Pseudobolodon

Pseudobolodon was a relatively early member of the also extinct order of mammals, Multituberculata. It lived in Portugal during the Upper Jurassic, part of 'the age of the dinosaurs'.
(For the more technically inclined, suborder "Plagiaulacida", family Paulchoffatiidae.)

Genus: Pseudobolodon Hahn G, 1977
'false Bolodon'
Remarks: A third one-time species, P. robustus Hahn, 1978, seems to have transformed into Meketibolodon robustus (Hahn G, 1978).

Species: Pseudobolodon krebsi Hahn G & Hahn R, 1994
Place: Guimarota
Country: Portugal
Age: Kimmeridgian, Upper Jurassic
Remarks: This is based on two upper jaws.
As for the septomaxilla mentioned in the title of the reference: "A small, triangular bone is placed between the premaxilla and the maxilla; this bone is interpreted as a septomaxilla. This is a bone that is typical for lower tetrapods (amphibians, reptiles), but is usually absent in mammals", (Hahn & Hahn 2000, p.98). The premaxilla is the front bit of your upper jaw, whilst the maxilla is the side of it. Like other existing mammals, you don't have this septomaxilla.
Reference: Hahn & Hahn (1994), Nachweis des Septomaxillare bei Pseudobolodon krebsi n.sp. (Multituberculata) aus dem Malm Portugals, p.9-29, in Miscellanea Palaeontologica 3. - 531 p., 67 pl., Berl. Geowiss. Abh. Vol 13, editors Kohring R & Martin T.
(Evidence of the septomaxilla in Pseudobolodon krebsi n.sp. (Multituberculata) from the Malm of Portugal.)

Species: Pseudobolodon oreas Hahn G, 1977
Place: Guimarota
Country: Portugal
Age: Kimmeridgian, Upper Jurassic
Remarks: Known from seven upper jaws.
Reference: Hahn G (1977), Neue Schädel-Reste von Multituberculaten (Mamm.) aus dem Malm Portugals. Geologica et Palaeontologica, 11, p.161-186.
(New skull remains of Multituberculates (Mammalia) from the Malm of Portugal.)

Page references: Hahn G & Hahn R (2000), Multituberculates from the Guimarota mine, p.97-107 in Martin T & Krebs B (eds), Guimarota - A Jurassic Ecosystem, Verlag Dr Friedrich Pfeil, München.
Kielan-Jaworowska Z & Hurum JH (2001), Phylogeny and Systematics of multituberculate mammals. Paleontology 44, p.389-429.

(This information has been derived from [1] (http://home.arcor.de/ktdykes/multis.htm) Multituberculata Cope, 1884. As that's my webpage, there are no issues of copyright. Trevor Dykes)