Among the contentious issues discussed by both Martin and Vincent (2013) and Young et al. (2014a) are the availability of the species name Machimosaurus mosae and its potential consequences on the taxonomy of the genus. Martin and Vincent (2013, p. 193) claimed indeed that the name Machimosaurus mosae is unavailable. It was published for the first time in a memoir (Sauvage and Liénard, 1879), in which a manuscript work (Liénard, 1876) is explicitly credited with the authorship of the species, funded at the time as Teleosaurus mosae. Because this work is not published according to articles 8 and 9 of the Code (ICZN, 1999), Martin and Vincent (2013) felt justified to declare Teleosaurus mosae and its later citations and combinations as invalid – nomenclaturally and therefore taxonomically.

However, the conclusion of Martin and Vincent (2013) is strongly contested by Young et al. (2014a, p. 32). They object notably that the erection of the name M. mosae by Sauvage and Liénard (1879) did fulfill the requirements of articles 8, 11, and 12 of the Code (ICZN, 1999), regardless of the credit originally given to Liénard (1876). The conclusion of Young et al. (2014a) about this matter is correct. In addition, Young et al. (2014a) refer to articles 11.6 and 50.7 of the Code (ICZN, 1999) to further justify the availability of Machimosaurus mosae and its authorship in spite of its use as a junior synonym of Teleosaurus mosae by Sauvage and Liénard (1879). However, this appeal is unnecessary. As defined in the Glossary of the Code, a synonym is indeed “Each of two or more names of the same rank used to denote the same taxonomic taxon” (ICZN, 1999). M. mosae and T. mosae are therefore not synonyms, but different “combinations” of the same specific name, even if the latter is a mere manuscript name. As such, Teleosaurus mosae is a nomen nudum and the species name Machimosaurus mosae is not a new combination as per the Code and retains Sauvage and Liénard, 1879 as original authorship.

In fact, another interesting issue has been raised by the creation of the new species name Machimosaurus buffetauti by Young et al. (2015), as defined by Young et al. (2014a). Besides the holotype SMNS 91415, the authors assign to this species the complete skull and mandible in occlusion from the Kimmeridgian of Montmerle, Ain and curated in the Musée de Brou, Bourg-en-Bresse (Buffetaut, 1982 and Chanel, 1905 and complementary views in Fig. 1). The latter specimen is of special interest because it has been a source of dispute during the decades following its discovery (see Buffetaut, 1982 and Chanel, 1905 for a detailed history). In particular, it has been given several species names which have been since considered as unavailable, notably by Buffetaut (1982) and Young et al. (2014a). Nevertheless, a careful re-examination of the available literature reveals that the nomenclature of the Bourg-en-Bresse specimen is more complex than previously thought.

The specimen was first trusted by the Société d’Émulation de l’Ain to E. Eudes-Deslongchamps for preparation and study. As recounted by Jarrin (1870), the palaeontologist identified it as a new species of Steneosaurus and asked for advice to the society, proposing the epithet “burdigalensis”. This offer was turned down by the members, who instead suggested “burgo-bressiensis” then the more simple “burgensis” for species name. Three years later, Jarrin (1873) provided a brief and rather lyrical account about the Bourg-en-Bresse skull in which it is designated as “Steneosaurus burgensis”. He also included portions of the correspondence of E. Eudes-Deslonchamps who explained the progress of the preparation. The same “Steneosaurus burgensis” is again cited by Jarrin (1876) in a short passage.

Later, the history of the Bourg-en-Bresse skull was published in detail by Chanel (1905) who included extended citations of the local press and various exchanges that occurred between the Société d’Émulation de l’Ain, Eudes-Deslongchamps, and the mayors of Bourg-en-Bresse. The repatriation of the skull to Bourg-en-Bresse was announced in 1875 in the Courrier de l’Ain in which the author ended regretting that the Steneosaurus had been named S. burgensis: “Pourquoi Burgensis ? Bourg est à 3 lieues de Montmerle et les terrains jurassiques qui contiennent les Sténéosaures s’arrêtent à moitié-chemin, à Jasseron. Pourquoi ne l’a-t-on pas appelé tout simplement Steneosaurus Montmerli ou Chanuti ? Ce dernier nom eût rappelé le généreux donateur d’une pièce paléontologique d’une grande valeur.” (Chanel, 1905, p. 16). The municipality agreed with this opinion and decided to make a concession by renaming the Bourg-en-Bresse specimen “Steneosaurus Burgensis Chanuti”.

Now, what is the respective status of “Steneosaurus burdigalensis”, “S. burgobressiensis”, “S. burgensis”, “S. montmerli”, “S. chanuti”, and “Steneosaurus burgensis chanuti”? S. burgensis and Steneosaurus burgensis chanuti have been explicitly considered as nomina nuda by Buffetaut (1982) and recently by Young et al. (2014a)–who misspelt it “chanti” – and in their addendum (2015). The latter authors, in particular, appeal to Article 12 of the Code (ICZN, 1999). They claim that neither Jarrin, 1873 and Jarrin, 1876 nor Chanel (1905) followed the requirements (Young et al., 2014a and Young et al., 2015). However, a close examination of Article 12 indicates that, in fact, Chanel (1905) established correctly – albeit involuntarily – the name Steneosaurus burgensis chanuti. Article 12 first states that: “12.1. Requirements. To be available, every new name published before 1931 must satisfy the provisions of Article 11 and must be accompanied by a description or a definition of the taxon that it denotes, or by an indication.” If we agree with Young et al. (2014a) regarding the absence of a description or a definition in Jarrin, 1870, Jarrin, 1873 and Jarrin, 1876 and Chanel (1905), the latter nevertheless included an indication as per Article 12.2. Eight kinds of indication are listed under this article, among which is “12.2.7. the proposal of a new genus-group name or of a new species-group name in association with an illustration of the taxon being named, or with a bibliographic reference to such an illustration” (ICZN, 1999). Hence, the presence of a plate on which the Bourg-en-Bresse skull is figured as “Steneosaurus Burgensis Chanuti” is alone sufficient to warrant its availability and to credit Chanel (1905) as its author. Conversely, the six other names appear to be actual nomina nuda.

It is still necessary to settle a few points before applying the name of Chanel (1905). According to the Principle of Coordination, alias Article 46, indeed, the erection of the species name “burgensis” and infraspecific name “chanuti” by Chanel (1905) implies that an infraspecific and a specific equivalents, respectively, have been created at the same time (ICZN, 1999). Also, both “burgensis” and “chanuti” have been funded in the same publication, so their relative precedence needs to be determined. Fortunately, Article 24.1 clearly indicates that, “When homonyms or synonyms are established simultaneously, but proposed at different ranks, in the family group, genus group or species group the name proposed at higher rank takes precedence” (ICZN, 1999).

As a consequence, the first available and valid name assigned to the Bourg-en-Bresse specimen is Steneosaurus burgensis Chanel, 1905 with Steneosaurus chanuti Chanel, 1905 as an objective senior synonym. Both names take therefore priority over Machimosaurus buffetauti Young et al., 2015, in the case SMNS 91415 and the Bourg-en-Bresse skull are conspecific as concluded by Young et al. (2014a). Conversely, the names “Steneosaurus burdigalensis”, “S. burgobressiensis”, and “S. montmerli” and the citations of the names “Steneosaurus burgensis” and “S. chanuti” predating the publication of Chanel (1905) are all nomina nuda.

The specific distinction of M. mosae from SMNS 91415 is questionable. Young et al. (2015) designated the holotype of Machimosaurus buffetauti on specimen SMNS 91415, originally described by Martin and Vincent (2013) and referred to M. hugii. The central argumentation of Young et al. (2014a) establishing differences between the M. mosae neotype and SMNS 91415 essentially rests in their paragraph 4.2. but other differences can be found in their diagnoses of the different proposed species of Machimosaurus. Their argumentation for the difference between the M. mosae neotype and SMNS 91415 is structured around four main points: •

ontogeny;

These are discussed below.

There is a single known occurrence of the genus Machimosaurus in the Late Jurassic of Ethiopia, which consists of the rostral end of sutured dentary ramii (Bardet and Hua, 1996). In their revision of Machimosaurus, Young et al. (2014a) recognized two diagnostic characters and erected the species M. nowackianus. These characters are based on relative dimensions of the inter-alveolar spaces compared to the size of the alveoli and to the transverse width at the level of the dentary tooth #4. Young et al. (2014a) state that in M. nowackianus, the inter-alveolar spaces between dentary alveoli #2 and #3 and between alveoli #3 and #4 is less than half the length of dentary alveolus #2. Although this seems right on the left dentary ramus, the inter-alveolar space appears to be as long as the length of dentary alveolus #2 on the right ramus. According to the figures available in Bardet and Hua (1996) and in Young et al. (2014a), the left dentary alveolus #2 in the Ethiopian specimen appears twice as large as the right dentary alveolus #2. Moreover, there exists some variability in the right versus left inter-alveolar space between dentary alveoli #1 and #2 in SMNS 91415 (see Fig. 7A in Martin and Vincent, 2013), thus questioning the validity of this character as diagnostic.

The second character used to diagnose M. nowackianus concerns the transverse width at the level of the large fourth dentary alveolus. Young et al. (2014a) state that this distance is smaller in the Ethiopian specimen than in other species of Machimosaurus, when the dentary is known. To quantify comparisons, we express this character as the ratio of the distance between the lingual margins of the opposing dentary alveoli #4, over the distance between the maximal widths of the dentary at the level of the alveoli #4. We find that SMNS 91415 has a ratio of 0.54 whereas the Ethiopian specimen has a ratio of 0.4, which are not substantially different. In addition, the lingual margin of the right and left alveoli #4 in the Ethiopian specimen are clearly damaged, giving the false impression that the alveolar outline is larger that it is actually in this specimen. According to the preserved labial contour, reconstructing the outline of the alveoli #3 in the Ethiopian specimen allows us to estimate a ratio of 0.5. Therefore, based on this only known specimen, we find no compelling evidence warranting a distinct species of Machimosaurus in Ethiopia. Certainly, this will have to be reevaluated with more complete discoveries.

To sum up, we recognize that the only significant differences between SMNS 91415 and the M. mosae neotype are the depressions on the quadrates of the former and the exostoses in the latter, but the taxonomic utility of such features appears unlikely if they result from pathologies. Moreover, individual variability and preservation should be taken into account. We consider the genus Machimosaurus as having a single valid species, Machimosaurus hugii Meyer, 1837, and we follow the revised diagnosis established in an earlier study (Martin and Vincent, 2013) for Machimosaurus. The holotype of ‘Simolestes’ nowackianus Huene (1938) is also too incomplete and should be referred to Machimosaurus sp. as originally proposed by Bardet and Hua (1996). As stated previously in Martin and Vincent (2013), we do not exclude the presence of other species of Machimosaurus, but a larger sampling of diagnostic specimens is currently lacking or await restoration and subsequent study.