Phylogeny of Desmostylia: Matsui and Tsuihiji 2019

Matsui and Tsuihiji 2019 bring us their views
on the phylogeny of taxa within their Desmostylia, an order of large aquatic (Pacific rim) mammals, best known from the early Oligocene (31mya) to the late Miocene (7.25mya). Traditionally there are relatively few taxa in the clade Desmostylia (Neoparadoxia (Fig. 2), Paleoparadoxia, Behemotops (Fig. 2), Desmostylus (Fig. 3) and a few others not as well represented in the fossil record.

Unfortunately the authors’ views
are too restricted with too few taxa under consideration. Desmostylians are not the extinct taxa Matsui and Tsuihiji think they are when more taxa are included (Fig. 1).

From their abstract:
“Background.
Desmostylia is a clade of extinct aquatic mammals with no living members.”

False. Although this is traditional thinking in the large reptile tree (LRT, 1638+ taxa; subset Fig. 1) living desmostylians include mysticete (baleen) whales. Their ancestors include oreodonts, mesonychids, hippos, cambaytheres and anthracobunids.

Figure 3. the Merycoidodon cladogram includes hippos, whales and a number of extinct taxa.

Figure 1. The Merycoidodon cladogram includes hippos, whales and a number of extinct taxa. Traditional desmostylians are in medium blue here.

 

The abstract continues:
“Today, this clade is considered belonging to either Afrotheria or Perissodactyla.”

Their figure 1 shows desmosytlians arising from either: (a) Equus, the horse, in the Perissodactyla hypothesis; (b) Elephas, the elephant, in the Afrotheria hypothesis, or (c) Procavia, the hyrax, in their Paenungulatomorpha hypothesis. In other words, the authors have no idea. Genomic studies deliver false positives like Afrotheria. and you can’t used genomic studies of deep time fossils. In the LRT, which uses traits, desmostylians arise from mesonychids, hippos and anthracobunids as we learned earlier here.

“In the currently-accepted taxonomic scheme, Desmostylia includes two families, 10
to 12 genera, and 1314 species. There have been relatively few phylogenetic analyses
published on desmostylian interrelationship compared to other vertebrate taxa, and
two main, alternative phylogenetic hypotheses have been proposed in previous studies.
One major problem with those previous studies is that the numbers of characters and
OTUs were small.”

So Matsui and Tsuihiji, are studying the details without understanding the big picture… which could affect the details. Better to have a firm foundation built, then afterwards add whatever decorations to your structure.

Figure 1. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

Figure 2. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

The abstract continues:
“Methods.

In this study, we analyzed the phylogenetic interrelationship of Desmostylia

based on a new data matrix that includes larger numbers of characters and taxa than in
any previous studies. The new data matrix was compiled mainly based on data matrices
of previous studies and included three outgroups and 13 desmostylian ingroup taxa.
Analyses were carried out using five kinds of parsimonious methods.”

Their three outgroups were: [1] Anthracobune, [2] Pezosiren + Moeritherium and [3] all three. Again, they are playing ‘pin the tail on the donkey‘ when the actual outgroups are available online (Fig. 1). No blind guesswork is necessary.

Figure 1. Taxa in the lineage of right whales include Desmostylus, Caperea and Eubalaena. The tiny bit of jugal posterior to the orbit (in cyan) is found in all baleen whales tested so far. The frontals over the eyes are just roofing the eyeballs in Desmostylus, much wider in Caperea and much, much longer in Eubalaena.

Figure 3. Taxa in the lineage of right whales include Desmostylus, Caperea and Eubalaena. The tiny bit of jugal posterior to the orbit (in cyan) is found in all baleen whales tested so far. The frontals over the eyes are just roofing the eyeballs in Desmostylus, much wider in Caperea and much, much longer in Eubalaena.

The abstract continues:
“Results.

Strict consensus trees of the most parsimonious topologies obtained in all

analyses supported the monophyly of Desmostylidae and paraphyly of traditional
Paleoparadoxiidae. Based on these results, we propose phylogenetic definitions of the
clades Desmostylidae and Paleoparadoxiidae based on common ancestry.”

That’s fine, but incomplete. This is another classic case of knowing so much about a few taxa, while knowing nothing about their ancestors, sisters and descendants, all based on taxon exclusion. That’s why the LRT is here. The LRT is the first instrument to report that the clade Cetacea was diphyletic. Members of the Odontoceti (toothed whales) are not related to members of the Mysticeti (baleen whales), contra traditional studies that exclude pertinent taxa.

Some workers insist
that I add characters to the LRT, but as you can see, adding more traits to the LRT would not reveal the ancestors, sisters or descendants of the Desmostylia. Only more taxa solve this problem. More taxa create greater resolution and nest all enigmas. More characters do not and cannot do that, so enough with that lame request.

If you want to add more or different traits
to your more focused studies, by all means, do so! But keep that taxon list complete. Let the LRT be your guide.


References
Matsui and Tsuihiji 2019. The phylogeny of desmostylians revisited: proposal of new clades based on robust phylogenetic hypotheses. PeerJ:e7430 http://doi.org/10.7717/peerj.7430

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