Extant baleen whales (Mysticeti) have a deciduous foetal dentition, but are edentulous at birth. Fossils reveal that the earliest mysticetes possessed an adult dentition. Aetiocetids, a diverse clade of Oligocene toothed mysticetes, have a series of small palatal foramina and associated sulci medial to the postcanine dentition. The openings have been homologized with lateral palatal foramina that transmit neurovascular structures to baleen in extant mysticetes, thereby implying a co-occurrence of teeth and baleen in aetiocetids. However, homology of the foramina and sulci have been questioned. Using CT-imaging, we report that the lateral palatal foramina of Aetiocetus weltoni are connected internally to the superior alveolar canal, which transmits neurovascular structures to baleen in extant mysticetes and to teeth in extant odontocetes. Furthermore, the lateral palatal foramina of Aetiocetus are separate from the more medially positioned canals for the greater palatine arterial system. These results provide critical evidence to support the hypothesis that the superior alveolar neurovasculature was co-opted in aetiocetids and later diverging mysticetes to serve a new function associated with baleen. We evaluate competing hypotheses for the transition from teeth to baleen, and explore the transition from raptorial feeding in early mysticetes to filter-feeding in extant species.

A partial nodosaurid ankylosaur skeleton, consisting primarily of the ilia, hindlimbs, posterior dorsal armor, plus partial forelimb elements and additional armor, was recovered from the marine Point Loma Formation, late Campanian age, north of San Diego, California. The specimen is similar to contemporaneous species of Panoplosaurus and Edmontonia from terrestrial sediments of the western interior, but there are also similarities to the armor of Stegopelta landerensis from marine sediments of earliest Cenomanian age from Wyoming. Skeletal elements critical for generic determination are not preserved, and the specimen is identified as Nodosauridae, incertae sedis. An associated marine invertebrate fauna and nannoplankton flora have revealed some discrepencies in the correlation systems used for Upper Cretaceous marine rocks of coastal California. Hollow limb bones of the specimen are interpreted as a preservational artifact. Nodosaurids had broad ecological tolerances, and visited riparian and coastal environments more frequently than other dinosaurs. However, a review of morphologic and distributional evidence fails to support a theory of amphibious or aquatic habits for nodosaurids.

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The transition in Mysticeti (Cetacea) from capture of individual prey using teeth to bulk filtering batches of small prey using baleen ranks among the most dramatic evolutionary transformations in mammalian history. We review phylogenetic work on the homology of mysticete feeding structures from anatomical, ontogenetic, and genomic perspectives. Six characters with key functional significance for filter-feeding behavior are mapped to cladograms based on 11 morphological datasets to reconstruct evolutionary change across the teeth-to-baleen transition. This comparative summary within a common parsimony framework reveals extensive conflicts among independent systematic efforts but also broad support for the newly named clade Kinetomenta (Aetiocetidae + Chaeomysticeti). Complementary anatomical studies using CTscans and ontogenetic series hint at commonalities between the developmental programs for teeth and baleen, lending further support for a 'transitional chimaeric feeder' scenario that best explains current knowledge on the transition to filter feeding. For some extant mysticetes, the ontogenetic sequence in fetal specimens recapitulates the inferred evolutionary transformation: from teeth, to teeth and baleen, to just baleen. Phylogenetic mapping of inactivating mutations reveals mutational decay of 'dental genes' related to enamel formation before the emergence of crown Mysticeti, while 'baleen genes' that were repurposed or newly derived during the evolutionary elaboration of baleen currently are poorly characterized. Review and meta-analysis of available data suggest that the teeth-to-baleen transition in Mysticeti ranks among the best characterized macroevolutionary shifts due to the diversity of data from the genome, the fossil record, comparative anatomy, and ontogeny that directly bears on this remarkable evolutionary transformation.

The Pliocene fossil whale, Eschrichtius davidsonii Cope 1872, is actually a balaenopterid mysticete referable to the modern genus Balaenoptera Lacépède 1804. Redescription of the holotype of B. davidsonii (a partial left dentary), together with the discovery and description of a nearly complete right dentary referrable to this taxon, demonstrates the taxonomic and systematic affinities of Balaenoptera davidsonii. Although originally thought to be Miocene in age, newspaper accounts of 1872 indicate that the holotype of B. davidsonii was actually collected from fossiliferous sandstones here referred to the San Diego Formation of Late Pliocene age (equivalent to the Blancan North American Land Mammal Age). Comparisons between the dentary of B. davidsonii and dentaries of other extant and fossil balaenopterids allow recognition of several taxonomically useful mandibular characters (i.e., degree of longitudinal curvature of horizontal ramus and form of transverse cross‐sectional outlines). A taxonomic review of other nominal Neogene species of Balaenoptera from Europe and eastern North America is an initial attempt at stabilizing the confusing nomenclatural history and taxonomy of this group. In this regard, the genus Burtinopsis Van Beneden 1872 is placed in synonymy with Balaenoptera. Generic reassignment of the fossil rorqual Balaenoptera davidsonii (Cope 1872) creates a nomenclatural problem of homonymy with the extant minke whale Balaenoptera davidsoni Scammon 1872. As Cope's species is a senior homonym of Scammon's, suppression of Scammon's name is recommended. The new trinomen Balaenoptera acutorostrata scammoni n. ssp. is here proposed for the North Pacific minke whale.