Plagiaulacida McKenna, 1971

Hahn, Gerhard & Hahn, Renate, 2003, New multituberculate teeth from the Early Cretaceous of Morocco, Acta Palaeontologica Polonica 48 (3), pp. 349-356 : 349-351

Suborder Plagiaulacida McKenna, 1971

[pro Plagiaulacoidea Ameghino, 1889]

Superfamily Paulchoffatioidea nov.

Suborder Paulchoffatoidea ; Kielan−Jaworowska and Ensom 1992: 99. Paulchoffatioidea ; Kielan−Jaworowska and Hurum 2001: 392. Paulchoffatiid line Kielan−Jaworowska and Hurum 2001: 402, 412.

Kielan−Jaworowska and Hurum (2001) grouped the Plagiaulacida into three “lines”, the allodontid line, the paulchoffatiid line and the plagiaulacid line. The Arginbaataridae Hahn and Hahn, 1983 are excluded as “Suborder incertae sedis ” ( Kielan−Jaworowska and Hurum 2001: 403, 415). In our opinion, this family constitutes a fourth arginbaatarid line. Each of these four lines represents its own evolutionary lineage, their common root still being unknown. We propose to stabilize these four lineages systematically as superfamilies, as is done here with the paulchoffatiid line.

Families included.— Paulchoffatiidae G. Hahn, 1969 , Hahnodontidae Sigogneau−Russell, 1991a , and Pinheirodontidae Hahn and Hahn, 1999b .

Distribution.—?Late Rhaetic of France;?Middle Jurassic (Bathonian) of England; Late Jurassic (Kimmeridgian) of Portugal; Early Cretaceous (~Berriasian) of Portugal, England and Morocco; Early Cretaceous (Barremian) of Spain.

Diagnosis.—A superfamily of the Plagiaulacida with the following characteristics: Tooth formula (known only in the Paulchoffatiidae ): 3.1–0.5–4.2./1.0.4–3.2. I2 with one main cusp and 1 to 5 small additional cuspules arranged transversely on the posterior portion of the crown in a line or in a semicircle. I3 enlarged, with an obliquely directed crest and 0 to 3 additional anterobuccally, and 0 to 3 posterolingually placed small cuspules. C single−rooted, premolariform, with 2to 5 cusps. Anterior upper premolars (P1–3/4) short, rounded to quadrangular, with 2to 5 cusps. Posterior upper premolars (usually P4–5, rarely also P3) elongate, molariform, with 2to 3 longitudinal rows of cusps. M1–2with two rows of cusps. p3–4 with 3 to 6 serrations and mostly a labial row of small basal cuspules. m1 with two rows of cusps. m2 with a central basin and the cusps more or less reduced in various ways. Skull known only in the Paulchoffatiidae , therefore excluded from the diagnosis.

Discussion.—The Paulchoffatioidea , especially the Paulchoffatiidae , are characterized by a peculiar combination of autapomorphic and plesiomorphic features (see also KielanJaworowska and Hurum 2001: 402, 412–413). The following autapomorphies are diagnostic for the superfamily:

– Premolarisation of I2−C. The I2–3 are, in contrast to younger multituberculates, enlarged, multicuspid, with a complicated structure of their crown (see diagnosis). A similarly enlarged I3 is present also in the plagiaulacid line ( Bolodon crassidens , see Simpson 1928: text−fig. 11a, b), but the oblique crest is less distinct. Moreover, in contrast to the Paulchoffatioidea , the canine is reduced in the plagiaulacid line.

– Presence of three rows of cusps on the posterior upper premolars (P4–5). This feature is present in the Paulchoffatiinae and the Pinheirodontidae , but missing in the Kuehneodontinae; in the Hahnodontidae , the posterior upper premolars are unknown. In most genera of the Paulchoffatiinae the third row of cusps is present on P4 and P5, but in Meketichoffatia G. Hahn, 1993 and in the Pinheirodontidae it is confined to P5 only. This tendency to broaden the posterior upper premolars is unknown in all other evolutionary lineages of the Plagiaulacida as well as in all younger multituberculates.

– Presence of a central basin on m2. The evolution of this basin is combined with a reduction of cusps. In the Paulchoffatiidae and the Pinheirodontidae , the buccal row of cusps is completely reduced ( Fig. 1C, D ) with the exception of Guimarotodon , where cusp b2is preserved ( Hahn and Hahn 1998: fig. 39a). The lingual cusps are retained to a different degree (see Hahn and Hahn 1998: text−fig. 39a–f; Hahn and Hahn 1999b: text−fig. 1g). In the Hahnodontidae , the anterior buccal cusp is preserved, and the posterior cusps of both rows are more or less reduced, as discussed below under “ Hahnodontidae ” ( Fig. 1A, B ). These autapomorphies definitely exclude the Paulchoffatioidea from the ancestry of younger multituberculates

(“Cimolodonta”). The Paulchoffatioidea are thus the oldest known side branch on the multituberculate evolutionary tree. These autapomorphies are combined with some very primitive structures in the skull (here excluded from discussion)

and dentition, representing the most plesiomorphic conditions known among multituberculates. It must be emphasized that these plesiomorphies are confined at least partially to the

Paulchoffatiidae , whereas the Pinheirodontidae represent an already more evolved and stratigraphically younger stage of evolution. The following plesiomorphic structures should be mentioned (see also the diagnosis of the Paulchoffatiidae in

Kielan−Jaworowska and Hurum 2001: 412–413):

– The number of teeth in the upper jaw remains large; canine and five premolars are present.

– p4 is not or only slightly longer than p3 with only four serrations.

– A row of relatively large basal cuspules is present on p3 as well as on p4.

– The function of the premolars is grinding, not cutting. The crowns of the lower premolars become completely eroded during the life of the animal.

– The angle between the longitudinal axis of the dentary and the tooth row is only 7 to 20°.

– The structure of the enamel is non−prismatic (studied only in Paulchoffatiidae ; see Fosse et al. 1985).

Figures

Fig. 1. Comparision of left lower m2in Paulchoffatioidea superfam. nov. A. Hahnodon taqueti Sigogneau−Russell, 1991a; redrawn from Sigogneau− Russell, 1991a: fig. 2c. B. Denisodon moroccensis gen. et sp. nov. C. Kuehneodon sp.; redrawn from Hahn and Hahn 1998: fig. 39b. D. Pinheirodon sp.; redrawn from Hahn and Hahn 1999b: fig. 29c.