Palaeophis oweni Zigno, 1881
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publication ID |
https://doi.org/ 10.4202/app.00711.2019 |
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persistent identifier |
https://treatment.plazi.org/id/C50687C5-F714-2447-D55D-F9800BAFFA40 |
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treatment provided by |
Felipe |
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scientific name |
Palaeophis oweni Zigno, 1881 |
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Type material: Lectotype (herein designated): MGP-PD 6981Za, an anterior trunk vertebra ( Figs. 1 View Fig , 3 View Fig ). Paralectotypes: 23 trunk vertebrae (MGP-PD 6976Za, 6976Zb, 6977Za, 6977Zb, 6977Zc, 6978Z, 6978Za, 6978Zb, 6978Zc, 6978Zd, 6978Ze, 6978Zf, 6978Zg, 6978Zh, 6979Z (two vertebrae plus several tiny vertebral fragments), MGP-PD 6980Z, 6981Z, 6981Zb, 6981Zc, 6981Zd, 6981Ze, 6981Zf) (Fig. 2), from the type locality and horizon.
Type locality: Monte Duello , near Verona, Veneto, Italy .
Type horizon: Nummulitic limestone, Orizzonte di Roncà, Bartonian, late middle Eocene.
Emended diagnosis.— Palaeophis oweni can be assigned to Palaeophiidae on the basis of its vertebrae being tall and laterally compressed, the presence of pterapophyses, the horizontality of the cotyle-condyle axis, the rather large cotyle and condyle, the presence of a second, small hypapophysis in its anterior trunk vertebrae (i.e., anterior hypapophysis, right ventrally to the cotyle), the distinct ventral projection of the paradiapophyses, the reduced prezygapophyses, and the presence of compressed prezygapophyseal buttresses that form a ridge extending from the dorsal border of the paradiapophyses up to the prezygapophyseal articular facets (characters from Rage 1983a, 1984; Rage et al. 2003; Houssaye et al. 2013). Palaeophis oweni can be referred to the genus Palaeophis on the basis of the relatively small pterapophyses and the neural spine rising posteriorly from the level of the zygosphenal roof (characters from Rage 1984; Parmley and Case 1988; Rage et al. 2003, 2008; Parmley and DeVore 2005; Houssaye et al. 2013). Palaeophis oweni can be differentiated from all other species of the genus Palaeophis by the following combination of features: zygosphene thick and almost trapezoidal in shape when seen in anterior view, with its dorsal margin distinctly convex; cotyle large and slightly, in some cases, laterally compressed; small pterapophyses; massive and elongated paradiapophyses that extend ventrally, well below the ventral level of the cotyle; posterior hypapophysis massive; neural spine high and posteriorly inclined; centrum not much widened anteriorly.
Description.—The lectotype vertebra MGP-PD 6981Za is incomplete, missing most of its neural spine, the posterior portion of the neural arch with large part of both postzygapophyses, and most of its right prezygapophysis and right pterapophysis ( Fig. 1 View Fig ). The vertebra is large, with a centrum length of 16.7 mm. In anterior view ( Fig. 1A 1 View Fig ), the vertebra is tall and distinctly laterally compressed. The zygosphene is thick with its dorsal roof being overall convex and almost triangular in shape. The neural canal is relatively small and trapezoidal. The prezygapophyses (only the left is partially preserved) do not seem to extend much above the ventral floor of the neural canal. There are prezygapophyseal buttresses, in the form of vertical ridges, which extend from the dorsal border of the paradiapophyses up to the prezygapophyseal articular facets. The cotyle is rather large and not particularly compressed. There are no paracotylar foramina, though large depressions are visible at each lateral side of the cotyle. The base of an anterior, moderately thick, hypapophysis is visible below the ventral level of the cotyle. The paradiapophyses are large and elongated, with their ventralmost tip reaching well below the ventral level of the cotyle. In posterior view ( Fig. 1A View Fig 2), the neural arch seems to be relatively vaulted, though this assumption can only be considered as tentative as this respective portion is damaged. The pterapophyses (only the left one is preserved) are relatively small and extend dorsolaterally forming an angle of around 45 o with the neural arch. The condyle is large. The posterior hypapophysis is large, with its ventral tip ending well below the level of the condyle. This element is laterally compressed; it is relatively thick at its base but its thickness diminishes gradually towards the level of its ventralmost tip. In dorsal view ( Fig. 1A View Fig 4 View Fig ), the zygosphene is rather concave; there is no sign of a medial lobe. The base of the neural spine runs throughout most of the neural arch, though still it commences posteriorly to the level of the zygosphenal roof. The prezygapophyses extend more anteriorly than laterally. The prezygapophyseal articular facets are rather narrow and small. The interzygapophyseal constriction is relatively shallow. In ventral view ( Fig. 1A View Fig 5), the centrum does not significantly widen anteriorly. Two hypapophyses are present: one large one (posterior) that is situated at the posterior portion of the centrum but still prior to the level of the condyle, and one smaller (anterior), that is situated at the anteriormost portion of the centrum, right below the cotyle. These two hypapophyses are united with a relatively thin, longitudinal ridge. The paradiapophyses are broad and extend anterolaterally. In lateral view ( Fig. 1A View Fig 3 View Fig , A 6), the zygosphenal facets are elongated. The interzygapophyseal ridge is almost straight. The axis of the cotyle and condyle is horizontal. The paradiapophyses are not divided into diapophyseal and parapophyseal portions; they are large, elongated and they project anteroventrally. The posterior hypapophysis develops at the posterior portion of the centrum and projects much ventrally; its posterior border is not vertical with the centrum but rather forms an angle of around 45°. This vertebra is considered to originate from the anterior trunk vertebral column on the basis of the presence of a second (i.e., anterior) small hypapophysis below the cotyle, united with the first (i.e., posterior), large one with a thin longitudinal keel (see Rage et al. 2003).
Apart from the lectotype, all other vertebrae are rather fragmentary (Fig. 2). All vertebrae pertain to the trunk region of the column, with no cloacal or caudal vertebrae known. MGP-PD 6976Za misses most of the neural spine, posterior portion of neural arch, prezygapophyses, postzygapophyses, and pterapophyses, and much of the zygosphene (Fig. 2A). MGP-PD 6976Zb preserves only the ventral portion of the centrum plus the right prezygapophysis (Fig. 2B). MGP-PD 6977Za misses the dorsal part of the neural spine, part of the pterapophyses, and the left prezygapophysis (Fig. 2F). MGP-PD 6977Zb and 6977Zc preserve only the ventral portion of the centrum (Fig. 2G). MGP-PD 6978Z misses the dorsal part of the neural spine and parts of prezygapophyses, postzygapophyses, and pterapophyses, as well as the ventralmost portion of the posterior hypapophysis (Fig. 2D). MGP-PD 6978Za preserves mostly the ventral portion of the centrum (Fig. 2C). MGP-PD 6978Zb misses the right prezygapophysis and pterapophysis, and part of the zygosphene and the neural spine (Fig. 2E). MGP-PD 6978Zc, 6978Zd, 6978Ze, 6978Zf, 6978Zg, and 6978Zh are only vertebral fragments. MGP-PD 6979Z consists of several large and tiny fragments pertaining to at least two vertebrae. MGP-PD 6980Z preserves only the ventral portion of the centrum. MGP-PD 6981Zb is a partial vertebra embedded in matrix, missing its posteroventral portion and pterapophyses (Fig. 2H). MGP-PD 6981Z misses most of the neural arch and neural spine, zygosphene, and zygantrum. MGP-PD 6981Zc is rather eroded specimen embedded on matrix, missing its anterior portion and the dorsal level of the neural spine (Fig. 2J). MGP-PD 6981Zd preserves solely the posteroventral portion of the vertebra along with the zygosphene, embedded on a matrix (Fig. 2I). MGP-PD 6981Ze preserves only the posteroventral portion of the centrum. MGP-PD 6981Zf preserves only remains of the ventral surface of the centrum, condyle, zygantrum, and the neural arch.
The neural spine is not fully preserved in most specimens. When it is partially preserved though, it seems that it develops in height gradually and always well posteriorly from the level of the zygosphenal roof (e.g., MGP-PD 6976Za, 6978Z). It is relatively thick in posterior view (e.g., MGP-PD 6981Zc, Fig. 2J 2). The neural spine is most complete in MGP-PD 6981Zb, where it is obvious that it attains a considerable height and a slight posterior inclination (Fig.
Fig. 2. Paralectotype trunk vertebrae of palaeophiid snake Palaeophis oweni Zigno, 1881 , from the late middle Eocene of Monte Duello. A. MGP-PD → 6976Za in left lateral (A 1) and ventral (A 2) views. B. MGP-PD 6976Zb in posterior view. C. MGP-PD 6978Za in ventral view. D. MGP-PD 6978Z in left lateral (D 1), anterior (D 2), and ventral (D 3) views. E. MGP-PD 6978Zb in left lateral view. F. MGP-PD 6977Za in left lateral (F 1), dorsal (F 2), ventral (F 3), anterior (F 4), and posterior (F 5) views. G. MGP-PD 6977Zb in left lateral (G 1) and posterior (G 2) views. H. MGP-PD 6981Zb embedded in matrix in left lateral view. I. MGP-PD 6981Zd in anterior view. J. MGP-PD 6981Zc in right lateral (J 1) and posterior (J 2) views.
2H). The same specimen possesses an unusual rugosity on its neural spine, probably due to some taphonomic/preservational factor. The zygosphene is situated rather high. The zygosphene is relatively thick and convex in anterior view (e.g., MGP-PD 6978Z, Fig. 2D 2). Such convexity is prominent at around the mid-length of the zygosphenal roof in anterior view, taking the shape of a triangle (MGP-PD 6981Zd, Fig. 2I; MGP-PD 6981Ze). Zygantrum is damaged in practically most specimens—in fact, the best preserved zygantrum can be observed in MGP-PD 6981Zc, where its roof is rather thick (Fig. 2J 2). Pterapophyses are always small. In MGP-PD 6981Zc, the left pterapophysis is almost complete—it is relatively short and moderately thick in posterior view, lying in parallel to the neural spine (Fig. 2J 2). Prezygapophyses are small and are not much tilted dorsally; in fact they are almost horizontal with the ventral level of the neural canal in certain specimens (MGP-PD 6978Z, Fig. 2D 2). Larger prezygapophyseal articular facets still exist among the material (e.g., MGP-PD 6976Zb, 6978Z), though still they are not considerably large. The postzygapophyses do not extend much laterally (e.g., MGP-PD 6981Zc, Fig. 2J 2). The interzygapophyseal constriction is shallow in all specimens. Cotyle is always large, though the degree of its lateral compression may vary. Condyle is also large and its shape varies as well (e.g., Fig. 2B, G 2). A (posterior) hypapophysis is present in all specimens. Similarly to the case of the lectotype described above, in anterior trunk vertebrae, there is also a small, second anterior hypapophysis, situated right below the ventral level of the cotyle (e.g., MGP-PD 6978Z, Fig. 2D 1; MGP-PD 6978Za, Fig. 2C); specimens that pertain to the mid-trunk or posterior trunk region totally lack an anterior hypapophysis e.g., MGP-PD 6977Za, Fig. 2F). The shape of the posterior hypapophysis also varies, apparently dependent on the intracolumnar position of the vertebrae. In some vertebrae,
is relatively small and/or does not protrude much ventrally (e.g., MGP-PD 6976Za, Fig. 2A 1; MGP-PD 6978Z). In others, it is massive (e.g., MGP-PD 6977Zb, Fig. 2G). Its lateral surface is smooth in most specimens but in one vertebra it is rather rugose, perhaps due to preservation reasons (e.g., MGP-PD 6977Zb, Fig. 2G). Paradiapophyses are much ventrally projected in all specimens (when preserved). However, their shape and anteroventral expansion varies significantly, apparently dependent on the intracolumnar position of the vertebrae. Hence, paradiapophyses can be either relatively slender and anteroventrally directed (e.g., the lectotype MGP-PD 6981Za; MGP-PD 6977Zb, Fig. 2G 1) or can be rather massive and face strictly ventrally (e.g., MGP-PD 6981Zb, Fig. 2H). The centra of all vertebrae are only rather slightly anteriorly widened.
Remarks.—As was a common case with establishments of new species during the 19th century, Zigno (1881) did not designate a holotype for Palaeophis oweni . Although Zigno 1881: figs. 9–12; Fig. 3 View Fig ) figured only one specimen, he clearly indicated that the available material from Monte Duello, consisted of 12 vertebrae; the vast majority of these vertebrae contained rock incretions and only two could be extracted (“Le vertebre di questo Ofidiano, trovate nel calcare nummulitico di m. Zuello, ammontano a dodici, ma la maggior parte di esse era talmente immedesimata nella roccia, che non fu possibile lo estrarne più di due discretamente conservate”; Zigno 1881: 8). It seems that Zigno (1881: 8) focused mostly on these two “better preserved” vertebrae, as he discussed their degree of completeness (“Le porzioni rimaste scoperte di queste due vertebre lascano vedere lo zigosfene, il foro neurico, le diapofisi anteriori, le ipapofisi ed il corpo della vertebra colla concavità anteriore e la protuberanza emisferica posteriore. La spina neurica od apofisi spinosa non è conservata ed il zigantro e le zigapofisi sono in gran parte nascosti dalla roccia”), however, we cannot be certain that he did not base part of his descriptions of P. oweni also on the other, incomplete vertebrae. As such, taking into consideration that Zigno (1881) had worked with more than one specimen upon the establishment of his new taxon, as well as the fact that there is no indication that all vertebrae pertained to the same individual (e.g., they were not articulated), then by definition these specimens have to be considered as syntypes ( ICZN 1999: Article 73.2). We here designate the most complete specimen, MGP-PD 6981Za (i.e., the vertebra figured also by Zigno 1881), as the lectotype of the species. Accordingly, the rest of the 12 vertebrae are considered paralectotypes ( ICZN 1999: Article 73.2.2). It is unclear to us which is the “second vertebra” (besides the lectotype) mentioned by Zigno (1881), as all of the remaining vertebrae are rather fragmentary—in any case, this specimen apparently is also one of the paralectotypes. The reason that we select to designate as lectotype one of the syntypes is in order to maintain nomenclatural stability that would secure that P. oweni is not a “chimaera” of different species (e.g., in [the unlikely] case that some of the fragmentary vertebrae eventually turn up to belong to a different palaeophiid taxon). We have to also note that in its current state of preservation, the palaeophiid material accompanying the labels with Zigno’s writings ( Fig. 4 View Fig ) consisted of 23 fragmentary vertebrae and other tiny vertebral fragments; this number contradicts and surpasses the 12 vertebrae originally mentioned by Zigno (1881). We may tentatively interpret this slight inconsistency in the original number of vertebrae by the probable fact that certain of the incomplete vertebrae were broken into more than one vertebral fragments during the past (almost) 140 years since their original description, or that the smaller fragments were not taken into consideration by Zigno (1881). This view is also supported by the fact that no other palaeophiid material has been subsequently found in Monte Duello (or any other Italian locality) since that time.
The precise authorship date of this taxon is also another issue that needs to be settled. The authorship date of Palaeophis oweni has been continuously erroneously cited as “1882” (e.g., Kuhn 1939, 1963; Rage 1983a, 1984; Rage and Augé 1993; Wallach et al. 2014), however, it is clear from the original publication of Zigno that it was published in 1881. This is further testified also by the author of the species himself, who, in a subsequent work, firmly stated that the respective paper was published in 1881 (“...pubblicai la descrizione e la figura sotto il nome di Palaophis (sic!) Oweni in una memoria stampata nel 1881”; Zigno 1890: 4).
Finally, frustratingly, in his figure captions, Zigno (1881) used a second, erroneous, binomen for his species: Paleophis owenii ; this has obviously to be considered as an incorrect spelling (lapsus calami) of both the genus name and the species epithet of Palaeophis oweni !
Note on Zigno’s (1881) lithograph. —It is worth noting that our direct observation of the material allows us to confirm that the depiction of the lectotype vertebra in Zigno’s (1881) lithograph is not fully accurate; among others, most principally, the shape of the zygosphene, the broadness and length of the paradiapophyses, the shape and robustness of the anterior hypapophysis, the height of the zygosphene, and even the shortness of the centrum are depicted erroneously in the original lithograph of Zigno (1881: figs. 9–12; Fig. 3 View Fig ). Admittedly, such inaccuracies in lithographs of snake fossil vertebrae in 19th century’s publications appear to be in fact a rather common case and have been demonstrated for other extinct ophidian taxa named at that time (see discussion in Georgalis et al. 2016); besides, unfortunately, such phenomenon is not confined only to snake descriptions but it has been demonstrated that it is a general issue in lithographs of fossil specimens during the 19th century (e.g., Anquetin and Joyce 2014; Georgalis 2017; Georgalis and Joyce 2017).
Geographic and stratigraphic range.—Known exclusively from the type locality and horizon.
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