Homoetreposciurus egerkingensis, Vianey-Liaud & Hautier, 2022
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publication ID |
https://doi.org/10.1186/s13358-022-00245-3 |
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persistent identifier |
https://treatment.plazi.org/id/497F1B1D-FFE7-DF66-C739-41FDFDE0FC99 |
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treatment provided by |
Felipe |
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scientific name |
Homoetreposciurus egerkingensis |
| status |
nov. gen. |
Homoetreposciurus egerkingensis nov. gen. nov. sp.
Holotype. Ek H004, lower left tooth row, with p4–m3.
Type locality. Egerkingen γ (Swiss Jura); middle Eocene ( MP 14).
Diagnosis. Te lower molars display some features considered derived for theridomyids (e.g., Vianey-Liaud & Marivaux 2016; 2021): p4 longer than m1, with metaconid and protoconid mesially positioned; long thick postprotocristid; high ridges on the lingual (postmetacristid) and distal (post-hypocristid + posterolophid) edges of the teeth; numerous granules and low extra-ridges and granules in the basin; metalophulid I complete, developed from the mesial edge of the metaconid (premetacristid) to the preprotocristid.
Tey also show: dp4 shorter than p4. Lower molars lengths increasing from m1 to m3. Anteroconid absent on p4 and mesiobuccally situated on molars; short on molars but extending buccolingually more and more from m1 to m3, reaching the middle of the mesial border on m3. Entolophid low and discontinuous. Ectolophid mesiodistal from p4 to m2 (nearly aligned with the postprotocristid on p4, a little oblique on m3), with mesoconid weakly marked. Ectomesolophid present on p4.
Te molar morphological features differs from that of Treposciurus in showing lower crowned and more concave occlusal surface of teeth, less individualized lophids (metalophulid I and entolophid), the metaconid fused in a curved and high crest with the postmetacristid, a smaller mesostylid, and smaller granules on enamel surface.
Material. Te holotype Ek 1004 (p4 to m3); Ek 79, a right lower dp4, and possibly a left M1 (Ek 85). Even if the material is poor, it is possible to erect a new taxon, due to the peculiar features of the lower teeth.
Upper tooth
M1 ( Fig. 52c View Fig ). Compared to Protadelomys of the same locality, the weakly worn M1 Ek 85 displays some peculiar features. It is larger, its paraconule and metaconule showing similar size and being both isolated. Te parastyle is mesiobuccal; the anterostyle is present. Te protoloph reduces to a short thin buccal ridge posteriorly oriented; it is followed lingually by the distinct paraconule A well-marked protocrista is present, its mesial end being free. Te strong mesostyle stretched mesiodistally and surrounded by two small cusps, closes the mesoflexus buccally. Te metacone shows a short premetacrista; the buccal metalophule II is present, but short. Two small granules could constitute the remnants of the buccal metalophule I. Te metaconule, not larger than the paraconule, is isolated both from the buccal metalophuleI and from the lingual cusps, protocone and hypocone. Te mesoflexus displays a few extra-ridges. Te hypocone appears smaller than the protocone. Te endoloph is relatively long, thin and high. It is slightly marked lingually by a shallow and short sinus.
LoWer teeth
dp4 ( Fig. 52b View Fig ). Te base of the crown EK 79 is poorly preserved and partly covered with glue. Despite these facts, at the metaconid level, the crown is clearly higher than that of dp4 of the other species of the same locality. Te postmetacristid is high and buccodistally compressed, overhanging the lower central basin; a tiny mesostylid is distinct. Te protoconid is merged in the oblique protocristid, which ends in a weak mesoconid. Te distal ectolophid is interrupted in front of the hypoconid. Te prehypocristid is long and oblique bucco-mesially. Te hypoconid and entoconid are equally robust, bulbous with their upper part tapered. Wrinklings are numerous on the enamel surface, some making a kind of ectocingulid at the buccal opening of the sinusid.
p4. Te specimen Ek H004 ( Fig. 52a View Fig ) was first described and figured by Hartenberger (1969, p. 54; pl. 1, Fig. 4 View Fig ) as gen. and sp. indet, close to Suevosciurus ; then as Treposciurus in Hartenberger (1990) and Escarguel (1999: 246). It is a little longer (2. 20 mm) than m1 (2.09 mm). Te protoconid is close to the metaconid, but it is somewhat lower and separated by a shallow and narrow groove. Te metaconid curves mesio-lingually and prolongs in the high and narrow mesiodistal postmetacristid. Te postmetacristid ends at the base of a low and small entoconid, leaving the wide mesosynclinid opened lingually. Several ridges run obliquely in both the mesosynclinid and the posterosynclinid. Te lophids are crenulated by short wrinkles. Te postprotocristid is slightly oblique, long, and marked at the base of its distal end by a short edge. Te sinusid is shallow, and the crown high below. Te ectolophid is located in the continuity of the postprotocristid; it is long and bears a long ectomesolophid reaching the floor of the sinusid. Te ectolophid joins a short prehypocristid. Te entolophid is low and interrupted between its buccal and lingual halves. One thin ridge connects the lingual half with the posterolophid, which does not join the apex of the entoconid.
Lower molars. Te lower molars have a concave talonid, with low and discontinuous transverse lophids and high edging ridges. Te basin enamel surfaces are strongly wrinkled, with short ridges and granules, while the lophids are crenulated. Te antesinusid–anteroflexid always opens buccally and lingually.
m1–m2. Te m1 (2.09 × 1.75 mm) differs from the m2 (2.34 × 2.13 mm) in displaying a smaller size, a metaconid closer to the protoconid than the entoconid to the hypoconid, a smaller anteroconid located closer to the protoconid than to the metaconid. On the m2 and m3, the anteroconid is equidistant from the protoconid and metaconid, and stretched in a short and low anterolophid. In both cases, the anteroconid does not connect with the metalophulid I; the anterolophulid is lacking but two to four low mesiodistal wrinkles are present in the anteroflexid. Te metalophulid I is rectilinear due to the alignment of its lingual and buccal halves; it connects to the preprotocristid. Te postprotocristid is thick, long, oblique, and its end bears a short premesoconid spur on the m1, but not on the m2–3. Te ectolophid is mesiodistally oriented, long, and swollen at the level of the mesoconid; it makes an obtuse angle with the postprotocristid. Its distal extremity is lower than the level of the connection between the prehypocristid and the entolophid. Te latter angles at an entoconulid level and it is low and incomplete lingually. Te post-hypocristid and the posterolophid are continuous. Te hypoconulid is not distinct or salient.
m3 (2.66 × 2.03 mm) is longer than m2. Tis elongation affects the anterior part of the tooth; while the posterior lobe width is slightly reduced with respect to m2. Consequently, its anterolophid is longer than that of the m2, ditto for the postmetacristid and the postprotocristid. Te short ectolophid is lower than the postprotocristid.
Comparison With Treposciurus mutabilis [from Ehrenstein 3 ( MP 18, upper Eocene)]
Because these specimens have been previously referred to Treposciurus , we compared them to a (younger) species of this genus, T. mutabilis , whose teeth are highly ornamented. Te major similarities between Homoetreposciurus and Treposciurus lie in the ornamentation of the enamel surface, with numerous wrinkles and granules. However, the wrinkles and ridges are more continuous and reticulated in Treposciurus . We also found a number of differences between the two genera. Compared to Homoetreposciurus , Treposciurus mutabilis is characterized by higher crown and higher main cuspids; a p4 smaller than or equal to m1, whereas m3 is equal or smaller than m2; better defined and higher transverse lophids (metalophulid I and entolophid), even if the anterolophid remains low; a longer and lingually developped anterolophid, while the anteroconid remains buccal and close to the protoconid; a higher metaconid that is tapered at its apex and not fused in a curved and high crest with the postmetacristid; a less oblique postprotocristid; a more salient mesoconid, with the ectomesolophid present on all the molars; a mesostylid often distinct and sometimes extending in a short lingual mesolophid; a less reduced posterior lobe of m3. Similar differences were observed with older species of Treposciurus , such as T. preecei from Creechbarrow (Bartonian), even if their teeth are smaller, with less ornamented enamel.
| MP |
Mohonk Preserve, Inc. |
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