Marsupial from the earliest Late Cretaceous of Western US

We report the discovery of mammalian tribosphenic teeth from the basal Cenomanian of southwestern France that we refer to a new primitive marsupial-like form identified as a basal taxon of Marsupialiformes, a new clade recognized here to include the crown group Marsupialia and primitive stem lineages more closely related to Marsupialia than to Deltatheroida. Arcantiodelphys marchandi gen et sp nov. shares several significant marsupial-like features ( s.l. ) with marsupialiform taxa known from the North American Mid-Cretaceous. Among marsupialiforms, it shows a closer resemblance to Dakotadens . This resemblance, which is plesiomorphic within “tribotherians,” makes Arcantiodelphys one of the most archaic known Marsupialiformes. Moreover, Arcantiodelphys is characterized by an original and precocious crushing specialization. Both the plesiomorphic and autapomorphic characteristics of Arcantiodelphys among Marsupialiformes might be explained by an Eastern origin from Asian stem metatherians, with some in situ European evolution. In addition, the presence of a mammal with North American affinities in western Europe during the early Late Cretaceous provides further evidence of a large Euramerican biogeographical province at this age or slightly before. Concerning the paleobiogeographical history of the first stem marsupialiforms during the Albian–Cenomanian interval, 2 possible dispersal routes from an Asian metatherian ancestry can be proposed: Asia to Europe via North America and Asia to North America via Europe. The main significance of the Archingeay-Les Nouillers mammal discovery is that it indicates that the beginning of the stem marsupialiforms history involved not only North America but also Europe, and that this early history in Europe remains virtually unknown.

mentioning

confidence: 73%

The oldest modern therian mammal from Europe and its bearing on stem marsupial paleobiogeography

Vullo

Gheerbrant

Muizon

et al. 2009

“…Furthermore, K. juddi lacks any known apomorphy that would preclude it from ancestry to all known marsupials. Whether the species is included in the group or considered as simply an advanced tribothere depends on definition (13,14); the earliest undoubted marsupials are from the Cenomanian of North America (17,18). Nevertheless, the most parsimonious explanation for the character distribution seen in this taxon is the hypothesis that the marsupial postcanine dental formula of three premolars and four molars evolved prior to the hallmark distinguishing character of the group, the twinning of hypoconulid with entoconid.…”

Section: Early Mammals and Marsupial Dental Charactersmentioning

confidence: 99%

Early Cretaceous mammal from North America and the evolution of marsupial dental characters.

Cifelli

1993

A mammal from the Early Cretaceous of the western United States, represented by a lower jaw exceptional in its completeness, presents unambiguous evidence of postcanine dental formula in an Early Cretaceous marsupial-like mammal, and prompts a reconsideration of the early evolution of marsupial dental characters. A marsupial postcanine dental formula (three premolars and four molars) and several marsupial-like features of the lower molars are present in the new taxon, but a hallmark specialization of marsupials (twinning of the hypoconulid and entoconid on lower molars) is lacking.

“…The proposed range of dates for the later duplications coincides with the geological period (100-135 million years ago) in which the stem-marsupials and stem-eutherians are thought to have diverged from their last common ancestor (9)(10)(11). Clearly, the p-chain-related hemoglobin genes of marsupials need to be examined and compared to those of eutherians to determine if more than two progenitors of E, y, 71, 8, and p loci existed at the time of the metatherian-eutherian split and whether the last common ancestor of marsupials and placental mammals already had p-chainrelated hemoglobin genes that were differentially expressed in embryonic and adult life.…”

mentioning

confidence: 99%

Evolutionary and developmental aspects of two hemoglobin beta-chain genes (epsilon M and beta M) of opossum.

Koop

Goodman²

1988

A series of gene duplications that began in a stem species of Mammalia and led to five developmentally regulated hemoglobin (i-chain loci (E, v, a, 6, and (3) in a common ancestor of eutherian orders Artiodactyla, Rodentia, Lagomorpha, and Primates had important consequences in mammalian evolution. Findings reported here indicate that two progenitors of the five linked genes existed by the time of the eutherian (placental mammal)-metatherian (marsupial mammal) split and that these two genes were already differentiated with respect to their promoter regions and developmental expression. Southern blot and sequence analyses of the hemoglobin (i-chain genes of the opossum (Didelphis virginiana) revealed only two genes, one with coding and promoter sequences similar to eutherian prenatally expressed E, y, and iq genes and the other coding for adult opossum hemoglobin (i-chains and having eutherian adult (i-type promoters. The most parsimonious arrangement of >80 (i-globin exon sequences depicts the opossum embryonic-type gene as orthologously related to eutherian E, y, and q genes and the opossum adult-type gene as orthologously related to 6 and (i genes. These data further indicate that after the initial (i duplication in the stem of Mammalia, the locus that became developmentally delayed in its expression evolved at a faster rate than the locus that became embryonically expressed.Previous studies have provided evidence that a series of tandem gene duplications during formative periods of mammalian evolution led to a cluster of five developmentally regulated hemoglobin p-chain loci (5' e-v-71-8-P 3') in which e, y, and q were embryonically expressed genes and 8 and p were adult-expressed genes (1-5). The first of the duplications occurred in the range of 155-200 million years ago (1, 6-8) and produced two gene lines, of which one was the progenitor of E, y, and -q loci and the other was the progenitor of 8 and p3 loci (2-4). The later duplications that separated E, y, and i1 from each other and in parallel 8 and p were estimated to have occurred in the range of 90-140 million years ago (1,(6)(7)(8).The proposed range of dates for the later duplications coincides with the geological period (100-135 million years ago) in which the stem-marsupials and stem-eutherians are thought to have diverged from their last common ancestor (9-11). Clearly, the p-chain-related hemoglobin genes of marsupials need to be examined and compared to those of eutherians to determine if more than two progenitors of E, y, 71, 8, and p loci existed at the time of the metatherian-eutherian split and whether the last common ancestor of marsupials and placental mammals already had p-chainrelated hemoglobin genes that were differentially expressed in embryonic and adult life.