Aeduellidae indet

Aeduellidae indet .

( Figs 9-11)

MATERIAL. — An isolated anterior supraorbital ( MHNT.PAL. 2023.9.3 [ Fig.9A, B]) , an isolated maxilla ( MHNT.PAL. 2023.9.5 [ Fig. 9E, H]), ( MHNT.PAL.2023.30.1a and MHNT.PAL.2023.30.1b [respectively Fig. 9F, I, G, J]) , an isolated dentary ( MHNT.PAL.2023.30.4 [ Fig. 9C, D]) , two isolated operculums ( MHNT.PAL. 2023.9.17 [ Fig. 10C, E]; MHNT.PAL. 2023.9.22 [ Fig. 10A, B]) , six isolated cleithra ( MHNT. PAL. 2023.9.13 [ Fig. 10 I-K]; MHNT.PAL. 2023.9.15 [ Fig. 10G, H]; MHNT.PAL. 2023.9.23 , MHNT.PAL. 2023.9.27 , MHNT. PAL. 2023.9.28 and MHNT.PAL.2023.30.2 ) , four isolated supracleithra ( MHNT.PAL. 2023.9.7 , MHNT.PAL. 2023.9.8 [ Fig. 10N, O]; MHNT.PAL. 2023.9.9 [ Fig. 10L, M]; MHNT.PAL. 2023.9.16 [ Fig. 10P, Q]) , two isolated indeterminate cranial bones ( MHNT. PAL. 2023.9.4 [ Fig. 10D, F]; and MHNT.PAL.2023.9.38 ) , an isolated ridge scale ( MHNT.PAL. 2023.9.6 [ Fig. 11D]) , articulated scales ( MHNT.PAL. 2023.9.20 [ Fig. 11A]; MHNT.PAL. 2023.9.24 [ Fig. 11B]; MHNT.PAL. 2023.9.25 ) and isolated scales ( MHNT. PAL. 2023.9.26 ; Fig. 11C]; MHNT.PAL.2023.9.42 ) .

DESCRIPTION

MHNT.PAL. 2023.9.3 ( Fig. 9A, B) is an oblong bone, measuring 4.5 mm by 1.5 mm. It is strongly ornamented with dorsoventrally elongated ridges and interpreted here as the anterior supraorbital. Its shape is ovoid-to-L-shaped, with rounded edges and a wider dorsal region.

MHNT.PAL. 2023.9.5 ( Fig. 9E, H) is clearly identifiable as a maxilla, while MHNT.PAL.2023.30.1 has two associated maxillae ( Fig. 9 F-I, G-J). The maxilla MHNT.PAL. 2023.9.5 is 21 mm long, 10 mm wide posteriorly (length/width ratio 2.1) and 5 mm wide anteriorly. The bone is missing in some areas, but is visible as a counterprart on the matrix, and the postero-dorsal part and the anterior tip of the bone are missing. Tubular teeth are only preserved in the most anterior region of the ventral margin of the maxilla. No flat tubercle ornamentation is visible on MHNT.PAL. 2023.9.5, but it is distinguishable on its counterpart. In MHNT.PAL.2023.30.1, the two associated maxillae are 36 mm apart. The more complete of the two (MHNT.PAL.2023.30.1a) is fully preserved and measures 25 mm long by 10 mm wide posteriorly (length/width ratio of 2.5) and 3 mm wide anteriorly. The second maxilla MHNT.PAL.2023.30.1b preserves only its posterior part and measures 20 mm wide posteriorly. Tubular teeth are only visible on MHNT.PAL.2023.30.1a but the ornamentation, composed of flat tubercles, is visible on the lateral face of the posterior part of both MHNT.PAL.2023.30.1a and MHNT.PAL.2023.30.1b. The identical dimensions and morphology of these maxillae MHNT.PAL.2023.30.1a and MHNT.PAL.2023.30.1b suggest they belong to the same individual.

MHNT.PAL.2023.30.4 ( Fig. 9C, D) is a dentary preserved in part and counterpart, its anterior end is missing. It measures 13 mm long, 6 mm wide posteriorly (length/width ratio of 2.1) and 1.3 mm wide anteriorly, is curved and presents a longitudinal mandibular canal as well as mandibular pores appearing as alveolar cavities. The posterior part is enlarged and rectangular and form the dentary plate.

MHNT.PAL. 2023.9.17 ( Fig. 10C, D) and MHNT. PAL. 2023.9.22 ( Fig. 10A, B) are both partial operculums:

MHNT.PAL. 2023.9.17 is rounded as preserved, of 14 mm of diameter, and slightly ornamented by ridges, which are parallel to the bone edges (growth lines), and flat tubercles on its lateral surface. MHNT.PAL. 2023.9.22 is rectangular as preserved, of 20 mm of anterior margin, and strongly ornamented by wrinkles parallel to the bone edges (growth lines) and flat tubercles on its lateral surface, along the growth lines.

MHNT.PAL. 2023.9.4 ( Fig. 10E, F) is an partial indeterminate cranial bone, ornamented with several ridges parallel to its edges (growth lines) and visible on its lateral surface. Only a portion is preserved, measuring 7 mm long and 5mm wide. Its incomplete nature prevents further identification. The shape of the ornamentation is similar to that of a postrostral bone, but the bone is too incomplete to confirm this.

MHNT.PAL.2023.9.38 is also a partial indeterminate cranial bone, ornamented with several ridges that follow its curvature. Its preserved portion is ovoid, of 7 mm long and 3 mm wide. Its incomplete nature renders its identification impossible.

MHNT.PAL. 2023.9.13 (14 mm long and 27 mm high [ Fig. 10 I-K]), MHNT.PAL. 2023.9.15 (13 mm long and 26 mm high [ Fig.10G, H]), MHNT.PAL. 2023.9.23 (4.5 mm long and 10 mm high), MHNT.PAL. 2023.9.27 (2.3 mm long and 4.5 mm high), MHNT.PAL. 2023.9.28 (5 mm long and 9 mm high) and MHNT.PAL.2023.30.2 (13 mm long and 25 mm high) are all identifiable as cleithra. They are ovoid in shape with a very pronounced relief, and have a large ridge that runs dorsoventrally and separates them into two branches (lateral and ventral). The lateral branch of these cleithra is elliptical and ornamented with marked ridges and a dorsally extending process and a concave anterior edge. The ventral branch is much narrower, has a concave edge and forms a ventrally extending process.MHNT.PAL. 2023.9.13, MHNT. PAL. 2023.9.23 and MHNT.PAL.2023.30.2 are preserved as parts and counterparts. The dorsal process of the lateral branch of MHNT.PAL. 2023.9.15 is partly missing. MHNT. PAL. 2023.9.27 and MHNT.PAL. 2023.9.28 are complete.

MHNT.PAL. 2023.9.8 (15 mm high and 4 mm long, length/width ratio 3.75 [ Fig.10L, M]), MHNT.PAL. 2023.9.9 (11 mm high and 4 mm long, incomplete [ Fig. 10N, O]) and MHNT.PAL. 2023.9.16 (18 mm wide and 5 mm high, length/width ratio 3.6 [ Fig. 10P, Q]) are elliptical, dorsoventrally elongated bones, and all with a sensory canal passing through the first dorsal quarter of the bone. They are identified here as supracleithra and the sensory canal as the lateral canal. The supracleithrum process is clearly visible on all specimens except MHNT.PAL. 2023.9.7 which is not complete: this process forms a small dorsal projection. MHNT. PAL. 2023.9.7 (10 mm high and 5 mm wide) preserves only its ventral half, but its shape and ornamentation are also characteristic of a supracleithrum. MHNT.PAL. 2023.9.8 and MHNT.PAL. 2023.9.9, preserved laterally, are ornamented with longitudinal ridges and a few flattened tubercles on their lateral surface. MHNT.PAL. 2023.9.9 is also preserved by its dorsal half. MHNT.PAL. 2023.9.16, preserved in medial view, presentmedially by two strong crests (crista anterior and crista posterior). The crista anterior starts from the lateral canal, runs ventrally and ends along the anterior margin of the bone. The crista posterior also starts from the lateral canal and ends at the last quarter of the posterior margin of the bone.

MHNT.PAL. 2023.9.6 ( Fig. 11D) is an isolated hexagonal to oval ridge scale (6.5 mm wide by 10 mm long) covered with a thin layer of ganoine. It has no serrations and its ornamentation consists of light growth lines and marked ridges. A marked ridge runs longitudinally across its middle, dividing it into two regions (left and right) of equal size.

MHNT.PAL. 2023.9.20 ( Fig. 11A) comprises five articulated scales, with four scales located in the same horizontal row and one straddling the second and third scales in this row. These scales are rhombic and also covered with a thin layer of ganoine. They have no serrations and their ornamentation consists of light growth lines. MHNT.PAL. 2023.9.24 ( Fig. 11B) comprises two articulated scales on the same vertical row. They are semi-rectangular in shape and also covered with a thin layer of ganoine. They have slight serrations on their posterior edge (nine on the dorsalmost scale and eight on the ventralmost scale) and their ornamentation consists of light growth lines. MHNT.PAL. 2023.9.25 includes two disarticulated scales, fragments of scales and the impression of four articulated scales in the same vertical row. These scales are semi-rectangular in shape and covered with a thin layer of ganoine. They have light serrations on their posterior edge and their ornamentation also consists of slight growth lines. One scale shows a peg process. MHNT. PAL. 2023.9.26 ( Fig. 11C) comprises a rectangular isolated scale covered with a thin layer of ganoine. Its dorsal part is missing but this scale shows eleven serrations on its posterior margin and its ornamentation consists of light growth lines. At least, MHNT.PAL.2023.9.42 is an isolated rhombic scale covered with a thin layer of ganoine. It has no serrations and its ornamentation consists of light growth lines.

COMPARISONS

The anterior supraorbital MHNT.PAL. 2023.9.3 is ornamented with parallel ridges and ovoid-to-L-shaped: these features allow it to be assigned to Aeduellidae ( Heyler 1969; Poplin & Dutheil 2005). This anterior supraorbital is not fused with a nasal, whereas other known aeduellid specimens show nasals fused to the anterior supraorbital: this variation in the fusion of the bones has already been observed within the Aeduellidae by Heyler (1969) and Štamberg (2007, 2018, 2024). The fusion of the nasal bone with the anterior supraorbital bone forms a bone which is sometimes referred to as the nasal sensu lato ( Heyler 1969). The ovoid shape and ornamentation of MHNT.PAL. 2023.9.3 are key features which are found in Aeduella blainvillei ( Štamberg 2018) . However, the nasal region of Decazella vetteri , which remains poorly described, could also correspond to the morphology observed in MHNT.PAL. 2023.9.3 ( Heyler 1969). Pending a more precise description of the nasal region of D. vetteri , we prefer staying prudent and referring MHNT. PAL. 2023.9.3 to Aeduellidae indet.

The three maxillae MHNT.PAL. 2023.9.5 and MHNT. PAL.2023.30.1a-b are very similar in morphology and proportions, suggesting the same taxon. They are attributable to Aeduellidae on the basis of their low triangular shape, their widen posterior region, and their ornamentation with flat tubercles and their tubular teeth ( Heyler 1969; Poplin & Dutheil 2005). Within the Aeduellidae , characters can be used to distinguish the maxillae: the absence of a prominent posteroventral angle and a length/width ratio between 2.1 and 2.5 in MHNT.PAL. 2023.9.5 and MHNT.PAL.2023.31.1a, MHNT.PAL.2023.31.1b, however, suggest that they are related to Bourbonnella spp. , Neslovicella spp. , Decazella vetteri, Amelangia ornata , Westollia crassa or Aeduella blainvillei ( Heyler 1969; Štamberg 2007, 2010, 2018, 2024; Štamberg & Werneburg 2023). As it is impossible to assign MHNT.PAL. 2023.9.5 and MHNT.PAL.2023.31.1a, MHNT.PAL.2023.31.1b to any of these taxa in particular, we prefer referring them to Aeduellidae indet.

The dentary MHNT.PAL.2023.30.4 does not preserve any tubular teeth that would allow to assign it confidently to Aeduellidae ( Poplin & Dutheil 2005) . However, its general curvature, its gracile morphology, the shape of the dentary plate and the presence of a mandibular canal support an attribution within Aeduellidae ( Heyler 1969; Poplin & Dutheil 2005). As with the maxillae described above, there are distinct dentaries within the Aeduellidae : the dentary plate of MHNT.PAL.2023.30.4 resembles that of Bourbonnella spp. , Neslovicella spp. , Decazella vetteri, Amelangia ornata , Westollia crassa or Aeduella blainvillei ( Heyler 1969; Štamberg 2007, 2010, 2018, 2024; Štamberg & Werneburg 2023). Once again, as it is impossible to choose here, we refer MHNT. PAL.2023.30.4 to Aeduellidae indet.

The operculums MHNT.PAL. 2023.9.22 and MHNT. PAL. 2023.9.17 are attributed to Aeduellidae on the basis of their typical ornamentation, size and shape (e.g. Poplin & Dutheil 2005). This is consistent with the multiple presence of Aeduellidae remains in the La Découverte locality ( Vetter 1968; Heyler 1969, 2000; this study). Due to the partial nature of MHNT.PAL. 2023.9.17 and MHNT.PAL. 2023.9.22, it is impossible to compare them with the operculums of known Aeduellidae , including those from the Bourran Formation. Consequently, we refer them to Aeduellidae indet.

The indeterminate cranial bones MHNT.PAL. 2023.9.4 and MHNT.PAL.2023.9.38 are attributed to Aeduellidae on the basis of their ornamentation and, to a lesser degree, of the great abundance of various remains of this family in the Bourran Formation ( Heyler 1969; Poplin & Dutheil 2005). Their shape and ornamentation rule out their identification as scapular bones, but it is difficult to assign them to a particular series of cranial bones MHNT.PAL. 2023.9.4 ornamentation is similar with the postrostrals of Decazella vetteri ( Fig. 5 A-D), but its very partial nature calls for caution in its identification. Moreover, considering the preservation state of MHNT.PAL. 2023.9.4 and MHNT.PAL.2023.9.38, it is preferable to assign them to Aeduellidae indet.

ThecleithraMHNT.PAL. 2023.9.13,MHNT.PAL. 2023.9.15, MHNT.PAL. 2023.9.23, MHNT.PAL. 2023.9.27, MHNT. PAL. 2023.9.28 and MHNT.PAL.2023.30.2 can be assigned to Aeduellidae on the basis of their ovoid shape, ornamentation and morphology of their two branches (lateral and ventral) ( Heyler 1969; Štamberg 2007, 2010, 2018). Their ovoid and elongated shape and their both dorsal and ventral processes resemble those of the cleithra of Neslovicella spp. , Aeduella blainvillei , Bourbonnella spp. , Decazella vetteri , Westollia crassa and Amelangia ornata ( Heyler 1969; Poplin 2001; Poplin & Dutheil 2005; Štamberg 2007, 2010, 2018, 2024; Štamberg & Werneburg 2023). Given the similarity between cleithra of different Aeduellidae , it is preferable to refer MHNT.PAL. 2023.9.13, MHNT.PAL. 2023.9.15, MHNT.PAL. 2023.9.23, MHNT.PAL. 2023.9.27, MHNT. PAL. 2023.9.28 and MHNT.PAL.2023.30.2 to Aeduellidae indet. MHNT.PAL. 2023.9.23, MHNT.PAL. 2023.9.27 and MHNT.PAL. 2023.9.28 are smaller, rounder, less ornamented and with less relief than MHNT.PAL. 2023.9.13, MHNT. PAL. 2023.9.15 and MHNT.PAL.2023.30.2. These differences in morphology and size suggest that MHNT.PAL. 2023.9.23, MHNT.PAL. 2023.9.27 and MHNT.PAL. 2023.9.28 are juvenile individuals.

The supracleithra MHNT.PAL. 2023.9.7, MHNT. PAL. 2023.9.8, MHNT.PAL. 2023.9.9 and MHNT. PAL. 2023.9.16 can be assigned to Aeduellidae on the basis of their ornamentation, the presence of the lateral canal, their proportions as well as the cristae observed on MHNT. PAL. 2023.9.16 ( Heyler 1969; Štamberg 2007, 2010, 2018). The morphology of the supracleithrum differs only slightly between the different Aeduellidae species. The arrangement of the anterior and posterior cristae of MHNT.PAL. 2023.9.16 are identical to what observed in Neslovicella rzehaki and Aeduella blainvillei ( Štamberg 2007, 2018). However, these data are missing for most other Aeduellidae for which the supracleithrum is not known in medial view. MHNT.PAL. 2023.9.7, MHNT.PAL. 2023.9.8 and MHNT.PAL. 2023.9.9 show ornamentation found in all Aeduellidae , including previously described specimens of Decazella vetteri from the Bourran Formation (e.g. MNHN.DEC.24 and MNHN.DEC.30, Heyler 1969: figs 122, 123). Given the similarity between the supracleithra of different Aeduellidae , it is preferable to refer MHNT.PAL. 2023.9.8, MHNT.PAL. 2023.9.9 and MHNT. PAL. 2023.9.16 to Aeduellidae indet.

The scales MHNT.PAL. 2023.9.20, MHNT.PAL. 2023.9.24, MHNT.PAL. 2023.9.25, MHNT.PAL. 2023.9.26 and MHNT. PAL.2023.9.42 can be assigned to Aeduellidae on the basis of their rectangular to rhombic shape, thin ganoine layer and peg and socket articulation when present (e.g. Heyler 1969; Yankevich & Minich 1998; Štamberg 2007, 2018). The ridge scale MHNT.PAL. 2023.9.6 can be assigned to Aeduellidae on the basis of its hexagonal to oval shape, its thin ganoid layer and the presence of a marked median longitudinal ridge (e.g. Heyler 1969; Štamberg 2007, 2018). This attribution is consistent with the multiple presence of Aeduellidae remains in the La Découverte locality ( Vetter 1968; Heyler 1969, 2000; this study). In Aeduellidae , the shape and ornamentation of the scales vary greatly depending on their position on the body and the individual age of the specimens (e.g. Štamberg 2007, 2018). The flank scales through which the lateral sensory canals pass are the largest scales, rectangular in shape, and with a posterior margin showing marked serrations (e.g. Štamberg 2007). Flank scales in the anterior region are rectangular in shape, with marked serrations on their posterior margin (e.g. Štamberg 2007). The isolated scale MHNT.PAL. 2023.9.26 is rectangular with serrations, which may correspond to a scale in the anterior part of the flanks or to a scale through which the lateral canal passes. These serrations become less and less distinct, and the shape of the scales becomes rhombic towards the posterior, ventral and dorsal regions (e.g. Štamberg 2007). The scales MHNT. PAL. 2023.9.24 and MHNT.PAL. 2023.9.25 have a semi-rectangular shape with small serrations, corresponding to an intermediate morphology between the scales of the anterior region and those of the extremities of the posterior, ventral or dorsal regions. The scales MHNT.PAL. 2023.9.20 and MHNT.PAL.2023.9.42 are rhombic and devoid of serrations, corresponding to scales at the ends of the posterior, ventral or dorsal regions. Due to their position anterior to the dorsal fin, they are rarely distinct on articulated specimens (e.g. Heyler 1969). The scales of Aeduellidae are particularly well known, but do not allow to distinguish taxa (e.g. Štamberg 2007, 2018). Similarly, the ridge scales of Aeduellidae are still poorly documented and currently do not allow more precise attributions ( Heyler 1969; Štamberg 2007, 2018). The scales described here cannot be attributed to one of the two Aeduellidae known from the Bourran Formation ( Aeduella and Decazella ) ( Heyler 1969). We therefore refer MHNT.PAL. 2023.9.6, MHNT.PAL. 2023.9.20, MHNT.PAL. 2023.9.24, MHNT.PAL. 2023.9.25, MHNT.PAL. 2023.9.26 and MHNT.PAL.2023.9.42 to Aeduellidae indet.