Picture of the Indiscriminate Interval #000008 - Eurhinodelphis longirostris

Eurhinodelphis longirostris at the American Museum of Natural History.

The most striking trait of Eurhinodelphidae is a toothless extension of the rostrum beyond the mandible (Lambert 2005), superficially similar to the bills of Billfish and Swordfish. Oddly, this morphology was speculative for a period of time (Kellogg 1925) although it has apparently been confirmed in several species as of Lambert (2005). Unfortunately, information on eurhinodelphids is scant and/or difficult to access and, among numerous other basics of their biology, I really don't know what the function of the extended rostrum would be. The only suggestion I could find is from one professor Abel who speculated that the cetaceans "swam on the surface of the sea, where they captured food - probably fishes - in much the same manner as does the skimmer (Rhynchops) [sic] among birds" (Anonymous 1909). Somehow, I find this even less plausible than azhdarchids-as-skimmers. On a curious note, there is a cetacean with the reverse of eurhinodelphid morphology (mandible extending past rostrum) unofficially known as the... skimmer porpoise.

Phylogenetically, eurhinodelphids have bounced around from being considered stem-ziphiids, the sister group to Delphinida, and the sister group to Squalodontidae + Squalodelphidae (Geisler et al. 2011 - citing various); within Geisler et al. (2011), they were placed outside crown-Odontoceti¹ in an unconstrained analysis and as the sister group of platanistoids in a constrained analysis. The authors regarded the latter position as more probable and placed eurhinodelphids within the new group Synrhina, which includes most odontocetes except for Sperm Whales and assorted extinct taxa. Whatever their placement, eurhinodelphids are certainly close relatives of living toothed whales, despite that whole extinct thing.

¹ It actually states they "did not fall inside crown Cetacea", but this is a typo. Otherwise, they'd be Miocene Archaeocetes. 

Eurhinodelphis longirostris seems to have an unusually long neck for a cetacean. The cervical vertebrae are not fused (Kellogg 1925), however this is a surprisingly common trait shared with river dolphins, monodontids, rorquals, and gray whales (Tinker 1988). The neck of E. longirostris appears to be proportionally longer than those of the baleen whales and Narwhal and is probably comparable to those of the Beluga and Dorudon. River dolphin skeletons are hard to find, but it seems likely they have similarly proportioned necks. It seems that Eurhinodelphis wasn't a total freak, well, except for the snout.

The Theatrical Tanystropheus covered Eurhinodelphis as well, and it doesn't even overlap that much!

References:

Anonymous. (1909). Notes. Nature 2088 (82), 16. Available.

Geisler, J. H., McGowen, M. R., Yang, G., Gatesy, J. (2011). A supermatrix analysis of genomic, morphological, and paleontological data from crown Cetacea. BMC Evolutionary Biology 11 (112). Available.

Kellogg, R. (1925). On the occurrence of fossil porpoises of the genus Eurhinodelphis in North America. Proceedings of the U. S. National Museum 66(26), 1-40. Available.

Lambert, O. (2005). Les dauphins longirostres et les baleines à bec du Néogène de la région d’Anvers: systématique, phylogénie, paléo-écologie et paléo-biogéographie. Doctoral Thesis. Partially Available.

Tinker, S. W. (1988). Whales of the World. E. J. Brill Publishing Company: New York. Partially Available.

Picture of the Indiscriminate Interval #000007 - Narwhal

Monodon monoceros at the American Museum of Natural History.

Narwhals are a bit strange even by cetacean standards. I'll let the title of this Tet Zoo article speak for itself: "A 3-m tooth that can bend 30 cm in any direction and is hypersentitive to salinity, temperature and pressure... and the sonic lance hypothesis".

They get weirder. Without the tooth (or sometimes, teeth) it is difficult to picture how this flat-skulled cetacean could be the same as a bulbous-headed Narwhal. As brought up in my Dorudon post, there are colossal amounts of soft tissue involved.

Another soft-tissue feature not hinted at by the skeleton are unusually shaped flukes... in males. Fontanella et al. (2010) suggest that the concave leading edge and lack of sweepback of the flukes increases lift and thrust to compensate for the drag caused by the tusk in males. The implications of the occasional tusked female narwhal were not discussed by the authors.

One female Narwhal was estimated to be 114.8 (± 10.2) years old (Garde et al. 2007) which, if correct, would make Narwhals the third oldest known mammals after humans (122 years) and Bowhead Whales (211 years?). Garde et al. (2007) used a sample of 75 individuals (15 juvenile) from a heavily hunted population, and subsequently speculated that Narwhals in other populations could potentially reach "considerably higher" ages. As for methodology, Garde et al. (2007) used aspartic acid racemization rate in the eye; this method was also used to calculate the extreme age estimate for Bowheads (George et al. 1999), and ages of over a hundred years have subsequently been supported by bomb lance fragments (George and Bockstoce 2008) and ovarian corpora counts (George et al. 2011). So it looks probable that aspartic acid racemization does not provide grossly inaccurate estimates of old age - why would Narwhals live to be centenarians? Garde et al. (2007) note that Narwhals and Bowheads are both year-round Arctic residents and speculate that their extreme longevity is an adaptation to drastic changes is climate. While an interesting idea, there does not seem to be much data available on cetacean longevity (Table 2 in Garde et al. 2007 has only 12 out of ~80 species) and Narwhals are apparently not far older than other cetaceans (for instance, Orcas apparently live to be 90). It could be possible that further investigation into cetacean longevity will reveal that lifespans of over a hundred years are perfectly normal.

References:

Fontanella, J. E., Fish, F. E., Rybczynski, N., Nweeia, M. T., & Ketten, D. R. (2010). Three-dimensional geometry of the narwhal (Monodon monoceros) flukes in relation to hydrodynamics. Marine Mammal Science 27(4), 889-898. Available.

Garde, E., Heide-Jørgensen, M. P., Hansen, S. H., Nachman, G., and Forchhammer, M. C. (2007). Age-specific growth and remarkable longevity in Narwhals (Monodon monoceros) from West Greenland as estimated by Aspartic Acid Racemization. Journal of Mammalogy 88(1), 49-58. Available.

George, J. C., Follmann, E., Zeh, J., Sousa, M., Tarpley, R., Suydam, R. Horstmann-Dehn, L. (2011). A new way to estimate the age of bowhead whales (Balaena mysticetus) using ovarian corpora counts. Canadian Journal of Zoology 89(9), 840-852. doi: 10.1139/z11-057

George, J. C., and Bocktoce, J. R. (2008). Two historical weapon fragments as an aid to estimating the longevity and movements of bowhead whales. Polar Biology 31(6), 751-754. Available.

George, J. C., Bada, J., Zeh, J., Scott, L., Brown, S. E., O'Hara, T., & Suydam, R. (1999). Age and growth estimates of bowhead whales (Balaena mysticetus) via aspartic acid racemization. Canadian Journal of Zoology 77, 571-578.