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Zygorhiza
Taxonomy
Zygorhiza was named by True (1908) [Sepkoski's age data: T Eo-m-u T Eo-u Sepkoski's reference number: 1022]. Its type is Basilosaurus kochii. It was considered monophyletic by Uhen (2008) and Martinez-Cáceres and Muizon (2011).
It was assigned to Zeuglodontidae by Abel (1914); to Prozeuglodontidae by Moustafa (1954); to Dorudontidae by Kellogg (1928), Hay (1930), Kellogg (1936), Simpson (1945), Thurmond and Jones (1981) and Hooker (1986); to Cetacea by Sepkoski (2002); to Basilosaurinae by Bouetel and Muizon (2006); to Dorudontinae by Fordyce (1982), Kohler and Fordyce (1997), McKenna and Bell (1997), Uhen (1998), Uhen (2002), van Vliet (2004), Uhen (2004), McLeod and Barnes (2008), Uhen (2008), Uhen (2009), Fordyce and Roberts (2009), Schouten (2011) and Gao and Ni (2015); and to Basilosauridae by Carroll (1988), Benton (1993), Geisler and Sanders (2003), Fitzgerald (2010), Martinez-Cáceres and Muizon (2011), Uhen (2013), Boessenecker and Fordyce (2015), Gingerich (2015), Marx et al. (2016), Martínez-Cáceres et al. (2017), Berta (2017) and Uhen (2018).
It was assigned to Zeuglodontidae by Abel (1914); to Prozeuglodontidae by Moustafa (1954); to Dorudontidae by Kellogg (1928), Hay (1930), Kellogg (1936), Simpson (1945), Thurmond and Jones (1981) and Hooker (1986); to Cetacea by Sepkoski (2002); to Basilosaurinae by Bouetel and Muizon (2006); to Dorudontinae by Fordyce (1982), Kohler and Fordyce (1997), McKenna and Bell (1997), Uhen (1998), Uhen (2002), van Vliet (2004), Uhen (2004), McLeod and Barnes (2008), Uhen (2008), Uhen (2009), Fordyce and Roberts (2009), Schouten (2011) and Gao and Ni (2015); and to Basilosauridae by Carroll (1988), Benton (1993), Geisler and Sanders (2003), Fitzgerald (2010), Martinez-Cáceres and Muizon (2011), Uhen (2013), Boessenecker and Fordyce (2015), Gingerich (2015), Marx et al. (2016), Martínez-Cáceres et al. (2017), Berta (2017) and Uhen (2018).
Synonymy list
| Year | Name and author |
|---|---|
| 1908 | Zygorhiza True p. 78 |
| 1914 | Zygorhiza Abel p. 220 |
| 1928 | Zygorhiza Kellogg p. 32 figs. Table 1 |
| 1930 | Zygorhiza Hay p. 568 |
| 1936 | Zygorhiza Kellogg p. 100 |
| 1945 | Zygorhiza Simpson p. 100 |
| 1954 | Zygorhiza Moustafa p. 87 |
| 1981 | Zygorhiza Thurmond and Jones p. 192 |
| 1982 | Zygorhiza Fordyce p. 422 |
| 1986 | Zygorhiza Hooker p. 342 |
| 1988 | Zygorhiza Carroll |
| 1993 | Zygorhiza Benton p. 761 |
| 1997 | Zygorhiza Kohler and Fordyce p. 575 |
| 1997 | Zygorhiza McKenna and Bell p. 369 |
| 1998 | Zygorhiza Uhen p. 38 |
| 2002 | Zygorhiza Sepkoski |
| 2002 | Zygorhiza Uhen p. 79 |
| 2003 | Zygorhiza Geisler and Sanders p. 27 |
| 2004 | Zygorhiza Uhen p. 12 |
| 2004 | Zygorhiza van Vliet p. 143 |
| 2006 | Zygorhiza Bouetel and Muizon p. 383 |
| 2008 | Zygorhiza McLeod and Barnes p. 93 |
| 2008 | Zygorhiza Uhen p. 562 |
| 2009 | Zygorhiza Fordyce and Roberts p. 553 |
| 2009 | Zygorhiza Uhen p. 93 |
| 2010 | Zygorhiza Fitzgerald p. 370 figs. Table 1 |
| 2011 | Zygorhiza Martinez-Cáceres and Muizon |
| 2011 | Zygorhiza Schouten p. 18 |
| 2013 | Zygorhiza Uhen p. 11 figs. Figure 8 |
| 2015 | Zygorhiza Boessenecker and Fordyce figs. Table 1 |
| 2015 | Zygorhiza Gao and Ni p. 156 figs. Table 1 |
| 2015 | Zygorhiza Gingerich p. 164 |
| 2016 | Zygorhiza Marx et al. p. 101 |
| 2017 | Zygorhiza Berta p. 159 |
| 2017 | Zygorhiza Martínez-Cáceres et al. p. 11 |
| 2018 | Zygorhiza Uhen |
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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.
G. †Zygorhiza True 1908
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†Zygorhiza kochii Carus 1847
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Invalid names: Zeuglodon brachyspondylum Abel 1914 [synonym], Zeuglodon hydrarchus Carus 1849 [synonym], Zygorhiza brachyspondylus True 1908 [synonym], Zygorhiza minor True 1908 [synonym]
Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| M. D. Uhen 2008 | Zygorhiza is much smaller than both Basilosaurus and Cynthiacetus. Zygorhiza also lacks the elongate trunk vertebrae of Basilosaurus. Zygorhiza can be distinguished from Dorudon and Chrysocetus by the presence of accessory denticles on the cingula of the upper premolars (Köhler and Fordyce, 1997). | |
| M. D. Uhen 2013 | Members of the species Zygorhiza kochii have strong vertical ornamentation on the enamel of the teeth, and well-developed cingula on the premolars with additional cuspules on these cingula (e.g. Kellogg, 1936; Köhler & Fordyce, 1997). These features are not shown in the type specimen, as it lacks teeth. See the discussion below regarding the replacement of the holotype with a neotype specimen, USNM 11962, which does show this di- agnostic feature clearly (Kellogg, 1936, plates 10-15).
Additional cranial features were investigated as pos- sible diagnostic characteristics of Zygorhiza kochii. All proved to be either too difficult to assess, or proved to be variable in nature. For instance, the periotic has proven to be a good source of diagnostic characters among taxa of Neoceti, but there are a very limited number of periotics associated with teeth and skulls for Zygorhiza kochii. Some small differences in the shape of the pars cochlearis and the anterior processes were observed, but it is impossible to know whether this is due to intraspecific variation or possible interspecific variation. Also, the area of the cranial vertex was investigated, but proved to be highly variable. Among the five skulls at- tributed to Zygorhiza that preserve this area (RMM 2739, TM 8501, USNM 11962, 16638, and 16639), all have nota- ble differences in the conformation of the sutures in this region. In RMM 2739, the premaxillae meet posterior to the external nares, excluding the anterior nasals from the narial opening. In USNM 16638, the lateral margin of the nasal presents a “notch” into which the posteriormost end of the premaxilla is sutured. TM 8501, USNM 11962 and USNM 16638 all have a large anterior process of the fron- tal (narial process of the frontal). RMM 2739, has a small anterior processes of the frontal, while USNM 16639 has none. Finally, in USNM 11962, the posterior end of the me- dial margin of the maxilla makes contact with the anterior process of the frontal, while in all of the others (this can- not be observed in TM 8501) it contacts the lateral margin of the nasal. Since none of these features seem to correlat- ed to one another, for the time being, Zygorhiza kochii is considered to be a highly variable species in these respects. |
Measurements
No measurements are available
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| Source: o = order | |||||
| Reference: Uhen 2004 | |||||
Age range: base of the Bortonian to the top of the Late/Upper Eocene or 42.60000 to 33.90000 Ma
Collections (14 total)
| Time interval | Ma | Country or state | Original ID and collection number |
|---|---|---|---|
| Bortonian | New Zealand (South Canterbury) | Z. sp. (32900) | |
| Priabonian | United Kingdom (England) | Z. sp. (184754) | |
| Priabonian | USA (Louisiana) | Z. kochii (32925 55251 75638) | |
| Priabonian | USA (Alabama) | Basilosaurus kochii (84754) Z. kochii (124707 131909 131910) Z. kochii, Dorudon sp. (28983) | |
| Priabonian | USA (Mississippi) | Z. kochii (45639 55869) Z. sp. (132843) | |
| Late/Upper Eocene | New Zealand (Canterbury) | Z. sp. (45041) |