LoveFauna

Axolotls

2007-06-04T20:27:00.000-07:00

Australians and New Zealanders frequently refer to the Axolotl as the Mexican Walking Fish, though the Axolotl is not a fish but an amphibian, a salamander, part of the order Caudata/Urodela. Because it's a salamander, it's part of one of the three branches of class Amphibia, which also includes the frogs and toads (the Anurans), and the mainly eel-like order, Gymnophiona, which are also known as the Caecilians. One common misconception is that axolotls and other salamanders are lizards or reptiles - in actual fact, amphibians are a completely separate group of animals, as are mammals, like ourselves.

Axolotls of various colours occur in captivity, including grey, shades of brown, leucistic (white with black eyes), golden albino, white albino, as well as other varieties, such as the melanoid (a near-black animal). The normally coloured axolotl, the "wild type", can be near-black like the one in the group photo to the left, chocolate brown like the one in the site's logo, or even creamy in colour, and anywhere in between. There are even "piebald" axolotls in various colours, and a variety that is piebald in more than one colour, known as the "harlequin".

The name "Axolotl" comes from the Aztec language, "Nahuatl". One of the most popular translations of the name connects the Axolotl to the god of deformations and death, Xolotl, while the most commonly accepted translation is "water-dog" (from "atl" for water, and "xolotl", which can also mean dog).

Prior to the growth of Mexico city in the basin of Mexico, the Axolotl was native to both Lake Xochimilco, and Lake Chalco. Of these two high altitude freshwater lakes, only the remnants of Xochimilco as canals can be seen today. The Axolotl is now on the CITES endangered species list. There have been recent efforts to breed and release the animal, in order to re-establish its numbers. Fortunately, due to the importance of the Axolotl in scientific research, it is unheard of for them to be taken from the wild because of the huge numbers bred in captivity each year.
Despite its endangered status, the use of the Axolotl as a laboratory animal should ensure the species' survival, if only in captivity. It has long been known that the Axolotl is a worthy study due to its amazing healing/regeneration abilities. Normal wound-healing in animals occurs through the growth of scar tissue, and this also means that most animals won't re-grow a lost limb. However the axolotl is fully capable of complete limb re-growth. The animal has the added scientific attraction of having especially large embryos, making it easier to deal with under laboratory conditions. Its embryo is also very robust, and can be spliced and combined with different parts of other axolotl embryos with a high degree of success.

The Axolotl is a fascinating creature for a number of reasons, including its grotesque appearance, its ability to regenerate, and primarily the fact that it exhibits the phenomenon known as neoteny. Ordinarily, amphibians undergo metamorphosis from egg to larva (the tadpole in frogs is a larva), and finally to adult form. The Axolotl, along with a number of other amphibians, remains in its larval form throughout its life. This means that it retains its gills and fins, and it doesn't develop the protruding eyes, eyelids and characteristics of other adult salamanders. It grows much larger than a normal larval salamander, and it reaches sexual maturity in this larval stage. Another term to describe this state is "perennibranchiate". The animal is completely aquatic, and although it does possess rudimentary lungs, it breathes primarily through its gills and to a lesser extent, its skin.

It is generally accepted that neoteny is a "backward" step in evolution, because the Axolotl is descended from what were once terrestrial salamanders, like the closely related species, the Tiger Salamander, Ambystoma tigrinum and Ambystoma mavortium spp. (in fact, one likely theory suggests that the Axolotl is in fact a Tiger salamander off-shoot, as it can interbreed with that species with some success). Through some quirk of nature, a neotenous form developed and, probably due to environmental conditions, prospered. Neoteny is sometimes found in other amphibians, but tends to be caused by low levels of iodine (an essential element for animals to make thyroxine hormones, necessary for growth and development), or random genetic mutation. Research has also shown that very low temperatures can also suppress the production of these hormones, also inducing neoteny.

Weird Lizard Fossil Reveals Clues to Snake Evolution

2007-06-04T19:20:00.000-07:00

A 95-million-year-old marine lizard with minuscule front legs may shed new light on the evolution of modern reptiles, particularly snakes, scientists have reported.
The fossilized remains of the reptile represent the earliest known example of a lizard evolving toward a limbless state, according to experts who described the new species.

The creature's vestigial, or no longer functional, forelimbs barely protrude from its long, snakelike body.
Although its rear legs were of normal size, researchers said the lizard was probably an eel-like swimmer that spent little time on land.
Michael Caldwell, of the University of Alberta, in Edmonton, led the team that made the discovery. He said the lizard, dubbed Adriosaurus microbrachis or "small-armed Adriosaurus," belongs to the lizard group most closely related to snakes.
Intriguingly, Caldwell noted, the new fossil dates to the same period as fossils of primitive snakes that also retained their hind legs.
"This animal appears to have been aquatic, like the rear-limbed snakes from the Middle East," Caldwell said.
He and Italian paleontologist Allessandro Palci reported the discovery in the March issue of the Journal of Vertebrate Paleontology.
Look, No Hands
Experts believe all lizards and snakes descended from a common reptilian ancestor that walked on four legs and lived on land.
Adriosaurus and early snakes probably evolved their elongated bodies and shortened front legs independently of one another, Caldwell noted.
But the similarities between the two may help explain the evolutionary origin of the snakelike body form.

Matthew Brandley, of the University of California, Berkeley, noted that the ancient fossil appears to have much in common with some modern lizard species.
"Limb reduction has evolved over 25 times in lizard groups we see today," Brandley said.
"We almost always see the forelimb reducing before the hindlimb [in lizards today]," he added.
"This fossil is interesting because it tells me that the same trend has been going on for a very long time."
Ocean Origins?
Despite its unusual features, the Adriosaurus fossil had long been overlooked by scientists. First collected from a limestone quarry in Slovenia in the 19th century, it sat on a shelf in a city museum in Trieste, Italy, until its recent rediscovery.
By demonstrating the antiquity of evolved limb loss in lizards, the fossil is now likely to play a role in a longstanding scientific debate over the evolutionary origin of snakes.
It was once widely believed that snakes first appeared on land, and some recent fossil discoveries still strongly support this view.
Other fossils, however, suggest the first snakes may have been sea creatures like Adriosaurus.
Forelimb reduction and body elongation in early marine lizards and snakes may have been adaptations to a watery environment, Caldwell said, but the connection is far from proven.
"What we can say is that limb loss has occurred many times [in different animal groups], and that in the majority this has occurred alongside other aquatic adaptations."

Notostraca

2007-06-04T19:11:00.000-07:00

Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Crustacea
Class:
Branchiopoda
Order:
NotostracaG. O. Sars, 1867
Family:
TriopsidaeKeilhack, 1909

Members of the order Notostraca (colloquially referred to as notostracans, called Triops, tadpole shrimp or shield shrimp) are small crustaceans in the class Branchiopoda. Triops have two internal compound eyes and one naupliar eye in-between, a flattened carapace covering its head and leg-bearing segments of the body. The order contains a single family, with only two extant genera. Their external morphology has apparently not changed since the Triassic appearance of Triops cancriformis around 220 million years ago. Triops cancriformis may therefore be the "oldest living animal species on earth." [1] The members of the extinct order Kazacharthra are closely related, having been descended from notostracans.

Notostracans can be found on every continent except Antarctica.
In Austria, two notostracan species (one spring species and one summer species) are documented: Lepidurus apus and Triops cancriformis. In the Americas, several species have been identified, including Triops longicaudatus and Triops newberryi. In Australia, Triops australiensis is found. Other common types are Triops numidicus from Africa, although it has been said that some papers refer to this as an outdated name for Triops granarius, which is from South Africa, China, Japan and Italy [2]. Triops cancriformis is also found in elsewhere in Europe, for example in Britain where it is endangered, occurring only in pools in two localities, one being in England at New Forest the other in Scotland at Wildfowl & Wetlands Trust Caerlaverlock, which is near Dumfries.

Tadpole shrimps usually live near the ground of astatic pools, where they move with their ventral side down. However, lack of oxygen can force them to swim upside-down with their gill-like legs close under the surface of the water. Notostraca are omnivorous; they dig around in the mud using the frontal part of their shield, looking not only for plankton but also for larger prey such as worms, chironomid larvae, small, dying or weak tadpoles, and even each other. Anostracans, often associated with notostracans, can also be a considerable part of their prey (especially when weak or dying).
Notostracans sometimes even cannibalise freshly moulted members of the same species. In northern and central Europe, with few exceptions, all tadpole shrimps are female, whereas the sexes in southern and western Europe as well as in northern Africa are nearly equal in number. These "females" possess hermaphroditic glands, but instead of selfing, parthenogenesis takes place. Modified appendages of the 11th pair of limbs bear the ovisacs with the mature eggs.
Triops survives in temporary pools all over the world, and are correspondingly short-lived. These ponds usually dry up during certain times of the year when there is no rainfall. Although the adult Triops die during these droughts, their embryos remain in a state of diapause (suspended animation) and can survive for several years until the next rains fill up the pools again, allowing them to hatch.
Triops are often the top predators in vernal pools, as they will eat anything smaller than themselves. They also are an important food source for visiting birds. In some areas, certain species of Triops are considered pests, as they damage young rice plants by uprooting them while searching for food.
The maximum life spans in the lab agree with data from field observations on Triops survival. In the lab, T. longicaudatus has a maximum lifespan of about 50 days and T. cancriformis a maximum lifespan of about 90 days, with some individuals beginning to die off as soon as two weeks after hatching. Secondarily, some may suffer premature deaths from moulting complications or other reasons.

American Crocodile Crocodylus acutus

2007-06-04T19:02:00.000-07:00

American crocodiles are primitive-looking reptiles native to the United States, Mexico, Central America, northern South America, and a number of islands in the Caribbean. This species of crocodile (there are 23 species of crocodilians around the world) primarily inhabits mangrove swamps, brackish creeks, and coastal canals. In the U.S., crocodiles only occur in salt and brackish water habitats in the southern tip of the Florida mainland and around the Florida Keys. American crocodiles are often confused with American alligators; both species can occur in the same habitats in South Florida, so differentiation between the two may be necessary. Fortunately, there are some noticeable differences between the two species. Crocodiles have longer, thinner snouts than alligators. Alligators are dark gray or black as adults, whereas crocodiles are a light gray or tan. Also, if you observe a basking animal and wonder which species it is, check out the teeth (from a distance, of course!). Crocodiles have a very noticeable tooth (the 4th tooth on each side of the lower jaw) that is visible even when the mouth is closed. The lower 4th tooth of alligators is not visible because they are hidden in grooves in the jaw.

Although crocodiles over 20 feet long have been recorded in Central and South America, individuals reaching 12-13 feet long in the U.S. are considered very large. Crocodiles are accomplished predators that feed on fish, crabs, birds, and small mammals. "Crocs" pose no real danger to humans unless provoked or molested; they should only be observed from a distance, and never be approached or fed. Female American "crocs" lay 20 - 70 eggs in either a hole or a mound nest. They do not guard the nest as aggressively as alligators but may stay near the nest until the babies hatch up to 100 days later. The mother "croc" may even dig out the hatchlings and carry them to the water in her mouth. The hatchlings face many predator species like raccoons, birds, fish, and other crocodiles — most are eaten before they reach adult size. American crocodiles are endangered in all parts of their range. Habitat destruction and overcollecting for the skin trade have reduced the number of crocodiles. Unlike American alligators, which have made a comeback in much of their range, crocodiles have not faired as well. Careful management of habitat, scientific research, and public education are essential if we want these magnificent animals to survive.