G
REGGF. G
UNNELL1, J
ÖRGH
ABERSETZER2, E
VELYNS
CHLOSSER-S
TURM2, N
ANCYB. S
IMMONS3, T
HIERRYS
MITH41Division of Fossil Primates, Duke Lemur Center, Durham, USA, gregg.gunnell@duke.edu; 2Senckenberg Forschungsinstitut, Frankfurt am Main, Germany; 3American Museum of Natural History, New York, USA; 4Royal Belgian Institute of Natural Sciences, Brussels, Belgium.
The bat component of the Messel mammalian as-semblage is represented by seven species, all but one (the emballonurid Tachypteron franzeni) belong-ing to the archaic bat families Archaeonycteridae, Palaeochiropterygidae, and Hassianycteridae (Haber-setzer and Storch, 1987; Storch et al., 2002).
Collectively, the Messel bats represent some of the best-preserved and most complete skeletons known for fossil chiropterans anywhere, often preserving soft tissue body outlines and stomach contents. However, one of the great ironies of such exquisite preservation is that some anatomical features traditionally used by mammalian systematists such as details of dental morphology are often obscured because the skele-tons are articulated and the dentitions are in occlu-sion. Due to advances in CT-scanning technology, it is now possible to examine details of dental anatomy even in specimens where the upper and lower jaws are in tight occlusion. Herein we described the com-plete dentition of one of the most primitive members of the Messel bat community, Archaeonycteris trigonodon (HLMD 16069, Fig. 1), and compare its dental anatomy with that of the most primitive bat known from North America, Onychonycteris finneyi (Simmons et al., 2008).
Archaeonycteris trigonodon has the presumably primitive chiropteran dental formula of 2.1.3.3/
3.1.3.3. Upper incisors (Fig. 1B C) are single-cusped, appressed and separated from C1 by a diastema. I1 extends farther ventrally, while I2 is slightly broader and has a small posterolabial cuspule at the base of the crown. C1 is relatively blunt, elongate, and bi-laterally compressed with a sharply defined posterior crest and a weak but continuous basal cingulum. P2 -P3 are reduced in size compared to P4. P2-P3 are relatively short (barely extending beyond the C1 cingu-lum) with a single, sharp cusp. P2 is single-rooted, P3 double-rooted, and both teeth have relatively robust and continuous basal cingula. P4 is dominated by a tall paracone with a steep preparacrista and a slightly
nearly to the labial margin, a relatively labiolingually compressed protofossa with the postpara- and premetacristae joining labially well short of the labial margin. M1 differs from M2 in having a distinct, rela-tively deeply excavated ectoflexus and in having weaker postcingulum. M3 has a greatly extended parastylar lobe with a strong preparacrista extending the length of the lobe, a reduced metacone with no postmetacrista, a relatively lower protocone and a more abbreviated protofossa.
Lower incisors (Fig. 1DE) are small, nearly equiva-lent in size, tricuspate, appressed, with I3 tightly ap-pressed to the anterior base of the C1. The lower ca-nine is mesiodistally shorter and less robust than C1. The anterior lower premolars (P2-3) are much less reduced than their upper counterparts, P2 being sin-gle-rooted and P3 double-rooted. P2-P3 are dominated by a tall, pointed protoconid extending from which are a relatively short preprotocristid and a more elongate postprotocristid, both extending to the pre- and postcingulid, respectively. The cingulid is continuous labially, but there is no lingual cingulid. Neither P2 nor P3 have a talonid developed, but each has a short basal distal projection formed by a broadened post-cingulid. Both P2 and P3 lack para- and metaconids, resulting in flattened and smooth lingual surfaces. P4
is a more complex version of P3 with a distinct but low paraconid and an equally developed but somewhat higher metaconid. P4 lacks a distinct talonid, but the distal surface is extended into a sloping shelf that is restricted lingually by a postprotocristid extending to the postcingulid. There is a distinct labial cingulid, a short precingulid that is truncated by the paraconid and no lingual cingulid. Lower molars are six-cusped, with M1 and M2 of subequal size and M3 somewhat smaller. The labial cusps (protoconid and hypoconid) are taller than the lingual cusps. Molar paraconids are located at the mesiolingual corner of the trigonid, are relatively small, and project mesially. The meta-conids are larger and more robust than the
para-Figure 1. Skull and dentition of Archaeonycteris trigonodon (HLMD 16069). A) skull in lateral view. B-C) upper dentition in labial and occlusal views. D-E) lower dentition in occlusal and labial views.
essentially being tribosphenic. The entocristid is low and does not wall off the talonid lingually. The cristid obliqua joins the postvallid just labial of center, pro-ducing a relatively deep hypoflexid, even on M3. There are strong pre-, post- and labial cingulids on M1-2, with labial and postcingulids being weaker on M3.
more elongate parastylar region, a weaker metacone, and lacking a postmetacrista (O. finneyi has a shorter and broader parastyle, postmetacrista still present and a more distinct metacone); P2 and P3 similar in size and morphology and both unreduced (O. finneyi with P3 reduced and simple, P2 relatively large and Figure 2. Dentition of Onychonycteris finneyi (ROM 55351A-B). A-C) lower dentition in lingual, occlusal and labial views. D) upper dentition in occlusal view.
finneyi differs substantially in dental morphology from A. trigonodon, indicating that establishing a bat den-tal morphotype will require more information. For ex-ample, O. finneyi lacks a paraconid and metaconid on P4 while A. trigonodon has both developed which of these represents the primitive condition? The disposi-tion of molar hypoconulids has also been used as an arbiter of more plesiomorphic vs. more apomorphic taxa. In general, taxa with a tribosphenic pattern (hypoconulid centered on postcristid) are viewed as most primitive, those showing a nyctalodont pattern (hypoconulid lingual and connected to hypoconid) as more derived and those with a myotodont pattern (hypoconulid lingual and isolated, postcristid con-nects hypoconid to entoconid) as most derived (Menu
and Sigé, 1971). However, Archaeonycteris and Onychonycteris differ in hypoconulid structure: A.
trigonodon can be best described as tribosphenic, while O. finneyi might well be myotodont (difficult to tell with certainty on the CT scans). These observa-tions suggest that the early evolution of the chirop-teran dentition was mosaic in nature, and that as-sumptions about the primitive chiropteran dental morphotype need to be carefully evaluated.
ACKNOWLEDGMENTS
The authors thank N. Micklich and G. Gruber (Hessisches Landesmuseum Darmstadt) and K.
Seymour (Royal Ontario Museum, Toronto) for access to specimens.
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