Eutheria : Zhelestidae

Taxa on This Page

1. Zhelestidae X

The Zhelestids are a poorly known group of either mostly Cretaceous Laurasian eutheria, mostly known only from teeth and upper and lower jaws.

Archibald & Averianov 2007 consider zhelestids might be basal laurasiatherian placentals, but if so they are not members of extant placental orders.

From the abstract: "Zhelestidae are best known by as many as ten species from the Cenomanian through Turonian of Uzbekistan and Kazakhstan. At the best-known sites at Dzharakuduk, four species are known (Aspanlestes aptap, Parazhelestes mynbulakensis, P. robustus, and Zhelestes temirkazyk) and an additional very small and very large species may be present. At the Cenomanian Sheikhdzheili sites to the west, two (Eozhelestes mangit and Sheikhdzheilia rezvyii) and maybe three species are present. These are the oldest published zhelestids. "Sorlestes" kara from Kazakhstan is Turonian in age. Other species from the Coniacian through Paleocene of Japan ("Sorlestes" mifunensis), Europe Lainodon orueetxebarriai, Labes quintanillensis, L. garimondi), and North America Alostera saskatchewanensis, Gallolestes pachymanibularis, G. agujaensis, Avitotherium utahensis) have been ascribed to this clade. Most taxa are known from fragmentary dental remains, but some of those from Uzbekistan are now known from associated cranial and dental remains. From the same localities ear regions and referred tarsal elements are known, although there is debate as to which tarsal elements belong to zhelestids. In all but a few phylogenetic analyses zhelestids cluster with early Tertiary archaic ungulates, largely because of dental characters. If these archaic ungulates are crown eutherians (placentals), then zhelestids are also crown eutherians (placentals). Most studies have used too few Cenozoic placentals or too few Cretaceous eutherians to determine whether this is the case" Archibald & Averianov 2007

However cladistic analyses by Wible et al. 2007 and Giallombardo 2009 in contrast places them as stem eutharia outside the crown Placental group; in which case similarities with ungulates are due to convergence. This interpretation is followed here

Zhelestidae: Aspanlestes, Eoungulatum, Kumsuperus, Parazhelestes, Sorlestes, Taslestes(?), Zhelestes.

Range: Late Cretaceous of Central Asia, Europe & North America. The North American taxa Allostera, Avitotherium, and Gallolestes, if zhelestids, would extend the range into the Early Paleocene. [Av00].

Phylogeny: Eutheria ::: Adapisoriculidae + ((Asioryctitheria + Cimolestidae) + (Zalambdalestidae + (Leptictida + Placentalia)) + *).

Characters: premolars premolars slender, not inflated [d&C00]; some forms with double-rooted (primitive) premolars [d&C00]; upper P3 larger than P4 and may be slightly more molariform [d&C00]; small paraconule may be present on P4 [d&C00]; but P4 (of 5) simple, consisting mostly of paracone and postparacrista, or not at all molariform [d&C00]; P5 small with "waist" created by concavity between protocone and paracone [d&C00]; P5 with small metacone and paraconule [d&C00]; lower p5 with no paraconid & small metaconid [d&C00]; p5 posterior (distal?) wall of trigonid not flattened [d&C00]; p5 with "incipient" talonid basin [d&C00]; molars, upper upper molars generally intermediate between primitive eutherians and ungulates [d&C00]; paracone larger than metacone on M1&2 [d&C00]; metacone distal and (? or?) slightly lingual to paracone [d&C00]; pre- & postcristae present on upper molars [d&C00]; postmetaconular cristae did not enter into interior region of tooth (primitive for eutherians) [d&C00]; but some invasion of interior by preparacristae [d&C00]; postcingulum not thickened and hypocone absent [d&C00]; pre- & postcingula reach protocone at its base [d&C00]; large parastyle shifted lingually, with large mesial projection [d&C00]; parastylar lobe primitive (see Note) [d&C00]; mesostyle absent [d&C00]; trigon basin small and/or shallow [d&C00];pre- & postparaconular cristae sharp & well-developed [d&C00]; lower trigonid cusps conical & well-separated [d&C00]; trigonid open lingually [d&C00]; talonid basin moderately large (?) [d&C00]; talonid basin closed lingually [d&C00]; $ m2 trigonid & talonid of equal width [d&C00]; metaconid only slightly posterior to protoconid [d&C00]; m1 & m2 hypoconulids and entoconids roughly equal in height & size [d&C00]; m3 hypoconulid only slightly expanded [d&C00]; hypoconid largest cusp on talonid [d&C00]; hyoconid forms labial half of talonid & has concave lingual flank [d&C00]; paraconid positioned lingually & somewhat smaller than other major cuspids [d&C00]; paracristid arcuate [d&C00]; cristid obliqua attaches to linguodistal side of protoconid [d&C00]; weak precingulid present [d&C00]; entocristid present and "extends anteriorly and dorsally on the base of the posterior face of the metaconid" [d&C00: 131].

Links: g00n1a4.pdf; Zhelestidae Nesov, 1985; vol3-p18; Nature Japan; 414062aa.

Image: Note how far Parazhelestes has progressed toward the ungulate condition. Only one reasonably good skull from a possible zhelestid is known. By contrast with the Parazhelestes dentition, the skull appears strikingly primitive, with a low skull table and narrow jaws.

Note: [1] Zhelestids have the primitive eutherian condition in which "the parastylar lobe is composed of three cusps: 1) the stylocone, which is labial to anterolabial to the paracone and connected to it by the preparacrista; 2) the parastyle, which is just anterior to the paracone; and 3) the preparastyle, which is lingual to the parastyle. The stylocone on the one hand and the parastyle + preparastyle on the other are separated by the parastylar groove, where the shearing action of the protoconid produces an important transverse wear facet." de Muizon & Cifelli 2000: 72) [citations omitted]. [2] may well be paraphyletic assemblage of ungulatomorph stem species. [3] most of the characteristics obtained from de Muizon & Cifelli are plesiomorphic. One of the main objectives of their article was to identify the primitive state of ungulatomorphs, and the authors relied heavily on zhelestids to determine that state. [4] Zhelestids were the first placentals to specialize in herbivory and may have dominated the small herbivore niche in the Late Cretaceous of Central Asia, a semitropical lowland and coastal environment. At the same time, multituberculates occupied the same niche in the more arid, upland environment of Mongolia. [K+00], [Av00]. ATW020210.