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Taxonomy
Horopeta was named by Tsai and Fordyce (2015). It was considered monophyletic by Tsai and Fordyce (2015).
It was assigned to Mysticeti by Tsai and Fordyce (2015); and to Mysticeti by Robinson et al. (2024).
It was assigned to Mysticeti by Tsai and Fordyce (2015); and to Mysticeti by Robinson et al. (2024).
Species
Synonymy list
| Year | Name and author |
|---|---|
| 2015 | Horopeta Tsai and Fordyce figs. Fig. 14 |
| 2024 | Horopeta Robinson et al. p. 578 |
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| C.-H. Tsai and R. E. Fordyce 2015 | Horopeta umarere has the following archaic features in Mysticeti: distinct and long dorsal exposure of sagittal crest of the parietal on the vertex, base of frontal sloping moderately from midline of skull, unfused posterior processes of periotic and bulla, presence of horizontal cleft and elliptical foramen in bulla, anterior pedicle attached on periotic (homolog of accessory ossicle). Shares with balaenopteroids: laterally bowed mandible; coronoid process of mandible deflected posterolaterally. Differs from other archaic baleen whales such as Aglaocetus and Diorocetus in: broad mandibular fossa of squamosal; largely unfilled and laterally dorsoventrally expanded external acoustic meatus (anterior and posterior meatal crests of squamosal enclose a triangular surface); large fenestra rotunda; posteroexternal sulcus running onto lateral surface of posterior process of periotic; curved anterior incisure separates anterior process from body and pars cochlearis of periotic; elongated, rod-shaped, and dorsoventrally stout sternum with at least three attachments for ribs or costal cartilages.
Horopeta umarere lacks mandibular alveoli, and the mandibular symphysis is interpreted as unfused. Horopeta umarere has remnants of broad and flattened maxillae, and is interpreted as a toothless baleen whale readily distinguished from toothed mysticetes (Aetiocetidae, Mammalodontidae, Llanocetidae). Horopeta umarere differs from Eomysticetidae in: laterally-bowed mandible; posteriorly divergent basioccipital crests; triangular coronoid process of mandible deflected laterally and posteriorly; lack of lower transverse process on seventh cervical vertebra; on the periotic, dorsoventral height of an- terior process is greater than length in medial view; internal acoustic meatus separated into well-defined proximal opening of facial canal and dorsal vestibular area by prominent transverse crest; posterior process of periotic leveled horizontally in medial view; prominent posteroexternal sulcus leads to posteroexternal foramen in periotic; indistinct bilobed tympanic bulla in posterior view; less developed horizontal cleft in tympanic bulla. Horopeta umarere differs from Mauicetus parki in: diverging basioccipital crests posteriorly in ventral view; posteriormost point of exoccipital anterior to posterior edge of occipital condyle in dorsal or ventral view; on the periotic, vertical orientation of anterior keel; distal opening of facial canal anterior to fenestra ovalis (fenestra vestibuli); aperture for cochlear aqueduct and fenestra rotunda confluent (as an open fissure); distance between fenestra rotunda and aperture for cochlear aqueduct (diam- eter of the open fissure) narrower than size of fenestra rotunda; irregular profile of fenestra rotunda; posterior processes of periotic and tympanic bulla unfused and short; elliptical foramen with long axis oriented ventrolaterally. Horopeta umarere differs from other Oligocene toothless mysticetes (e.g., Micromysticetus and Cetotheriopsis) in: absence of external occipital crest on supraoccipital; later- ally dorsoventrally expanded external acoustic meatus. Further differs from Micromysticetus rothauseni in: well- developed transverse crest to separate proximal opening of facial canal from dorsal vestibular area; large and ventrally-positioned fenestra rotunda; horizontally oriented posterior process of periotic. Horopeta umarere further differs from all six extant genera in four families (Balaenidae, Balaenopteridae, Cetotheriidae/Neobalaenidae, and Eschrichtiidae) in: ba- se of frontal sloping moderately from skull midline; parietal considerably exposed at sagittal crest; unfused and short posterior processes of periotic and tympanic bulla; a distinct pedicle plate situated in fovea epitubaria; presence of horizontal cleft, elliptical foramen, and sigmoidal cavity (new term) in tympanic bulla. Horopeta umarere also differs from other fossil cetotheriids sensu stricto and other unranked fossil baleen whales (e.g., Pelocetus, Diorocetus, and Parietobalaena) in: parietal largely exposed at sagittal crest (102.5 mm); unfused and short posterior process of periotic and tympanic bulla; prominent superior process of periotic; presence of elliptical foramen and sigmoidal cavity in tympanic bulla. |