Re: How To Write a Harry Turtledove AH

In article <e0rh2t$a6a$1@xxxxxxxxxxxxxxxxx>, James Nicoll
<jdnicoll@xxxxxxxxx> wrote:

2: Usually, species from smaller landmasses have a hard time competing
with ones from large ones. I'll just skip over the part where NorAm
families of animals, like the horses and the primates, spread to
the Old World and prospered.

Primates?

In <The Human Career>^2 by Richard Klein, I see that allegedly
Purgatorius, allegedly primate, lived in Montana 70-80 Mya.
By 70 Mya or so, the <Atlas of Mesozoic and Cenozoic Coastlines>
I recently mentioned here shows a land bridge between western North
America and northern Asia; Klein says there was also one from
western North America via Greenland to western Europe. This is
the only Cretaceous fossil Klein knows.

Next Klein talks in limited detail about "Euramerican" primates from
the Paleocene. At *some* point in the Paleocene, the <Atlas> shows
the Arctic Ocean fully ringed by land, so OK, at this point I can
buy this. Anyway, he says of these (long quote, in which I signal
that I've snipped the numeric codes he uses for references with the
@ sign):

"Curiously, in spite of their abundance and diversity, the presumed
Euramerican Paleocene primates provide few clues to the origins of
later, Eocene to Recent forms. They are unlikely ancestors themselves,
because they evolved dental specializations that later forms lack @.
These specializations include large, procumbent central incisors,
perhaps used to grasp food, and a reduced number of lateral incisors,
anterior premolars, or both. Except for some basically Paleocene taxa
that survived into the early Eocene before becoming extinct, Eocene
primates tended to have smaller, more generalized incisors, and they
commonly retained incisors or premolars that the Paleocene forms
had lost (fig. 3.15). Among known Paleocene taxa, only the earliest,
Purgatorius, was sufficiently generalized to be ancestral to Eocene to
Recent forms, but there is no reason to suppose it evolved in their
direction. More likely it gave rise to later, more specialized
Paleocene primates.
"Because the Euramerican Paleocene primates combined very primitive
features with specializations lacking in all other primates, they are
now commonly placed in their own infraorder, the Plesiadapiformes,
named for Plesiadapis, the best-known genus @. In vernacular terms,
they might equally well be called *archaic primates* @ as opposed to
the primates of modern aspect, or *euprimates*, that succeeded them @.
Alternatively, they may simply be the most primatelike of known
Paleocene mammals @, in which case they could be removed from the
Primates altogether and placed in a separate order that shared a
close Cretaceous ancestor with true Primates. One authority @ has
proposed such an order, the Proprimates, whose content would be
essentially the same as the previously proposed primate suborder,
Praesimii, listed here in table 3.1. [Plesiadapiformes plus
tree shrews.]
"None of the known Plesiadapiformes survived the Eocene, and
their extinction could have resulted at least in part from
unsuccessful competition with evolving rodents, bats, and
euprimates @. The origins of euprimates remain obscure for lack of
fossil evidence. A plesiadapiform root is unlikely for reasons
given above, and North America or the combined North American-
European landmass thus becomes an unlikely birthplace. South
America can probably also be excluded, since its relatively
well known late Cretaceous to Eocene fossil record contains no
early primates or likely primate ancestors. Asia remains possible,
and a case can be made from three jaws recovered in mid-Paleocene
deposits of the Wanghudun Formation, Anhui Province, southern
China @. These have been assigned to the genus Decoredon, whose
teeth have been likened to those of Eocene tarsiiform euprimates
discussed below. The specimens are poorly preserved, however, and
the primate status of Decoredon is questionable @.
"That leaves only Africa, which is arguably most plausible
a priori @, since it hosted so many later major events in primate
evolution. Unfortunately, African Paleocene and Eocene fossil
sites formed mainly on the continental margin, and they tend to be
poor in terrestrial mammals @. An important exception is the site
of Adrar Mgorn 1 at the foot of the High Atlas Mountains in
southern Morocco @. Here relatively abundant fossils of terrestrial
mammals occur in association with sharks' teeth indicating a late
Paleocene age, roughly 60 my ago. The mammalian fossils include
ten isolated teeth that share several derived features with teeth
of Eocene tarsiiforms in the family Omomyidae. The Adrar Mgorn
specimens have been assigned to a previously unknown omomyid
genus and species, Altiatlasius koulchii @, and if this diagnosis
is correct it supports an African origin for more advanced
primates in the Paleocene or late Cretaceous, followed by their
spread to northern continents in the very late Paleocene or
earliest Eocene."

Now, as Klein says, he's basically biased towards sourcing
everything to Africa. But assuming what he says is true, I don't
see any reasonable possibility of sourcing any primates ancestral
to us to North America later than the early Paleocene Purgatorius.
I'm taking for granted that the late Cretaceous and early Paleocene
faunas of western North America are, in general, absurdly well known,
so if there were an ancestor of ours there we would've found it.

References upon request; they get as late as 1994, only, and
plenty are as old as the 1970s. So sure, if there've been discoveries
in the last twelve-fourteen years, then this should be easy to answer.
Otherwise, am I just overly trusting to Klein's uncertainty about
Purgatorius being a primate? Or what?

Joe Bernstein

--
Joe Bernstein, writer joe@xxxxxxxxxxx
<http://www.panix.com/~josephb/> "She suited my mood, Sarah Mondleigh
did - it was like having a kitten in the room, like a vote for unreason."
<Glass Mountain>, Cynthia Voigt
.

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