Allomys harkseni, MACDONALD, 1963
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publication ID |
https://doi.org/ 10.1111/j.1096-3642.2008.00399.x |
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persistent identifier |
https://treatment.plazi.org/id/087287DB-FFBD-FF88-FAF1-FEBF8B4AFD22 |
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Felipe |
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scientific name |
Allomys harkseni |
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ALLOMYS HARKSENI MACDONALD, 1963
Allomys harkseni Macdonald, 1963 .
Alwoodia harkseni Korth, 1992b .
Material examined: Holotype & SDSM (59155), and paratype SDSM 59156 View Materials , both isolated upper molars from SDSM V592 , SDSM 6273 View Materials , a left dentary with P 4 –M 3, from loc V627 , as well as additional undescribed specimens from the same localities.
Geographic and stratigraphic range: From the Early Miocene (Late Arikareean NALMA) of South Dakota and Nebraska .
Discussion: Macdonald (1963) originally described this taxon as a species of Allomys from the Wounded Knee faunas of South Dakota. It was later recognized ( Rensberger, 1983) that the type locality for this species included two distinct species of allomyines, both of which were lumped together in Macdonald’s (1970) treatment of additional material from A. harkseni . Korth (1992a) described this second species as ‘ Parallomys ’ americanus , but referred A. harkseni to the genus Alwoodia . Here, I return the species to its original placement in the genus Allomys .
ALLOMYS MAGNUS ( RENSBERGER, 1983) COMB. NOV.
Alwoodia magna Rensberger, 1983 .
Material examined: Holotype & UCMP (76941), from UCMP Loc. V 66116 View Materials , and additional referred specimens UCMP 76938 View Materials , 76946 View Materials , 76945 View Materials , 105022 View Materials , 76933 View Materials , and 105023 from UCMP Loc. V 66111 View Materials , as well as UCMP 76995 View Materials and 105021 from UCMP Loc. V6581 .
Geographic and stratigraphic range: From the Late Oligocene (Early Arikareean NALMA) of Oregon.
Discussion: This species was described as the type of the genus Alwoodia by Rensberger (1983). For the reasons discussed above, it is now placed as the type of the subgenus Alwoodia in the genus Allomys . The change in generic assignment requires alteration of the specific epithet to match the gender of the genus to which it is now assigned.
MENISCOMYINAE RENSBERGER, 1981
Definition: The node group arising from the last common ancestor of Ameniscomys selenoides Dehm, 1950 and Meniscomys hippodus Cope, 1879 .
Revised diagnosis: Mesodont to hypsodont aplodontids with relatively simple cusp morphology, thick, bulbous cusps and crests, and distinctly enlarged premolars (relative to the size of the molars). The mesostyle of P 4 is situated in the centre of the labial end of the central valley. The paracone is level with the metacone on the labial side of the tooth, not displaced lingually; this represents a reversal from the state in nonmeniscomyine allomyines. The anterolabial spur of the protocone, present basally in aplodontids, is lost in this clade. There is no lingual ridge on the anterior end of the protocone. The central fossettid is extremely deep and persists with wear, and has a simple, convex shape, and is round or transversely elongated, in all meniscomyines. The crest from the entoconid to the mesoconid is a large, prominent feature, and is always directed obliquely, anterolabially in meniscomyines. The mesostylid is strongly connected to the mesoconid by a crest, and the entoconid crest of M 2 is bent anteriorly. The posterior inflection between the entoconid and hypoconulid is closed all the way to the top of the crown, and the hypoconulid is posterior to the hypoconid on M 3. The hypoconulid is anteroposteriorly compressed and linear on all the cheek teeth. The mesoconid of P 4 is reduced relative to that in the molars, but the mesostylid has a distinct lingual prominence on P 4. The crenulate enamel found in the basins of the upper cheek teeth of derived nonmeniscomyine allomyines is lost in meniscomyines.
Referred taxa: See Table 1.
Geographic and stratigraphic range: From the Late Oligocene to recent times in North America, from the Late Oligocene to the Late Miocene of Asia, and in the Early Miocene of Europe.
Discussion: This taxon is defined in such a way as to include most of the taxa traditionally assigned to the Meniscomyinae. The immediate outgroups to the Meniscomyinae, P. sinensis and S. cadurcensis , are left out of the group in order to use the most stable definition. Sciurodon lacks the crown height and wear pattern generally associated with meniscomyines, and Promeniscomys is not entirely stable in its placement. Similar to the Allomyinae, the monophyletic Meniscomyinae includes a number of derived taxa that nest within this group, which have not traditionally been included. The transition from earlier allomyines to meniscomyines is characterized by the simplification of cusp morphology and an increase in crown height.
HOMALODONTIA NEW TAXON
Definition: The node group arising from the last common ancestor of Aplodontia rufa Rafinesque, 1817 and Alphagaulus vetus Matthew, 1924 .
Etymology: ‘Homalo-’ from the Greek word meaning ‘flat’ and ‘-odontia’ from the Greek word meaning ‘tooth’, referring to the flat chewing surfaces of the teeth in these rodents.
Diagnosis: Derived aplodontids with subhypsodont to hypsodont, lophodont teeth and broad, flat skulls. The occipital region of the skull is widened, and is often the widest part of the skull. The external auditory meatus is elongated into a tube, which is at least as long as the mediolateral width of the bulla itself. This elongated external auditory meatus extends the ear opening laterally to a point directly anterior to the lateral edge of the widened occipital plate. The bulla is somewhat reduced in relative size, and is not ventrally prominent on the skull. The mastoid process of the skull is enlarged and separated from the bulla, and the anterior edge of the basioccipital is expanded ventrolaterally around the outer surface of the bulla. The protoconule of P 4 is expanded anteroposteriorly and connected to the anteroloph, which is composed of a single cusp, the anterocone. The posterolabial crest of the anterocone meets the anterior crest of the paracone, without leaving a groove down the anterolabial face of the paracone, and the posterolabial fossette on P 4 remains closed throughout wear. The upper molars have reduced roots and are rectangular or oval in occlusal outline. The posterolabial and posterolingual inflections on M 3 are closed by the posterior cingulum, and the mesostylid does not protrude lingually on M 3. Both represent reversals from the condition derived within the nonhomalodontian meniscomyine line. The posterolabial fossettid of P 4 is large, elongated, and oval, and extends posteriorly to be closed by the posterior cingulum.
Referred taxa: See Table 1.
Geographic and stratigraphic range: From the Late Oligocene to recent times in North America, and from the Middle to Late Miocene in Asia.
Discussion: The grouping of mylagaulids with aplodontines is one of the strongest associations found in phylogenetic analyses of aplodontids ( Hopkins, 2001a; Hopkins, 2001b; Hopkins, 2003). This taxon is composed of all the fully hypsodont (having cheek tooth crown height greater than crown length) aplodontids, as well as the mesodont aplodontine precursor R. mcgrewi .
APLODONTINAE TROUESSART, 1897
Definition: The stem group composed of all homalodontians more closely related to Aplodontia rufa Rafinesque, 1817 than to Alphagaulus vetus Matthew, 1924 .
Revised diagnosis: Homalodontians with subhypsodont to hypselodont cheek teeth that lose the cusps early in wear, leaving shield-shaped upper molars and crescent- or B-shaped lower molars ( Fig. 9 View Figure 9 ). Both upper and lower molars are often a simple enamel band surrounding a dentine peg. The lower incisor is convex anteriorly, and the mental foramen is positioned relatively posteriorly, just anterior to P 4. The zygomatic arches are relatively lightly built, and the skull is low and flat. The paracone of the M 3 has a concave labial face. The cheek teeth become more transversely compressed from M 1 to M 3. The ectoloph on the anterocone of P 4 is relatively short. The metaconids of M 1–3 are compressed labiolingually. The entoconid is anterolabially elongated and roughly rectangular. The inflection posterior to the mesostylid is very broad.
Referred taxa: See Table 1.
Geographic and stratigraphic range: Frome the Late Oligocene to recent times in Oregon, Nevada, and Montana.
Discussion: Like Ansomys , the Aplodontinae are easily diagnosed by a consistent morphology. All have hypsodont premolars and molars, and tend to wear the cusps away completely. The taxon is defined as a stem group and is sister to the Mylagaulidae . There is a substantial interval between the divergence of aplodontines and mylagaulids and the first fossil record of aplodontines, and therefore it may be expected that more basal members of this clade will be found. The two Asian species, Pseudaplodon asiatica Schlosser, 1924 and Tschalimys chhikvadzei Shevyreva, 1971 are included, as they are morphologically similar to the other species in the clade. Unfortunately, their fossil remains are too fragmentary to include them in the phylogenetic analysis, because both are known from single specimens that are significantly worn. The current analysis indicates that Sinomylagaulus halamagaiensis Wu, 1988 may also be an aplodontine, but it is also known from a single specimen, and the published images leave some ambiguity about its affinities.
Definition: The stem group composed of all homalodontians more closely related to Alphagaulus vetus Matthew, 1924 than to Aplodontia rufa Trouessart, 1897 .
Revised diagnosis: Medium to large aplodontids with greatly enlarged premolars and a thick, heavily built skull. The zygomatic arch is thickened in the area where the jugal and squamosal overlap, making a distinct knot on the posterior end of the zygomatic arch. The infraorbital foramen is oval, and the skull is broad between the orbits. There more than three closed fossettes on the cheek teeth. The central valley of the upper molars is lost, as the metaloph and protoloph are joined in the centre of the tooth, emphasizing the anteroposteriorly elongated enamel lakes instead. The mesostyle is round, as in early aplodontids, and the ectoloph is convex on the metacone and sometimes on the paracone as well. The anteroloph of P 4 is broad. The mesostylid is bulbous, with its greatest anteroposterior thickness near its labial end, and does not protrude lingually on P 4. The precise occlusion of cusps is lost, as the wear surfaces are all flat, rather than angled, as in all other aplodontoids. The posterolophid is anterolabially directed, not labiolingually as in other aplodontids. The entoconid is reduced in M 3 relative to other molars in early mylagaulids, as well as the derived forms; some mylagaulids from the Middle Miocene reverse this condition. The hypoconulid is triangular, not anteroposteriorly compressed as in meniscomyines. All mylagaulids have premolars that are more than twice the size of any of the molars.
Referred taxa: See Table 1. Geographic and stratigraphic range: From the Late Oligocene to the Late Miocene in North America.
Discussion: Mylagaulids are defined as the stem group that is the sister group of the aplodontines. This leads to the inclusion of the ‘promylagaulines’ (see below), as well as the larger and more hypsodont species that are more typical of the Mylagaulidae . It is defined as a stem group because the apparent paraphyly of the promylagaulines suggests a high probability of discovering additional taxa that will be morphologically very similar to known species, but will fall outside the node group defined by all known mylagaulids. Promylagaulines are relatively poorly known, mostly from isolated teeth. Because only a limited number of partial skulls and jaws of these early mylagaulids are known, it is difficult to describe the characteristic morphology with any precision.
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