Dyrosaurus maghribensis Jouve, Iarochene, Bouya & Amaghzaz 2006
Creators: name: Scavezzoni, Isaure
name: Fischer, Valentin
name: Johnson, Michela M.
name: Jouve, Stéphane
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Crocodylia
Dyrosauridae
Dyrosaurus
Dyrosaurus maghribensis

description: DYROSAURUS MAGHRIBENSIS (JOUVE, IAROCHÈNE, BOUYA & AMAGHZAZ, 2006)   
For measurements, see Tables 7-9.   Ilium   
 The ilium of Dyrosaurus maghribensis (OCP DEK-GE 252 and OCP DEK-GE 255; Fig. 69) is similar to that of other dyrosaurids in possessing a well-developed postacetabular process, large peduncles, a wide acetabular perforation, and a relatively short preacetabular process. In this way Dyrosaurus maghribensis differs from Thalattosuchia and Crocodylia.   
 Dyrosaurus maghribensis specifically differs from Congosaurus bequaerti, Hyposaurus natator, Acherontisuchus guajiraensis in displaying a wide acetabulum and a long supraacetabular crest bordering it dorsally. Moreover, the sacral rib attachment sites for the sacrals are proportionally larger in Dyrosaurus maghribensis than in Congosaurus bequaerti or Hyposaurus natator. Dyrosaurus maghribensis also stands out from other dyrosaurids in having a large and ’blunt’ preacetabular process and a relatively flat dorsal margin, that is slightly bulged in the way of Congosaurus bequaerti and opposed to Acherontisuchus guajiraensis.   
 The preacetabular process of the ilium of Dyrosaurus maghribensis (OCP DEK-GE 252 and 255; Fig. 69) takes the shape of a right angle whose sides and peak are rounded, thus giving a blunt appearance to the preacetabular hook. The orientation of the preacetabular process of OCP DEK-GE 252 and 255 is not entirely clear due to its preservation state, but it appears to be mainly anterior. Comparatively, the preacetabular process of Dyrosaurus maghribensis OCP DEK-GE 254 (Jouve et al. 2006) seems sharper and oriented anterodorsally. Also, the anterior margin of the preacetabular process of OCP DEK-GE 254 is greater than those of OCP DEK-GE 252 and 255, resulting in a shorter distance between the preacetabular hook and the pubic peduncle for OCP DEK-GE 254.   
 Laterally emerging from the preacetabular process is an oblong area culminating in the supraacetabular crest. Directly underneath the preacetabular process is a straight surface corresponding to the anterior margin of the ilium; this margin is relatively long in the case of OCP DEK-GE 252 and OCP DEK-GE 255, whereas it is shorter for OCP DEK-GE 254 (Jouve et al. 2006). This surface forms the junction between the preacetabular process and the pubic peduncle. In Dyrosaurus maghribensis OCP DEK-GE 252 and 255, the articular facet of the pubic peduncle does not significantly protrude anteriorly and remains within the extension of the anterior margin of the ilium, as in Hyposaurus natator YPM VP. 000753. In contrast, Dyrosaurus maghribensis OCP DEK-GE 254 displays a more embossed articular facet for the pubic peduncle which make it protrude slightly anteriorly, similar to Congosaurus bequaerti, Hyposaurus natator NJSM 23368, and Acherontisuchus guajiraensis. Yet the pubic peduncle of Congosaurus bequaerti is longer anteroposteriorly than that of Dyrosaurus maghribensis (Figs 69; 72). Like many other crocodyliforms, the pubic peduncle of Dyrosaurus maghribensis is less elevated dorsoventrally than the ischial peduncle is (e.g. Mecistops cataphractus, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804; Thalattosuchus superciliosus, Congosaurus bequaerti, etc.). Both peduncles are taller than the acetabular perforation, as in other dyrosaurids (e.g. Congosaurus bequaerti, Acherontisuchus guajiraensis). Similar to other dyrosaurids and extant crocodylians (e.g. Palaeosuchus palpebrosus, Mecistops cataphractus, Caiman crocodilus, Congosaurus bequaerti, Hyposaurus natator, Acherontisuchus guajiraensis), the pubic peduncle of Dyrosaurus maghribensis is composed of two small adjoined triangles: the first one forming the anterior rim of the pubic peduncle, and the second one constituting the lateral surface of the peduncle. The latter resembles a flattened isosceles triangle oriented towards the acetabulum (i.e. posteriorly), whereas the first one appears more like a right angled triangle facing partly laterally and anteriorly, similar to other dyrosaurids and extant crocodylians (e.g. Palaeosuchus palpebrosus, Mecistops cataphractus, Caiman crocodilus, Congosaurus bequaerti, Hyposaurus natator, and Acherontisuchus guajiraensis).   
 The pubic peduncle of the ilium of Dyrosaurus maghribensis (Fig. 69) is entirely separated from the ischial peduncle by the acetabular perforation, like other dyrosaurids and extant crocodylians.   
 The acetabular perforation of Dyrosaurus maghribensis is longer anteroposteriorly than it is deep dorsally; similar proportions are found for Congosaurus bequaerti (for which it is less high dorsoventrally than Dyrosaurus, and Hyposaurus natator). However, Acherontisuchus guajiraensis strongly differs from Dyrosaurus maghribensis with its anteroposteriorly short and dorsally deep acetabular perforation. The acetabular perforation of Dyrosaurus maghribensis is relatively well developed in all specimens as it reaches more than half the length of either peduncle of the ilium. In this way, the acetabular perforation of Dyrosaurus maghribensis is closer to that of Hyposaurus natator than Congosaurus bequaerti, for which the acetabular perforation is less deep dorsoventrally. Yet, the acetabular perforation of Dyrosaurus maghribensis is still distinct from that of Hyposaurus natator in being shallower dorsally. The ischial peduncle succeeds the acetabular perforation posteriorly, and forms the posterior border of the acetabulum. Contrary to the pubis peduncle, the ischial peduncle is strongly oblique so that its posterior part protrudes from the overall plane formed by the postacetabular process. In this way, the post acetabular process forms a bony barrier posteriorly, hence it was presumably the attachment site of a structure similar to the antitrochanter of extant crocodylians (Tsai & Holliday 2015). As in Crocodylia, Thalattosuchia and other dyrosaurids (i.e. Congosaurus bequaerti, Hyposaurus natator, Acherontisuchus guajiraensis), the lateral articular surface of the ischial peduncle of Dyrosaurus maghribensis resembles a tilted isosceles triangle pointing globally dorsally. This triangular lateral surface is also oriented anteriorly towards the centre of the acetabulum, mirroring the inclination of the pubic peduncle. This effect is actually emphasized by the posterior protrusion of the ischial peduncle. The ventral portion of the ischial peduncle meets with the dorsal part of the posterior peduncle of the ischium, and is slightly truncated so that the medial extremity of the ischial peduncle is more ventrally situated that the lateral one. Consequently, the lateral surface of the ischial peduncle appears like a titled triangle.   
 The postacetabular process of Dyrosaurus maghribensis (Fig. 69) is relatively small compared to other dyrosaurids as it accounts for less than half of the total length of the ilium. The ventral margin of the postacetabular process directly stems from the posterior corner of the ischial peduncle. The junction between the two appears smooth similar to that of extant crocodylians (e.g. Mecistops cataphractus, Caiman crocodilus). However, it differs from that of Congosaurus bequaerti, and Hyposaurus natator which display a small concave indentation between the ischial peduncle and the postacetabular process, and further differs from that of Acherontisuchus guajiraensis which possesses a large but shallow concave recess. Overall, the postacetabular process of all specimens of Dyrosaurus maghribensis is asymmetrical and appears like a beak: its ventral margin is almost exclusively concave whereas its dorsal margin is convex, thus giving a global hooked look. This effect is actually accentuated by the relative height of the postacetabular process, with those bearing a smaller process also show a more emphasized beak appearance (e.g. OCP DEK-GE 252; Fig. 69B). Hence, the ventral margin of the postacetabular process of Dyrosaurus maghribensis is distinct from that of Congosaurus bequaerti, and Hyposaurus natator for which the ventral margin shows an overall greater convexity, and also differs from Acherontisuchus guajiraensis for which the convex margin extends up to half the length of the postacetabular process. The extremity of the postacetabular process (Fig. 69D) looks like a Lancet arch as in other dyrosaurids; indeed, the posterior-most portion of the ventral margin changes concavity to become convex in this area. The dorsal rim of the postacetabular process, known as the ’iliac crest, is entirely convex from its junction with the preacetabular process up to its posterior peak. On its lateral surface, the whole area is scarred perpendicularly to its margin which conveys the existence of a cartilaginous cap in vivo. The convexity of the dorsal margin of the postacetabular process is subtle as in Congosaurus bequaerti. Moreover, the junction between the postacetabular process and the preacetabular process is also marked by a shallow recess for OCP DEK-GE 252 and 255 like Congosaurus bequaerti and Acherontisuchus guajiraensis, and like the extant crocodylians Mecistops cataphractus (Fig. 8) and Caiman crocodilus (Fig. 9), adding to the smooth overall profile of the iliac crest. In OCP DEK-GE 254, the junction between the postacetabular process and the preacetabular process displays a greater concavity, not unlike that of Hyposaurus natator.   
 The preacetabular process of Dyrosaurus maghribensis is not well preserved (Fig. 69), but seems large and bulky, unlike those of extant crocodylians (e.g. Mecistops cataphractus and Caiman crocodilus) and other dyrosaurids (i.e. Congosaurus bequaerti, Hyposaurus natator, Acherontisuchus guajiraensis). Indeed, the preacetabular process of Dyrosaurus maghribensis OCP DEK-GE 252 and 255 does not sharpen anteriorly, but rather forms a rounded right angle due to its slightly convex margins. In the case of OCP DEK-GE 254, the preacetabular process appears to have been more angular than those of OCP DEK-GE 252 and 255. The area encased between the margins of the preacetabular process and the supraacetabular crest is inclined and culminates at its junction with the supraacetaular crest. The latter forms the dorsal margin of the acetabulum, and appears like a prominent arch (like that of Acherontisuchus guajiraensis) which extends as far posteriorly as the acetabulum. In Congosaurus bequaerti, and Hyposaurus natator, the supraacetabular crest is not so well defined and does not extend as far back posteriorly. The supraacetabular crest of Dyrosaurus maghribensis however differs from that of Acherontisuchus guajiraensis in displaying a wider concavity.   
 The acetabulum of Dyrosaurus maghribensis (Fig. 69; see Table 11) is proportionally large compared to the ilium as a whole. Also, the acetabulum of Dyrosaurus maghribensis is almost as high as it is wide, giving it a semi-spherical appearance unlike the rather elliptical appearance of other dyrosaurids. Its deepest portion seems to be located directly above the acetabular perforation, in between the pubic and ischial peduncles. In other dyrosaurids (i.e. Congosaurus bequaerti, Hyposaurus natator, Acherontisuchus guajiraensis), the deepest point of the acetabulum appears to be located more dorsally, closer to the suparaacetabular crest.   
 Medially, the ilium of Dyrosaurus maghribensis bears two distinct scars for the attachment of the sacral ribs. In OCP DEK-GE 255 (Fig. 69D) and OCP DEK-GE 254 (see Jouve et al. 2006) the anterior attachment site is the largest, and covers the area extending from the pubic peduncle up until the peak of the preacetabular process. In OCP DEK-GE 255, however, the outline of the anterior attachment site differs from that of OCP DEK-GE 254 in resembling an asymmetrical parabola whose vertex points dorsoposteriorly. The shape of the anterior attachment site in OCP DEK-GE 254 appears more semicircular. The posterior attachment site of Dyrosaurus maghribensis is deeper than the anterior one but also more limited spatially. The overall shape of the posterior attachment site approximates that of two joined parabolas, with the upper one being the smallest. The actual anchoring site for the sacral rib was limited to the lower parabola. In OCP DEK-GE 255, the lower parabola covers half of the ischial peduncle and a similar area over the postacetabular process, whereas in OCP DEK-GE 254 the lower parabola extends over the entire ischial peduncle.The upper parabola constitutes a shallower depression dorsally to the posterior attachment site which presumably bore the ’winglet’ posterior extension of the second sacral rib similar to extant crocodylians (e.g. see Alligator mississippiensis (Daudin, 1801) on Fig. 74C).    Ischium   
 The ischium of Dyrosaurus maghribensis (Fig. 69) resembles that of other dyrosaurids in displaying: a thick shaft; limited anterior and posterior processes (which do not protrude much beyond the peduncles); a well-developed anterior peduncle; and a twisted distal blade in relation to the shaft.   
 Consequently, the ischium of Dyrosaurus maghribensis (Fig. 69) differs from that of other thalattosuchians in lacking: a posterior process extending beyond more than half the proximal anteroposterior length (defined by the peduncles); a reduced anterior peduncle (smaller in size than the posterior peduncle); a short shaft; a large and flat distal blade.   
 Overall, the ischium of Dyrosaurus maghribensis (Fig. 69) is similar to that of extent crocodylians and other dyrosaurids as it displays relatively large peduncles separated by a wide acetabular perforation (e.g. Palaeosuchus palpebrosus, Mecistops cataphractus, Caiman crocodilus, Congosaurus bequaerti, Hyposaurus natator, Acherontisuchus guajiraensis). The latter is as long as its twin borne on the ilium but is slightly deeper. The total length of the proximal extremity encompassing both peduncles almost reaches the length of the distal blade of the ischium, unlike Hyposaurus natator for which the distal blade exceeds the proximal extremity in size. Mediolaterally, the anterior peduncle of the ischium of Dyrosaurus maghribensis is as wide as the ventral surface of the pubic peduncle of the ilium as both peduncles were connected in vivo (Fig. 69D). The anterior peduncle is separated from the shaft by a narrow bridge, ventral to the acetabular perforation. More anteriorly, the anterior peduncle of the ischium expands dorsally to contact the pubic peduncle of the ilium, and ventrally to form the distinct ‘button’ or ‘knob’ (see OCP DEK-GE 254 in Jouve et al. (2006), or Fig. 69D) for the articulation with the pubis (Jouve et al. 2006). Indeed, similar to other dyrosaurids and extant crocodylians (e.g. Palaeosuchus palpebrosus, Mecistops cataphractus, Caiman crocodilus, Congosaurus bequaerti, Hyposaurus natator, Acherontisuchus guajiraensis), the anterior peduncle of Dyrosaurus maghribensis (Fig. 69) is well developed: its dorsoventral height accounts for more than twice its anteroposterior width (see Table 8), hence offering a large articular surface for the pubis as mentioned above. The presence of an extra articular area for the pubis being almost similar to a peduncle on the ventral side of the articular surface of the anterior peduncle of the ischium is a characteristic of Dyrosauridae, and is not found in either Crocodylia (e.g. Palaeosuchus palpebrosus RVC-JRH-PP1 [Fig. 7], Mecistops cataphractus [Fig. 8], Caiman crocodilus [Fig. 9] or Thalattosuchia (e.g. ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763 [Fig. 22] or Lemmysuchus obtusidens [Fig. 59]). Hence, the articular surface of the anterior peduncle of Dyrosaurus maghribensis significantly flares out, in the way of other dyrosaurids (i.e. Hyposaurus natator, Acherontisuchus guajiraensis), and is thus quite different from what is observed in extant crocodylians (e.g. Palaeosuchus palpebrosus, Mecistops cataphractus, Caiman crocodilus).   
 In extant crocodylians (e.g. Palaeosuchus palpebrosus [Fig. 7], Mecistops cataphractus [Fig. 8], Caiman crocodilus [Fig. 9]), the relative dorsal expansion of the anterior peduncle compared to the posterior peduncle can be attributed to the difference in inclination between both iliac peduncles (i.e. when their ventral margins are not parallel). Conversely, the anterior peduncle of the ischium of Dyrosaurus maghribensis and other dyrosaurids (i.e. Hyposaurus natator, Acherontisuchus guajiraensis) and thalattosuchians (e.g. Torvoneustes carpenteri or Neosteneosaurus edwardsi) never extends dorsally over the dorsal margin of the posterior peduncle of the ischium. Still, the anterior peduncle of the ischium of Dyrosaurus maghribensis and dyrosaurids appears to be more expanded dorsally compared to that of thalattosuchians due to a deeper acetabular perforation, especially on the lateral side of the ischium.   
 The peduncle bridge of the ischium of Dyrosaurus maghribensis OCP DEK-GE 252 and 254 are shorter and thicker than that of OCP DEK-GE 255 and other dyrosaurids (i.e. Hyposaurus natator, Acherontisuchus guajiraensis) and extant crocodylians (e.g. Palaeosuchus palpebrosus, Mecistops cataphractus, Caiman crocodilus) on top of their short extension, which does not help in the matter, the dorsal and ventral margins of the peduncle bridge are merely concave resulting in a thick appearance.Such a short peduncle bridge in OCP DEK-GE 252 and 254 gives the impression that the anterior peduncle directly emerges from the shaft. Conversely, the holotype OCP DEK-GE 255 displays a consequently longer peduncle bridge (Fig. 69D), similar to what is observed in other dyrosaurids (i.e. Hyposaurus natator, Acherontisuchus guajiraensis).   
 The posterior peduncle of Dyrosaurus maghribensis is large with its mediolateral length being equivalent to the dorsoventral height of the anterior peduncle, and robust. Also, its articular surface is truncated resulting in an additional triangular portion facing towards the acetabulum, in line with the lateral surface of the ischial peduncle of the ilium. The main articular facet of the posterior peduncle, its dorsal surface, is connected to the ilium through the ischial peduncle. Similar to other dyrosaurids (i.e. Hyposaurus natator, Acherontisuchus guajiraensis), the posterior peduncle appears short and bulky due to a thick neck connecting it to the main shaft. This effect is created by the shape of the anterior and posterior margins of the neck of the posterior peduncle of Dyrosaurus maghribensis, which are respectively concave and convex. Unlike extant crocodylians (e.g. Palaeosuchus palpebrosus, Mecistops cataphractus, Caiman crocodilus), the posterior peduncle of dyrosaurids is slightly elevated, giving them a deeper acetabular perforation.   
 The shaft of the ischium of Dyrosaurus maghribensis (Fig. 69) is thick, and does not significantly slim down from the bases of the peduncles, unlike Hyposaurus natator and Acherontisuchus guajiraensis. This effect is imputable to the feeble concavity and shortness of the ventral margin of the peduncle bridge of the ischium. In OCP DEK-GE 252, this effect is even more emphasized by the important convexity of the posterior margin of the neck of the posterior peduncle. Consequently, in OCP DEK-GE 252 the posterior margin of the ilium appears convex on the first half, and only becomes concave on the second half of its total dorsoventral height. In OCP DEK-GE 254 and 255, the posterior margin of the shaft is more subtlety convex (Fig. 69 D and Jouve et al. 2006), similar to Hyposaurus natator. In parallel, the anterior margin of the ischium underneath the anterior peduncle is entirely concave in all specimens. The relative thickness of the shaft of the ilium added to shortness of the distal blade (anteroposteriorly) convey a less intense impression of flaring out of the ischium compared to Hyposaurus natator. As in extant crocodylians and other dyrosaurids (i.e. Hyposaurus natator and Acherontisuchus guajiraensis), the posterior portion of the ischium directly underneath the posterior peduncle is thicker mediolaterally than its anterior counterpart. Moreover, the section joining, in a direct line, the peduncle bridge of the ischium and the posterior process of the distal blade corresponds to the thickest part of the ischium, similar to extant crocodylians and other dyrosaurids. Hence, there is an abrupt change in thickness anteriorly to and posteriorly to this line, which emphasises it. This line also corresponds to the axis along which the rotation of the distal blade (in relation to the peduncles) occurs, so that the anterior corner of the distal blade is actually set more medially than its posterior corner (as in extant crocodylians).   
 The distal blade of the ischium only subtly protrudes posteriorly from the posterior peduncle (i.e. it does not extend over more than half of the total proximal length of the ischium) unlike thalattosuchians (e.g. Thalattosuchus superciliosus or Charitomenosuchus leedsi). The anterior process of the distal blade is located slightly more dorsally than the posterior corner (unlike Hyposaurus natator where this is more emphasised), and the margin connecting both is concave. As in other dyrosaurids but unlike thalattosuchians, the distal processes of the ischium of Dyrosaurus maghribensis (Fig. 69) are relatively blunt, and the posterior process does not exceed more than twice the size of the anterior process. Similar to Hyposaurus natator, the peak of the anterior process is oriented anteriorly whereas that of the posterior process faces another direction. However, in Dyrosaurus maghribensis the peak of the posterior process appears to be oriented more posteriorly than ventrally unlike Hyposaurus natator. There is a difference in the shape of the processes between the specimens, with OCP DEK-GE 255 displaying a thicker anterior process and a thinner (and slightly longer) posterior one compared to those of OCP DEK-GE 252.    Pubis   
 The pubic peduncle of Dyrosaurus maghribensis (Fig. 69) is narrow, and its mediolateral width almost equals that of the shaft underneath it. This contrasts with that of Hyposaurus natator for which the shaft widens greatly to form the pubic peduncle proximally. In Cerrejonisuchus improcerus (Fig. 65), the proximal enlargement is more subtle than in Hyposaurus natator and is hence more similar to Dyrosaurus maghribensis. For this reason, the shaft of the pubis of Dyrosaurus maghribensis appears to display essentially straight margins laterally and medially. The shaft itself stretches from the peduncle proximally up until the distal widening, which marks the beginning of the pubic apron.   
 Overall, the pubis of Dyrosaurus maghribensis (Fig. 69) appears relatively slender as its pubic apron does not flare out drastically. Indeed the lateral and medial margins of the pubis (up to the inflection point, which corresponds to the pubic symphysis medially) display a low concavity, with the medial margin being the lowest. Yet, the pubic apron of Dyrosaurus maghribensis is proportionally larger than that of Hyposaurus natator (see Table 9), but is more limited than that of Cerrejonisuchus improcerus. Geometrically, the pubic apron of Dyrosaurus maghribensis is quite symmetrical with the lateral margin of the bone almost mirroring the medial one. This effect is mainly due to the size and orientation of the pubic symphysis, which is relatively short and parallel to the pubic shaft. Indeed, depending on the inclination and length of the pubic symphysis, the pubic apron is subject to deflect more or less laterally as in Hyposaurus natator or Cerrejonisuchus improcerus. In the case of Dyrosaurus maghribensis, the pubis was positioned slightly more upright than for Hyposaurus natator, similar to Cerrejonisuchus improcerus.   
 Distally, the pubic apron is bordered by a convex margin, joining the pubic symphysis with the lateral margin of the bone. The junction between the lateral margin of the bone and the distal one forms a small lateral protuberance in the way of Hyposaurus natator (Figs 66; 67) or Cerrejonisuchus improcerus.
description: Published as part of Scavezzoni, Isaure, Fischer, Valentin, Johnson, Michela M. & Jouve, Stéphane, 2024, Form and function of the pelvic girdle of Thalattosuchia and Dyrosauridae (Crocodyliformes), pp. 135-326 in Geodiversitas 46 (6) on pages 266-271, DOI: 10.5252/geodiversitas2024v46a6, http://zenodo.org/record/11106598