Galulatherium is an extinct genus of possibly gondwanathere mammal, from the Late Cretaceous (Turonian-Campanian)-aged Galula Formation of Tanzania.[1] It is known solely from the type specimen TNM 02067 (Tanzanian National Museums specimen 02067)[Note 1] a fragmentary fossil dentary (lower jaw). The short, deep bone is about 19.5 mm (0.77 in) long, but the back part is broken off. It contains a large, forward-inclined incisor with a root that extends deep into the jaw, separated by a diastema (gap) from five cheekteeth. Very little remains of the teeth, but enough to determine that they are hypsodont (high-crowned). The third cheektooth is the largest and the roots of the teeth are curved. First described in 2003, TNM 02067 has been tentatively identified as a sudamericid—an extinct family of high-crowned gondwanathere mammals otherwise known from South America, Madagascar, India, and Antarctica. If truly a gondwanathere, it would be the only African member of the group and may be the oldest. The describers could not exclude other possibilities, such as that the jaw represents some mammalian group known only from younger, Cenozoic times (less than 66 million years ago). In 2019 the fossil was CT scanned, which revealed additional details of the specimen.[1]
Galulatherium was discovered in 2002[2] in the locality TZ-07 in the Mbeya Region of southwestern Tanzania, which has also yielded remains of various other vertebrates, including birds and other saurischian dinosaurs. The discovery was reported in a 2003 paper by David Krause and colleagues. TZ-07 lies in the "Red Sandstone Unit" (RSU), an informal, poorly defined rock unit. Age estimates for the RSU have ranged from middle Jurassic to Miocene, but according to Krause and colleagues, part of this discrepancy is the result of confusion between two superficially similar rock units that outcrop nearby; the older one, where TZ-07 is located, is undoubtedly Mesozoic and the younger is Cenozoic.[3] The former was later identified as the mid-late Cretaceous aged Galula Formation, and the latter as the Oligocene aged Nsungwe Formation. Based on the presence of non-avian dinosaurs and osteoglossomorph fishes, Krause and colleagues assigned TZ-07 to the Cretaceous (146–66 million years ago).[4] In 2007, Nancy Stevens and colleagues identified the unit that produced TNM 02067 as likely belonging to the middle part of the Cretaceous (around Aptian to Cenomanian).[5] TNM 02067 is significant as one of the very few mammals from the Cretaceous of the southern continents (Gondwana).[6]
TNM 02067 is a damaged, partial left dentary (lower jaw bone). It preserves much of the body of the bone, which is short and deep, but is broken along a vertical fracture behind the toothrow. There is another fracture in the front part of the jaw.[4] The bone is 19.5 mm (0.77 in) long and 11.4 mm (0.45 in) deep.[7] All the teeth are incomplete or absent, and lack both enamel and cementum, but what remains indicates that there was a large incisor at the front and five cheekteeth further back, separated by a diastema (gap) of about 2.5 mm (0.098 in). On the labial (outer) surface of the dentary, there is one large mental foramen (opening). The mandibular symphysis, where the two halves of the lower jaw meet, is poorly preserved, but there is nothing to suggest that the left and right dentaries were fused. The lower margin of the bone is convex at the front, but concave further back, so that the depth of the dentary is 8.3 mm (0.33 in) below the diastema, but only 7.0 mm (0.28 in) below the third cheektooth.[4] The origin of the coronoid process, a projection at the back of the dentary, lies far to the front.[8]