[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: More reptile stuff




> -----Original Message-----
> From: Thomas R. Holtz, Jr. [SMTP:th81@umail.umd.edu]
> Sent: Thursday, December 17, 1998 8:39 AM
> To:   dinosaur@usc.edu
> Cc:   Stewart, Dwight
> Subject:      More reptile stuff
> 
> Dwight Stewart writes:
> >     Basically, we are taught that mammals are "superior" to reptiles.
> >Usually birds are placed
> >     in "2nd place", with reptiles and amphibians ranked only above
> >insects, IF that.
> 
> I REALLY hope people aren't still being taught that, especially in
> schools.
> Value judgements of "superiority" and "inferiority" hearken back to the
> pre-Darwinian idea of a Scale (Ladder) of Nature.
        ###########################################

        I wish I could say they aren't, but my now adult children used to
come home
        with some very unscientific ideas from school, when they were in
school
        during the 80's, early 90's.  Sadly, Texas schools are almost
notoriously 
        deficient.  Luckily for our children, we supplied other, more
up-to-date 
        sources of information.  
        ###########################################

> >The facts simply don't bare that out; it's a kind of
> >prejudice (IMHO!).  Reptiles are better suited for certain niches.
> 
> Damn straight!!  Depending on how you define "superiority", even
> amphibians
> can be considered superior to mammals (at least in terms of species
> numbers:
> some studies, mentioned in a recent issue of _Herpetological Review_,
> suggest that amphbians, like squamates and birds, might outnumber
> mammals).
        #####################################

        Precisely!  I'm well adapted for my lab & office environment, but
put me in
        an Amazonian jungle & the Anaconda boa is MUCH better adapted! :-)
        #########################################

> >The fact that dinosaurs
> >     don't fit the model of modern reptiles, doesn't mean that dinosaurs
> >WEREN'T reptiles.
> 
> Therein lies the interesting sociological thing.  Here we have lots of
> people on the net who want to stay as current as possible with regards to
> new fossils, new paleobiological interpretations, etc., but still clinging
> to old-fashioned ideas of taxonomy.  Taxa (groups of organisms) aren't
> "models": they are historical entities, groups of common descent.
> 
> Reptiles aren't "creepy crawlies" anymore (even if that is the derivation
> of
> the name).  They represent a particular branch of the tree of life.
> 
> You can check numerous sites (including the dinosaur listserve archive or
> the U Cal Berkeley Museum of Paleontology (http://www.ucmp1.berkeley.edu))
> for more info.
> 
> >        Correct me if I'm wrong (really asking for it here!), but aren't
> >both birds and mammals evolved
> >     from reptiles? 
> 
> You're wrong, at least under modern vertebrate systematics.  To be
> terribly
> unfashionable and quote myself:
> "The category Reptilia is now considered a node-based taxon: the most
> recent
> common ancestor of turtles, lepidosaurs (lizards [including snakes] and
> the
> tuatara), and archosaurs (crocodiles and birds and their extinct
> relatives).
> Thus Aves (the birds) is part of the larger monophyletic Reptilia.
> Mammals,
> however, are not part of this clade, because our ancestors diverged from
> the
> common ancestor of all reptiles (as now defined) before the
> turtle-lepidosaur-archosaur divergence.  Thus under cladistics, the
> ancestors of mammals by definition were not reptiles (i.e., were not part
> of
> the clade Reptilia), while birds' ancestors and birds themselves are true
> reptiles (i.e., members of the clade Reptilia)."  p. 105 in Farlow &
> Brett-Surman's The Complete Dinosaur.
> 
> Following Peter Bucholz's response (which contained much of the same info
> I
> provided), Dwight asks:
> >        I see what you mean.  But, at some more distant point, mammals &
> >reptiles would share a common ancestor.
> 
> Yes.  Together, mammals and their ancestors (Synapsida) and reptiles and
> their ancestors (Sauropsida) comprise the group Amniota.  (None of these
> terms are new to cladistics: they are many, many decades old).
> 
> >     Which brings up a point about so-called "mammal-like" reptiles like
> >Dimetrodon.  Is that term still applicable?
> 
> Not really, since under modern systematics, they aren't reptiles.  Some
> prefer the term "protomammals", but this has its own teleological problems
> (that is, these animals weren't part of a "mammal factory": they were
> their
> own diverse clade, of which only the line containing mammals survives).
> Basal synapsids, or "pelycosaurs", might do the trick.
> 
> >     If so, were these animals an "evolutionary dead-end"?
> 
> In as far as we are here, the basal synapsids per se aren't an
> evolutionary
> dead-end.  Of course, the huge numbers of individual species within
> Synapsida were evolutionary dead ends (i.e., haven't left living
> descendants), but that's true of every single group of animal.
> 
> >I frankly wonder if non-avian dinosaurs had not become extinct, if we
> would
> even be > here to discuss this?  :-)
> 
> Greg Paul, in his review of Dougal Dixon's _The New Dinosaurs_, pointed
> out
> that as primate ancestors were already around by the latest Cretaceous,
> and
> as Mesozoic dinosaurs never seemed to compete directly with these arboreal
> herbivores/omnivores, there doesn't seem to be any evidence for
> competative
> exclusion of Primates by Dinosauria.  He suggested that human-like forms
> might well have been possible in a world dominated by dinosaurs, although
> large herd mammals, big carnivorous mammals, and the like might not have
> appeared (since dinos were already doing those things).
        #######################

        So, direct competition for a given niche would be the defining issue
here?
        There's a lot of food for thought there.  But, one wonders if we
would ever
        have dared come down from the trees under those circumstances? :-)
        Of course, there WERE large mammal carnivores about when we actually
did.
        Interesting...

        ########################
> For an interesting update to this, the evidence of latest Cretaceous
> parrots
> does suggest that some Mesozoic dinosaurs were arboreal
> herbivores/frugivores.  However, parrots and arboreal primates do coexist
> in
> South America, Africa, and tropical Asia.  (And, of course, there still
> remains the question of whether competative exclusion is a real phenomenon
> or not, but that's a question for another time).
> 
> Hope this helps.
> 
> Thomas R. Holtz, Jr.
> Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
> Dept. of Geology              Email:tholtz@geol.umd.edu
> University of Maryland        Phone:301-405-4084
> College Park, MD  20742       Fax:  301-314-9661
        ################################

        Yes, it does - much thanks
        Dwight Stewart