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RE: Species & Giraffe necks



At 11:40 AM 4/12/99 -0400, G. Derkits wrote:

>I have read, but do not know it to be true, that even specialists
>cannot tell a lion from a tiger on the basis of the skeleton alone.
>Can anyone comment on this?

Basically, yes.  As Josh has pointed out, they are just about impossible to
tell apart from postcranial skeletons.  Ostrom taught (in his vert. paleo.
course) a quick & dirty way to tell them apart from their skulls (which he
learned from Simpson, I think): put the dentary on a flat surface: if you
can rock it back and forth, it is a lion; if you can't, it's a tiger.
(Incidentally, this makes _Smilodon_ a sabre-toothed "tiger" :-).

However, in terms of more detailed anatomy: I believe there was a paper in
_Neues Jarbuch_ four or five years ago talking about how to tell lions from
tigers in terms of their venous drainage patterns on the base of the skull.
Based on this, the author(s?) demonstrated that the big North American form
sometimes called _Panthera atrox_ or _Panthera leo atrox_ should instead be
_Panthera tigris atrox_ (in other words, a bigass North American tiger
rather than a bigass North American lion).

Incidentally, lions & tigers can interbreed and produce living offspring.  I
don't know how interfertile these so-called "tigrons" and "ligers" are, though.

Implications for dinosaur paleontology:
We have two closely related forms with very different external appearances
and very different behaviors.  If tigers were extinct but lions survived, we
might assume that tigers were maned pack hunters: if vice versa, we might
assume that lions were maneless solitary or small-group hunters.  It shows
that when we find evidence for some behaviors in the fossil record (i.e.,
evidence for pack hunting in _Deinonychus_), we should not automatically
assume that all of its closest relatives (_Velociraptor_, _Utahraptor_,
etc.) had the same behavoirs.

On the other paw, certain other behaviors are shared between lions and
tigers.  Some, like locomotion and the mechanics of predation, are closely
tied in to the musculo-skeletal system.  It might be easier to recover these
behaviors from the sort of evidence that remain in the fossil record.

Oh, and before the mega-splitters start using the tiger-lion similarity as
"proof" that there were four or five different species within the assemblage
currently called "_T. rex_", let me mention a different example:
The Cape buffalo (_Syncerus caffer_) has a couple of different
ecomorphotypes (subspecies associated with different environments).  In some
of these, the bosses of the horns meet along the midline: in others,
however, the bosses are quite well separated.  If this species were extinct,
I think that these might well be considered different species (if not
different genera!); however, these forms are fully interfertile with each other.

So, it's not "all or nothing" in Nature: sometimes there is very little
skeletal variation between species clearly distinct from soft tissues and
behavior; in others, there can be a lot of variation within a single
(Biological Species Concept) species.

As promised, the giraffe paper reference:

Solounias, N.  1999.  The remarkable anatomy of the giraffe's neck.  J.
Zoology 247:257-268.

>From the Summary:
"Each of the mammalian cervical vertebrae C6 and C7 and thoracic vertebra
T1, possess several distinguishing characteristics.  In the giraffe, these
three vertebrae and their associated soft tissue structures are identical to
other mammals but are displaced posteriorly by one vertebral position.  Many
morphological conditions (characters) including vertebral morphology, longus
colli and longus capitis muscles and the configuration of the roots of the
brachial plexus support this finding.  Thus, the first thoracic of the
giraffe (vertebra number 8) is morphologically equivalent to the seventh
cervical vertebra, and the second thoracic (vertebra number 9) is identical
to the first thoracic of other mammals"
and
"The first rib is unusual in articular position and in relation to
surrounding structures and attaches on C7 (vertebra number 8), masking the
recognition of the true C7."

Incidentally, this explains the odd profile of giraffe chests: the
anatomical position where their neck meets the thorax is displaced
posteriorly relative to typical ungulates.

In the same issue:
Lemelin, P. 1999.  Morphological correlates of substrate use in didelphid
marsupials: implications for primate origins.  J. Zoology 247:165-175.

How to tell forms which use small-diamter supports (vines, terminal
branches, etc.) from other climbers, based on metapodial and phalangeal
proportions and angles.

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