Hi, Trolidus,

This may be my first direct reply to you, and I want to thank you for joining
sci.bio.paleontology. I hope you will hang around for many years.

On Thursday, July 1, 2021 at 4:34:03 PM UTC-4, Trolidous wrote:
> On 6/30/21 6:29 PM, Oxyaena wrote:
> > On 6/29/2021 3:14 AM, Trolidous wrote:
> >> On 6/26/21 5:00 PM, Oxyaena wrote:
> >>> On 6/26/2021 7:32 PM, Trolidous wrote:
> >>>> On 6/25/21 6:33 AM, John Harshman wrote:
> >>>>> Here's the currently hot (pun unintended) news on dinosaurs at the
> >>>>> poles:
> >>>>>
> >>>>> https://www.cell.com/current-biology/fulltext/S0960-9822(21)00739-9
> >>>>>
> >>>>> Fossils of the young of many species, good evidence that they
> >>>>> nested there, which is interpreted as evidence that they lived
> >>>>> there year-round, interpreted as further evidence of endothermy.
> >>>>> There are tyrannosaurids, hadrosaurs, ceratopsians, dromaeosaurs,
> >>>>> and perhaps pachycephalosaurs.
> >>>>>
> >>>>> Here's the abstract (called "summary", but potato potahto):
> >>>>>
> >>>>> "The unexpected discovery of non-avian dinosaurs from Arctic and
> >>>>> Antarctic settings has generated considerable debate about whether
> >>>>> they had the capacity to reproduce at high latitudes—especially the
> >>>>> larger-bodied, hypothetically migratory taxa. Evidence for
> >>>>> dinosaurian polar reproduction remains very rare, particularly for
> >>>>> species that lived at the highest paleolatitudes (>75°). Here we
> >>>>> report the discovery of perinatal and very young dinosaurs from the
> >>>>> highest known paleolatitude for the clade—the Cretaceous Prince
> >>>>> Creek Formation (PCF) of northern Alaska. These data demonstrate
> >>>>> Arctic reproduction in a diverse assemblage of large- and
> >>>>> small-bodied ornithischian and theropod species. In terms of
> >>>>> overall diversity, 70% of the known dinosaurian families, as well
> >>>>> as avialans (birds), in the PCF are represented by perinatal
> >>>>> individuals, the highest percentage for any North American
> >>>>> Cretaceous formation.

This is really remarkable, and goes far beyond the diversity I suspected until now.

> >>>>>These findings, coupled with prolonged
> >>>>> incubation periods, small neonate sizes, and short reproductive
> >>>>> windows suggest most, if not all, PCF dinosaurs were nonmigratory
> >>>>> year-round Arctic residents. Notably, we reconstruct an annual
> >>>>> chronology of reproductive events for the ornithischian dinosaurs
> >>>>> using refined paleoenvironmental/plant phenology data and new
> >>>>> insights into dinosaur incubation periods. Seasonal resource
> >>>>> limitations due to extended periods of winter darkness and freezing
> >>>>> temperatures placed severe constraints on dinosaurian reproduction,
> >>>>> development, and maintenance, suggesting these taxa showed
> >>>>> polar-specific life history strategies, including endothermy."
> >>>>
> >>>> So do lizards shiver when they are cold?
> >>>
> >>> Lizards are ectotherms, so no. Dinosaurs however were endotherms,
> >>> like mammals, and so they would've shivered.
> >>
> >> Do you have any references? Have you verified this?
> >
> > http://libgen.rs/fiction/8713E83994CA2B0BCE8ABA7A3B7451E5
> >
> > The link in question is "The Dinosaur Heresies" by Robert T Bakker. It's
> > a bit dated, having been written in 1987 I believe, but it presents a
> > compelling case for dinosaur endothermy and helped kickstart a paradigm
> > shift when it comes to how we view dinosaurs.

On the contrary, Bakker is a notorious popularizer who regularly goes out on limbs,
and the claim that ALL dinosaurs were endothermic is still very much up in the air.

On the other hand, some arguments for endothermy in at least some dinosaurs
go back to a 1969 paper by the great paleontologist, John Ostrom. His beliefs
on this evolved over time, to where he decided endothermy was largely restricted to theropods.

There have been some "outliers" in this debate, including Paul Sereno, Chenggang Rao,
and John Ruben, who have hypothesized that *Archaeopteryx* was an ectotherm..
Given the warm climate of the Late Jurassic, well above any seen in the last 5 million
years, this seems tenable. Also, see below about some surprising facts about modern birds.

> Thank you for the link, however the term 'endotherm' and 'ectotherm'
> has a lot of different variables thrown in with each other with
> the terms that are actually separate and not obvious.

In fact, the terms need to be supplemented by another: homeothermy. Its
chief merit is in the thesis that a large enough dinosaur could have maintained
a fairly stable body temperature throughout the day. This could have happened
in two ways: long storage of heat in the body of a large ectotherm, and the
"turning off" of endothermy when an endotherm attained a large enough size.

Jack Horner, a much more prolific researcher than Bakker, told me about
the latter possibility in a personal appearance at the South Carolina State Museum,
here in Columbia.

> Some are - keeping a body temperature in a narrow range - how
> narrow is it?
>
> How hot or cold is that narrow range?

There seems to be no one good answer. The situation is complicated by
many things, including the way there are intermediate conditions between
ectothermy and endothermy, as you yourself note later.

Even in some birds, there is a wide variation in daily body temperature:

"The well-known turkey vulture, (*Cathartes* *aura*) ... normally lowers its body temperature about at night 6 C (11 F) to 34 C (93 F) -- in other words, it becomes mildly hypothermic. Some small species with excessive surface exposure, such as hummingbirds (Trochilidae), are capable of entering a state of torpor, or profound hypothermia, in which they are unresponsive to most stimuli; their oxygen consumption can drop by some 75 percent when their body temperature drops by 10 C (18 F). By far the most dramatic example of torpor is exemplified by the common poorwills (*Phalaenoptilus* *nuttallii* : Caprimugiformes), which hibernate at a body temperature of 6 C [42.8 F] for up to two to three months during the winter; these birds normally require some seven hours to warm up."
-- Alan Feduccia, _Riddle_of_the_Feathered_Dragons, Yale University Press, 2012, p. 271.

> and then
>
> Frost or freezing resistance - if that range can
> go as low as near freezing - does the organism undergo
> freezing - or can it move somewhere or adopt a strategy
> at that low temperature to keep the body from freezing?
See above about poorwills!

<snip for the sake of brevity -- but only for the sake of brevity!>

> Animals however have nervous systems and they can move.
>
> For ectotherms however there is a first basic question. Can
> their nervous systems and muscles still operate at 2 degrees
> Celsius or maybe 35 degrees Farenheit? Can some different
> species of reptiles do this but not others?

Some arctic and antarctic fish are able to do this, obviously.
Stephen Jay Gould wrote something about this
in one of his essays; I'll try and look it up.

Peter Nyikos
Professor, Dept. of Mathematics -- standard disclaimer--
Univ. of South Carolina at Columbia
http://people.math.sc.edu/nyikos

PS you bring up some interesting possibilities below, which I don't know
enough about to comment on.

> If they can do this then there is the question, can they
> sense when body temperature has dropped to near freezing and
> then do something else to keep warm enough to not freeze?
>
> Well, one strategy might to build a good shelter or burrow
> in autumn, and if it is not good enough then you may not
> survive until spring unless you are like specific freeze
> resistant amphibians at the bottom of lakes.
>
> However there is the possibility that if a burrow gets
> too cold a reptile might wake up and start digging deeper
> to produce better insulation or to warm up slightly. Then
> again, maybe it needed to produce a good burrow and if
> it goes through something like hibernation it needed to
> do something like that before winter started.
>
> Either way the search terms 'ectotherm' or 'endotherm'
> may not automatically come up with something that
> specific, and it is not obvious to what extent research
> might have been done on it. Wikipedia seems to have
> the term 'mesotherm' and other 'therm' variants. A lot
> of endotherms however generally tend to keep their body
> temperature so far above freezing that starvation from
> energy loss from heat production may be a much more
> significant factor for warm blooded animals.
> >>
> >> Muscles are not one hundered percent efficient when
> >> it comes to the conversion of chemical energy into
> >> movement, and so exertion as well as brown fat does produce
> >> heat.
> >>
> >> So if an animal in winter does get near to freezing
> >> point and it does not have frost resistance in its
> >> tissues one way of surviving might be to burrow further
> >> down into heat insulating soil, but as a short term
> >> solution shivering might raise temperature enough to
> >> avoid freezing. That is, if the nervous system is able
> >> to detect when body temperature has dropped low enough
> >> that there is danger of freezing.
> >>
> >> There are some reptiles that live in places where there
> >> is freezing in winter, like southern Canada. Maintaining
> >> body heat within a narrow range is different from strategies
> >> for avoiding freezing.
> >