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Friday, 11 December 2015

The lifestyle of Tanystropheus, part 2: coastal fisher or first-day-on-the-job aquatic predator?

The new Tanystropheus cf. longobardicus skeletal reconstruction I presented in my last post. What the dickens did this crazy animal do? That's what we're discussing today.
What sort of animal was the Triassic, long-necked Eurasian protorosaur Tanystropheus? As we discovered in the last post, the lifestyle of Tanystropheus remains controversial over a century after it was first discovered. There is near universal agreement that it ate swimming prey such as fish and squid, but opinion is divided over whether it was obligated to aquatic, swimming lifestyles because of the burden of its long neck, or whether it was a water margin specialist that plundered small prey from shorelines. Previously, we discussed a core argument for the aquatic hypothesis, that the Tanystropheus neck would over-balance the animal. Calculations presented in the last post suggested that the mass distribution of Tanystropheus is not as weird as we might think, and certainly less so than than that of another group of long necked reptiles we are confident lived out of water, the azhdarchid pterosaurs. Based on this very basic test, I expressed some scepticism about the neck being simply too heavy to permit a terrestrial existence.

In this second discussion, I want to look at some finer aspects of Tanystropheus anatomy and palaeontology, how they've been interpreted, and what they might mean for its lifestyle. There are several areas which are relevant here: what we know of Tanystropheus diet, the palaeoenvironmental context of Tanystropheus fossils, aspects of tail and limb anatomy, and of course, the functionality of its neck. There's a lot to get through here, so let's not waste any more time on preamble.

Fossil record

An obvious line of inquiry about ancient animal habits is the palaeoenvironmental bias of its fossil remains, and the fossil organisms it is found with. We mentioned last time that Tanystropheus was a wide-ranging taxon, occurring across Europe, Israel and China in locations representing coasts and shallow waters around the ancient Tethys ocean. About half of Tanystropheus fossils come from shallow marine settings, the rest being derived from more coastal environments: river and estuarine environments, lagoons, intertidal settings and so forth (for a brief overview, check out the Fossilworks entry on this animal: there's a few localities missing, and the 'terrestrial' occurrence of Tanystropheus there is erroneous, but it gives a flavour of its depositional context). We often find marine fish and seagoing reptiles in the same beds as Tanystropheus, but it also occurs alongside terrestrial or freshwater species such as temnospondyls, terrestrial reptiles, stem mammals and plants in a number of locations. The link of Tanystropheus to these faunas seems complex: in one locality, Tanystropheus fossils only occur in horizons containing a mix of highly terrestrial and highly marine reptiles, without many 'intermediate' semi-aquatic species (Renesto 2005). Because Tanystropheus was likely not adapted for a truly seagoing lifestyle, this has been argued as evidence of it being part of a terrestrial community rather than a marine one (Renesto 2005).

Collectively, it seems difficult to argue a strong terrestrial or marine bias in this record. Tanystropheus seems to have lived in or around aquatic environments, maybe with a bias to those under marine influences, but it does not seem a stranger to brackish or freshwater settings either. There is perhaps something of a skewed association with marine animals, but it occurs with enough 'terrestrial' forms to keep the idea of a coastal fishing lifestyle buoyant. It would be interesting to put some actual numbers on this and see how commonly associated with terrestrial influences Tanystropheus is, or whether a couple of sites are skewing our perception of data. Maybe that's a job for another blog post - until then, we probably need to look at other sources of information for clearer lifestyle indications.

Gut content

The idea that Tanystropheus ate swimming prey is verified by the association of digested fish remains and cephalopod hooks in the gut regions of articulated specimens (Wild 1973; Li 2007). The latter is sometimes considered smoking gun evidence for the swimming Tanystropheus lifestyle hypothesis, it being reasoned that cephalopods are exclusively marine animals, mostly found far out to sea, and unlikely to be eaten from land (e.g. Nosotti 2007).

A number of heron species, including the globally distributed black-crowned night heron (Nycticorax nycticorax), are known squid-eaters. Image from Wikimedia (CC ), by Kuribo.
The fossilised squiddy gut content of some Tanystropheus specimens certainly matches the idea of a marine-influenced lifestyle, but several non-marine, and sometimes non-aquatic, birds and mammals challenge the idea that it had to be a swimming animal to have obtained them. Examples include night herons (Hall and Cress 2008) and several types of mustelid (e.g. Hartwick 1983; Beja 1991). Exactly how night herons obtain squid is not documented in detail, but photographs of two other heron species demonstrate squid can be apprehended without venturing out to sea, or even into deep water. As might be expected, cephalopods also frequently wash up on beaches (sometimes still alive, and in huge numbers) allowing animals such as bears and wolves to also access cephalopod meat. Humans are also adept predators of squid in coastal settings. Shore-based squid angling is reportedly a growing hobby around the world (and apparently requires only very basic fishing equipment) and we routinely collect cephalopods from intertidal environments for use as bait or cooking ingredients (Denny and Gains 2007). Contrary to expectations, accessing cephalopod prey from shore environments appears quite possible for a number of differently adapted species. It seems premature to rule out a coastal fishing lifestyle for Tanystropheus just because it sometimes ate squid-like animals.


Anatomy

One of the most famous and complete Tanystropheus longobardicus specimens known, MSNM BES SC 1018. This illustration is from Nosotti's huge (2007) monograph.
With the fossil record and gut content providing slightly ambiguous insight into Tanystropheus habits, its functional anatomy is probably going to be a deciding card here. A lot has been said about the functional morphology of Tanystropheus, and there is a lack of consensus on many issues. For instance, its neck flexion has been described as almost 'swan-like' (Wild 1973); broom handle-stiff (Tschanz 1988), or somewhere inbetween (Renesto 2005). Its tail has been considered lousy for aquatic propulsion by some (Wild 1973; Renesto 2005) but well suited for the job by others (Tschanz 1988; Nosotti 2007). Clearly, some of these ideas must be erroneous, them being too polarised for all contributing parties to be correct. Such confused functional interpretations are not without precedent: Darren Naish and I noted a similar situation with azhdarchid pterosaurs in our 2008 paper: maybe this is simply what happens when we try to understand weird fossil species.

The main points of contention about Tanystropheus functional anatomy concern its tail, limbs and neck. We might link these attributes to two principle functions: locomotion and foraging. Let's start with the former. Proponents of the aquatic Tanystropheus hypothesis suggest the tail was the likely propulsive organ, it being considered that the limbs are too long and gracile to function as effective paddles (Tschanz 1988; Nosotti 2007), even if the foot might have some aquatic adaptations (below; Kuhn-Schnyder 1959; Wild 1973). Near 'horizontal' articulations between the posterior trunk and tail vertebrae appear to have permitted this part of the body to undulate laterally, permitting a crocodile-like sculling approach to swimming.

Soft-tissue preservation around the tail of Tanystropheus cf. longobardicus specimen MCSN 4451. We're looking at the underside of the tail in the left of the image here - note the width of the soft-tissue (the big grey mass). The verts on the right are shown in left lateral view. From Renesto (2005).
A fly in the ointment here is the gross tail anatomy of Tanystropheus. Rather than being long, and comprised of the robust, tall vertebrae expected of a sculling aquatic reptile, its tail is slender, relatively short and actually broader than tall - hardly an ideal sculling organ (Renesto 2005). This fact has been noted by proponents of the swimming lifestyle hypothesis, and it has been proposed that the tail sported some sort of fin to modify it into a swimming organ (Nosotti 2007). Well, maybe, but this idea is entirely without support from fossil data. Readers may recall that marine reptile workers have been quite ingenious in their ability to detect fins and flukes from osteological correlates, none of which are obvious in the tail of Tanystropheus. Moreover, preserved soft-tissues from the anterior Tanystropheus tail region (above) show no signs of fins but instead a broad tail base poorly suited to aquatic propulsion (Renesto 2005). Also worth mentioning is recent work on the relationship between vertebral articulation and swimming capability in crocodyliforms. They can reflect sculling behaviour, but articulations like those seen in Tanystropheus can also be linked to preventing trunk collapse during non-aquatic locomotion (Molnar et al. 2014). We could go on, but I think the point has been made that arguments for the Tanystropheus tail being a swimming organ are, at best, not without complication, and, at worst, uncompelling.

Turning our attention to the limbs, I mentioned in the last post that I was surprised how 'leggy' Tanystropheus was when restored as walking rather than, as we're used to seeing it, squatting. The limb proportions and girdle sizes of Tanystropheus compare well with non-aquatic protorosaurs such as Macrocnemus and Langobardisaurus (e.g. Renesto 2005; Nosotti 2007) and, as alluded to above, it is immediately clear that these limbs are not flippers. Not only are they too long and gracile for effective use as hydrofoils, but their long bones are hollow - unexpected features of an aquatic animal. Another protorosaur - Dinocephalosaurus - gives an insight into how these reptiles could modify their limbs into efficient flippers (below), and, without going into detail, they're nothing like the limbs of Tanystropheus (see Renesto 2005 for a long discussion of this). Tanystropheus limb joints are mostly robust and well-defined (but see below), and its hands and feet are strongly built and compactly structured. Some differences between hand and foot proportions can be seen: the hands are short, the feet rather long, and the latter characterised by a peculiarly long first bone in the fifth toe. The limb girdles are well developed, looking proportionally comparable (speaking from pure eyeballing here, not precise measurements) to those of large monitor lizards and crocs. I find the shoulder blade of particular interest, as it is rather large and broad, subequal in proportions to the coracoid (the lower portion of the shoulder girdle). This contrasts with many aquatic animals, which tend to maximise the size of the coracoids while reducing the scapula.

Variations in protorosaur limb anatomy, demonstrated by the aquatic Dinocepahlosaurus (A-B) and Tanystropheus (C-D). Note how both the arm (A) and leg (B) of Dinocephalosaurus are short and wide compared to their equivalents in Tanystropheus (forelimb = C, hindlimb = D), making them much more effective flippers. You can also see the reduced mineralisation in the Tanystropheus wrist here. From Renesto (2005).
I have to agree that Tanystropheus limbs were probably unchallenged by non-aquatic habits (Renesto 2005) and, if this were any other species, I don't think we'd be disputing the fact that its limbs were likely capable of terrestrial locomotion. That said, there are undeniably some hints that Tanystropheus was not always walking on land. Several authors have noted that the wrist and ankle bones of Tanystropheus are not as well ossified as those of other protorosaurs (e.g. Rieppel 1989; Nosotti 2007), and some have suggested that the pelvic bones may also be somewhat less defined (Rieppel 1989). Moreover, the elongation of the fifth toe is atypical for a purely terrestrial reptile, but common among aquatic creatures (see Kuhn-Schnyder 1959 for a good illustration of this point). Proposals that this made the foot somewhat paddle-like, or supported Tanystropheus on soft, saturated substrates do not seem unreasonable. These are fairly minor modifications to the skeleton when viewed overall however: the reduced ossification in the wrist, ankle and pelvis is pretty minor - especially when we consider how cartilage-filled the joints of many giant terrestrial archosauromorphs can be (Holliday et al. 2010) - and the reconfiguration of foot bones do not override the otherwise elongate, gracile structure of the hindlimb. My overall interpretation of these limbs broadly agrees with that proposed by Renesto (2005): a bauplan suited to terrestrial locomotion with some aquatic leanings, rather than sustained aquatic propulsion.

Finally, we come to the neck. I've saved discussion of this for last because I consider much of its anatomy so significant to Tanystropheus habits that discussing it earlier might have rendered other points a bit superfluous. We make a lot of noise about how strange the neck of this animal is, but Tanystropheus neck anatomy frequently converges with those of other long necked reptiles - pterosaurs and sauropods - and even some long-necked mammals. That doesn't necessarily make it less weird - it's definitely still an 'extreme' biological structure - but does help us put its neck anatomy in perspective with other animals, as well as highlighting significant adaptive differences to neck elongation in aquatic and non-aquatic species.

As with pterosaurs and sauropods, Tanystropheus went to great lengths to lighten its neck. Firstly, its neck is comprised of relatively few (13), slender vertebrae rather than dozens of short ones (see Rieppel et al. 2010 for discussion of cervical vertebra counts in this animal). This is about half as many as some other protorosaurs had (Reippel et al. 2008), and a far cry from the vertebral counts of some dinosaurs (including birds). A low vertebral count reduces the number of heavy joints and muscle attachments in any part of the axial column, so this is a good basis to having a lightweight neck. More weight was lost through hollowing the bony core of each vertebra, a condition Tanystropheus took so far as to need bony struts supporting the interior cavities of each vertebra. Note that there is no evidence that these bones were pneumatised, seemingly lacking openings through which airsacs could penetrate the bone walls. However, simply removing bone - one of the densest, heaviest materials in our bodies - would still throw out a lot of weight. The neck was likely lightly muscled, the mid-series vertebrae being long tubes with highly reduced processes for muscle anchorage (below). In many respects, the vertebral bodies are similar to those of azhdarchid pterosaurs. The role of these tubular, slender mid-series neck vertebrae is confusing at first, but they make a bit more sense once we realise that most terrestrial animals control their necks via musculature anchoring to the top and base of the neck. This was likely true for Tanystropheus and azhdarchids because anterior and posteriormost neck vertebrae are the most complex parts of the neck skeleton, presumably reflecting attachment of more muscles in these regions. We might therefore assume their necks worked in a broadly similar to those of modern animals, weird as they are.

Three dimensionally preserved mid-series Tanystropheus vertebra described by Dalla Vecchia (2005).
The seemingly lessened set of neck muscles on the Tanystropheus neck would likely limit neck performance (i.e. the size of prey that could be lifted into the air) but, again, would facilitate weight reduction. Strong, restricting joints between the majority of the neck bones and bundles of elongate cervical ribs aided reduction of musculature further, passively resisting inter-vertebral movements which otherwise require muscle action or thick ligaments to control. Elongation of cervical ribs provides another bonus for mass reduction, this trait being linked to shifting muscles down the neck in sauropods and thus lightening the cranial end (Taylor and Wedel 2013). With passive support structures in place, muscles operating around the neck base may have been able to support and move the neck quite easily. Indeed, areas where neck elevator muscles (such as levator scapulae and the trapezius) anchor on the shoulder blade are unusually broad and well developed in Tanystropheus compared to other protorosaurs, and certainly a lot larger than those of long-necked aquatic animals (Araújo and Correia 2015). These are useful muscles to emphasise if you're looking to economise neck mass, being able to both lift and turn the neck by simply varying the symmetry of their activation. We also see a good set of short, robust cervical ribs and broad coracoids at the base of the neck, anchoring muscles related to strong downward neck motion (unless Tanystropheus differed from all other tetrapods). As Mark Robinson preemptively commented on my last post, this is starting to sound a lot like a mechanical crane: a lightweight, strong beam operated by long muscles and ligaments (cables and pulleys in our analogy) from a powerful, mobile base. Quite how much motion was possible at the neck base is debated, but the fact that a number of articulated Tanystropheus specimens are preserved with distinctly elevated neck bases suggests it was more flexible than the rest of the neck, and perhaps capable of a large range of motion (Renesto 2005). This, of course, has implications for balance: if the neck could be drawn up as in fossil specimens the centre of mass would be quite far back in the body (see the last post for more on Tanystropheus mass distribution).

To me, this is all sounding quite sauropod- and azhdarchid-like: an economically constructed neck capable of somewhat limited, but sufficient motion to procure food in terrestrial habits, albeit food that doesn't put up too much of a fight. By contrast, the Tanystropheus neck compares poorly to those of long necked aquatic animals. For one, we expect a large number of short vertebrae in long-necked aquatic species, this permitting greater numbers of muscles working on the neck skeleton. Aquatic animal neck bones are frequently expanded to enlarge the size of muscles attaching to them, these being required to move any long appendage through water. This makes for a heavy neck, but perennial aquatic support renders this a moot issue. Indeed, weight is often a commodity in water rather than a problem, it providing ballast against air-filled lungs or positively buoyant tissues - it's widely known that swimming tetrapods often have entirely solid bones to increase their mass further. The neck of Tanystropheus doesn't really match any of these features. While the number of neck bones is somewhat increased compared to other protorosaurs, the aquatic Dinocephalosaurus has almost twice as many more - 25 - in a neck of similar proportions. Tanystropheus neck length is mainly achieved by stretching each vertebra tremendously, the addition of another three vertebrae perhaps merely being a secondary measure to boost neck length overall (birds and sauropods do the same thing - adding more neck vertebrae is not strictly an aquatic adaptation). Reduction of neck mass in Tanystropheus neck (and limb) bones is also at odds with expectations for an aquatic animal, the hollow cores, stiffened joints and posterior displacement of musculature being unnecessary and even disadvantageous in an aquatic setting. It's actually hard to imagine the neck of Tanystropheus being pulled through water efficiently at all, the reduced muscle profile and long vertebrae being quite problematic and under-powered for this task. It certainly does not seem well suited to chasing and grabbing fast moving aquatic prey such as squid and fish. To me, Tanystropheus neck anatomy just seems to make a lot more sense out of water and, given how much emphasis Tanystropheus put on its neck tissues, I think this is a pivotal consideration when attempting to understanding its lifestyle.

Summary time: a twist in the tale?

Let's sum up these three lines of discussion. The fossil record of Tanystropheus suggests we could find it in a variety of aquatic settings - we might average these out to say it was a denizen of coastal and nearshore environments. It clearly had a taste for seafood, although we need to be careful not to over-state what this might mean about its lifestyle. Anatomically, it seems its propulsor apparatus is best suited to non-aquatic settings and that strange neck finds overwhelmingly superior comparison to terrestrial tetrapods than it does aquatic ones. I therefore have to agree with pretty much everything said about Tanystreopheus anatomy reflecting a 'coastal fishing' habit rather than a strictly aquatic one (e.g. Renesto 2005). I actually really struggle to see how this animal can be argued as a swimming predator, and note that even proponents of this lifestyle acknowledge that Tanystropheus must have been a sluggish, ineffectual aquatic animal, limited to ambushing prey from darkness (e.g. Nosotti 2007). This brings us to a twist to our Tanystropheus story: acknowledging some big issues with the Tanystropheus swimming hypothesis, Nosotti (2007) proposed that it was a newcomer to the aquatic realm, still carrying a lot of anatomical baggage from terrestrial ancestors. It doesn't look much like an aquatic animal because, in evolutionary terms, it's Tanystropheus first day on the job and it's still learning the adaptive ropes for being a successful marine predator.

My preferred lifestyle interpretation for Tanystropheus: a Triassic croc-o-heron which snatched prey from shorelines and promontories around coastal waterways. Note the animals perched on rocks out to sea - I have no problem with this animal swimming per se (as noted above, there is reason to think it was somewhat aquatically adapted), I just don't think it lived in water.
Personally, I find this sort of argumentation weak. It implies Tanystropheus is somehow exempt from relationships between morphology and function well established in other animals, and seems like an excuse to dismiss contrary evidence more than it does a robust hypothesis. It elevates the proposal of aquatic Tanystropheus to a foregone truth of its palaeobiology and structures other lines of evidence around that, which I cannot see as a positive approach to these sort of palaeontological investigations. To my mind, Tanystropheus taphonomy, gut content and functional anatomy are fully consistent with it being a Triassic variant on a heron, an animal which struck at swimming prey while supported on land or in bodies of shallow water. Its smattering of minor aquatic adaptations might have been useful to cross small bodies of water, support itself on wet, soft substrates and access better fishing sites. However, the morphological onus seems to be on movement unsupported by deep water, and it might be assumed these formed a minority of adaptive pressures on Tanystropheus anatomy. Although it is difficult to think of a perfect modern analogue for this, we might find comparable functionality and behaviours in a variety of birds, crocodylians and lizards.

OK, time to call it a day with Tanystropheus for now, although we're not done with weird Triassic taxa yet. I've definitely caught their bug, and I'm sure we'll be spending time with several more of these fascinating oddballs in the near future. Before then, the last post I have planned this year returns us to familiar dinosaur territory, featuring an especially obscure species none of you will be familiar with. I can barely remember what it's called... Threecerasaurus? Trihornedabottoms? Dang - I'm sure I'll remember by next time.

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References

  • Araújo, R., & Correia, F. (2015). Plesiosaur pectoral myology. Palaeontologia Electronica, 18(1), 1-32.
  • Beja, P.R. (1991). Diet of otters (Lutra lutra) in closely associated freshwater, brackish and marine habitats in south-west Portugal. Journal of Zoology (London), 225: pp. 141-152
  • Dalla Vecchia, F. M. (2005). Resti di Tanystropheus, saurotterigie e “rauisuchi”(Reptilia) nel Triassico Medio della Val Aupa (Moggio Udinese, Udine). Gortania, 27, 25-48.
  • Denny, M. W., & Gaines, S. D. (2007). Encyclopedia of tidepools and rocky shores (No. 1). Univ of California Press.
  • Hall, C. S., & Kress, S. W. (2008). Diet of nestling Black-crowned Night-herons in a mixed species colony: implications for tern conservation. The Wilson Journal of Ornithology, 120(3), 637-640.
  • Hartwick, B. (1983). Octopus dofleini. In Cephalopod Life Cycles, Vol. I: Species Accounts, ed. P.R. Boyle, pp. 277-293. Academic Press, London
  • Holliday, C. M., Ridgely, R. C., Sedlmayr, J. C., & Witmer, L. M. (2010). Cartilaginous epiphyses in extant archosaurs and their implications for reconstructing limb function in dinosaurs. PLoS One, 5(9), e13120.
  • Kuhn-Schnyder, E. (1959). Hand und Fuss von Tanystropheus longobardicus (Bassani). Paläontologisches Institut der Universität Zürich. 921-941.
  • Li, C. (2007). A juvenile Tanystropheus sp.(Protorosauria, Tanystropheidae) from the Middle Triassic of Guizhou, China. Vertebrata PalAsiatica, 45(1), 41.
  • Molnar, J. L., Pierce, S. E., & Hutchinson, J. R. (2014). An experimental and morphometric test of the relationship between vertebral morphology and joint stiffness in Nile crocodiles (Crocodylus niloticus). The Journal of experimental biology, 217(5), 758-768.
  • Nosotti, S. (2007). Tanystropheus longobardicus (Reptilia, Protorosauria): Re-interpretations of the Anatomy Based on New Specimens from the Middle Triassic of Besano (Lombardy, Northern Italy). Società Italiana di Scienze Naturali e Museo Civico di Storia Naturale.
  • Renesto, S. (2005). A new specimen of Tanystropheus (Reptilia, Protorosauria) from the Middle Triassic of Switzerland and the ecology of the genus. Rivista Italiana di Paleontologia e Stratigrafia, 111(3), 377-394.
  • Rieppel, O., Li, C., & Fraser, N. C. (2008). The skeletal anatomy of the Triassic protorosaur Dinocephalosaurus orientalis Li, from the Middle Triassic of Guizhou Province, southern China. Journal of Vertebrate Paleontology, 28(1), 95-110.
  • Rieppel, O., Jiang, D. Y., Fraser, N. C., Hao, W. C., Motani, R., Sun, Y. L., & Sun, Z. Y. (2010). Tanystropheus cf. T. longobardicus from the early Late Triassic of Guizhou Province, southwestern China. Journal of Vertebrate Paleontology, 30(4), 1082-1089.
  • Taylor, M. P., & Wedel, M. J. (2013). Why sauropods had long necks; and why giraffes have short necks. PeerJ, 1, e36.
  • Tschanz, K. A. R. L. (1988). Allometry and heterochrony in the growth of the neck of Triassic prolacertiform reptiles. Palaeontology, 31(4), 997-1011.
  • Wild, R., (1973). Tanystropheus longobardicus Bassani: neue Ergebnisse. In: Kuhn-Schnyder, E., & Peyer, B. (eds). Die Triasfauna der Tessiner Kalkalpen, XXIII. Schweizerische Paläontologische Gesellschaft 95, 1-162.
  • Witton, M. P., & Naish, D. (2008). A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS One, 3(5), e2271.

13 comments:

  1. Nice post(s). Look forward to more weird Triassic stuff, hopefully drepanosaurs get some attention.

    The arguments all make sense. One thing that I want to iterate again - something that you hinted at in this post- is this penchant for some paleontologists to argue that an animal "has unusual adaptations because it is just in the incipient stages of adapting to an amphibious or aerial mode of life..." For me this argument is pretty weak >most of the time<. 1) For starters it almost sounds Lamarckian as if the animal is striving to achieve some more perfect mode of existence. 2) This piggybacks on the first point - there is no "end game" in evolution. An extinct gliding animal that lived in dense canopy forest - when seen through the hindsight 20/20 looking glass of the fossil record - might appear to be an under-equipped flyer, but for what the animal has to do in its day to day life it is just fine. Same argument for proto-whales. From our perspective they might appear to be a "less perfect" predecessor to modern whales but for their environment sloshing around intertidal estuaries they were just fine.

    Hopefully that make sense I just think that it is important to take a wider view of these animals and - at the end of the day - they have to make reasonable sense as animals that live, breathe, eat, mate, feed in their respective environments. Sometimes just taking this more practical, common sense view is lacking.

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  2. Duane hit the nail on the head already reinforcing your point. We do have intermediary forms (I was thinking of fish becoming terrestrially adapted, but proto-whales are a better example), but none of these are considered mal-adapted, just adapted to different environments and situations at those specific points in time. Or for a modern analogue (er, kind of), the mudskipper is very good at living in the intertidal zone, scampering about perfectly well out of water, hunting, but also fleeing to water when necessary. It is not particularly good at swimming, or at terrestrial locomotion compared to animals more specialised to either realm, but no one looks at the mudskipper and declares this some sort of incipient stage that is crap at what it's trying to do (becoming totally terrestrial presumably). We should not look at fossil animals and apply these weird rules that we absolutely do not apply to modern animals, because that rather strongly implies we're wrong. If this sort of thing was ever true, we'd see it at least ONCE in a modern species, but we just don't. Applying stupid arbitrary ideas solely to extinct animals is certainly an ongoing issue...I remember Darren bringing up the apparently popular theory of elaborate dinosaur headgear being basic species recognition signalling. I'll consider it when someone convinces me that antelope horns or narwhal tusks are modern species recognition devices.

    Anyway, the main reason I was commenting was on the squid dietary element. You said that some arguments suggest it must be an aquatic animal to feed on squid. Aside from your good arguments citing terrestrial animals successfully hunting squid, why the assumption at all that these ancient cephalopods were open ocean animals in the first place? Even if they're comparable to modern squid, assuming based on vague morphological similarity that all squid from such deep pre-history were deep, open ocean dwellers by habit is absolutely ridiculous. And that is ignoring the habit of modern squid to still come near the shore on occasion. Is there any proof we didn't have near shore, shallow water specialist squid species at this time? Arguably, if squid are a really frequent Tanystropheus dietary component, that could be used as evidence of such a species existing. Even in the most aquatically adapted scenario we could attempt to force Tanystropheus into (ignoring all of your arguments entirely), this animal was certainly not going to be entering the sort of deep open water that we typically associate with squid anyway. They'd still need to be inhabiting or visiting rather shallow water anyway.

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  3. Great article. Agree with Duane and Unknown that the poorly-/not-yet adapted theory sounds like special pleading based on the hypothesis of it being mostly-aquatic presumed to be the case a priori. Another way to look at it is, given the relative rarity of fossilisation events - even in littoral environments - it's difficult to imagine that an animal so maladapted for its purported day to day lifestyle would be around long enough to have given us the fossils that we currently have. A case of evolve or go extinct.

    Unknown also broached an aspect that I wanted to comment on - the apparent assumption that squid from 230 million years ago lived and behaved just like squid today. They ask whether there could have been squid species that lived mostly in shallow marine waters. There are a number of living species of "inshore squid" (Uroteuthis) that live in varying depths of coastal marine waters and at least 3 species here in Australia which are commonly found (and fished) in estuarine waters. And who knows, perhaps there were freak species that were capable of living in brackish or even fresh water?

    This leads on to my next question, regarding the taphonomy of the Tanystropheus and associated fossils. There are countless example of the remains of wholly-terrestrial taxa being found in fully marine, non-shore environments. There is even a bivalve-encrusted ankylosaur - Aletopelta. I don't think that anyone seriously suggests that this was therefore an aquatic animal. Surely, where the remains of Tanystropheus have been found in marine sediments in association with other obviously terrestrial fauna, the more parsimonious conclusion is that these animals died in or near estuaries or rivers and were subsequently transported out to sea, perhaps following a flooding event in the case of estuaries?

    Lastly, I think that obscure dinosaur you're thinking of is called Triacornifacies.

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  4. As far as I'm concerned, and the research I've done, Tanystropheus was a totally marine animal. I ah,,, don't see my abstract listed in or mentioned...(I really need to finish the paper)Ford, T. L., 2002, A new interpretation of the skull of Tanystropheus: Journal of Vertebrate Paleontology, v. 22, supplement to n. 3, Abstracts of Papers, Sixty-second annual Meeting of the Society of Vertebrate Paleontology, Sam Noble Oklahoma Museum of Natural History, University of Oklahoma, Norman Oklahoma, October 9-12, p. 53a.

    I'm also not convinced T. conspicuus (which I believe was the largest marine non fish vertebrate at the time) and T. longobardicus are the same genus.

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  5. Note that as currently interpreted, the sediments of the Xingyi biota (which has produced articulated Tanystropheus) were deposited in the vicnity of small offshore islands near the edge of the Yangzte platform at a considerable distance (60km+) from the nearest major landmass. Would suggest that animal has at least some maritime capabilities.

    LEHRMANN, D. J., MINZONI , M., ENOS, P., YU, Y.-Y., WEI , J.-Y. and LI , R.-X. 2009. Triassic depositional history of the Yangtze platform and Great Bank of Guizhou in the Nanpanjiang Basin of South China. Journal of Earth Sciences and Environment, 31, 344–367.

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  6. @Tracy Ford I looked up your abstract and while it is interesting that the nasals are located somewhat dorsally I should expect that if this animal was truly an underwater ambush predator it should show thicker bone density and a more muscular neck for dealing with the resistance of moving against water. As to why the nasals are dorsal there is no reason to presume that this animal did not do a lot of surface swimming navigating offshore islands, tidal channels, barrier islands - which would also explain their wide distribution and as Brian Choo above noted their presence on islands relatively far offshore (although rafting can do that too). Keep in mind that modern herons have the liberty of flight so that they can move around easily to choice feeding grounds - spawning fish, tidal choke points, fish runs - while Tanystropheus would have to move around by either walking or swimming to highly concentrated but ephemeral feeding opportunities. So we should expect these critters to get around fine by swimming and even have some incipient adaptations for such i.e. dorsally placed nares. As far as interlocking teeth that Tracy argues as evidence in his abstract for being totally marine I don't think that feature is a clincher - such teeth would be useful for a wading stalker of aquatic prey as well.

    BTW here is the link to Tracy's abstract on page 53A: http://www.miketaylor.org.uk/tmp/svp-abstracts/SVP%202002%20abstracts.pdf

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  7. Also, speaking of night herons there is a roost near me that hangs out in some ol' podocarps during the day and crap all over cars and then at dusk they fly off towards the harbor, or at least in that direction, a good 4/5 miles away. I want to speculate that they feed on the abundant rock crabs in the jetty breakwater, at least that seems the obvious choice to me if I was a night heron.

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  8. Duane, I'm currently drafting a Drepanosaurus article for my own blog, so look for that in the next week or so!

    Agree with what everyone's saying about special pleading. I imagine someone may find a Tany fossil in the future with stomach contents that are not strictly marine. Also, I really need to get that Nosotti monograph--what a gorgeous specimen!

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  9. David Marjanović14 December 2015 at 02:48

    terrestrial or freshwater species such as temnospondyls

    Ooh, be careful with that. Almost all Mesozoic temnospondyls seem to have been fully aquatic (with widespread evidence for internal gills even – Schoch & Witzmann 2010, Witzmann 2013; I'll dig up the full refs later); and many temnospondyls of all ages were clearly euryhaline. There were even two million years at the beginning of the Triassic when all big marine tetrapods were temnospondyls!

    The traditional assumption that temnospondyls were amphibious freshwater animals by default is simply an extrapolation from crown-group amphibians – and thus unsupported for at least one obvious reason.

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  10. Answers to those mysteries might come from an examination of ancestral taxa, which I don’t see in your report. Just like azhdarchids, basal tanystropheids were long-necked and tiny, in the size range of sister taxa Fuyuansaurus, Amotosaurus, Tanytrachelos and Langobardisaurus. The gradual phylogenetic increase in size ipso facto accompanied a gradual ability to reach further or stand deeper in an aquatic environ. The giant chevrons on certain Tanystropheus specimens suggest a tripodal stance and this would make the balance problem go away, at least while tripodal.

    Another closely related taxon is tiny Cosesaurus at the base of the flapping clade, the Fenestrasauria. All bipeds based on the bird-like coracoid shape, they all had virtually identical feet, with an abbreviated mt5 and propodial p5.1, one reason why the first Tanystropheus specimens were confused with pterosaurs. Right?

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  12. Great article(s). I've been fascinated with Tanystropheus since I was a kid (sure I wasn't the only one...)

    I especially like this statement: "It implies Tanystropheus is somehow exempt from relationships between morphology and function well established in other animals, and seems like an excuse to dismiss contrary evidence more than it does a robust hypothesis."

    I think this could equally apply to arboreality in certain 'winged' theropods (such as Microraptor and Archaepteryx). I'm not convinced this is a robust hypothesis.

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