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Tuesday Tetrapod: Atelopus zeteki

Posted by tigerhawkvok on December 09, 2009 02:49 in tuesday tetrapod

Another Tuesday! And I've noticed a horrible fact: I've so far neglected an entire, speciose, clade! To work on remedying the situation, I present Atelopus zeteki, or the Panamanian Golden Frog.

A. zeteki by Flickr user brian.gratwicke

Part of the horribly polytomacious (is that a word? Of many polytomies?) bufonid family in the neobatrachian clade, A. zeteki is probably extinct in the wild. They communicate by visual signals, such as 'hand waving', rather than primarily vocally.

A. zeteki is almost certainly extinct in the wild, and remains only in isolated populations maintained in captivity. Their populations were decimated by the chytrid fungus affecting frogs and salamanders, and numbers were further supressed by poaching. As such, they are IUCN critically endangered.

You can also see more about them in Attenbourough's Life in Cold Blood.

Tuesday Tetrapod: Opisthocomus hoazin

Posted by tigerhawkvok on December 01, 2009 22:37 in tuesday tetrapod

Reading Dawkins' Greatest Show on Earth has got me feeling the "groove" for ancestral relationships and the like, so today's Tuesday Tetrapod reflects that. I bring to you Opisthocomus hoazin, or the Hoatzin:

Hoatzin

O. hoazin. Image CC-BY-NC by Flickr user codiferous.

The bird is endemic to northern South America, roughtly pheasant-sized. It has the dubious honor of being perhaps the worst phyletically resolved of extant aves.

Hoatzin chick

An image of a Hoatzin chick climbing by virtue of its claws. Sadly, this image comes from a protheist, history-denying site over here. That's a surprisingly hard image to find. Image is copyright the owner, and linked on their server.

O. hoazin is also interesting for a number of phylogenetic reasons. It's the only member of opisthocomiformes, part of the poorly-resolved area of avian phylogeny in neoaves. It also has the interesting adaptation of having three fully articulated digits, in an apparent atavism (reversion) to the basal deinonychosaurian form. These digits fuse in adults to the more standard neoavian condition. Needless to say, aside from an interesting fact, it's a wonderful peice of persuasive evidence of the archosaurian lineage of birds.

Emu manus claw

Image of an Dromaeus novaehollandiae's manual claw from Matt Wedel's Dr. Vector blog.

Primarily herbiverous, the Hoatzin performs fermentation in its crop, similar to the function of the rumen in ruminants. This means that the odors associated with fermentation are unusually ... available ... with O. hoazin, giving it the nickname of 'stinkbird'. The size of the crop displaces the flight muscles and reduces the keel, thus impacting the flight ability of these birds. Luckily for the birds, though, this is reputed to give the meat a poor taste, meaning they are rarely hunted (though occassionally tamed).

The hoatzin population is stable over a large area, and as of 2009 is rated IUCN least concern. Feels good to talk about an animal that isn't about to disappear for a change!


Tuesday Tetrapod: Budorcas taxicolor

Posted by tigerhawkvok on November 24, 2009 22:05 in tuesday tetrapod

This week's proper Tuesday Tetrapod is an animal that rather confused Kit and I when we saw it at the San Diego Zoo: Budorcas taxicolor, or the Takin

Burdorcas taxicolor

B. taxicolor CC-BY-NC by Flickr user Silvain de Munck

Believe it or not, this thing is not that closely related to a muskox. Despite appearances, mitochondrial dna and genetic profiling has indicated that this animal is a caprin bovid, that is, a member of the "goat-antelope" subfamily. The closest living relatives to these guys are, improbably, sheep. The degree to which they appear like muskoxen is a compelling example of convergent evolution.

Interestingly, the "golden" phenotype is hypothesized by some to be the inspiration for the Greek myths about the Golden Fleece. B. taxicolor is IUCN "Vulnerable", due to over hunting and habitat loss, with a population decline of 30% in 24 years.

Tuesday Tetrapod: Pelecanus occidentalis

Posted by tigerhawkvok on November 24, 2009 16:24 in tuesday tetrapod

This week's Tuesday Tetrapod will take a small turn from the dismal list of endangered and vulnerable species in light of a critter that's been seeing some good times of late. Last week Two weeks ago, the US Fish and Wildlife service removed today's tetrapod from the US Endangered Species list. So here we have it — Pelecanus occidentalis, or the Brown Pelican

Pelecanus occidentalis

P. occidentalis by Flickr user MikeBaird

Yes, the generic name is spelled with an "e'"! It is the smallest of the pelicans, living primarily on the eastern coasts — though, to be fair, "smallest" in this context means "only" a wingspan of 1.83 m. Pelecaniiformes are diagnosed by the large, distinctive pouch occurring under their beaks. Congratulations, Pelican, on your rebound!

Tuesday Tetrapod: Varanus komodoensis

Posted by tigerhawkvok on November 11, 2009 01:18 in tuesday tetrapod

As promised, part two of the double feature (though both of these posts are going to be "up" before either has pictures). Taking a glance over the archives, I realized I've neglected lepidosauria since August! In a step toward correcting this criminal neglect, I bring you the largest non-archosaurian diapsid alive today: Varanus komodoensis, or the Komodo Dragon

Varanus komodoensis

V. komodoensis

Sadly, phylogentically correct terminology means I can't use the decidedly more impressive epithet of "largest extant lizard" in the crocodylomorphs and turtles, such as Dermocheleys. Even the word largest is difficult — as there are elapids that can reach 6m. However, we can unequivocally say that the Dragon of the Komodo Isles is the most massive varanid lizard, and in fact the most massive member of extant lepidosaurs.

skull comparison

Note the highly kinetic skull morphology

This unusual size has garnered it an unusual degree of familiarity with the public, as well as their rare vertebrate condition of conditional parthenogenesis. They have also been a test bed for studies on unifying lepidosaurian venom characteristics; while their bite was once thought to be lethal by virtue of sepsis, it appears that nonlethal initial bite may be envenomating (DOI: 10.1073/pnas.0810883106).

Like most varanids, Komodos have been shown to be highly intelligent, and capable of recognizing individual humans in zoos — even behaving differently around familiar vs. unfamiliar keepers.

The Komodo Dragon is IUCN classed vulnerable

Tuesday Tetrapod: Ailurus fulgens

Posted by tigerhawkvok on November 11, 2009 01:06 in tuesday tetrapod

Wrapping up our streak of non-lepidosaurs (who needs charismatic fauna anyway?), we look at a creature that is not commonly known to be a musteloid — Ailurus fulgens, or the so-called "Red Panda":

Picture of A. fulgens

A. fulgens. Picture (CC-BY-ND) by Flickr user Tambako the Jaguar

Yes, despite the name, the "Red Panda" is not an ursid, but is in fact a musteloid, being most closely related to the node comprised of weasels, otters, raccoons, and skunks. Ailurus owns its confusing taxonomic history due to superficial similarities to felids, and the effect of its common name on public perception ("panda" is possibly derived from a Nepalese word meaning "eater of bamboo").

Roughly the size of a large cat, its appearance and size are reminiscent of its sister taxa procyonidae, or the raccoons. While hunting is illegal, deforestation is leading to population declines, and the Red Panda is listed as IUCN Vulnerable.

Tuesday Tetrapod: Buteo jamaicensis

Posted by tigerhawkvok on October 27, 2009 19:12 in tuesday tetrapod

For today's Tuesday Tetrapod, we take a bit of a break from the depressing round of endangered animals and turn to Buteo jamaicensis, or the Red-Tailed Hawk:

B jamaicensis

B. jamaicensis. Photo (CC-BY-NC) by Flickr user Minette Layne

B. jamaicensis is the most common accipitrid on the west side of North America. From above, they have a distinctive set of red tail feathers, and a dark patagial bar on the fore edge of the wing. Below, the tail is pale with a hint of rust Below, they vary depending on color morph. On juveniles particularly, there may be a messy black band on their bellies, with multiple bars on the underside of the tail that fade with age.

Juvenile B jamaicensis

Immature B. jamaicensis, photographed on the San Diego coast.

Red tails eat small reptiles, birds, and rodents, up to a maximum of about four kilograms in weight. They are readily trainable when young, and are the most common falconry bird in North America. They are rated IUCN Least-Concern.


Tuesday Tetrapod: Andrias davidianus

Posted by tigerhawkvok on October 21, 2009 03:06 in tuesday tetrapod

Between catching up for missed work last week and a personal project that's not quite ready to go live, I didn't realize that I completely missed Tuesday. So, though two hours late, here is a "Tuesday" Tetrapod for this week -- Andrias davidianus, or the Chinese Giant Salamander.

.

A. davidianus. Image (CC-BY-NC-ND) by Flickr user Silvain de Munck

Andrias contains two species of giant salamander, of which A. davidanus is the largest in the world, reaching lengths of up to 1.8 m. They belong to the family Cryptobranchidae, with the lone (monotypic) sister genus Cryptobranchus.

Cryptobranchids undergo an incomplete metamorphosis and thus have some paedomorphic (neotenic) traits, such as lidlessness and no tongue pad. They feed by asymmetrical suction feeding, accomplished by a flexible mandibular symphisis that allows the animal to depress only one side of it's jaw (for a description and images of this interesting feeding mechanism, see Cundall et al., Asymmetric suction feeding in primitive salamanders, Experientia 43:1229-1231 (1987), fig. 3). They primarily respire through their skin.

Decline in water quality and human predation seriously threatens their populations, they are IUCN Critically Endangered, with an 80% population decline in the past 45 years. They are rare enough that I was only able to find three photos of them (with the Creative Commons license) on Flickr.

Tuesday Tetrapod: Okapia johnstoni

Posted by tigerhawkvok on October 14, 2009 00:01 in tuesday tetrapod

This week's Tuesday Tetrapod brings a cervoid giraffid: Okapia johnstoni

O. jonstoni. Photo by Flickr user ZacharyTirrell.

Commonly called Okapi, they are the only non-giraffe giraffids, and family giraffidae is the most basal extant outgroup to cervoidea. Despite appearance evocative of a zebra, the first cranial analyses in the early 1900s correctly identified the okapi as giraffids. They share the long tongue with G. camoleopardis, which given their smaller size, gives them the curious award of being the only mammal capable of licking its own ears.

Okapi are shy in the wild, and despite "only" being near threatened, they were first photographed in the wild in 2006. They are native to the Congo area.

Tuesday Tetrapod: Dermochelys coriacea

Posted by tigerhawkvok on October 07, 2009 12:16 in tuesday tetrapod

Since last week was lacking in the usual Tetrapod, I wanted to do a double-feature yesterday. However, a bug in my phylogenetic page search code (affecting side-cases where you were a certain number of nodes deep with a certain number of closing nodes above you) postponed this post. However, I make it up today, with a makeup post in which we look at Dermochelys coriacea, or the Leatherback Turtle:

Juvenile D. coriacea. Modified photo by Flickr user algaedoc (CC-BY-NC)

D. coriacea is the only extant member of the family demochelidae, a group united by the lack of a hardened keratinous covering within the cryptodires, or turtles that retract their head linearly into their shell. It is worth noting that though this is a synapomorphy for living turtles, basal members of both cryptodira and pleurodira were unable to retract their neck, and better synapomorphies are found in the connective morphology for the adductor muscles. The peculiar shell of Dermochelidae is instead composed of polygonal osteoderms embedded in skin, which covers a carapace 3 - 4 mm thick.

The chelonioids (marine turtles) are the clade of seagoing turtles, which includes Dermochelidae. Dermochelys is the only fully pelagic turtle, and has a metabolic rate higher than most other non-archosaurian sauropsids, allowing it to maintain a body temperature 18 K or more above ambient. Most of this metabolic heat is generated by muscular activity. This is assisted by a network of 'heat exchangers' in its body, keeping warmer blood internal. These features enable the leatherback's wide distribution, including waters as cool as 281 K (8o C).

Females will lay on tropical and subtropical beaches, with clutches of 40-170, averaging 65-80. They nest bi- or tri-annually, navigating via the Earth's electromagnetic field. Their generally pelagic nature is due to the fact that their primary food source is jellyfish, complemented by other soft-bodied marine organisms. They lack both the dentition and jaw strength to consume anything more rigid.

You can easily identify the leatherback by its non-rigid carapace with lengthwise toothed ridges, and a serrated upper jaw. The animal will measure 120 cm - 245 cm. They have a worldwide distribution, from tropical to sub-polar regions. The subspecies along the western coast of the US is known as D. c. schlegelii, or the Pacific Leatherback. Dermochelys is listed as IUCN critically endangered, with population devastation due primarily to trash interfering in their feeding (plastic bags and nets can look like jellyfish), and declines in nesting sites, nesting success, and increases in nesting mortalities and egg harvesting. This has resulted in a nearly 80% global population reduction in as little as one generation.

Tuesday Tetrapod: Gymnogyps californianus

Posted by tigerhawkvok on October 06, 2009 23:36 in tuesday tetrapod

It's Tuesday again — so time for a Tuesday Tetrapod! Today we look at Gymnogyps californianus, or the California Condor:

California Condor

G. californianus. Image by Flickr user Don van Dyke (CC-BY-NC-ND)

G.californianus is a cathartid, or a new-world vulture. Unusually for birds of prey, sexual dimorphism favors males rather than females in condors. They are rated by the IUCN as critically endangered, with such devastation to their habitat and numbers that now captive rearing plays a large role in their current populations. Part of the reason for their declining numbers is attributed to the extinction of north American megafauna, reducing the carrion selection for the birds. In modern populations, lead poisoning from game has led to serious population declines, leading to legislation to ban use of lead bullets in their home ranges.

You can identify the bird by looking for the white underwing linings toward the fore edge of the wing in adults. Young birds are dusky-headeed, and but are twice the size of Cathartes aura, or the Turkey Vulture, and have much broader proportions. You can also look for the tufted feathers around the neck, rather than the smooth feathers characteristic of the other cathartids. They may have a SVL of as much as 138 cm, and a wingspan of 290 cm. Once extirpated in the wild and reduced to two dozen members in the San Diego and Los Angeles zoos, they are slowly being reintroduced into the wild and are about 300 in population.

You can take a look at what you can do to help the condor populations by checking out CACondorConservation.org.

Tuesday Tetrapod: Cariama cristata

Posted by tigerhawkvok on September 22, 2009 20:33 in tuesday tetrapod

After a brief tour around non-eutherian synapsids, we return to the far more prosperous sauropsids with Cariama cristata, or the red-legged seriema.

c cristata

C. cristata. Modified image by Flickr user kradlum.

c cristata

Seriema face, close up. By Flickr user Toni Barros (CC-BY-NC-SA).

Cariamids are comprised of two species, each belonging to its own genus (the other being Chunga burmeisteri), within the order cariamae. The order shares a common set of characteristics relating to their overall behavior focused on terrestrial predation. In fact, the cariamaen birds include the famous "terror birds" of the Phorusrhacid family. Cariamids maintain the ancestral range of the order, being most prevalent in Argentinian and Brazilian grasslands, and exclusive to South America. They occupy a very similar niche to the Secretarybird in Africa, eating small/medium rodents, insects, and reptiles.

c cristata

Killing a rubber boa. Image by Flickr user Dunleavey family.

In an interesting reversion to primitive traits, Cariama has a recurved and extensible claw on its second toe, convergent on the features found in early avialans and in deinonychosaurs. These claws are often used assistively for feeding.

Unlike Phororhacos and other Phorusrhacids, the wings are not vestigial, and Cariama is capable of flight. It will, however, preferentially run at up to 25 kph before flying, and nests on the ground.


Tuesday Tetrapod: Sarcophilus harrisii

Posted by tigerhawkvok on September 15, 2009 22:58 in tuesday tetrapod

Oddly enough, working on phylogenies made time fly by fast enough that I didn't realize it was already Tuesday — and time for another Tuesday Tetrapod! Let's go for another non-eutherian synapsid. Enter Sarcophilus harrisii:

S. harrisii, by Flickr user ccdoh1 (CC-NC-ND).

Don't let their tiny size fool you. These guys are mean, and their common name is given for a good reason - the Tasmanian Devil. While fairly small (males average ~25 cm and 8 kg), they have attained their moniker for various reasons. When stressed, they release an odor nearly as pungent as a skunk, and their call is said to resemble a very loud and disturbing scream. Their bite pressure is the strongest of any living mammal, running at 35 MPa (the equivalent pressure of 350 m underwater). This prodigous force is used to consume the bones of carrion, which are consumed with fur, meat, and organs. While they largely scavange, Devils are capable of taking down small kangaroos.

Currently, Sarcophilus has been extirpated from mainland Australia, and their closest extant relative is the Numbat. Once relatively stable, a face cancer has infected the population of Devils and has downgraded them to "endangered". The frequent fighting between Devils allow the cancer to be spread by face wounds to different individuals, the disease has nearly a 100% mortality rate, as it interferes with feeding in late stages and leads to starvation. Their low genetic diversity helps facilitate the spread of the transmissble cancer among members. The situation is serious enough that some estimates say they may be extinct within the decade. To read more, check out the official website to save the Devil, as sponsored by the Tasmanian government and the University of Tasmania.

Tuesday Tetrapod: Ornithorhynchus anatinus

Posted by tigerhawkvok on September 08, 2009 23:34 in tuesday tetrapod

In an attempt to bring some equality to synapsids, and talk about something novel, for today's Tuesday Tetrapod, I bring Ornithorhynchus anatinus, or the platypus.

O. anatinus. Flickr image by kookr.

The platypus is a mammal known as a prototherian, or monotreme. "Prototheria" ("First" or "early" beasts) is in contrast to "Metatheria", or marsupials ("middle beasts") and "Eutheria", or placental mammals ("true beasts"). It is the sole member of its family, ornithorhynchidae, and the other four species of protetherians all belong to tachyglossidae (the echidnas). They have the common synapomorphies of all mammals, with a jaw composed only of the dentary, hair, and the production of milk; however, various other traits commonly associated with mammals are in a different form or absent in prototherians. For example, milk is produced, but it is not excreted from a nipple. Instead, it is excreted directly from glands on the skin. In addition, the live birth that is commonly associated with mammals is only a synapomorphy of the [ metatheria + eutheria ] node, and prototherians, in fact, lay eggs. While extant monotremes lack teeth, their ancestors had tribosphenic molars (though there is debate on common ancestry or independent evolution in the lineage).

Flickr image by ccdoh1.

The platypus in particular is unique in a few other ways. Its bill is electrosensitive, similar to the electrosensitivity of a shark. This works by detecting the electrical potentials generated by the nervous system of animals, in conjunction wit the largely saline solution that the animal is composed of moving with respect to any general ion gradients in the water (though the platypus lives in freshwater). By emitting a low strength E-field from its bill, specialized cells can "expect" a certain field measurement adjacent to it, based on properties of electric fields, and other living organisms distort this field, which then differs by this "expectation" in a characteristic manner. Additionally, the platypus is one of very few venomous mammals. The male platypus possess a spur on its hind feet with a hollow tube for venom delivery.The venom is produced in the crural gland, and the proteins involved are non-necrotic / non-lethal, and instead are designed to produce incapacitating pain and shock in their targets, rather than death.The indirect effects of oedema and shock may be enough to kill smaller animals, however.

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Tuesday Tetrapod: Ambystoma mexicanum

Posted by tigerhawkvok on September 01, 2009 14:24 in tuesday tetrapod

I was going to post another mammal to work on the dearth of synapsids here, but there is (unfortunate) timely news about these guys; so, today's Tuesday Tetrapod is Ambystoma mexicanum, or the Axolotl:

A. mexicanum, wild-type coloration. Flicker photo CC-BY-NC-SA by Flickr user widdowquinn, cropped.

Axolotl are highly paedomorphic (neotenic : retention of juvenile features into adulthood) ambystomatid salamanders, arresting development in their larval stage and thus retaining gills and other structures for living in water. They are adapted for living in isolated lakes with little competition. They are capable of short durations in the air, however, using buccal pump respirations to feed oxygen into their lungs; however, their skin is extremely skin and subject to drying out.

A. mexicanum, second wild-type coloration. Note the gill rakers clearly visible. Flicker photo CC-BY-NC by Flickr user pabloneco.

Unfortunately, A. mexicanum are only native to Lake Xochimilco and Lake Chalco in central Mexico; the former has been heavily impacted by humans, and is no longer a fully-formed lake, and the latter no longer exists, having been drained by the local population to avoid flooding. In addition, introduction of invasive fish has exerted pressure on the primary food source of A. mexicanum, as well as consumed their eggs. These factors have combined on the critically endangered species (as of 2006) to bring its population down to an estimated 700-1200 individuals as very recently surveyed (2009/08/28).

Albino captive specimen. Flicker photo CC-BY-NC-ND by Flickr user Isidr-Cea.

While often found in pet stores, the morphotypes found are often the mutant leucistic or albino variants, rather than the natural black and brown types. They live in vivarium temperatures of 14 - 20 C, with an optimal temperature around 17 C. They are often used in laboratory settings for their abilities to repair almost any wound, including complete limb regeneration. Occassionally, environmental stressors or artificial introduction of iodine / thyroxine will prompt the Axolotl to metamorphose — you can see an image of an adult-form salamander (copyrighted image) at the bottom of this page or at the top of this BBC article (partial metamorphosis).

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