A Sampling of ScienceBlogs

First up, here is a smattering of odd odontocetes from Tetrapod Zoology.

Then, Pharyngula has some genetic research on cetacean limb formation here.

Finally, Dr. Tom Holtz from the University of Maryland's pet project, Dinosaur, has here compiled just this season's entries into his archosaurian compendium.

Embryology of a cetacean; of note is the development of the hind limbs/fins in the first three stages, which then atrophy and disappear in the last; the genetic component for the development of legs is still present, but inactivated, and this is essentially conclusive evidence pointing to the terrestrial origin of whales, dolphins, and porpoises

Giant Lanky Rhinoceros

Baluchitherium "osborni"

National Museum of Natural History, Smithsonian Institution, Washington, DC

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This monstrous mammal reached the height of a giraffe and the girth of a mammoth, though it was a relative of the rhino. Convergence in tooth structures with grazers of trees shows the formidable front teeth (partially obscured in the photo) were for stripping leaves from twigs. It should be noted that there are some taxonomic problems with this genus. It is currently properly known as Paraceratherium, though Indricotherium is also commonly used. As per usual, a life restoration follows; it appears as a large, lanky rhino.

Crow Shark

Squalicorax

Cretaceous formation of Alabama

Hell Pig

Archaeotherium
National Museum of Natural History, Smithsonian Institution, Washington DC

This is a type of entelodont, a distant relative of modern pigs. It's odd teeth, though similar to pigs, indicate scavenging on meat playing a larger part of the diet. Though one might not think a pig is the scariest thing in the world, this animal could have looked you in the eye, with a shoulder height of about two meters. They were the apex predators of around the Oligocene-Miocene boundary across the northern hemisphere.

Roofed Lizard

Stegosaurus
National Museum of Natural History, Smithsonian Institution, Washington DC

I'm sure everyone who might read this knows what this thermoregulating, Jurassic ornithischian knows what this looks like, but here goes:

Whorl-tooth

Helicoprion
National Museum of Natural History, Smithsonian Institution, Washington DC

Though it is not clear by looking at it, this is perhaps one of the most interesting vertebrate dentitions. It is actually the teeth of the lower jaw of an ancient shark that lived from 280 to 225 million years ago. The entire set of lower teeth is visible. How it captured prey with this unique structure is not understood. Here is what it would have looked like in life:

And Now, For Something a Bit Older

Triceratops horridus

National Museum of Natural History, Smithsonian Institution

Miocene Anapsid Scute

From Brownie's Beach, Chesapeake Beach, MD; Miocene Epoch

Marine Mammal Warehouse at the Garber Facility

The Office

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This is taken from my little nook in the paleontology curator's office. My research subject is the little thing in the bottom left, which I'll have a more detailed photo of later. It is a piece of cetacean rib with evidence of a shark bite in it. The mission will be to figure out the taxa of whale and shark.

End of the Semester

Carcharodon megalodon

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Today was the day of my last final. I'll actually be heading to the Calvert Marine Museum on Monday to decide on my project. That means I'll be seeing this reconstruction of the extinct giant white shark on a daily basis. This is pretty much the pride and joy of the museum and Calvert Cliffs, given the abundance of teeth found. You probably would not have wanted to have approached this close when it was alive though.

Monster Mouth

Dunkleosteus terrelli

Members of Order Arthrodira, meaning joint-necked, composed the majority of the Class Placodermi and, for that reason, are the most familiar to science. Truly the top carnivores of their time, aquatic monsters such as Dunkleosteus terrelli filled the role of the largest sharks or even crocodiles in our time. They are named arthrodires due to a peculiar craniovertebral joint behind the skull, allowing the chondrocranium to rise as the splanchnocranium drops, resulting in a monstrous maw (Linzey 2001, Murphy 2004). Also unique amongst the arthrodires is the presence of gnathals, a structure performing the same function as teeth in more advanced gnathostomes. This means that teeth arose at least twice, convergently, given that placoderms have no living relatives and some arthrodires have very unique gnathal structure (Smith and Johanson 2003, Stokstad 2003).

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Major differences, however, are structure and replacement methods. In the latter, the general opinion is that arthrodires had no replacement, unlike most fish which are polyphyodonts, though that has been recently questioned (Smith and Johanson 2003). Instead of many small teeth for capturing or rending prey, which other fishes of the time had, the arthrodires had what can be likened to broad axes in their mouths rather than daggers. These semidentine blades, supragnathals on top and infragnathals below, had a biting power surpassed only by archosauromorphs while being able to open with lightning speed (Stokstad 2003). This creates a truly frightening picture of arthrodires like Dunkleosteus. Not only did the up to thirty foot long creature have a bite surpassing anything in the oceans today, but its quickly opening gape created a pressure gradient causing suction, meaning the smallest and swiftest of prey had as much to fear as other heavily armored arthrodires.

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Because of its size, it is supposed Dunkleosteus was an ambush predator, not unlike crocodilians. However, unlikely evidence seems to point to otherwise. A specimen was recovered with intact skin cells, bringing attention to color as well as behavior. Black and red pigments were recovered from the dorsum, while the venter was covered in a silvery, reflection layer (Waggoner 2000, Linzey 2001). This could be a shared trait, similar to the iridocytes found in modern fish, gleaming from guanine crystals. Determining the first instances of color would be crucial in determining whether this is a homology or homoplasy. This discovery had two major implications. The first was that color vision could have been around at the time, given that Dunkleosteus would have blended in with the reddish sediment if viewed from above and looked similar to the surface if viewed from the sea floor. It would have needed some visual camouflage from members of its own species, given little else could have done it harm and gouges matching gnathals from the same species have been found on their four-foot-wide armored heads (Waggoner 2000). The second point is that if Dunkleosteus was a benthic, ambush predator, it would not have evolved ventral camouflage. Needing camouflage on the venter means if was viewed enough from the bottom, and was vulnerable, to be selected for. This indicates that arthrodires are much more active predators that what was once thought, swimming as much in the middle of the water column as on the bottom of the sea.

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Arthrodires had a range covering most seas of the Devonian, from species of the genera Confractamnis, Atlatuidosteus, and Doseyosletts of Queensland, Australia, to species in Morocco (Young 2005). Individuals have also been found in Scotland, such as Cosmacanthus, which was initially confused with an acanthodian (Newman 2004). This means that placoderms have an interesting zoogeography, their total range is sub-Equatorial, from Euramerica to Australia. However, there appears to be no evidence of placoderms unearthed from Arabia or India, lands that are between Euramerica and Australia, though areas further south in what would become North Africa have fossils. Therefore, an argument for a Gondwanan distribution could be made, though this would be tenuous. Arthrodire placoderms were apex predators, filling the niche of sharks today (Young 2005).

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Linzey, D. 2001. Gnathostome Fishes. Pages 91-128. Vertebrate Biology. McGraw Hill, New York.

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Murphy, DC. 2006. “Devonian Times.” Retrieved 05 Apr 2008 from http://www.devoniantimes.org/index.html.

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Smith, MM & Z Johanson. 2003. “Separate Evolutionary Origins of Teeth from Evidence in Fossil Jawed Vertebrates.” Science, Vol. 299 (5610), 1235.

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Stokstad, E. 2003. “Primitive Jawed Fishes had Teeth of Their Own Design.” Science, Vol. 299 (5610), 1164.

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Waggoner, B. 2000. “Introduction to the Placodermi.” Retrieved 29 Mar 2008 from http://www.ucmp.berkeley.edu/vertebrates/basalfish/placodermi.html.

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Young, GC. 2005. “A New Middle Devonian Arthrodire (Placoderm Fish) from
the Broken River Area, Queensland.” Records of the Australian Museum, Vol. 57
(2), 211-220.

Popular Dissent

It is an odd thing that evolution is disputed so much. Physics and chemistry do not have nearly so much dissent, especially from a religious or organized group. Astronomy and geology have had some problems, but they have been overlooked by the masses. For instance, the Coperinican heliocentric solar system spat on the belief that the Earth is the center of the Universe. In geology, it is not hotly debated that the formation of canyons and mountains must take place on the scale of millions of years. Perhaps it is because those things seem so distance, impersonal, and dead to most people to be relevant. Biology, on the other hand, takes the brunt of the populace's largely misinformed critiques.

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The reason why, as I alluded to above, is that biology is something personal both to the individual and to humans as living beings. Sure, most people have a general idea about how the human body works, with basic structures, systems, and so forth. However, that limited knowledge, without thorough, or sometimes even remedial, knowledge of the mechanisms and history behind them adds a sense of mystery and awe. That cannot be argued with. Biologists working for decades are probably still as enraptured with life as ever. The layman, however, seems to have a special, dual-pronged belief about the human body that refutes evolution before any scientist can explain. The first is the religiosity of the United States, in which includes the tenet that people are on a special level compared to the rest of the material of the universe. We are too complex, they might say, to have not been created by an outside force. The argument from incredulity is the basis for the intelligent design movement, or as some have called it, 'creationism dressed up in a cheap tuxedo.'

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The second idea about life is almost opposite to the first. It is that life is simple. Everyone has seen nature shows and watches Discovery Channel and fancies themselves knowledgeable on life. However, many creationists and intelligent design proponents laugh at the idea of Australopithecus, jesting that it appears to be some kind of joke based on the old 'Planet of the Apes' movies. Obviously, they say, this is a farce. They think they know how evolution occurs - which is usually completely random events in a progressive fashion, as they would understand it. Based on that limited, erroneous information, of course evolution is a fraud. The problem is that it is so much more complex than that. The genetic basis of mutations in the chromosome and genome up to climatic changes and ecology are all crucial to evolutionary theory.

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Personal incredulity, therefore, actually has two bases. The first is that the body is too complex to have come about naturally, invoking a deity. The second is that life is so simple that anyone can understand it, making everyone a personal authority on it. It cannot be overstated that evolution by natural selection can be simply stated as genetic change in a population over time, but there are many, many facets of evolutionary study that such a maxim barely does it justice. The fact of the matter is that evolution is supported so thoroughly by science that it should not even be a question. Sure, there is debate about punctuated equilibrium versus gradualism, but that is one aspect of a massively supported theory.

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Consider string theory, a hypothesis in physics which I will not even pretend to understand. There is no public outcry, however, about string theory appearing in school texts. Perhaps it is because it does not speak to the very humanity of the individual that he or she thinks they understand. It certainly does not include any tenets of religion, which may be why evolution is a prime target. Both are complex theories. The problem is with perceived understanding, which the general population claims to have much of regarding biology and little regarding physics. In reality, both are probably rather low. A little less arrogant anthrocentrism may go far in public understanding of evolution, though it will be more difficult to convince people that they may know less than they really do on their own histories, complexities, and indeed life as a whole. Evolution is not as simple as they think.

The Little Placoderm Who Could

Bothriolepis

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When one considers the placoderms, the image of Dunkleosteus terrelli probably comes to mind. However, the class is much more diverse than the arthrodires, with a myriad of body forms arising over the group’s fifty million year run. Bothriolepis is a good example of this. Though they share armor plating, the similarities between these general seem to end there. Size, for instance, provides a stark contrast. Dunkleosteus grew to between twenty and thirty feet long, with a head up to four feet wide, whereas the diminutive Bothriolepis had a head only four inches wide (Waggoner, 2000).

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Bothriolepis lacks the craniovertebral joint of the arthrodires that allowed its chondrocranium to rise as its splanchnocranium drops. However, this may have allowed for a larger braincase in this benthic creature (Young, 1984). This genus, along with the rest of the placoderms, went extinct in the Mississippian Period with no modern relatives. The reason for placoderm extinction, especially when members of Class Chondrichthyes survive today, is mysterious.
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Young, G.C. (1984). “Reconstruction of the Jaws and Braincase in the Devonian Placoderm Fish, Bothriolepis .” Palaeontology, Vol. 27 (3), 635-661.
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Waggoner, B. (2000). “Introduction to the Placodermi.” Retrieved 29 Mar 2008 from http://www.ucmp.berkeley.edu/vertebrates/basalfish/placodermi.html.

To Be or Not to Be ... an Acanthodian

Groenlandaspis disjectus

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Found in the Upper Devonian (~365 million years ago) of Scotland, Cosmacanthus malcolmsoni caused a bit of confusion when it was unearthed in the mid-1800's. It had a peculiar spine that seemed to place it with the members of Class Acanthodia, which all sported a spine structure on their dorsum and venter that had membranous connections to the body mass. However, upon further comparison, the difference between C. malcolmsoni and acanthodians widened, and it was placed in Class Placodermi. Newman (2004) reviewed this taxonomic revision and found it to be better, seeing as it is similar spinal plates to, and was nearby, the known placoderm Groenlandaspis disjectus.

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Newman, M.J. (2004). “A Systematic Review of the Placoderm Genus Cosmacanthus and a Description of Acanthodian Remains from the Upper Devonian of Scotland.” Paleontology, Vol. 48 (5), 1111-1116.

Was It Ever Safe to Go in the Water?

Guarinisuchus munizi

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In what I'm sure will be a long line of blogging on ScienceBlogs posts as well as on peer reviewed research - and sometimes both - here is a summary of a post from Laelaps on a new crocodilian, G. munizi. After the K-T extinction that finished off the non-avian dinosaurs, especially the monstrous aquatic mosasaurs, the three-meter long archosauromorph fluorished. These sauropsids have a Gondwanan distribution, most likely moving from North Africa to the (then nearby) South America. G. munizi would certainly have made a snack out of the other major group filling the space left by the absent dinosaurs - mammals.

What Big Teeth You Have

Smilodon populator

An interesting piece of research published recently describes what it perceives to be the point of such long canine teeth in Smilodon and members of Nimravidae. Initially conceived to rend wounds into their prey, it has been shown that such force would snap those teeth right off. New tests propose a stabbing motion. Whether mainly for slicing or stabbing, the awe at this spectacularly singular dentition remains.

Introductions

The point of this blog, at its inception, is to chronicle experiences while partaking in a research internship with the Calvert Marine Museum's paleontology department. However, that is not to say other material will not appear here, or that were will be regular upkeep of this space. Expecting greatness from this piece of the interwebs is certainly setting oneself up for disappointment. For a random diversion, story, photo, or link, this page might be something of a useful timekiller. Hey, one might even learn a thing or two. No promises.