Saltoposuchus connectens Huene 1921

Field: Earth and Planetary Sciences (Physical Sciences)

Saltoposuchus connectens Huene 1921 Diagnosis: A medium-sized non-crocodyliform crocodylomorph (femoral length SMNS 12596: 106 mm) distinguished by the following combination of character states (autapomorphies among non-crocodyliform crocodylomorphs are indicated with an asterix): enlarged anterior maxillary teeth (also present in Junggarsuchus sloani); antorbital fossa well defined, forming a complete circumference around the antorbital fenestra (also present in CM 29894, Kayentasuchus walkeri, and Dromicosuchus grallator); antorbital fenestra that is approximately half the size of the orbit*; an oval fossa on the ventral surface of the palatine outlined by a radially striated surface medially*; a dorsally expanded anterior end of the dentary (also present in Trialestes romeri and Hesperosuchus agilis, AMNH FARB 6758); splenial slightly involved in the symphysis (also present in Kayentasuchus walkeri); and a notch on the lateral side of the proximal head of the tibia*. Saltoposuchus connectens is additionally distinguished from Terrestrisuchus gracilis and Litargosuchus leptorhynchus in possessing a longitudinal crest along the dorsolateral surface of the squamosal; a distinct depression for the supratemporal fossa on the posterior end of the dorsal surface of the frontal; strongly sculpted and transversely wide osteoderms; a wide and short, robust ischial shass; and a robust femur that is longer than the tibia and fibula. Holotype: SMNS 12597 a–d (Fig. 2A–E), an associated skeleton comprising a partial skull and much of the postcranium. An isolated less angular SMNS 12597 e (Fig. 2F) and isolated right calcaneum SMNS 12597 f (Fig. 2G, H) were previously considered to belong to the holotype specimen (Huene 1921) but are here shown to not belong to the same individual as the holotype (see descriptions of respective bones below). Their assignment to Saltoposuchus connectens is tentatively maintained based on their corresponding morphology to other elements in SMNS 12597 a–d. Referred material: SMNS 12597e–f (Fig. 2F–H), isolated less angular and isolated right calcaneum; SMNS 12596 (Figs 3–5), a disarticulated skeleton including several skull elements; SMNS 55009 (Figs 6, 7), several postcervical vertebrae and part of the right hindlimb, including an incomplete pes; SMNS 12591a (Figs 8, 9), a largely complete, strongly dorsoventrally compressed skull and mandible. This specimen has undergone acidbased preparation since the description of this specimen by Sereno and Wild (1992), revealing additional morphological information, particularly on the palate (Fig. 9C, D); SMNS 12352 (Fig. 10), a largely complete, well preserved snout, and a less manus. Locality and horizon: The discontinued ‘Weisser Steinbruch’ sandstone quarries near Pfaffenhofen. Middle Stubensandstein Member of the Löwenstein Formation, middle Keuper (Norian, Late Triassic; Sues and Schoch 2013). Ontogenetic assessment: The relative sizes of the Saltoposuchus connectens specimens are compared in Table 2. Size discrepancy between the smallest (SMNS 12591a) and largest specimen (SMNS 55009) is inferred at 58.1%. The right femur of SMNS 12596, the second-largest specimen (90.2%), has been histologically sectioned. The interpretation of its relative age is somewhat ambiguous but the individual probably represents a sub-adult, since it is neither an early juvenile, based on the relative size and robusticity of its skeleton, nor skeletally mature, based on the presence of open neurocentral sutures in some of the presacral vertebrae and the absence of an outer circumferential layer (OCL; also known as an external fundamental system, EFS) and secondary osteons in the histological section (see discussion below). Description Skull Premaxilla: SMNS 12352a is the only specimen to preserve remains of the premaxilla and even in this specimen only a badly broken right premaxilla and a small fragment of the posterodorsal process of the less premaxilla are present (Fig. 10A, B). The premaxilla connects to the maxilla posteriorly and to the nasal posterodorsally. The right premaxilla preserves two teeth and is incomplete anteriorly. It bears a prominent posterodorsal process, which wedges between, and overlaps with, both the maxilla and nasal, as in other non-crocodyliform crocodylomorphs like Dromicosuchus grallator (Sues et al. 2003), differing from the tight suture between the premaxilla and maxilla seen in crocodyliforms (e.g. Colbert and Mook 1951). Thus, the maxilla did not contribute to the margin of the external naris in Saltoposuchus connectens, as was also indicated by Sereno and Wild (1992). Maxilla: The maxilla is preserved in SMNS 12596a, SMNS 12352a, and SMNS 12591a, and it thus allows for comparison betweenaspecimenunambiguouslyaưributableto Saltoposuchus connectens (SMNS 12596) and specimens with a controversial taxonomic identification (SMNS 12352, SMNS 12591a; Table 1). In fact, most of the features put forward to distinguish these specimens taxonomically have revolved around the maxilla (Ostrom 1981, Knoll and Rohrberg 2012). SMNS 12596a preserves a disarticulated, virtually complete, less maxilla (Fig. 3A). Based on the length of this element, this specimen is considerably larger than SMNS 12352 and SMNS 12591a (Table 2). It preserves four teeth, with the largest, the second counted from anterior, being partially shissed out of its alveolus, exposing much of the root. At least eight nutrient foramina are present dorsal to the alveolar margin in lateral view. SMNS 12352a has a virtually complete right maxilla, which preserves 14 teeth (Fig. 10A, B). A single tooth is clearly missing and therefore the maxillary tooth count is tentatively established at 15. Many nutrient foramina can be observed dorsal to the alveolar margin. Both maxillae of SMNS 12591a preserve nine teeth, an incomplete count (Fig. 8). On both sides, the posteriormost teeth are only represented by small protuberances. The posterior extent of the maxillary teeth is similar to that in SMNS 12352a, namely roughly at the level of the ventral foot of the lacrimal. This thus corroborates the interpretation of Sereno and Wild (1992) and opposes Ostrom (1981), who considered both specimens to be distinguishable taxonomically in part based on a difference in posterior extent of the maxillary teeth. The angle formed between the main body of the maxilla and its ascending process is 24° in SMNS 12596a, 29° in SMNS 12352a, and 9° in SMNS 12591a. The very sharp angle of SMNS 12591a can clearly be aưributable to the considerable dorsoventral compression of this specimen, as has been pointed out by previous authors (e.g. Sereno and Wild 1992). The alveolar margin is slightly convex in lateral view in its anterior half and very slightly concave in its posterior half in both SMNS 12596a and SMNS 12352a. In SMNS 12591a this curvature is much less distinct, but this too is clearly aưributable to its dorsoventral compression. This compression also led to the misinterpretation of Ostrom (1981) that the antorbital fenestra of SMNS 12591a is restricted to the anterior portion of the antorbital fossa, and that the lacrimal had a considerable extent anteriorly. The element considered to be the anterior part of the lacrimal in the antorbital fossa in fact represents the palatine, which has been displaced dorsally on its medial side due to dorsoventral compression, as was already indicated by Huene (1921: fig. 22), and which has been corroborated by other authors (Sereno and Wild 1992, Allen 2010). The outline of the antorbital cavity and the relative contribution of the antorbital fenestra and fossa are virtually identical between SMNS 12596a and SMNS 12352a (Figs 3A, 10A, B). Both have a considerable anterior contribution of the antorbital fossa, but neither form a pit in the anteroventral corner of the fossa, in contrast to Terrestrisuchus gracilis (Crush 1980, 1984, contra Clark 1986). The interpretation by Knoll and Rohrberg (2012) that the anterior corner of the antorbital fenestra is more acute in SMNS 12596a, and that in SMNS 12352a the anterior end of the antorbital fenestra diverges from the ventral margin of the antorbital fossa, are both rejected. Both specimens clearly possess a rounded anterior end of the antorbital fenestra and the anterior outline of the antorbital fossa is virtually indistinguishable between both specimens. The relative distribution of the antorbital fossa within the antorbital cavity is less extensive in SMNS 12591a, but this is aưributable to the incomplete preservation of the thin lamina that comprises the antorbital fossa (Fig. 8). The considerable extent of the thin lamina of the antorbital fossa within the antorbital cavity, and the corresponding relatively small opening of the antorbital fenestra, seen particularly in SMNS 12596a and SMNS 12352a (Figs 3A, 10A, B), reflects the anatomy seen in most non-crocodyliform crocodylomorphs except Carnufex carolinensis (e.g. Crush 1984, Walker 1990, Ruebenstahl et al. 2022), but conflicts with the morphology seen in early theropod dinosaurs, including coelophysoids (Raath 1977, Colbert 1989, Nesbiư et al. 2009). The acid preparation of SMNS 12591a has also revealed much of its palatal region, including what are very likely the posterior portions of the palatal processes of the maxillae (Fig. 9C, D). They meet in the midline and are located quite far posteriorly in the snout. This provides a clear indication of the crocodylomorph affinities of this specimen, as it represents a typical character of this group that foreshadows the maxillary ‘secondary palate’ of later crocodylomorphs (Nesbiư 2011, Dollman and Choiniere 2022). Nasal: Clearly identifiable nasals are preserved in SMNS 12352a and SMNS 12591a. In addition, Crush (1980) identified a flat bone fragment on SMNS 12597b as a poorly preserved nasal. However, due to the incompleteness of this element it is not possible to corroborate this identification with confidence, alth