Is it odd when even-toed nest with odd-toed ungulates?

This all started
when I wondered which taxa represented the last common ancestor of hippos and desmostylians, like Paleoparadoxia.

In a recent PLOSOne paper,
Cooper et al. 2014 discussed the enigmatic Anthracobune and nested it between  horses (Mesohippus + Equusthree or one toes) and desmostylians (four toes).

Figure 1. Cooper et al. 2014 nested even-toed desmostylians within the odd-toed ungulates.

Figure 1. Cooper et al. 2014 nested even-toed desmostylians within the odd-toed ungulates. Let’s ignore, for the moment, the bad nesting of all the other mammals here.

Fossil fingers and toes are not known
for Anthracobune, but we have enough of it (Fig. 2) to nest it with Paleoparadoxia, as Cooper et al. did (Fig. 1). Unfortunately, Hippopotamus (four toes) was not tested by Cooper et al. In the large reptile tree, it nests with Paleoparadoxia and Anthracobune, all derived from a sister to Mesonyx (four toes), also not tested by Cooper et al. So Cooper et al. were right about Anthracobune having desmostylian affinities, wrong about having Equus affinities.

Figure 2. Anthracobune, colorized here, but grayscale image comes from Cooper et al.

Figure 2. Anthracobune, grayscale image comes from Cooper et al. 2014 and here colored with symmetries added and broken mandible tip tipped down a few degrees. Note the diverging canines, as in hippos. That giant angular process takes on several shapes in this clade, all lager than in other clades.

Traditionally
Hippos are considered artiodactyls (aka even-toed ungulates) along with giraffes, camels deer and pigs, but Wikipedia reports, “hippopotamuses are not closely related to these groups.”  Here hippos and their kin are considered mesonychids, a clade of ungulates traditionally considered carnivorous and extinct. Here the tested ones are neither carnivorous nor extinct.

Figure 3. Four mesonychids to scale. Here Mesonyx, Anthracobune, Paleoparadoxia and Hippopotamus are compared.

Figure 3. Four mesonychids to scale. Here Mesonyx, Anthracobune, Paleoparadoxia and Hippopotamus are compared.

Mesonychids
don’t have to be carnivores just because they have large canines. They are commonly regarded as ungulates and descendants of condylarths. No tested sister taxa are carnivores. And, as a reminder, mesonychids are not related to whales, tenrecs are (Fig. 4).

Figure 4. subset of the large reptile tree divides hippos and kin (mesonychids) from even-tied ungulates (artiodactyls).

Figure 4. Subset of the large reptile tree divides hippos and kin (mesonychids) from even-tied ungulates (artiodactyls).

Tomorrow I will nest Vintana with wombats, not multituberculates. Thanks to reader AdamtheQuirky for suggesting Vintana. Good selection. It is weird!

I continue to find it amazing how much the large reptile tree continues to diverge from traditional trees yet delivers sisters that look alike and have gradual accumulations of derived traits.

References
Cooper LN, Seiffert ER, Clementz M, Madar SI, Bajpai S, Hussain ST, Thewissen JGM 2014. Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls. PLoS ONE. 9 (10): e109232. doi:10.1371/journal.pone.0109232. PMID 25295875.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s