Sunday, March 30, 2014

Megaherbivore Multiplier Effect: Maybe We Should Not Get So Excited About Giant Herbivorous Dinosaurs Coexisting


Ok for this post I want to get back to the terrestrial realm, although I do have a load of posts on aquatic stuff planned, and talk about some ideas in ecology/evolution that may have gone unnoticed in paleo circles with some pertinent thoughts to dinosaur niche partitioning. Why would ecology papers go unnoticed in paleontology? Well because Nanuqasaurus, and umm Cambrian filter feeding invertebrates, and Cosmos was on TV and creationists got all butt-hurt about it... No really it is important for paleontology to stay abreast with ecology/evolutionary theory because if you accept that the present is the key to the past then maybe you should keep your mind open to all avenues of thought and guard against a myopic view of the history of life.

Now dinosaurian niche partitioning has been a rather en vogue avenue of study with regards to dinosaur paleoecology.  It is an elegant and, with morphometrics, quantitative way to potentially explain how such large animals, orders of magnitude larger than current land mammals, coexisted in chunks of land often times significantly smaller than contemporary continents (higher eustatic sea levels in Mesozoic). The skull ecomorphology paper on late Cretaceous Albertan herbivores by Mallon and Anderson (2013) which I talked about here (although I have changed my views a bit as noted in post) might be good review and also the various papers on sauropod skull differences/niche partitioning you can find on the web/blogs etc etc may be useful. What these papers suggest is that through niche partitioning, resources can be in a way divvied up allowing situations like we see in Cretaceous Laramidia or the late Jurassic Morisson formation with multiple multi-tonne taxa coexisting. Through character displacement, species- especially closely related and/or morphologically similar ones -that might compete for food, space, resources will tend to diverge more and more from each other where their ranges over lap. Sauropods might have differing neck lengths to feed at different heights or perhaps have stronger jaws/teeth to handle rougher forage (i.e. Camarasaurus) versus weaker slender jawed taxa (diplodocids). Ornithischians coexisting on Laramidia are construed to be high to mid browsers (hadrosaurs), mid level browsers (ceratopsids), or low level grazers (ankylosaurs). But all in all this partitioning of resources is construed as a necessary corollary of the crucible of evolution- competition - as the guiding light that allowed such a diverse Mesozoic bestiary to coexist without overwhelming the resources.


But how secure are we in positing competition as the engine that drove these adaptations towards niche partitioning in dinosaur communities?

I want to direct your attention to an article Competition May Not Be the Driving Force of Species Diversity After All, which suggests an alternative take on the evolution of ecological diversity. The article, more or less a summary of several papers by Joseph Tobias of Oxford University, calls into question the seeming ubiquity of character displacement driven by competition as the primary impetus towards diversity. Looking at the natural and evolutionary histories of species often interpreted as textbook examples of character displacement driven by competition Tobias found the evidence lacking in a majority of these cases. Instead, Tobias offers, species tend to diverge- with or without competition -given enough time to evolve. Looking at ovenbirds, a new world tropical bird family, Tobias performed a rather exhaustive study of bill shapes. Although he found that the species that lived together had the most divergent bills, as predicted with classic Darwinian competition, when the evolutionary history of these cohabiting birds was taken into account the signal for an evolutionary bump due to competition was lacking. Instead the ovenbirds that lived in the same environment also had the longest evolutionary histories. It was evolution over time and in isolation, allopatric speciation, that best explained the signal of species diversity in ovenbirds. That species which cohabited had the longest evolutionary histories made sense- they had enough time to evolve on their own unique evolutionary trajectories- that ultimately allowed them to effectively partition resources when their ranges once again overlapped after isolation.

To study the role of competition in evolution, Joseph Tobias and collaborators mapped out the evolutionary relationships and variation in beak size among 350 lineages of ovenbirds. Image: Joseph A. Tobias and D. Seddon
I should clarify Tobias' work by pointing out that he maintains character displacement does occur- it has just been overstated by researchers. Allopatric speciation and then later cohabitation with niche partitioning is the more common scenario Tobias suggests. Controversial for sure, but very interesting and pertinent to dinosaur speciation/character displacement.

On more of a cultural note ( I do have a background in anthro after all) it does make sense for biologists to perhaps foster a bit of bias towards competition as being a chief catalyst towards diversity. Competition is very Darwinian, competition is a very masculine, and competition is very western and often times intimately associated with capitalism (social Darwinism). And let's face it, biology and science is still very masculine and western dominated. Of course scientists imagine that they are above social biases and cultural leanings, but I beg to differ. We are all cultural animals and bring some amount of baggage with us into any endeavor, no matter how rigorous, we pursue.

Ok now with those thoughts in mind I want to direct you to a recent paper on Plos One: Reconstructing Grazer Assemblages for Protected Area Restoration (March 2013). You should go read it but what these researchers were looking at is the most optimal way to recover successful and complete herbivore guilds on a managed, but depauperate, African range. What is critical is that they looked at the question from the lens of size classes, competition, and facilitatory effects. And basically what they found was that competition inhibited a high diversity of species that occupied the same general size cluster- which plays into what is fairly well established in terms of the link between herbivore and digestive efficiency, optimal grazing sites etc etc. But what was most critical in terms of stabilizing the whole system and allowing for maximum diversity, sustainability, and health of all size classes of herbivores was what they referred to as the facilitatory effects of large megaherbivores such as rhinos, hippos, and elephants. Basically the movements and feeding envelopes of these megaherbivores enhanced pasture, broke up woody debris, altered fire regimes, and created pathways that benefitted all the players in a highly disproportionate manner.

Venter et al. 2014. Plos One


"... the lack of large grazers creates an ecosystem devoid of facilitatory effects which in turn leads to an ecosystem which is unable to maintain its herbivore assemblage structure."

Hopefully you can see that the two examples to the far right with abundant megaherbivores, show the most diversity and balance between all the size guilds. It might at first seem counterintuitive but a healthier, more stable system is the one with abundant and diverse megaherbivores.

I like to call this phenomena the megaherbivore multiplier effect and if you start to look at where you see megaherbivores today guess what you see generally- more megaherbivores - as well as more small and medium sized herbivores. African savanna- large herbivores and all sorts of small, medium, and large guys. In India places like Kaziranga park host Indian elephants, Indian one-horned rhinos, wild water buffalo,  gaur, sambar, swamp deer, Indian muntjac, wild boar, hog deer. You do not need to go very far back into the Pleistocene to see that this pattern of abundant and diverse megaherbivores with complete guilds of various sized herbivores was the rule rather than the exception. Now you might be thinking well that is just because those systems are productive enough to support a diverse assemblage... But even in semiarid habitats such as in the Namib and Kalahari deserts there are more abundant and diverse large herbivores- including elephants, rhinos, and giraffes as well as smaller guys -found there than in say a place like the Mojave desert. At the other extreme let's compare rain forests. West African rain forests are heavily modified by forest elephants which are pivotal engineers of open bai habitats which provide food/habitat/mineral resources for forest buffalo, lowland gorilla, giant forest hog, red-river hog, and bongo among others. Contrast that situation with the depauperate large herbivore fauna of south/central American rain forests- what do you have... a couple of tapirs, some peccaries, some rodents and a couple of deer? But chances are you will not see much in the way of large herbivore activity in south American rain forests if you go there. Just loads of leaf-cutter ants.

Dzanga Bai
Ok so now back to the dinosaur dilemma where multiple mega ton species are stacked on top of each other in a seemingly untenable manner.

But the dinosaurs were sooooo much bigger- does this comparison really hold true for berbivores several orders of magnitude larger?

True but bear in mind that dinosaur reproductive strategy was a lot different than large mammalian reproductive strategy. At any one time in a dinosaur population there would be gazillions of newborn/hatchlings running around, one year olds, two years olds, three year olds from previous breeding cycles..... and then a bunch of promiscuous teenage dinos making babies even before their skeletons were ossified and paying no heed at all to responsible family planning. And then maybe just a couple of old stodgy, weather-beaten adults talking about the good ol' days. It was a live fast die young strategy and for the most part seems to have worked for dinos. More importantly, and diverging strongly from mammals, is that the average size of a dinosaur would be a lot smaller than the maximum adult size that could be reached. The mean was brought down quite a bit. Which is why whenever I see a herd of fully mature ceratopsids/sauropods in movies/pictures, with no variety in size classes, I throw up in my mouth just a little bit... Look at the range of sizes in a population of say nile crocodiles, this gives a better view, in the broadest strokes, of how these populations may have varied in size. Again contrast with large mammals, where small broods and intensive natal care via mothers milk brings up baby quickly to adult size.

Ok but where are all the small and medium dinosaur herbivore species? Many locations show really small species and then really big species- but few in betweeners?

Two points here:

1) The notion of dinosaurs acting as various ecological species- ontogenetic species -throughout their growth trajectories has gained considerable traction. Additionally if we look at this idea through the lens of what I discussed earlier where megaherbivores enhance systems for small and medium species- then it could be possible that the activities of adults megaherbivorous dinos augmented habitat for their own young!!

2) We may in fact be missing quite a bit of the diversity of small and medium sized herbivorous dinosaurs. Fossil bias exists and if they tended to stay in more upland/drier habits they may have stood less chance of fossilization.

And one final word on niche partitioning/competition in dinosaurs. I think it is a bit overstated. Did it exist? Sure. Various sized mouths, tooth structure, jaw muscle leverage, neck length all point to various herbivores being better equipped to handle such and such resource better than others. But if we are talking about the big guys here, the megaherbivores, I think these suggestions of partitioning are more or less moot. They just ate everything. I know, I know what about tooth wear studies? Well I will offer how much do tooth studies really tell us? If dinos were shedding their teeth constantly maybe the wear patterns reflect what they were eating during that particular season? There are lots of examples of modern herbivores partitioning resources but I see a lot of examples of herbivores overlapping considerably and there just being enough of that green stuff that it doesn't really matter. Maybe there was room for 'em all with some partitioning but often times high degrees of dietary overlap. And in the Mesozoic with high eustatic seas, year round balmy temperatures, dino-dung fertilizer, monsoonal climate regimes, high CO2, and often times rich volcanic soils maybe these were just systems that could foster multiple taxa of berbivores with highly overlapping diets and that was just ok.



Cheers!!





Sunday, March 16, 2014

Dinoturbation, Barfing Brachiosaurs, and the "Real" Fossil Record: Anthony Martin's Dinosaurs Without Bones

BUY
Often overshadowed by skeletal remains, the nuts and bolts of dinosaur paleontology, the study of trace fossils, ichnology, offers a parallel- but no less fascinating -avenue into the lives and times of the ancient saurian bestiary. In Dinosaurs Without Bones Anthony Martin, a professor of paleontology/geology at Emory University, offers perhaps the most succinct, accessible, and readable account of this strand of dinosaur discourse to date. And not only does Martin write a coherent and eminently readable book on this interesting subject he does not shy away from sounding the battle cry for the importance, dare say dominance, of the trace fossil record over the skeletal record writing:

"If through some miraculous disaster every dinosaur bone in the world disappeared tomorrow, the fossil record for dinosaurs would still be represented quite well by their tracks alone... each dinosaur had, on average, about 200 bones per individual. Yet you could bet that those dinosaurs that made it from hatchling to rambunctious juvenile to surly angst-filled teenager to a full-fledged responsible adult probably made many more than 200 tracks during their lifetimes... Other than their sheer abundance, another comforting thought about dinosaur tracks is that they very often are in places where dinosaur bones are rare or absent... As a result I like to argue that dinosaur tracks constitute the "real" fossil record of dinosaurs rather than their bones, which are nice but, well, just a little too dead. Tracks breathe life back into dinosaurs."

Tony Martin. Theropod/Sauropod tracks. Michael Blair. Dinosaur Valley State Park
In addition to taking this interesting, but not without merit, stance on dinosaur paleontology Martin is not shy about putting his neck out on, what many of his peers may consider, reckless speculation. In fact he starts off the book with a captivating predatory clash involving a T-rex (although it begs the question did the editors insist on T-rex?) and later describing ichnology as "that exciting intersection between science and flights of fantasy... I like to argue that for us to truly grasp how dinosaurs behaved... we absolutely must study their trace fossils."

Well no argument from me there. The issue of how much speculation is warranted or even necessary is a common discourse in paleontology. With extremes ranging from "we can only talk about the hard data" to the more out-there whimsical notions of the All-Yesterdays movement there is a lot of strands of thought out there. For those working and employed professionally as paleontologists I can certainly understand not wanting to be associated with such and such crazy idea. But that leaves a lot of the speculative slack to be taken up by dino-fanatics or bloggers (like yours truly) who may or may not offer the most accurate depictions in lieu of professionals not wanting to put their neck out on some unvetted idea. However I do wish that this was not the case and that the people with the most expertise and experience felt more at ease with speculation, as long as it is couched in those terms.

But back to the book. Probably my favorite aspect of the book is that Martin took the credo All Killer, No Filler to the hilt. What I am getting at, and this is a problem I have with the vast majority of dinosaur books written for a popular audience, is that popular dino books have so much foreplay before they get to the really meat of the book. You have a chapter on geology and the geological record then a chapter on Darwin and the theory of evolution, maybe even some basic biology, a history of dinosaur discoveries, the bone wars between Cope/Marsh told ad nauseam (seriously do we need to go over them in every dino book?), and then of course Bakker/dinosaur renaissance, blah, blah, blah. So by the time the author gets to what the book is about a good 1/4 to 1/3 of the pages are already used up. And publishers only give you so many pages to use. If you are already well versed in these subjects you do not need to review it. And if dinosaur paleontology is new to you, well there is something called google where you can review stuff if you want. Martin does give some cursory background on some issues, but by and large the book hits the ground running and I hope this sets a precedent for how future dino books go. Please future writers of dino books, don't go over the bone wars again, I will throw up just a little bit in my throat...

There are a lot of chapters in this book that cover a wide range of topics in dinosaur ichnology, Martin even cheats a little and looks at bones via dino pathologies and tooth abrasion. But what I want to talk about are the two chapters that I found most captivating and hopefully they will pique your interest as well so you go buy the book.

Burrowing Dinosaurs

Mother Earth-Mother Dinosaur. Ruth Showalter (c) 2007. BUY HERE
The above beautiful image by Ruth Showalter (wife of Anthony Martin) for the Spanish language book El Dinosaurio que Excavo su Madriguera (The Dinosaur that Dug Its Burrow) highlights the discoveries in recent years of dinosaur burrows, especially by small ornithopods. In the chapter Dinosaurs Down Under Martin takes you on a first hand account of the scientific trajectory of this discovery, himself playing no small part in the saga of burrowing dinosaurs. What I found so fascinating about this chapter is the wave of emotions/setbacks/triumphs involved in such a find. From careful skepticism, to ebullition, back to sound scientific investigation and the perils of publication- this chapter could have easily been expanded out into its own book. One of my favorite pieces is where Dave Varicchio, who discovered the burrowing dino and contacted Martin via email uses Martin to test his hypothesis: "Dave has used me- in an intellectually sordid way, I might add -to test his hypothesis. His exclusion of much information about the find, such as its age. location, interpretation of the original environment, and the oh-so minor detail that it involved a dinosaur, was purposeful and sneakily effective. Still, it reduced the possibility of bias in my assessing the photo and ensured that I would interpret it solely on its face value as a possible trace fossil and not as something I was hoping to see." That is science in action folks!!!

"Dinoturbation" and the Rerouting of Rivers

Thulborn. Sauropod Tracks Australia 2012
Ok when I got this book I actually skipped to this last chapter Dinosaurian Landscapes and Evolutionary Traces. If you read this blog you are probably aware that how dinosaurs interacted and affected their landscape and vice versa is a subject of much interest to me. What did a sauropod modified habitat look like? Well this chapter offers much food for thought in these regards. Central to this chapter is a paper by Thulborn (2012) from Plos One and available for free. What Thulborn found was a veritable sauropod highway traversing through lagoonal substrates in Early Cretaceous, Western Australia. And these were some big boomer sauropods and they repeatedly used the same travel routes over time. How or why this paper eluded me until now and that the possible inferences drawn from it are not more widely discussed and debated in paleo circles is beyond me. By analogy from the manner in which modern multi-tonne taxa (hippos, elephants) use repeated paths- paths of the least resistance more or less - landscapes dominated by such megafauna take on certain features. Most interesting is that these trails which intersect with waterways, through repeated travels breaks down banks that confine water channels. In a sense they can, over time, reroute rivers or allow water to be more widely distributed on the landscape. Martin even uses the term ecosystem engineer!! This reminds me of two things; beavers, as you may know my sister blog southland beaver is all about that rodent (shameless self promotion new beaver revelations!!) and; the enigmatic Morrison formation, usually characterized as semi-arid but replete with numerous sauropods and a fairly diverse suite of rivers, lakes, marshes, and fens. By inference from the behavior of elephants and hippos- a 2002 paper by DeoCampo documented hippos creating an avulsion of a river, they literally created a new 30 meter wide and 2 meter deep wallow- Martin opens up the suggestion that several modern large rivers, which originate in the Mesozoic, may at least owe some of their modern shape to dinosaur modifications. A very startling and mystifying idea!!

Hippo Track. McCarthy et al 1998

However this being a science book and me writing from a scientific perspective (most of the time) I do not think I would be doing my job if I did not offer some critique and can't just offer eulogy and praise. And the criticism is very specific on page 170 Martin, discussing holes in the head shields of ceratopsids, states: "So where the(y) *typo* delivered by their theropod contemporaries and presumed archenemies Tyrannosaurus rex? No, because Centrosaurus head shields showed almost no holes. Yet because Centrosaurus lived at the same time as Triceratops and Tyrannosaurus, it also should have been on a T. rex menu."

As far as I know, unless new data has come to light, Centrosaurus was Campanian (Dinosaur Provincial Park) while T-rex and Triceratops were Maastrichtian genera. This also might poke holes (pun, pun) in the hypothesis that T. rex was not gouging into ceratopsid frills because Centrosaurus did not live concurrently with T-rex.


Last but not least I do appreciate the humor, anecdote, and wit Martin employs- it keeps the reading interesting and moving along. All in all a great read, easy to digest, and approachable to a wide audience. Go buy it and support ichnology. Oh yeah, I did not talk about barfing brachiosaurs- I guess you have to go buy the book....

Dinosaurs Without Bones. 2014. Amazon

Cheers!!!


Monday, March 3, 2014

Yes Another Hypothesis on Long Necked Plesiosaur Feeding Ecology

Well I could not resist spilling the beans over on Tetrapod Zoology where Darren Naish has a piece up on plesiosaurs. This piece is part of a larger, almost collective unconscious thing going on in the paleoblogosphere concerning all things oceanic, piscivorous, fishy, salty, smelly, filter feeding, teuthophagy, and flippery going on at all kinds of blogs, including mine. Yes a salt spray is in the air and it is splattering everywhere. I have developed a hypothesis on plesiosauromorph feeding ecology. Yes, another wacky internet theory on long necked plesiosaurs.

I know that a blog on the interwebz is not considered standard protocol in science but, well things are changing and the pace of discovery, spread of news and discourse is going up and since I already sort of said it over at Tet Zoo as well as hinting at it here I might as well put it up here as well. I am working on a paper (my first ever) that can hopefully get published and enter the literature. Because I have put it out on such visible mediums as Tet Zoo comments section and over here I do not think anyone will attempt to get the scoop on me, lest they want the scorn of academic dishonesty. But if you like what I am saying and want to help or have some pertinent papers shoot me a line in comments. But I have my work cut out for me.

The T-Handled Socket Wrench of Death (thanks Yodelling Cyclist)



I think the chief impetus in plesiosauromorph morphological evolution was predation on ammonites.

Ammonites were abundant, diverse, and widespread through out the Mesozoic.

We should expect that predators as long lasting and abundant as plesiosauromorphs would seek to exploit them.

While small ammonites could have been swallowed whole or crunched up and further ground up with gastroliths I think large ammonites were predated upon as well.

Plesiosauromorphs would have attacked these large ammonites not by crunching through the shell as pliosauromorphs and mosasaurids did but through a unique method of rotational feeding.

1) Attacking from below in a slow stealthy approach the plesiosauromorph would grab any exposed fleshy part of the ammonite before it could recoil into shell or jet away.

2) After the mouth established a good anchoring bite the plesiosauromorph would then roll it's neck into and against the ammonite shell and begin a series of death rolls.

3) The ammonite shell, being a buoyancy device, would maintain an upright position even as this occurred.

4) By leveraging against the shell of the ammonite and continuing to roll against it the plesiosaur would be able to ratchet the cephalopod out of it's shell. Keep in mind the brunt of the force is not on the small head- that is simply the anchoring point. It is the massive neck that takes and distributes the torque until the ammonite is pulled out of it's shell.

5) After the cephalopod is pulled out the plesiosaur could use rotational feeding to pull off bits to be swallowed or, if living in groups, pull it apart together.



Furthermore I do not think it a coincidence that Cenozoic oceans lack abundant shelled pelagic prey and also lack predators similar in design to long necked plesiosaurs.

The largest and most long necked plesiosaurs, the Elasmosaurids, were coincident with the largest ammonites during the Cretaceous. 

The above scenario is of course very wild and not without a lot of speculation. But I believe it accounts for the strange anatomy of long necked plesiosaurs. As a mental exercise consider snakes that kill by constriction. If snakes were extinct today imagine the dilemma in reconstructing the feeding ecology of constrictors. Losing limbs imposes a lot of constraints on snakes, not the least of which is relatively slow movement. Why would a group of animals embark on this evolutionary course? Because the evolutionary advantage outweigh the disadvantages.

I also want to stipulate that this feeding strategy is part of a larger generalist strategy many of these animals employed. But I do think ammonites were the prime driver and after the neck evolved it was useful for other things as well.

I made some quick 5 minute sketches to hopefully allow you to visualize what I think was going on. Not done for artistry or even accuracy, just to help the concept. Would also love comments , feedback, criticism.


Step 1. Bite and hold


Step 2. Initiate Spin after leveraging neck against shell


Step 3. Keep spinning until dinner is served!!

All artwork Duane Nash. use with attribution for free.



Wednesday, February 19, 2014

Death Roll: Not Just for the Crocs...


Few predatory maneuvers are as visceral, jaw dropping, and just plain brutal as a crocodile putting it's prey through a battery of death rolls. Whether to stun, drown, incapacitate, dismember or kill  the hapless victim a death roll, or if you prefer the more sciencey terms twist/rotational feeding, is a full contact predatory sport. From the tip of the snout to the tip of the tail the death roll utilizes every inch of the crocodiles' length. But since the action happens so fast it may be useful to slow things down, as in the pics below, to really get an appreciation of this synthesis of predatory power.

J. Ex Bio. Death Roll of the Alligator: Mechanics of Twist Feeding
Spinning maneuver of juvenile alligator after initiation (0 ms). The alligator has bitten onto a piece of meat. During the spinning maneuver, the rotational axes of the head, body and tail maintain a fixed relative orientation to the frame of reference of the aquarium. Note that the relative orientation of the body parts do change with respect to each other. For instance, the tail starts bent to the left side of the alligator at 20 ms, but is bent to the right side of the animal by 120 ms, although still on the left side of the image. The limbs are appressed against the body and the head and tail are canted at angles to the body axis. The head, body and tail all spin in the same rotational direction with the same angular speed.
Feel free to follow the link above to read the article and get the mathy discussion there full of vector angles and angular momentum. But what is interesting when you look at this series of photos is that although the head, body, and tail maintain the same general orientation to the viewer the body parts do change with respect to each other. There are loads of death roll clips on you tube, below is a good one that shows what is going on fairly well.


And some slow-mo death roll....



Why the death roll is so devastating is that it creates significant torsional forces, and animal tissue does not respond well to torsional stress. This is due to the anatomical orientation of Langer's lines or lines of cleavage which are the natural orientation of collagen fibers that roughly
parallel muscle orientation. Surgeons, whenever possible, attempt to make incisions parallel with these lines to avoid scarring/keloids.

While crocodilians are most notorious and well known for the death roll, what is not well known is how common a manoeuvre the death roll actually is throughout the animal kingdom.

Many fish do the death roll. At about the 2:30 mark in this video you can see two Polypterus bichirs do a little death roll. And here are some nice death rolls by some more bichirs with some hilarious commentary to boot- makes me miss my ornate bichir. Also check out Bichir's midnight snack crazyfest for more nice bichir death roll action. Amphibians get in on the fun to with many salamanders, amphiumas, caecilians, and mudpuppies often reportedly using the tactic to dismantle prey too large to swallow. Lizards will occasionally death roll, especially monitor lizards, and even for small lizards the death roll may be a more common activity than realized when dealing with prey that can not be swallowed as the video below suggests.


But probably the group of animals most known for death rolling after crocodilians are the Anguilliformes- the eels. In eels you see the attributes that more or less unite all death rollers; a long, low body; legs or fins that are small or can be tucked against the body; pincerlike teeth with a strong bite: minimal or non-existent dorsal fin.

Remember when Jeremy Wade covered himself with fish guts and was subsequently nibbled by New Zealand Longfin "flesh ripper" eels? One does a little death roll on his kevlar gloved hand. But check out this video of some longfins death rolling a deer carcass.. kinda grim.


Moray eels will also death roll, especially when tackling octopi, but even in water too cold for moray eels you have massive Conger eels.


An unprovoked attack on an Irish scuba diver, Mr. Jimmy Griffin, by a Conger eel took place in 2013. The attack occurred 25 meters down and the impact knocked his regulator off. According to Griffin the hit felt like a punch to the face and it then rag-dolled him before spinning off a chunk of his face, presumably in a death roll.


Well as you can see, death-rolls, no matter what critter is performing them are no joke!!! So roll with them LOL!!!



Pertinencia


Fish FE, Bostic SA, Nicastro AJ, Beneski JT (2007) Death roll of the alligator: mechanics of twist feeding in water. Journal of experimental biology 210: 2811–2818.

Helfman, G. S. and Clark, J. B. (1986). Rotational feeding: overcoming gape-limited foraging in anguillid eels. Copeia 1986,679 -685.


Measey, G. J. and Herrel, A. (2006). Rotational feeding in caecilians: putting a spin on the evolution of cranial design. Biol. Lett. 2,485 -487.

 






Wednesday, February 12, 2014

Cephalopod: It's What's For Dinner


Much of this post was inspired by a discussion I had in the comments over at Jaime Headen's heady blog the bite stuff about Rhamphorynchus muensteri.

When I lived in the Bay Area one of my favorite past times was exploring Asian food markets. Not so much to shop for food (though they often had killer deals on beer) but just to get a kick out of the seafood selection. Seriously, the amount and sheer variety of oceanic critters on display at these places is astounding- kind of like going to an aquarium without feeling guilty over the imprisoned killer whales. All sorts of fish, cute little dried sea horses on sticks, crustaceans, molluscs- hell even dried jellyfish snacks (or jellies if you want to be PC)- were there either canned, dried, salted, butchered or even alive.
To western palates, and more specifically American palates, this seafood bonanza highlights how limited our diets really are in terms of amount of oceanic phyla consumed. And one group that I want to focus on today which is in no short supply in these Asian markets are cephalopods- the "head-footed" clan of mollusks that includes octopi, squid, nautilus, and cuttlefish. You western readers might be thinking: squid are not so exotic I enjoy a bit of calamari now and again. Yeah, you eat breaded, fried calamari rings- wowee. Go check your cabinet right now- how many cans of squid with ink do you have? How many cans of tuna do you have? Probably a lot more chicken of the sea, no? Us westerners have a very fish biased diet in terms of seafood choice. And it is this fish bias- a certain penchant for backbones - that I want to speak of today. And ultimately discuss how this tendency to look towards all things fishy may actually imbue our interpretation of certain long ago extinct beasties and how they lived.



Humboldt Squid. Bill Erhardt (c). Baja CA 2008
Kinda creepy looking, no? These are Humboldt Squid, Rojo Diablos- Red Devils, scientific name Dosidicus gigas. They are feeding on pelagic red crabs and it almost looks like a type of cooperative hunting is going on here- a behavior that has been attributed to these guys before. In recent years this species has been undergoing significant range shift, moving from a stronghold in the Sea of Cortez right up the coast of California sometimes as far north as Alaska. And this expansion speaks to a worldwide increase in squid numbers. It is now widely regarded that squid biomass exceeds human biomass and may be making serious inroads on fish biomass supremacy. Why? We have over-harvested many of their chief predators- billfish, tuna, sharks. But perhaps more importantly intrinsic changes in the ocean itself may be spurring on an increasingly tentacled ocean ecosystem. A paper on the Humboldt Squid, Combined Climate and Prey Mediated Range Expansion of Humboldt Squid, suggest expansion of an oceanic hypoxic layer allows refugia from predators and unfettered access to areas it had formerly been nonexistent. Another study comparing the differential ability of various fishes, cephalopods, and zooplankton to survive oxygen minimum zones comes to a similar conclusion. So when it comes to areas where oxygen is limiting, cephalopods seem to outcompete fish. Why this is so is less clear to me. Perhaps it has something to do with their chief form of locomotion via jet propulsion and the amount of water they can pump through their gills through their mantle?

Never the less if we paint with very broad strokes cephalopods seem to be winning in warm, oxygen deprived waters. I am looking at you Mesozoic oceans. Indeed in Mesozoic oceans we have not only squid, including big ones, but ammonites and belemnites. A very tentacle ridden, cult of Ctulhu styled scuba dive you might have if you explored the Western Interior Sea. Not only were cephalopods abundant and diverse but the work of the Jurassic Spitsbergen Research Group shows that fish were ecologically insignificant in some Mesozoic oceans. If you don't know now you know, calamari in form or another was a common food for aquatic predators during the Mesozoic.

And here is where I want to tie together the whole cultural bias against tentacled stuff and how our view of many deep time marine predators might be skewed by our fishy bias. Piscivore, say it with me, pis-civ-ore, one who consumes fish. If you are a animal/paleo-geek like me you are surely familiar with the term. But what is the name of a squid eater? I actually did not know when I asked myself this question but it is teuthophage, a word not so commonly thrown about as much as piscivory. Ok, so big whoopee if you can eat fish you can eat squidy type stuff too can't you? Well maybe in some cases, maybe not so much in others...

Do Brown Pelicans Avoid Squid... and if so Why?


Whenever I get a chance I love to talk to fishermen to glean any kind of info I can from them. Now we all know what they say about fisherman's tales but sometimes they will give you some info that perks your interest. And one of the more interesting bits I have heard on several occasions is that brown pelicans, Pelecanus occidentalis, assiduously avoids squids. And where I live on the coast of California  this struck me as a bit odd because we are having record hauls of market squid, which form huge shoals, and pelicans are ubiquitous here. Maybe these admittedly anecdotal accounts speak to a larger truth -why avoid such a tasty nutritious treat? As the you tube video above suggests maybe pelicans are not so dissimilar to humans when it comes to food. If you have a bad experience with a certain food type you are not apt to repeat that same mistake. And when a plunge diving pelican gets a beakfull of squid in it's gular pouch
and realizes that these creepy little things ain't anchovies and sucker on to my skin, block my throat, and some even have little switch-blade suckers that draw blood- it is a mistake not soon to be forgotten. And now go back and look at that gif of the unfortunate cat with a face-full of octopus. I was not trying to be cute there but actually trying to illustrate what works and what does not work to be a teuthophage- especially an air breathing one. Just because you can catch and eat fish well does not mean you can catch and eat cephalopods as well. Or you can put it this way: piscivores are not always teuthophages, but teuthophages can always be piscivores. If you are a teuthophage you can tackle tentacled prey in a couple of ways; beaked whales are very much larger than their squid prey and simply inhale their prey whole; sharks, pinnipeds, and predatory fish have the dental equipment/bills to dismember squidy prey on the spot negating the tentacled counterattack; sea birds that eat squid have longer bills, sometimes have ridged tongues for killing. Something like Pelagornis comes to mind when imagining the penultimate avian teuthophage. Ultimately when the cephalopod and the teuthophage are more equally matched in size- the would be predator wants to have a long, sharp mandible to keep Mr. Squiggly at arms length. And this is double important when the teuthophage in question is an air-breathing tetrapod.

Mesozoic Calamari


Now with the perils and pitfalls of teuthophagy in mind let us revisit the Mesozoic and remind ourselves that not only were there often abundant squid, but also shelled ammonites/belemnites. And given that many ammonites may have indeed been plankton consumers and were so common that their fossils constitute index fossils I want to pay special attention to them. Predation scores left on the shells of ammonites are well known, mosasaurs usually indicted as the culprit. And it is not too hard to imagine the heavy maw of a mosasaur, pliosaur, robust snouted icthyosaur or sea-going croc having a go at these shelled delicacies.

Does this imply the more daintier snouted icthyosaurs, plesiosaurs, elasmosaurs, and other more slender snouted/toothed marine predators simply left ammonites alone? I would argue no- they simply had other ways to retrieve the flesh and leave the shell alone. A quick snap at an exposed tentacle by any one of these critters at an ammonite. Establish a good grip. And then the predator can either shake off a piece, or... ready for this... go into a death roll pulling off a tentacle or maybe even yanking out the whole squishy body. And I know you love death rolls, now just imagine a 14 meter Elasmosaurus, grabbing onto the fleshy part of a large ammonite,  and spinning on it's own axis with a two tonne body creating tremendous torque funnelled down that long neck yanking the
doomed ammonite from it's shelly home....
I once saw a documentary on Moray eels and a similar death spin tactic was used by the eel to rip off a tentacle from a much larger octopus.

Now keep in mind that I am not suggesting fish and other critters were not routinely consumed by marine reptiles. The fossil evidence of stomach contents, coprolites tells us specifically that fish, turtles, pterosaurs and even benthic invertebrates were common dinner fare for some of these guys. In fact for the record, all things being equal, I automatically assume a generalist diet for just about any predator- especially marine reptiles. For me proving an obligate specialist diet requires more of a burden of proof than a more opportunistic/generalist strategy. What I am suggesting is that where we have an abundant prey base of shelled cephalopods- we should expect predators on hand to consume them and start looking for ways that they accessed such prey.



But it is also worth mentioning that fish remains have a better preservational potential in coprolites/gut remains than cephalopods because, you know, skeletons. And this bias would be even more pronounced if predators were just ripping off chunks and isolated tentacles from cephalopods.

Pterosaur Ptroubles 

As many have learned to their peril, putting forth thoughts on pterosaurs on the interwebz is a touchy subject. But since it was a discussion of Rhamphorynchus that started this whole train of thought here we go.

Rhamphorynchus. wiki
OK if you are up to date on pterosaur paleoecology then it should not be news to you that the traditional "deranged sea-gull" interpretation of pterosaur lifestyle has been laid to rest for the majority of pterosaurs. If you don't know about this change GTFO and go buy Mark Witton's book. But I want to talk about those oceanic pterosaurs for which a piscivorous lifestyle has been retrieved. Starting with our friend Rhamphorynchus muensteri I am intrigued by the hooked jaws and procumbent dentition- especially towards the tip. Remember what happened to the cat with the octopus on its face- if you are handling tentacled prey you want to keep all those moving parts away from your face. Expectations met. And those weird teeth and hooked jaw tip? My interpretation is that such a design was great for digging into shelled/coiled ammonites. Again they are not busting through the shell but probing into it. Do we have any modern analogues? Snail kites, Rostrhamus sociabilis, comes to mind- feeding almost

Snail Kite. Cornell Education
exclusively on apple snails, scooping out the flesh and leaving the shell. But bear in mind that although such a lifestyle today seems overwhelmingly specialized- in the Mesozoic ocean with scores of shelled, pelagic molluscs such a penchant for molluscivory may have been more widespread. Oh yeah, I almost forgot, Dave Hone does have some evidence of cephalopods in the diet of Rhamphorynchus as well from 2013 if you google it you can find reference...

Anhanguera blittersdorfi. wiki. Ghedoghedo
When you start to look at Ornithocheirids the pattern continues- long jaws with a spear like tip rosette of teeth to keep struggling tentacles away from the eyes/ears/throat. Also good potential for deep probing into shelled cephlapods- killed or scavenged. Again I am not arguing that pterosaurs did not eat fish also, but for me many of these adaptation of "piscivorous" pterosaurs are optimal for a teuthophage as well. And yes many of these guys lived at inland lakes lacking cephalopods- dual functionality for fish and cephlapods would conserve the design.

Pteranodon. Smokeybjb. wiki
And I want to leave you with the classic "piscivorous" pterosaur group the Pteranodontids. For me I imagine these as very special oceanic predators/savengers of late Cretaceous open ocean. Often compared to albatross in terms of flight ability I would venture to say the comparison also extends to their ecology. Their long, slightly upcurved, sharp fore-cep like eduntulous beaks in my mind appear optimal for snatching wriggly, tentacled things and also for probing deep into the chambers of ammonites. Again, not saying that they were wholly dependent on cephalopod food, just that the ecological conditions of their time- with loads of such prey- suggest to me that there was ecological imperative to access such foods.

Matt Martyniuk. wiki
Night was falling on the Western Interior Sea. And with this change in light conditions, the largest and oldest continual migration in the history of the planet commenced- the vertical migration. A myriad of creatures that took shelter in the darker, oxygen deprived water during the day to escape fishy predators of the sunlit upper realms commenced their nightly rise in the water column. And the most visually conspicuous members of this guild were cephalopods. 

Belemnite shells
Shoals of squid-like armored belemnites darted about, making a go at some of the larger bits of zooplankton. Large and predatory squid rose from the depths and aggressively preyed on whatever they could overcome. Their supercharged metabolism and growth rate a necessary corollary of their annual lifespan- growing from barely visible larvae to several hundred pounds in weight in about 1 year. And most dramatic of all were the numerous and diverse ammonites with the ability to effortlessly change their position in the water column through manipulation of the gas concentrations in the septae of their coiled shells. Despite the imposing physicality of the ammonites many of the largest types were harmless filter feeders- able to grow so large by sifting through the planktonic soup of the Cretaceous ocean. But these big boys, the largest ammonites, were not alone- night was also the time for mosasaurs, their chief nemesis, to ramp up their activities as well...


And with the commencement of this strange and scary nightwatch an aerial division also ramped up it's activities as well. An old Pteranodon sternbergi had reached a size and level of experience that distinguished it from younger and smaller pteranodons. He no longer squabbled with flocks of ocean birds and smaller pteranodons over small bait-fish balls and cephalopods but sought bigger fare- the largest cephalopods the ocean had to offer in fact. And he secured great big calamari steaks not by killing them himself (although he did sometimes dispatch disabled and wounded cephalopods he found on the surface) but by following pods of mosasaurs. And in a manner foreshadowing fellow long distance ocean travelers such oceanic white tips following pilot whales and albatross following killer whales the old Pteranodon hooked up with a pod of Tylosaurus kansasensis which the big pterosaur would follow for weeks at time for food.


Albatross Encounter. NZ. Sperm whale leftovers. 


Sakamoto, Takahashi, Trathan. wiki. Albatross & killer Whales




Sometimes scraps and chunks of ammonite would float up to the surface or sometimes the mosasaurs would drive to the surface a big boil of ammonites- but what the Pteranodon really relished was when a mosasaur would surface after a deep dive with a big ammonite. The ammonite, either dead or nearly dead, would float to the surface because of the gas filled chambers in it's shell. 


At this point, with the mosasaur replenishing it's oxygen after the long dive, the Pteranodon had unmitigated access to the carcass. Perhaps grab a tentacle and flap vigorously to dismember it, or if the mantle is open start probing into it with the long, sharp beak for choice bits of reproductive organelles, eggs, and other viscera.


Duane Nash

Above I have depicted such an event. A wounded, slowly dying large ammonite has been pulled up from the depths by a mosasaur. The mosasaur, recuperating from the dive and struggle, is in the background to the right. Seizing the opportunity a Pteranodon has swooped in to pull off a tentacle.

Cheers!!

*thanks to Lloyd Lustina for letting me borrow his phone to capture photos of the ammonites/belemnites at WFVZ collection


Squid Fishing Boats Japan. 

Thursday, February 6, 2014

Mammoths in the Flower Bed

Coming down the pipeline is a new paper in Nature with a slew of authors: Fifty thousand years of Arctic vegetation and megafuanal diet.

Abstract
Although it is generally agreed that the Arctic flora is among the youngest and least diverse on Earth, the processes that shaped it are poorly understood. Here we present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr BP (before present). For much of the period investigated, Arctic vegetation consisted of dry steppe-tundra dominated by forbs (non-graminoid herbaceous vascular plants). During the Last Glacial Maximum (25–15 kyr BP), diversity declined markedly, although forbs remained dominant. Much changed after 10 kyr BP, with the appearance of moist tundra dominated by woody plants and graminoids. Our analyses indicate that both graminoids and forbs would have featured in megafaunal diets. As such, our findings question the predominance of a Late Quaternary graminoid-dominated Arctic mammoth steppe.

Now you just know I am gonna find this paper very, very interesting as I love the intersection of vegetation, landscape, and megaherbivore. Let us remind ourselves that this paper is about the fabled "mammoth steppe"- the stomping ground for much of the northern latitude megafauna that bit the dust about 10,000 years ago.

Maurico Anton. wiki
For the sake of brevity mammoth steppe has traditionally been imagined as basically an arctic Serengeti. Grasses, or as the authors like to call them "graminoids", were ubiquitous and accounted for the bulk of the diet of the herbivore hordes. But the study calls this interpretation of the mammoth steppe into question. Instead of grasses being the predominant plant type and fodder- forbs, essentially wildflowers, would have been numerous and diverse on the mammoth steppe.

Specifically these wild flowers would have been not too far off from the seasonal wildflowers that grow in alpine meadows today. And intuitively this makes sense; the arctic tundra is a relatively new environment on the earth therefore one would expect that a guild of plants already pre-adapted to a short growing season to have an advantage in getting a good toehold in the tundra. And, as evinced from the gut contents and coprolites of the herbivores studied, forbs augmented a diet of grass for these animals and the high protein of these plants may have been pivotal in allowing such a diverse and large bestiary of northern megafuana to thrive in these high latitudes.

How and why this diverse landscape of brightly hued wildflowers diminished, seemingly in lock step with the herbivores that thrived on them, is up for debate. Parsimony would suggest that changing climate regimes, from cold and dry to more wet, likely played a role.

As the paper relates to some more broader issues in reconstructing past environments there are a couple take home messages that register for me.

Bias in the paleobotanical record. Grasses were assumed to be dominant because their pollen record is the richest. But grasses are dispersed by wind and therefore broadcast a relatively huge amount of pollen into the environment. Colorful flowers on the other hand are largely pollinated via insects and thus invest less heavily in amount of pollen. And therefore the pollen of flowers will be underrepresented compared to grasses.

If we have been missing the mark in reconstructing relatively recent environments of the Pleistocene, then this folly begs the question- how much are we missing/misinterpreting from environments going back deeper in time? I'm looking at you Mesozoic...

How much of a role did the large herbivores play in maintaining these wildflower habitats? Why do grasses dominant in east African large mammal dominated environments but forbs in the Pleistocene arctic? Does fire favor grasses in hot environments compared to forbs in relatively cooler and less fire prone environments?

As always more questions...











Wednesday, January 22, 2014

A Dog's World? Carnivoran Wars...

Check out this highly adorable video of some grey seals on vimeo (I don't endorse petting/approaching seals btw). On fb my friend said : "So cute! They're like the dogs of the ocean."  Now I want to use the second sentence; They're like the dogs of the ocean... as a springboard to look at how the comparison, apt as it is, does betray a certain tendency on our part when describing critters of the ocean. What I mean is a commonality of appearance or habit to some well known land-lubbing critter- given to the more alien marine critter. Think about canned tuna- the chicken of the sea- or even common names like elephant seal, sea lion, sea cow. This ocean-land doppelganger pattern even extends into the middle ages when it was believed a marine bestiary existed that matched counterpart to land animals.

12th century
And as terrestrial based creatures ourselves it makes sense that humans have often compared marine critters to land ones due to familiarity. But when viewed through the lens of other parameters- evolutionary history, diversity, abundance- this persistent land based bias in comparing marine critters to terrestrial ones does fall down a bit for me. Let us compare dogs against seals with regards to some perameters that short-circuit this bias.

Evolutionary History- Pinnipeds- walrus (family Odobenidae), true seals (family Phocidae), and eared seals; sea lions; fur seals (family Otarriidae). While traditionally viewed as forming a diphyletic group, arising from two ancestors, recent molecular evidence supports a monophyletic origin (singel ancestor) for pinnipedia with the various groups splitting off later (Berta, A. 2009). And how far back does the family go? Well it appears mammalian carnivorans didn't waste much time getting their feet wet after predaceous marine reptile went extinct. Pinnipeds appear to have split from other carnivorans about 50 mya and we have several putative species showing aquatic adaptations such as Puijila and Enaliarctos, both predators from about 21-24 mya. Of the two Enaliarctos was more firmly dedicated to an aquatic existence.
Puijila. wiki

So give or take a few million years we really start seeing animals that would have appeared very similar to modern seals by around 20 mya.

Enaliarctos. Evolution of Mammals




How far back do dogs go? Dog like carnivores (caniformes) split off from cat like carnivores (feliformes) about 50 mya and the first truly dog-like critters date to about 40 mya, guys like
Prohesperocyon wilsoni. Three main lineages diverged about 34 mya- Hesperocyoninae, Borophaginae, and Canidae- but only one group survived to the present the Canidae. And we really don't see this group asserting itself until about 9-10 mya. So although dog-like animals go back pretty far it is not until relatively recent that we see dogs of the fox/wolf type familiar today. In terms of species there are about 38 species give or take a few here or there.

All in all though it appears that pinniped evolution and canid evolution have quite comparable trajectories into deep time. Hard to really assert that one group predates another. But what about species diversity? Wikipedia claims about 33 species of pinnipeds and about 36 species of dogs- but we know how contentious taxonomic issues can be and new species/subspecies are still being found. But again comparing the two groups in terms of species diversity is also a bit of a wash- if there are more dog species it is not by a high count.

Of course diversity in terms of size/form is another parameter we can look at. As pictured on the left dogs do come in a wide variety of shapes and sizes- but all are immediately recognizable as dogs. They range in size from the 1.5 kg fennec fox to the robust timber wolf at 80 kg. But this 78.5 kg weight differential is paltry compared to the weight differential of 3155 kg between a 45 kg Baikal seal and a 3200 kg southern elephant seals (also largest carnivoran of all time?).

What about biomass comparisons? One way to compare different groups is by looking at how ubiquitous they are in terms of the earth's biosphere. If you were to weigh the mass of all the earth's pinnipeds against all the earth's canids which group would dominate? I know what you are thinking- surely domestic dogs will tip the scale in favor of canids- and I would have to agree. A 2001 estimate suggested the world population of domestic dogs at 400 million. But, for arguments sake, let us exclude domestic dogs which have benefited from cohabitation with man (and vice versa), and only look at wild populations. Ringed seals are thought to number about 1 million individuals and are the most widespread and common of Arctic seals. In Antarctica the Weddel seal is the most abundant seal and it is estimated to have a population of about 800,000 individuals- plus it is big, growing to about half a tonne. Now even just counting these two seals are there any wild canid species that get anywhere close? Coyotes in North America are probably one of the more abundant wild canids but I can't find any good data on numbers and they are pretty small compared to seals. It would be interesting to get a number on wolf populations prior to the widespread eradication campaigns as they have such a wide geographical range. Here is a link to extant wolf populations by country. I would not be surprised if there was at one point more than 1 million wolves worldwide prior to the advent of agriculture/domestication. But this appears to be the pattern for most wild canids- small size, restricted range or large size but reduced numbers/range. In addition to seals I mentioned earlier California sea lions have been increasing in number since 1975 and most estimates place the population at roughly a quarter million individuals. Likewise grey seals have also been increasing as well.


So canids and pinnipeds are quite comparable to one another in terms of depth of evolutionary history, species count, and diversity of form. But pinnipeds steal the show when it comes to size variability and gross biomass of naturally occurring wild stock. Can we really say it is a dog's world? Not when it comes to naturally occurring, evolving populations where seals have the upper hand (flipper) in terms of size range, commonality, and biomass.

Sascha Grabow

Cheers!!





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