Zofia Kielan-Jaworowska

Dual origin of tribosphenic mammals

Marsupials, placentals and their close therian relatives possess complex (tribosphenic) molars that are capable of versatile occlusal functions. This functional complex is widely thought to be a key to the early diversification and evolutionary success of extant therians and their close relatives (tribosphenidans). Long thought to have arisen on northern continents, tribosphenic mammals have recently been reported from southern landmasses. The great age and advanced morphology of these new mammals has led to the alternative suggestion of a Gondwanan origin for the group. Implicit in both biogeographic hypotheses is the assumption that tribosphenic molars evolved only once in mammalian evolutionary history. Phylogenetic and morphometric analyses including these newly discovered taxa suggest a different interpretation: that mammals with tribosphenic molars are not monophyletic. Tribosphenic molars evolved independently in two ancient (holotherian) mammalian groups with different geographic distributions during the Jurassic/Early Cretaceous: an australosphenidan clade endemic to Gondwanan landmasses, survived by extant monotremes; and a boreosphenidan clade of Laurasian continents, including extant marsupials, placentals and their relatives.

Eutherian mammals from the Early Cretaceous of Mongolia

A collection of eutherian mammals consisting of 39 specimens (teeth and jaw fragments) from the ?Aptian or Albian Khoboor Beds in the Gobi Desert, Mongolia, is described. It contains 3 taxa: Prokenna1estes gen.n., assigned to the Otlestidae Nessov, new rank, with 2 shrew size species; P. trofimovi sp.n. and P. minor sp.n.; a heavily worn larger lower molar which will be described elsewhere. It cannot be excluded that P. trofimovi and P. minor are only sexual morphs within the same species. Prokennalestes and Bobolestes Nessov are possibly the oldest known eutherian mammals, but Prokennalestes is morphologically more primitive than Bobolestes. It has a labial mandibular foramen, 5 premolars and 3 molars, 3 cusps in parastylur region, paracone larger than metacone, unwinged conules, no pre‐ and posteingula, and lower molars with a 3‐cusped talonid, which is narrower than the trigonid, Otlestes and Kennalestes may be derived with little modification from Prokennalestes. Prokennalestes gen.n. is congeneric with Prokennalestes Trofimov and Prozalambdalestes Trofimov, which are both nomina nuda.

Phylogeny and Systematics of Multituberculate Mammals

We present a synopsis of high-rank multituberculate systematicsand a manually generated cladogram illustrating multituberculate interrelationships. We divide the Multituberculata into the paraphyletic suborder ‘Plagiaulacida’, an apparently monophyletic suborder Cimolodonta, and one family incertae sedis. Within ‘Plagiaulacida’ we recognise three informal lines: paulchoffatiid (three families), plagiaulacid (three families) and allodontid (two families and the genus Glirodon). The Cimolodonta are divided into an informal Paracimexomys group; three superfamilies: Ptilodontoidea, Djadochtatherioidea (new), and Taeniolabidoidea (restricted to Taeniolabididae); and five families (superfamily incertae sedis): Eucosmodontidae, Microcosmodontidae, Cimolodontidae, Boffiidae, and Kogaionidae; and some genera incertae sedis. New characters used in our analysis are (1) a tendency of molar cusps to coalesce; and (2) ornamentation of grooves, pits, and ridges on the molars. We argue that the Ptilodontoidea, and less certainly also the Cimolodontidae and Boffiidae, might have originated from amongthe plagiaulacid line, a possible intermediate link being the Paracimexomys group. The remaining Cimolodonta might have originated from unknown members of the Paracimexomys group with separated molar cusps and smooth enamel. The origin of two types of prismatic enamel and a relationship between them are stumbling blocks in understanding the origin of the Cimolodonta; we conclude that microprismatic enamel made its appearance only once. Revised diagnoses of high-rank multituberculate taxa, including lists of all known genera, are given.

EVOLUTION OF DENTAL REPLACEMENT IN MAMMALS

Abstract We provide a review of dental replacement features in stem clades of mammals and an hypothetical outline for the evolution of replacement frequency, mode, and sequence in early mammalian evolution. The origin of mammals is characterized by a shift from a primitive pattern of multiple, alternating replacements of all postcanines in most cynodonts to a derived pattern of single, sequential replacement of postcanines. The stem mammal Sinoconodon, however, retained some primitive replacement features of cynodonts. The clade of Morganucodon + crown mammals is characterized by the typical mammalian diphyodont replacement in which antemolars are replaced by one generation in anteroposterior sequence, but molars are not replaced. The stem clades of crown mammals including multituberculates and eutriconodonts have an anteroposterior sequential and diphyodont replacement of premolars. By contrast, stem taxa of the trechnotherian clade (Zhangheotherium, Dryolestes, and Slaughteria) are characterized by an alternating (p2 → p4 → p3) and diphyodont replacement, a condition that is shared by basal eutherians. The sequential replacements of premolars in most extant placentals (either anteroposteriorly p2 → p3 → p4 as in ungulates and carnivores, or postero-anteriorly p4 → p3 → p2 as in some insectivores) would represent secondarily derived conditions within eutherians. The single replacement of P3/p3 of metatherians is the most derived for all therian mammals.

Interrelationships of Mesozoic mammals

Polyphyletic or monophyletic origins of mammals have been subjects of considerable controversy for a century. Late Triassic—Early Jurassic mammals are more diverse than previously thought. The stumbling block in establishing mono‐ or polyphyletic origins of mammals is the uncertain position of the Haramiyidae (the oldest Multituberculata, and possibly the oldest mammals), known only from isolated teeth. Triconodonta and Theria probably shared an unknown common ancestor, while Monotremata possibly branched from early Eupantotheria at the end of the Early Jurassic, before the Dryolestoidea did, from the forms in which the cochlea started to coil and small cerebellar hemispheres developed. Aegialodontia gave rise to Metatheria but not to Eutheria. Deltatheroida belongs to Metatheria. A group of Cretaceous therian mammals with tribosphenic molars informally classified as “Tribotheres”; cannot be assigned either to Metatheria or Eutheria.

Postcranial Skeleton of a Cretaceous Multituberculate Mammal Catopsbaatar

We describe an incomplete postcranial skeleton of Catopsbaatar catopsaloides from the?late Campanian red beds of Hermiin Tsav I, in the Gobi Desert, Mongolia. The skeleton is fragmentary and the preservation of bone surface does not permit reconstruction of the musculature. The studied skeleton contains some parts not preserved or incompletely known in other multituberculate genera, such as a long spinous process in a single lumbar vertebra, which together with long transverse processes preserved in Nemegtbaatar, might indicate that at least some multituberculates had jumping ability. The calcaneus of Catopsbaatar is unusual, differing from most other multituberculates (where known) and other mammals by having a short tuber calcanei, with a large proximal anvil-shaped process strongly bent laterally and ventrally, arranged obliquely with respect to the distal margin of the calcaneus, rather than arranged at 90° to it, as in other mammals. This suggests the presence of strong muscles that attached to the tuber calcanei, perhaps further attesting to jumping abilities in Catopsbaatar. We also describe an unfused pelvic girdle and the first extratarsal spur bone (os cornu calcaris) known in multituberculates.

Cheirurina (Trilobita) from the Upper Ordovician of Västergötland and other regions of Sweden

Abstract Upper Ordovician (Ashgill) Cheirurina (Trilobita) from Vastergotland, Sweden, are described on the basis of a new collection from Skultorp, as well as old collections housed in Swedish museums. Some Ashgill trilobites from other regions of Sweden and Poland are discussed for comparison. Where available, the relevant originals of Linnarsson (1869), Holm (1898), Olin (1906), Tornquist (1905) and Warburg (1925) are refigured. Eighteen species belonging to ten genera (one not determined) are described or discussed. Two new species, Pseudosphaerexochus parallelus and Pseudosphaerexochus? dubius are described. Sphaerocoryphe thomsoni Reed, 1906 from the Ashgill of Girvan, Scotland, is regarded as a junior subjective synonym of S. dentata Angelin, 1854 from the Ashgill of Vastergotland. The Swedish Cybeloides loveni (Linnarsson, 1869) differs from the Scottish Cybeloides girvanensis (Reed, 1906) only on a subspecific level. In addition to nineteen species previously known to be common to the lower-middl...