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Vivipary in metriorhynchids
Topic Started: Jan 20 2017, 09:15 AM (727 Views)
Carlos
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https://www.cambridge.org/core/journals/earth-and-environmental-science-transactions-of-royal-society-of-edinburgh/article/div-classtitlemorphology-of-the-sacral-region-and-reproductive-strategies-of-metriorhynchidae-a-counter-inductive-approachdiv/AE3A4183C5925CFE4F6F3108B3B2C147

At this point, the only argument against is their position as archosaurs. And as I've explained about the soft-shelled eggs in pterosaurs and baurusuchids, that's not a good counter-argument.
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Scrublord
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I thought your position was that they weren't viviparous.
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Dakka!
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So you mean the embryo is kept inside the mother? And not that the egg itself is carried inside? Because that would be ovoviviparity. Snakes do that too.
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Scrublord
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More importantly, does this mean we might be able to have whale-penguins after all?
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Carlos
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Read the OP. Birds still have hard-shelled eggs
Edited by Carlos, Feb 4 2017, 06:03 PM.
Lemuria:
http://s1.zetaboards.com/Conceptual_Evolution/topic/5724950/

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LittleLazyLass
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So wait, ancestral archosaurs didn't have hard-shelled eggs?
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Zorcuspine
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Feb 4 2017, 10:40 PM
So wait, ancestral archosaurs didn't have hard-shelled eggs?
It doesn't seem like it. We've known pterosaurs leighed soft-shelled eggs for some time now, so this isn't too surprising.
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kusanagi
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Pterosaurs might not be crown archosaurs at all. Bennett has them as more basal archosauriforms whereas Renesto and Binelli recovered a clade comprising pteroaurs and simiosaurs that is crownward of tanystropheids etc but still outside of the crown group. In many ways they feel like odd men out among the Ornithodira so they might well have diverged earlier. On the other hand pterosaur pulmonary airscs and pycnofibrils seem homologous with those in dinosaurs and the simiosaur Kyrgyzsaurus which was preserved with skin impressions showed no sign of hairy ptero-plumage as one would have expected were simiosaurs really near-pterosaurs.

The eggshell thing is on a continuum not either-or as many people seem to think it is. As you probably know monotreme eggs are amniotic but the eggshells are unmineralised, so in a sense all reptile eggs are a bit "chalked" whereas mammal eggs are not. Chalking is when a bird's egg hardens into a brittle shell but to some degree this happens to all reptile eggs and some reptiles moreso than others. Turtle and crocodilian eggs might still appear to be leathery but they are sufficiently crystalised and bird-like that the late embryo stage requires an airsac present to breathe by that point, exactly as in birds.

What is also important to notice is that birds, crocodiles, turtles and tuataras all deposit their eggs very early in embryonic development whereas squamates generally complete 25-50% of their embryonic development within their mothers (exceptions like monitor lizards deposit their eggs early). On this phylogenetic basis it is squamates that are unique and not the birds and egg retention may contribute to squamate supremacy at the expense of other diapsids. Although this is only to examine living reptiles for viviparity and therefore egg retention is known now in mammals, mesosours, Dinocephalosaurus, squamates, ichthyopterygians, choristoderes and sauropterygians. There isn't yet enough known about the life cycles of fossil amniotes to make phylogenetic bracketing a useful predictor and its too early to say that the eggshell constraint is irreversible. In particular the squamates and pterosaurs both display a range of chalking in their eggshell structures.
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Carlos
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Yeah, not going to trust those studies, especially given how back in time they were published. With Mark Witton 2015 showcasing speciations towards hopping in basal pterosaur hindlimbs - in addition to many other already established similarities -, I think it's clear that they evolved from a Scleromochlus-like ancestor.
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LittleLazyLass
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It's rather unhelpful that you just give the authors of the papers in question, and don't give any other information like the names of the papers that would be very helpful in trying to research them in order to debate your claims. Anyway, this is what I found about Renesto and Binelli, form here:

Quote:
 
I should also note Renesto and Binelli's (2006) analysis suffers from the opposite problem most do. While most analyses analyzing pterosaurs' position exclude prolacertiforms, drepanosaurs and Longisquama (or just have Prolacertiformes as an OTU), Renesto and Binelli's exclude proposed archosaur relatives of pterosaurs. The only included archosaurs are Ornithosuchus, Archaeopteryx and Sinosauropteryx. A useful test would include Scleromochlus, Lagerpeton, Marasuchus and such as well. Renesto and Binelli's matrix is also quite small, only including one proximal tarsal character, for instance. There has yet to be a published matrix usefully testing pterosaurs' phylogenetic position among archosauromorphs.
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kusanagi
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Jul 21 2017, 11:19 AM
It's rather unhelpful that you just give the authors of the papers in question, and don't give any other information like the names of the papers that would be very helpful in trying to research them in order to debate your claims. Anyway, this is what I found about Renesto and Binelli, form here:

Quote:
 
I should also note Renesto and Binelli's (2006) analysis suffers from the opposite problem most do. While most analyses analyzing pterosaurs' position exclude prolacertiforms, drepanosaurs and Longisquama (or just have Prolacertiformes as an OTU), Renesto and Binelli's exclude proposed archosaur relatives of pterosaurs. The only included archosaurs are Ornithosuchus, Archaeopteryx and Sinosauropteryx. A useful test would include Scleromochlus, Lagerpeton, Marasuchus and such as well. Renesto and Binelli's matrix is also quite small, only including one proximal tarsal character, for instance. There has yet to be a published matrix usefully testing pterosaurs' phylogenetic position among archosauromorphs.
Right so whereas people still think of pterosaurs as though they were firmly stem group dinos, they are actually incertae sedis to date. So far no Archaeopteryx for the pterosauria at all.
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LittleLazyLass
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No; just because a placement isn't outright confirmed does not mean we should throw out all the papers investigating the issue and say "I guess we just don't know". As of right now, is it possible they were outside of Archosauria? Sure, but right now the evidence seems to points to the Ornithodira model, which is why it's the consensus and only a few papers here and there argue otherwise.

That source I used is over ten years old, so you can't just point to the fact that it says the relationships haven't been tested properly, plenty of other studies have looked at the issue and added to our current data (for example). However, nothing would have come up refuting the points regarding why your source in flawed (the fact that the paper doesn't include Marasuchus or Scleromochlus isn't going to change with time), which is why it works with that and not the larger issue.
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kusanagi
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There is nothing at all wrong with doubt and errant placements of morphologically disparate taxa are to be expected. Yes within reason it is fine to have doubt about an avemetatarsalian position for pterosaurs. Yes, there is a very important difference between a scientific concensus based upon facts and one based upon the absence of data neccessary to establish a clear sequence in pterosaur evolution. To be honest I don't see how including Marasuchus is different to including a dinosaur it was that similar to them in the hindlimbs - just scoring for a dinosaur would probably be enough. Scleromochlus is a poorly preserved problematicum of the sort that cannot even be scored properly and ought to be excluded from matrices. Only reason S. is considered relevant to pterosaur evolution is because of what it might be in the absence of anything more definite about it. S. does seem to be a total group dinosaur but nothing more definite may be said.
Edited by kusanagi, Jul 21 2017, 03:48 PM.
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LittleLazyLass
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Yes, there is a very important difference between a scientific consensus based upon facts and one based upon the absence of data necessary to establish a clear sequence in pterosaur evolution.

Sure, but it's not like there isn't evidence pointing to the Ornithodira model, that we just place it there because we have absolutely no idea where they go. You can't just equate lack of confirmation to lack of any evidence.

Quote:
 
To be honest I don't see how including Marasuchus is different to including a dinosaur it was that similar to them in the hindlimbs.

The paper I cited in my last post points out that Pterosauria and Dinosauromorpha are similar in more features than just the foot; it stands to reason something as advanced as Sinosauropteryx will be farther form the basal condition than Marasuchus is, so the latter is simply better for testing the placement of the (supposed) sister group to Dinosauromorpha.

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Scleromochlus is a poorly preserved problematicum of the sort that cannot even be scored properly and ought to be excluded from matrices.

Are you sure? The material certainly isn't fantastic, but it's also not awful, and given how important it might be to the question of pterosaur evolution, I'd say it's worth trying to include whenever possible. You can at least try to include it, and remove from the matrix should it prove to problematic to include.

Quote:
 
Only reason S. is considered relevant to pterosaur evolution is because of what it might be in the absence of anything more definite about it.

Once again, a lack of complete certainty doesn't mean the placement has no weight. Isn't the whole point to test whether it's indeed relevant to pterosaur evolution?
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kusanagi
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Thinking about Scleromochlus: too much imagination is needed to be precisely certain of either its anatomy or phylogeny from the Lossiemouth remains, but it is probably an oblicate biped and so more dinosaur-like than the Prorotodactylus (lagerpetonid) trackway makers. And that means it was probably too crownward to be a pterosaur ancestor following the model of the evolution of flight from a quadropedal bounding form. (Sharovipteryx shows that elongated hindlimbs may sport a delta wing design but Sharovipteryx was not a pterosaur ancestor either, nor a plausible analog of one.) To me Scleromochlus seems like a dinosauromorph crownward of the lagerpetonids but of uncertain placement. If pterosaurs are avemetatarsalian - and assuming they were not modified unrecognisably by their flight adaptations - they were probably stemward of lagerpetonids and Scleromochlus and also crownward of aphanosaurs (Nesbitt), with a total group present in the Olenekian. They don't seem to be of prolacertiform grade but their most specifically dinosaurian trait - their pulmonary airsac system - would possibly drag them into Saurischia were it truly homologous and its extent as soft tissue actually codable. Pycnofibrils do seem to be early feathers of a simple grade observed in ornithischians and tetanurans but a general absence of dermal data from avemetatarsalians means arguments are circular.
Edited by kusanagi, Aug 7 2017, 09:11 PM.
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