Re: Mesozoic mammals

["David Marjanovic" <david.marjanovic@gmx.at>]

----- Original Message -----
From: "Dino Rampage" <dino_rampage@hotmail.com>

> I recently sent a query regarding the proto-mammals & mammals of the
> Mesozoic, but not many seemed to notice.

Er, yeah, sorry, at that time I thought the thread on what mammals may have
died out at the K-T was recent enough. But it certainly wasn't detailed
enough.

> 1)I've read somewhere that many of our early mammals may have been like
> monotremes in that they were oviparous. How likely is this and which
groups
> may have [... retained] this lifestyle?

All more basal than Monotremata in any case. Within the crown-group it gets
difficult because eggs without hard shells don't preserve easily and because
AFAIK no pregnant specimen is known from the Mesozoic. Theria sensu stricto
( = Metatheria, Eutheria and their MRCA) can parsimoniously be assumed to
have been viviparous from the start. For everything in between, and there's
much, it becomes largely guesswork.

> Where and in which time period are there
> signs that mammals adopted viviparous birth?

Nothing whatsoever AFAIK.

> Or is it possible that live
> birth has evolved repeatedly among many separate mammal lineages

I'd say that's unlikely. But who knows.

> (say, more
> than once in the multis, once in the dryolestids, and once in the common
> ancestor of eutherians & metatherians?)

Dryolestida is very close to Theria (in Boreosphenida in
www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Synapsida/B
asal_Mammalia/Cladotheria.htm), so I guess they shared the same origin of
vivipary, but there's no evidence. Multis are rather far away, but nobody
knows how far. (Sometimes they came out as the sister group to the
monotremes in the last decade. I've read, and forgot where, that they share
something with Eutriconodonta -- if that group is real -- some characters in
the feet. Usually they are in the crown group's basal polytomy. If the old
idea that they are related to Haramiyida is correct, though, then they are
outside, and should have been oviparous.)

> 2) I need more info about the cladistics and systematics of the following
> groups: Morganucodontids, Docodonts, Multituberculates, Haramyids,
> Dryolestids, Triconodonts, Pantotheres and Symmetrodonts.

Pantotheria is dissolved, most members have found themselves in Dryolestida.
Symmetrodonta is a wastebasket full of little teeth and a few jaws; attempts
to dissolve it have been made (Trechnotheria = Spalacotheriidae +
Cladotheria, if *Zhangheotherium* belongs into the tooth-&-jaw taxon
Spalacotheriidae). Triconodonta was a wastebasket, Eutriconodonta may not be
(www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Synapsida/
Basal_Mammalia/Triconodonta/triconodonta.htm), or it may be
(www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Synapsida/
Basal_Mammalia/Holotheria.htm -- some names, like Holotheria and
Trechnotheria, are wrongly applied there). Docodonta is outside the crown
group. Morganucodontidae is near the base of Mammalia sensu lato (and per
definitionem at the base of Mammali[a?]formes).

> Any good
> cladograms besides those on the Dinosauricon?

Good... I fear not. Mikko Haaramo is usually very good (click around from
the above), but some of his sites are very confusing because they
incorporate details from contradicting sources, and many names are not in
the right places.

> Which of these survived up until the K-T?

I've been through my lamentations about how little is known...

> And just how similar were multis to extant rodents?

Depends on which multis and which rodents.

> 3) What ecological niche would these mammals have occupied? Listed below
are
> a few examples I can think of:
>
> Opossums, Phascogales, Planigale, Antechinus, Numbats, Brushtail &
ringtail
> possums, honey possums, solenodons, shrews, desmans (semi-aquatic moles of
> Eurasia), moonrats or gymnures, tree shrews, mouse lemurs, rodents
(similar
> to multis?), and elephant shrews just to name a few.

I don't know moonrats. All others may well have had Mesozoic analogs. The
only docodont known from more than jaws, *Haldanodon exspectatus*, is
thought to have been a desman analog. (Desmans occur only in the Pyrenees
and around the Volga AFAIK.) *Henkelotherium*, the only paurodontid, if not
the only dryolestidan, that's known from more than jaws, was a climbing
insectivore, and so was *Eomaia*. Eutriconodonta, monophyletic or not,
consists of carnivores of varying sizes (look up *Repenomamus* in the
archives). Numbats, on the other hand, are ant specialists... no such mammal
is known from the Mesozoic. Honey possums need angiosperm flowers that were
unavailable most of the Mesozoic, and no Mesozoic mammals (but IIRC some
Paleocene primates) have been suggested to be specialized in a similar way.
*Ichthyoconodon* (tentatively put into Triconodontidae in the Triconodonta
page mentioned above) was suggested to be a triconodont fish-eater... well,
it's "the tooth, the whole tooth and nothing but the tooth", so who knows.

> 3) Besides the small scurrying forms, what other niches could Mesozoic
> mammals have occupied? I know Didelphodon was badger-sized, so could it
have
> been a generalist like the badger or wolverine?

Yes. Though its strong jaws have led many people to compare it to the
Tasmanian Devil. Deltatheroida may come closer to a badger (I guess).
        And *Repenomamus* was bigger still...

> And are there any other
> mammals that evolved forms like those of palm civets, linsangs, genets and
> weasels?

Some eutriconodonts might fit here. Those that I know well enough
(*Jeholodens*, *Gobiconodon*) were still sprawlers, making them sort of more
weasel-like than a weasel. :-)