Democricetodon fejfari, Lindsay, 2017

Lindsay, Everett, 2017, Democricetodon Fejfari Sp. Nov. And Replacement Of Cricetidae By Muridae In Siwalik Deposits Of Pakistan, Fossil Imprint 73 (3 - 4), pp. 445-453 : 448-451

Democricetodon fejfari new species

Text-fig. 3a–f

H o l o t y p e. Left dentary with m1–3 (YGSP 19321) ( Text-fig. 3c ); type specimen will be deposited in collection of the Geological Survey of Pakistan .

E t y m o l o g y. fejfari , named for Oldřich Fejfar a distinguished vertebrate palaeontologist and long-time friend who is well known for his numerous contributions and insight on the history and evolution of small mammals.

T y p e l o c a l i t y. YGSP locality 388, Pakistan.

D i s t r i b u t i o n. Middle Miocene, about 13.8 to 8.7

Ma (YGSP locality 491 to YGSP locality 387).

D i a g n o s i s. Democricetodon fejfari sp. nov. is a large cricetid rodent (see Tab. 1), larger than any currently known species of Democricetodon in Pakistan, comparable in size to Democricetodon lindsayi in Asia, to Democricetodon affinis and Democricetodon gaillardi in Europe, and to D. (Copemys) longidens and D. (Copemys) barstowensis in North America. Democricetodon fejfari sp. nov. has a small single cusped anterocone on M1 that is slightly asymmetrical, elongated transversely with a short labial and longer, thinner lingual side; the anteroconid on m1 is also small and single cusped, with near equal (slightly longer labial) side lophs. Principal cusps in upper molars are nearly opposite to the opposing cusps, with only slight anterior shift in position of lingual cusps relative to labial cusps; principal cusps of lower molars are more offset, with lingual cusps located opposite to the anterior side of labial cusps. In upper molars the distal end of the anterior arm of the protocone is often flexed labially, forming a short protocone anterior loph (that resembles a mesoloph) directed toward the paracone; and in lower molars the distal arm of the protoconid posterior arm is flexed lingually (to resemble the mesolophid), directed toward the lingual margin.A thin mesoloph, and mesolophid, are usually short, if present.

D i f f e r e n t i a l d i a g n o s i s. Democricetodon fejfari sp. nov. differs from Democricetodon lindsayi in having a single cusped anterocone on M1, which is slightly bilobed in D. lindsayi; D. fejfari sp. nov. differs from D. affinis that has the paraloph descend posteriorly from the paracone apex, to join the posterior arm of the protoconid whereas the paraloph on M1 of D. fejfari sp. nov. is always directed anteriorly to join the anterior arm of the protoconid; D. fajfari sp. nov. differs from D. gaillardi that usually has two lophs from the paracone that join both the anterior and posterior arms of the protoconid, while the paraloph in D. fajfari sp. nov. is always directed anteriorly, never joining the posterior arm of the protoconid. D. fejfari sp. nov. differs from Democricetodon kohatensis and all of the other species of Democricetodon recorded from the Siwalik sequence in being larger in size.

D e s c r i p t i o n. Details of the dentition are described by tooth, in the following format.

M1. Occlusal outline is lozenge shape, longer than wide, and narrow anteriorly. Largest cusp is the anterocone, followed by the hypocone that is slightly smaller, and about equal to size of the metacone, both are slightly larger than the protocone that is slightly larger than the paracone. Lingual cusps are positioned slightly anterior to labial cusps with minimal transverse offset of opposing cusps. The anterocone is large, single cusped, elongated transversely with the cusp apex located slightly labial to the midline. Protocone anterior arm is medium length, directed toward the lingual side of the anterocone where it usually joins the anteroloph lingual to the midline and joins the paraloph near the midline; protocone posterior arm is medium length, directed toward the metacone where it usually joins the posterior mure and/or the paraloph near the midline. As noted in the methods section, the protocone posterior spur is identified by a pronounced change in orientation of the protocone posterior arm, that resembles a mesoloph. Hypocone anterior arm is prominent and medium length, it is usually directed toward the paracone and usually joins the posterior mure near the midline; hypocone posterior arm is short, directed toward the posterior midline where it merges with the posterior cingulum. The paracone lacks a posterior spur. The anteroloph is short and low, directed posteriorly from the lingual side of the anterocone to usually join the protocone arm or the paraloph lingual to the midline; an anterior paraloph is usually absent (present in 3 of 22) directed antero-lingually from the paracone to join either the protocone anterior arm or the anteroloph (or both) lingual to the midline; a posterior paraloph, descends lingually from the paracone apex and is flexed posteriorly to join the anterior mure near the midline. Protoloph I is usually minute or absent. A mesoloph is usually minute or indistinct (12/20) or long (8/20), directed posterolabially from the mure near the midline. A mesostyle, ectoloph, ectostyle and anterior metaloph are all absent. A posterior metaloph is medium length and low, it descends posterolingually from the metacone apex toward the posterior cingulum to (usually) join the posterior cingulum near the midline. The central mure is short and low, it weakly joins the protocone posterior arm and the hypocone anterior arm. A lingual anterior cingulum is short, descending lingually from the anterocone apex, then curving posteriorly to terminate anterior to the base of the protocone; a labial anterior cingulum is short, of moderate height, directed labially from the anterocone apex to terminate near (or join) the anterolabial base of the paracone. Transverse shelves are low and synclinal (lower in middle), usually aligned (more or less) opposite to one another, and closed medially by the mure. The lingual sinus is elongated transversely and narrow, it is slightly closed by the low lingual cingulum. The lingual cingulum is short and low; a labial cingulum is minute or indistinct; the posterior cingulum is long and straight, rarely with a slight expansion in mid-length (possibly an incipient hypoconulid II), and either terminates posterior to the metacone or rarely curves anteriorly to ascend the posterior metacone. There are three roots, a large, transversely elongated medial root plus a large round anterior root and smaller round posterolabial root.

M2. Occlusal outline is a rounded rectangle with a short posterolingual corner, longer than wide and slightly wider anteriorly. Largest cusp is usually the hypocone (22/31) or the protocone which is almost as large, followed in size by the paracone, and the smaller metacone. Lingual cusps are usually (26/34) located opposite to the center of labial cusps, or labial cusps are located opposite to the anterior side of lingual cusps (7/34), with a slight transverse offset of cusps. Protocone anterior arm is short, it is directed anterolabially to join the anteroloph near (19/29) or slightly lingual to (10/29) the midline. Protocone posterior arm is short and narrow, directed toward the metacone to join the protocone posterior spur (33/35) and the anterior mure near the midline; the protocone posterior spur is directed toward the paracone and is usually shorter than the mesoloph and terminates freely. Hypocone anterior arm is prominent and long, directed toward the paracone to join the entoloph and posterior mure near the midline; hypocone posterior arm has features like M1, except that several (8/35) M2 show an incipient hypolophid II. A paracone posterior spur is usually absent or indistinct.

The anteroloph is short or minute, it is located near or slightly lingual to the midline. A paraloph is medium length, it descends lingually or anterolingually from the paracone apex to usually join both the anteroloph and the protocone arm (24/30), or only the protocone arm (6/30), near the midline. Protoloph I is minute and usually joins the paraloph. Protoloph II is interpreted the “Protocone posterior spur”. A mesoloph is low, directed labially from the posterior mure, it is usually (25/32) low and medium length, or short (7/32), and terminates freely. A mesostyle, ectoloph and ectostyle are all absent. The metaloph is medium length, it descends lingually from the metacone apex to usually (32/34) join the hypocone anterior arm or the hypocone posterior arm (1/34) or both (1/34) near the midline. The central mure is short and low; it usually joins the protocone posterior arm and the hypocone anterior arm. A lingual anterior cingulum is medium length, it descends lingually from the anterocone and curves posteriorly to terminate near the lingual base of the protocone; the labial anterior cingulum remains relatively high and straight, until it approaches the tooth margin then curves posteriorly and descends to terminate near the anterior base of the paracone. The transverse shelves are narrow and synclinal (lower in middle), placed more or less opposite to one another, and are closed medially by the mure. The lingual sinus has features like that seen on M1. A lingual cingulum is short to medium length; a labial cingulum is short and low (or indistinct); the posterior cingulum is long, gently curving anteriorly and descending to terminate at the base of the metacone, or rarely to ascend the metacone. A short hypolophid II may be developed (8/35) on the posterior cingulum near the midline. There are three roots, as on M1.

M3. Occlusal outline is a rounded and inflated triangle, with a more straight anterior margin. Largest cusp is the protocone that is slightly larger than the paracone; the hypocone is small and the metacone is usually minute (2/4) or indistinct (2/4). Protocone anterior arm is medium length, directed anteriorly to join the anterior cingulum lingual to the midline. Protocone posterior arm is medium length, it is directed posterolabially and is continuous with the hypocone and posterior cingulum. A protocone posterior spur is usually absent (3/4) or short (1/4), it is directed toward the paracone from the distal protocone arm to join the small hypocone and the posterior cingulum. The hypocone anterior arm is short, it bifurcates distally to join the posterior mure and the metaloph near the midline. Hypocone posterior arm is high and robust, it is confluent with the posterior cingulum. The anteroloph is high and short, it is located near the midline to join the paraloph and, distally, the mure. The paraloph descends lingually from the paracone apex to join the anteroloph (3/4) or the anterior cingulum (1/4) near the midline. Protoloph I is absent; protoloph II is interpreted the protocone posterior spur. A thin mesoloph is directed labially (2/3) from the central mure, or is absent (1/3). A mesostyle, ectoloph and ectostyle are all absent. A metaloph descends lingually from the indistinct metacone to join the mure near the midline; metaloph II is absent. The central mure is medium length and relatively high, oriented anteroposteriorly, and joining the paraloph and metaloph near the midline. Lingual anterior cingulum is high, it descends lingually from the high anterior cingulum lingual to the midline and curves posteriorly to terminate near the lingual base of the protocone; labial anterior cingulum is high and relatively long, it curves posteriorly near the tooth margin to merge with the anterior base of the paracone slightly short of the labial tooth margin. Transverse shelves are indistinct. A lingual sinus is indistinct between the protocone and hypocone, marked only by a slight but distinctive inflection of the lingual margin. A labial cingulum is low and continuous; a lingual cingulum is absent or indistinct; the posterior cingulum is moderately high and thin, directed labially from the hypocone and gently curving labial to the minute metacone near the posterolingual margin. Roots are unknown.

m1. Occlusal outline is lozenge shape, longer than wide, and wider posteriorly. Largest cusp is usually the entoconid or the hypoconid, both are slightly larger than the metaconid and the protoconid, which are much larger than the anteroconid. Lingual cusps are placed opposite to the anterior side of labial cusps with noticeable but slight transverse offset of opposite cusps. The anteroconid is small, centrally located on the anterior cingulum and may be symmetrical (8/18), or shorter lingually (6/18), or longer lingually (4/18). Protoconid anterior arm is medium length, it is directed anterolingually to weakly join the paralophid and anterolophid (9/18), or only the paralophid (2/18), or the anterior cingulum (2/18), or only the anterolophid (1/18), or terminate (4/18) near the midline. Protoconid posterior arm is usually medium length, it is directed toward the entoconid to join the protoconid posterior spur (15/19), or to join the anterior mure (3/19) near the midline, or it is indistinct (1/19). The protoconid posterior spur (like the protocone posterior spur of M1) is interpreted the distal end of the protoconid posterior arm that is marked by an angular change in orientation; it is variable in length, directed lingually and terminates freely. The hypoconid anterior arm is short or medium length, directed anterolingually toward the metaconid to join the entolophid and posterior mure near or slightly labial to the midline. The hypoconid posterior arm is short, directed toward the posterior midline to merge with the inflated posterior cingulum. The anterolophid is usually short and low, or indistinct, located slightly labial to the midline. A protolophid is usually minute (15/20) or absent (5/15); it is directed lingually from the protoconid toward the metaconid. The metalophid is highly variable, it descends labially or anterolabially from the metacone apex and either curves anteriorly (8/18) to joins the anterolophid, or bifurcates (7/18) to join both the protoconid and the anterolophid, or it continues labially to weakly join (3/18) the protoconid. There is neither a metalophid II nor a mesolophid. Note that either a protoconid posterior spur or a mesolophid is developed in these teeth, but that both lophs, (which resemble one another) usually never occur in the same tooth. A mesostylid, hypolophid I, hypolophid II, and an ectostylid are also absent. An ectolophid is usually (18/21) absent, or rarely low and medium length (3/21) but terminating freely. The entolophid descends labially from the entoconid apex to join the hypoconid anterior arm slightly labial to the midline. The central mure is short, usually straight (or slightly curved), located slightly labial to the midline. A lingual anterior cingulum is usually medium length (15/19) or short, it descends lingual to the anteroconid and curves posteriorly to either terminate (18/19) or ascend (1/19) the anterolingual base of the metaconid. A labial anterior cingulum is long, it descends labial to the anteroconid, curves posteriorly and terminates near the labial base of the protoconid. Transverse shelves are slightly offset with lingual side slightly anterior to the labial side that is slightly lower and more synclinal than the lingual shelf; transverse shelves are closed medially by the mure. A labial sinusid is deep and wide, with a gently rounded (9/18) or straight (9/18) inner margin. A lingual cingulum is indistinct or low and short; a labial cingulum is medium length and low; posterior cingulum is long, high and slightly inflated, gently curving anteriorly to terminate at the posterolingual base of the entoconid and partially close a shallow posterolingual basin. Posterior labial sulcus is shallow. There are two roots, a round anterior root and a transversely elongated posterior root.

m2. Occlusal outline is a rounded rectangle, longer than wide, slightly wider posteriorly. The four main cusps are very uniform in size although usually (18/31) the labial cusps appear slightly larger than the lingual cusps. Lingual cusps are placed opposite to the anterior side of labial cusps, with a slight transverse offset of opposing cusps. Protoconid anterior arm is medium length, directed toward the anterior midline to join either the minute anteroloph (16/31) or the anterior cingulum (15/31) slightly labial to the midline. Protoconid posterior arm is usually short or medium length, it is directed toward the entoconid to join the protoconid posterior spur and the anterior mure slightly labial to the midline. A protoconid posterior spur is usually short or medium length, it is directed labially from the junction with the protoconid arm and usually (31/35) terminates freely, or weakly joins (4/35) the posterior mure.A metaconid posterior spur is absent.Hypoconid anterior arm is usually short or medium length, it is directed toward the metaconid to join the posterior mure slightly labial to the midline; the hypoconid posterior arm has similar features to those seen on m1. Anterolophid is minute or indistinct, it is located slightly labial to the midline. Metalophid I is usually short (26/32), or absent (6/32); it descends anterolabially from the metacone apex to usually join the anterior cingulum lingual (26/32) to the midline, or (6/32) the protoconid anterior arm near the anterolophid. Metalophid II is absent. Mesolophid and mesostylid are absent or indistinct. An ectolophid is usually absent, it is weakly developed and long on a single specimen (inv. no. 44137). Ectostylid is absent. Entolophid I is medium length, it descends labially from the entoconid apex and is flexed anteriorly to join the posterior mure near the midline. Hypolophid I is minute; hypolophid II is absent. The central mure is short, it is rarely (4/35) oriented slightly oblique (anterior end more lingual) to the tooth, located near the midline and joins the protoconid posterior arm with the hypoconid anterior arm. Labial anterior cingulum is high near the midline, it descends labially and curves posteriorly to terminate near the labial base of the protoconid; lingual anterior cingulum is high, it merges with the metaconid short of the lingual tooth margin. Transverse shelves are synclinal; the labial shelf is slightly lower and wider than the lingual shelf; shelves are closed medially by the central mure. A labial sinusid has features like that seen on m1. A lingual cingulum is short or indistinct; a labial cingulum is medium length and low; the posterior cingulum has features like those seen on m1. Roots have features similar to those of m1.

m3. Occlusal outline is lozenge shape, longer than wide, and much more narrow posteriorly. Largest cusp is the protoconid which is slightly larger than the hypoconid, and both are larger than the metaconid; the entoconid is absent or indistinct. The metaconid is located opposite to the anterior side of the protoconid, and the hypoconid is placed posterior to the protoconid. Protoconid anterior arm is short, it is directed toward the anterior midline to join either the anterior cingulum (7/8) or anterolophid (1/8) near the midline. Protoconid posterior arm is medium length, it is directed toward the lingual margin where an entoconid should be located, and joins both the protoconid posterior spur (if present) and the anterior mure near the midline. Protoconid posterior spur is short and narrow, it is directed lingually and terminates short of the lingual margin. Metaconid posterior spur is absent. Hypoconid anterior arm is short, it is directed toward the lingual margin to join the remnant lophid of the entoconid near the midline. Hypoconid posterior arm is short, it merges with the posterior cingulum near the midline. Anterolophid is indistinct or absent; metalophid I is short, it descends anterolabially from the metaconid apex and gently curves anteriorly to join the anterior cingulum (or rarely the anterolophid) lingual to the midline. Metalophid II, mesolophid, mesostylid, ectolophid, and ectostylid are all absent. An entolophid remnant is represented by its distal loph (the entoconid is absent) that joins the posterior mure near the midline and is posterior to the protoconid posterior spur; the entolophid remnant terminates short of the lingual margin. Hypolophid II is absent. The central mure is short, located near the midline; it is slightly flexed near the middle and joins the protoconid arm and the hypoconid arm near the midline, with two thin lophs (protoconid posterior arm and the entolophid remnant) directed lingually. Labial anterior cingulum may be indistinct or, if distinct, descends from the high anterior cingulum near the midline, and gently curves posteriorly to terminate near the labial base of the protoconid; lingual anterior cingulum is medium length, high and straight, it is directed lingually from the midline to terminate short of the lingual margin anterior to the metaconid. Transverse shelves and lingual sinusid have features similar to those in m2. Lingual cingulum is moderately high and continuous between the metaconid and posterior cingulum; labial cingulum is short and low; posterior cingulum is high and slightly inflated on the gently curving posterolingual tooth margin, weakly joining the labial cingulum. Labial sulcus is deep and relatively wide, as in m2. Roots have features similar to those on m2.

Democricetodon fejfari sp. nov. was a relatively large cricetid rodent, the last species of cricetid rodent to inhabit Pakistan, replaced by advanced rodents of the family Muridae . Muroid rodents in Siwalik deposits of Pakistan represent three closely related taxonomic groups, the Cricetinae , Myocricetinae, and Murinae . As pointed out by Barry et al. (2002) the fossil record of later Miocene deposits (Chinji and Dhok Pathan Formations) in Pakistan is rich and highly informative; the earlier fossil record in Pakistan (Kamlial Formation) is not so rich but is also very informative, especially as we search for climatic information in the fossil record. The success or failure of diverse and widespread taxa, such as Cricetinae , Myocricetinae, and Murinae in Siwalik deposits remains poorly understood. The climatic significance of Murinae replacing Cricetinae warrants more scrutiny in hope of learning the role of climate change with regard to faunal replacement.

Figures

Text-fig. 3. Selected specimens of Democricetodon fejfari sp. nov. a: right M3, YGSP 19262; b: right maxilla with M1 and M2, YGSP 19285; c: left dentary with m1, m2, and m3 (holotype), YGSP 19321; d: left right m3, YGSP 19330; e: right m2 (reveresed), YGSP 19324; f: right m1, YGSP 19279.