Thursday, December 17, 2015

[PaleoMammalogy • 2015] Fucaia buelli • A New Early Oligocene Toothed ‘Baleen’ Whale (Mysticeti: Aetiocetidae) from western North America: One of the Oldest and the Smallest

Fucaia buelli  
Marx, Tsai & Fordyce, 2015  DOI: 10.1098/rsos.150476
  illustration: Bran-Artworks

Archaic toothed mysticetes represent the evolutionary transition from raptorial to bulk filter feeding in baleen whales. Aetiocetids, in particular, preserve an intermediate morphological stage in which teeth functioned alongside a precursor of baleen, the hallmark of all modern mysticetes. To date, however, aetiocetids are almost exclusively Late Oligocene and coeval with both other toothed mysticetes and fully fledged filter feeders. By contrast, reports of cetaceans from the Early Oligocene remain rare, leaving the origins of aetiocetids, and thus of baleen, largely in the dark. Here, we report a new aetiocetid, Fucaia buelli, from the earliest Oligocene (ca 33–31 Ma) of western North America. The new material narrows the temporal gap between aetiocetids and the oldest known mysticete, Llanocetus (ca 34 Ma). The specimen preserves abundant morphological detail relating to the phylogenetically informative ear bones (otherwise poorly documented in this family), the hyoid apparatus and much of the (heterodont) dentition. Fucaia comprises some of the smallest known mysticetes, comparable in size with the smallest odontocetes. Based on their phylogenetic relationships and dental and mandibular morphology, including tooth wear patterns, we propose that aetiocetids were suction-assisted raptorial feeders and interpret this strategy as a crucial, intermediary step, enabling the transition from raptorial to filter feeding. Following this line of argument, a combination of raptorial and suction feeding would have been ancestral to all toothed mysticetes, and possibly even baleen whales as a whole.

KEYWORDS: Mysticeti, baleen whale, Aetiocetidae, suction feeding, filter feeding, baleen

Systematic Palaeontology

Cetacea Brisson, 1762
Mysticeti Gray, 1864

Aetiocetidae Emlong, 1966

Fucaia, gen. nov.

Type species. Fucaia buelli, sp. nov.

Etymology. After the Strait of Juan de Fuca, the area surrounding which yielded both F. buelli and its sister species F. goedertorum.

Remarks. Comparisons with Chonecetus sookensis, Ashorocetus and Willungacetus are hampered by the poor state of preservation of the available material. This especially applies to Ashorocetus, which is currently only known from the fragmentary posterior portion of a braincase [1]. Based on the lack of diagnostic characters, Fitzgerald [8] reclassified Willungacetus, previous tentatively referred to Aetiocetidae [7], as Mysticeti incertae sedis and proposed that Ashorocetus may represent a nomen dubium. We concur with this assessment, pending the discovery of better-preserved material that could help to clarify relationships.

Included taxa. Fucaia buelli, sp. nov.; Fucaia goedertorum, comb. nov.

Fucaia buelli, sp. nov.

Holotype. UWBM 84024, partial skeleton comprising the cranium including both periotics and the right tympanic bulla, a part of the right mandible, 17 isolated teeth, most of the hyoid apparatus, 20 vertebrae, part of the left scapula, a heavily eroded radius, and several non-diagnostic, partially prepared fragments.

Locality and horizon. UWBM Locality C716, between Shipwreck Point and Neah Bay, Clallam County, Olympic Peninsula, WA, USA (figure 1). The specimen was collected by J.L. Goedert and B.R. Crowley as a concretion less than 1 m in length, derived from siltstone forming part of the Makah Formation (either the Jansen Creek Member or the horizon immediately below). Details as to the exact location and horizon are available directly from UWBM.

Etymology. Named after Carl Buell, in honour of his artistic achievements in illustrating extant and fossil cetaceans.

Diagnosis. Small-sized mysticete (approx. 2 m in length) corresponding in all preserved features with the diagnosis of Fucaia. Differs from F. goedertorum in having a more elevated posterior portion of the nuchal crest (and thus a more concave supraoccipital shield), an ascending process of the premaxilla that is narrower than the ascending process of the maxilla, an ascending process of the maxilla that extends as far posteriorly as the nasal, a clearly defined (as opposed to interdigitating) naso-frontal suture, a flat, tabular dorsal surface of the involucrum, and an anterior process of the periotic with a dorsally deflected anterodorsal angle.

Figure 18. Phylogenetic relationships of archaic mysticetes.
Individual families are labelled. . Abbreviations: Pli, Pliocene, Pls., Pleistocene.
For details of the analysis, see Marx and Fordyce [13] || DOI: 10.1098/rsos.150476

Fucaia buelli is a previously unrecognized aetiocetid that extends the range of this family to the Early Oligocene. Along with its congeners, F. buelli is among the smallest of known mysticetes, with a size comparable with that of small odontocetes. The heterodont dentition of F. buelli probably functioned in prey capture and mastication, which could have compromised the putative ability of aetiocetids to filter feed. Instead, F. buelli might have employed a form of raptorial and suction feeding, with suction being used either to capture prey items or to transport them to the back of the mouth following ingestion. Under this scenario, structures homologous with the palatal nutrient foramina and sulci of extant mysticetes would have carried blood vessels nourishing enlarged gingiva, rather than baleen plates as such. We argue that a transition from raptorial feeding, to combined raptorial/suction feeding, to combined suction/filter feeding and, ultimately, to filter feeding is functionally more plausible than a direct switch from a raptorial to a filter feeding strategy.

Felix G. Marx, Cheng-Hsiu Tsai and R. Ewan Fordyce. 2015. A New Early Oligocene Toothed ‘Baleen’ Whale (Mysticeti: Aetiocetidae) from western North America: One of the Oldest and the Smallest. Royal Society Open Science. DOI: 10.1098/rsos.150476

Ancient Tiny Whale Hunted with Pointy Teeth, Oversize Gums via @LiveScience

Fucaia buelli
 by Bran-Artworks