Back in 2006, a very detailed fossil of the one known Mesozoic gliding mammal
was discovered in Northern China. Named *Volaticotherium antiquum*, it has a hip joint
that sets it apart from all other known mammals. It is not a ball-and-socket joint:

"The femur has a small, oval-shaped head and lacks a femoral neck (Fig. 3c, d), which is unique among mammals [9]. Although the hip structure was not preserved, the shape of the femoral head alone reveals that the acetabulum is probably shallow and open, perhaps similar to those of arboreal didelphids [24]."

https://www.nature.com/articles/nature05234

However, even *Didelphis*, the oposssum, has a standard-looking hip joint.

The article is paywalled , but I have free access whenever I am at my university.

There is a very clear set of pictures of the femoral head, from the side and from the
top, and they suggest that the hip joint is basically a hinge joint.

The Wikipedia entry says this about it:

"its femur has unique adaptations among mammals that make it resistant to flight stresses, and render terrestrial locomotion cumbersome."

This is based on the following statement in the *Nature* article:

"Unlike the ball-and-socket hip joint that provides ample excursion for legs in other mammals [25], the peculiar femoral head of Volaticotherium must have restricted flexibility of the leg in rotational movements, but could have allowed the leg to be extended laterally and remain steady during a glide."

The enigma here is just how the hypothesized advantages of the joint
outweighed its obvious drawbacks.

More about the adaptations for gliding in my next post to this thread.

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

On 6/14/21 2:29 PM, Peter Nyikos wrote:
> Back in 2006, a very detailed fossil of the one known Mesozoic gliding mammal
> was discovered in Northern China. Named *Volaticotherium antiquum*, it has a hip joint
> that sets it apart from all other known mammals. It is not a ball-and-socket joint:
>
> "The femur has a small, oval-shaped head and lacks a femoral neck (Fig. 3c, d), which is unique among mammals [9]. Although the hip structure was not preserved, the shape of the femoral head alone reveals that the acetabulum is probably shallow and open, perhaps similar to those of arboreal didelphids [24]."
>
> https://www.nature.com/articles/nature05234
>
> However, even *Didelphis*, the oposssum, has a standard-looking hip joint.
>
>
> The article is paywalled , but I have free access whenever I am at my university.
>
> There is a very clear set of pictures of the femoral head, from the side and from the
> top, and they suggest that the hip joint is basically a hinge joint.
>
> The Wikipedia entry says this about it:
>
> "its femur has unique adaptations among mammals that make it resistant to flight stresses, and render terrestrial locomotion cumbersome."
>
> This is based on the following statement in the *Nature* article:
>
> "Unlike the ball-and-socket hip joint that provides ample excursion for legs in other mammals [25], the peculiar femoral head of Volaticotherium must have restricted flexibility of the leg in rotational movements, but could have allowed the leg to be extended laterally and remain steady during a glide."
>
> The enigma here is just how the hypothesized advantages of the joint
> outweighed its obvious drawbacks.
>
>
> More about the adaptations for gliding in my next post to this thread.

Mammals aren't my thing, but the Wikipedia article has some interesting
additions. First,

"The closely related and significantly older Argentoconodon shows
similar post-cranial adaptations for aerial locomotion also seen in
Volaticotherium.[3]"

The reference is Leandro C. Gaetano and Guillermo W. Rougier (2011).
"New materials of Argentoconodon fariasorum (Mammaliaformes,
Triconodontidae) from the Jurassic of Argentina and its bearing on
triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4):
829–843. doi:10.1080/02724634.2011.589877

And the article says it's a triconodont, within Triconodontidae, based
on these:

Leandro C. Gaetano and Guillermo W. Rougier (2012). "First Amphilestid
from South America: A Molariform from the Jurassic Cañadón Asfalto
Formation, Patagonia, Argentina". Journal of Mammalian Evolution. 19
(4): 235–248. doi:10.1007/s10914-012-9194-1.

A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and
Symmetrodonts and the Origin of Extant Mammals. Doklady Biological
Sciences 436:32-35

On Monday, June 14, 2021 at 5:29:15 PM UTC-4, Peter Nyikos wrote:

> Back in 2006, a very detailed fossil of the one known Mesozoic gliding mammal
> was discovered in Northern China. Named *Volaticotherium antiquum*, it has a hip joint
> that sets it apart from all other known mammals. It is not a ball-and-socket joint:
>
> "The femur has a small, oval-shaped head and lacks a femoral neck (Fig. 3c, d), which is unique among mammals [9]. Although the hip structure was not preserved, the shape of the femoral head alone reveals that the acetabulum is probably shallow and open, perhaps similar to those of arboreal didelphids [24]."
>
> https://www.nature.com/articles/nature05234
>
> However, even *Didelphis*, the oposssum, has a standard-looking hip joint..
>
>
> The article is paywalled , but I have free access whenever I am at my university.
>
> There is a very clear set of pictures of the femoral head, from the side and from the
> top, and they suggest that the hip joint is basically a hinge joint.
>
> The Wikipedia entry says this about it:
>
> "its femur has unique adaptations among mammals that make it resistant to flight stresses, and render terrestrial locomotion cumbersome."
>
> This is based on the following statement in the *Nature* article:
>
> "Unlike the ball-and-socket hip joint that provides ample excursion for legs in other mammals [25], the peculiar femoral head of Volaticotherium must have restricted flexibility of the leg in rotational movements, but could have allowed the leg to be extended laterally and remain steady during a glide."

Note that "remain steady" and "make it resistant to flight stresses" are not completely synonymous.
Unfortunately, there is no detailed explanation of this in the article.

> The enigma here is just how the hypothesized advantages of the joint
> outweighed its obvious drawbacks.

The patagium is unlikely to shed much light on this question, but it does provide some
information about its gliding technique. Quoting from the *Nature* article:

"The patagium impression continues with skin and hair impressions surrounding the area where the skeletal elements are concentrated; it stretches to the phalange area of the foot and sandwiches the tarsal region. These suggest that the limbs, probably including the pes and manus, had participated in supporting the patagium."

I've seen two attempts to reconstruct *Volaticotherium*, both in popularizations.
The first one below does a good job of hewing to the last sentence; the second does not.

https://carnegiemnh.org/mesozoic-monthly-volaticotherium/

https://en.wikipedia.org/wiki/Volaticotherium

On the other hand, the first webpage completely ignored the continuation of the above quote, while the
second was in harmony with the continuation:

"These structures and their relationships with the patagium suggest the participation of the proximal caudal vertebrae in supporting the patagium and thus presence of uropatagia between the tail and hind limbs. The morphologies of caudal vertebrae and haemal arches also indicate a stiff tail that had limited lateral and dorsoventral movements, and could act as a stabilizer when the animal was gliding, consistent with the hypothesis that longitudinal control and stability of a glider are achieved more easily with a long, dorsoventrally flattened tail [14], [15], [16]."

In fact, the Carnegie webpage showed it with a raccoon tail, with generously long fur, completely loose
from the rest of the anatomy and free to wave in the breeze.
["The Davy Crockett reconstruction."] :)

But it's fun to read the article, which was written by a student and volunteer. The picture was
done by Jose Antonio Peñas, who seems to be quite a versatile artist. The following short (1:13 min) video
by him of *Pteranodon sternbergi* is a joy to watch.

https://video.search.yahoo.com/search/video?fr=mcafee&ei=UTF-8&p=Jose+Antonio+Pe%C3%B1as&type=E210US105G91483#id=5&vid=373708384003dbb5badd7e6a21b03006&action=click

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

On Monday, June 14, 2021 at 6:26:32 PM UTC-4, John Harshman wrote:

> Mammals aren't my thing, but the Wikipedia article has some interesting
> additions. First,
>
> "The closely related and significantly older Argentoconodon shows
> similar post-cranial adaptations for aerial locomotion also seen in
> Volaticotherium.[3]"

> The reference is Leandro C. Gaetano and Guillermo W. Rougier (2011).
> "New materials of Argentoconodon fariasorum (Mammaliaformes,
> Triconodontidae) from the Jurassic of Argentina and its bearing on
> triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4):
> 829–843. doi:10.1080/02724634.2011.589877

I saw no mention of post-cranial adaptations for aerial locomotion.

The article is available here for free:

https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877

See if you can find any hints here or in the next reference.

> And the article says it's a triconodont, within Triconodontidae, based
> on these:
>
> Leandro C. Gaetano and Guillermo W. Rougier (2012). "First Amphilestid
> from South America: A Molariform from the Jurassic Cañadón Asfalto
> Formation, Patagonia, Argentina". Journal of Mammalian Evolution. 19
> (4): 235–248. doi:10.1007/s10914-012-9194-1.

Paywalled and pricey at the doi address, but free here:
https://www.researchgate.net/publication/257591809_First_Amphilestid_from_South_America_A_Molariform_from_the_Jurassic_Caadn_Asfalto_Formation_Patagonia_Argentina/link/0deec52836ef432de9000000/download

From the abstract:
" Condorodon spanios is only distantly related to Argentoconodon fariasorum, the other triconodont known from Queso Rallado quarry.
another triconodont.
> A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and
> Symmetrodonts and the Origin of Extant Mammals. Doklady Biological
> Sciences 436:32-35

This one is freely available here:
https://www.researchgate.net/publication/50272438_Phylogeny_of_triconodonts_and_symmetrodonts_and_the_origin_of_extant_mammals

It has a long first paragraph giving past and present classification of mammals. It proposes a phylogenetic tree
that varies significantly from most of the recent ones I have seen, classifying monotremes as being
closer to us than either triconodonts or symmetrodonts. The authors do not disguise the fact that their
tree is a departure from almost all previous trees of mammaliform synapsids in this respect.

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

On 6/15/21 7:35 AM, Peter Nyikos wrote:
> On Monday, June 14, 2021 at 6:26:32 PM UTC-4, John Harshman wrote:
>
>> Mammals aren't my thing, but the Wikipedia article has some interesting
>> additions. First,
>>
>> "The closely related and significantly older Argentoconodon shows
>> similar post-cranial adaptations for aerial locomotion also seen in
>> Volaticotherium.[3]"
>
>> The reference is Leandro C. Gaetano and Guillermo W. Rougier (2011).
>> "New materials of Argentoconodon fariasorum (Mammaliaformes,
>> Triconodontidae) from the Jurassic of Argentina and its bearing on
>> triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4):
>> 829–843. doi:10.1080/02724634.2011.589877
>
> I saw no mention of post-cranial adaptations for aerial locomotion.

Well, the abstract says "Postcranial similarities between Argentoconodon
and Volaticotherium make it possible that the Argentinean taxon might
have had gliding capabilities; if this is the case, our cladistic
analysis highlights the possible existence of a gliding clade of
triconodonts of wide distribution from at least as early as the Early
Jurassic."

> The article is available here for free:
>
> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877

That's paywalled for me. But the abstract seems to promise what you're
looking for. You can't find anything in the actual paper that delivers
on the abstract?

> See if you can find any hints here or in the next reference.
>
>
>> And the article says it's a triconodont, within Triconodontidae, based
>> on these:
>>
>> Leandro C. Gaetano and Guillermo W. Rougier (2012). "First Amphilestid
>> from South America: A Molariform from the Jurassic Cañadón Asfalto
>> Formation, Patagonia, Argentina". Journal of Mammalian Evolution. 19
>> (4): 235–248. doi:10.1007/s10914-012-9194-1.
>
> Paywalled and pricey at the doi address, but free here:
> https://www.researchgate.net/publication/257591809_First_Amphilestid_from_South_America_A_Molariform_from_the_Jurassic_Caadn_Asfalto_Formation_Patagonia_Argentina/link/0deec52836ef432de9000000/download
>
> From the abstract:
> " Condorodon spanios is only distantly related to Argentoconodon fariasorum, the other triconodont known from Queso Rallado quarry.
> another triconodont.
>
>> A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and
>> Symmetrodonts and the Origin of Extant Mammals. Doklady Biological
>> Sciences 436:32-35
>
> This one is freely available here:
> https://www.researchgate.net/publication/50272438_Phylogeny_of_triconodonts_and_symmetrodonts_and_the_origin_of_extant_mammals
>
> It has a long first paragraph giving past and present classification of mammals. It proposes a phylogenetic tree
> that varies significantly from most of the recent ones I have seen, classifying monotremes as being
> closer to us than either triconodonts or symmetrodonts. The authors do not disguise the fact that their
> tree is a departure from almost all previous trees of mammaliform synapsids in this respect.

Not really of interest for me. I only mentioned it because I know you
like triconodonts.

On Tuesday, June 15, 2021 at 10:52:55 AM UTC-4, John Harshman wrote:
> On 6/15/21 7:35 AM, Peter Nyikos wrote:
> > On Monday, June 14, 2021 at 6:26:32 PM UTC-4, John Harshman wrote:
> >
> >> Mammals aren't my thing, but the Wikipedia article has some interesting
> >> additions. First,
> >>
> >> "The closely related and significantly older Argentoconodon shows
> >> similar post-cranial adaptations for aerial locomotion also seen in
> >> Volaticotherium.[3]"
> >
> >> The reference is Leandro C. Gaetano and Guillermo W. Rougier (2011).
> >> "New materials of Argentoconodon fariasorum (Mammaliaformes,
> >> Triconodontidae) from the Jurassic of Argentina and its bearing on
> >> triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4):
> >> 829–843. doi:10.1080/02724634.2011.589877
> >
> > I saw no mention of post-cranial adaptations for aerial locomotion.

This time I saw a bit of "circumstantial evidence":

"Some postcranial characteristics of Argentoconodon are similar to those described for Volaticotherium, suggesting similar locomotory habits (Gaetano and Rougier, 2010). These similarities include the orientation and morphology of the proximal portion
of the femur, with a poorly differentiated head in line with the main shaft of the femur and greater and lesser trochanters confluent with the femoral head. Hence, a sister-group relationship between these two taxa might imply the existence of a widely distributed gliding clade of mammals at least as old as the EarlyJurassic, but the preservation of Argentoconodon is insufficient
to go beyond these tantalizing possibilities."

Unlike with Volaticotherium, there is no mention of any sign of a patagium,
so the last clause is a healthy cautionary note.

> > The article is available here for free:
> >
> > https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877

> That's paywalled for me.

I truncated the url without realizing that what I snipped was necessary. This is the full url:

https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877?casa_token=qwG6zKvdhVcAAAAA:CgOj49mStFIcuzpf-pdA0kaFuSV5zGu4M7XE09uUyrqDSrKkoIFbmd13jtGGt2wSdGYr9YzGuZo

The way I originally got there was via the Wikipedia article that you used, then clicking on the doi featured in [3] there.
This took me to a page with "PDF" in white on a dark gray background in the upper extreme right, with a smaller
"Help" on a light gray background. Clicking on PDF took me to the article.

> But the abstract seems to promise what you're
> looking for. You can't find anything in the actual paper that delivers
> on the abstract?

Only the indirect evidence that I quoted.

<snip for focus>
> >> A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and
> >> Symmetrodonts and the Origin of Extant Mammals. Doklady Biological
> >> Sciences 436:32-35
> >
> > This one is freely available here:
> > https://www.researchgate.net/publication/50272438_Phylogeny_of_triconodonts_and_symmetrodonts_and_the_origin_of_extant_mammals
> >
> > It has a long first paragraph giving past and present classification of mammals. It proposes a phylogenetic tree
> > that varies significantly from most of the recent ones I have seen, classifying monotremes as being
> > closer to us than either triconodonts or symmetrodonts. The authors do not disguise the fact that their
> > tree is a departure from almost all previous trees of mammaliform synapsids in this respect.
> Not really of interest for me. I only mentioned it because I know you
> like triconodonts.

Yes, my fondness for triconodonts goes back to my 12-year-old acquaintance with them in
Romer's _Vertebrate Paleontology_. Mammals of the Jurassic fascinated me all the way back then.

Also, the teeth of the Lower Cretaceous monotreme *Steropodon* reminded me very much of triconodont teeth
when I first read about them three decades ago. I think it would be "way cool" if monotremes
turned out to be [descended from] triconodonts.

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

On 6/15/21 9:37 AM, Peter Nyikos wrote:
> On Tuesday, June 15, 2021 at 10:52:55 AM UTC-4, John Harshman wrote:
>> On 6/15/21 7:35 AM, Peter Nyikos wrote:
>>> On Monday, June 14, 2021 at 6:26:32 PM UTC-4, John Harshman wrote:
>>>
>>>> Mammals aren't my thing, but the Wikipedia article has some interesting
>>>> additions. First,
>>>>
>>>> "The closely related and significantly older Argentoconodon shows
>>>> similar post-cranial adaptations for aerial locomotion also seen in
>>>> Volaticotherium.[3]"
>>>
>>>> The reference is Leandro C. Gaetano and Guillermo W. Rougier (2011).
>>>> "New materials of Argentoconodon fariasorum (Mammaliaformes,
>>>> Triconodontidae) from the Jurassic of Argentina and its bearing on
>>>> triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4):
>>>> 829–843. doi:10.1080/02724634.2011.589877
>>>
>>> I saw no mention of post-cranial adaptations for aerial locomotion.
>
> This time I saw a bit of "circumstantial evidence":
>
> "Some postcranial characteristics of Argentoconodon are similar to those described for Volaticotherium, suggesting similar locomotory habits (Gaetano and Rougier, 2010). These similarities include the orientation and morphology of the proximal portion
> of the femur, with a poorly differentiated head in line with the main shaft of the femur and greater and lesser trochanters confluent with the femoral head. Hence, a sister-group relationship between these two taxa might imply the existence of a widely distributed gliding clade of mammals at least as old as the EarlyJurassic, but the preservation of Argentoconodon is insufficient
> to go beyond these tantalizing possibilities."
>
> Unlike with Volaticotherium, there is no mention of any sign of a patagium,
> so the last clause is a healthy cautionary note.
>
>
>>> The article is available here for free:
>>>
>>> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877
>
>> That's paywalled for me.
>
> I truncated the url without realizing that what I snipped was necessary. This is the full url:
>
> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877?casa_token=qwG6zKvdhVcAAAAA:CgOj49mStFIcuzpf-pdA0kaFuSV5zGu4M7XE09uUyrqDSrKkoIFbmd13jtGGt2wSdGYr9YzGuZo

That doesn't work either. You may be exercising an institutional login
without knowing it.

> The way I originally got there was via the Wikipedia article that you used, then clicking on the doi featured in [3] there.
> This took me to a page with "PDF" in white on a dark gray background in the upper extreme right, with a smaller
> "Help" on a light gray background. Clicking on PDF took me to the article.
>
>> But the abstract seems to promise what you're
>> looking for. You can't find anything in the actual paper that delivers
>> on the abstract?
>
> Only the indirect evidence that I quoted.
>
> <snip for focus>
>>>> A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and
>>>> Symmetrodonts and the Origin of Extant Mammals. Doklady Biological
>>>> Sciences 436:32-35
>>>
>>> This one is freely available here:
>>> https://www.researchgate.net/publication/50272438_Phylogeny_of_triconodonts_and_symmetrodonts_and_the_origin_of_extant_mammals
>>>
>>> It has a long first paragraph giving past and present classification of mammals. It proposes a phylogenetic tree
>>> that varies significantly from most of the recent ones I have seen, classifying monotremes as being
>>> closer to us than either triconodonts or symmetrodonts. The authors do not disguise the fact that their
>>> tree is a departure from almost all previous trees of mammaliform synapsids in this respect.
>> Not really of interest for me. I only mentioned it because I know you
>> like triconodonts.
>
>
> Yes, my fondness for triconodonts goes back to my 12-year-old acquaintance with them in
> Romer's _Vertebrate Paleontology_. Mammals of the Jurassic fascinated me all the way back then.
>
> Also, the teeth of the Lower Cretaceous monotreme *Steropodon* reminded me very much of triconodont teeth
> when I first read about them three decades ago. I think it would be "way cool" if monotremes
> turned out to be [descended from] triconodonts.

Isn't that just a primitive mammal character?

On Tuesday, June 15, 2021 at 1:08:16 PM UTC-4, John Harshman wrote:
> On 6/15/21 9:37 AM, Peter Nyikos wrote:
> > On Tuesday, June 15, 2021 at 10:52:55 AM UTC-4, John Harshman wrote:
> >> On 6/15/21 7:35 AM, Peter Nyikos wrote:
> >>> On Monday, June 14, 2021 at 6:26:32 PM UTC-4, John Harshman wrote:
> >>>
> >>>> Mammals aren't my thing, but the Wikipedia article has some interesting
> >>>> additions. First,
> >>>>
> >>>> "The closely related and significantly older Argentoconodon shows
> >>>> similar post-cranial adaptations for aerial locomotion also seen in
> >>>> Volaticotherium.[3]"
> >>>
> >>>> The reference is Leandro C. Gaetano and Guillermo W. Rougier (2011).
> >>>> "New materials of Argentoconodon fariasorum (Mammaliaformes,
> >>>> Triconodontidae) from the Jurassic of Argentina and its bearing on
> >>>> triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4):
> >>>> 829–843. doi:10.1080/02724634.2011.589877
> >>>
> >>> I saw no mention of post-cranial adaptations for aerial locomotion.
> >
> > This time I saw a bit of "circumstantial evidence":
> >
> > "Some postcranial characteristics of Argentoconodon are similar to those described for Volaticotherium, suggesting similar locomotory habits (Gaetano and Rougier, 2010). These similarities include the orientation and morphology of the proximal portion
> > of the femur, with a poorly differentiated head in line with the main shaft of the femur and greater and lesser trochanters confluent with the femoral head. Hence, a sister-group relationship between these two taxa might imply the existence of a widely distributed gliding clade of mammals at least as old as the EarlyJurassic, but the preservation of Argentoconodon is insufficient
> > to go beyond these tantalizing possibilities."
> >
> > Unlike with Volaticotherium, there is no mention of any sign of a patagium,
> > so the last clause is a healthy cautionary note.
> >
> >
> >>> The article is available here for free:
> >>>
> >>> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877
> >
> >> That's paywalled for me.
> >
> > I truncated the url without realizing that what I snipped was necessary.. This is the full url:
> >
> > https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877?casa_token=qwG6zKvdhVcAAAAA:CgOj49mStFIcuzpf-pdA0kaFuSV5zGu4M7XE09uUyrqDSrKkoIFbmd13jtGGt2wSdGYr9YzGuZo

When I clicked on the above url, it didn't take me immediately to the article. But I saw the gray rectangles
I described below, and when I clicked on the big one, it took me to the article.

> That doesn't work either. You may be exercising an institutional login
> without knowing it.

Did you notice the rectangles with the gray background? They should be on the right edge of the page, with
the smaller beginning where the bigger ends.

Not at the top, and perhaps closer to the bottom of what appears on your screen when you first click on the url.

> > The way I originally got there was via the Wikipedia article that you used, then clicking on the doi featured in [3] there.
> > This took me to a page with "PDF" in white on a dark gray background in the upper extreme right, with a smaller
> > "Help" on a light gray background. Clicking on PDF took me to the article.
> >
> >> But the abstract seems to promise what you're
> >> looking for. You can't find anything in the actual paper that delivers
> >> on the abstract?
> >
> > Only the indirect evidence that I quoted.
> >
> > <snip for focus>
> >>>> A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and
> >>>> Symmetrodonts and the Origin of Extant Mammals. Doklady Biological
> >>>> Sciences 436:32-35
> >>>
> >>> This one is freely available here:
> >>> https://www.researchgate.net/publication/50272438_Phylogeny_of_triconodonts_and_symmetrodonts_and_the_origin_of_extant_mammals
> >>>
> >>> It has a long first paragraph giving past and present classification of mammals. It proposes a phylogenetic tree
> >>> that varies significantly from most of the recent ones I have seen, classifying monotremes as being
> >>> closer to us than either triconodonts or symmetrodonts. The authors do not disguise the fact that their
> >>> tree is a departure from almost all previous trees of mammaliform synapsids in this respect.
> >> Not really of interest for me. I only mentioned it because I know you
> >> like triconodonts.
> >
> >
> > Yes, my fondness for triconodonts goes back to my 12-year-old acquaintance with them in

By this I meant that I was twelve years old at the time.

> > Romer's _Vertebrate Paleontology_. Mammals of the Jurassic fascinated me all the way back then.

> > Also, the teeth of the Lower Cretaceous monotreme *Steropodon* reminded me very much of triconodont teeth
> > when I first read about them three decades ago. I think it would be "way cool" if monotremes
> > turned out to be [descended from] triconodonts.

> Isn't that just a primitive mammal character?

The molars of Morganucodon aren't like that, so my guess is that the answer is no.

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

On 6/15/21 11:40 AM, Peter Nyikos wrote:
> On Tuesday, June 15, 2021 at 1:08:16 PM UTC-4, John Harshman wrote:
>> On 6/15/21 9:37 AM, Peter Nyikos wrote:
>>> On Tuesday, June 15, 2021 at 10:52:55 AM UTC-4, John Harshman wrote:
>>>> On 6/15/21 7:35 AM, Peter Nyikos wrote:
>>>>> On Monday, June 14, 2021 at 6:26:32 PM UTC-4, John Harshman wrote:
>>>>>
>>>>>> Mammals aren't my thing, but the Wikipedia article has some interesting
>>>>>> additions. First,
>>>>>>
>>>>>> "The closely related and significantly older Argentoconodon shows
>>>>>> similar post-cranial adaptations for aerial locomotion also seen in
>>>>>> Volaticotherium.[3]"
>>>>>
>>>>>> The reference is Leandro C. Gaetano and Guillermo W. Rougier (2011).
>>>>>> "New materials of Argentoconodon fariasorum (Mammaliaformes,
>>>>>> Triconodontidae) from the Jurassic of Argentina and its bearing on
>>>>>> triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4):
>>>>>> 829–843. doi:10.1080/02724634.2011.589877
>>>>>
>>>>> I saw no mention of post-cranial adaptations for aerial locomotion.
>>>
>>> This time I saw a bit of "circumstantial evidence":
>>>
>>> "Some postcranial characteristics of Argentoconodon are similar to those described for Volaticotherium, suggesting similar locomotory habits (Gaetano and Rougier, 2010). These similarities include the orientation and morphology of the proximal portion
>>> of the femur, with a poorly differentiated head in line with the main shaft of the femur and greater and lesser trochanters confluent with the femoral head. Hence, a sister-group relationship between these two taxa might imply the existence of a widely distributed gliding clade of mammals at least as old as the EarlyJurassic, but the preservation of Argentoconodon is insufficient
>>> to go beyond these tantalizing possibilities."
>>>
>>> Unlike with Volaticotherium, there is no mention of any sign of a patagium,
>>> so the last clause is a healthy cautionary note.
>>>
>>>
>>>>> The article is available here for free:
>>>>>
>>>>> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877
>>>
>>>> That's paywalled for me.
>>>
>>> I truncated the url without realizing that what I snipped was necessary. This is the full url:
>>>
>>> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877?casa_token=qwG6zKvdhVcAAAAA:CgOj49mStFIcuzpf-pdA0kaFuSV5zGu4M7XE09uUyrqDSrKkoIFbmd13jtGGt2wSdGYr9YzGuZo
>
> When I clicked on the above url, it didn't take me immediately to the article. But I saw the gray rectangles
> I described below, and when I clicked on the big one, it took me to the article.

Not me.

>> That doesn't work either. You may be exercising an institutional login
>> without knowing it.
>
> Did you notice the rectangles with the gray background? They should be on the right edge of the page, with
> the smaller beginning where the bigger ends.
>
> Not at the top, and perhaps closer to the bottom of what appears on your screen when you first click on the url.

Yes.

>>> The way I originally got there was via the Wikipedia article that you used, then clicking on the doi featured in [3] there.
>>> This took me to a page with "PDF" in white on a dark gray background in the upper extreme right, with a smaller
>>> "Help" on a light gray background. Clicking on PDF took me to the article.
>>>
>>>> But the abstract seems to promise what you're
>>>> looking for. You can't find anything in the actual paper that delivers
>>>> on the abstract?
>>>
>>> Only the indirect evidence that I quoted.
>>>
>>> <snip for focus>
>>>>>> A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and
>>>>>> Symmetrodonts and the Origin of Extant Mammals. Doklady Biological
>>>>>> Sciences 436:32-35
>>>>>
>>>>> This one is freely available here:
>>>>> https://www.researchgate.net/publication/50272438_Phylogeny_of_triconodonts_and_symmetrodonts_and_the_origin_of_extant_mammals
>>>>>
>>>>> It has a long first paragraph giving past and present classification of mammals. It proposes a phylogenetic tree
>>>>> that varies significantly from most of the recent ones I have seen, classifying monotremes as being
>>>>> closer to us than either triconodonts or symmetrodonts. The authors do not disguise the fact that their
>>>>> tree is a departure from almost all previous trees of mammaliform synapsids in this respect.
>>>> Not really of interest for me. I only mentioned it because I know you
>>>> like triconodonts.
>>>
>>>
>>> Yes, my fondness for triconodonts goes back to my 12-year-old acquaintance with them in
>
> By this I meant that I was twelve years old at the time.
>
>>> Romer's _Vertebrate Paleontology_. Mammals of the Jurassic fascinated me all the way back then.
>
>>> Also, the teeth of the Lower Cretaceous monotreme *Steropodon* reminded me very much of triconodont teeth
>>> when I first read about them three decades ago. I think it would be "way cool" if monotremes
>>> turned out to be [descended from] triconodonts.
>
>> Isn't that just a primitive mammal character?
>
> The molars of Morganucodon aren't like that, so my guess is that the answer is no.

But Morganucodon had triconodont (here referring to three cusps, not to
membership in any taxonomic group) molars.

On Tuesday, June 15, 2021 at 7:11:40 PM UTC-4, John Harshman wrote:
> On 6/15/21 11:40 AM, Peter Nyikos wrote:
> > On Tuesday, June 15, 2021 at 1:08:16 PM UTC-4, John Harshman wrote:
> >> On 6/15/21 9:37 AM, Peter Nyikos wrote:
> >>> On Tuesday, June 15, 2021 at 10:52:55 AM UTC-4, John Harshman wrote:
> >>>> On 6/15/21 7:35 AM, Peter Nyikos wrote:
> >>>>> On Monday, June 14, 2021 at 6:26:32 PM UTC-4, John Harshman wrote:
> >>>>>
> >>>>>> Mammals aren't my thing, but the Wikipedia article has some interesting
> >>>>>> additions. First,
> >>>>>>
> >>>>>> "The closely related and significantly older Argentoconodon shows
> >>>>>> similar post-cranial adaptations for aerial locomotion also seen in
> >>>>>> Volaticotherium.[3]"
> >>>>>
> >>>>>> The reference is Leandro C. Gaetano and Guillermo W. Rougier (2011).
> >>>>>> "New materials of Argentoconodon fariasorum (Mammaliaformes,
> >>>>>> Triconodontidae) from the Jurassic of Argentina and its bearing on
> >>>>>> triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4):
> >>>>>> 829–843. doi:10.1080/02724634.2011.589877
> >>>>>
> >>>>> I saw no mention of post-cranial adaptations for aerial locomotion.
> >>>
> >>> This time I saw a bit of "circumstantial evidence":
> >>>
> >>> "Some postcranial characteristics of Argentoconodon are similar to those described for Volaticotherium, suggesting similar locomotory habits (Gaetano and Rougier, 2010). These similarities include the orientation and morphology of the proximal portion
> >>> of the femur, with a poorly differentiated head in line with the main shaft of the femur and greater and lesser trochanters confluent with the femoral head. Hence, a sister-group relationship between these two taxa might imply the existence of a widely distributed gliding clade of mammals at least as old as the EarlyJurassic, but the preservation of Argentoconodon is insufficient
> >>> to go beyond these tantalizing possibilities."
> >>>
> >>> Unlike with Volaticotherium, there is no mention of any sign of a patagium,
> >>> so the last clause is a healthy cautionary note.
> >>>
> >>>
> >>>>> The article is available here for free:
> >>>>>
> >>>>> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877
> >>>
> >>>> That's paywalled for me.
> >>>
> >>> I truncated the url without realizing that what I snipped was necessary. This is the full url:
> >>>
> >>> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877?casa_token=qwG6zKvdhVcAAAAA:CgOj49mStFIcuzpf-pdA0kaFuSV5zGu4M7XE09uUyrqDSrKkoIFbmd13jtGGt2wSdGYr9YzGuZo
> >
> > When I clicked on the above url, it didn't take me immediately to the article. But I saw the gray rectangles
> > I described below, and when I clicked on the big one, it took me to the article.
> Not me.
> >> That doesn't work either. You may be exercising an institutional login
> >> without knowing it.
> >
> > Did you notice the rectangles with the gray background? They should be on the right edge of the page, with
> > the smaller beginning where the bigger ends.
> >
> > Not at the top, and perhaps closer to the bottom of what appears on your screen when you first click on the url.
> Yes.

So you saw them? and clicking on them still didn't work?

> >>> The way I originally got there was via the Wikipedia article that you used, then clicking on the doi featured in [3] there.
> >>> This took me to a page with "PDF" in white on a dark gray background in the upper extreme right, with a smaller
> >>> "Help" on a light gray background. Clicking on PDF took me to the article.

In contrast, when I used the truncated url, there were no such rectangles, and everything was paywall-oriented.

> >>>
> >>>> But the abstract seems to promise what you're
> >>>> looking for. You can't find anything in the actual paper that delivers
> >>>> on the abstract?
> >>>
> >>> Only the indirect evidence that I quoted.
> >>>
> >>> <snip for focus>
> >>>>>> A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and
> >>>>>> Symmetrodonts and the Origin of Extant Mammals. Doklady Biological
> >>>>>> Sciences 436:32-35
> >>>>>
> >>>>> This one is freely available here:
> >>>>> https://www.researchgate.net/publication/50272438_Phylogeny_of_triconodonts_and_symmetrodonts_and_the_origin_of_extant_mammals
> >>>>>
> >>>>> It has a long first paragraph giving past and present classification of mammals. It proposes a phylogenetic tree
> >>>>> that varies significantly from most of the recent ones I have seen, classifying monotremes as being
> >>>>> closer to us than either triconodonts or symmetrodonts. The authors do not disguise the fact that their
> >>>>> tree is a departure from almost all previous trees of mammaliform synapsids in this respect.
> >>>> Not really of interest for me. I only mentioned it because I know you
> >>>> like triconodonts.
> >>>
> >>>
> >>> Yes, my fondness for triconodonts goes back to my 12-year-old acquaintance with them in
> >
> > By this I meant that I was twelve years old at the time.
> >
> >>> Romer's _Vertebrate Paleontology_. Mammals of the Jurassic fascinated me all the way back then.
> >
> >>> Also, the teeth of the Lower Cretaceous monotreme *Steropodon* reminded me very much of triconodont teeth
> >>> when I first read about them three decades ago. I think it would be "way cool" if monotremes
> >>> turned out to be [descended from] triconodonts.
> >
> >> Isn't that just a primitive mammal character?
> >
> > The molars of Morganucodon aren't like that, so my guess is that the answer is no.

> But Morganucodon had triconodont (here referring to three cusps, not to
> membership in any taxonomic group) molars.

There's the rub: the taxonomic group doesn't just have three cusps, but three cusps
of almost equal heights, in a straight row parallel to the dentary.

All Jurassic mammals known in Romer's time had molars with three cusps, including symmetrodonts and pantotheres (trituberculates).
The one Middle Jurassic pantothere known at the time was *Amphitherium,* and Romer (1945) says about it:
"The molars show a three-cusped, asymmetrical trigonid..."

However, I mis-remembered the teeth of Steropodon and the very similar teeth of Obdurodon, a
Miocene platypus. They had two cusps where triconodonts have three, but the cusps were
subdivided into two smaller cusps that were perpendicular to the dentary. So I'm shelving my hypothesis for now.

On the other hand, another fossil mammal identified for a long time as a monotreme has been reclassified:

"Kollikodon is an australosphenidan species, often classified as a monotreme but more recently recovered as a haramiyidan.[1]"

Back in 1995, a jaw of Kollikodon was discovered and became the type specimen. When I first heard about it a year or two later
in s.b.p., I could not figure out why it was classed as a monotreme. The teeth did not look like any other monotreme teeth. I remarked
on this in s.b.p., and now I'm sorry I didn't try to get in touch with the researchers who first described it. [1] is to a 2019 paper,
two decades after I got curious about it.

Peter Nyikos
Professor, Dept. of Mathematics -- standard disclaimer--
University of So. Carolina in Columbia
http://people.math.sc.edu/nyikos

On 6/17/21 12:35 PM, Peter Nyikos wrote:
> On Tuesday, June 15, 2021 at 7:11:40 PM UTC-4, John Harshman wrote:
>> On 6/15/21 11:40 AM, Peter Nyikos wrote:
>>> On Tuesday, June 15, 2021 at 1:08:16 PM UTC-4, John Harshman wrote:
>>>> On 6/15/21 9:37 AM, Peter Nyikos wrote:
>>>>> On Tuesday, June 15, 2021 at 10:52:55 AM UTC-4, John Harshman wrote:
>>>>>> On 6/15/21 7:35 AM, Peter Nyikos wrote:
>>>>>>> On Monday, June 14, 2021 at 6:26:32 PM UTC-4, John Harshman wrote:
>>>>>>>
>>>>>>>> Mammals aren't my thing, but the Wikipedia article has some interesting
>>>>>>>> additions. First,
>>>>>>>>
>>>>>>>> "The closely related and significantly older Argentoconodon shows
>>>>>>>> similar post-cranial adaptations for aerial locomotion also seen in
>>>>>>>> Volaticotherium.[3]"
>>>>>>>
>>>>>>>> The reference is Leandro C. Gaetano and Guillermo W. Rougier (2011).
>>>>>>>> "New materials of Argentoconodon fariasorum (Mammaliaformes,
>>>>>>>> Triconodontidae) from the Jurassic of Argentina and its bearing on
>>>>>>>> triconodont phylogeny". Journal of Vertebrate Paleontology. 31 (4):
>>>>>>>> 829–843. doi:10.1080/02724634.2011.589877
>>>>>>>
>>>>>>> I saw no mention of post-cranial adaptations for aerial locomotion.
>>>>>
>>>>> This time I saw a bit of "circumstantial evidence":
>>>>>
>>>>> "Some postcranial characteristics of Argentoconodon are similar to those described for Volaticotherium, suggesting similar locomotory habits (Gaetano and Rougier, 2010). These similarities include the orientation and morphology of the proximal portion
>>>>> of the femur, with a poorly differentiated head in line with the main shaft of the femur and greater and lesser trochanters confluent with the femoral head. Hence, a sister-group relationship between these two taxa might imply the existence of a widely distributed gliding clade of mammals at least as old as the EarlyJurassic, but the preservation of Argentoconodon is insufficient
>>>>> to go beyond these tantalizing possibilities."
>>>>>
>>>>> Unlike with Volaticotherium, there is no mention of any sign of a patagium,
>>>>> so the last clause is a healthy cautionary note.
>>>>>
>>>>>
>>>>>>> The article is available here for free:
>>>>>>>
>>>>>>> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877
>>>>>
>>>>>> That's paywalled for me.
>>>>>
>>>>> I truncated the url without realizing that what I snipped was necessary. This is the full url:
>>>>>
>>>>> https://www.tandfonline.com/doi/pdf/10.1080/02724634.2011.589877?casa_token=qwG6zKvdhVcAAAAA:CgOj49mStFIcuzpf-pdA0kaFuSV5zGu4M7XE09uUyrqDSrKkoIFbmd13jtGGt2wSdGYr9YzGuZo
>>>
>>> When I clicked on the above url, it didn't take me immediately to the article. But I saw the gray rectangles
>>> I described below, and when I clicked on the big one, it took me to the article.
>> Not me.
>>>> That doesn't work either. You may be exercising an institutional login
>>>> without knowing it.
>>>
>>> Did you notice the rectangles with the gray background? They should be on the right edge of the page, with
>>> the smaller beginning where the bigger ends.
>>>
>>> Not at the top, and perhaps closer to the bottom of what appears on your screen when you first click on the url.
>> Yes.
>
> So you saw them? and clicking on them still didn't work?
>
>>>>> The way I originally got there was via the Wikipedia article that you used, then clicking on the doi featured in [3] there.
>>>>> This took me to a page with "PDF" in white on a dark gray background in the upper extreme right, with a smaller
>>>>> "Help" on a light gray background. Clicking on PDF took me to the article.
>
> In contrast, when I used the truncated url, there were no such rectangles, and everything was paywall-oriented.
>
>
>>>>>
>>>>>> But the abstract seems to promise what you're
>>>>>> looking for. You can't find anything in the actual paper that delivers
>>>>>> on the abstract?
>>>>>
>>>>> Only the indirect evidence that I quoted.
>>>>>
>>>>> <snip for focus>
>>>>>>>> A. O. Averianov and A. V. Lopatin. 2011. Phylogeny of Triconodonts and
>>>>>>>> Symmetrodonts and the Origin of Extant Mammals. Doklady Biological
>>>>>>>> Sciences 436:32-35
>>>>>>>
>>>>>>> This one is freely available here:
>>>>>>> https://www.researchgate.net/publication/50272438_Phylogeny_of_triconodonts_and_symmetrodonts_and_the_origin_of_extant_mammals
>>>>>>>
>>>>>>> It has a long first paragraph giving past and present classification of mammals. It proposes a phylogenetic tree
>>>>>>> that varies significantly from most of the recent ones I have seen, classifying monotremes as being
>>>>>>> closer to us than either triconodonts or symmetrodonts. The authors do not disguise the fact that their
>>>>>>> tree is a departure from almost all previous trees of mammaliform synapsids in this respect.
>>>>>> Not really of interest for me. I only mentioned it because I know you
>>>>>> like triconodonts.
>>>>>
>>>>>
>>>>> Yes, my fondness for triconodonts goes back to my 12-year-old acquaintance with them in
>>>
>>> By this I meant that I was twelve years old at the time.
>>>
>>>>> Romer's _Vertebrate Paleontology_. Mammals of the Jurassic fascinated me all the way back then.
>>>
>>>>> Also, the teeth of the Lower Cretaceous monotreme *Steropodon* reminded me very much of triconodont teeth
>>>>> when I first read about them three decades ago. I think it would be "way cool" if monotremes
>>>>> turned out to be [descended from] triconodonts.
>>>
>>>> Isn't that just a primitive mammal character?
>>>
>>> The molars of Morganucodon aren't like that, so my guess is that the answer is no.
>
>> But Morganucodon had triconodont (here referring to three cusps, not to
>> membership in any taxonomic group) molars.
>
> There's the rub: the taxonomic group doesn't just have three cusps, but three cusps
> of almost equal heights, in a straight row parallel to the dentary.

Morganucodon has three cusps in a linear row, with relative sizes
similar to what's seen in many triconodonts. In fact it was sometimes
classified as a triconodont.

> All Jurassic mammals known in Romer's time had molars with three cusps, including symmetrodonts and pantotheres (trituberculates).
> The one Middle Jurassic pantothere known at the time was *Amphitherium,* and Romer (1945) says about it:
> "The molars show a three-cusped, asymmetrical trigonid..."
>
> However, I mis-remembered the teeth of Steropodon and the very similar teeth of Obdurodon, a
> Miocene platypus. They had two cusps where triconodonts have three, but the cusps were
> subdivided into two smaller cusps that were perpendicular to the dentary. So I'm shelving my hypothesis for now.
>
>
> On the other hand, another fossil mammal identified for a long time as a monotreme has been reclassified:
>
> "Kollikodon is an australosphenidan species, often classified as a monotreme but more recently recovered as a haramiyidan.[1]"
>
> Back in 1995, a jaw of Kollikodon was discovered and became the type specimen. When I first heard about it a year or two later
> in s.b.p., I could not figure out why it was classed as a monotreme. The teeth did not look like any other monotreme teeth. I remarked
> on this in s.b.p., and now I'm sorry I didn't try to get in touch with the researchers who first described it. [1] is to a 2019 paper,
> two decades after I got curious about it.
>
>
> Peter Nyikos
> Professor, Dept. of Mathematics -- standard disclaimer--
> University of So. Carolina in Columbia
> http://people.math.sc.edu/nyikos
>

On 6/14/21 2:29 PM, Peter Nyikos wrote:
> Back in 2006, a very detailed fossil of the one known Mesozoic
gliding mammal
> was discovered in Northern China. Named *Volaticotherium antiquum*,
it has a hip joint
> that sets it apart from all other known mammals. It is not a
ball-and-socket joint:
>
> "The femur has a small, oval-shaped head and lacks a femoral neck
(Fig. 3c, d), which is unique among mammals [9]. Although the hip
structure was not preserved, the shape of the femoral head alone reveals
that the acetabulum is probably shallow and open, perhaps similar to
those of arboreal didelphids [24]."
>
> https://www.nature.com/articles/nature05234
>
> However, even *Didelphis*, the oposssum, has a standard-looking
hip joint.
>
>
> The article is paywalled , but I have free access whenever I am
at my university.
>
> There is a very clear set of pictures of the femoral head, from the
side and from the
> top, and they suggest that the hip joint is basically a hinge joint.
>
> The Wikipedia entry says this about it:
>
> "its femur has unique adaptations among mammals that make it
resistant to flight stresses, and render terrestrial locomotion cumbersome."
>
> This is based on the following statement in the *Nature* article:
>
> "Unlike the ball-and-socket hip joint that provides ample excursion
for legs in other mammals [25], the peculiar femoral head of
Volaticotherium must have restricted flexibility of the leg in
rotational movements, but could have allowed the leg to be extended
laterally and remain steady during a glide."
>
> The enigma here is just how the hypothesized advantages of the joint
> outweighed its obvious drawbacks.
>
>
> More about the adaptations for gliding in my next post to this thread.
>
>
> Peter Nyikos
> Professor, Dept. of Mathematics -- standard disclaimer--
> University of South Carolina
> http://people.math.sc.edu/nyikos

Were these supposed to be island animals that died out
when the north China or south China cratons finished
drifting through the Tethys Ocean and made contact with
Laurasia or Pangaea or Cimmeria?

Did very similar animals have a much broader range across
the Earth's continents at the time?

On 6/18/2021 3:12 PM, Trolidous wrote:
> On 6/14/21 2:29 PM, Peter Nyikos wrote:
> > Back in 2006, a very detailed fossil of the one known Mesozoic
> gliding mammal
> > was discovered in Northern China. Named *Volaticotherium antiquum*,
> it has a hip joint
> > that sets it apart from all other known mammals.  It is not a
> ball-and-socket joint:
> >
> > "The femur has a small, oval-shaped head and lacks a femoral neck
> (Fig. 3c, d), which is unique among mammals [9]. Although the hip
> structure was not preserved, the shape of the femoral head alone reveals
> that the acetabulum is probably shallow and open, perhaps similar to
> those of arboreal didelphids [24]."
> >
> > https://www.nature.com/articles/nature05234
> >
> > However, even *Didelphis*, the  oposssum, has  a  standard-looking
> hip  joint.
> >
> >
> > The  article  is paywalled , but  I have free access whenever I  am
> at  my university.
> >
> > There  is a very clear set of pictures of the femoral head, from the
> side and from the
> > top, and they suggest that the hip joint is basically a hinge joint.
> >
> > The Wikipedia entry says  this about it:
> >
> > "its femur has unique adaptations among mammals that make it
> resistant to flight stresses, and render terrestrial locomotion
> cumbersome."
> >
> > This is based on the following statement in the *Nature* article:
> >
> > "Unlike the ball-and-socket hip joint that provides ample excursion
> for legs in other mammals [25], the peculiar femoral head of
> Volaticotherium must have restricted flexibility of the leg in
> rotational movements, but could have allowed the leg to be extended
> laterally and remain steady during a glide."
> >
> > The enigma here is just how the hypothesized advantages of the joint
> > outweighed its obvious drawbacks.
> >
> >
> > More about the adaptations for gliding in my next post to this thread.
> >
> >
> > Peter Nyikos
> > Professor, Dept. of Mathematics   -- standard disclaimer--
> > University of South Carolina
> > http://people.math.sc.edu/nyikos
>
> Were these supposed to be island animals that died out
> when the north China or south China cratons finished
> drifting through the Tethys Ocean and made contact with
> Laurasia or Pangaea or Cimmeria?
>
> Did very similar animals have a much broader range across
> the Earth's continents at the time?
>

*Volaticotherium* was found in China. *Argentoconodon* was found in
Argentina, it doesn't take a rocket scientist to extrapolate that
Volaticotherini had a cosmopolitan or near cosmopolitan distribution at
the time.

On 6/24/21 5:35 PM, Oxyaena wrote:
> On 6/18/2021 3:12 PM, Trolidous wrote:
>> On 6/14/21 2:29 PM, Peter Nyikos wrote:
>>  > Back in 2006, a very detailed fossil of the one known Mesozoic
>> gliding mammal
>>  > was discovered in Northern China. Named *Volaticotherium antiquum*,
>> it has a hip joint
>>  > that sets it apart from all other known mammals.  It is not a
>> ball-and-socket joint:
>>  >
>>  > "The femur has a small, oval-shaped head and lacks a femoral neck
>> (Fig. 3c, d), which is unique among mammals [9]. Although the hip
>> structure was not preserved, the shape of the femoral head alone
>> reveals that the acetabulum is probably shallow and open, perhaps
>> similar to those of arboreal didelphids [24]."
>>  >
>>  > https://www.nature.com/articles/nature05234
>>  >
>>  > However, even *Didelphis*, the  oposssum, has  a  standard-looking
>> hip  joint.
>>  >
>>  >
>>  > The  article  is paywalled , but  I have free access whenever I  am
>> at  my university.
>>  >
>>  > There  is a very clear set of pictures of the femoral head, from
>> the side and from the
>>  > top, and they suggest that the hip joint is basically a hinge joint.
>>  >
>>  > The Wikipedia entry says  this about it:
>>  >
>>  > "its femur has unique adaptations among mammals that make it
>> resistant to flight stresses, and render terrestrial locomotion
>> cumbersome."
>>  >
>>  > This is based on the following statement in the *Nature* article:
>>  >
>>  > "Unlike the ball-and-socket hip joint that provides ample excursion
>> for legs in other mammals [25], the peculiar femoral head of
>> Volaticotherium must have restricted flexibility of the leg in
>> rotational movements, but could have allowed the leg to be extended
>> laterally and remain steady during a glide."
>>  >
>>  > The enigma here is just how the hypothesized advantages of the joint
>>  > outweighed its obvious drawbacks.
>>  >
>>  >
>>  > More about the adaptations for gliding in my next post to this thread.
>>  >
>>  >
>>  > Peter Nyikos
>>  > Professor, Dept. of Mathematics   -- standard disclaimer--
>>  > University of South Carolina
>>  > http://people.math.sc.edu/nyikos
>>
>> Were these supposed to be island animals that died out
>> when the north China or south China cratons finished
>> drifting through the Tethys Ocean and made contact with
>> Laurasia or Pangaea or Cimmeria?
>>
>> Did very similar animals have a much broader range across
>> the Earth's continents at the time?
>>
>
> *Volaticotherium* was found in China. *Argentoconodon* was found in
> Argentina, it doesn't take a rocket scientist to extrapolate that
> Volaticotherini had a cosmopolitan or near cosmopolitan distribution at
> the time.

Thank you for helping to partially answer the question.

As for 'it doesn't take a rocket scientist' I guess you have
a propensity to distribute facts with variants of 'you're stupid'.

I guess that's your pleasure. Different strokes for different folks.