Saturday, July 22, 2017

Pierced From Within: Utahraptor Cometh and the Return of the Killing Claw

Utahraptor by Duane Nash


You know its that time again folks, more dromie madness. Antediluvian salad has a bit of a controversial history with these most pernicious of stem birds. You can be sure that part is not going to change, the controversial bit, that is.

For a brief review:

Making Dromaeosaurids Nasty Again Part I: Wing Pummeling Abuse In which I discuss the current state of affairs with regards to killing claw use and hypothesize that prey restraint by the foot "killing claw" coupled with clawed wing pummeling may have been utilized. As you will see in this post I no longer consider such a method of restraint and killing as preeminent. That is - shades of grey here folks - I don't think that both the raptor prey restraint model and the wing pummeling hypothesis were chief strategies for prey dispatch in most dromies. Could both style of attack been used on occasion by some dromies? Yes, but as I will explain both theses methods become vanishingly tenable tactics especially at larger sizes (hello Utahraptor).

Making Dromaeosaurids Nasty Again Part II: No Shame in the Scavenging Game I start building the case for many dromies as excellent facultative scavengers. Not only is there fairly unequivocal fossil evidence for it, the size range of dromies slots in nicely to an ecological "sweet spot" where terrestrial scavenging is most utilitarian. Also Dakotaraptor as a large, cursorial carcass bully.

Making Dromaeosaurids Nasty Again Part III: Life Appearance - Dapper of Deranged Probably - at least based on the comments - the most controversial of the series. I would say it has held up nicely, especially in light of the compelling evidence that tyrant lizards "de-feathered" significantly. "Wut you mean that dromies did not all look like carbon copies of each other in the 100 million years of evolution they underwent? Get out!" Look folks it's not even that wild of a suggestion, in fact pretty common sense actually. Almost boringly so.

Making Dromaeosaurids Nasty Again Part IV: New Hypotheses on Dromaeosaurid Feeding Technique & Role of Tail in Movement For me this was the most fun and interesting post in the series as it combines unusual oral feeding styles with a novel idea on dromaeosaur locomotive strategy.

I introduced, for lack of a better term, the "woodpecker hypothesis" of dromie carcass feeding technique. In this scenario quick twitch muscles generated in the body vibrate culminating energy at the tooth tip where strange apically hooked serrations on the teeth allow the tooth to literally dig into carcasses. Several examples of worn dromie teeth and inexplicable bone damage on Tenontosaurus can be potentially explained by this hypothetical feeding style.

I then discussed how the pattern of caudal rods in dromie tails could potentially work as an elastic recoil allowing energy efficient, long distance travel, useful for reaching ephemeral food sources and carcasses. I make the comparison to wolverines which, despite their short legs, are remarkable and unstoppable moderate paced long distance cursors. I augmented this suggestion with a review of dromie ichnological traces - the footprint record shows that these animals had not only large foot and toe pads but that they most likely cruised at a fairly high pace.

Here I have to admit to having a bit of mud on face here folks as a frequent theme of my "Making Dromaeosaurids Nasty Again" series was a diminishing of the  role of the killing claw in predatory endeavors, highlighting wing pummeling and biting as more preeminent tactics for dispatch while the feet grappled and held prey. So I'm gonna eat some crow here in coming around full circle in my opinion on that most famed of claws - foot ungual #2, aka the "killing claw" I now believe really was a killing claw just not in the way that we have been interpreting it.

Full disclosure, the genesis of this idea is not mine own although after mulling it over and especially with the Utahraptor reveals I think it should be the leading hypothesis. What I want to document is the transmutations and permutations an evolving hypothesis should go through and in this case I believe did go. New ideas rarely come fully realized and perfected into the world. They need refinement. In the case of this idea which I will dub the "pierced from within" hypothesis the first semblance of it to my knowledge was put forth by Kenneth Carpenter. However the man who improved - but didn't perfect it - is.... wait for it... a certain chap named John Jackson.

Upon writing that name I can almost hear the sound of mouses clicking on the close window for this page. But bear with me. To those uninitiated John Jackson is best known as a chief proponent of the "Birds Came First" BCF idea of theropod/dinosaur evolution. He also has a reputation online for a particularly prickly correspondence to put it mildly. You can do your own internet sleuthing on John Jackson if you are new to this idea or the man - here is a good place to start (read comments). But let me unequivocally state I don't subscribe to the BCF idea of dinosaur/bird evolution (ironically someone brought up a retooled version of this in the comments from my last post). I'll admit it had a certain intuitive appeal to it in the 90's and was fresh and original - but the evidence has not borne it out. John got in contact with me after reading several of my dromaeosaurid posts and we had a brief series of email exchanges (we don't correspond anymore, you can take a wild guess why). I try to keep an open mind on things and gave his self published book - The Secret Dinobird Story (free on kindle) - a read. The book is a bit of a slog to get through, and I told John this. I came away still unconvinced about BCF and this post is not about this topic nor do I want to discuss BCF in the comments. But nestled within John's writings on the philosophy of science, unorthodox family trees, "arboreal stem dinos",  and complete eschewing of cladistics ( I have problems with cladistics too but don't think we should discount them), is hidden what I believe is an important and unrecognized broad stroke analysis of how dromaeosaurids actually used the famed killing claw. I can only assume that people who know of John or have perused his book glossed over his bit on the killing claw. It is in my opinion an unpolished gem and should see the light of day. With whatever light I can give this idea I will shine upon it.

The killing claw is not a tool used as a crampon to hang onto the sides of other dinosaurs, nor is it a tool used to pin and hold subequal sized prey items ala the raptor prey restraint hypothesis. It is a tool used with almost surgical precision to slice into and penetrate a prey item in select spots. Such a claw is not optimized to scythe style cut long gashes in the tough hides of prey but instead cuts a single entry hole into prey. A laterally compressed horny sheath with a cutting edge can, after the initial entry into said prey item, now repeatedly plunge into, explore, and cut into the underlying soft tissues. Such trauma will perforate vessels, arteries, lungs, and viscera. Although from the outside trauma will be evinced by a simple entry hole the interior damage will be substantial and often times fatal. Arms and/or jaws assist in stabilizing struggling prey in such a manner to allow entry of killing claws into prey for fatal dispatch. Such a tool is every bit the theropod equivalent to saber - toothed predators and allowed dromaeosaurids an ability to punch well above their weight class in predatory endeavors.




John called it the toe and tail, grab and stab method. He believed that the caudal tendons of the tail worked somehow to help "kick into" the prey item deeper but the (unpublished) revelation that Utahraptor dispensed with these caudal rods causes me to distance myself from that aspect of the idea. As I have discussed before I think that those caudal rods assisted in long range, mid paced efficient travel and it makes sense that Utahraptor dispensed with them as it likely was the >the most predatory< and least adapted to facultative scavenging among known dromaeosaurids due to its size, extreme robusticity, and heavy investment in weaponry. Furthermore the loss of such rods helped the tail in flexibility as it could both deliver and take a beating.

To better understand and see how we got to where we are today and where I think we will be going a quick review of the pertinent thought on the use of the killing claw in these animals dominated by two papers Manning et. al. (2005) and Fowler et. al. (2011) with necessary criticisms.

Not a Slicing Weapon But a Puncture and Pierce Weapon

The main death knell to the "ride the back of iguanodonts and slash at the sides with toe claws" hypothesis of dromaeosaurid killing technique came in the form of a mechanized Deinonychus leg built and utilized by the team of Manning et. al. back in 2005. They found that not only was the hole created by the claw very superficial but slicing through skin in order to create long gashes would be inefficient due to the skin tending to bunch up prevent said slicing. However, as John points out in his book such an analysis is lacking in terms of puncture depth because the experiment did not take into account the compliant nature of body tissue and that the claw can be pressed into the prey animal deeper via body weight and/or muscular force. Long story short the experimenters did not think with enough murderous intention. They did not think like prison inmates trying to achieve fatal blows with self made prison shanks. When body tissue is not put under pressure all the soft, delicate and gushy stuff is relatively safe due to the layer of integument, muscle, adipose tissue etc etc. But press into this tissue - with a prison shank or a dromie killing claw - and the margin of safety diminishes.  Stick the knife in and twist.

Critical reception to Manning et. al. is not however new and not isolated to John Jackson. Both Dave Hone (archosaur musings) and Mike Taylor (SV-POW) express similar notions in this interesting back and forth from Ask a Biologist. Many of the points they raise, especially with regards to the problems of "puncture and hold" and the likely inference of a sharp cutting edge to the killing claw can be extended out to criticisms of the now dominant RPR model of Fowler et. al. (2011).

Not a Holding Claw But a Cutting Claw

After Manning et. al. prescribed their case against killing claws slicing meter long gashed into the side of prey items the next big chapter in this saga came in a paper by Fowler et. al. (2011) that brought us the now dominant hypothesis of the Raptor Prey Restraint model (RPR) that proposes a certain commonality with modern birds of prey that grab prey with foot talons, flap with wings to maintain dominant position, and eat/dispatch with the head. As I have said in the past there is much to like here and it is not surprising that many have become somewhat smitten with the RPR restraint model. But as the authors themselves concede the grasping ability of dromaeosaurids is not >as mechanically strong< as modern raptorial birds of prey. Add to this; dromaosaurids do not have truly opposable halluxes like raptors - they can't do a good strong vice grip; longer legs decrease mechanical advantage further diminishing the strength of the grip; and dromaeosaurids had big foot and toe pads which would diminish the tightness of the grip. Because of the big foot and toe pads that dromies had getting a firm grasp becomes problematic, sort of like trying to grasp things with your own toes to a lesser extent. Not impossible for us and not impossible for dromies, but issues arise suggesting a less than optimal performance.

But the final nail in the coffin for the dominance of the RPR model lies in the shape of the claw itself. It is not circular in cross section as we see in extant raptorial birds of prey but is laterally compressed like a knife is. It is just begging us to infer a sharpened cutting edges for the keratin sheath.

credit Robert DePalma  killing claw Utahraptor (L) Dakotaraptor (R)


The Diminishing Utility of Stability Flapping in Larger Dromaeosaurids

Not to dismiss the RPR restraint model in its totality - I can picture small game and smallish dromies (troodontids especially) - pinning small with their #2 claw and even flapping with their arm wings a bit to maintain top dominance. However in larger and larger dromies this tactic becomes vanishingly feasible and outright ludicrous in Utahraptor sized dromies. It is, in essence the bio-functional equivalent to a fat guy in a little coat, two things combined that don't make sense.



Think about it, Utahraptor was big and robust, like polar bear sized. It was no light weight. The notion that arm wings on such an animal - if they even existed and were not functionally reduced - could generate enough power and lift to achieve any semblance of control and lift necessary for stability flapping should be tossed in the scrap heap of bad ideas. Again, not sail gliding Stegosaurus bad, and it is entirely possible that some small dromies/microraptorines/troodontids engaged in some stability flapping in choice circumstances. But pretty indefensible when we imagine what stability flapping really means - that dominant vertical position is maintained via wing-arm strength flapping strong enough to control not just one body but two struggling bodies - then the utility of stability flapping becomes vanishingly small in dromaeosaurids much larger than - ball parking here - turkey sized? I definitely would say stability flapping is pretty nonsensical in full grown Deinonychus and maybe even Velociraptor...

What Does the Evidence Actually Show?

Which is exactly what the fossil record tells us. Remember we do have a certain Velociraptor locked in mortal combat with a Protoceratops.

CC2.0 credit Yuya Tamai Protoceratops & Velociraptor fighting dinosaurs

We shouldn't feel compelled to explain such a situation as abnormal or a very rare occurrence. It was common enough to enter the fossil record after all.  And it is doing exactly what should be expected in the scenario John Jackson laid out in his book. Velociraptor is not hitching a ride on the side of the Protoceratops, not is it stability flapping or grasping the animal with all of its foot claw in some weird type of proto-raptor foot grasp. The head of the Velociraptor is poised to strike but may not be all that important for the killing. The arms and hand claws are very important in the predatory endeavor as they seek to restrain and stabilize the prey animal for ultimate dispatch by the killing claws. Given their increased range of motion and length compared to other theropods they performed a different role in predatory actions. They grappled with prey and helped to hold and stabilize prey which in turn allowed the killing claw to strike with better precision and accuracy. This is directly analogous to the manner in which large felids will grapple with prey using their forelimbs and secure the prey for dispatch via throat bite or nasal blockage. Finally the killing claws are doing exactly what they should be doing... killing!! They appear to be literally gouging into the neck region!! Poor Protoceratops!!

We actually had an earlier iteration of this idea laid out to us by Kenneth Carpenter in a review paper titled Evidence of Predatory Behavior by Carnivorous Dinosaurs (GAIA, 1998). Carpenter raises concerns with the idea of sickle clawed theropods disemboweling prey items but in his analysis of the fighting dinosaurs he makes specific mention of the likely killing style as evinced by this most remarkable of preserved interactions:


Carpenter also provides several diagrams of sickle claws with specific mention of a likely sharp cutting edge. Unfortunately Carpenter strangely backs off of the cutting edge aspect of the claw likening it to being "less sharp than a dull knife". Perhaps he was being a tad overly conservative, in any case Carpenter reasons that sickle clawed dinosaurs had  such blunt claws because: "although we don't know how sharp the keratin sheath of a dromaeosaurid claw was, it was probably less sharp than a dull knife because there was no way for a dromaeosaur to hone an edge."


Let's reason this out. Dromaeosaurs revamped their entire hindlimb morphology, literally raising digit two off the ground in walking posture. And we are to presume all of these sweeping morphological changes were done merely to create a claw with a sharpness less than a dull knife?!? Come on now.

If we merely make the defensible assumption that the keratin sheath grew constantly then we can safely assume that the animal had to hone it down through use on prey items or why not simply hone its claw like a felid does? What's going to stop it?

So when we add it all together we see this first iteration of the stab and kill from the inside hypothesis from Carpenter. Unfortunately Carpenter downplays several aspects of it such as the likelihood of a sharp cutting edge and for whatever reason the idea doesn't get much traction, even though it better explains the evidence than what Ostrom suggested or even subsequent works by Manning (2005) & Fowler (2009). Then comes along John Jackson, whom I don't recall if he cited or read Carpenter, but suggests an improved, but still problematic hypothesis, of sickle claw killing. Jackson gets it right I think in assuming a sharp cutting edge and that once the claw had penetrated and pressed into tissue it was free to repeatedly stab and traumatize tissue from the inside. Jackson thinks that the caudal tail rods of dromaeosaurids were necessary for this motion but I have my doubts and the revelation that Utahraptor lost its tail caudal rods but otherwise shows hyper carnivorous attributes supports this. Finally it should come as none too great a shock that the burly iguanodonts, nodosaurs, and sauropods that Utahraptor shared its habit with and which formed its prey base all had a singular vulnerability - a vulnerable neck.



So that is where I stand with what I regard is the leading hypothesis on dromaesaur killing claw function. It is interesting I think not so much for what it says about dromaeosaur killing claws but what it says about us. It is a tale on the transmission of ideas and hypotheses - what counts as a good hypothesis and who is allowed to advance such hypotheses. It also shows how good ideas - though not necessarily perfect when advanced - sometimes get pushed aside or disregarded. Lost in the mix so to speak. But then later on they can get rediscovered, dusted off, and shown the light of day.

I do think that this idea - or collection of ideas, the evolution of a hypothesis via disjointed bits and pieces - will ultimately be one that is nursed back to health, retooled and refashioned.

The Raptor Fossils Project (Utahraptor) w/link to gofundmeUtahraptor



Refs

Carpenter, Kenneth Evidence of Predatory Behavior by Carnivorous Theropods. GAIA no 15 (1998) December pp 135-144 online pdf

Fowler DW, Freedman EA, Scannella JB, Kambic RE (2011) The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds. PLoS ONE 6(12): e28964. doi:10.1371/journal.pone.0028964

Jackson, John. The Secret Dinobird Story December, 2013

Manning, PL, Payne, D, Pennicott, J, Barrett, PM, Ennos, RA (2006) Dinosaur killer claws or climbing crampons. Biology Letters (2006) 2 110-112 pdf


"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine


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Tuesday, July 4, 2017

Meathook Parade: Permutations, Iterations and Revelations On Predatory Theropod Forelimb Use

The following will be a blending of several under appreciated ideas on theropod forearm use combined with some of my own ideas. It seeks to drive at better answers by asking better questions.



Ahhh those theropod forelimb. They are a bit of an enigma, no? As bipedal primates descended from a brachiating pedigree of ape we have an intuitive awareness of our ability and utility to reach out and grab things.  Predatory theropods, despite being bipedal and equipped with arms and fingers like us, were a bit more constrained in their forelimb movements. The neck and head would be the first to contact with prey, the arms and claws being substantially rearward. Furthermore, the range of forearm extension and wrist movement was severely limited. Essentially the forearm and wrist acted as one single unit with the wrist unable to rotate and the radius and ulna locked together unable to rotate as well. The shoulder was likewise constrained to a relatively smal range of motion. Would it not have benefited predatory theropods to have freed up their forearms, wrists, and shoulders for a wider range of motion to assist in prey capture and manipulation? So that they could "reach out and grab stuff" like we do?

Suchomimus credit Duane Nash


Interestingly, there appears to have been at least one instance of theropods increasing both wrist and shoulder mobility and thus evolving the ability to "reach out and grab stuff" (Zanno et al., 2006). From wikipedia: "Within Therizinosauridae, broad changes to both the structure of the forelimb, pelvic, and pectoral girdles likely corresponded to changes in the lifestyle of the animals. The forelimb has undergone a drastic increase in robustness, the flexibility of the wrist has increased, and the presumed reach of the animal is believed to have lengthened. Moreover, the pectoral girdle has been modified to further augment upright reach, however the grasping ability of the animals is thought to have decreased. As with the modifications to the head, these adaptations are thought to have assisted with an herbivorous lifestyle, as they may have increased the ability to harvest and collect vegetation.[3]The obvious implication is that when the need arose to "reach out and grab things" the commensurate forelimb adaptations did arise - except that they did not arise in a predatory theropod but a likely herbivorous/omnivorous one!! Maybe the predatory theropod forelimb arsenal was not functionally adapted for "reaching and grabbing things" but served a separate purpose? Perhaps we are not satisfied with theropod forelimbs - that they are a bit enigmatic - because we are assuming the wrong job for them?

credit IsisMasshiro


There is currently a strong notion that whatever the forelimbs were doing - they were of secondary importance to what the head was doing in predatory theropods. And that if the hands were involved in prey capture they stabilized and held prey for the benefit of the head to deliver the dispatch. This notion is actually impractical for several reasons. Theropods neck musculature studies on Allosaurus indicate a design optimized to strike ventro-flexively (Snively et al, 2013). In other words they struck down and out away from the body. They were not optimized to strike back towards the body as would be expected if they bit into prey held in place by the arms. Furthermore the sheer implausibility of such a design is patently obvious when one tries to align the kinematics of such an action in the theropods with especially reduced forearms and short powerful necks such as tyrannosaurids and carcharodontosaurids.  Can anyone point me to one convincing depiction of short armed theropods holding prey with their arms as the bead bites into it?  It is also a bit of a myth that grasping hands are even necessary for the killing and dispatching of reluctant prey items by the mouth. Even a cursorary overview of both terrestrial and aquatic predators reveals that this is not the case - that the skull can be both a grasping and killing instrument - no hands need be involved.

Crylophosaurus credit Duane Nash


For this piece I am going to approach these "limitations" in wrist/arm/shoulder mobility from a different perspective. That these limitations were not at all limitations - they were in fact adaptive benefits. And that these benefits were not actually in place to assist in the capture of prey i.e. "the reaching out and grasping of prey", that was the job of the head. The forearms and wrists of predatory theropods were in fact so severely limited because of two, not mutually, exclusive reasons; 1)  many theropods would have dispatched prey with hand claws after the initial grasp by the jaws and 2) all predatory theropods - with notable exception of abelisaurids - would have used their forearms to transport food parcels to localized feeding locations and perhaps mates/offspring.

In other words it proves useful in flipping the equation: " the arms held prey for the head to dispatch" into " the head grabbed prey for the arms to dispatch" in order to understand the forearm use in a great many predatory theropods.

credit Brian Engh.

An important distinction that will color these arguments arose from an observation that Andrea Cau brought up to me in discussions on abelisaurids, theropods, and forearms. That there is a roughly inverse relationship between the power and bite of the head and the bulk and importance of the forearm in predatory endeavors. That is, for the theropods with weaker, slashing, and more modest skulls and teeth,  forearm strength and killing capacity are enhanced: spinosaurids, allosaurids, neovenatosaurids, megaraptors, basal tyrannosauroids, among others . Alternatively, where head power is enhanced arm strength and killing capacity is diminished: carcharodontosaurids, ceratosaurids, tyrannosaurids, abelisaurids. Now certainly this is not a hard and fast distinction, there were shades of grey, but I think it is a useful way to parcel out the discussion. No I am not saying that Suchomimus never killed with its mouth, nor am I saying that T. rex never killed anything in its hand claws. But they did invest in different arsenals and this should matter.
*Note that only in abelisaurids do we see the arms mutated into vestigial structures. This is an important distinction because even in theropods with reduced forearms they were not vestigial but offered an important functional usage in the transport and relocation of food resources. Dromaeosaurid forearm use will be discussed in a future piece.

In order to disabuse ourselves of the  notion of theropod forearms as tools for "reaching out and grabbing" or "holding onto prey for head dispatch" I want to revisit a term often used in the discussion of predatory theropod hand claws: meathooks. The term is a useful one, not only because it alludes to a human contrivance, but expresses quite succinctly the use of these forearms with due credit to notions of form and function having applicability not only in natural systems but culturally mediated systems of butchery. In both situations form follows function.

Megaraptor hand. author raffaeli serge CC2.0

Enough with all these academic pedantry I want to give you, the reader, an immersive feeling on what it was like to be young sauropod skewered alive on the Megaraptor meathook claws.





Ladies and gentlemen it is disturbing because the Mesozoic was disturbing - a real horror show. Now keep in mind the meathook claws of theropods, combined with a rather inflexible, strong, and stoutly built arm, work in conjunction to lock a food item in place. Such food items are pinned by either the opposing arm and claws or are wedged in against the torso. It is the meathook morphology of the claw combined with the limited range of motion of the arm and wrist that actually make escape from such a contraption very remote. In other words, the exact flaws that we have felt for so long are built into the system actually in this view are benefits. The prey can't squirm out of the arms due to the inherent inflexibility of the arms!!

credit Brian Engh used w/permission
Brian Engh (Don't Mess With Dinosaurs) did this evocative mural depicting speculative dinosaurs of the early Jurassic Navajo sand-stone of New Mexico. Brian made the rather atypical depiction of the putative top predatory holding a coelophysid in its claws. Also check out Brian Engh and other paleo goodies on July 13th 2017 at nerd night in L.A. if possible. I will try and make it too!!



There have been some detailed studies on large predatory forelimbs. One of the most interesting and little heralded studies is by Senter & Robins 2005. What I want to draw attention to in this abstract is; the extreme flexibility of the manus - the fingers can hyperextend; the permanently locked and bent elbow, unable to straighten; the notion of struggling prey further impaling itself on digit 1; and the noted difference between coelurosaur finger flexibility (they were doing different stuff) and other theropods .


What this study gets really right I believe is where they say "Acrocanthosaurus could manually grasp prey that was beneath its chest, towards which it may have used its mouth to move prey. Struggling prey would have impaled itself further upon the permanently and strongly flexed first ungual." Perfect, they really nail it here because they are the first - that I know of - to really decouple the forearms from the head as killing instruments in their own right. That is, it is not the claws holding the prey for the head to dispatch it is the head moving prey towards the claws for dispatch!! And this notion of the head deliberately moving prey items towards the killing hand claws does mesh well with the idea of sub equal sized prey items (i.e. loads of baby dinos) forming a heavy part of the diet of these animals. So while I am not the first to make this distinction - that the hands were killing implements independent of the head - I see no reason why this method can not be extended out to a whole range of other meathook handed theropods. Again, I'm not the first to advance this idea but I still maintain it has not garnered widespread exposure and knowledge.

The almost preternatural flexibility of some theropod fingers is something that does not get enough press. Once you look at the range of extension one has to wonder, why? The answer I would suggest is that the fingers took a lot of abuse from prey items squirming while engaged in the meathook bear hug. In order for the fingers to remain hooked in such flexibility would be paramount. No matter how hard and strongly the prey item squirmed the fingers would just flex and move to keep the hapless victim ensnared. Furthermore the basic function of an animal lifted off the ground and struggling against gravity would dictate that the claws dug in deeper to the animals; body cavities penetrated; lungs punctured; ribs cracking; viscera perforated; tendons gouged; and spinal integrity compromised. Abso-fucking-lutley brutal.

It is an ingenious solution: the fingers can bend and extend all over the place to absorb the struggles of the prey item, alternatively the extremely inflexible wrist, forearm, and shoulder maintain a rigid "meathook bear hug". Diabolical.

Probably the best visual I can find for the crazy hyper extendable meathook claws of some theropods is this visual from the recent study on Australovenator forelimb motion.





"I'll Show You the World" Australovenator credit Duane Nash



The megaraptoridae took this forearm dominance to the hilt, they also appear to show a bit more forward mobility in the shoulder joint perhaps even allowing food clenched in the hands to be brought up to the face - an unsettling manner of eating due to the similarity to our own feeding style.


credit Matt A. White, Phil R. Bell, Alex G. Cook, David G. Barnes,
Travis R. Tischler,Brant J. Bassam,David A. Elliott
Also of note is that by allowing the arms to engage in the killing activity the head - and most importantly the eyes - are safeguarded from retaliatory jabs of struggling prey. Many a prey item probably met their end after the initial grasp of the head in the clutches of the meathook bear hug. Trenchant hand claws - especially massive ungual one - dealing the death blow via grievous bodily insults much quickly and safely than injury incurred by the slashing teeth.

Of course I would be remiss to not give a mention to the several studies documenting abundant - and often extreme - forearm pathologies in predatory theropods (Senter & Juengst, 2016) in which a Dilophosaurus got absolutely wrecked, like freaking Monty Python style.

from Senter & Juengst. credit L. Walters (LWPaleoArt)
Senter & Juengst do a nice summary of documented forearm pathologies in theropods in the introduction - therefore saving me a load of work so I will put that here:

Some comments - a lot of mention of T. rex here. That might be a bit surprising considering T. rex should fall more into the "kill with mouth" gestalt. But there might be some reasons. As I will discuss later specific circumstances may have necessitated live prey being put in the arms of T. rex and other mouth dominant killers; the public, and researchers, like to obsess on T. rex so it might just be more looked over; multiple specimens; pathological features may often be omitted or overlooked in descriptions. Overlooked and omitted pathologies is interesting and Senter & Juengst go into some detail in these regards:

I should also give a mention to the work of Rothschild et al, 2001 that did some work on stress fractures and tendon avulsions in theropods as indicative of an active predatory lifestyle. I don't have the original work but it is heavily cited in the wikipedia articles on Ceratosaurus and Allosaurus both of which evince evidence of forearm and manus pathologies. Indeed the well documented trauma that Allosaurus sustained might be indicative of a willingness to sink its meathooks into prey substantially larger than itself!!

Earlier in this discussion I alluded to some of the reasons why a T. rex or other "mouth killing" theropods would have put a live or still struggling prey item in the grasp of its forearms. I also want to suggest some reasons why we should be optimistic about the utilitarian benefits of hauling parcels of food around in the arms (except for abelisaurids of course wink, wink). Let's remain mindful that as reduced as tyrannosaurid arms were, they were not vestigial. They were actually pretty damn powerful, conservative estimates give T. rex about 430 lbs on the bicep curl - a feat no human, not even pro-body builders can ever hope to achieve.

Removal of food from a highly competitive/dangerous arena to a more secure locale. Modern predators do it all the time. Hyenas haul off bits or whole carcasses. Raptors will take their prey off the ground to a safer location to eat. Leopards haul their kills up into trees. Carcasses can attract a lot of undue attention and if you have a way to move your larder to a more secure locale all the better for you.

*Note that, unlike quadrupedal predators that have to carry food in their mouth, theropods carrying food in their hands can still lash out and defend against would be usurpers with their mouth.



Transport of food to a mate and/or offspring. It is weird to think of such prosocial behavior in these animals but not without merit. Especially in light of the recent incubation lengths given for some dinosaurs - if such lengths were emblematic of theropods - then I think the discussion swings more and more into this realm.

Southern Ground Hornbill feeding mate. credit Steve Upton
Maximize exploitation of an abundant ephemeral food source. This is one of the funnest ones for speculative and humorous depictions. A bivouac of baby dinosaurs, a trapped pool of lungfish, a beach full of nesting/hatching sea turtles. Every once in a while predators get a gargantuan smorgasbord of easily acquired and abundant food stuffs and then it is gone. Theropods I would put forth as champions at taking advantage of these windfalls. First swallow as many as you can, then have each arm carry one, and finally cram as many into your maw as possible.

Greedy Daspleto credit Duane Nash


Atlantic Puffin w/sand eels credit Paul Mcllory CC2.0

So to review some of the main points:

- Predatory theropod forearm use has been stymied by our own intuitive understanding of having flexible, grasping forearms. We expect that theropods should have the same use of forearms in "reaching out and grabbing stuff" as we do, so that when we see they are limited in this regard it is thought of as an imperfect, problematic system.

- A study on the forearms of Acrocanthosaurus is one of the first mentions of theropod forearms being decoupled from the head as a killing mechanism in their own right. Forearm killing dominance has also been suggested for megaraptorids but can be extended out towards other theropods to varying degrees.

- There is a general pattern showcasing a trend from more mouth dominant predators to more arm dominant predators. Towards the extreme of forearm dominant predators would be spinosaurids and megaraptorids, towards the mouth dominant extreme would be tyrannosaurids and carcharodontosaurids.

- A meathook type claw morphology combined with a rigid arm anatomy would allow predatory theropods to not only kill but to carry prey/remains manually, useful for several very practical and not mutually exclusive reasons i.e. relocation of carcass, feeding of mates/offspring, hoarding of ephemeral rich food source.

- Forearm pathology in theropods is consistent with a heavy dependence on forearms in acts of predation.





References

Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.

Senter, Phil; Robins, James H. (2005). "Range of motion in the forelimb of the theropod dinosaur Acrocanthosaurus atokensis, and implications for predatory behaviour". Journal of Zoology266 (3): 307–318.doi:10.1017/S0952836905006989

  1. Snively, E., Cotton, J. R., Ridgely, R. & Witmer, L. M. Multibody dynamics model of head and neck function in Allosaurus (Dinosauria, Theropoda), Palaeontol. Elect. 16(2), 11A 29p (2013).


White MA, Bell PR, Cook AG, Barnes DG, Tischler TR, Bassam BJ, et al. (2015) Forearm Range of Motion in Australovenator wintonensis (Theropoda, Megaraptoridae). PLoS ONE 10(9): e0137709. https://doi.org/10.1371/journal.pone.0137709

Zanno, Lindsay E. (2006-01-01). "The Pectoral Girdle and Forelimb of the Primitive Therizinosauroid Falcarius utahensis (Theropoda, Maniraptora): Analyzing Evolutionary Trends within Therizinosauroidea". Journal of Vertebrate Paleontology26 (3): 636–650. JSTOR 4524610doi:10.1671/0272-4634(2006)26[636:tpgafo]2.0.co;2.









"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

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Wednesday, June 21, 2017

An Issue of Scale

Depending on how you deeply you read into the title of this post it can be not only a double but a triple entendre.

 "How many angels can dance on the head of a pin?"

Can be rephrased as "how many T. rex scales can fit on the head of a pin?"  That is the size of a millimeter and that is a little more than the average size of the T. rex "scale" documented in the recent Bell et al. (2017) paper that has got everyone flummoxed from here to kingdom come. Another visual is that more than 20 T. rex scales can be lined up across a penny. Take home point: these "scales" were small.



From Bell (2017) Note the scale bars in C & E are 5 mm while the scale bars in G & H are 10 mm.
These scales were minuscule!!


I think such dramatic issues of scale have been a bit washed over in the more hyperbolic proclamations  of the scale loyalists: "Yes, we have won!! Good riddance feather nazi elves!!" versus the recalcitrant permutations of the suddenly defensive feather crowd; "This tells us nothing new"; "Taphonomy washed away the feathers"; "Maybe T. rex had a feathered petty-coat?" Now I don't mean to mock such ideas and criticisms on the part of the pro-feather contingent but one can't deny there has been a palpable shift in sentiment from mainly feathered to mainly scaled in tyrant lizards (and by extension other largish theropods). Ironically many of the charges leveled at "awesomebros" or JP stylized scale loyalists are now being charged at the pro-feather faction; clinging to an ideal; putting an aesthetic before data; emotional attachment etc. etc.

Things are definitely a bit more unsettled and chaotic than many are comfortable with. Which is something I have been highlighting for some time in this blog; things are going to be getting more testy; a bit more non-consenus; a bit more uncomfortable for some time before things start to simmer down. Most of all things are going to be getting a bit weirder.

And those Wyrex scales are awfully weird. As I highlighted at the top of the post they are ridiculously small. Mark Witton called it the "Revenge of the Scaly Tyrannosaurus" in his blog post on the topic. If this is revenge via sub-millimetere "scales" it is perhaps the most underwhelming revenge story ever told. Sorry, I've had pimples bigger than those scales. I mean they are freaking small?! What is up with them? To put the size of these scales in perspective they are approximately equal to gila monster scales - komodo dragon scales would dwarf them. For all intents and purposes T. rex adorned in these minuscule scales would look pretty much nekkid. Especially so considering the absolute lack of any larger feature scales, larger keeled scales, osteoderms etc etc. Now, jokes about the puny size of T. rex scales aside, I do agree with Mark Witton on major points - and I'm glad he made this jump - that naked hided tyrannosaurids are not only a defensible option, but a likely one. He also raises the pertinent question - again something that I've been clamoring for here for a while - that many larger traditionally feathered dinosaurs may have lost significant amounts of fluff upon attaining larger size  (I do have some reservations on the osteological correlates for large facial scales that Mark seems to abide by but that is for another time). Another pertinent read is Andrea Cau's post on the subject. He makes some very valid and strong arguments, as he has for some time now, that taphonomy is key to a more detailed understanding of the nuances for feather, scale, "integument" preservation. Cau also raises issue with the strange shape and morphology of these scales - an observation I share and if you read the comments on his blog and know my history you can already probably guess where I am going in this piece … C-----A-----R-----U-----N------C…..

I don't know of any concrete studies linking scale size to body size but intuitively such a connection makes sense. I mean larger crocs have larger scales, larger monitor lizards have larger scales, larger boas have larger scales. That is just my off the cuff observations and I'm sure there are exceptions. But, generally speaking, scale size in a related group should get larger as the animals get larger both ontogenetically and in between related species. Did tyrant lizards break this pattern? Should smaller specimens have even smaller scales? Or are they all the same size regardless of size/species? The connection between scale size and body size both ontogenetically and between related species is probably a topic rife for potential studies.

*Turns out there are some studies linking scale size to body size. I went back and read the chapter of hadrosaur integument, authored by a certain guy named Bell, from the epic Hadrosaurs book from Indiana University Press and came across this gem which I will put here:

from A Review of Hadrosaurid Skin Impressions

"Scale morphology (especially scale counts) in modern squamates and crocodilians is typically conserved intraspecifically and is highly important in species identification (Spearman 1973; Brazitis, 1987; Hall, 1989; Cox et al., 1993; Charette, 1995; Branch, 1998). However, scale size (inferred by the inverse relation to number of scales) has been shown to vary positively with body size in some lizard species (e.g. Scleroporus, Ouferio et al., 2011). Similarly, body size (and hence, scale count) is variable both intra- and interspecifically among some squamates in relationship (both positive and negative) to Bergmann's Rule (i.e. body size decreases at lower latitudes or in warmer climates), which is correlated with minimum annual temperature and aridity (Sears and Angilleta, 2004; Oufiero et al., 2011). Despite these variations, scale morphology is one of the most reliable in the identification of extant squamates and crocodilians, especially in closely related species (Brazaitis, 1987; Charette, 1995). It is notable also that tarsal- and toe-scale patterns have been used successfully to identify individual species of extant avians, particularly raptors (Clark, 1972; Stauber, 1984, 1985; Palma, 1996)."

It is useful to note that the above paragraph is couched in a general discussion asking "can scales be used to identify individual hadrosaur species?". The promise for this sort of inquiry is great for hadrosaurs. For tyrannosaurids - as I will get into below - the promise for this sort of species identification based on scales is not looking as promising. But just for starters, who wants to venture a count on how many sub-millimeter sized scales covered a T. rex? What is the morphology of these scales? Any sort of repeating pattern? Architecture?

Are retro '90s Tyrannosaurs making a comeback? is a recent post by Paleo-King (Nima) on deviantart. While the general thrust of his piece is useful he makes a claim in the comments section that the various tyrannosaurid scale impressions are exactly the same as the well documented hadrosaur scales/mummifications. I do have to take issue with this comparison.

1) Extent of preservation. In hadrosaurids we have full on mummies that give us real life confident appraisals of where and how far scales occurred. So far in tryannosaurids we just have bits and pieces. Together these pieces suggest that "scaly" type integument is our most parsimonious appraisal for most of the body, if not all of it. But keep in mind that we as of yet don't have proof of "scaly" integument on the face and those persistent rumors of non-scaly neck displays in Tarbosaurus. Remember both crocs and birds have dispensed with scales on the face. Why? I'm not sure. It is interesting that both crocs and birds both have highly sensitive, tactile faces as well.

2) Size of scale and variety. While some hadrosaurs show scales on the millimeter range such as the Osborn "Trachodon Mummy" which are 1-5 mm and are described as "pavement scales" these patches of small scale are interspersed with regular patches of "feature scales" which are much larger at 5-10 mm.  What we see in terms of scale variety in tyrannosaurids so far is quite limited to very small "basement" type scales of a size smaller than in hadrosaurs. Hadrosaurs both at a distance and up close would have appeared much more textured than tyrannosaurids based on what we know so far. Unless you have some super X-men levels of visual acuity tyrant lizards would have looked basically nekkid.

3) Architecture. Nima points to an obvious architecture in the scales of tyrannosaurids. I have to admit that I can't see it. Carnotaurus shows architecture in the regularity of larger 4-5 cm tubercles arising every 10 cm or so from a more "basement" size scale of 5 mm tubercles. Sauropod and hadrosaur scales show a more obviously repeating scale architecture than tyrannosaurid tubercles. What I see in the tyranosaurid tubercles is something of a much more random, haphazard pattern. Apart from a size threshold of about 1 mm for the tubercles I can't discern any consistency in size; some appear more than twice as big as others and shape - apart from being generally polygonal there is a wide variety of shapes. Some of the tubercles appear rounder; others ovoid; some taper to a point; some wrap around others; and some almost to appear to bud off into other tubercles. This is a far cry from the more standardized scale pattern of hadrosaurs, which are often in repeated hexagonal patterns. Additionally given the 30 square cm patch of ilium scales we can be pretty confident that there was no larger patches of feature scales or repeating rows of larger keeled scales/osteoderms as in Carnotaurus, titanosaurs etc etc.

*Update. looks like a spoke too hastily, Nick Fonsesca says that Tarbosaurus has some feature scales form the supplementary info and then there is this from the paper:


Although I could not see the feature scales pictured in the supplementary there is indeed some evidence for a more orderly pattern of tubercles on some tyrannosaurid specimens, although not from the Wyrex material. It is of note that these feature scales are from the abdomen. Can they in fact reflect a more basal state retained? (i.e. never became completely feathered). Things are always aflux!!


So are 90's tyrannosaurs making a comeback? Sort of, I would say, but not exactly. The lack of discernible rows of feature scales or keeled scales is an obvious departure from GSP tyrannosaurids or any sort of organized row of larger scales so prominent in 90's style GSp tyrannosaurids.

And here I have to admit a weakness of not trusting my own gut and capitulating to the whole shaggy T. rex visage that has come into vogue in recent years. I blame Saurian. No, just kidding, I jest just a bit. Some have construed some of my posts as an attack on Saurian game design or that saurian should be changed or whatever. I can't disagree more. In fact I feel a bit sorry for the development team at Saurian, they must get pestered by young dino obsessives all the time. Just leave 'em alone at this point!! If Saurian is wrong fundamentally in some ways I think - at this point - these potential errors should be preserved for posterity. It's always interesting and iluminating to look back on paleoart to see how thought and ideas have changed. Saurian can be a great time capsule for what the general thought was of this period.

I do feel a bit of edification in getting back to my gut feeling for my latest tyrannosaurid art, in which I went with mainly nekkid skinned tyrant lizards with some manes and petty-coats of filaments. Proud to say this was completed before the new data came in. Boo - ya!! No need for revisions here, folks! Who says intuition, gut feelings, and following your muse have no place in science!! First published March 23, 2017 Gaslighting the Dinosaur: Just How Weird Can Dinosaurs Get?

Revelations by Duane Nash


Another argument that I would like to weigh in on is why Yutyrannus would go fully feathered while similarly sized northern tyrants like Albertosaurus went nekkid in a climate that was presumably not too different in temperature. Not to discount some of the other suggestions but merely augment, let's keep in mind that Yutyrannus was a normal slab chested theropod. Tyrannosaurids came wit da thikkness, they were barrel chested beefcakes, much more better heat retention in the torso. Big bois. Throw in some nice counter current heat exchange for the extremities, maybe a bit of a fat layer too, and you have a pretty good heat retaining system - much better than slimmer, earlier theropods at least. Perhaps a seasonal coat was a thing in northern variants, perhaps the young sported downy coat.

Back to the topic, again, my argument is not one of denying the overall message - that tyrannosaurids had a mainly "scaly" integument - but that the tyrannosaurid "scale" in both size, shape, architecture and pattern is quite distinct from those qualities of scales discerned in Carnotaurus, sauropods, and hadrosaurids. The differences in tyrannosaurid scales between these, presumably more basal integumentary patterns, very well might indicate secondarily derived "scale" patterns. In short that tyrannosaurids - like modern birds - had to reinvent the scale from a mainly feathered ancestral state.

This of course is not a novel concept, indeed the authors of the paper (Bell et al. 2017) seem to lean this way themselves. What I want to offer is that this T. rex "scale" - as suggested by the patterns discerned already - is best approximated by looking not at the exposed skin states of crocodilians with their regularly repeating, consistent, large, and architecturally sound scale designs. No the exposed skin state of tyrannosaurids is best approximated by comparison with the other archosaurs (i.e. birds) that have had to "reinvent" scales after losing them initially upon evolving a completely feathered countenance. When we look at both the small turberculate "scales" on the legs of birds and… wait for it... the minute "scaly" pattens discerned on some examples of carunculate skin of birds we can imagine a sort of novel tyrannosaurid integument that splits the difference between bird leg scales and carunculate skin. This novel skin morphology would be a lot more thicker and durable than carunculate skin but offer adequate blood flow for thermoregulatory and color flushes. Such a novel skin type combining elements of carunculate skin and bird leg tubercles would be consistent with the preposterously small tubercles of tyrannosaurids, their haphazard shapes, and offer immediate benefits for thermoregulatory and display functions.

Carunculate skin answers the question of why - when compared to other scaled dinosaurs - T. rex scales are diminuitive, non-architectural, no consistent shape, sort of globular, and devoid of rows, repeating patterns etc etc.

Oh yeah, and before you go "there goes Duane and his caruncles again" know that others have been pointing out this similarity between tyrannosaurid "scales" and carunculate skin as well…

credit Marco Muscioni
If you go back and review the T. rex skin impressions there are some very bumpy, textures reminiscent of carunculate skin. You will also notice the skin infoldings and the small size of the tubercles in carunculate skin is consistent with the unparalleled small size of T. rex "scales" and the skin creases shown in preservation.

Bell, 2017



You can take a wild guess how often the term caruncle comes up in the Bell paper (or the Carr paper for that matter). A big fat nada, zero, zilch, ninguno. I guess we don't have to talk about carunculate skin if we pretend it does not exist. Robert Bakker, I'm disappointed in you, especially since you have worked a lot with Luis Rey who gave us one of our first caruncle ridden theropods. Robert Bakker, you should read more antediluvian salad. Yes, the hate, disdain, disapproval, and ignorance for carunculate skin knows no bounds both from professionals and lay enthusiasts. And so perpetuates the false dichotomy of feather vs. scale, leaving out the retarded stepchild of carunculate skin… always the bridesmaid, never the bride.

Ye shall know it when ye sees it…

What was once scaled becomes feathered then becomes something new…

A quasi scaled, nekkid skinned, caruncled beast. Not completely serpent or fowl.

Ladies and gentlemen this is what modern theropods (i.e. birds) do when they get rid of their feathers. If we assume feathers and scales are more than a little competitive developmentally, when feathers diminish a nekkid skin is left. In order to toughen up this nekkid skin faux scales can be reinvented as they have been on the legs of modern birds. In other areas, especially of the head, nape, and neck a more motley growth pattern of various carunculate skin devices can commence. Carunculate skin can also have a superficially scaly facade. In large and gigantic theropods that mostly or completely lost feathers carunculate skin and tuberculate scales analogous to modern bird leg scales can potentially combine and envelope the torso as well, creating new motley and outlandish textures.

The dark little secret of carunculate skin is that it is found in not just one modern bird family, but many. We are left to consider two possibilities. Carunculate skin is basal to birds and quite possibly goes way back into theropods or: that it evolved independently in many different bird lineages. Both scenarios bode well for such epidermal growth to be quite common and expected in theropods that dispensed with feathers or possibly even some dinosaurs that never evolved feathers?!? (I'm looking at you Edmontosaurus)

Dang Tao Chicken "Do these caruncles make my feet look fat?"
And finally I leave you with a soft tissue preservation of another extinct giant theropod, a Moa. Do you detect some integumentary patterns that might in fact be construed as "scales"?



And finally, for the haters, social media harassers, stalkers, chastisers, discounters, "don't listen to Duane he is not teh true paleontologist", and all around perpetrators. You inspire me. Keep it coming. I stole the show with Spinosaurus and I'm doing it again right here. This C-walk is for you.
CARUNCLES BIATCH!! Up in Your Grill!!




Refs
  • Bell, P. R., Campione, N. E., Persons, W. S., Currie, P. J., Larson, P. L., Tanke, D. H., & Bakker, R. T. (2017). Tyrannosauroid integument reveals conflicting patterns of gigantism and feather evolution. Biology Letters, 13(6), 20170092.
  • Bell, P.R. A Review of Hadrosaur Skin Impressions. Hadrosaurs. Indiana University Press 2014
  • Carr, T. D., Varricchio, D. J., Sedlmayr, J. C., Roberts, E. M., & Moore, J. R. (2017). A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports, 7.
  • Cau, Andrea. Those Scales Are Scales? Theropoda. June 7, 2017 webpage
  • Nima (Paleo-King) Are retro 90's Tyrannosaurs making a comeback? 2017 webpage
  • Witton, Mark. Revenge of the Scaly Tyrannosaurus. Mark-Witton.blogspot June 16, 2017. webpage


"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine


Support me on Patreon.
Like antediluvian salad on facebook. Visit my other blog southlandbeaver.blogspot

Watch me on Deviantart @NashD1Subscribe to my youtube channel Duane Nash.


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