Tubby right whales
like Eubalaena (Fig. 1) are different from sleek rorquals, like the blue whale (Balaenoptera). Right whales don’t have the huge throat sack that rorquals expand with sea water + krill. Instead longer baleen fringes and huge lower lips filter right whale meals and usually in a horizontal, rather than a vertical, attack formation.
According to Wikipedia:
“The pygmy right whale (Caperea marginata), a much smaller whale of the Southern Hemisphere, was until recently considered a member of the Family Balaenidae. However, they are not right whales at all, and their taxonomy is presently in doubt. Most recent authors place this species into the monotypic Family Neobalaenidae, but a 2012 study suggests that it is instead the last living member of the Family Cetotheriidae, a family previously considered extinct.”
That 2012 study was by Marx and Fordyce. The large reptile tree (LRT, 1060 taxa) does not support that assignment, perhaps because Marx and Fordyce omitted tenrecs and desmostylians from their whale analysis. At present all cetiotheres in the LRT have straight rostra and mandibles, a far cry from the dipped snout of these taxa. Note the deep baleen in Caperea (Fig. 1). That’s a right whale trait.
Caperea marginata (The pygmy right whale; Bisconti 2012, Fordyce and Marx 2013) looks like a small blue whale, but has long, inclned ribs, only one lumbar vertbra, and a short tail. The mandible is deep and concave ventrally. Like Eubalaena the lacrimal is deeper than the maxilla. Note the tiny forelimb. The manus has a few extra bones that, when put back together, create a digit 1. Mid-phalanges (3.2, 4.2, 4.3) lost in basal therapsids reappear in this taxon with a netonous tiny manus.
We’ve seen this before.
Remember Limusaurus? (If not, check out Fig. 3) That’s the oviraptorid-like theropod with an equally tiny manus provided with an extra medial digit (digit zero). Same thing here provides the reappearance of digit 1, reduced or absent in all ancestors beginning with Mesonyx. And THAT explains the reappearance of manual digit 1 (the thumb) in the right whale, Eubalaena (Fig. 1), the only exception in this clade of thumbless taxa.
Little things to look for in desmostylians retained by baleen whales
- The mandible is wider than the rostrum (Fig. x). That’s where the giant lower lips arise.
- A bit of jugal is attached to the front of the squamosal, even when the portion below the orbit is missing.
- The reduction of teeth is completed in baleen whales
- The ventral portion of the rostrum is visible in lateral view
- The anterior tips of the mandibles either have tusks or the alveoli from which tusks once emerged. Here (Fig. x) the tusks are tiny.
- Same with the anterior maxillae, but smaller because those tusks disappear earlier. Here (Fig. x) the tusks are tiny. Blame it on neotony.
- The tail series of Caperea is really quite short (Fig. 2)—and shorter still IF you imagine a former pelvis the size of the one in Desmostylus, now greatly reduced (Fig. 1). And that is a big part of the solution to the lack of a large tail in desmostylians: don’t lengthen the tail…shrink that giant pelvis!!! And blame it on neotony.
We’ll look at
cetiotheres and rorquals in the next few days.
Domning DP, Ray, CE and McKenna, MC 1986. Two new Oligocene desmostylians and a discussion of Tethytherian systematics. Smithsonian Contributions to Paleobiology. 59. pp. 1–56.
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.
Marsh OC 1888. Notice of a new fossil sirenian, from California. American Journal of Science 25(8):94–96.
Reinhart RH 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36(1):1–146.
Santos G, Parham J and Beatty B 2016. New data on the ontogeny and senescence of Desmostylus (Desmostylia, Mammalia). Journal of Vertebrate Paleontology. doi: 10.1080/02724634.2016.1078344
Tsai C-Hi and Fordyce RE 2015. Ancestor–descendant relationships in evolution: origin of the extant pygmy right whale, Caperea marginata. Biol Lett. 2015 Jan; 11(1): 20140875.