Canaanimys maquiensis, Antoine et al., 2012
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publication ID |
https://doi.org/ 10.26879/742 |
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publication LSID |
lsid:zoobank.org:pub:540D23AA-F705-4A05-8E10-FADAD3356D9C |
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persistent identifier |
https://treatment.plazi.org/id/03A587B4-E520-AC1C-FC9B-D770FB381461 |
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treatment provided by |
Felipe |
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scientific name |
Canaanimys maquiensis, Antoine et al., 2012 |
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Canaanimys maquiensis, Antoine et al., 2012
Figure 4.14 View FIGURE 4 -16, Appendix 3
Referred material. In addition to the holotype ( MUSM 1890 , right M2; in Antoine et al., 2012, figure 2u) - MUSM 1895 , right dp4 (in Antoine et al., 2012, figure 2z) ; MUSM 1894 (in Antoine et al., 2012, figure 2y) and 2787–2788, left m1s ; MUSM 2789–2790 , right m1s ; MUSM 1893 , left m2 (in Antoine et al., 2012, figure 2x) ; MUSM 1892 (in Antoine et al., 2012, figure 2w) and 2791, right m3s ; MUSM 1891 , left M1 (in Antoine et al., 2012, figure 2v) ; MUSM 2792 , left M3 ( Figure 4.16 View FIGURE 4 ) ; MUSM 1889 (in Antoine et al., 2012, figure 2t) and 2793–2794 ( Figure 4.14 View FIGURE 4 -15), right M3s .
Type locality. Contamana CTA-27, Loreto Department, Peru .
Formation and age. Pozo Formation, lower member, late middle Eocene ( Antoine et al., 2012, 2016).
Emended diagnosis (modified after Antoine et al., 2012, p. 1321). Tiny rodent (body mass estimated at approx. 40 g) characterized by brachydont and bunolophodont teeth. It differs from all other caviomorphs in having teeth with moderately low and sharp transverse crest(id)s, lower molars having generally incomplete second transverse cristid, and pentalophodont upper molars with a well-developed metaloph that turns anteriorly (not posteriorly) and connects either to the third transverse crest lingually or to the mesial extremity of the anterior arm of the hypocone, a primitive condition that is reminiscent of that found in stem Hystricognathi (e.g., Baluchimys , Protophiomys , Waslamys , Phiomys , Hodsahibia , Bugtimys and Ottomania ). The lingual protoloph is either slightly developed or lacking (i.e., taeniodont pattern).
Description. The lower dentition is documented by several molars and one deciduous premolar. There is no permanent premolar identified in the recovered material.
The dp4 is damaged in its mesial part, and as such, it is impossible to describe the protoconid region (in Antoine et al., 2012, figure 2z). This tooth appears somewhat slender, with thin and low transverse and longitudinal cristids. The main cuspids are salient and well-defined. The metaconid is labiolingually compressed and bears a posterior arm that extends backwardly and connects a strong mesostylid. The latter is as large as the metaconid. There is a supernumerary cuspid (nearly reaching the size of the mesostylid) occupying a central position within the mesoflexid and that could be related to a local enlargement of a mesolophid. Thin enamel cristulids radiate from this central cuspid, directed either to the mesostylid, to the ectolophid, or forward. The latter, the longest one, may correspond to the posterior arm of the protoconid. The ectolophid is complete and does not bear any mesoconid. On the talonid, the hypoconid and entoconid are labiolingually opposed, and linked together by a long hypolophid that connects a thin and short anterior arm of the hypoconid. The latter, grooved in its middle part, is formed by two cristulids. Distally, the hypoconid and entoconid are linked by a massive and curved posterolophid. This latter plus the hypolophid isolate a broad metaflexid.
Lower molars (m1–3s) share the same dental structure (in Antoine et al., 2012, figure 2w–y). On m1s, the protoconid and metaconid, as well as the hypoconid and entoconid, are labiolingually opposed. On the unique m2 recognized, the same is true for the mesial cuspids. In contrast, the m2 talonid cuspids differ in showing the entoconid noticeably displaced mesially with respect to the hypoconid. On pristine teeth, cuspids are salient and clearly dominate the cristids, which remain relatively low (moderately elevated). Mesially, there is no trace of an anterocingulid at the neck. Lingually, between the metaconid and entoconid, generally there is a prominent and isolated mesostylid. There is no strong or elevated posterior arm of the metaconid. On the only unworn lower molar (MUSM 1893; in Antoine et al., 2012, figure 2x), the metaconid-mesostylid connection is absent. On other molars, the metaconid is connected to the mesostylid but the latter remains distinct, albeit minute. Like in Cachiyacuy , the second transverse cristid is highly variable and always composite. It can be continuous labiolingually (i.e., long posterior arm of the protoconid + long neomesolophid; MUSM 1892 and 2790; in Antoine et al., 2012, figure 2w), but it is usually interrupted and divided into two (i.e., long posterior arm of the protoconid + short neomesolophid MUSM 2787) or three parts (i.e., long posterior arm of the protoconid short neomesolophid + accessory cuspid; MUSM 1893, 1894, and 2789; in Antoine et al., 2012, figure 2x– y). There is no mesoconid on the complete and obliquely oriented ectolophid. The hypolophid is strong, trenchant, and slightly oblique. Labially, it connects a short anterior arm of the hypoconid, sometimes grooved in its middle part as for the dp4. The posterolophid is massive and strongly connected to the hypoconid, without a hypoconulid. The posterolophid runs lingually and slopes gently to finish its course distolingually at the base of the entoconid.
There is neither deciduous nor permanent upper premolar recovered for this taxon.
The upper molars are brachydont and bunolophodont (in Antoine et al., 2012, figure 2t –v; Figure 4.14 View FIGURE 4 -16). The transverse crests are thin and low; the main cusps are well-marked and salient as a result. There is no conule. We identify as M1 a rectangular tooth that is slightly wider than long. While M1 has a hypocone distally opposed to the protocone, the M2 is recognizable by its hypocone, slightly smaller and more labial. M3s are rectangular with a labiolingual long axis (MUSM 1889 [in Antoine et al., 2012, figure 2t] and 2794 [ Figure 4.14 View FIGURE 4 ]) or mesiodistally expanded on the labial part (MUSM 2792 and 2793; Figure 4.15 View FIGURE 4 -16). The hypocone of the M3s occupies a more labial position than it does on M2. On upper molars, the protocone, mesially canted, usually develops a strong and long posterior outgrowth, which nearly closes the hypoflexus lingually. Mesially, the protocone is connected to an anteroloph running labially to join the base of the paracone mesially, thereby closing the paraflexus labially. There is no trace of parastyle. The protoloph, long and oblique (slightly backwardly directed), does not reach the protocone. There is no lingual protoloph, and as such, the hypoflexus is confluent with the paraflexus, thereby involving a taeniodont pattern. However, some M3s (MUSM 1889, 2792, and 2794) may have a residual lingual protoloph: a thin, very low, and short spur extends from the protoloph lingually to the protocone, or another crestule stemming from the protocone. On M1-3, the anterior arm of the hypocone is thin and moderately long, running mesiolabially. A thin, short, and longitudinal mure links the lingual extremity of the protoloph to the anterior arm of the hypocone. The third transverse crest is a thin and long mesolophule running labially to reach the lingual base of a small and isolated mesostyle. Unlike MUSM 1889 and 1890 (in Antoine et al., 2012, figure 2t –u), the linguolabial course of the mesolophule is sinuous on all other upper molars. On MUSM 2793 ( Figure 4.15 View FIGURE 4 ), the mesolophule is lower and more oblique (i.e., labiomesially oriented), and it displays a weaker connection with the anterior arm of the hypocone. On the unique M 1 specimen (MUSM 1891; in Antoine et al., 2012, figure 2v), the mesolophule, shorter, does not reach the labial margin. On this tooth, the mesostyle is practically indistinct, as it is entirely merged with the metacone. Interestingly, some upper molars of Canaanimys maquiensis (MUSM 1889, 1890, and 1891) exhibit a very unusual arrangement of the metaloph among caviomorphs. Indeed, the metaloph is slightly oblique, forwardly directed, and connected either to the mesolophule lingually or to the mesial extremity of the anterior arm of the hypocone. On some M3s (MUSM 2792 and 2793; Figure 4.15 View FIGURE 4 -16), a small crestule stems from a cusp on the posteroloph, likely the relic of a metaloph or a secondary crestule. This crestule may be absent (on MUSM 2794; Figure 4.14 View FIGURE 4 ). Distally, the teeth show a well-developed posteroloph that connects the hypocone to the base of the metacone. The posteroflexus is generally closed labially (= posterofossette), but in some cases (e.g., MUSM 1890 and 1891), a narrow and very shallow furrow persists between the posteroloph and the metacone.
Comparisons. Canaanimys differs from all other caviomorphs in having teeth with moderately low and sharp transverse crests and cristids, a long outgrowth of the protocone on upper molars, and pentalophodont M1–2 with a well-developed metaloph that turns anteriorly (not posteriorly) and connects either to the mesolophule lingually or to the mesial extremity of the anterior arm of the hypocone a plesiomorphic condition reminiscent of that found in stem Hystricognathi (e.g., Baluchimys Flynn et al., 1986 , Protophiomys Jaeger et al., 1985 , “ Waslamys ” Sallam et al., 2009, Phiomys Osborn, 1908 , Hodsahibia Flynn et al., 1986 , Bugtimys Marivaux et al., 2002 , or Ottomania de Bruijn et al., 2003 ). The lingual protoloph is either slightly developed or lacking (i.e., taeniodont pattern) like in Eobranisamys , Branisamys , Eoincamys and Incamys ( Hoffstetter and Lavocat, 1970; Lavocat, 1976; Frailey and Campbell, 2004). As for Cachiyacuy , Canaanimys differs from Eoincamys and Incamys in having brachydont instead of hypsodont teeth, pentalophodont instead of tetralophodont upper molars, and thinner and transverse instead of strong and oblique crests. Canaanimys has transverse crests labiolingually longer on its upper molars than in Draconomys from La Cantera ( Argentina, late early Oligocene; Vucetich et al., 2010), and a composite second cristid including a neomesolophid and a posterior arm of the protoconid on lower molars, whereas lower molars of Draconomys lack a neomesolophid.
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