Monthly Archives: December 2013

A Delawarean Pterosaur: Maybe the Coolest Thing From Delaware Ever

It’s strange now to think how difficult it once was to dig up information.  Growing up, I couldn’t just sit in my family room and browse through scientific papers.  Basic research required a trip to the public library.  Serious research required a trip to the University of Delaware library.  Mostly, though, I relied on a set of c. 1960 World Book Encyclopedias I inherited from my great grandmother.  Now there’s the internet.

This is a long way of saying that there’s a lot about Delaware I can easily learn now that I had essentially no way of knowing then.

For example, I never knew there was a fossiliferous Cretaceous formation accessible about ten miles from the house I grew up in.

And I definitely never knew that pterosaur remains had been recovered from this formation.

Modern rendering of the azhdarchid pterosaur Quetzalcoatlus, courtesy of Witton & Naish 2008.

The Chesapeake and Delaware canal runs across a narrow strip of Delaware and Maryland, connecting the Delaware River to the Chesapeake Bay via the Elk River, a Chesapeake tributary.  In the 1960s and 1970s, the canal’s muddy banks were accessible, and dredged material from the canal was dumped in heaps on the canal’s north side.  The sediments along the banks and in the heaps were rich in fossils (in fact, I just learned that my mom used to go fossil hunting with my grandfather there).

In the early 1970s, a vertebra, humerus, femur, and tibia were recovered from these sediment heaps.  A 1981 paper by Baird and Galton identified these bones as pterosaur remains in part because they were “extremely insubstantial,” with a “paper-thin” outer layer and “pneumatic cavities” inside the bone.  Beyond that, though, the authors declared more specific identification of the specimens “fraught with uncertainty” — their best guess was Pteranodon.

In 1994, Bennett tentatively agreed that the bones were likely Pteranodon: “A short midcervical vertebra of a large pteranodontid (the only large short necked pterosaurs known in the Upper Cretaceous) and other pterosaur fragments are known from the Merchantville Formation (early Campanian) of Delaware (Baird and Galton, 1981). These materials are identified tentatively as Pteranodon.”

But in 2008, Averianov, Arkhangelsky, and Pervushov called the Delaware pterosaur’s identification as Pteranodon into question: “The incomplete cervical vertebra of a pterosaur from the Campanian of Delaware, United States, that was referred to Ornithocheiridae (Baird and Galton, 1981, text-fig. 2), is almost identical to specimen SGU, no. 47/104a and could have been cervical vertebra 3 of an azhdarchid.”  Ornithocheiridae, by the way, is the family that houses Pteranodon.

Now there seems to be an implicit debate: a 2010 paper by Averianov definitively identifies the Delaware remains as those of an azhdarchid, while a 2011 paper by Sullivan and Fowler attributes the remains to the family Ornithocheiridae.  I don’t know enough to take sides, but I’m rooting for an azhdarchid.

Why?

Pteranodon is fine and all — it’s impressive in its way, and certainly iconic.  But the azhdarchids were much more tremendously impressive.  Here’s a quick-hit recap of azhdarchid morphology from Witton and Naish (2008): “All azhdarchids exhibit large skulls …, elongate, cylindrical cervical vertebrae, proportionally short wings …, and elongate hindlimbs. These anatomical features, combined with the large size of some taxa, make azhdarchids one of the most striking and distinctive pterosaur groups.”  Striking and distinctive is perhaps an understatement. Alien-looking azhdarchids could reach approximately 20 feet in height, with  35-foot wingspans.  Wow.

This image just a bout sums up the ornithocheirid versus azhdarchid competition:

Pteranodon, Homo sapiens, and the azhdarchid Hatzegopteryx, courtesy of Mark Witton via Flickr.

And that’s just basic morphology.  Ecology actually bumps azhdarchids up a notch on the impressive scale.

Witton and Naish (2008) have demonstrated convincingly that azhdarchids were probably “terrestrial stalkers,” roaming field and forest on foot while snacking on “small
vertebrates and large invertebrates, possibly supplemented with fruit and carrion.”  Bear in mind that these are 20-foot-tall beasts with beaks as big as entire people — to them, we may well have been snackable “small vertebrates.”

Earlier this year, Averianov apparently challenged Witton and Naish’s terrestrial-stalking hypothesis in part because, he said, azhdarchids would have been vulnerable to predation on the ground — these mighty beasts might themselves have been T. rex snacks.  But Witton and Naish quickly responded [pdf] in another 2013 article,* noting that some azhdarchids were actually taller than the largest theropods and possessed intimidating (or weird) enough features that T. rex and its cousins likely would have sought out easier prey.  In fact, even if a tyrannosaur had targeted a large azhdarchid, the pterosaur might well have been able to hold its own.  Witton and Naish note that “azhdarchid like rostra [beaks] are dangerous weapons in some circumstances,” and they compare azhdarchids to some modern storks known “to repeatedly stab human attackers when provoked.”  (Side note: I’ve seen one of the storks referenced — the Jabiru — and it’s an impressive bird indeed.)  Not to mention that if the azhdarchid didn’t feel like fighting back, it could have used its quadrupedal-launch capabilities to flee rapidly into the air.  Again, wow.

All of which is to say that if the Delwarean pterosaur specimen is in fact an azhdarchid, it may well be the coolest thing from Delaware ever.

* If you don’t want to tackle the paper itself, you can read more about these 2013 azhdarchid papers in this post on Darren Naish’s tetrapod zoology blog.  Given their disagreements with Averianov over azhdarchids, I wonder how Witton and Naish would classify the Delaware pterosaur?

References:

D. Baird and P. M. Galton (1981) Pterosaur Bones from the Upper Cretaceous of Delaware.  J. Vertebr. Paleontol. 1 (1), 67–71.

Bennett, C. (1994) Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea): University of Kansas Museum of Natural, Occasional Papers, n. 169, p. 1-70. [Link]

Averianov, A., Arkhangelsky, M., and Pervushov, E. (2008) A New Late Cretaceous Azhdarchid (Pterosauria, Azhdarchidae) from the Volga Region”. Paleontological Journal 42 (6): 634–642. doi:10.1134/S0031030108060099 [Link]

Witton, M. and Naish, D. (2008) A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. PLoS ONE 3(5): e2271. doi:10.1371/journal.pone.0002271.

Averianov, A. (2010) The osteology of Azhdarcho lancicollis Nessov, 1984 (Pterosauria, Azhdarchidae) from the Late Cretaceous of Uzbekistan. Proceedings of the Zoological Institute RAS 314, 264–317 [Link]

Averianov, A. (2013) Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae). Paleontological Journal 47:203-209.
doi: http://dx.doi.org/10.1134/S0031030113020020

Witton, M. and Naish, D. (2013) Azhdarchid pterosaurs: water-trawling pelican mimics or “terrestrial stalkers”? Acta Palaeontologica Polonica doi: http://dx.doi.org/10.4202/app.00005.2013 [link]

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Clouded Leopards: Modern Semi-Sabertooth Cats

When I read Brian Switek’s excellent longform piece “Once and future cats” — about the history of the sabertooth cats — one passage jumped out at me:

While the future course of evolution is unknowable, there is a possibility that we are only in a short lull between sabercats. Long killing fangs have evolved so many times in the past 20 million years that there’s every reason to believe that a newly derived sabercat might evolve again. In fact, Per Christiansen, a zoologist at the University of Aalborg in Denmark, argued in 2012 that the clouded leopard — a mid-sized cat that prowls the tropical forests of Indonesia — has relatively elongated teeth and shows a great deal of similarity to true sabercats. Given a few million years, might the saber-toothed descendants of today’s clouded leopards slash at the throats of mid-sized herbivores of the future?

There’s something called a “clouded leopard” that’s alive right now but very similar to sabercats?  Intrigued, I did some homework.  Then I kept reading.

Let’s start at the very beginning — what is a clouded leopard?  The name “clouded leopard” actually refers to two “somethings,” separate species of the genus Neofelis.  Both are midsized, southeast Asian cats as Switek says, both are listed as “vulnerable” — a step short of endangered — and both are covered with gorgeous cloud-shaped markings.

But it’s not the markings that really impress — it’s the teeth.

The formidable teeth of the clouded leopard, courtesy of Eric Kilby via flickr.

Modern “big cats” — lions, tigers, jaguars &c. — generally have upper canines that measure less than 20% of the length of their skulls.  But not the clouded leopard.  Neofelis nebulosa has an average ratio of 23%, with some individuals possessing upper canines that measure a full 25% of the length of their skull.  This ratio is an “outlier” among modern cats — an indicator of very long teeth indeed.  It doesn’t approach the famed sabertooth cat Smilodon, whose impressive canines were a full 50% of the length of their skull, but it’s impressive nonetheless.

(As Smilodon enters the conversation, it should be noted that felids are generally broken down into three major “subfamilies”: the true sabertooth cats like Smilodon, all classified as machairodontines, are all extinct; the clouded leopard is a pantherine like many big cats; while housecats and some big cats like mountain lions and cheetahs are felines.  Now back to the narrative.)

The clouded leopard’s impressive teeth led the previously mentioned cat-skull specialist Per Christiansen to publish a paper back in 2006 titled “Sabertooth Characters in the Clouded Leopard (Neofelis nebulosa Griffiths 1821).”  Christiansen found that long teeth weren’t the only morphological outlier among the clouded leopard’s skull dimensions.  For one thing, the clouded leopard’s face slopes back more like Smilodon‘s than a lion’s, allowing for a wider bite.  And that wider bite showed up even more clearly when Christiansen looked at just how far a clouded leopard can open its jaw: he found that the clouded leopard is capable of achieving a “maximum gape” of almost 90 degrees.  This is not only “the largest gape of any extant carnivoran” but also “a value normally considered feasible in extinct sabertooths only.”

In sum, the clouded leopard is not just “divergent and peculiar,” Christiansen said.  Instead, his “analysis demonstrates that several of its peculiar features are actually characters present in, and in some cases considered characteristic of, sabertooth predators exclusively, and thus simply assumed to be absent in extant animals.”

The natural question is why — why does the clouded leopard alone among modern cats possess the peculiar combination of extra-long teeth and extra-wide gape?  It’s hard to know for sure, given how little we know about the ecology of clouded leopards.  Here’s what Christiansen proposed (edited lightly):

[The clouded leopard] is known to feed on a variety of arboreal mammals, such as monkeys and lorises, but also kills much larger prey, such as bearded pigs, hog deer, and muntjak, which either rival or exceed the body mass of Neofelis, demonstrating its ability to subdue large prey. There is one potential difference between the killing mode of Neofelis and other large felids, however. Large felids, such as the puma and the pantherines, often kill small prey with a powerful nape bite, but usually subdue large prey with a suffocating throat bite.  In contrast, available evidence suggests that Neofelis kills even large prey and each other with a powerful nape bite. It may be that its enlarged gape and hypertrophied canines are an adaptation for nape killing of large prey, but this is, at present, speculation.

This “powerful nape bite” has been proposed as the evolutionary driver of “enlarged gape and hypertrophied canines” in past creatures like sabertooth cats.  When competition is fierce, a predator’s ability to kill quickly — for example, by using huge teeth to puncture or tear out a throat as opposed to slowly strangling prey with a vise-like bite — provides a clear advantage.

That said, the clouded leopard does not appear to live in a particularly competitive environment for predators.  Why the long teeth, then?

Well, Christiansen has an answer to that too: “potentially the Neofelis lineage may have evolved a number of primitive sabertooth morphological adaptations soon after the split from the pantherine lineage, but never became specialized owing to a lack of competition from other carnivores in the dense forest habitats.”  In other words, if I have this right, several million years ago the clouded leopard diverged from the other big cats.  At this point, there was intense competition that drove the clouded leopard into rapid sabertooth-ification.  Then, when the clouded leopard came to fill a sufficiently unique ecological niche, competition died down and evolutionary change slowed down.  The clouded leopard simply stayed semi-sabertoothed and carried on to today.

References:

Christiansen P (2006) Sabertooth characters in the clouded leopard (Neofelis nebulosa Griffiths, 1821). J Morphol 267: 1186–1198. doi: 10.1002/jmor.10468.

Christiansen P (2008) Evolution of Skull and Mandible Shape in Cats (Carnivora: Felidae). PLoS ONE 3(7): e2807. doi: 10.1371/journal.pone.0002807.

Christiansen, P., Kitchener, A.C. (2010) A neotype of the clouded leopard (Neofelis nebulosa Griffith 1821). Mammal. Biol. doi: 10.1016/j.mambio.2010.05.002.

King, Leigha M. (2012) Phylogeny of Panthera, Including P. atrox, Based on Cranialmandibular Characters. Electronic Theses and Dissertations. Paper 1444. http://dc.etsu.edu/etd/1444.

Orb-weaving Spiders Eat Plant Pollen (And Their Own Webs)

We all know spiders as crafty predators, building sticky webs to snare unsuspecting insects as well as the occasional frog, mouse, lizard, or bird.  Then, as I learned it, they’ll wrap up their captured prey, inject it with digestive enzymes, and slurp up the resulting product.

Just look at this spider: creepy, and definitely bloodthirsty, right?

Araneus diadematus, courtesy of Frode Inge Helland via wikimedia commons.

Well, that’s what I always thought, anyway.  It turns out, though, that some spiders (like the orb-weaver A. diadematus pictured above, for one) eat more than just other animals.

Herbivory in Spiders: The Importance of Pollen for Orb-Weavers,” an evocatively named article recently published in PLOS ONE, explains that some spiders capture pollen in their webs, digest it externally, and slurp it up to the tune of 25% of their diets.  A side salad with every slab of steak, so to speak.  How genteel.  Anyway, the article shows convincingly that spiders’ pollen consumption is not just a fluke — through an array of experiments, its authors provide “direct proof that orb-weaving spiders (Araneidae) indeed feed on pollen captured in the sticky spirals of their webs and incorporate this into their body tissue, even when prey is available.”

The article is good reading.  In fact, I can’t resist sharing another fascinating detail of spider diets: “Orb-weaving spiders (Araneidae) take down and eat their webs at regular intervals, which enables them to recycle the silk proteins efficiently.”  I am happy I now know this, and I hope you are too.

I’ll close with the article’s abstract and leave it to you to click through and read for yourself if you like:

Orb-weaving spiders (Araneidae) are commonly regarded as generalist insect predators but resources provided by plants such as pollen may be an important dietary supplementation. Their webs snare insect prey, but can also trap aerial plankton like pollen and fungal spores. When recycling their orb webs, the spiders may therefore also feed on adhering pollen grains or fungal spores via extraoral digestion. In this study we measured stable isotope ratios in the bodies of two araneid species (Aculepeira ceropegia and Araneus diadematus), their potential prey and pollen to determine the relative contribution of pollen to their diet. We found that about 25% of juvenile orb-weaving spiders’ diet consisted of pollen, the other 75% of flying insects, mainly small dipterans and hymenopterans. The pollen grains in our study were too large to be taken up accidentally by the spiders and had first to be digested extraorally by enzymes in an active act of consumption. Therefore, pollen can be seen as a substantial component of the spiders’ diet. This finding suggests that these spiders need to be classified as omnivores rather than pure carnivores.

Reference:

Eggs B, Sanders D (2013) Herbivory in Spiders: The Importance of Pollen for Orb-Weavers. PLoS ONE 8(11): e82637. doi:10.1371/journal.pone.0082637

Diplodocus For Sale – Sold! – And Going to Copenhagen

I previously worried about a rare Diplodocus skeleton going up for auction.  Then I worried again when it was sold.

There was good reason for my worries — unique specimens enter private hands all the time and are lost to science.  But it turns out that this particular Diplodocus will be well housed after all.  It’s going to Copenhagen as a centerpiece of an impressive-looking Natural History Museum of Denmark, scheduled to open in 2018.

If you find yourself in Copenhagen five years from now, be sure to pay the museum and its Diplodocus a visit.

Snowy Owls Everywhere!

Everyone loves snowy owls, right?

A snowy owl in Canada, courtesy of David Syzdek via wikimedia commons.

A bright white, two-foot-tall, diurnal owl possessing piercing yellow eyes and a 4.5 foot wingspan, Bubo scandiacus is the very definition of a charismatic megafauna.  The Cornell Lab of Ornithology says that “[t]he regal Snowy Owl is one of the few birds that can get even non-birders to come out for a look.”  And, in fact, a snowy owl sighting at Aquidneck Island’s Sachuest Point National Wildlife Refuge drew me, my wife, our then-11-month-old, and my parents out to peer through binoculars on a frigid January day about two years ago, where, yes, we saw one of these impressive birds.

Two years ago, a single snowy owl in Rhode Island was a rarity.  This year, though, there have apparently been 15 sightings here.  And some down in Delaware, where “they’re just excited the owls are there.”  And some “already reaching North Carolina and Bermuda!”  In New York, airport officials even shot three of them (big bird plus planes equals potential disaster — I guess not everyone loves snowy owls after all) before deciding to trap them instead.

Why are there so many snowy owls along the east coast of the United States this year?  Some say a banner year for Arctic lemmings (a favorite snowy-owl snack) has led to lots of breeding success for the owls — and now lots of offspring dispersing across great distances as a result of competition for food.

But, as reported in USA Today, New Jersey Audubon’s Pete Dunne says the answer might be more complicated.  Maybe there were so few Arctic lemmings this year that famished owls are flying farther afield for food (though this seems less likely given that apparently most southward-migrating owls are young).  Or maybe melting polar ice is displacing female owls’ breeding grounds, forcing the entire snowy-owl operation further south, beginning even before birth.

Dunne says this last point is speculation.  But still, one wonders — lemmings or no lemmings, things certainly are changing in the Arctic.  And now here snowy owls are in Rhode Island.

Mystery Mushroom

My daughter found this mushroom (at least, I assume it’s a mushroom) while we were picking out our Christmas tree.

IMG_0076

Here’s another look.

IMG_0077

I can’t figure out what it is.  Russula brevipes?  Doesn’t seem quite right.

But in trying to figure it out, I did enjoy browsing this U.S. Forest Service Field Guide to Common Macrofungi in Eastern Forests and Their Ecosystem Functions” [pdf] and this University of Wisconsin, Green Bay guide to Biodiversity of Macrofungi in Northern Door County, WI.  Even a casual glance through these guides is a great reminder of how weirdly interesting fungi are — and, for me, how little I know about them.

So if anyone knows what the fungus pictured above is, please let me know!  It came from a spot very near the coast of the Narragansett Bay.

Therizinosaurs Were Bizarre and Probably Had Beaks

Long-necked, gigantic-clawed, feathered, herbivorous T. rex cousins, therizinosaurs were some of the weirdest creatures ever to walk the earth.  A study published in PNAS earlier this week offers an explanation for how and why these beasts developed beaks.

A sketch of E. andrewsi courtesy of ArthurWeasley via wikimedia commons.

At the ends of their usually long necks, therizinosaurs had rather small heads.  One particularly well-preserved skull of the therizinosaur Erlikosaurus andrewsi lacked teeth at the front of its jaw.  This toothless portion seemed to suggest that Erlikosaurus likely featured a beak.  (And a beak would not be surprising given that other dinosaur species from the same geologic era probably had beaks too — ceratopsians, for instance.)  More specifically, Erlikosaurus‘s partial lack of teeth suggests that the toothless portion of the jaw was likely covered with a rhamphotheca, the keratinous sheath that makes up the exterior of most beaks.  But what benefit would a beak bring to a bizarre creature like a therizinosaur?

University of Bristol paleontologist Emily Rayfield and some of her colleagues used the Erlikosaurus skull to answer that question.  They scanned the skull to create a very precise digital model, then modified that model in different ways — adding a modest beak in one, adding a large beak in another, and adding teeth to the front of the jaw in a third.  They then used the model in its original and modified forms to simulate the stresses caused by biting.  They found that a beak would have helped Erlikosaurus harvest tough plants:

Evidence … suggests that the tip of the snout (i.e., edentulous
premaxilla plus overlying rhamphotheca) was used as the main
device to procure and process food. The presence of a keratinous
rhamphotheca in this region would have helped to dissipate and
absorb stress and strain while making the snout less susceptible
to bending and displacement. As an ever-growing material,
keratin has the advantage over bone that it is able to rapidly
repair fractures and has a slower crack propagation rate, thus
reducing the risk of constant damage.

So there’s the answer: beaks are useful for eating.

This might not seem surprising, but given some context it is — at least somewhat.  Previously, it had been thought that beaks evolved as lighter alternatives to teeth, a feature valuable to flying animals or those in the process of developing flight.  This new paper calls that view into question.  (In fact, the paper notes that “a more extensive rhamphotheca would actually have increased the weight (mass) of the cranium” in Erlikosaurus.)  A press-release quote from the paper’s lead author Stephan Lautenschlager sums the issue up nicely:

“It has classically been assumed that beaks evolved to replace teeth and thus save weight, as a requirement for the evolution of flight. Our results, however, indicate that keratin beaks were in fact beneficial to enhance the stability of the skull during biting and feeding.”

Of course that doesn’t mean beak necessarily evolved in birds for the same purpose, but it does add some complexity to the question of why beaks exist.