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Taxonomy
Tlaxcallicetus was named by Cisneros (2018). Its type is Tlaxcallicetus guaycurae.
It was assigned to Chaeomysticeti by Cisneros (2018).
It was assigned to Chaeomysticeti by Cisneros (2018).
Species
T. guaycurae (type species)
Synonymy list
| Year | Name and author |
|---|---|
| 2018 | Tlaxcallicetus Cisneros p. 6 figs. Figures 3-9 |
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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.
Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| A. E. H. Cisneros 2018 | Group of stem mysticetes characterized by a massive cranium. Broad supraoccipital with a concave surface and triangular profile (Figure 3); opening of the foramen magnum with an inverted trapezoidal outline; as well a thick zygo- matic process, dorsoventrally and mediolaterally (Figure 6). The posterior end of the nuchal crest is elevated in vertical as in basilosaurids (Figure 7). Tlaxcallicetus shows the following autapomorphic features: i) a periotic with a long and flattened anteroposteriorly compound posterior process (derived feature); ii) a head of the periotic (pars
cochlearis, body of the periotic and anterior pro- cess) anteroposteriorly compressed and dorsoven- trally expanded with ovoid form, in lateral and medial views; iii) an anterior process transversally thin like a lamina with an anterodorsal angle promi- nent as a linguiform outline, which is approximately more than twice the dorsoventral depth size of the pars cochlearis; iv) presence of a basioccipital crest anteroposteriorly longest and thick with a similar profile as “J”; v) a prominent exoccipital directed posteriorly, and dorsoventrally thick (~50 mm at posterior end) with a semicircular outline in dorsal view; vi) and presence of a non-prominent postglenoid process. Tlaxcallicetus mainly differentiates from other described Oligocene stem Mysticeti (Aetiocetidae, Mammalodontidae, Eomysticetidae, and Sitsqwayk, Mauicetus, Horopeta, and Whakakai) in a periotic bone with a compound posterior process (posterior processes of bulla and periotic fused) and the ovoid head of the periotic. Tlaxcallicetus is interpreted as a chaeomysticete based on the next derived features: a compound posterior process of the periotic; transversally widened intertemporal constriction; and a postglenoid process of the squamosal posteriorly directed in lateral view (Hernández-Cisneros et al., 2017). Thus, Tlaxcalli- cetus is readily distinct from toothed forms (Llano- cetidae, Mammalodontidae, Aetiocetidae) but remnant teeth as in eomysticetids is unknown (see Boessenecker and Fordyce, 2015a). It is largely different from Eomysticetidae: in a zygomatic pro- cess of squamosal with an inflated and rounded squamosal prominence, as well as a posteriorly divergent basioccipital crest; from Sitsqwayk cor- nishorum, in an opening of the foramen magnum with an inverted trapezoidal outline, presence of a thick basioccipital crest that is laterally directed near to or at right angle to the long axis of the skull; from Mauicetus parki, in a deeply concave and broad supraoccipital, a posteriorly divergent basioccipital crest, a periotic with a vertical anterior keel and a reduced suprameatal area; from Horop- eta umarere and Whakakai waipata, in a deeply concave and broad supraoccipital, an internal acoustic meatus as a single aperture, and a reduced suprameatal area. Tlaxcallicetus shows several plesiomorphic features: a vertical profile of the nuchal crest at the posterior part, a developed superior process of the periotic, an internal acous- tic meatus as a single aperture and a presence of a low transverse crest, a straight medial profile of pars cochlearis, and a presence of fovea epi- tubaria. The latter features make Tlaxcallicetus different from the crown Mysticeti (Balaenidae, Cetotheriidae, and Balaenopteroidea, sensu Marx and Fordyce [2015]). |