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Arktocara yakataga
Taxonomy
Arktocara yakataga was named by Boersma and Pyenson (2016). Its type specimen is USNM 214830, a partial skull (incomplete skull lacking the rostrum anterior of the antorbital notches, tympanoperiotics, dentition and mandibles), and it is a 3D body fossil. Its type locality is Lawrence Creek, which is in a Chattian marine siltstone in the Poul Creek Formation of Alaska. It is the type species of Arktocara.
Synonymy list
| Year | Name and author |
|---|---|
| 2016 | Arktocara yakataga Boersma and Pyenson p. 7 figs. Figs. 2-9 |
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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.
†Arktocara yakataga Boersma and Pyenson 2016
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| A. Boersma and N. D. Pyenson 2016 | Arktocara is a small to medium sized platanistoid odontocete (approximately 2.26 m in total length), which belongs, based on one equivocal synapomorphy, to the node-based Platanistoidea: width: width of the premaxillae >50% of the width of the rostrum at the antorbital notch (character 51[1]). More convincingly, Arktocara belongs to Platanistoidea based on its affinities to other members of the Allodelphinidae that possess unequivocal synapomorphies of the Platanistoidea (see ‘Discussion’ for further commentson the relationship of Allodelphinidae within the Platanistoidea). We also note that, for the purposes of this diagnosis, we use a broad definition of Waipatiidae that includes Otekaikea spp. (see Tanaka & Fordyce (2015a)), and Squalodelphinidae sensu Lambert, Bianucci & Urbina (2014). See ‘Discussion’ for further comments on systematics of these groups.
Arktocara can be differentiated from all other platanistoids by the following combination of character states. Arktocara differs from Waipatiidae and Squalodelphinidae in having: a postglenoid process of squamosal greatly reduced (character 114[1]); an occipital shield bearing a distinct sagittal crest (character 118[1]); length of the zygomatic process as percent of the greatest width of the maxillae across the postorbital processes <30% (character 152[1]); lacking a dorsal condyloid fossa (character 119[0]); and lacking any asymmetry in the vertex (character 98[0]). Arktocara also differs from Waipatiidae and Platanistidae in having: frontals posterior to the nasals and between the premaxillae wider than the maximum transverse width across the nasals (character 95[0]); and lacking an anterior transverse ridge and largetympanosquamosal recess, with middle sinus still inferred to be present (character 144[1]). Arktocara further differs from Waipatiidae in having: a lacrimal that wraps around the anterior edge of the supraorbital process of frontal and slightly overlies its anterior end (character 37[0]); maxilla forming the dorsolateral edge of the internal opening of the infraorbital foramen (character 43[0]); ventromedial edge of the internal opening of infraorbital foramen formed by maxilla and palatine (character 44[1]); a nuchal crest weakly convex anteriorly in dorsoposterior view (character 117[1]); a lateral end of the groove for the mandibular branch of the trigeminal nerve wrapping laterally around posterior end of pterygoid sinus fossa and opening primarily anteriorly (character 148[0]); the angle formed by the basioccipital crests in ventral view between 15–40◦ (character 157[1]); and in lacking a premaxillary crest or posterior maxillary crest adjacent to the nasal (character 72[0]). Arktocara differs from all Platanistidae and Squalodelphinidae in having the anterolateral corner of the maxilla overlying the supraorbital process of frontal being thin and of even thickness to parts posteromedial (character 64[0]). Arktocara also differs from all Platanistidae in having: the apex of the postorbital process of frontal projected posterolaterally and slightly ventrally (character 46[0]); the ratio of the greatest width of the premaxillae to the greatest width of maxillae at the level of postorbital processes between 0.49–0.38 (character 76[1]); a shallow emargination of the posterior edge of zygomatic process by the sternomastoid muscle fossa in lateral view (character 111[1]); the width of the squamosal lateral to the exoccipital in posterior view as a percent of the greatest width of the exoccipitals <15% (character 112[0]); fossae for the preorbital lobe of the pterygoid sinus present in the orbit (character 134[1]); shallow posterior portion of the periotic fossa of the squamosal (character 151[1]); posteroventral-most point on the basioccipital crest forming a closely appressed flange with a narrow crease separating exoccipital dorsally from the rest of crest (character 156[1]); and lacking a pneumatic maxillary crest overhanging medially (character 65[0]). Finally, Arktocara differs from all Squalodelphinidae in having: a narrower width of the premaxillae at the antorbital notches as a percent width of the rostrum at the antorbital notch (50–64%) (character 51[1]). Arktocara differs from all other Allodelphinidae in having: a reduced postglenoid process of the squamosal (character 114[1]); and the posteroventral-most point of the basioccipital crest forming a closely appressed flange separating the exoccipital dorsally from the rest of the crest by a narrow crease (character 156[1]). Arktocara differs from Allodelphis pratti and Goedertius oregonensis in having: both premaxillae extending posterior to the nasals (character 58[1]); and the ratio of the greatest width of the premaxillae to greatest width of the maxillae at the level of the postorbital processes between 0.49–0.38 (character 76[1]). Arktocara also differs from Goedertius oregonensis and Zarhinocetus errabundus in having: the width of the premaxillae between 50–64% of the width of the maxillae a the level of the antorbital notches (character 51[1]); a uniformly thin anterolateral corner of the maxilla overlying the supraorbital process of the frontal (character 64[0]); length of the zygomatic process of the squamosal ≤30% of the width of the maxillae at the postorbital processes (character 152[1]); lacking a rostral basin (character 50[0]), lacking a posterior dorsal infraorbital foramen placed posteromedially near the posterior extremity of the premaxilla (character 60[0]); lacking a dorsal condyloid fossa (character 119[0]) and having a symmetrical cranial vertex (character 98[0]). Arktocara also differs from Allodelphis pratti and Zarhinocetus errabundus in having: two anterior dorsal infraorbital foramina (character 49[1]); and a shallow emargination of the posterior edge of the zygomatic process by the sternomastoid muscle fossa in lateral view (character 111[1]). Arktocara further differs from Goedertius oregonensis having: a fused lacrimal and jugal (character 39[1]); the apex of the postorbital process of the frontal directed posterolaterally and slightly ventrally (character 46[0]); a triangular or anteroposteriorly widened falciform shaped postorbital process of the frontal (character 47[2]); one posterior dorsal infraorbital foramina of the maxilla (character 59[1]); nuchal crest weakly convex anteriorly in dorsoposterior view (character 117[1]); and the posterior edge of the vomer terminating on the basisphenoid (character 154[0]). Arktocara further differs from Zarhinocetus errabundus in having: the transverse width of the nasal >70% the length of the nasal (character 91[2]); a distinct sagittal crest on the occipital shield (character 118[1]); and in lacking an anterior transverse ridge and large tympanosquamosal recess (character 144[1]). Lastly, Arktocara displays the following apomorphies: a weakly developed antorbital notch (character 10[0]); straight lateral margin of the right premaxilla posterior to premaxillary foramen (character 56[1]); a U-shaped nasal frontal suture (character 94[2]); and a greatly reduced postglenoid process of the squamosal (character 114[1]). |
Measurements
No measurements are available
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| Source: subo = suborder, o = order | |||||
| Reference: Uhen 2004 | |||||