Dyrosauridae de Stefano 1903
Year: 2025
Type: other
Abstract: Dyrosauridae de Stefano 1903 Hyposaurinae Nopcsa 1928 Hyposaurinae indet. Type horizon and age: Recovered in a marine sandstone (bed 11, Fig. 1D), provisionally associated with a topmost unit of the Mocuio Formation, Maastrichtian (Upper Cretaceous) (Strganac et al. 2014). Type locality: Cemitério de Bentiaba, Municipality of Moçâmedes, Namibe Province, Angola (14°17′05.5′′S; 12°22′34.8′′E). Material: Posterior portion of the skull including the braincase, right quadratojugal, part of the left ectopterygoid wing, one tooth and bone fragments accessioned as MGUAN-PA548 (Fig. 2). State of preservation: The specimen comprises an articulated posterior part of the skull, a part of the left ectopterygoid, one tooth, and several small bone fragments (Fig. 2A). The tooth is eroded at its base, but is in good condition, unlike the rest of the material. The exposed and covered bone surface was eroded to a similar degree, precluding the identification of some details of the suture lines. Due to the non-preservation of the entire parietal process, only the base of the process is preserved with a cavity in the centre. In posterior view, the supraoccipital/exoccipital have been severely eroded in their central right side. However, it is possible to observe the posterior part of the parietal, the posterior parts of the squamosal, the supraoccipital, the exoccipitals, part of the basioccipital, the quadrates, and part of the quadratojugals (Supporting Information, Figs S1 and S 2). Description Parietal (Fig. 2B–D) The parietal is preserved only by the posterior portion and a part of the interfenestral bar, observable in dorsal view. The poor preservation of the specimen makes the suture lines with the squamosal hard to discern; however, comparison with data in the literature and extant crocodylians allow us to infer that these suture lines are closer to the interfenestral bar than to the lateral margin of the squamosal (Fig. 2D). Both the posterior and the anterior margins of the parietal are strongly eroded, and the posterior one is concave in dorsal view (ch. 90 [1]) (Fig. 2D). The parietal forms part of the posterior margin of the supratemporal fenestrae and creates a thin interfenestral bar dorsally (12-mm wide) (ch. 19 [1], 20 [0], and 25 [2]). The presence of ornamentation on the margins of the supratemporal fenestrae and on the parietal of MGUAN-PA548 cannot be ascertained due to the state of preservation (ch. 21 [1/2] and ch. 93 [3/4]). The posterior margin forms a gently sinuous suture with the supraoccipital and the parietal has a small occipital portion (ch.92 [1] and 96 [0]). Squamosal (Fig.2B–E) Dorsally, the squamosal is anteriorly extended to form part of the skull roof, constituting the posterior region of the supratemporal arch (= upper temporal bar or postorbital-squamosal bar) (Fig. 2D). The preserved supratemporal arch is situated more ventrally than the interfenestral bar, resulting in the cranial table being more convex than horizontal/flat in posterior view (ch. 159 [2]). The squamosal forms a part of the lateral and posterior margin of the supratemporal fenestrae. The margin is large and rounded. The posterior margins of the infratemporal fenestrae are unornamented. The parieto-squamosal transition is hard to recognize because of the poor state of preservation of the specimen. What can be discerned, is that these limits are not in the posteriormost margin of the supratemporal fenestra, but they are closer to the median axis of the cranium (Fig. 2D). The posterior surface of the squamosal is concave in the region lateral to the occipital tuberosities, with the squamosal extending posteriorly to a lesser extent than the occipital condyle (ch. 105 [1] and 107 [0]). In occipital view, the squamosal is also ventrally extended and the suture line with the left exoccipital can be observed running ventrolaterally, exhibiting a sharp prong (ch.103 [1], 104 [1], 106 [1], and 108 [1]) (Fig. 2B). In occipital view, above the occipital tuberosities, the squamosal and the parietal appear to have a small posterior lamina (also visible in dorsal view) that can be associated with the top of the post-temporal canal (Fig. 2B, D). This feature corresponds to character 94 of Jouve et al. (2021) described as the ‘posterior extension of the parietal’. However, in MGUAN-PA 548, the suture between the squamosal and parietal is unclear due to erosion. To avoid confusion, we will refer to this feature as an extension of the squamosal–parietal region, acknowledging the possibility that, in the studied specimen, the squamosal may also contribute to the extension. Supraoccipital/exoccipitals (Fig.2B–D) The supraoccipital is the most eroded element of the bones preserved in this specimen, and as such, in occipital view, informative morphological details are very difficult to discern. Although, the suture with the exoccipital is eroded, the parietal suture is visible, slightly concave, and gently sinuous ventrally (Fig. 2B). The supraoccipital presents a large hole (due to the preservation), measuring 60 mm wide and 20 mm high. The occipital tuberosities, even though not entirely preserved, are well-developed, widely separated and overhanging by an extension from the squamosalparietal region (ch. 94 [1] and 120 [2]). However, due to the state of preservation their shape is not clear. The right occipital tuberosity, more developed, is diagonally flattened due to the aforementioned hole on the occipital side. The left tuberosity has a rounded base, but the rest of it is not preserved. It is also unclear whether the occipital tuberosity and the post-temporal fenestra participate in the supraoccipital or not. The paraoccipital processes of the exoccipitals are well preserved, especially the left one. In occipital view (Fig. 2B), the large lateral suture of the left contact with the squamosal can be observed well, while the right one can only be inferred due to erosion (ch. 122 [1]). The paroccipital processes of the exoccipitals are ventrally directed along the quadrate, and they end with rounded and well-developed processes at the same level as the occipital condyle (ch. 119 [1]). The suture between the exoccipital and basioccipital is partially discernible, allowing for an approximate placement on the occipital condyle but the exoccipital largely participates (ch. 118 [0]). In ventral view, the exoccipitals do not bear any crest or ornamentation (ch. 123 [0] and 124 [0]). In occipital view, the foramen magnum is symmetrically flanked by two rounded structures positioned laterally and slightly dorsally (Fig. 2B). These bony projections, referred to here as bosses, measure approximately 15 mm in diameter and exhibit an occipital projection of just under 5 mm. Basioccipital (Fig.2B, D) The basioccipital is 26 mm long anteroposteriorly, 37 mm wide lateromedially and shows a depression on the ventral surface (ch. 129 [1]). In occipital view, MGUAN-PA548 presents a ‘V’-shaped morphology (tipping ventrally), and the occipital condyle is twice as wide as it is high (ch. 2 [2]). The posterior surface of the main body of the basioccipital below the condyle is not vertical; it is inclined, faces posteroventrally, and is visible in posterior view (ch. 132 [1]). Basisphenoid (Fig.2C) Only the posteriormost part of the basisphenoid is preserved. The medial 7 ustachian foramen is present, well visible in ventral view but not in occipital view (ch. 127[0]). Only the contact with the basioccipital has been preserved. A small fragment of the basisphenoid is also preserved and is placed to the right of the central block of the basisphenoid. Quadrate (Fig.2B–E) The quadrate is very long, almost flattened, directed posteroventrally (very verticalized), and sutured completely laterally with the squamosal (ch. 135 [2], 136 [0], 140 [1], and 141 [2]). Both the right and left quadrates are well-preserved, their suture lines with the exoccipitals are straight, and their condyles extend further ventrally than the occipital condyle (ch. 139 [1]). Contact with the squamosal is made along the posterior wall of the supratemporal fenestra, ventrally and laterally to the presumed location of the temporal canal. The quadrate has no ornamentation, and its entire surface is smooth. Only a small portion of the left quadratojugal is preserved and follows the same orientation as the quadrate. Lastly, the posterior margin of the infratemporal fenestra is posterior to the supratemporal fenestra margin (ch. 29 [1]). Foramen magnum (Fig.2D) Although its limits are severely eroded, the foramen magnum is located above the occipital condyle with a similar diameter as the latter in occipital view. In anterior view, the diameter of the foramen is reduced by half, forming a conical hole. In ventral view, it is possible to distinguish different foramina, here identified as: the foramen of the anterior bundle of the hypoglossal nerve (Fig. 2D —XII), the foramen of the posterior bundle of the hypoglossal nerve (Fig. 2D —XII), the cranioquadrate canal foramen (Fig. 2D —cqc), the foramen of the glossopharyngeal nerve (Fig.2D — IX), the foramen of the vagus nerve (Fig. 2D—X), the foramen of the accessory nerve (Fig. 2D —XI) and the median 8 ustachian foramen (Fig. 2D —mef). All these foramina have been named and identified following the nomenclature of Erb and Turner (2021). The first four foramina border the basisphenoid laterally (ch. 133 [0]). In ventral view, the medial 8 ustachian foramen is situated anterior to the posterior margin of the supratemporal fenestra (ch. 134 [1]). In the same view, it is possible to identify the cranioquadrate canals, which are hidden in occipital view by the exoccipital (ch. 131 [1]). These canals are positioned on the ventral side of the quadrate, just at the beginning of the exoccipital tuberosities. The temporal canals are filled with sediment and are indistinguishable in anterior view; however, an iron spot on the left side may indicate the position
Authors: Maréchal, Arthur, Rotatori, Filippo Maria, Merella, Marco, Puértolas-Pascual, Eduardo, Sequero, Cristina, Pereira, Ricardo, Nsungani, Pedro, Mateus, Octávio
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7083006286
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