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Re: Elephants and hyenas

Argh, stupid new Yahoo mail decided that one of my cut and pastes should count 
as a send command. 

Anyway, here's the Witmer reference.

Witmer, L. M.  1995.  The Extant Phylogenetic Bracket and the importance of 
reconstructing soft tissues in fossils.  pp. 19–33 in Functional Morphology in 
Vertebrate Paleontology, J. J. Thomason (ed.), Cambridge Univ. Press, New York.


----- Original Message -----

> From: Jura <pristichampsus@yahoo.com>
> To: "dinosaur@usc.edu" <dinosaur@usc.edu>
> Cc: 
> Sent: Monday, 8 April 2013 12:37 AM
> Subject: Re: Elephants and hyenas
> From: Raptorial Talon <raptorialtalon@gmail.com>
>> To: Jura <pristichampsus@yahoo.com> 
>> Cc: "dinosaur@usc.edu" <dinosaur@usc.edu> 
>> Sent: Sunday, 7 April 2013 9:35 PM
>> Subject: Re: Elephants and hyenas
>> Question from a novice: couldn't convergence to fill comparable niches 
> lead to convergences in behavior? If, for example, large ceratopsians and 
> rhinos 
> have evolved broadly similar biomechanical solutions to quadrupedal 
> locomotion, 
> such that their gaits are more comparable to each other's than either's 
> is to a modern crocodile, couldn't something similar be true of their 
> behaviors? (Obviously physiology is a bigger factor in determining k- versus 
> r-strategists and so on, but even so.)
>> I mean, sure, the value of such
> inferences would be low because they're so broad, but isn't it possible
> that convergence could make a dinosaurian group more similar to a 
> mammalian group than to a croc or lepidosaur, whether we're speaking 
> behaviorally or biomechanically? I guess I'm suggesting that the 
> constraints of specific ecological roles can overwrite the signal from 
> phylogenetic bracketing to some extent, making the latter potentially 
> dubious for highly derived taxa . . . I don't entirely trust volant 
> hyper-endotherms and aquatic ambush predators to elucidate the 
> strategies of relatives which had radically different and 
> non-overlapping niches.
>> Thoughts?
>> +++++++
>> Certainly. Extensive convergence is something that we see in many animals 
> groups including extant birds and mammals. Both mammals and birds share a 
> suite 
> of behavioural and (grossly) physiological traits to the exclusion of other 
> amniotes. These gross similarities were enough for Owen (1866) to erect the 
> haematothermia. So extant birds and mammals show that extensive convergence 
> can 
> happen in distantly related groups subjected to the same environmental 
> pressures.
>> So mammals and birds show many features in common with one another. 
> Unfortunately, few of these features leave marks on the bones. Physiology and 
> behaviour may be observed today, but can only be inferred for prehistoric 
> animals. This brings us to the whole bugaboo regarding inferring dinosaur 
> behaviour based on mammals. When we use crocs and birds (and even lizards) we 
> are limiting what we can say about dinosaurs based on what we know of their 
> extant relatives. However, when we do infer things like nest making / 
> guarding, 
> or unidirectional flowing respiratory systems in dinosaurs based on what 
> extant 
> archosaurs are doing, we at least have some level of confidence in our 
> inferences. Since birds and crocs both show this particular trait we can 
> hypothesize that said trait was present in their last common ancestor. Should 
> that trait leave a mark on the bone then we can even test our hypothesis by 
> looking for those osteological correlates in the fossils. 
>> This then leads us to the problem. If we infer that mammals and dinosaurs 
> had some type of similar physiology / behaviour then we are making what 
> Witmer 
> (1995) called a level 3 prime inference. If mammals and dinosaurs shared a 
> particular trait in common, and this trait was to the exclusion of extant 
> archosaurs, then the trait must have evolved two separate times (and was 
> later 
> lost on the lineage that gave rise to birds). For behavioural and 
> physiological 
> traits that means inferring mamm
 inference up. It is basically just speculation. Yes it may have 
> happened, but what we see in mammals may also be one of dozens of solutions 
> to 
> the problems posed by that particular environment. We have no way of knowing 
> and 
> no way of testing these level 3' inferences out. 
>> So yeah, using extant archosaurs, or even extant diapsids as our hard limits 
> for dinosaurs is bound to result in the underestimation of certain dinosaur 
> qualities. However by forcing this conservative view on our interpretations, 
> we 
> (theoretically) keep ourselves from having our speculations run beyond the 
> reach 
> of our data.
>> All this isn't to say that a strict extant phylogenetic bracket approach 
> is the only way. Mammals can provide insights into how large terrestrial 
> animals 
> cope with things. Traits in dinosaurs may even be hypothesized to be 
> analogous 
> to traits seen in mammals, especially when these traits seem to have no real 
> analogue/homologue among extant diapsids. Though given what little we know of 
> extant diapsids, I'm often left wondering how many of those traits actually 
> exist.
>> Jason
>> Refs
>> Owen, R. 1866. On the Anatomy of Vertebrates, Volume 2. Longmans Green and 
> Co., London.
>> On Sun, Apr 7, 2013 at 7:36 PM, Jura <pristichampsus@yahoo.com> wrote:
>>> ----- Original Message -----
>>>>  From: Dann Pigdon <dannj@alphalink.com.au>
>>>>  To: dinosaur@usc.edu
>>>>  Cc:
>>>>  Sent: Sunday, 7 April 2013 6:42 PM
>>>>  Subject: RE: Elephants and hyenas
>>>>  On Mon, Apr 8th, 2013 at 4:39 AM, john-schneiderman@cox.net wrote:
>>>>>   I think that the ways of birds and crocodylia are our best 
> models for
>>>>>   parental care and/or defense of the young within the 
> dinosauria.
>>>>>   Dinosaurs were not mammals and mammal behaviour shouldn't 
> be used as a
>>>>>   guide to what we consider dinosaur behaviour. Tempting as it 
> is.
>>>>  Then again, birds and crocs are highly specialised archosaurs.
any more like modern archosaurs than they did 
> modern mammals.
>>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> Despite their specializations, the similarities between these two extant 
> groups make for our best inferences of what dinosaurs did. We could extend 
> our 
> bracket out a bit further to lepidosaurs, to look for traits that were shared 
> with birds and crocs, and incorporate those too. We might even use seeming 
> lepidosaur only traits if we can justify it in dinosaurs.
>>> The point is that dinosaurs and mammals are extremely far removed from 
> one another. Even when we take into account the specializations seen in our 
> extant archosaurs, inferences based on their behaviour are still better for 
> reconstructing dinosaurs than comparisons with basal amniotes like mammals.
>>> Jason