Revision of the Late Jurassic teleosaurid genusMachimosaurus(Crocodylomorpha, Thalattosuchia)

Abstract

Machimosaurus was a large-bodied genus of teleosaurid crocodylomorph, considered to have been durophagous/chelonivorous, and which frequented coastal marine/estuarine ecosystems during the Late Jurassic. Here, we revise the genus based on previously described specimens and revise the species within this genus. We conclude that there were three European Machimosaurus species and another taxon in Ethiopia. This conclusion is based on numerous lines of evidence: craniomandibular, dental and postcranial morphologies; differences in estimated total body length; geological age; geographical distribution; and hypothetical lifestyle. We re-diagnose the type species Machimosaurus hugii and limit referred specimens to only those from Upper Kimmeridgian–Lower Tithonian of Switzerland, Portugal and Spain. We also re-diagnose Machimosaurus mosae, demonstrate that it is an available name and restrict the species to the uppermost Kimmeridgian–lowermost Tithonian of northeastern France. We re-diagnose and validate the species Machimosaurus nowackianus from Harrar, Ethiopia. Finally, we establish a new species, Machimosaurus buffetauti, for the Lower Kimmeridgian specimens of France and Germany (and possibly England and Poland). We hypothesize that Machimosaurus may have been analogous to the Pliocene–Holocene genus Crocodylus in having one large-bodied taxon suited to traversing marine barriers and additional, geographically limited taxa across its range.

First evidence of denticulated dentition in teleosaurid crocodylomorphs

“…However, Martin and Vincent (2013) consider this likely to be an underestimate. This specimen does have a lower pre-palatine maxillary count than the M. hugii specimen described by Martin and Vincent (2013) Young et al 2014aYoung et al , 2015. And, as the maxillary tooth row in Machimosaurus terminates level to the anterior margin of the suborbital fenestrae (Martin and Vincent 2013), a maxillary tooth count of under 20 is not unreasonable (18 or 19).…”

“…However, the distal (posterior) teeth have a ratio less than 1.8, and are smaller in overall size. Isolated teeth referred to Machimosaurus hugii from the Kimmeridgian of Germany also show this difference in tooth size/dimensions (Karl and Tichy 2004;Young and Steel 2014;Young et al 2014a). The apices are blunt and rounded.…”

“…However, Martin and Vincent (2013) contend that there is no basis to separate the specimen referred to M. mosae (the holotype of which was destroyed during World War One) from M. hugii. They conclude that all known Machimosaurus specimens from the Kimmeridgian of Europe can be referred to M. hugii (although they did not discount the presence of a second Kimmeridgian taxon; see Young et al 2014a, 2015 for a revision of Machimosaurus and the species within). They also argued that "S." obtusidens, although the sister taxon to M. hugii, should not be referred to M. hugii or the genus Machimosaurus.…”

“…However, "S." obtusidens differs from Machimosaurus hugii and M. mosae in: (i) retaining antorbital fenestrae, which are absent in Machimosaurus (Martin and Vincent 2013); (ii) in retaining four premaxillary alveoli, whereas in Machimosaurus there are only three (Table 2); (iii) having a higher maxillary and dentary tooth count than any known Machimosaurus specimen (Table 2); (iv) a proportionally longer rostrum (Table 2); (v) a proportionally narrower posterior skull (Table 2); (vi) proportionally shorter supratemporal fenestrae (Table 2); and (vii) well-developed mesiodistal tooth carinae, whereas in Machimosaurus the carinae are generally low, restricted to the apex or completely absent (Krebs 1968;Hua 1999;Martin and Vincent 2013;Young and Steel 2014;Young et al 2014a).…”

The first definitive Middle Jurassic atoposaurid (Crocodylomorpha, Neosuchia), and a discussion on the genus Theriosuchus

“…In teleosaurids: (1) the anterior region is spatulate, with the maximal mediolateral width being present at the level of the D3 alveolus; (2) the D3 and D4 alveoli are closely set and are confluent, with the D4 and D5 alveoli separated by a diastema; (3) there are no large foramina medial to the alveoli; (4) the alveolar margins are not vertically festooned; and (5) in dorsal view, the alveolar margin is convex at the D3-D4 region, resulting in those alveoli being positioned dorsal to the D1 and D2 alveoli (e.g. Andrews, 1913;Phizackerley, 1951;Hua, 1999;Lepage et al, 2008;Martin & Vincent, 2013;Young et al, 2014a). As none of these features is present in the Skye specimen, we can disregard a teleosaurid origin for this specimen.…”