Journal articles on the topic 'Eutherian mammals'
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1
V.R. Prasad, Guntupalli, Omkar Verma, Ashok Sahni, and Ashu Khosla. "Cretaceous mammals of India–Stratigraphic distribution, diversity and intercontinental affinities." Journal of Palaeosciences 70, no. (1-2) (September 10, 2021): 173–92. http://dx.doi.org/10.54991/jop.2021.14.
Abstract:
Extensive research carried out on the Cretaceous deposits of Laurasia has revealed an overwhelming presence of eutherian, metatherian and multituberculate groups of mammals in the Cretaceous ecosystems of Northern Hemisphere continents. In contrast, the relatively poorly documented fossil record of Cretaceous mammals from Gondwanan continents is represented by gondwanatherians, dryolestoids, and a few multituberculates and haramiyidans. Until now, no undoubted eutherian mammals have been reported from the Cretaceous strata of the southern continents except for India. In this context, Indian Cretaceous mammals assume great significance for understanding the origin and evolution of these mammals in Gondwana. Currently, the Cretaceous mammals of India include three groups, viz., eutherians, gondwanatherians, and haramiyidans. These three mammalian groups were recovered primarily from the Upper Cretaceous Deccan infra–and inter–trappean beds of peninsular India exposed near Bacharam, Naskal and Rangapur (Telengana), Upparhatti (Karnataka) and Kisalpuri (Madhya Pradesh) villages. Eutheria is by far the most diverse clade comprising three named genera (Deccanolestes, Sahnitherium, Kharmerungulatum) and one unnamed taxon (Eutheria incertae sedis). The gondwanatherians are known by Bharattherium bonapartei and Sudamericidae gen. et sp. indet. The third mammalian group, a possible haramiyidan, is represented by a solitary species Avashishta bacharamensis. Overall, the Cretaceous mammal fauna of India presents a complex biogeographic history with eutherians of Laurasian affinity, pan–Gondwanan gondwanatherians and a possible late surviving haramiyidan. Numerically abundant and speciose Deccanolestes, identified as an adapisoriculid, has been interpreted to have had originated in northward drifting Indian Plate in the Late Cretaceous and dispersed out of India into Africa and Europe over island arc systems (Oman–Kohistan–Dras) and the Ladakh magmatic arc at or near the Cretaceous–Paleogene boundary. A similar dispersal mode has also been visualized for Kharmerungulatum and Eutheria incertae sedis of Laurasian affinities.
2
Edwards, Carol A., Nozomi Takahashi, Jennifer A. Corish, and Anne C. Ferguson-Smith. "The origins of genomic imprinting in mammals." Reproduction, Fertility and Development 31, no. 7 (2019): 1203. http://dx.doi.org/10.1071/rd18176.
Abstract:
Genomic imprinting is a process that causes genes to be expressed according to their parental origin. Imprinting appears to have evolved gradually in two of the three mammalian subclasses, with no imprinted genes yet identified in prototheria and only six found to be imprinted in marsupials to date. By interrogating the genomes of eutherian suborders, we determine that imprinting evolved at the majority of eutherian specific genes before the eutherian radiation. Theories considering the evolution of imprinting often relate to resource allocation and recently consider maternal–offspring interactions more generally, which, in marsupials, places a greater emphasis on lactation. In eutherians, the imprint memory is retained at least in part by zinc finger protein 57 (ZFP57), a Kruppel associated box (KRAB) zinc finger protein that binds specifically to methylated imprinting control regions. Some imprints are less dependent on ZFP57invivo and it may be no coincidence that these are the imprints that are found in marsupials. Because marsupials lack ZFP57, this suggests another more ancestral protein evolved to regulate imprints in non-eutherian subclasses, and contributes to imprinting control in eutherians. Hence, understanding the mechanisms acting at imprinting control regions across mammals has the potential to provide valuable insights into our understanding of the origins and evolution of genomic imprinting.
3
Gerkema, Menno P., Wayne I. L. Davies, Russell G. Foster, Michael Menaker, and Roelof A. Hut. "The nocturnal bottleneck and the evolution of activity patterns in mammals." Proceedings of the Royal Society B: Biological Sciences 280, no. 1765 (August 22, 2013): 20130508. http://dx.doi.org/10.1098/rspb.2013.0508.
Abstract:
In 1942, Walls described the concept of a ‘nocturnal bottleneck’ in placental mammals, where these species could survive only by avoiding daytime activity during times in which dinosaurs were the dominant taxon. Walls based this concept of a longer episode of nocturnality in early eutherian mammals by comparing the visual systems of reptiles, birds and all three extant taxa of the mammalian lineage, namely the monotremes, marsupials (now included in the metatherians) and placentals (included in the eutherians). This review describes the status of what has become known as the nocturnal bottleneck hypothesis, giving an overview of the chronobiological patterns of activity. We review the ecological plausibility that the activity patterns of (early) eutherian mammals were restricted to the night, based on arguments relating to endothermia, energy balance, foraging and predation, taking into account recent palaeontological information. We also assess genes, relating to light detection (visual and non-visual systems) and the photolyase DNA protection system that were lost in the eutherian mammalian lineage. Our conclusion presently is that arguments in favour of the nocturnal bottleneck hypothesis in eutherians prevail.
4
Griffith, Oliver W., Arun R. Chavan, Stella Protopapas, Jamie Maziarz, Roberto Romero, and Gunter P. Wagner. "Embryo implantation evolved from an ancestral inflammatory attachment reaction." Proceedings of the National Academy of Sciences 114, no. 32 (July 26, 2017): E6566—E6575. http://dx.doi.org/10.1073/pnas.1701129114.
Abstract:
The molecular changes that support implantation in eutherian mammals are necessary to establish pregnancy. In marsupials, pregnancy is relatively short, and although a placenta does form, it is present for only a few days before parturition. However, morphological changes in the uterus of marsupials at term mimic those that occur during implantation in humans and mice. We investigated the molecular similarity between term pregnancy in the marsupials and implantation in eutherian mammals using the gray short-tailed opossum (Monodelphis domestica) as a model. Transcriptomic analysis shows that term pregnancy in the opossum is characterized by an inflammatory response consistent with implantation in humans and mice. This immune response is temporally correlated with the loss of the eggshell, and we used immunohistochemistry to report that this reaction occurs at the materno–fetal interface. We demonstrate that key markers of implantation, including Heparin binding EGF-like growth factor and Mucin 1, exhibit expression and localization profiles consistent with the pattern observed during implantation in eutherian mammals. Finally, we show that there are transcriptome-wide similarities between the opossum attachment reaction and implantation in rabbits and humans. Our data suggest that the implantation reaction that occurs in eutherians is derived from an attachment reaction in the ancestral therian mammal which, in the opossum, leads directly to parturition. Finally, we argue that the ability to shift from an inflammatory attachment reaction to a noninflammatory period of pregnancy was a key innovation in eutherian mammals that allowed an extended period of intimate placentation.
5
Royall, Amy H., Stephen Frankenberg, Andrew J. Pask, and Peter W. H. Holland. "Of eyes and embryos: subfunctionalization of the CRX homeobox gene in mammalian evolution." Proceedings of the Royal Society B: Biological Sciences 286, no. 1907 (July 24, 2019): 20190830. http://dx.doi.org/10.1098/rspb.2019.0830.
Abstract:
ETCHbox genes are fast-evolving homeobox genes present only in eutherian (placental) mammals which originated by duplication and divergence from a conserved homeobox gene, Cone-rod homeobox ( CRX ). While expression and function of CRX are restricted to the retina in eutherian mammals, ETCHbox gene expression is specific to preimplantation embryos. This dramatic difference could reflect the acquisition of new functions by duplicated genes or subfunctionalization of pleiotropic roles between CRX and ETCHbox genes. To resolve between these hypotheses, we compared expression, sequence and inferred function between CRX of metatherian (marsupial) mammals and ETCHbox genes of eutherians. We find the metatherian CRX homeobox gene is expressed in early embryos and in eyes, unlike eutherian CRX , and distinct amino acid substitutions were fixed in the metatherian and eutherian evolutionary lineages consistent with altered transcription factor specificity. We find that metatherian CRX is capable of regulating embryonically expressed genes in cultured cells in a comparable way to eutherian ETCHbox. The data are consistent with CRX having a dual role in eyes and embryos of metatherians, providing an early embryonic function comparable to that of eutherian ETCHbox genes; we propose that subfunctionalization of pleiotropic functions occurred after gene duplication along the placental lineage, followed by functional elaboration.
6
Renfree, Marilyn B., Shunsuke Suzuki, and Tomoko Kaneko-Ishino. "The origin and evolution of genomic imprinting and viviparity in mammals." Philosophical Transactions of the Royal Society B: Biological Sciences 368, no. 1609 (January 5, 2013): 20120151. http://dx.doi.org/10.1098/rstb.2012.0151.
Abstract:
Genomic imprinting is widespread in eutherian mammals. Marsupial mammals also have genomic imprinting, but in fewer loci. It has long been thought that genomic imprinting is somehow related to placentation and/or viviparity in mammals, although neither is restricted to mammals. Most imprinted genes are expressed in the placenta. There is no evidence for genomic imprinting in the egg-laying monotreme mammals, despite their short-lived placenta that transfers nutrients from mother to embryo. Post natal genomic imprinting also occurs, especially in the brain. However, little attention has been paid to the primary source of nutrition in the neonate in all mammals, the mammary gland. Differentially methylated regions (DMRs) play an important role as imprinting control centres in each imprinted region which usually comprises both paternally and maternally expressed genes ( PEG s and MEG s). The DMR is established in the male or female germline (the gDMR). Comprehensive comparative genome studies demonstrated that two imprinted regions, PEG10 and IGF2-H19 , are conserved in both marsupials and eutherians and that PEG10 and H19 DMRs emerged in the therian ancestor at least 160 Ma, indicating the ancestral origin of genomic imprinting during therian mammal evolution. Importantly, these regions are known to be deeply involved in placental and embryonic growth. It appears that most maternal gDMRs are always associated with imprinting in eutherian mammals, but emerged at differing times during mammalian evolution. Thus, genomic imprinting could evolve from a defence mechanism against transposable elements that depended on DNA methylation established in germ cells.
7
Zhang, Xuzhe, Mihaela Pavlicev, Helen N. Jones, and Louis J. Muglia. "Eutherian-Specific Gene TRIML2 Attenuates Inflammation in the Evolution of Placentation." Molecular Biology and Evolution 37, no. 2 (October 9, 2019): 507–23. http://dx.doi.org/10.1093/molbev/msz238.
Abstract:
Abstract Evolution of highly invasive placentation in the stem lineage of eutherians and subsequent extension of pregnancy set eutherians apart from other mammals, that is, marsupials with short-lived placentas, and oviparous monotremes. Recent studies suggest that eutherian implantation evolved from marsupial attachment reaction, an inflammatory process induced by the direct contact of fetal placenta with maternal endometrium after the breakdown of the shell coat, and shortly before the onset of parturition. Unique to eutherians, a dramatic downregulation of inflammation after implantation prevents the onset of premature parturition, and is critical for the maintenance of gestation. This downregulation likely involved evolutionary changes on maternal as well as fetal/placental side. Tripartite-motif family-like2 (TRIML2) only exists in eutherian genomes and shows preferential expression in preimplantation embryos, and trophoblast-derived structures, such as chorion and placental disc. Comparative genomic evidence supports that TRIML2 originated from a gene duplication event in the stem lineage of Eutheria that also gave rise to eutherian TRIML1. Compared with TRIML1, TRIML2 lost the catalytic RING domain of E3 ligase. However, only TRIML2 is induced in human choriocarcinoma cell line JEG3 with poly(I:C) treatment to simulate inflammation during viral infection. Its knockdown increases the production of proinflammatory cytokines and reduces trophoblast survival during poly(I:C) stimulation, while its overexpression reduces proinflammatory cytokine production, supporting TRIML2’s role as a regulatory inhibitor of the inflammatory pathways in trophoblasts. TRIML2’s potential virus-interacting PRY/SPRY domain shows significant signature of selection, suggesting its contribution to the evolution of eutherian-specific inflammation regulation during placentation.
8
Fernando, Prithiviraj, and Don J. Melnick. "Molecular sexing eutherian mammals." Molecular Ecology Notes 1, no. 4 (December 2001): 350–53. http://dx.doi.org/10.1046/j.1471-8278.2001.00112.x.
9
Bedford, JM. "What marsupial gametes disclose about gamete function in eutherian mammals." Reproduction, Fertility and Development 8, no. 4 (1996): 569. http://dx.doi.org/10.1071/rd9960569.
Abstract:
The gametes of eutherian mammals present some fundamental enigmas in regard to their structure and behaviour that have not been solved by a focus on the Eutheria alone. Although the evidence is limited still, some clues are suggested in comparison with representative American and Australian marsupials, whose gametes have undergone parallel, although sometimes quite different, evolutionary changes to those of eutherian mammals. The contrasts between them illuminate basic questions about the functions of the epididymis and sperm capacitation, about sperm numbers and sperm production, about the function of the cumulus oophorus and the configuration of the Fallopian tube and, not least, about gamete design and its bearing on the mechanisms by which spermatozoa penetrate the egg coat.
10
Goswami, Anjali, Nick Milne, and Stephen Wroe. "Biting through constraints: cranial morphology, disparity and convergence across living and fossil carnivorous mammals." Proceedings of the Royal Society B: Biological Sciences 278, no. 1713 (November 24, 2010): 1831–39. http://dx.doi.org/10.1098/rspb.2010.2031.
Abstract:
Carnivory has evolved independently several times in eutherian (including placental) and metatherian (including marsupial) mammals. We used geometric morphometrics to assess convergences associated with the evolution of carnivory across a broad suite of mammals, including the eutherian clades Carnivora and Creodonta and the metatherian clades Thylacoleonidae, Dasyuromorphia, Didelphidae and Borhyaenoidea. We further quantified cranial disparity across eutherians and metatherians to test the hypothesis that the marsupial mode of reproduction has constrained their morphological evolution. This study, to our knowledge the first to extensively sample pre-Pleistocene taxa, analysed 30 three-dimensional landmarks, focused mainly on the facial region, which were digitized on 130 specimens, including 36 fossil taxa. Data were analysed with principal components (PC) analysis, and three measures of disparity were compared between eutherians and metatherians. PC1 showed a shift from short to long faces and seemed to represent diet and ecology. PC2 was dominated by the unique features of sabre-toothed forms: dramatic expansion of the maxilla at the expense of the frontal bones. PC3, in combination with PC1, distinguished metatherians and eutherians. Metatherians, despite common comparisons with felids, were more similar to caniforms, which was unexpected for taxa such as the sabre-toothed marsupial Thylacosmilus . Contrary to previous studies, metatherian carnivores consistently exhibited disparity which exceeded that of the much more speciose eutherian carnivore radiations, refuting the hypothesis that developmental constraints have limited the morphological evolution of the marsupial cranium.
11
Menzies, B. R., G. Shaw, T. P. Fletcher, A. J. Pask, and M. B. Renfree. "208. Absence of GH-R exon 3 in marsupials and monotremes argues for a eutherian specific origin and fetal specific purpose of this domain." Reproduction, Fertility and Development 20, no. 9 (2008): 8. http://dx.doi.org/10.1071/srb08abs208.
Abstract:
Growth hormone receptor (GH-R) plays a critical role in the control of growth and metabolism in all vertebrates. GH-R consists of 9 coding exons (2–10) in all eutherian mammals, while the chicken only has 8 coding exons, and does not have an orthologous region to eutherian exon 3. To further understand the evolutionary origins of exon 3 of the GH-R we have cloned the full-length GH-R sequence in a marsupial, the tammar wallaby to determine whether exon 3 was present or absent in marsupial liver cDNA. There was no evidence for the presence of an exon 3 containing mRNA in sequence of tammar pouch young and adult livers. We next examined the genomes of the platypus (a monotreme mammal) and the grey short-tailed opossum (another marsupial). Like the tammar, the GH-R gene of neither species contained an exon 3. GH receptor can obviously function in the absence of this exon, raising speculation about the function of this domain, if any, in eutherians. A comparison of exon 3 protein sequences within 16 species of eutherian mammals showed that there was ~75% homology in the domain despite only 3 residues being identical (Leu12, Gln13 and Pro17). Interestingly, we detected greater evolutionary divergence in exon 3 sequences from species that have variants of GH or prolactin (PRL) in their placentas. These data show that exon 3 was inserted into the GH-R after the divergence of marsupial and eutherian lineages at least 130 million years ago.
12
Renfree, Marilyn B., Eleanor I. Ager, Geoff Shaw, and Andrew J. Pask. "Genomic imprinting in marsupial placentation." REPRODUCTION 136, no. 5 (November 2008): 523–31. http://dx.doi.org/10.1530/rep-08-0264.
Abstract:
Genomic imprinting is a widespread epigenetic phenomenon in eutherian mammals, which regulates many aspects of growth and development. Parental conflict over the degree of maternal nutrient transfer is the favoured hypothesis for the evolution of imprinting. Marsupials, like eutherian mammals, are viviparous but deliver an altricial young after a short gestation supported by a fully functional placenta, so can shed light on the evolution and time of acquisition of genomic imprinting. All orthologues of eutherian imprinted genes examined have a conserved expression in the marsupial placenta regardless of their imprint status. Differentially methylated regions (DMRs) are the most common mechanism controlling genomic imprinting in eutherian mammals, but none were found in the marsupial imprinted orthologues of IGF2 receptor (IGF2R), INS or mesoderm-specific transcript (MEST). Instead, histone modification appears to be the mechanism used to silence these genes. At least three genes in marsupials have DMRs: H19, IGF2 and PEG10. PEG10 is particularly interesting as it is derived from a retrotransposon, providing the first direct evidence that retrotransposon insertion can drive the evolution of an imprinted region and of a DMR in mammals. The insertion occurred after the prototherian–therian mammal divergence, suggesting that there may have been strong selection for the retention of imprinted regions that arose during the evolution of placentation. There is currently no evidence for genomic imprinting in the egg-laying monotreme mammals. However, since these mammals do have a short-lived placenta, imprinting appears to be correlated with viviparity but not placentation.
13
Amann, R. P., and D. N. R. Veeramachaneni. "Cryptorchidism in common eutherian mammals." Reproduction 133, no. 3 (March 2007): 541–61. http://dx.doi.org/10.1530/rep-06-0272.
Abstract:
Cryptorchidism is failure of one or both testes to descend into the scrotum. Primary fault lies in the testis. We provide a unifying cross-species interpretation of testis descent and urge the use of precise terminology. After differentiation, a testis is relocated to the scrotum in three sequential phases: abdominal translocation, holding a testis near the internal inguinal ring as the abdominal cavity expands away, along with slight downward migration; transinguinal migration, moving a cauda epididymidis and testis through the abdominal wall; and inguinoscrotal migration, moving a s.c. cauda epididymidis and testis to the bottom of the scrotum. The gubernaculum enlarges under stimulation of insulin-like peptide 3, to anchor the testis in place during gradual abdominal translocation. Concurrently, testosterone masculinizes the genitofemoral nerve. Cylindrical downward growth of the peritoneal lining into the gubernaculum forms the vaginal process, cremaster muscle(s) develop within the gubernaculum, and the cranial suspensory ligament regresses (testosterone not obligatory for latter). Transinguinal migration of a testis is rapid, apparently mediated by intra-abdominal pressure. Testosterone is not obligatory for correct inguinoscrotal migration of testes. However, normally testosterone stimulates growth of the vaginal process, secretion of calcitonin gene-related peptide by the genitofemoral nerve to provide directional guidance to the gubernaculum, and then regression of the gubernaculum and constriction of the inguinal canal. Cryptorchidism is more common in companion animals, pigs, or humans (2–12%) than in cattle or sheep (≤1%). Laboratory animals rarely are cryptorchid. In respect to non-scrotal locations, abdominal testes predominate in cats, dogs, and horses. Inguinal testes predominate in rabbits, are common in horses, and occasionally are found in cats and dogs. S.c. testes are found in cattle, cats and dogs, but are most common in humans.
14
LILLEGRAVEN, JASON A., STEVEN D. THOMPSON, BRIAN K. McNAB, and JAMES L. PATTON. "The origin of eutherian mammals." Biological Journal of the Linnean Society 32, no. 3 (November 1987): 281–336. http://dx.doi.org/10.1111/j.1095-8312.1987.tb00434.x.
15
Fléchon, Jacques-Edmond. "The acrosome of eutherian mammals." Cell and Tissue Research 363, no. 1 (August 15, 2015): 147–57. http://dx.doi.org/10.1007/s00441-015-2238-0.
16
Archibald;, J. D. "Divergence Times of Eutherian Mammals." Science 285, no. 5436 (September 24, 1999): 2031a—2031. http://dx.doi.org/10.1126/science.285.5436.2031a.
17
Dooley, James C., Michaela S. Donaldson, and Leah A. Krubitzer. "Cortical plasticity following stripe rearing in the marsupialMonodelphis domestica: neural response properties of V1." Journal of Neurophysiology 117, no. 2 (February 1, 2017): 566–81. http://dx.doi.org/10.1152/jn.00431.2016.
Abstract:
The functional organization of the primary visual area (V1) and the importance of sensory experience in its normal development have been well documented in eutherian mammals. However, very few studies have investigated the response properties of V1 neurons in another large class of mammals, or whether sensory experience plays a role in shaping their response properties. Thus we reared opossums ( Monodelphis domestica) in normal and vertically striped cages until they reached adulthood. They were then anesthetized using urethane, and electrophysiological techniques were used to examine neuronal responses to different orientations, spatial and temporal frequencies, and contrast levels. For normal opossums, we observed responses to the temporal and spatial characteristics of the stimulus to be similar to those described in small, nocturnal, eutherian mammals such as rats and mice; neurons in V1 responded maximally to stimuli at 0.09 cycles per degree and 2.12 cycles per second. Unlike other eutherians, but similar to other marsupials investigated, only 40% of the neurons were orientation selective. In stripe-reared animals, neurons were significantly more likely to respond to vertical stimuli at a wider range of spatial frequencies, and were more sensitive to gratings at lower contrast values compared with normal animals. These results are the first to demonstrate experience-dependent plasticity in the visual system of a marsupial species. Thus the ability of cortical neurons to alter their properties based on the dynamics of the visual environment predates the emergence of eutherian mammals and was likely present in our earliest mammalian ancestors.NEW & NOTEWORTHY These results are the first description of visual response properties of the most commonly studied marsupial model organism, the short-tailed opossum ( Monodelphis domestica). Further, these results are the first to demonstrate experience-dependent plasticity in the visual system of a marsupial species. Thus the ability of cortical neurons to alter their properties based on the dynamics of the visual environment predates the emergence of eutherian mammals and was likely present in our earliest mammalian ancestors.
18
Messer, M., D. C. Shaw, A. S. Weiss, P. Rissmiller, and M. Griffiths. "Estimation of Divergence Dates for Monotremes From Comparisons of A-Lactalbumin Amino Acid Sequences." Australian Mammalogy 20, no. 2 (1998): 310. http://dx.doi.org/10.1071/am98323.
Abstract:
cx-Lactalbumins were isolated from milk of the platypus (Ornithorhynchus anatinus) and the echidna (Tachyglossus aculeatus). Their amino acid sequences were determined and compared with those of the cx- lactalbumins often eutherian and two marsupial species, using the computer programme ("Distances") to calculate the number of differences (substitutions) between a total of 36 pairs of cx-lactalbumins. As expected, the amino acid sequences of the monotreme cx-lactalbumins were more similar to each other than to those of other mammals, as were the sequences of the marsupial and the eutherian cx-lactalbumins. If one makes the common assumption that marsupials and eutherians diverged from each other 135 Myr ago then simple calculations from the data would suggest that the platypus and echidna lineages diverged 56 ± 8 (SD) Myr ago and that monotremes diverged from the other mammals 152 ± 29 Myr ago. These values are not inconsistent with the little that is known about the palaeontology of the monotremes and are very similar to those derived from previous studies on globin sequences. If, however, monotreme cx-lactalbumins evolved more slowly than the cx-lactalbumins of eutherians and marsupials, these dates could be underestimates.
19
Bakker, Anthony J., Ann L. Parkinson, and Stewart I. Head. "Contractile properties of single-skinned skeletal muscle fibres of the extensor digitorum longus muscle of the Australian short-nosed echidna." Australian Journal of Zoology 53, no. 4 (2005): 237. http://dx.doi.org/10.1071/zo05011.
Abstract:
Eutherian mammal fast-twitch muscle fibres share similar contractile activation properties, suggesting that these properties are highly conserved in mammals. To investigate this hypothesis, we examined the contractile properties of skeletal muscle from the order Monotremata, a mammalian order that separated from eutherians 150 million years ago. The Ca2+- and Sr2+-activation properties of single mechanically skinned skeletal muscle fibres from the extensor digitorum longus (EDL) muscle of the short-nosed echidna were determined. Sigmoidal curves fitted to force response data plotted as a function of pCa (–log[Ca2+]), had a mean slope of 4.32 ± 0.28 and a mean pCa50 and pCa10 value of 6.18 ± 0.01 and 6.41 ± 0.02 respectively (n = 20). The mean pSr50, pSr10 and slope values of curves fitted to the force-response data after activation with Sr2+ were 4.80 ± 0.03, 5.29 ± 0.07 and 2.75 ± 0.18 respectively (n = 20). The mean pCa50–pSr50 value for the echidna EDL fibres was 1.37 ± 0.04. In five of the echidna fibres, exposure to submaximal Ca2+ concentrations produced myofibrillar force oscillations (mean frequency, 0.13 ± 0.01 Hz), a phenomenon found only in eutherian slow and intermediate muscle fibres. These results show that echidna EDL fibres generally have similar contractile properties to eutherian fast-twitch skeletal muscle fibres, such as those found in the EDL of the rat.
20
Polymeropoulos, E. T., G. Heldmaier, P. B. Frappell, B. M. McAllan, K. W. Withers, M. Klingenspor, C. R. White, and M. Jastroch. "Phylogenetic differences of mammalian basal metabolic rate are not explained by mitochondrial basal proton leak." Proceedings of the Royal Society B: Biological Sciences 279, no. 1726 (June 2011): 185–93. http://dx.doi.org/10.1098/rspb.2011.0881.
Abstract:
Metabolic rates of mammals presumably increased during the evolution of endothermy, but molecular and cellular mechanisms underlying basal metabolic rate (BMR) are still not understood. It has been established that mitochondrial basal proton leak contributes significantly to BMR. Comparative studies among a diversity of eutherian mammals showed that BMR correlates with body mass and proton leak. Here, we studied BMR and mitochondrial basal proton leak in liver of various marsupial species. Surprisingly, we found that the mitochondrial proton leak was greater in marsupials than in eutherians, although marsupials have lower BMRs. To verify our finding, we kept similar-sized individuals of a marsupial opossum ( Monodelphis domestica ) and a eutherian rodent ( Mesocricetus auratus ) species under identical conditions, and directly compared BMR and basal proton leak. We confirmed an approximately 40 per cent lower mass specific BMR in the opossum although its proton leak was significantly higher (approx. 60%). We demonstrate that the increase in BMR during eutherian evolution is not based on a general increase in the mitochondrial proton leak, although there is a similar allometric relationship of proton leak and BMR within mammalian groups. The difference in proton leak between endothermic groups may assist in elucidating distinct metabolic and habitat requirements that have evolved during mammalian divergence.
21
Moffett, Ashley, and Charlie Loke. "Immunology of placentation in eutherian mammals." Nature Reviews Immunology 6, no. 8 (August 2006): 584–94. http://dx.doi.org/10.1038/nri1897.
22
Ong, Oselyne T. W., Lauren J. Young, and Julie M. Old. "Preliminary genomic survey and sequence analysis of the complement system in non-eutherian mammals." Australian Mammalogy 38, no. 1 (2016): 80. http://dx.doi.org/10.1071/am15036.
Abstract:
The complement system is a major mediator of the vertebrate immune system, which functions in both innate and specific immune responses. It comprises more than 30 proteins working to remove foreign cells by way of anaphylatoxins, opsonins or the membrane attack complex. Over the last few years, whole genome sequences of non-eutherian mammals (marsupials and a monotreme), the gray short-tailed opossum (Monodelphis domestica), tammar wallaby (Macropus eugenii), Tasmanian devil (Sarcophilus harrisii), koala (Phascolarctos cinereus) and platypus (Ornithorhynchus anatinus), have become publicly available. Using these sequences, we have identified an array of complement components in non-eutherians using online search tools and algorithms. Of 57 complement and complement-related genes investigated, we identified 46 in the gray short-tailed opossum genome, 27 in the tammar wallaby genome, 44 in the Tasmanian devil genome, 47 in the koala genome and 40 in the platypus genome. The results of this study confirm the presence of key complement components in the immune repertoire of non-eutherian mammals and provide a platform for future studies on immune protection in young marsupials.
23
Greenwood, PJ, C. Seamer, and DJ Tisdall. "Cloning, sequencing and expression of stem cell factor (c-kit ligand) cDNA of brushtail possum (Trichosurus vulpecula)." Reproduction, Fertility and Development 8, no. 4 (1996): 789. http://dx.doi.org/10.1071/rd9960789.
Abstract:
By means of reverse transcription polymerase chain reaction (RT-PCR), three stem cell factor (SCF) cDNAs (822-738 bp in size) were amplified from brushtail possum ovarian poly (A)+ RNA. The largest and smallest of these cDNAs were cloned and sequenced. Characterization of these cDNAs has revealed that possum SCF has approximately 75% and 66% homology to SCF of eutherian mammals at the nucleotide level and the predicted amino acid level respectively. Nucleotide sequencing shows that the 738-bp cDNA represents an mRNA splice variant, equivalent to that found in eutherian mammals, in which an exon (84 bp) encoding a potential proteolytic cleavage site is removed. Comparison of the predicted possum SCF amino acid sequence with the predicted SCF amino acid sequences from eutherian mammals reveals conservation of all cysteine residues and 3 of 4 potential N-linked glycosylation sites. In addition, the hydropathicity profile of the possum SCF protein is similar to that of eutherian SCF suggesting that protein conformation is conserved. Northern analysis was used to characterize possum SCF gene expression in adult ovary and testis. A major transcript of 9 kb was observed in both ovarian and testicular tissue. The conservation of the SCF gene and its predicted protein, suggests that SCF in the possum has similar biological activities to SCF in eutherian mammals.
24
Frankenberg, S., A. J. Pask, and M. B. Renfree. "259. Pluripotency genes in a marsupial, the tammar wallaby." Reproduction, Fertility and Development 20, no. 9 (2008): 59. http://dx.doi.org/10.1071/srb08abs259.
Abstract:
Markers of pluripotency and early differentiation in the early embryo have been extensively characterised in eutherian species, most notably the mouse. By comparison, mechanisms controlling pluripotency and early lineage specification have received surprisingly little attention in marsupials, which represent the second major infraclass of mammals. Early marsupial embryogenesis exhibits overt morphological differences to that of eutherians, however the underlying developmental mechanisms may be conserved. In order to characterise early marsupial development at the molecular level, we have identified, cloned and analysed expression of orthologueues of several eutherian genes encoding transcription factors and signalling molecules involved in regulating pluripotency and early lineage specification. These genes include POU5F1 (OCT4), SOX2, NANOG, FGF4, FGFR2, CDX2, EOMES, TEAD4, GATA6 and KITL and are all expressed at early stages of development in the tammar. In addition, we have identified and cloned tammar POU2, which has orthologueues in non-mammalian vertebrates. POU2 is a paralogue of POU5F1 – a master regulator of pluripotency in eutherians. Genomic analysis indicates that POU5F1 arose via gene duplication of POU2 before the monotreme-therian divergence. Both genes have persisted in marsupials and monotremes, while POU2 was lost early during eutherian evolution. Similar expression profiles of tammar POU5F1 and POU2 in early embryos and gonadal tissues suggest possible overlapping roles in the maintenance of pluripotency.
25
McGaugh, Suzanne, and Tonia S. Schwartz. "Here and there, but not everywhere: repeated loss of uncoupling protein 1 in amniotes." Biology Letters 13, no. 1 (January 2017): 20160749. http://dx.doi.org/10.1098/rsbl.2016.0749.
Abstract:
Endothermy is an evolutionary innovation in eutherian mammals and birds. In eutherian mammals, UCP1 is a key protein in adaptive nonshivering thermogenesis (NST). Although ucp1 arose early in the vertebrate lineage, the loss of ucp1 was previously documented in several reptile species (including birds). Here we determine that ucp1 was lost at the base of the reptile lineage, as we fail to find ucp1 in every major reptile lineage. Furthermore, though UCP1 plays a key role in mammalian NST, we confirm that pig has lost several exons from ucp1 and conclude that pig is not a sole outlier as the only eutherian mammal lineage to do so. Through similarity searches and synteny analysis, we show that ucp1 has also been lost/pseudogenized in Delphinidae (dolphin, orca) and potentially Xenarthra (sloth, armadillo) and Afrotheria (hyrax). These lineages provide models for investigating alternate mechanisms of thermoregulation and energy metabolism in the absence of functional UCP1. Further, the repeated losses of a functional UCP1 suggest the pervasiveness of NST via UCP1 across the mammalian lineage needs re-evaluation.
26
Dos Santos, Sandra E., Jairo Porfirio, Felipe B. da Cunha, Paul R. Manger, William Tavares, Leila Pessoa, Mary Ann Raghanti, Chet C. Sherwood, and Suzana Herculano-Houzel. "Cellular Scaling Rules for the Brains of Marsupials: Not as “Primitive” as Expected." Brain, Behavior and Evolution 89, no. 1 (2017): 48–63. http://dx.doi.org/10.1159/000452856.
Abstract:
In the effort to understand the evolution of mammalian brains, we have found that common relationships between brain structure mass and numbers of nonneuronal (glial and vascular) cells apply across eutherian mammals, but brain structure mass scales differently with numbers of neurons across structures and across primate and nonprimate clades. This suggests that the ancestral scaling rules for mammalian brains are those shared by extant nonprimate eutherians - but do these scaling relationships apply to marsupials, a sister group to eutherians that diverged early in mammalian evolution? Here we examine the cellular composition of the brains of 10 species of marsupials. We show that brain structure mass scales with numbers of nonneuronal cells, and numbers of cerebellar neurons scale with numbers of cerebral cortical neurons, comparable to what we have found in eutherians. These shared scaling relationships are therefore indicative of mechanisms that have been conserved since the first therians. In contrast, while marsupials share with nonprimate eutherians the scaling of cerebral cortex mass with number of neurons, their cerebella have more neurons than nonprimate eutherian cerebella of a similar mass, and their rest of brain has fewer neurons than eutherian structures of a similar mass. Moreover, Australasian marsupials exhibit ratios of neurons in the cerebral cortex and cerebellum over the rest of the brain, comparable to artiodactyls and primates. Our results suggest that Australasian marsupials have diverged from the ancestral Theria neuronal scaling rules, and support the suggestion that the scaling of average neuronal cell size with increasing numbers of neurons varies in evolution independently of the allocation of neurons across structures.
27
Enciso, María, Stephen D. Johnston, and Jaime Gosálvez. "Differential resistance of mammalian sperm chromatin to oxidative stress as assessed by a two-tailed comet assay." Reproduction, Fertility and Development 23, no. 5 (2011): 633. http://dx.doi.org/10.1071/rd10269.
Abstract:
Protamines of eutherian species are cysteine-rich molecules that become cross-linked by disulfide bonds during epididymal transit, whereas the protamines of most marsupial species lack cysteine residuals. The present study made use of the differences in protamine structure between eutherian and metatherian mammal spermatozoa to examine the comparative resistance of sperm DNA to oxidative damage in three eutherian species (Mus musculus, Homo sapiens, Sus domesticus) and three metatherian species (Vombatus ursinus, Phascolarctos cinereus, Macropus giganteus). Sperm DNA fragmentation of samples exposed to increasing concentrations of hydrogen peroxide was assessed by means of the two-tailed comet assay. The sperm DNA of the marsupial species studied were significantly more sensitive to oxidative stress than the spermatozoa of eutherian species. Such susceptibility is consistent with the lack of disulfide cross-linking in marsupial sperm chromatin and suggests that the oxidation of thiols to disulfides for chromatin condensation during epididymal transit in eutherian mammals is likely to be important in order to provide stability and protect these cells from the genotoxic effects of adverse environments.
28
Shevchenko, A. I., I. S. Zakharova, and S. M. Zakian. "The Evolutionary Pathway of X Chromosome Inactivation in Mammals." Acta Naturae 5, no. 2 (June 15, 2013): 40–53. http://dx.doi.org/10.32607/20758251-2013-5-2-40-53.
Abstract:
X chromosome inactivation is a complex process that occurs in marsupial and eutherian mammals. The process is thought to have arisen during the differentiation of mammalian sex chromosomes to achieve an equal dosage of X chromosome genes in males and females. The differences in the X chromosome inactivation processes in marsupial and eutherian mammals are considered, and the hypotheses on its origin and evolution are discussed in this review.
29
Bartkowska, Katarzyna, Beata Tepper, Krzysztof Turlejski, and Ruzanna Djavadian. "Postnatal and Adult Neurogenesis in Mammals, Including Marsupials." Cells 11, no. 17 (September 1, 2022): 2735. http://dx.doi.org/10.3390/cells11172735.
Abstract:
In mammals, neurogenesis occurs during both embryonic and postnatal development. In eutherians, most brain structures develop embryonically; conversely, in marsupials, a number of brain structures develop after birth. The exception is the generation of granule cells in the dentate gyrus, olfactory bulb, and cerebellum of eutherian species. The formation of these structures starts during embryogenesis and continues postnatally. In both eutherians and marsupials, neurogenesis continues in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus of the hippocampal formation throughout life. The majority of proliferated cells from the SVZ migrate to the olfactory bulb, whereas, in the dentate gyrus, cells reside within this structure after division and differentiation into neurons. A key aim of this review is to evaluate advances in understanding developmental neurogenesis that occurs postnatally in both marsupials and eutherians, with a particular emphasis on the generation of granule cells during the formation of the olfactory bulb, dentate gyrus, and cerebellum. We debate the significance of immature neurons in the piriform cortex of young mammals. We also synthesize the knowledge of adult neurogenesis in the olfactory bulb and the dentate gyrus of marsupials by considering whether adult-born neurons are essential for the functioning of a given area.
30
Hunter, R. H. F. "Components of oviduct physiology in eutherian mammals." Biological Reviews 87, no. 1 (August 23, 2011): 244–55. http://dx.doi.org/10.1111/j.1469-185x.2011.00196.x.
31
Carter, A. M., and A. Mess. "Evolution of the Placenta in Eutherian Mammals." Placenta 28, no. 4 (April 2007): 259–62. http://dx.doi.org/10.1016/j.placenta.2006.04.010.
32
Fléchon, Jacques-Edmond. "Erratum to: The acrosome of eutherian mammals." Cell and Tissue Research 363, no. 1 (October 24, 2015): 313. http://dx.doi.org/10.1007/s00441-015-2308-3.
33
Capellini, Isabella, Charles L. Nunn, and Robert A. Barton. "Microparasites and Placental Invasiveness in Eutherian Mammals." PLOS ONE 10, no. 7 (July 13, 2015): e0132563. http://dx.doi.org/10.1371/journal.pone.0132563.
34
Montellano-Ballesteros, Marisol, Richard C. Fox, and Craig S. Scott. "Species composition of the Late Cretaceous eutherian mammal Paranyctoides Fox." Canadian Journal of Earth Sciences 50, no. 7 (July 2013): 693–700. http://dx.doi.org/10.1139/cjes-2012-0184.
Abstract:
Although the known record of Mesozoic eutherian mammals has been significantly enriched in recent years, early eutherian evolution is still not well understood. Among the more controversial of Mesozoic eutherians is Paranyctoides Fox, which was described in 1979 from the Judithian Dinosaur Park Formation, Alberta, Canada. It is a rare taxon and therefore has been identified in only a few other North American Late Cretaceous local faunas since. Within the past decade, dental and gnathic remains discovered in Central Asia have also been referred to Paranyctoides, thereby expanding the geographic range of the genus substantially and making it the only Late Cretaceous eutherian ostensibly occurring in both continents. As a result of our detailed study of Paranyctoides, however, we find that the Central Asian species lack the diagnostic characters of Paranyctoides and must be referred to other taxa. We conclude that this genus was limited to North America, ranging from Aquilan to Lancian time, and accordingly we recognize as valid only the following species: Paranyctoides sternbergi (Judithian, Alberta), P. maleficus (Aquilan, Alberta), Paranyctoides Wahweap sp. A and sp. B (Judithian, Utah), Paranyctoides Kaiparowits sp. A and sp. B (Judithian, Utah). Another purported species of Paranyctoides, P. megakeros, from the Lancian of Wyoming, is a junior synonym of Alostera saskatchewanensis.
35
Prasad, G. V. R., and M. Godinot. "Eutherian tarsal bones from the Late Cretaceous of India." Journal of Paleontology 68, no. 4 (July 1994): 892–902. http://dx.doi.org/10.1017/s0022336000026342.
Abstract:
Eutherian tarsal bones of Late Cretaceous age are reported for the first time from sedimentary beds intercalated with the Deccan Traps of peninsular India. The tarsal bones, represented mainly by calcanea and astragali, occur in association with dental elements of palaeoryctid mammals: Deccanolestes hislopi Prasad and Sahni and D. robustus Prasad, Jaeger, Sahni, Gheerbrant, and Khajuria. Two size variants in the tarsals correlate well with the teeth of D. hislopi and D. robustus. Morphologically, the tarsal complex of Deccanolestes is quite different from that of other Cretaceous eutherians for which the relevant anatomy is known (Protungulatum and Procerberus). Rather, the tarsals of Deccanolestes exhibit a close affinity to the tarsal morphology of Archonta. A large number of tarsal characters indicate a highly arboreal mode of life for these animals. Presence of such specialized animals as early as the Cretaceous suggests that mammals had already diversified their locomotor adaptations by this time.
36
Kress, A. "A comparison of oocyte organelles in Monodelphis domestica with those of other marsupials and eutherians." Reproduction, Fertility and Development 8, no. 4 (1996): 521. http://dx.doi.org/10.1071/rd9960521.
Abstract:
This paper reviews the current knowledge of oocyte cytology in marsupials, particularly Monodelphis domestica, and eutherian mammals. Some of the conspicuous features will be described and their function discussed. Despite many fundamental similarities between the oocytes of eutherian mammals and marsupials, some aspects are different (e.g. growth pattern, final size, timetable of cytoplasmic maturation and utilization of storage material during early cleavage stages), when most of the vesicles are extruded into the perivitelline space in marsupials.
37
Witton, C. J., K. Swann, J. Carroll, and H. D. M. Moore. "Injection of a boar sperm factor causes calcium oscillations in oocytes of the marsupial opossum, Monodelphis domestica." Zygote 7, no. 4 (November 1999): 271–77. http://dx.doi.org/10.1017/s0967199499000660.
Abstract:
At fertilisation, the sperm triggers an abrupt and transient increase in intracellular calcium ([Ca2+]i) in the oocyte cytoplasm. In eutherian mammals, oocytes exhibit multiple [Ca2+]i transients which are necessary for egg activation. We investigated [Ca2+]i in the marsupial opossum, Monodelphis domestica. Embryo development in this therian mammal is quite distinct from that in most Eutheria. Oestrus was induced in an adult female opossum by introduction of a male into her cage. Injection of a boar sperm extract induced repetitive increases in [Ca2+]i. Each oscillation travelled across and around the periphery of the egg in a wave-like manner. A control injection of KCl elicited no change in [Ca2+]i. This is the first observation of [Ca2+]i oscillations in the oocyte of a marsupial. The repetitive nature of the [Ca2+]i changes were more similar to those in oocytes of Eutheria than those in oocytes of non-mammalian vertebrates.
38
Davies, Thomas W., Mark A. Bell, Anjali Goswami, and Thomas J. D. Halliday. "Completeness of the eutherian mammal fossil record and implications for reconstructing mammal evolution through the Cretaceous/Paleogene mass extinction." Paleobiology 43, no. 4 (August 22, 2017): 521–36. http://dx.doi.org/10.1017/pab.2017.20.
Abstract:
AbstractThere is a well-established discrepancy between paleontological and molecular data regarding the timing of the origin and diversification of placental mammals. Molecular estimates place interordinal diversification dates in the Cretaceous, while no unambiguous crown placental fossils have been found prior to the end-Cretaceous mass extinction. Here, the completeness of the eutherian fossil record through geological time is evaluated to assess the suggestion that a poor fossil record is largely responsible for the difference in estimates of placental origins. The completeness of fossil specimens was measured using the character completeness metric, which quantifies the completeness of fossil taxa as the percentage of phylogenetic characters available to be scored for any given taxon. Our data set comprised 33 published cladistic matrices representing 445 genera, of which 333 were coded at the species level.There was no significant difference in eutherian completeness across the Cretaceous/Paleogene (K/Pg) boundary. This suggests that the lack of placental mammal fossils in the Cretaceous is not due to a poor fossil record but more likely represents a genuine absence of placental mammals in the Cretaceous. This result supports the “explosive model” of early placental evolution, whereby placental mammals originated around the time of the K/Pg boundary and diversified soon after.No correlation was found between the completeness pattern observed in this study and those of previous completeness studies on birds and sauropodomorph dinosaurs, suggesting that different factors affect the preservation of these groups. No correlations were found with various isotope proxy measures, but Akaike information criterion analysis found that eutherian character completeness metric scores were best explained by models involving the marine-carbonate strontium-isotope ratios (87Sr/86Sr), suggesting that tectonic activity might play a role in controlling the completeness of the eutherian fossil record.
39
Dacheux, Jean-Louis, Francoise Dacheux, Valerie Labas, Heath Ecroyd, Brett Nixon, and Russell C. Jones. "New proteins identified in epididymal fluid from the platypus (Ornithorhynchus anatinus)." Reproduction, Fertility and Development 21, no. 8 (2009): 1002. http://dx.doi.org/10.1071/rd09091.
Abstract:
The platypus epididymal proteome is being studied because epididymal proteins are essential for male fertility in mammals and it is considered that knowledge of the epididymal proteome in an early mammal would be informative in assessing the convergence and divergence of proteins that are important in the function of the mammalian epididymis. Few of the epididymal proteins that have been identified in eutherian mammals were found in platypus caudal epididymal fluid, and the major epididymal proteins in the platypus (PXN-FBPL, SPARC and E-OR20) have never been identified in the epididymis of any other mammal.
40
McKenzie, LM, and DW Cooper. "Low MHC class II variability in a marsupial." Reproduction, Fertility and Development 6, no. 6 (1994): 721. http://dx.doi.org/10.1071/rd9940721.
Abstract:
The major histocompatibility complex (MHC) loci have been shown to be highly polymorphic in most eutherian ('placental') species studied. Several hypotheses have been advanced for the maintenance of this exceptional level of genetic variation, one of which suggests that it is necessary for successful eutherian reproduction. Marsupials (metatherians) and eutherians are the only two groups of viviparous mammals, but their modes of reproduction are quite distinct. Although marsupials have placentae, they are generally shorter lived and less invasive than in eutherians. Other investigations have shown that genetic variation at marsupial MHC class I loci is probably high. Weak or non-existent mixed lymphocyte culture responses previously reported in several marsupial species have suggested a lack of class II variation. Data have therefore been collected on the level of restriction fragment length polymorphism at MHC class II beta-chain encoding loci of a marsupial, Macropus eugenii (the tammar wallaby). This level is shown to be low, between the level of MHC variation found in cheetahs and a population of lions with a restricted genetic base. Attention is drawn to the need to collect more data on the level of class II variability in both eutherians and marsupials, and to the potential of marsupials for understanding the relation, if any, between mode of reproduction and MHC variability.
41
Rohozinski, Jan. "Lineage-independent retrotransposition of UTP14 associated with male fertility has occurred multiple times throughout mammalian evolution." Royal Society Open Science 4, no. 12 (December 2017): 171049. http://dx.doi.org/10.1098/rsos.171049.
Abstract:
In mammals, gamete production is essential for reproductive success. This is particularly true for males where large quantities of sperm are produced to fertilize a limited number of eggs released by the female. Because of this, new genes associated with increased spermatogenic efficiency have been accumulating throughout the evolution of therian mammals. Many of these new genes are testis-specific retrotransposed copies of housekeeping genes located on the X chromosome. Of particular interest are retrotransposed copies of UTP14 that are present in many distantly related eutherian mammals. Analysis of genomic data available in ENSEMBL indicates that these UTP14 retrogenes have arisen independently in the various eutherian clades. They represent an interesting aspect of evolution whereby new homologues of UTP14 have become independently fixed in multiple mammalian lineages due to the reproductive advantage that may be conferred to males. Surprisingly, these genes may also be lost, even after being present within a lineage for millions of years. This phenomenon may potentially be used to delineate evolutionary trees in closely related groups of mammals, particularly in the case of South American primates. Studying these retrogenes will yield new insights into the evolutionary history of male gamete production and the phylogeny of eutherian mammals.
42
Hopson, James A. "Synapsid Evolution and the Radiation of Non-Eutherian Mammals." Short Courses in Paleontology 7 (1994): 190–219. http://dx.doi.org/10.1017/s247526300000132x.
Abstract:
The Synapsida is the mammal-like ramus of the Amniota, the sister group of the Sauropsida (or Reptilia of Gauthier et al., 1988). Synapsids are characterized by the possession of a lateral temporal fenestra (Fig. 1A), among other features (see Gauthier, this volume). Of all the great transitions between major structural grades within vertebrates, the transition from basal amniotes to basal mammals is represented by the most complete and continuous fossil record, extending from the Middle Pennsylvanian to the Late Triassic and spanning some 75 to 100 million years. Structural evolution of particular functional systems has been well investigated, notably the feeding mechanism (Barghusen, 1968; Crompton, 1972; Crompton and Parker, 1978; Crompton and Hylander, 1986) and the middle ear (Hopson, 1966; Allin, 1975, 1986; Allin and Hopson, 1992), and these studies have demonstrated the gradual nature of these major adaptive modifications.
43
Jolly, SE, GA Morriss, S. Scobie, and PE Cowan. "Composition of Milk of the Common Brushtail Possum, Trichosurus Vulpecula (Marsupialia: Phalangeridae): Concentrations of Elements." Australian Journal of Zoology 44, no. 5 (1996): 479. http://dx.doi.org/10.1071/zo9960479.
Abstract:
The concentrations of 11 elements (calcium, copper, iron, magnesium, manganese, phosphorus, potassium, sodium, strontium, sulphur and zinc) were measured in milk samples collected from 193 lactating brushtail possums, Trichosurus vulpecula, at all stages of lactation. Most elements showed patterns of change during lactation similar to those of other marsupials. The most marked changes occurred at about 80-120 days, when the growth rate of the pouch young increased and developmental changes took place, such as eye opening and fur growth. Compared with eutherians, copper and iron concentrations were high in possum milk, as in other marsupials, but zinc levels were exceptionally high. Strontium and manganese levels, not measured before in marsupial milk, were considerably higher than levels reported in eutherian milk. In contrast to eutherian mammals, marsupial young must be supplied with large quantities of minerals in the milk as almost all growth and development occurs after birth, and possum young are entirely dependent on milk supplied by the mother for about the first 100 days.
44
Watson, JM. "Monotreme Genetics and Cytology and a Model for Sex-Chromosome Evolution." Australian Journal of Zoology 37, no. 3 (1989): 385. http://dx.doi.org/10.1071/zo9890385.
Abstract:
The protherian mammals consist of three species: the platypus, the Australian echidna and the Niugini echidna. These mammals diverged from the therian line of descent about 150-200 million years ago; hence comparisons of gene arrangements and gene control mechanisms between prototherian and therian mammals may yield significant data about gene rearrangements during mammalian evolution and about the evolution of complex genetic control systems. The chromosome complements of the three monotreme species are highly conserved. In particular, the X (or X1) chromosomes are G-band identical and share considerable G-band homology with the Y chromosomes. Replication asynchrony between X chromosomes suggests that X chromosome inactivation operates in females, and is apparently tissue- specific (as it is in marsupials), and confined to the differential region of the X (X1) chromosome (as it is in eutherian mammals). These results suggest that sex chromosome differentiation in the monotremes represents an intermediate stage in the evolution of the dimorphic sex chromosomes of therian mammals and that X-chromosome inactivation may also represent a comparatively primitive stage. Studies of gene location in the platypus using platypus-rodent cell hybrids suggested that HPRT and PGK are syntenic in the platypus, but it was not possible to assign the syntenic group to a particular chromosome. In situ hybridisation was used to assign three genes, located on the X in eutherians and marsupials, to the monotreme X. However, human X short-arm markers were found by in situ hybridisation to be autosomal in monotremes (as they are in marsupials). A model for the evolution of mammalian sex chromosome differentiation and X-chromosome inactivation is presented in which a gradual reduction of the Y chromosome, and recruitment of newly unpaired loci on the X into a system of X-chromosome inactivation, has accompanied eutherian evolution.
45
Temple-Smith, PD. "Comparative structure and function of marsupial spermatozoa." Reproduction, Fertility and Development 6, no. 4 (1994): 421. http://dx.doi.org/10.1071/rd9940421.
Abstract:
Marsupial sperm structure has been the focus of many comparative studies in the last 30 years. Although the basic organization of the marsupial spermatozoon is similar to that of eutherian mammals, spermatozoa from this branch of therian evolution have developed a specific suite of characters which clearly distinguish them from the Eutheria. This review surveys these specializations and examines current knowledge on their respective functions and the forces which shaped their evolution. Nuclear shaping and stability, the asymmetric positioning of the acrosome, and the unusual neck articulation are discussed. Although recent observations have provided evidence of a marsupial equatorial segment and posterior ring, the marsupial equivalent of the eutherian postacrosomal sheath has not been identified. The unusual neck structure of marsupial spermatozoa and the mobile articulation of the connecting piece are discussed in relation to nuclear rotation and the events associated with this process. Increasing flagellar length in some species is associated with extremes in flagellar organization and its effect on sperm motility is discussed.
46
Deakin, Janine E. "Marsupial X chromosome inactivation: past, present and future." Australian Journal of Zoology 61, no. 1 (2013): 13. http://dx.doi.org/10.1071/zo12113.
Abstract:
Marsupial and eutherian mammals inactivate one X chromosome in female somatic cells in what is thought to be a means of compensating for the unbalanced X chromosome dosage between XX females and XY males. The hypothesis of X chromosome inactivation (XCI) was first published by Mary Lyon just over 50 years ago, with the discovery of XCI in marsupials occurring a decade later. However, we are still piecing together the evolutionary origins of this fascinating epigenetic mechanism. From the very first studies on marsupial X inactivation, it was apparent that, although there were some similarities between marsupial and eutherian XCI, there were also some striking differences. For instance, the paternally derived X was found to be preferentially silenced in marsupials, although the silencing was often incomplete, which was in contrast to the random and more tightly controlled inactivation of the X chromosome in eutherians. Many of these earlier studies used isozymes to study the activity of just a few genes in marsupials. The sequencing of several marsupial genomes and the advent of molecular cytogenetic techniques have facilitated more in-depth studies into marsupial X chromosome inactivation and allowed more detailed comparisons of the features of XCI to be made. Several important findings have come from such comparisons, among which is the absence of the XIST gene in marsupials, a non-coding RNA gene with a critical role in eutherian XCI, and the discovery of the marsupial RSX gene, which appears to perform a similar role to XIST. Here I review the history of marsupial XCI studies, the latest advances that have been made and the impact they have had towards unravelling the evolution of XCI in mammals.
47
KIELAN-JAWOROWSKA, ZOFIA, and DEMBERLYIN DASHZEVEG. "Eutherian mammals from the Early Cretaceous of Mongolia." Zoologica Scripta 18, no. 2 (April 1989): 347–55. http://dx.doi.org/10.1111/j.1463-6409.1989.tb00460.x.
48
Gilissen, Emmanuel. "Scaling patterns of interhemispheric connectivity in eutherian mammals." Behavioral and Brain Sciences 29, no. 1 (February 2006): 16–17. http://dx.doi.org/10.1017/s0140525x06269012.
Abstract:
Because network scaling costs tend to limit absolute brain size, Striedter suggests that large cetacean brains must have evolved some novel ways to cope with these costs. A new analysis of available data shows that the scaling pattern of interhemispheric connectivity in cetaceans is isometric and differs from that observed in terrestrial mammals.
49
Langer, Peter. "The phases of maternal investment in eutherian mammals." Zoology 111, no. 2 (March 2008): 148–62. http://dx.doi.org/10.1016/j.zool.2007.06.007.
50
Liu, F. G. R. "Molecular and Morphological Supertrees for Eutherian (Placental) Mammals." Science 291, no. 5509 (March 2, 2001): 1786–89. http://dx.doi.org/10.1126/science.1056346.