MACHIMOSAURINI

Johnson, Michela M., Young, Mark T. & Brusatte, Stephen L., 2020, Re-description of two contemporaneous mesorostrine teleosauroids (Crocodylomorpha: Thalattosuchia) from the Bathonian of England and insights into the early evolution of Machimosaurini, Zoological Journal of the Linnean Society 189, pp. 449-482 : 459-460

MACHIMOSAURINI (JOUVE ET AL., 2016)

MACHIMOSAURINI INDETERMINATE

( FIG. 2)

v 1995 Steneosaurus larteti (Deslongchamps) ; Vignaud, p. 188.

We have examined two partial mandibles (OUMNH J.1406 and OUMNH J.1417) with in situ teeth that have the characteristic Machimosaurini dental pattern (which consists of blunt, conical teeth with a noticeable anastomosing pattern on all apices). The first partial mandible, OUMNH J.1406 ( Fig. 2A), is from the Great Oolite Group (Bathonian, Middle Jurassic) of North Oxfordshire and is part of the E. A. Walford collection. The anterior-most and posterior areas of the mandible are not preserved. The dentary is an elongate, slender bone that makes up the majority of the lower jaw in crocodylomorphs ( Andrews, 1909, 1913; Romer, 1956; Nesbitt, 2011). It is difficult to determine where exactly the mandibular symphysis begins, as the dorsal surface of the dentary is poorly preserved, but it starts approximately at the 16 th or 17 th alveolus. There are at least 23 dentary alveoli preserved on the left side. The interalveolar spacing is variable throughout the dentary and the alveoli are subcircular in shape ( Fig. 2A). In lateral view ( Fig. 2A) there are deep reception pits throughout the entirety of the mandible, as well as a single line of large foramina running parallel to the tooth row. OUMNH J.1406 is well ornamented with pits and rugosities in lateral and ventral views ( Fig. 2A). There is one partially erupted tooth preserved ( Fig. 2A) in the 16 th right alveolus. The tooth has a blunt, conical apex with the characteristic anastomosing pattern, and high relief enamel ridges.

The second mandible, OUMNH J.1417 ( Fig. 2B), is relatively broad, with only the articulars, posterior surangulars and angulars missing (more so on the right side than the left).As in OUMNH J.1406, the dentary is an elongate bone and makes up the majority of the mandible, with the mandibular symphysis beginning at the 16 th alveolus ( Fig. 2B). There are 29 alveoli preserved, and the posterior-most alveoli are only slightly smaller than those positioned in the anterior and middle sections of the dentary ( Fig. 2B). All alveoli are subcircular in shape with interalveolar spacing varying throughout. The Meckelian groove of OUMNH J.1417 is deep, which differs from other Machimosaurini (e.g. L. obtusidens LPP.M. 21; Ma. buffetauti SMNS 91415).In left lateral view,the surangular is a thin, anteroposteriorly elongated bone. There are deep reception pits present along the lateral margins of the entirety of the mandible, as well as a single line of large foramina running parallel to the tooth row ( Fig. 2B). There are numerous large subcircular fenestrae in dorsal, lateral and ventral views in the anterior-most part of the dentary ( Fig. 2B), arranged in a semicircular pattern around the D1 to D4 alveoli. There are five partially erupted teeth (third left alveolus and second, 16 th, 18 th and 22 nd right alveoli) ( Fig. 2B). All teeth are robust with a blunt apex and all preserve the characteristic anastomosing pattern.