens in nature as well: during one field season in Costa Rica I used to admire a large iguana that sunned himself every day on a high and slender branch of a cecropia tree along the Puerto Viejo river.  One day I noticed that the branch had broken off…I never saw that particular iguana again. 

Stretch immediately preceded Charro.  He was never a happy or friendly iguana, and died of old age/ill health earlier this year (2009), less than two years after he came to us.   Charro was acquired for us earlier this summer by Olga, one of the visitor services staff who has a friend at the Brownsville Zoo, Charro’s previous home.
From our previous experiences we’ve learned that individual iguanas, once you get to know them, definitely have personalities!  So far Charro seems to be a very laid-back, tolerant, and well-behaved iguana.  However, we always impress upon visitors that iguanas can bite, although it is usually a last resort and they usually give plenty of warning.  However, when it happens, an iguana bite can be serious.  They have lots of very sharp little teeth – it’s like getting slashed with a hacksaw.

Fortunately, we have learned to read the signs:  iguanas typically give behavioral clues about their mood.  When an iguana is comfortable and happy (for example when we pour water over Charro’s head, something he seems to particularly enjoy) it will stand up on its front legs, raising its head in the air.  Most iguanas also enjoy being petted, particularly behind the head, or under the chin and jowls, or along the back.  Sometimes they close their eyes in pleasure, leaning into the caress just like a dog or cat, and even look as if they are smiling!

An angry iguana, however, is quite fearsome.  If frightened or seriously irritated, it will typically turn its side to whatever is bothering it and stand up on all four legs, apparently trying to maximize its size.  It may also walk forward in a stiff-legged manner, sometimes opening its mouth and wagging its tail.  This is not a friendly wag – it means the iguana may whip with its tail or even bite!  At this point it’s time to back off and give the iguana some space.

People sometimes voice concerns about iguanas and salmonella.  Yes, some iguanas can carry it.  So after handling Charro or any other reptile, for that matter, it is a good idea to wash one’s hands thoroughly, especially before eating.

summer-09-043If you don’t see Charro in the Butterfly Center when you visit, check outside by the Kugel Ball.  A number of docents have volunteered to take him out for a “sunbath” on sunny days.  Iguanas need the heat, as well as the UV A and B wavelengths provided by the sun’s rays (or the simulated sunshine provided by a UV lamp), to get warm enough to move and to eat/digest food, as well as to manufacture vitamin D (just like humans).  We try to get Charro outside for at least half an hour, several times a week.  It’s also a good way to let people see him up close!

Any of you iguana experts out there – I’d be happy to hear feedback about any aspect of iguanas and their care.  We’re always learning about them!