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Hesperornis sp. nov.



I just got _Proceedings of the 5th Symposium of the Society of Avian
Paleontology_ in the mail, and some of the articles are very cool,
indeed.

The first article I read in any depth was "New Information on the
Hesperornithiform Radiation" by Larry D. Martin and Jong-Deock Lim.
Very cool.
The authors studied the hesperornithiforms of the Pierre Formation
(South Dakota, Campanian) and named several new species of Hesperonis
found there.
These new species are:
        H. chowi: (right tarsometatarusu) about the same size as H.
regalis, but with "a more elongate tarsometatarusu with a slender shaft
and less enlarged outer trochlea, anterior metatarsal ridge more
slender, and the inner metarartsal ridge shorter and less prominent."
Authors say that "many if not all such reports" are H. chowi.
        H. bairdi (left tarsometatarusus and partial pelvis) "smaller
than H. gracilus. Differs from _Parahesperornis_ in having the outer
trochlea more enlarged and distal to the middle one."  "Similar in size
to Parahesperornis alexi", but more similar to other Hesp. Species.  
        H. mengeli (right tarsometatarus) "Smaller than H. bairdi" with
a very slender tarsomet., also very small trochela for digit 3 and
"distal end more compressed with the trochlea for digit 2 completely
behind digit 3." This thing is "about the size of a loon" Authors state
that while H. mengeli was small, it was an advanced diver, showing that,
while some Hespies were small and primitive (few diving adaptations),
others were small and advanced.
        And finally H. macdonaldi (right femur) "Smallest known
hesperornithid, with a C-shaped lateral margin of femur, characteristic
of Hesperornis." (femur length is 44.7mm).  The authors say that this is
probobably _not_ a juvenile H. mengeli, because in juveniles of
Baptornis, the "articular surfaces are nott as well formed as in [H.
macdonaldi], but it has nearly reached adult size.  Even if [H.
macdonaldi] is [a] juvenile bird (doubtful in any case) it is still old
enough that the discrepancy in size would be too great to consider it H.
mengeli."

The authors go on to say that there were likely two populations of
Hespornorthithans by the late K, one northern, and one southern.  The
southern ones had started their migration southward and so were more
primitive, and existed in more genera (Hesperornis, Parahesperornis,
Baptornis), while the northern fauna (which also extended into
Asia---Asiahesperornis) was more advanced (in diving features, anyway)
and existed as many species of a single genus, Hesperornis. They also
link small size in these species to ecology, with the small species
found most often in near-shore habitats, and the larger species further
out.

There is, finally, a paragraph from the intro that I'd like to quote.
This is pretty wild stuff:

"It is likely that ornithurines owe much of their success to an early
colonization of water marginal habitats (martin, 1983, 1987).  The
absence of trees on beaches and sandbars and the need to take off from
the water surface put a premium on the ability to take off from flat
surfaces and promoted the perfection of a triosseal system and a keeled
sternum.  The need for extended flight over water, the higher heat
conductance [-ivity?] of water and the effects of evaporative cooling
all may have  contributed to the development of avian endothermy in
ornithurines and its absence in even Maestrichtian [sic]
enantiornithines (Chinsamu et al., 1998)." P. 166

Fascinating---I thought the jury was still out on the enantironithine
exothermy thing, but it's an interesting point to consider.  All the
early neorniths _are_ shorebirds, after all (except maybe for that
parakeet).  

Other articles in this book include a description of Polarornis
(finally!) and a comparison of birds and oviraptorosaurs, which puts
Ovies closer to modern birds than Archaeopteryx (and Alvarezsaurs).

Dan