Introduction
Fossil egg capsules of chimaeroids (holocephalian fishes), although rare, have been known for more than 150 years (Bessels, Reference Bessels1869; Meunier, Reference Meunier1891a) and have been found in rocks as old as Upper Triassic (Gottfried and Fordyce, Reference Gottfried and Fordyce2014). Egg capsules of extant chimaeroids are spindle shaped, with a smooth central body where the embryo develops, an elongate anterior beak through which the hatchling emerges, and an elongate posterior pedicle. The capsules are flanked by a lateral membrane or web on both sides, and the web is reinforced with branching or unbranching rib-like costae that extend laterally from the central body, beak, and pedicle. Specimens are typically about 10–30 cm long. Egg capsules of extant chimaeroids are made of collagen (Hamlett et al., Reference Hamlett, Kormanik, Storrie, Stevens, Walker and Hamlett2005) and as fossils, chimaeroid egg capsules are typically preserved as external casts (Fischer et al., Reference Fischer, Licht, Kriwet, Schneider, Buchwitz and Bartsch2014).
There are two schools of thought on how to handle these fossils taxonomically. One assigns them to extant chimaeroid genera that produce morphologically similar egg capsules (Obruchev, Reference Obruchev1967; Vozin, Reference Vozin1968; Stahl, Reference Stahl and Schultze1999). However, it was pointed out that Mesozoic chimaeroid teeth are different from those of modern genera, hence, egg capsules with a morphology nearly identical to that of extant chimaeroids have apparently been produced by completely different genera (Jaekel, Reference Jaekel1901; Fischer et al., Reference Fischer, Licht, Kriwet, Schneider, Buchwitz and Bartsch2014; Duffin et al., Reference Duffin, Lauer and Lauer2022). Therefore, the second school favors a parataxonomic scheme of ichnogenera and ichnospecies, already in use by the late 1800s (Meunier, Reference Meunier1891a) and adopted by most modern scholars (Brown, Reference Brown1946; Fischer et al., Reference Fischer, Licht, Kriwet, Schneider, Buchwitz and Bartsch2014; Gottfried and Fordyce, Reference Gottfried and Fordyce2014; Harrison et al., Reference Harrison, Kirkland, Fischer, San Miguel, Wood and Santucci2021; Duffin et al., Reference Duffin, Lauer and Lauer2022). Such a system is widely used and accepted for fossil shark egg capsules ranging as far back as the Carboniferous (Böttcher, Reference Böttcher2010; Fischer et al., Reference Fischer, Licht, Kriwet, Schneider, Buchwitz and Bartsch2014; Krüger et al., Reference Krüger, Slater and Vajda2021; Mottequin et al., Reference Mottequin, Goolaerts, Hunt and Olive2021, Reference Mottequin, Fischer, Goolaerts and Olive2022).
The currently used ichnogenus for chimaeroid egg capsules is Chimaerotheca Brown, Reference Brown1946 (Brown, Reference Brown1946; Gottfried and Fordyce, Reference Gottfried and Fordyce2014; Harrison et al., Reference Harrison, Kirkland, Fischer, San Miguel, Wood and Santucci2021; Duffin et al., Reference Duffin, Lauer and Lauer2022). Here, we argue that Vaillantoonia Meunier, Reference Meunier1891a, being the first generic name introduced for a fossil chimaeroid egg capsule, has priority over Chimaerotheca and should be used instead.
The specimen reported here is from Oligocene deep-water deposits of the Lincoln Creek Formation in western Washington State, USA. Western Washington hosts a wide range of deep-water deposits of Eocene to Miocene age, which have produced a number of elasmobranch fossils (e.g., Jordan and Hannibal, Reference Jordan and Hannibal1923; Welton, Reference Welton1974, Reference Welton2015; Welton and Goedert, Reference Welton and Goedert2016; Goedert et al., Reference Goedert, Kiel, Thomas and Kriwet2024). This record includes egg capsules of catsharks, found at a late Eocene methane-seep deposit (Treude et al., Reference Treude, Kiel, Linke, Peckmann and Goedert2011). The parataxon Scyliorhinotheca goederti Kiel, Peckmann, and Simon, Reference Kiel, Peckmann and Simon2013, was introduced for these fossils, which feature a mineralized capsule wall rather than being casts.
Material and methods
Specimens were measured with an analog caliper and were coated with ammonium chloride prior to photography.
Repositories and institutional abbreviations
LACMIP, Natural History Museum of Los Angeles County, Invertebrate Paleontology, Los Angeles, USA. MNHN, Museum National d'Histoire Naturelle, Paris, France. NRM, Swedish Museum of Natural History, Stockholm, Sweden.
Systematic paleontology
Ichnogenus Vaillantoonia Meunier, Reference Meunier1891
- Reference Brown1946
Chimaerotheca Brown, p. 262.
Type species
Cycadospadix virei Meunier, Reference Meunier1891b, by monotypy; Upper Jurassic, Meuse, France. The holotype should be housed in the Geology collections of the MNHN in Paris (Leriche, Reference Leriche1914, caption of pl. 9). However, according to the records at MNHN, the specimen was loaned to Maurice Leriche ‘before the war’ and has apparently not been returned (C. Noyer, personal communication, 2024). At the time of Leriche's (Reference Leriche1914) publication, he was working at the Musée royal d'Histoire naturelle de Belgique (Royal Belgian Natural History Museum) in Brussels, Belgium, as well as the Université libre de Bruxelles and the University of Lille, France. But the specimen is not present in the Royal Belgian Natural History Museum (A. Folie, personal communication, 2024), and it was neither found in the collection of the University of Lille, nor is it recorded in the database of the Lille Natural History Museum (J. Cuvelier, personal communication, 2024). Hence, the holotype must be considered lost, and Leriche's (Reference Leriche1914, pl. 9) figure is here re-illustrated as Figure 1.1.
Fossil chimaeroid egg capsules. (1) Holotype of Vaillantoonia virei (Meunier, Reference Meunier1891b), Upper Jurassic, France (reproduced from Leriche, Reference Leriche1914, pl. 9). (2, 3) Vaillantoonia sp. from the Lincoln Creek Formation in western Washington State, USA (NRM PAL P19808), probably representing part of the pedicle and attached web.
Remarks
Vaillantoonia was introduced by Meunier (Reference Meunier1891a) after he was made aware that the Jurassic fossil he reported earlier as Cycadospadix virei Meunier, Reference Meunier1891b, was not a cycad fruit but a chimaeroid egg capsule. Thus, Vaillantoonia is the first generic name introduced for a fossil chimaeroid egg capsule. In his study on Jurassic chimaeroid fossils from Germany published ten years later, Jaekel (Reference Jaekel1901) overlooked Meunier's work and assigned two fossil egg capsules to the fossil chimaeroid Aletodus ferrugineus (Riess, Reference Riess1887). The genus Aletodus was introduced in the same work (Jaekel, Reference Jaekel1901, p. 548–551), but explicitly based on teeth rather than on the egg capsules. Vaillantoonia was subsequently mentioned by Leriche (Reference Leriche1914), who illustrated the specimen for the first time. Vaillantoonia had also been listed by Jordan (Reference Jordan1920) as a valid genus, but Brown (Reference Brown1946) was obviously unaware of this when he introduced Chimaerotheca Brown, Reference Brown1946, an ichnogenus intended to encompass all fossil chimaeroid egg capsules.
Obruchev (Reference Obruchev1967, p. 571) dismissed Vaillantoonia using the following arguments: “The generic name Vaillantoonia Meunier, 1891 has priority over Harriotta Good et Bean, 1894 [sic], but, as a nomen dubium and nomen oblitum, based on a fossil capsule in incomplete state of preservation, should not be used instead of Harriotta Good et Bean, which is known from complete specimens of the fishes.” Considering that Obruchev belonged to the school that preferred assigning fossil egg capsules to extant genera, giving the name of an extant fish priority over a fossil is understandable. However, the presently favored approach of using parataxonomic ichnogenera for such egg capsules makes a comparison to Harriotta Goode and Bean, Reference Goode and Bean1895, irrelevant.
Obruchev's second argument (incomplete preservation) is also questionable because the holotype of Vaillantoonia virei (Meunier, Reference Meunier1891b) was actually quite complete. The specimen, as illustrated by Leriche (Reference Leriche1914, pl. 9) and herein (Figure 1.1), is only missing the tip of the beak and part of the lateral web at the pedicle. It is thus as complete as the holotype of Chimaerotheca wyomingana Brown, Reference Brown1946, which is the type species of Chimaerotheca. Subsequently, workers have followed Obruchev (Reference Obruchev1967) in regarding Vaillantoonia as invalid and used Chimaerotheca for fossil chimaeroid egg capsules (Warren, Reference Warren1948; Fischer et al., Reference Fischer, Licht, Kriwet, Schneider, Buchwitz and Bartsch2014; Gottfried and Fordyce, Reference Gottfried and Fordyce2014; Harrison et al., Reference Harrison, Kirkland, Fischer, San Miguel, Wood and Santucci2021; Duffin et al., Reference Duffin, Lauer and Lauer2022).
However, Vaillantoonia is the oldest generic name based on a fossil chimaeroid egg capsule, and it was used by Leriche in 1914 and Jordan in 1920. This point is critical because a necessary condition for suppressing an older name: “the senior synonym or homonym has not been used as a valid name after 1899” is not met (ICZN, 1999; Article 23.9.1.1). Hence, Vaillantoonia remains valid and should be used as the ichnogenus for fossil chimaeroid egg capsules instead of Chimaerotheca.
Vaillantoonia sp.
Figure 1.2, 1.3
Description
The specimen is a fragment preserving a part of the central filament, and a lateral web on one side. It is approximately 52 mm long and 22 mm wide, and the central axis is 5.5 mm wide. It preserves nine bifurcating costae, with an average distance of 3 mm between them. The costae start pointing anteriorly(?) at the central axis; about 4 mm away from the axis, they bifurcate and bend posteriorward(?) at an angle of ~60–70°.
Material
One specimen from the upper part of the Lincoln Creek Formation, found in weathered talus, north-facing roadcut in the southwest corner of Sec. 31, T.17N., R.6W., Grays Harbor County, Washington State; coordinates: 46.909866°N, 123.489352°W. The specimen is housed at the Swedish Museum of Natural History, Department of Paleobiology, under catalog number NRM PAL P19808. The only identifiable fossil associated with the egg capsule is a heterodont bivalve, possibly belonging to Astarte.
The locality is approximately 30 m or less stratigraphically below LACMIP loc. 17102, upper part of the Lincoln Creek Formation, possibly latest Oligocene. Squires et al. (Reference Squires, Goedert and Benham1999) assigned LACMIP loc. 17102 to the early Miocene on the basis of overlapping age ranges of several invertebrates, including the gastropod Turritella oregonensis (Conrad, Reference Conrad1865), known from early to middle Miocene rocks of Oregon and Washington (e.g., Moore, Reference Moore1963; Addicott, Reference Addicott1976a, Reference Addicottb). However, T. oregonensis has been reported from rocks of the Clallam Formation and along with the associated molluscan fauna formed the basis of the regional Pillarian molluscan stage, previously thought to encompass most of the early Miocene (Addicott, Reference Addicott1976a, Reference Addicottb; Moore and Addicott, Reference Moore and Addicott1987). Magnetostratigraphic work in Oregon and Washington has shown that the Pillarian might actually have been of very short duration, and entirely or mostly latest Oligocene (Prothero et al., Reference Prothero, Bitboul, Moore, Niem and Prothero2001; Prothero and Burns, Reference Prothero, Burns and Prothero2001). Deposition is thought to have occurred at depths of as much as 200 m (Squires et al., Reference Squires, Goedert and Benham1999); however, a concentrated zone of reworked and bivalve-bored fossiliferous concretions encrusted by bryozoans, barnacles, and serpulids at LACMIP loc. 17102 indicates an abrupt shallowing and depositional hiatus of unknown duration in this part of the Lincoln Creek Formation (Feldmann et al., Reference Feldmann, Schweitzer and Goedert2018).
Remarks
The missing embryo cavity makes interpretation of this fossil as being part of either the beak (anterior part of the capsule) or the pedicle (posterior part of the capsule) difficult. We interpret it as part of the pedicle because the preserved central filament shows no widening in any direction, which seems more commonly the case in the pedicle than in the beak of chimaeroid egg capsules. The apparent shortening of the costae toward the anterior (in the orientation in our figures) is likely an artifact because the lateral ends of the costae are not preserved in the more anterior costae.
Vaillantoonia sp. is most similar to the Late Cretaceous V. newmexicana (Brown, Reference Brown1946), whose costae are also somewhat bent and point posteriorly after the bend. The only other Cenozoic chimaeroid ichnospecies, the Oligocene V. alaskana (Brown, Reference Brown1946) from the Katalla Formation in Alaska, differs by having more densely spaced costae that hardly bend. Ichnospecies with similar bifurcating costae include V. stelcki (Warren, Reference Warren1948) from the Upper Jurassic of Alberta, Canada, V. schernfeldensis (Duffin et al., Reference Duffin, Lauer and Lauer2022) from the Upper Jurassic of southwestern Germany, and V. gilli Hay, Reference Hay1929 from the Upper Cretaceous of Wyoming and Colorado, USA (Hay, Reference Hay1929; Harrison et al., Reference Harrison, Kirkland, Fischer, San Miguel, Wood and Santucci2021).
A more complete specimen with the same morphological features as Vaillantoonia sp. from Washington was found in the early Oligocene part of the Keasey Formation in Oregon. It is curated in the Condon Fossil Collection (University of Oregon) as no. 42802, from locality no. 3951. Unfortunately, this specimen was not available to us for study.
Acknowledgments
We thank J. Fischer (Thallichtenberg) and an anonymous reviewer for their insights, and J. Fischer also for subsequent discussions. T. Neubauer (Munich) is thanked for advice on the ICZN, and D. Merle and C. Noyes (Paris), A. Folie (Brussels), and J. Cuvelier (Lille) are thanked for their help with trying to locate the holotype of Vaillantoonia virei.
Declaration of competing interests
The authors declare no competing interests.
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