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Crisocetus lydekkeri
Taxonomy
Crisocetus lydekkeri was named by Gaetán et al. (2023). Its type specimen is MPEF-PV 1362, a partial skull (ncomplete skull preserved from the orbit to the occipital condyles, lacking the rostrum, jugals, nasals, part of the vertex, and tympanoperiotics), and it is a 3D body fossil. Its type locality is Estancia El Crisol, which is in a Burdigalian estuary/bay sandstone in the Gaiman Formation of Argentina. It is the type species of Crisocetus.
Synonymy list
| Year | Name and author |
|---|---|
| 2023 | Crisocetus lydekkeri Gaetán et al. p. 2 figs. Figs. 2–5 |
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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.
†Crisocetus lydekkeri Gaetán et al. 2023
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| C. M. Gaetán et al. 2023 | Crisocetus lydekkeri is a small to medium-sized odontocete (total body length estimated between 270–315 cm) characterized by a unique combination of characters: premaxil- lae joining dorsomedially at least in the posterior part of the mesorostral groove, a basioccipital width wider than 51% of the skull width in ventral view, basioccipital crests forming an angle of 70–90° with each other; the presence of a premaxillary crest adjacent to the nasal, teardrop-like, lateromedially narrow external bony nares, premaxilla overhanging maxilla lat- erally, nasal-frontal suture approximately straight transversely, and presence of a supraorbital crest in the supraorbital region built by the thickening of the frontal, but not the maxilla. Criso- cetus lydekkeri differs from Squaloziphius emlongi and Yaquina- cetus meadi in having the suture between premaxillary and maxilla laterally convex in dorsal view, instead of straight, and a lower vertex. It further differs from Y. meadi in having the nuchal crest reaching dorsally the same level as the frontals on the vertex. It further differs from S. emlongi in the lack of a maxillary intrusion medially to the premaxillae in the mesoros- tral groove. It differs from Chilcacetus cavirhinus in having a deep emargination posterodorsal in the zygomatic process, in the posterior contact of the maxilla with the supraoccipital, in the presence of a premaxillary crest, in having a nuchal crest with a rectangular outline, the nuchal crest that reaches dorsally the same level as the frontals in the vertex, in having a very large tympanosquamosal recess and the lack of a posterior portion of the periotic fossa. Crisocetus lydekkeri differs from all eurhino- delphinids in having an anteroposteriorly wider than dorsoven- trally high postglenoid process (width/high ratio of 1.19), and
in having a lower vertex. It further differs from all eurhinodelphi- nids except Ziphiodelphis abeli, in having an almost rectangular dorsal outline of the occipital shield in posterior view. It further differs from Ziphiodelphis abeli in having the occipital condyle dorsal to the level of the orbit in lateral view. From Macrodelphi- nus kelloggi it differs in the premaxilla laterally overhanging the maxilla at the nasal level and in the absence of an external occi- pital crest. From Dolgopolis kinchikafiforo it differs in having an anteriorly squared zygomatic process instead of anteriorly pointed, a much more robust zygomatic and postglenoid pro- cesses, a premaxillae joined medially just anterior to the external bony nares, a pterygoid sinus fossa more posteriorly placed, the lateral extension of the frontal not completely covered by the maxilla in the orbital region in dorsal view, and in having a convex dorsal margin of the supraorbital process formed by the thickening of the frontal instead of the thickening of the maxilla. It differs from Aondelphis talen in having proportionally smaller occipital condyles and an anteroposteriorly shorter neck of the occipital condyles, a more robust and ventrally extended postglenoid process, a wider external auditory meatus in ventral view, a well-defined rectus capitus anticus muscle fossa in the basioccipital and a narrower jugular notch in posterior view. From Argyrocetus patagonicus it differs in having the pre- maxillae contacting in the midline just anterior to the nares instead of being widely separated, a more concave tympanosqua- mosal recess, much blunter zygomatic and postglenoid processes, a higher and as long as wide vertex in dorsal view, and in having a narrower jugular notch in posterior view. From Prosqualodon australis it greatly differs in its smaller size, in lacking an external occipital crest, in having smaller preorbital and postorbital pro- cesses, a shallower optic canal, a strongly rectangular nuchal crest in posterior view and an anteroposteriorly longer than dorsoventrally higher temporal fossa. Crisocetus lydekkeri differs from Notocetus vanbenedeni in having a postglenoid process that is blunter and anteroposteriorly wider, a zygomatic process being dorsoventrally lower, in the lack of a premaxillary cleft, in having a narrower jugular notch in posterior view, and a less developed fossae for the posterior and pterygoid sinuses. From Phoberodon arctirostris it differs in having a supraorbital crest, a premaxillary crest, the premaxillae joined medially just anterior to the external bony nares, and a concave ventral edge of the zygomatic process. |
Measurements
No measurements are available
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| Source: subo = suborder, o = order | |||||
| Reference: Uhen 2004 | |||||
Age range: Burdigalian or 20.45000 to 15.98000 Ma
Collections: one only
| Time interval | Ma | Country or state | Original ID and collection number |
|---|---|---|---|
| Burdigalian | Argentina (Chubut) | Crisocetus lydekkeri (type locality: 203129) |