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Cretaceous cormorants -- really?
I've recently reported on the paper that makes a good argument against
Cretaceous loons. From this perspective, it could be interesting that
cormorants seem to be highly derived members of whatever fragment of
"Pelecaniformes", according to both molecules (Fain & Houde) and morphology
The oldest Cenozoic cormorants are from the late Eocene, like the loons and
many others (source: Feduccia 1996). Naturally I haven't tested if
calibration with Cretaceous cormorants makes their relatives impossibly old
(or just the tongue twist). But let's have a look at the Cretaceous material
referred to cormorants.
For, perhaps, some reason I always imagined in my infinite wisdom that this
material consisted of tarsometatarsi. Only today did I check this in
Mesozoic Birds. Behold, although I had read the whole book before, I was
wrong! Everything Hope refers to Phalacrocoracidae is a scapula from the
Nemegt Fm and a femur from the Lance Fm. Here's what she writes about these
two bones (p. 367):
"Limited diagnosis -- Specimens are placed in Pelecaniformes based on the
following feature: iliac facet of the femur entirely convex (unique). In
addition, the lack of elevation of the trochanteric crest of the femur
differentiates Pelecaniformes from many other birds."
So in case the scapula turns out not to be phalacrocoracid, there's no
reason to consider it pelecaniform.
"Limited diagnosis -- The specimens are placed in Phalacrocoracidae based on
the following derived features:"
Then follows a list of 3 to 6 characters of the scapula, depending on how
one counts, and 6 to 14 or so unquantified characters of the femur;
afterwards comparisons are made of the scapula to Pelecanidae and of the
femur to Anhingidae and the late Eocene to early Miocene Plotopteridae; the
differences sound like they were adaptations to foot-propelled diving in
cormorants, and those between Phalacrocoracidae and Anhingidae are
explicitely ascribed to this lifestyle.
The scapula from the Nemegt Fm and the femur from the Lance Fm (p. 368)
"Remarks -- Kurochkin (1995a, b) determined that this specimen came from a
very large cormorant. My comparisons with diverse cormorants and other
pelecaniforms are consistent with this determination. [...] The specimen is
not yet described."
Therefore it is not illustrated, and this means that there is no indication
of how complete the scapula is. Personally I would be interested of what a
scapula of, say, *Judinornis* (a hesperornithian known from an isolated
vertebra from the Nemegt Fm) looked like... One neornithine synapomorphy of
the scapula is mentioned on p. 348, but not on p. 368: "the humeral facet of
the scapula faces laterally or craniolaterally".
"Remarks -- In the absence of known derived features of the femur in
earliest neornithines, the present specimen is referred to Neornithes based
on unique features of Phalacrocoracidae."
"The head of the femur is damaged,"
This means that one of the two "pelecaniform" characters cannot be coded.
I'm not sure whether the trochanteric crest counts as "elevated" or not
(fig. 15.9 A), but then this one character is already not considered unique
to "Pelecaniformes", see above, so I don't even need to mention the recent
dismantling of this group.
"and the shaft is broken off just proximal to the condyles, with a fragment
remaining that indicates the very large size and lateral orientation of the
Judging from fig. 15.9 A, I'll buy that. But fig. 15.9 C shows an extant
cormorant femur. Its lateral condyle is large -- perhaps smaller than what
the Cretaceous fragment indicates --, but only slightly laterally oriented
from the long axis of the femur, and slightly _medially_ oriented compared
to the sagittal plane of the animal! The latter is the case because the
femur is strongly bent in cranial view. The Cretaceous femur, on the other
hand, is completely straight in caudal view. I wonder if this counts.
Mediolateral curvature is not mentioned in the list of phalacrocoracid
characters, though, so perhaps it's an autapomorphy of some smaller clade
that includes *Phalacrocorax pelagicus*.
"part of the popliteal fossa remains."
But this part doesn't contain any diagnostic characters of cormorants.
"A small but probably significant difference from extant cormorants is the
angular truncation of the trochanteric crest. This feature precludes
referral to either of the two major extant lineages of Phalacrocoracidae
recognized by Siegal-Causey (1988)."
Well. I for one don't think we should expect a _crown_ cormorant in the
Cretaceous anyway. :-}
Fig. 15.9 shows the presence of most or all of the other diagnostic
characters. But I wonder how many of them are adaptations to foot-propelled
diving, and therefore partially correlated with each other. Only 2 to 4 of
the 6 to 14 femoral characters in the list are said to be unique to
Phalacrocoracidae, but it isn't mentioned where else they occur. Certainly
Hope would have noticed if the femur came from a hesperornithid or
*Baptornis*, even though she doesn't mention any comparisons to them; but
considering the fact that only two characters of the femur are diagnostic
for "Pelecaniformes", the femur in question could easily drop out of
Neornithes once it would be removed from Phalacrocoracidae. So what other
foot-propelled diving birds were there in the Maastrichtian?
I see three possibilities. One are basal, perhaps flying hesperornitheans,
like what *Potamornis* seems to have been. No femora or for that matter
practically nothing at all is known of these animals. The other are the
apparently-not-loons like *Polarornis* and *Neogaeornis* -- if the femur
from the Lance Fm belongs in there, it doesn't need to be removed from
Neornithes. The third is *Yungavolucris*, according to some interpretations
of this isolated tarsometatarsus.
To settle this question, someone should:
- Find out where cormorants, and many others, sit on the family tree of
Neoaves. This would have to be done both with molecules -- so that the
calibration experiment can be repeated for both loons and cormorants -- and
with morphology -- so that fossils from the Cretaceous to the Eo- or
Oligocene can be safely inserted into that tree. Well, don't we all wish.
Fortunately both approaches are being pursued and have yielded promising
preliminary results (Fain & Houde; Livezey & Zusi).
- Find more fossils of Cretaceous birds, so we get an idea on how realistic
my alternative suggestions are. Well, don't we all wish.
- Find out which parts of Hope's diagnosis of Phalacrocoracidae are
adaptations to foot-propelled diving and can therefore be partly expected to
occur in other foot-propelled divers. This can be done with today's
knowledge of phylogeny, and has probably been done years ago.
While I am at it, one important feature that was said to tie *Polarornis* to
the loons was its cnemial crest: in hesperorniths it's formed by the
patella, in grebes by both tibia and patella, and in loons and *Polarornis*
by the tibia alone. But if foot-propelled diving evolved more often than 3
times, then some of these possibilities should have evolved more than once.
It already has evolved 4 or more times within Neornithes. Does someone know
what the cnemial crest of cormorants and finfoots look like?