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A large Late Miocene cetotheriid (Cetacea, Mysticeti) from the Netherlands clarifies the status of Tranatocetidae - PubMed

  • ️Tue Jan 01 2019

A large Late Miocene cetotheriid (Cetacea, Mysticeti) from the Netherlands clarifies the status of Tranatocetidae

Felix G Marx et al. PeerJ. 2019.

Abstract

Cetotheriidae are a group of small baleen whales (Mysticeti) that evolved alongside modern rorquals. They once enjoyed a nearly global distribution, but then largely went extinct during the Plio-Pleistocene. After languishing as a wastebasket taxon for more than a century, the concept of Cetotheriidae is now well established. Nevertheless, the clade remains notable for its variability, and its scope remains in flux. In particular, the recent referral of several traditional cetotheriids to a new and seemingly unrelated family, Tranatocetidae, has created major phylogenetic uncertainty. Here, we describe a new species of Tranatocetus, the type of Tranatocetidae, from the Late Miocene of the Netherlands. Tranatocetus maregermanicum sp. nov. clarifies several of the traits previously ascribed to this genus, and reveals distinctive auditory and mandibular morphologies suggesting cetotheriid affinities. This interpretation is supported by a large phylogenetic analysis, which mingles cetotheriids and tranatocetids within a unified clade. As a result, we suggest that both groups should be reintegrated into the single family Cetotheriidae.

Keywords: Baleen whale; Body size; Evolution; Phylogeny; Systematics.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. Type locality (A) and horizon (B) of Tranatocetus maregermanicum.

Curly bracket in (B) marks the type horizon, as judged from the dinoflagellate fauna associated with the whale fossils. Modified from Marx, Bosselaers & Louwye (2016) under a Creative Common Attribution Licence (CC-BY 4.0). Dates in (B) based on Ogg, Ogg & Gradstein (2016). Drawing of cetotheriid by Carl Buell.

Figure 2
Figure 2. Holotype cranium of Tranatocetus maregermanicum (NMR9991-16680) in dorsal view.

Photograph by Felix G. Marx.

Figure 3
Figure 3. Paratype cranium of Tranatocetus maregermanicum (NMR9991-16681) in (A) ventral and (B) posterior view.

Photographs by Felix G. Marx.

Figure 4
Figure 4. Holotype cranium of Tranatocetus maregermanicum (NMR9991-16680) in oblique right anterolateral view.

Photograph by Felix G. Marx.

Figure 5
Figure 5. Holotype cranium of Tranatocetus maregermanicum (NMR9991-16680) in (A) lateral and (B) anterior view.

Photographs by Felix G. Marx.

Figure 6
Figure 6. Holotype cranium of Tranatocetus maregermanicum (NMR9991-16680) in ventral view.

basiocc., basioccipital; pter., pterygoid; hamular proc., hamular process; ty., tympanic bulla. Photograph by Felix G. Marx.

Figure 7
Figure 7. Auditory anatomy of Tranatocetus maregermanicum.

(A) Auditory region of the holotype cranium (NMR9991-16680) in oblique right posterolateral view. (B) Periotic of the paratype (NMR9991-16681) in ventral view. exocc., exoccipital; post. sulcus, posteroventral sulcus. Photographs by Felix G. Marx.

Figure 8
Figure 8. Holotype mandible of Tranatocetus maregermanicum (NMR9991-16680).

(A) Right mandible in lateral view; (B) left mandible in medial view. Photographs by Felix G. Marx.

Figure 9
Figure 9. Comparison of the mandibular ramus of (A, C) Tranatocetus maregermanicum (NMR9991-16680, holotype) and (B, D) Tranatocetus argillarius (GMUC VP2319, holotype).

(A, B) medial, (C) lateral and (D) posterior view. Photographs by Felix G. Marx.

Figure 10
Figure 10. Damage to the mandible and auditory region of Tranatocetus argillarius (GMUC VP2319, holotype).

Mandible in (A) anterior, (B) medial and (C) lateral view. (D) Auditory region in oblique right posterolateral view. Photographs by Felix G. Marx.

Figure 11
Figure 11. Results of the total evidence phylogenetic analysis, showing the nesting of tranatocetids, including Tranatocetus itself, inside Cetotheriidae.

Drawings of cetaceans by Carl Buell.

Figure 12
Figure 12. Comparison of the auditory regions of (A, C) the presumed tranatocetid ‘Cetotherium’ megalophysum (USNM 10593, holotype) and (B, D) the cetotheriid Piscobalaena nana (MNHN SAS 1616).

(A) Right and (B) left auditory region in ventral view; (C) left compound posterior process in ventrolateral view; (D) right compound posterior process in oblique posterolateral view. Photographs by Felix G. Marx.

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Grants and funding

Felix Georg Marx was supported by a Fonds de la Recherche Scientifique (FNRS) postdoctoral fellowship (32795797), and an EU Marie Skłodowska-Curie Global Postdoctoral fellowship (656010/ MYSTICETI). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.