Adding Cetotherium to the LRT

Since we’re still talking about whales today…
Dr. RW Boessenecker was kind enough to let me know that one of the mandibles in Tokahahira was rotated 180º and so the mandible I thought bowed in for a narrow tip actually bowed out for a Gothic arch shape (Fig. 1). That earlier error has been repaired.

Figure 1. Tokarahia in situ and as originally reconstructed (on right). Flipping the right mandible and reconstructing the skull anew (at left).

Figure 1. Tokarahia in situ and as originally reconstructed (on right). Flipping the right mandible, taking the bow out of the left mandible and reconstructing the skull anew (at left).

Figure 2. Subset of the large reptile tree, the mesonychids, desmostylians and mysticetes.

Figure 2. Subset of the large reptile tree, the mesonychids, desmostylians and mysticetes (in blue).

Then I added Tokarahia to the LRT and it nested within the mysticetes between Isanacetus and Cetiotherium (Fig. 2). It looks like cetotheres were basal to at least two clades of extant mysticetes.

The basal mysticete,
Cetotherium riabinini (Cope 1895, Hofstein 1948, Gol’din et al. 2014; Late Miocene; NMNH-P 668/1; 2m in lenth), is known from a fairly complete dolphin-sized skeleton (Fig. 2). It had a relatively huge skull, massive rib cage, large manus (but see below) and a relatively short tail. Cetotheres, according to Wikipedia, are “archaic mysticetes with a cranium that has ‘a long ascending process of the maxilla with anteriorly diverging lateral border that interdigitates with the frontal’ and some other characters”,

That short tail
complements what we learned earlier about stem mysticetes arising from short-tailed desmostylians, including one with a possible robust tail, Behemotops.

Figure 3. Cetotherium skeleton with color overlays to help identify bones.

Figure 3. Cetotherium skeleton with color overlays to help identify bones. Three hypotehtical fluke sizes are suggested.  According to Hofstein (1965), the carpals, metacarpals and most of phalanges have not been preserved.

In the LRT
Cetotherium nests with Eubalaena (Fig. 4) the Southern right whale, which has greatly deepened its maw. They share, among other obvious traits, short chevrons. Eubalaena has five fingers after a long run of four-fingered ancestors. So the ‘thumb’ is new!

Figure 5. Eubalaena australis, the Southern right whale nests with Cetotherium in the LRT.

Figure 4. Eubalaena australis, the Southern right whale nests with Cetotherium in the LRT. The down curved rostrum appears to be secondarily evolved based on more primitive taxa with straight rostra.

Here’s an interesting Wiki-factoid
listed under Cetotherium“Cetotheriidae were thought to have gone extinct during the Pliocene until 2012, when it was hypothesized that the Pygmy right whale was the sole surviving species of this family. (Fordyce and Marx 2013)”

Figure 5. Caperera, the pygmy right whale, has fewer lumbar vertebrae, smaller forelimbs and broad ribs resembling those of Cetotherium.

Figure 5. Caperea, the pygmy right whale, has fewer lumbar vertebrae, smaller forelimbs and broad ribs resembling those of Cetotherium.

The pygmy right whale (Caperea marginata; Bisconti 2012) looks like a small blue whale, but has an oversized rib cage and a short tail. We’ll look at it more closely in a future blog.

Figure 6. Blue whale (Balaenoptera musculus) skull and skeleton. This image is presented again to compare and contrast with the above taxa. 

Figure 6. Blue whale (Balaenoptera musculus) skull and skeleton. This image is presented again to compare and contrast with the above taxa.

Sorry about the earlier error with Takarahia
(see above). I hate making those, but they happen. In Science you own up to your mistakes. And then you fix them. I’ll emphasize again, nearly every added taxon here is new to me. I gain any and all expertise by study. And, after finding a mistake, or adding a new taxon, by reexamination. Several other errors were corrected during the course of this blog post writing. Thank you for alerting me to mistakes. They are corrected as soon as I understand the problem.

References
Bisconti M 2012. Comparative osteology and phylogenetic relationships of Miocaperea pulchra, the first fossil pygmy right whale genus and species (Cetacea, Mysticeti, Neobalaenidae). Zoological Journal of the Linnean Society 166(4) 876—911.
Fordyce RE and Marx FG 2013. The pygmy right whale Caperea marginata: the last of the cetotheres. Proceedings of the Royal Society B: Biological Sciences 280(1753):1–6.
Gol’din P, Startsev D and Krakhmalnaya T 2014. The anatomy of Cetotherium riabinini Hofstein, 1948, a baleen whale from the late Miocene of Ukraine. Acta Palaeontologica Polonica. In press. doi:10.4202/app.2012.0107

wiki/Cetotherium
wiki/Pygmy_right_whale

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