Talk:Australosphenida

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Isn't Australosphenida the same as Prototheria? --Philo 17:31, 15 December 2006 (UTC)

I can't find any reference to Australosphenida as a subclass, only a clade. The Paleobiology database does not list a rank for this group, and the only subclass listed that includes monotremata is Prototheria. i'm going to change the listings that call this a subclass, unless a cite is provided that refers Australosphenida to this rank. Dinoguy2 01:58, 31 December 2006 (UTC)

• The article currently lists Australosphendia as a subclass in the infobox, but identifies it as a clade in the first sentense. Granted, I am no zoologist, but this appears to be contradictory. Can a grouping be both a clade and a subclass at the same time? Snagglepuss (talk) 14:34, 25 November 2008 (UTC)

Ideally, every taxon is a clade. - UtherSRG (talk) 15:24, 25 November 2008 (UTC)

"Nearly entirely died out"

Hello Ucucha,

I do know that living eutherians are outnumbered by extinct eutherians, but that's a very different case since living eutherians are still numerous and not reduced to a handful of species. The problem I see here is that you are claiming present diversity of species as a reason for saying the group has not almost disappeared. If there were only 5 living species of vertebrates (say, a lamprey, a bird and 3 mammals), the subphylum would be highly diversified. It would also have "nearly entirely died out". This is exactly parallel to the case here. Diverse, yes; numerous, no. Most species in the group are extinct. That is precisely what is meant by "nearly entirely died out", irrespective of present diversity.

I think it's rather simple. Today we have 5 species belonging to just 2 monotreme families (out of the 4 that are known to have existed), and all of these belonging to the same order (out of the 2 that are known to have existed). Most of the present diversity is within just one family and most of that is within just one genus. Maybe there are more species known to be alive at the present time than at any one point in prehistory, but they are restricted to fewer taxa. By any reckoning this must count as a reduction in overall diversity. The remaining Australosphenida are less diversified than they would have been if kollikodontids, steropodontids and/or ausktibosphenidans had survived. But even if they were more diversified today (say, one species from each of the five groups), as long as there were only a handful of them it wouldn't change the fact that they have "nearly entirely died out".

If you dispute this, can I invite you to say how you would express the fact that there are currently but few species, from fewer lineages than ever before? Gnostrat (talk) 05:48, 21 September 2008 (UTC)

I think I disagree fundamentally with you on the historical diversity of this group. Allow me to give a recapitulation of their fossil record. The oldest australosphenidan (Ambondro from Madagascar) is from the Bathonian, about 165 Ma. There are two other slightly later Middle Jurassic species, both from Argentina (Asfaltomylos and Henosferus). Subsequently, they disappear until Teinolophos, Ausktribosphenos and Bishops appear in the Aptian (ca. 120 Ma), followed in the subsequent Albian (ca. 105 Ma) by Kryoryctes (perhaps the ancestor of the echidnas), Kollikodon, and Steropodon. The echidnas then disappear completely and the Tertiary fossil record of the platypus appears, consisting of a single species (Monotrematum) from the Paleocene and two others (both Obdurodon) in the Oligocene and Miocene, respectively. The next fossil record appears in the Upper Pliocene, when the first of a total of three to five fossil Zaglossus-like echidnas appears (some are sometimes placed separately in Megalibgwilia). After that, in the Holocene, we get one platypus, the first Tachyglossus, and at least three species of Zaglossus (probably more, according to unfinished research). Therefore, the current three genera represent the highest genus-level diversity of australosphenidans ever (tied with the Aptian and the Albian) and also the highest species-level diversity ever (tied with the Pleistocene when you accept all fossil species). It is true, as you say, that most species have died out, but you can expect nothing else from a group that has been around for more than 160 million years. Besides, even much younger groups with a reasonable fossil record usually have more extinct species than living ones (for example, I once counted over one thousand fossil species of perissodactylans and over two thousand of cetartiodactylans, and I am pretty sure that you will not say that cetartiodactylans have nearly entirely died out).

You also say that higher-level diversity of australosphenidans is lower than before. I happen to disagree also on that point. The article currently says that there are two orders, Ausktribosphenida and Monotremata, but that does not seem to be the accepted classification in the primary literature, and at the very least it is misleading, since Ausktribosphenida is decidedly paraphyletic when you accept the australosphenidan hypothesis (Asfaltomylos and Henosferus are apparently the basal forms, according to the phylogenetic analysis in the description of Henosferus). Some of the fossil australosphenidans have been placed in separate families, but there is no reason to assume that these were ever more than short side-branches of the main australosphenidan line leading to living monotremes—some may even have been directly ancestral to the platypus. In addition, there are two extremely distinct living groups of monotremes, and the authoritative Classification of mammals even placed them in separate orders (which is not unreasonable considering that they must have been distinct in the Middle Cretaceous if we accept that Kryoryctes was an early echidna and Teinolophos, an early platypus).

So, have australosphenidans nearly entirely died out? No: they still have a diversity that is comparable to, if not higher than, the diversity they had in the Cretaceous. They have always been a species-poor group, and have remained so until the present day.

I think a note on the historical diversity of australosphenidans would be a good idea, but such a note should not contain dubious language such as the formulation you prefer. Rather, it should give a summary of the fossil record and let the reader decide what to make of it. Ucucha 07:23, 21 September 2008 (UTC)