A new species of rorqual whale (Cetacea, Mysticeti, Balaenopteridae) from the Late Miocene of the Southern North Sea Basin and the role of the North Atlantic in the paleobiogeography of Archaebalaenoptera

Background The rich fossil record of rorqual and humpback whales (Cetacea, Mysticeti, Balaenopteridae) is mainly characterized by monotypic genera since genera including more than one species are extremely rare. The discovery of new species belonging to known genera would be of great importance in order to better understand ancestor-descendant relationships and paleobiogeographic patterns in this diverse group. Recent discoveries in the southern North Sea Basin yielded a number of reasonably well preserved fossil balaenopterids from the Late Miocene; this sample includes a balaenopterid skull from Liessel, The Netherlands, which shares key characters with Archaebalaenoptera castriarquati from the Pliocene of Mediterranean. This skull is permanently held by Oertijdmuseum, Boxtel, The Netherlands, with the number MAB002286 and is investigated here. Methods A detailed comparative anatomical analysis of the skull MAB002286 is performed in order to understand its relationships. The age of the skull is determined by dinocyst analysis of the associated sediment. A paleobiogeographic analysis is performed to understand paleobiogeographic patterns within the balaenopterid clade the new skull belongs to. Results Our work resulted in the description of Archaebalaenoptera liesselensis new species. The geological age of the holotype skull is between 8.1 and 7.5 Ma. The phylogenetic relationships of this species reveals that it is monophyletic with Archaebalaenoptera castriarquati from the Italian Pliocene. Moreover, in combination with a more basal species of Archaebalaenoptera from the late Miocene of Peru, our paleobiogeographic analysis suggests that the North Atlantic ocean played a major role as a center of origin of a number of balaenopterid clades including Protororqualus, Archaebalaenoptera and more advanced balaenopterid taxa. From a North Atlantic center of origin, two dispersal events are inferred that led to the origins of Archaebalaenoptera species in the South Pacific and Mediterranean. The distribution of Archaebalaenoptera was antitropical in the late Miocene. The role played by the Mediterranean salinity crisis is also investigated and discussed.


MPTAM 207-13307
This specimen represents a new genus and species of Balaenopteridae whose description is now complete. It includes an incomplete skull with periotic still in articulation and part of the postcrania. The estimated age is earliest Piacenzian.

NMR 999100007096
This specimen includes skull, periotic and part of the postcrania. Its morphology suggests a close relationship to 'Balaenoptera' portisi. In the remainder of the paper and in the illustrations it is called NMR 7096. The estimated age is early Piacenzian.

RBINS M. 2231
This specimen includes skull, periotics, dentaries and part of the postcrania. It is closely related to 'Balaenoptera' sibbaldina of which it represents the first reasonably complete skeleton. The specimen is briefly presented in Bisconti & Bosselaers (2014) and a full description is currently in progress. The specimen is currently held by RBINS. The estimated age is Early Pliocene.

RBINS M. 2315
The specimen includes partial skull and postcrania of a Pliocene individual very close to Protororqualus cuvieri. The description of this specimen is currently in progress.

MHNL 1613
The specimen includes a large skull with periotics still in articulation. It represents a new balaenopterid genus characterized by wide exposure of parietal at the cranial vertex. A description is currently close to be finished. The estimated age is Late Miocene.

MHNL 1610
The specimen includes a partially prepared skull with fragments of dentary. Its morphology suggests close relationships with Archaebalaenoptera castriarquati of which it could be an additional species. A description is currently in progress. The estimated age is Late Miocene.

Table S4
Geographic occurrences and ages of the taxa Stratigraphic and geographic data for the taxa used in the analyses.

Character list
The following character list is developed from the morphological dataset of Bisconti et al. (2019). In the present dataset, selected character states were commented in order to warrant clear understanding. In defining character states, we made use of personal observations on specimens listed above and of literature. In particular, we need to cite the following papers that we used for character definitions and codings: Boessenecker & Fordyce (2015) (2) Anterior to nasal. 10) Sutural contact between rostrum and frontal limited to ascending process of the maxilla: (0) No; (1) Yes.

17) Length of lateral process of maxilla:
Comment: a very long lateral process of the maxilla is observed in those taxa where this structure is longer than the transverse diameter of the maxilla at the level of the antorbital notch; a long lateral process is observed in those taxa where this structure is longer 50% of the transverse diameter of the maxilla at the level of the antorbital notch but is shorter than the whole transverse diameter. (0) Short; (1) Long.

36) Articulation between maxilla and frontal:
(1) Nasal reaching approximately rostrum midlength; (2) Nasal reaching the posterior 20% of rostrum; (3) Nasal reaching a point close to the anterior border of the supraorbital process of frontal.
(4) Nasal reaching a point located within the interorbital region of the frontal.

SQUAMOSAL 89) Dorsoventral height of squamosal: Comment: high dorsoventral height of squamosal in lateral view is observed only in Balaenidae and
Neobalaenidae.

90) Anteroposterior length of zygomatic process of squamosal with respect to its height: Comment: a very long zygomatic process of the squamosal is observed in archaeocetes, Aetiocetidae and Eomysticetidae; state 1 is observed in basal thalassotherian taxa and Balaenopteridae; state 2 is observed in Cetotheriidae and Eschrichtiidae; state 3 is observed in Balaenidae and Neobalaenidae.
(0) Very long; (1) Long; (2) Short.

106) Nuchal crest in dorsal view:
Comment: state 0 corresponds to a nuchal crest with wide and round shape; state 1 corresponds to a nuchal crest with round but narrow shape; state 2 corresponds to a triangular nuchal crest. (0) Wide; (1) Narrow; (2) Very narrow. (2) Reaching a point at the same level as occipital condyle. (2) Reduced.

133) Elevation of anterior border of supraoccipital in lateral view:
(0) High elevation formed by dorsal protrusion of parietals lateral and in front of the anterior border of supraoccipital; (1) Low elevation without contribution by the parietal; (2) No elevation at all. (1) Uniformly convex;

147) Shape of interparietal:
Comment: as shown in Wada et al. (2003), in Balaenopteridae, the interparietal may be anteroposteriorly long and transversely narrow and anteroposteriorly short and transversely wide; characters 147 and 148 relate to this observation. (2) Very small.

182) Anterior process length:
Comment: a short anterior process is observed when the anterior process length is less-to-equal to the posterior process length otherwise the anterior process is long. (0) Short; (1) Long. (1) Elongated.

Supplementary Figure S7
Stratigraphic consistency of the balaenopterid phylogeny Phylogenetic relationships of Balaenopteridae (as from Fig. 16) plotted against a temporal scale to show the agreement between phylogentic position and stratigraphic ages of the OTUs.

Supplementary Figure S8
Experimental paleobiogeographic analysis Experimental study of the paleobigeography of Archaebalaenoptera in the case a new find from South Atlantic is included within the phylogenetic analysis. Method: Fitch's (1985) parsimony (see Methods for explanation). Caption: M, Mediterranean; NA, North Atlantic; SA, South Atlantic; SP, South Pacific.