Danjiangia: not a chalicothere, not a brontothere…

It’s an early Eocene pig
according to the large reptile tree (LRT, 1003 taxa). A large gamut minimizes inclusion set bias and gains greater authority with every added taxon. It also reduces the average phylogenetic distance between taxa, all of which are species and individuals, not suprageneric taxa.

Figure 1. Danjiangia nests with the extant pig, Sus, in the LRT.

Figure 1. Danjiangia nests with the extant pig, Sus, in the LRT. Note the very low naris and nasal. The lost skull could have been elevated, as imagined here after phylogenetic analysis.

Danjiangia pingi (Wang 1995; early Eocene) was originally described as a basal chalicothere with brontothere traits. Then Hooker and Dashzeveg (2003) nested it as a basal brontothere (without including any other brontotheres). Mihlbacher 2008 and others used it as an outgroup to the brontotheres. The posterior skull is not known, but note the rise over the orbits suggesting a tall cranium, as in Sus (Fig. 2). Also note the very low naris below the low nasals. Usually you don’t see nasals so low, and perhaps that is due to taphonomic shifting.

Figure 2. Skull of the extant pig, Sus in several views.

Figure 2. Skull of the extant pig, Sus in several views. Note the elevated cranium and squamosal.

The long fused dentary 
of Danjiangia is a trait also shared with pigs and other taxa, like chalicotheres, by convergence.

Figure 1. Skeleton of Sus, the pig, a taxon commonly used as an outgroup for whales. In the LRT it is a sister to other even-toed ungulates, like Giraffa, not Odontoceti nor Mysticeti.

Figure 3. Skeleton of Sus, the pig. It provides good clues as to the missing postcranial skeleton of Danjiangia.

Sus the pig
(Fig. 3) provides good clues as to the missing postcranial skeleton of its sister taxon, Danjiangia. The other model for post-cranial details is the basal artiodactyl, Cainotherium (Fig. 4).

Fig. 1. Cainotherium nests at the base of the Artiodactyla or even-toed ungulates. I wonder if it had five fingers, even if vestiges, given that Ancodus, a derived artiodactyl, retains five fingers.

Fig. 4. Cainotherium nests at the base of the Artiodactyla or even-toed ungulates. I wonder if it had five fingers, even if vestiges, given that Ancodus, a derived artiodactyl, retains five fingers.

Why was the pig connection missed by others?
For the same reason that modern workers continue to include pterosaurs with archosaurs. It’s a tradition. Nobody wants to do the extra work of testing other candidate taxa. Nobody wants to acknowledge contrarian studies. Paleontology tends to run very slowly as we learned earlier here. Hail, hail the status quo!

Figure 1. Subset of the LRT focusing on ungulates, which split into three clades here.

Figure 5. Subset of the LRT focusing on ungulates, which split into three clades here. Note the nesting of Sus together with Danjiangia.

References
Beard KC 1998. East of Eden: Asia as an important center of taxonomic origination in mammalian evolution; pp. 5–39 in Beard and Dawson (eds.), Dawn of the Age of Mammals in Asia. Bulletin of Carnegie Museum of Natural History 34.
Mihlbachler MC 2004. Phylogenetic systematics of the Brontotheriidae (Mammalia, Perissodactyla). PhD dissertation. Columbia University. p. 757.
Mihlbachler MC 2008. Species taxonomy, phylogeny and biogeography of teh Brontotheriidae (Mammalia: Perissodactyla). Bulletin of the American Museum of Natural History 311:475pp.
Wang Y 1995. A new primitive chalicothere (Perissodactyla, Mammalia) from the early Eocene of Hubei, China. Vertebrata Palasiatica 33: 138–159.

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2 thoughts on “Danjiangia: not a chalicothere, not a brontothere…

  1. Dude. Your matrix lacks almost all characters that have been used in artiodactyl phylogenetics. Your enormous confidence is built on thin air.

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