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Tuesday Tetrapod: Acinonyx jubatus

Posted by tigerhawkvok on August 27, 2009 21:05 in tuesday tetrapod

Moving eats up time like no other, so here's a late Tuesday Tetrapod, where I'll try to balance my sauropsid bias with another mammal: Acinonyx jubatus, or the cheetah.

A. jubatus, "King Cheetah" morph. From Wikipedia.

The cheetah is fascinating for many reasons; in particular, its highly derived state results in a number of unique adaptations. It has lost much of the skin sheath around the claws, meaning that it's claws are effectivley non-retractable, unlike most cats. This means that the claws are exceptionally good for the purposes of traction, and assist the cheetah in its 100+ kph speeds and sharp turns (which are assisted by the long tail).

Cheetahs are believed to have genetically bottlenecked in the last Ice Age, possibly dropping as low as 100 individuals. This means that cheetahs are so undiverse that they can accept skin grafts from each other with no rejection, and due to inbreeding males have low sperm counts (and the sperm themselves lack motility).

The cheetah can be diagnosed from the leopard by noting the overall more gracile form, and the lack of spots-within-spots (rosettes).

Finally, on a more personal note, for a very long time, cheetahs were actually my favorite extant wild animal, to be later usurped by the Siberian tiger. Nowadays, I'm actually not sure which animal is my favorite!

Tuesday Tetrapod: Contia tenuis

Posted by tigerhawkvok on August 18, 2009 21:47 in tuesday tetrapod

For today's Tuesday Tetrapod, I bring another snake: Contia tenuis.

Close up of head


Head, lateral, and ventral sides


Close up of tail

Contia tenuis, or the sharp-tailed snake, as an adaptation of its final tail scale that makes it into a sharp spur. As a defensive mechanism, they coil into a ball with their tail protruding to dissuade predators.

To identify it, note that the pattern of head scalation is unlike the "head shield" pattern that is the namesake of the Lampropeltis genus, with a regular crossbar patterning on the ventral side that is not found in Thamnophis. If worst comes to worst, look for the light yellow/orange/reddish stripe on the dorsolateral side of the animal running down its length,and the black stripe along the side of its head.

Photos courtesy Rachael, and snake courtesy Rachael's cat.

Tuesday Tetrapod: Columbia liva

Posted by tigerhawkvok on August 11, 2009 18:04 in tuesday tetrapod

As of the time of this daft, another Trekcon Photoblog post is pending, but for now — time for another Tuesday Tetrapod, in the form of Columba livia, or the Columbian Rock Dove, more commonly known as the pigeon.

< !-- Image here --> Columbian Rock Dove, image from Wikipedia and naturespicsonline.com

C. liva. Photo from Wikipedia; original by Alan D. Wilson.

The most common bird in the world, the pigeon is found on all the continents except for Antarctica. Columbidae are part of "near passerine" birds, for which the terms "dove" and "pigeon" are generally used interchangeably. Like all passerines, the pigeon has a large reversed hallux that provides for automatic perching behavior with no need for conscious control, due to an interior "ratcheting" mechanism.. The family Columbidae encompasses all doves, which have a variety of color phenotypes but a more restricted degree of obvious physiological / morphological differences. At LHS, I've in fact worked with ring-necked doves, Streptopelia capicola, which are starkly similar in morphotype to the rock dove.

Pigeons are able to produce "crop milk", which is a fatty fluid produced by cells in their crop that serves a similar function to, but is quite different from, milk. It is also used to feed their young.

Tuesday Tetrapod: Heterodon nasicus

Posted by tigerhawkvok on August 04, 2009 00:03 in tuesday tetrapod

For today's Tuesday Tetrapod, I'll focus a bit on microcharacters as we look at Heterodon nasicus, or the Western Hog-Nose

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Wally, H. nasicus

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Scales

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Sorry for the yellowish last two photos, I forgot to manually adjust my white balance. H. nasicus is well adapted for a subterranean lifestyle, and it has a whole suite of characters to that end. Note the ridges on the scales, which help prevent dirt from adhering to the animal, and the blunted rostrum with a keratinzed "hog nose" tip, used for digging.

Behaviorally, the snake tends to dig and is rarely on the surface of it's substrate. For a defense mechanism, it hisses and shakes it tail similar in manner to kingsnakes, though the substrate they usually occupy make this less effective. They tame well as pets, though may still hiss from time to time. < !-- behaviours -->

Tuesday Tetrapod (2 of 2): Ophisaurus apodus

Posted by tigerhawkvok on July 29, 2009 01:23 in tuesday tetrapod

I was out much later than I thought tonight, so today's part two for the Tuesday Tetrapod won't have that much of an attached explanation. Without further adieu, Ophisaurus apodus, also known as Pseudopus apodus, or more commonly the scheltopusik.

Legless lizard

O. apodus. Photo by Flickr user Joachim S Mueller.

What's snazzy about this guy is that he's not a snake, he's in fact a legless lizard. As an anguid, it's a member of autarchoglossa whereas snake phylogenetic placement is uncertain. It is possible that snakes are within that node (which would make a degree of sense), but serpentes are not especially closely related to anguids in any case. They have a vaguely segmented appearance with a long lateral groove to permit breathing and give flexibility while still providing maximum protection. Additionally, they have eyelids (snakes have a clear scale over their eyes), visible ear holes, and sometimes vestigial hind limbs.

Tuesday Tetrapod (1 of 2): Fishapod?

Posted by tigerhawkvok on July 28, 2009 17:27 in paleontology , tuesday tetrapod

For today's first Tuesday Tetrapod, I present ... an unidentified "fishapod" fossil.

Fossil

Basal tetrapod (?) fossil find.

Fossil anterior portion

Anterior portion of the fossil. Penny for scale.

Fossil posterior portion

Posterior portion of the fossil.

Whole fossil, rotated

This find was located by Sara's aunt and uncle (though I won't disclose the location — things are in process to get it into the proper hands for museum care). Since this is unidentified, it'll be a walk through the features we can currently see in the rock — though it is actually not wholly clear if it is actually a tetrapod yet (via discussions with UCMP contacts)!

So, here are some nifty features I think that lend toward identification as a basal tetrapod, or what is sometimes jokingly called a "fishapod":

Ribs on fossil tail

Note the ribs on the fossil tail. These are commonly found on animals with fleshy tails used for swimming.

  • Looking at the anterior portion of the fossil, there are obvious ribs along the caudal vertebrae. While these are apparently in the transverse direction, they could easily just be distortion from the process of fossilization.
  • There are structures adjacent to a large mass on the posterior half of the animal. While not quite clear in the photographs, it seems to be fairly robust and narrow element, and possibly two other connected elements near the midline. I postulate that these could be the pelvic girdle, femur, and a fibia/tibula
  • The pelvic structure appears mirrored across the vertebral column, though perhaps not strongly joined, indicated a basal state.
Fossil pelvic girdle

Region around the presumed pelvic girdle of the fossil. Light outline is one hypothesized articulation for the detached bone.

Finally, the anterior portion of the fossil has a well developed jaw that appears not exceptionally "fish-like" and more like early tetrapods. In addition, the cervical vertebrae have well-developed bones by them (processes?) that could be hyoid bones / remnants of gill arches, and well-developed hyoids are also seen in modern amphibians for feeding — though this part of my analysis is admittedly more sketchy, as I am not up on my fish anatomy.

So perhaps this entry is a week late -- but hopefully it was worth the wait!

Please note that all photos in this blog post were taken by Sara Weinstein, and copyright (or copyleft or any other form of release) belongs wholly to her. Please visit her blog and drop her a line there if you'd like to use the photos!


Tuesday Tetrapod: Mus musculus

Posted by tigerhawkvok on July 14, 2009 11:55 in tuesday tetrapod

Today's (late) Tuesday Tetrapod is Mus musculus, or the house mouse.

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Feeder mice

Mice, as a member of the clade Glires, are one of the closest relatives to the primate clade Euarchonta, and the closest living non-primate relatives to humans.

That's it for today -- I'll try to get up another post some time this week, though!

Tuesday Tetrapod: Gymnopis multiplicata

Posted by tigerhawkvok on July 07, 2009 22:48 in tuesday tetrapod

Today's Tuesday Tetrapod is to be a bit enlightening — as I introduce a tetrapod that is a bit lacking in the "pod", and in addition, is very little known. I introduce Gymnopis multiplicata, a caecilian.

G. multiplicata

G. multiplicata. The "smile" is where its mouth is. Photo from Flickr user teague_o, taken in Costa Rica.

Often described as looking like large worms, caecilians are tetrapods — they have the whole tetrapod complement of parts, with a vertebra, occasionally with limb remnants, noses, jaws, teeth, and so on. However, they are also very unique in their morphology in many ways. Among their odder features include eyes covered by skin and two (very small) chemosensitive tentacles. Furthermore, their jaw musculature is unique in having two sets of jaw muscles for closing their jaws, unique among vertebrates in a condition known as streptostyly.

It's worth taking a look at their skull morphologies over on Digimorph: Typhlonectes, Scolecomorphus, Icthyophis, and Dermophis. Their skulls are strongly akinetic and completely roofed except for sensory openings, known as stegokrotaphy (with minor exceptions). Other interesting morphological traits include highly reduced or absent tails (their cloaca is at the terminus of their body), and the annular rings around their body, thought to be homologous to salamander costal grooves.

As lissamphibia, they are dependant on water in their environment for reproduction and to prevent dessication. You can see their relevant phylogeny here. Caecilians are known from the lower Jurassic.

Watch some fascinating behaviours from caecilians as they effectively nurse their young with their skin. They strip the flesh off their mother, which exudes a white, milky substance, and the skin grows back rapidly, often within 24 hours. I couldn't find a good general feeding video, though.

Tuesday Tetrapod: Elgaria coerulea

Posted by tigerhawkvok on July 01, 2009 16:12 in tuesday tetrapod

For this week's Tuesday Tetrapod, here is an Elgaria coerulea, or Alligator Lizard, picked up by Rachael's cat last week:

E. coerulea, side

Note the smooth, evently lined-up scales.



E. coerulea, dorsal

Note the dark eyes and dark banding, diagnosing it from E. multicarinata

Note the smooth scaling, which helps protect it. There is a fold of loose lateral skin along its side to let its body expand while it breathes, but still enabling it to be well-protected. Lizards are pretty robust, and this guy later dropped his tail. No idea if he survived, though.

Sorry for the late post, and its brevity!

Edit: Looks like the ID on this is ambiguous. The belly scales are not quite distinct, though possibly mid-scalar; the dorsal patterning is not quite as definitive as it might be. So lets call this "Elgaria spp."

Tuesday Tetrapod: Sphenodon spp.

Posted by tigerhawkvok on June 22, 2009 18:17 in tuesday tetrapod

A little bit early, but I have time today! Having covered caudata, avialae, non-avian saurischia, and squamata in the past two weeks, today's post is on the only surviving non-squamate lepidosaur still around: Sphenodon spp., or the Tuatara.

Sphenodon spp.

Sphenodon spp. by Flickr user digitaltrails.

Sphenodon has an interesting history and interesting set of skeletal characterisitcs. One of the most obvious differences is the presence of two, clear, temporal fenestrae, a basal diapsid condition compared to the skull modification of avians and that of squamates, who have lost the lower temporal bar to allow for greater skull kinesis.

Additionally, Sphenodon teeth are acrodont, where the teeth are fused to the jawbone. Thus, its teeth appear as projections of bone from the maxilla and dentary that fit within each other, and terminate at the premaxilla with a beak-like structure, thus the order name "Rhynchocephalia" (beak-head). This beak structure is an outgrowth of bone that replaces the premaxillary teeth during ontegeny. Also notable is the fact that teeth are present on the palatine bones, which is not true for squamates.

Recently, there has been a push to use a new ranked order of "Sphenodontia", though usage is still mixed. There are only two extant species, S. puncatatus and S. guntheri. Their common name, "tuatara", is based on Maori wods for "spines on the back".

The earliest Sphenodon finds are known from the Triassic, where up to nine genera lived in what is now Britain. Significantly for phylogenetic systematics, Triassic sphenodontians show lepidosaurian characteristics such as a thyroid fenestra, fused astragaclus and calcaneum, and a hooked metatrsal 5. The group was diverse through the Mesozoic, but became extinict in Asia and Laurasia by the mid-Cretaceous, and are virtually absent from Cenozoic deposits. Tuatara are classified as ICUN "Vulnerable", with invasive mammals intruding on their niches and consuming their eggs, which is a large hazard. Sphenodon mate about every four years, leaving 5-15 eggs incubating over 11-16 months. Sphenodon utiilize temperature-dependant sex determination, or TSD.

Sources:

  • Benton. Vertebrate Paleontology, 3rd edition. 2005. ISBN 0-632-05637-1.
  • Pough et al. Herpetology, 3rd edition. 2003. ISBN 0-13-100849-8.

Read more about temporal fenestration: The Tree of Life

Tuesday Tetrapod: Diplodocus spp.

Posted by tigerhawkvok on June 16, 2009 21:16 in tuesday tetrapod

Today's Tuesday Tetrapod will shake things up a bit. Did I ever say they had to be extant?

Diplodocus_stitch

Diplodocus carnegii from the London Museum of Natural history

I've already talked a bit about sauropods before, but this is beyond a doubt the actual species I have worked on the most. Diplodocids were a group of long-necked saurischians, and include other well-known specimens such as Apatosaurus and Amargasaurus, as well as a few oddballs like Dicraeosaurus. The type species, D. longus was found by OC Marsh in 1878. Approximately 28 m in total length, mass estimates range from around 10 to 12 tonnes, with the torso accounting for as much as 80% of this mass.

The generic name derives from the Greek roots diplos and dokos meaning "double beam", based on the dual cheverons in its vertebrae.

I could spend a lot of time talking about posture, but as I agree with for Taylor et al (2009) for the most part, I'll direct you there, as many of my comments have already been published.

Additional information:

Key references:

Other references available in bibliography of my paper draft.

Tuesday Tetrapod: Phyrnosoma platyrhinos

Posted by tigerhawkvok on June 09, 2009 23:08 in tuesday tetrapod

Today's Tuesay Tetrapod is another California herp: Phyrnosoma platyrhinos:

< !-- Modified Flickr Code --> IMG_5815

P. platyrhinos, photographed in Death Valley, CA

The desert horned lizard, it is very similar diagnostically to P. coronatum, or the Coast Horned Lizard. It is diagnosed primarily by only one row of well-developed spikes along the sides of its body. Phyrnosomatids include the famous ability to squirt blood from their eyes as a defense mechanism, in addition to the spikes and spines around them.

As far as relationships among squamates, they are iguanians, part of the massive, ill-resolved polytomy that is Iguania. The node Phrynosomatinae (its rank varies) is possibly paraphyletic, including diverse genera from Callisaurus, Uma and Uta, and of course Phyrnosoma.

Sources:

  • Pough et al. 2004. Herpetology, 3rd edition.
  • Stebbins, RC, 2003. Western Reptiles and Amphibians, Third Edition.

Tuesday Tetrapod: Ceratotherium simum

Posted by tigerhawkvok on June 02, 2009 18:00 in tuesday tetrapod

Noticing I was a bit lacking in the mammal department, I bring to you the first mammal contestant in Tuesday's Tetrapods: Ceratotherium simum, or the White (or Square-Lipped) Rhinoceros

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C. simum

The generic name is derived from Greek keras meaning "horn" (think "ceratopsian", as in Triceratops), and therion, meaning "beast" (think "theropod", meaning beast-foot). The specific name derives from simus, meaning "flat-nosed", referring to its large square lips, clearly visible in the photo.

Rhinoceros have the interesting position of being one of only three extant perissodactyls (odd-toed ungulates), and being one of the few remaining true megafauna. Perissodactyls were once much more common (and included giants like brontotheres, and the largest land mammal on record, Indricotherium at 5.4 m / 15 tonnes), but have slowly ceded niches to artiodactyls. The perissodactyl foot structure comes from a mesaxonic foot structure, which runs the symmetry and primary weight-bearing of the foot through the third toe, and remaining toes atrophy around that axis, leading to the odd toed hoof.

Perissodactyls are a sister group to (carnivora + pholidota [pangolins]). You can view their phylogeny here.

Sources:

  • Benton 2005. Vertebrate Paleontology
  • Honolulu Zoo (Specimen photographed)

Tuesday Tetrapod: Gopherus agassizii

Posted by tigerhawkvok on May 26, 2009 21:32 in tuesday tetrapod

A quick one today — an threatened herp from right here in California, Gopherus agassizii.

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G. agassizii, from Death Valley, CA

They can survive very long times (up to one year) without access to liquid water. The desert tortoise is classified IUCN "Vulnerable", almost strictly due to human interference (habitat destruction, invasive plants, etc). They are illegal to handle or collect in the wild.

Tuesday Tetrapod: Struthio camelus

Posted by tigerhawkvok on May 19, 2009 04:04 in tuesday tetrapod

This tetrapod needs little introduction — Struthio camelus, or the ostrich.

DSCF5233

S. camelus, the ostrich. Photographed at the Honolulu Zoo, Hawai'i.

< !-- Ratites --> The largest living bird, Ratites were once a much more diverse group, including the moas. Interesting, this does not include the "Terror birds" (Phorusrhacidae), which were more closely related to falcons and such. Generally their wings are strongly reduced, terminating in a single large claw hidden beneath their feathers. You can see a good emu deconstruction over at TetZoo.

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