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Review of the monotreme fossil record and comparison of palaeontological and molecular data
Abstract
Monotremes have traditionally been considered a remnant group of mammals descended from archaic Mesozoic stock, surviving to the present day on the relatively isolated Australian continent. Challenges to this orthodoxy have been spurred by discoveries of 'advanced' Cretaceous monotremes (Steropodon galmani, Archer, M., et al., 1985. First Mesozoic mammal from Australia-an Early Cretaceous monotreme, Nature. 318, 363-366) as well as by results from molecular data linking monotremes to therian mammals (specifically to marsupials in some studies). This paper reviews the monotreme fossil record and briefly discusses significant new information from additional Cretaceous Australian material. Mesozoic monotremes (including S. galmani) were a diverse group as evidenced by new material from the Early Cretaceous of New South Wales and Victoria currently under study. Although most of these new finds are edentulous jaws (limiting dental comparisons and determination of dietary niches), a range of sizes and forms has been determined. Some of these Cretaceous jaws exhibit archaic features-in particular evidence for the presence of a splenial bone in S. galmani-not seen in therian mammals or in post-Mesozoic (Tertiary and Quaternary) monotreme taxa. Tertiary monotremes were either archaic ornithorhynchids (toothed platypuses in the genera Monotrematum and Obdurodon) or tachyglossids (large echidnas in the genera Megalibgwilia and Zaglossus). Quaternary ornithorhynchid material is referable to the sole living platypus species Ornithorhynchus anatinus. Quaternary echidnas, however, were moderately diverse and several forms are known (Megalibgwilia species; 'Zaglossus' hacketti; Zaglossus species and Tachyglossus aculeatus).
... 8. Monotremes themselves are not found in the Mesozoic of SA, however, australosphenidans ) are recovered as basal members of the monotreme clade, therefore implying that they, or members of their stem, were present in the early SA faunas and can be seen as yet another group that survived the Cretaceous extinction. In support of this view is the Cretaceous record of monotremes in Australia (e.g., Rich et al. 2001bMusser 2003) and the presence of the ornithorhynchid Monotrematum sudamericanum in the Paleocene of Patagonia. It is possible, but less likely, that Monotremata originated in Australia, Antarctica, or other southern landmasses, and Monotrematum represents a Paleocene migration into South America of already differentiated monotremes. ...
... Living monotremes are known by two families and five species: Ornithorhynchidae, represented by the Australian platypus Ornithorhynchus anatinus, and Tachyglossidae, represented by the small short-beaked echidna Tachyglossus aculeatus, and the larger long-beaked echidnas Zaglossus that includes the species Z. bruijnii (western New Guinea), Z. bartoni (central and eastern New Guinea), and Z. attenboroughi (restricted to the Cyclops Mountains in north New Guinea) (e.g., Flannery and Groves 1998;Musser 2003;Helgen et al. 2012;Bino et al. 2019). ...
... The monotreme fossil record is not abundant but it has considerably increased in the last few decades, in particular, that from the Australian fossil sites (e.g., Musser 2003Musser , 2013. Known fossil echidnas include Megalibgwilia ("Zaglossus") robustus from a Middle Miocene (13-14 Ma) lead golden mine from New South Wales and the Pleistocene Megalibgwilia oweni, "Zaglossus" hacketti, and fossil material of the current species Zaglossus cf. ...
The sparse record of archaic Mesozoic South American mammals extends from the latest Early Jurassic to the latest Cretaceous, involving about 115 Ma, which can be further extended to about 160 Ma, including the post-K/Pg evidence. We review here the distribution, predicted time of origin, and likely place of origin for the lineages covered in the preceding chapters during that span of time and against the evolving geological backdrop of continental drift and paleogeography. Size, dental diversity, and likely dietary specializations of the Mesozoic South American mammals are discussed in the context of Mesozoic mammals in general. A few of the many surprising advances in comparative genetic and molecular evolution are discussed as part of a holistic view of early mammalian evolution to which fossils can, and should, be integrated. Social, financial, and geographical issues affecting paleontological research in South America, early mammals, in particular, are highlighted. We recognize that we are still in the early stages of development and that much of what we know about Mesozoic South American mammals is likely to be drastically altered by finds in the continent or underrepresented areas from formely Gondwanan landmasses such as Antarctica or Africa. Their scarce mammalian fossil record has hampered their full incorporation into an integrated view of early mammalian evolution. The relatively robust paleontological community present in several South American countries, relatively inexpensive nature of the discipline, and extensive outcrops are likely to ensure continuity of a synergistic research agenda. The potential for novel data, regional strengths in systematics, and the global resurgent importance of time as integral to model-based phylogenies are auspicious signs for the future of Mesozoic mammal research in South America.
... 8. Monotremes themselves are not found in the Mesozoic of SA, however, australosphenidans ) are recovered as basal members of the monotreme clade, therefore implying that they, or members of their stem, were present in the early SA faunas and can be seen as yet another group that survived the Cretaceous extinction. In support of this view is the Cretaceous record of monotremes in Australia (e.g., Rich et al. 2001bMusser 2003) and the presence of the ornithorhynchid Monotrematum sudamericanum in the Paleocene of Patagonia. It is possible, but less likely, that Monotremata originated in Australia, Antarctica, or other southern landmasses, and Monotrematum represents a Paleocene migration into South America of already differentiated monotremes. ...
... Living monotremes are known by two families and five species: Ornithorhynchidae, represented by the Australian platypus Ornithorhynchus anatinus, and Tachyglossidae, represented by the small short-beaked echidna Tachyglossus aculeatus, and the larger long-beaked echidnas Zaglossus that includes the species Z. bruijnii (western New Guinea), Z. bartoni (central and eastern New Guinea), and Z. attenboroughi (restricted to the Cyclops Mountains in north New Guinea) (e.g., Flannery and Groves 1998;Musser 2003;Helgen et al. 2012;Bino et al. 2019). ...
... The monotreme fossil record is not abundant but it has considerably increased in the last few decades, in particular, that from the Australian fossil sites (e.g., Musser 2003Musser , 2013. Known fossil echidnas include Megalibgwilia ("Zaglossus") robustus from a Middle Miocene (13-14 Ma) lead golden mine from New South Wales and the Pleistocene Megalibgwilia oweni, "Zaglossus" hacketti, and fossil material of the current species Zaglossus cf. ...
Dryolestoids are iconic members of the Mesozoic mammalian associations in South America. They achieved a large taxonomic diversity in this region with disparate dental and cranial morphotypes ranging from the classical role of sharp-toothed insectivores to bunodont, complex dentitions reflecting omnivore/herbivore adaptations. The South American radiation of dryolestoids, the meridiolestidans, are among the most abundant Cretaceous mammals, surviving the K/Pg mass extinction and continuing until the Miocene as minor members of the South American biotas. New specimens have been recently discovered, some of them including associated upper and lower jaws, and exceptionally preserved skulls. These high-quality fossils provide crucial intraspecific dental variation, both along the tooth row and from upper to lower, allowing critical re-interpretation of some taxa originally named on the basis of isolated teeth or very incomplete material. The Cretaceous diversity of meridiolestidans has been grossly overestimated, with taxa based on different dental positions of what was later determinied to be a single taxon. One relatively poorly known Late Cretaceous taxon, Groebertherium, shares many features with the classical Holartic dryolestoids and may represent a Late Jurassic/Early Cretaceous foundational morphology expected for meridiolestidans.
... 8. Monotremes themselves are not found in the Mesozoic of SA, however, australosphenidans ) are recovered as basal members of the monotreme clade, therefore implying that they, or members of their stem, were present in the early SA faunas and can be seen as yet another group that survived the Cretaceous extinction. In support of this view is the Cretaceous record of monotremes in Australia (e.g., Rich et al. 2001bMusser 2003) and the presence of the ornithorhynchid Monotrematum sudamericanum in the Paleocene of Patagonia. It is possible, but less likely, that Monotremata originated in Australia, Antarctica, or other southern landmasses, and Monotrematum represents a Paleocene migration into South America of already differentiated monotremes. ...
... Living monotremes are known by two families and five species: Ornithorhynchidae, represented by the Australian platypus Ornithorhynchus anatinus, and Tachyglossidae, represented by the small short-beaked echidna Tachyglossus aculeatus, and the larger long-beaked echidnas Zaglossus that includes the species Z. bruijnii (western New Guinea), Z. bartoni (central and eastern New Guinea), and Z. attenboroughi (restricted to the Cyclops Mountains in north New Guinea) (e.g., Flannery and Groves 1998;Musser 2003;Helgen et al. 2012;Bino et al. 2019). ...
... The monotreme fossil record is not abundant but it has considerably increased in the last few decades, in particular, that from the Australian fossil sites (e.g., Musser 2003Musser , 2013. Known fossil echidnas include Megalibgwilia ("Zaglossus") robustus from a Middle Miocene (13-14 Ma) lead golden mine from New South Wales and the Pleistocene Megalibgwilia oweni, "Zaglossus" hacketti, and fossil material of the current species Zaglossus cf. ...
Non-mammaliaform cynodonts, formerly called “mammal-like reptiles,” illustrate earlier states of the morphological architecture in the mammalian lineage. These mammalian forerunners show unique character combinations without direct counterparts among living vertebrates reflecting adaptations long lost along the millions of years of cynodont history. The fossil record from South America, originating mostly from the Middle to Late Triassic of Argentina and Brazil, is one of the most prolific worldwide. SA non-mammalian cynodonts are systematically diverse, including approximately 40 species that present great morphological disparity in skull shape, tooth morphology, pattern of tooth replacement, masticatory mechanisms, and locomotory architectures. In this chapter, we summarize the record of SA non-mammaliaform cynodonts.
... The short-beaked echidna (Tachyglossus aculeatus) is a member of one of three extant species of monotremes together with the long-beaked echidnas and the platypus. Fossil records and genetic studies indicate monotremes have evolved independently from all other mammals for at least 120 million years and likely more than 200 million years (Clemens, 1979;Krubitzer & Campi, 2009;Madsen, 2009;Musser, 2003;O'Brien & Graves, 1990;Phillips, Bennett, & Lee, 2009;Woodburne, Rich, & Springer, 2003). ...
... Their evolutionary history has influenced how monotremes are viewed in the scientific community, particularly as they are generally considered to be the mammals most distantly related to humans (Krubitzer, Manger, Pettigrew, & Calford, 1995). They have historically been referred to as mammals of the "lowliest status" (Elliot Smith, 1902) and "living fossils" (Darwin, 1959), and are still viewed by many scientists as "primitive" (Ashwell, Paxinos, & Watson, 2007;Musser, 2003). This view is compounded by the fact that monotremes, in addition to their mammalian characteristics, display numerous plesiomorphic reptilian traits in their anatomy, physiology, and reproduction, such as laying keratin-covered eggs and having a single cloacal outlet (Augee, Gooden, & Musser, 2006;Griffiths, 1989). ...
... An alternative approach to the phylogenetic hierarchy theory is that of mosaic evolution, in which each ecological problem leads to the development of a separate cognitive mechanism, or module (Musser, 2003;Northcutt & Kaas, 1995;Shettleworth, 1998). According to this approach, each ecologically distinct group will evolve those modules required by the demands of its environment (Shettleworth, 1998). ...
Echidnas have evolved separately from other mammalian groups for around 200 million years and incorporate a mixture of reptilian and mammalian features. Because of these attributes, they have historically been considered “primitive” animals. However, they have successfully adapted to a wide variety of ecological niches and their neurophysiology demonstrates a number of unusual and apparently sophisticated characteristics, including a relatively large brain and cerebral cortex and a comparatively massive frontal cortex. Studies of learning in the echidna have thus far been limited to only a handful of experiments which demonstrated relatively basic abilities such as forming a position habit in a T-maze, successive habit-reversal learning, and simple visual and instrumental discrimination. This study aimed to expand on these results and test the “primitive” echidna on what are generally considered more advanced cognitive tasks—same/different and conditional same/different concept learning. The results demonstrated that echidnas are able to discriminate on the basis of a relational same/different concept, using simultaneously presented multi-element stimuli, and transfer that discrimination to novel stimuli. After further training, they were then able to repeat the performance when the correct choice was conditional on the background color of the stimulus panels.
... Other putative records of monotremes from the Cretaceous of Australia are more uncertain. The dentally bizarre Kollikodon ritchiei ( Figure 3d), also from Lightning Ridge, was originally identified as a probable monotreme (Flannery et al. 1995) but more recently has been suggested to be a non-mammalian mammaliaform (Musser 2006;. A "tachyglossid-like" partial right humerus from the Albian Dinosaur Cove site (Figure 3a) in southern Victoria has been named Kryoryctes cadburyi, and tentatively identified as a monotreme (Pridmore et al. 2005). ...
... Turning now to the fossil record of tachyglossids, possibly the oldest known remains are from a gold mine in New South Wales (Dun 1895), which has been suggested to date to the middle Miocene, but which may in fact be Pleistocene in age (Augee et al. 2006;Musser 2006). This material has been referred to the modern genus Zaglossus or to the extinct genus Megalibgwilia¸ as Z. or M. robusta, by different authors (Griffiths et al. 1991;Beck, R. M. D. (accepted). ...
... Boca Raton, Florida, USA: CRC Press. Augee et al. 2006;Musser 2003;Musser 2006;Long et al. 2002). The next oldest tachyglossids are from Plio-Pleistocene deposits in mainland Australia. ...
... Possible explanations included inhospitable climate preventing colonisation, extinction after their arrival, or dispersal of marsupials to proto-Australia after Zealandia had separated from it (Fleming 1975(Fleming : 24, 1979Stevens 1980Stevens , 1989Stevens et al. 1988: 44). Fossil finds have shown that monotremes were certainly present in proto-Australia in the Early Cretaceous (Steropodon galmani, Teinolophos trusleri and probably several other taxa: Archer et al. 1985;Musser 2003Musser , 2006Pridmore et al. 2005). This supports Fleming's (1979) theory that monotremes were present in Zealandia when it split from Australis (contra Bull & Whitaker 1975: 267;Fleming 1975: 15;Stevens et al. 1995: 44). ...
... Although fossils of the third group of living mammals (placentals) have been claimed from the Cretaceous (Ausktribosphenos nyktos, Bishops whitmorei) and Eocene (Tingamarra porterorum) of Australia (Godthelp et al. 1992;Rich et al. 1997Rich et al. , 1999, these identifications are contentious (Woodburne & Case 1996;Kielan-Jaworowska et al. 1998;Luo et al. 2001Luo et al. , 2002Musser 2003Musser , 2006Wroe & Archer 2006). What is clear is that there was a considerable diversity of mammals (monotremes, multituberculates (Corriebaatar marywaltersae, Multituberculata) and the enigmatic forms: Kollikodon ritchiei, Ausktribosphenos nyktos, Bishops whitmorei and Kryoryctes cadburyi) living in proto-Australia during the Early Cretaceous (Musser 2003;Rich & Vickers-Rich 2004;Pridmore et al. 2005;Rich et al. 2009) and that many forms were present early enough to have reached Zealandia (contra Fleming 1982: 22). ...
... Although fossils of the third group of living mammals (placentals) have been claimed from the Cretaceous (Ausktribosphenos nyktos, Bishops whitmorei) and Eocene (Tingamarra porterorum) of Australia (Godthelp et al. 1992;Rich et al. 1997Rich et al. , 1999, these identifications are contentious (Woodburne & Case 1996;Kielan-Jaworowska et al. 1998;Luo et al. 2001Luo et al. , 2002Musser 2003Musser , 2006Wroe & Archer 2006). What is clear is that there was a considerable diversity of mammals (monotremes, multituberculates (Corriebaatar marywaltersae, Multituberculata) and the enigmatic forms: Kollikodon ritchiei, Ausktribosphenos nyktos, Bishops whitmorei and Kryoryctes cadburyi) living in proto-Australia during the Early Cretaceous (Musser 2003;Rich & Vickers-Rich 2004;Pridmore et al. 2005;Rich et al. 2009) and that many forms were present early enough to have reached Zealandia (contra Fleming 1982: 22). The grounddwelling mammal from the Early Miocene of New Zealand is, surprisingly, neither a monotreme nor apparently similar to the other Cretaceous mammals found so far as fossils in Australia (Worthy et al. 2006b). ...
Since the 1980s, morphological and molecular research has resulted in significant advances in understanding the relationships and origins of the recent terrestrial vertebrate fauna in the New Zealand biogeographic region. This research has led to many taxonomic changes, with a significant increase in the number of bird and reptile species recognised. It has also resulted in the recognition of several more Holocene (<10 000 years ago) bird species extinctions. The conclusion that Holocene extinctions were primarily caused by human-hunting and predation by other introduced mammals (particularly rats and cats) has been supported by new data. Despite many local eradications of introduced pests, the number of introduced species has increased, with the establishment of five more foreign birds and (on Norfolk Island) the house gecko (Hemidactylus frenatus). Many new, significant New Zealand vertebrate fossils have been reported, including more dinosaurs from the Cretaceous, and the first Tertiary records of frogs, rhynchocephalids, lizards, crocodylians, bats and a terrestrial "Mesozoic ghost" mammal from the Early Miocene near St Bathans. For birds, the earliest known penguins in the world have been discovered, and there are intriguing Late Cretaceous - Early Paleocene remains still awaiting detailed description. Other significant Tertiary bird fossils reported include a rich avifauna from the Early Miocene St Bathans sites and a small terrestrial fauna from the Early Pleistocene near Marton. In line with the traditional theory, new research has supported the vicariant Gondwanan origin of some distinctive New Zealand terrestrial vertebrates, such as leiopelmatid frogs, tuatara and moa, and the immigration of many others, including New Zealand wattlebirds and piopio, during the Cenozoic. Extinctions caused by an asteroid impact and climate fluctuations probably explain the absence of many groups, such as crocodylians, dinosaurs, monotremes, palaelodids and swiftlets, from the modern fauna.
... All occur exclusively in Meganesia sensu Filewood (1984): the continental shelf of Tasmania, Australia and New Guinea which was exposed as a single unit above Pleistocene sea levels. This land mass separated from Antarctica around the Oligocene (Quilty 1994;Wilford and Brown 1994) and fossil evidence confirms Gondwanan affinities for the monotremes (Musser 2003). Formerly considered primitive, these highly specialised mammals are, in fact, intriguing combinations of ancestral (e.g. ...
... edentate jaws, at least in adults) characters. Such combinations are explained by the ancient heritage of the monotremes, arising as they probably did before the Cretaceous (Musser 2003) and evolving separately from, but in sympatry with, the marsupial and 'placental' Theria. Such 'mosaic evolution' (sensu Ji et al. 1999;Musser 2003) is probably not confined to their anatomy. ...
... Such combinations are explained by the ancient heritage of the monotremes, arising as they probably did before the Cretaceous (Musser 2003) and evolving separately from, but in sympatry with, the marsupial and 'placental' Theria. Such 'mosaic evolution' (sensu Ji et al. 1999;Musser 2003) is probably not confined to their anatomy. It should be expected that the physiology of monotremes also features plesiomorphies and apomorphies, though in the absence of any reference material it would be challenging to determine which are which. ...
The three extant genera of the Monotremata have evolved, probably from a pre-Cretaceous Gondwanan origin, independently of the Theria to display a variety of ancestral and derived features. A comparison of their thermoregulation reveals a diversity of physiology that might represent both plesiomorphic and apomorphic elements within this mosaic. In the tachyglossids, the echidnas Tachyglossus and Zaglossus, body temperature is often labile, rising as a result of activity and allowed to decline during inactivity. This daily heterothermy, which is not necessarily torpor, may combine with typical mammalian hibernation to provide substantial energy economy in a wide variety of often unproductive habitats. Only when incubating do free-ranging echidnas display classic mammalian thermoregulation, the facultative nature of which suggests echidna-like physiology as an example of a protoendothermic stage in the evolution of endothermy. Similarly, physiological response to heat in Tachyglossus, at least, may be plesiomorphic, relying on the cyclic loss of heat stored during activity. Tachyglossids neither exhibit a panting response nor spread saliva to facilitate evaporative cooling and Tachyglossus, though not Zaglossus, lacks functional sweat glands. By contrast, the only extant ornithorhynchid, the platypus Ornithorhynchus, does not utilise heterothermy of any kind and maintains its body temperature more tightly than several semiaquatic eutherians. Although not necessarily required, it responds to heat via sweating, but not panting or saliva spreading. The classic nature of ornithorhynchid thermoregulation stands in marked contrast to the more diverse thermoregulatory responses shown by the tachyglossids, making it difficult to determine which aspects of monotreme thermoregulation are plesiomorphic and which are apomorphic.
... The current estimate for when monotremes diverged from other mammals is 166 million years ago (MYA) [7]. Although the echidnas (family Tachyglossidae) are thought to have diverged from the platypus lineage (family Ornithorhynchidae) (reviewed in [8][9][10]) ~32 MYA [10], ancient monotremes were much more diverse than extant members monotremes [8], and monotreme evolutionary rates were potentially slow [9]. It is thus difficult to extrapolate the features of the basal monotreme and it should not be assumed that it was platypus-like (reviewed in [8]). ...
... The current estimate for when monotremes diverged from other mammals is 166 million years ago (MYA) [7]. Although the echidnas (family Tachyglossidae) are thought to have diverged from the platypus lineage (family Ornithorhynchidae) (reviewed in [8][9][10]) ~32 MYA [10], ancient monotremes were much more diverse than extant members monotremes [8], and monotreme evolutionary rates were potentially slow [9]. It is thus difficult to extrapolate the features of the basal monotreme and it should not be assumed that it was platypus-like (reviewed in [8]). ...
... Although the echidnas (family Tachyglossidae) are thought to have diverged from the platypus lineage (family Ornithorhynchidae) (reviewed in [8][9][10]) ~32 MYA [10], ancient monotremes were much more diverse than extant members monotremes [8], and monotreme evolutionary rates were potentially slow [9]. It is thus difficult to extrapolate the features of the basal monotreme and it should not be assumed that it was platypus-like (reviewed in [8]). ...
The monotremes (platypuses and echidnas) represent one of only four extant venomous mammalian lineages. Until recently, monotreme venom was poorly understood. However, the availability of the platypus genome and increasingly sophisticated genomic tools has allowed us to characterize platypus toxins, and provides a means of reconstructing the evolutionary history of monotreme venom. Here we review the physiology of platypus and echidna crural (venom) systems as well as pharmacological and genomic studies of monotreme toxins. Further, we synthesize current ideas about the evolution of the venom system, which in the platypus is likely to have been retained from a venomous ancestor, whilst being lost in the echidnas. We also outline several research directions and outstanding questions that would be productive to address in future research. An improved characterization of mammalian venoms will not only yield new toxins with potential therapeutic uses, but will also aid in our understanding of the way that this unusual trait evolves.
... In the context of extant flea-host associations, this process limits the number of observable ecological relationships if few host lineages survived through evolutionary time. For example, Monotremata have only 5 contemporaneous species (out of at least 12 fossil species (Musser, 2003)). One paradigm of parasite evolution is that descendant host species inherit the parasites of their ancestors. ...
... The two latter groups are considered primary fleas of Monotremata, and both occupy relatively deep positions in the flea tree (Fig. 2). Considering the strong Australian connection of monotreme diversification (Archer et al., 1985;Musser, 2003), one may reasonably argue that the monotreme-flea association may be ancient, too (Grimaldi and Engel, 2005). Yet the low likelihoods of Monotremata at the basal node make this scenario less likely, which is biologically consistent with the Cretaceous age estimation of the earliest flea node being younger than the estimated Middle Jurassic split of Monotremata and Theria (Bininda-Emonds et al., 2007;dos Reis et al., 2012;Meredith et al., 2011;O'Leary et al., 2013). ...
Fleas (order Siphonaptera) are highly-specialized, diverse blood-feeding ectoparasites of mammals and birds with an enigmatic evolutionary history and obscure origin. We here present a molecular phylogenetic study based on a comprehensive taxon sampling of 259 flea taxa, representing 16 of the 18 extant families of this order. A Bayesian phylogenetic tree with strong nodal support was recovered, consisting of seven sequentially derived lineages with Macropsyllidae as the earliest divergence, followed by Stephanocircidae. Divergence times of flea lineages were estimated based on fossil records and host specific associations to bats (Chiroptera), suggesting that the common ancestor of extant Siphonaptera diversified during the Cretaceous. However, most of the intraordinal divergence into extant lineages took place after the K-Pg boundary. Ancestral states of host association and biogeographical distribution were reconstructed, suggesting with high likelihood that fleas originated in the southern continents (Gondwana) and migrated from South America to their extant distributions in a relatively short time frame. Theria (placental mammals and marsupials) represent the most likely ancestral host group of extant Siphonaptera, with marsupials occupying a more important role than previously assumed. Major extant flea families evolved in connection to post K-Pg diversification of Placentalia. The association of fleas with monotremes and birds is likely due to later secondary host association. These results suggest caution in casually interpreting recently discovered Mesozoic fossil ?dinosaur fleas? of Northeast Asia as part of what we currently consider Siphonaptera.
... The earliest date for the onset of I. holocyclus-marsupials relationship is about 70 mya (Mitchell et al., 2014;Gallus et al., 2015) and probably consolidated after the K-Pg boundary. Dietrich et al. (2014) dated the split of I. uriae and I. holocyclus when Australia and Antarctic was still connected and available mammal hosts there were monotremes (Archer et al., 1985;Musser, 2003). Avialae was established by early Cretaceous in Australasia (Chiappe, 1996;Close et al., 2009;Fitzgerald et al., 2012;Martin et al., 2014) and by late Cretaceous in Antarctica (Chiappe, 1996;Clarke et al., 2005) therefore this split event should have occurred in Australasia coinciding with the origin of I. uriae proposed by Dietrich et al. (2014). ...
... Probably Australasian Ixodes uriae passed the K-Pg boundary feeding on MB and Ixodes holocyclus or their ancestors, surpassed it as a parasite of Monotremata (eventually on early Australian marsupials or both). (Musser, 2003). The latter author emphasized that early Cretaceous was a time of diversification of monotremes rather than a time of origin that according to van Rheede et al. (2006) occurred in late Triassic (231-217 mya). ...
The relationship between birds (Aves) and hard ticks (Ixodidae) was analyzed for the 386 of 725 tick extant species whose larva, nymph and adults are known as well as their natural hosts. A total of 136 (54 Prostriata= Ixodes, 82 Metastriata= all other genera) are frequently found on Aves, but only 32 species (1 associated with Palaeognathae, 31 with Neognathae) have all parasitic stages feeding on birds: 25 Ixodes (19% of the species analyzed for this genus), 6 Haemaphysalis (7%) and 1 species of Amblyomma (2%). The species of Amblyomma feeds on marine birds (MB), the six Haemaphysalis are parasites of non-marine birds (NMB), and 14 of the 25 Ixodes feed on NMB, one feeds on NMB and MB, and ten on MB. The Australasian Ixodes + I. uriae clade probably originated at an uncertain time from the late Triassic to the early Cretaceous. It is speculated that Prostriata first hosts were Gondwanan theropod dinosaurs in an undetermined place before Pangaea break up; alternatively, if ancestral monotromes were involved in its evolution an Australasian origin of Prostriata seems plausible. As for Prostriata the Motherland of Ixodida is probably Gondwana.
RESUMEN. Aves y garrapatas duras (Ixodidae), con discusión sobre hipótesis sobre evolución de las garrapatas. En esta revisión se analizó la relación entre aves y garrapatas duras (Ixodidae) para las 386 de 725 especies de garrapatas que utilizan aves como hospedadores para larvas, ninfas y adultos. Un total de 136 especies (54 Prostriata= Ixodes, 82 Metastriata= restantes géneros) son frecuentemente encontradas sobre aves, pero solo 32 especies (1 asociada con Palaeognathae, 31 con Neognathae) tienen ciclos donde todos los estadios se alimentan sobre aves: 25 Ixodes (19% de las especies analizadas para este género), 6 Haemaphysalis (7% del total) y 1 especie de Amblyomma (2% del total). Las especies de Amblyomma se alimentan sobre aves marinas (MB), las seis de Haemaphysalis son parásitas de aves no-marinas (NMB), y 14 de las 25 especies de Ixodes se alimentan sobre NMB, una sobre NMB y MB, y diez sobre MB. El clado de Australasia Ixodes + I. uriae probablemente se originó entre el fin del Triásico y comienzos del Cretácico. Se especula que los primeros hospedadores de Prostriata fueron dinosaurios terópodos con distribución Gondwánica; alternativamente, si monotremas ancestrales estuvieron involucrados en su evolución, un origen de Prostriata en Australasia es plausible. Al igual que para Prostriata, el área de origen de Ixodida es probablemente Gondwana.
... Flannery et al., (1995) described Kollikodon ritchiei as a possible monotreme, placing it in its own monotypic family, the Kollikodontidae. This assignation has proved more controversial, with suggestions that it may be a basal mammaliaform rather than a monotreme and as such more appropriately placed outside crown-group Mammalia (Musser, 2003). This controversy rejects in part the limited morphological information available on the basis of the previously only known specimen, a partial dentary with three highly autapomorphic, bunodont molars. ...
... A further stumbling block is the limited fossil record of other Mesozoic australosphenidans, because no upper dentitions or maxillae have yet been published. Nevertheless maximum parsimony and Bayesian methods of phylogenetic analysis support the inclusion of K. ritchiei within crown-group Mammalia, in contrast to recent suggestions that it may have been a stem-mammaliaform (Musser, 2003). Both methods also place K. ritchiei as sister group to definitive monotremes within Australosphenida, albeit with varying degrees of support. ...
Pian, R., Archer, M., Hand, S.J., Beck, R.M.D. and Cody, A. 2016. The upper dentition and relationships of the enigmatic Australian Cretaceous mammal Kollikodon ritchiei. Memoirs of Museum Victoria 74: 97–105. Mesozoic mammals from Australia are rare, so far only known from the Early Cretaceous, and most are poorly represented in terms of dentitions much less cranial material. No upper molars of any have been described. Kollikodon ritchiei is perhaps the most bizarre of these, originally described on the basis of a dentary fragment with three molars. Here we describe a second specimen of this extremely rare taxon, one that retains extraordinarily specialised upper cheekteeth (last premolar and all four molars). Each molar supports rows of bladeless, rounded cuspules many of which exhibit apical pits that may be the result of masticating hard items such as shells or chitin. Reanalysis of the phylogenetic position of this taxon suggests, based on a limited number of apparent synapomorphies, that it is an australosphenidan mammal and probably the sister group to Monotremata. This reanalysis also supports the view that within Monotremata, tachyglossids and ornithorhynchids diverged in the early to middle Cenozoic.
... They belong to the mouse-sized Teinolophos trusleri from Flat Rocks, Victoria, and the much larger (perhaps cat-sized) Steropodon galmani from Lightning Ridge, New South Wales [Kielan-Jaworowska et al. 2004]. Other possible prototherian fossils from this time period are an echidna-like humerus, which has been named Kryoryctes cadburyi, from Dinosaur Cove, Victoria [Pridmore et al. 2005], and the dentally unusual Kollikodon ritchiei ; the authors nearly named this species "Hotcrossbunodon" due to the resemblance of the teeth to hot cross buns, see Long et al. 2002], also from Lightning Ridge, which was originally described as a monotreme but more recently has been suggested to belong to an entirely different branch of the mammalian family tree [Musser 2003;Musser 2013]. There is then a gap of Box 2: Jaw bones. ...
... Based on recent studies that have used "molecular clocks" to estimate when the modern platypus and echidna lineages diverged from each other, Teinolophos, Steropodon, and Monotrematum pre-date this split [Phillips et al. 2009]; however, all three are poorly known due to the fragmentary nature of their fossils, and so we can say relatively little about the anatomy and biology of the earliest monotremes. After the South American Monotrematum, there is another gap of around 38 million years, until approximately 25 million years ago when we see the first fossils that can probably be referred to as either platypus or echidnas, found at various fossil sites in Australia [Musser 2003;Musser 2013]. Of these, the platypus lineage is much better documented. ...
This chapter provides an evolutionary context to comparative research on monotremes and marsupials. It
explains the evolutionary origins of the three mammalian clades in the mammalian (and pre-mammalian) from the ancient lineage of synapsids, summarizes their most obvious biological differences, and briefly the
difference between the terms “Monotremata, Marsupialia, Placentalia” vs. “Prototheria, Metatheria, Eutheria”.
The monotreme and marsupial families are briefly introduced through short characterizations of their general
biology and evolution. An up-to-date family-level phylogeny is provided for marsupials, together with a
summary of previous, morphology-based phylogenetic hypotheses vs. more recent molecular works. The fossil record for both radiations is summarized in a biogeographical context. Particular attention is given to a recent paradigm shift on monotreme evolution, with the latest research suggesting that monotremes are part of an ancient, Gondwanan radiation of mammals with independently derived tribosphenic dentition. The unusual biogeography of marsupials and their extinct relatives, including a possible origin near China and final distribution across South America, Antarctica, and Australia, is also covered.
... The closest living relative of the platypus, the echidna, has a large olfactory organ, including a well-developed cribriform plate (Kuhn, 1971). The fossil record indicates that the platypus is anatomically closer to the last common ancestor of the modern monotremes than are echidnas (Musser, 2003). This raises the interesting possibility that echidnas have evolved from platypus-like ancestors and are thus secondarily terrestrial (Gregory, 1947;Musser, 2003). ...
... The fossil record indicates that the platypus is anatomically closer to the last common ancestor of the modern monotremes than are echidnas (Musser, 2003). This raises the interesting possibility that echidnas have evolved from platypus-like ancestors and are thus secondarily terrestrial (Gregory, 1947;Musser, 2003). It is not at present known whether the last common ancestor of modern monotremes had a fully functional, perforated cribriform plate. ...
... When we refer to the HGP we are talking about the international effort that formally started in October 1990 and which delivered the draft sequence of the human genome in 2003 [59,60] . In addition to determining the complete sequence of the 3 billion DNA base pairs in the human genome, the HGP carried out a number of parallel, preliminary studies, mainly on Escherichia coli [11] and mouse [81] , in order to develop new approaches to optimize the tools used to handle the amount of information generated for human. This process helped to extend our understanding of human gene function (for a more detailed account see [21] ). ...
... In addition, complete sequences had been obtained for over 30 microorganisms (including the bacteria E. coli [11] and Mycobacterium tuberculosis [20] ; Table 29.2.1 ). Work was progressing on many other genomes, some mammalian species (chimpanzee [116] , opossum [78] , rat [43] , mouse [81] , rhesus macaque [95] ), chicken [53] , Danio rerio [108] , Takifugu rubripes [3] , Tetraodon nigroviridis [98] , Caenorhabditis briggsae [110] , and Drosophila pseudoobscura [96] , but also plants such as rice [45,127] , amongst others (see Table 29 [39] . Since different algorithms are used to annotate genomes this can lead to different gene sets, a less than ideal scenario. ...
Recent years have seen the release of huge amounts of sequence data from genome sequencing centers. However, this raw sequence data is most valuable to the laboratory biologist when provided along with quality annotation of the genomic sequence. Ensembl provides access to genomic information with a number of visualization tools, becoming one of the world's primary resources for genomic research, a resource through which scientists can access the human genome as well as the genomes of other model organisms. Thus, researchers can download data directly, whether it is the DNA sequence of a genomic contig, or positions of SNPs in a given gene. The key Ensembl web pages are highlighted in this chapter. Because of the complexity of the genome and the many different ways in which scientists want to use it, Ensembl provides many levels of access with a high degree of flexibility. Through the Ensembl website a wet-lab researcher with a simple web browser can for example perform BLAST searches against the assembly of a genome, download a genomic sequence, or search for all members of a determined protein family. But Ensembl is also an all-round software and database system that can be installed locally to serve the needs of a genomic center or a bioinformatics division in a pharmaceutical company, enabling complex data mining of the genome or large-scale sequence annotation.
... In the context of extant flea-host associations, this process limits the number of observable ecological relationships if few host lineages survived through evolutionary time. For example, Monotremata have only 5 contemporaneous species (out of at least 12 fossil species (Musser, 2003)). One paradigm of parasite evolution is that descendant host species inherit the parasites of their ancestors. ...
... The two latter groups are considered primary fleas of Monotremata, and both occupy relatively deep positions in the flea tree (Fig. 2). Considering the strong Australian connection of monotreme diversification (Archer et al., 1985;Musser, 2003), one may reasonably argue that the monotremeflea association may be ancient, too (Grimaldi and Engel, 2005). Yet the low likelihoods of Monotremata at the basal node make this scenario less likely, which is biologically consistent with the Cretaceous age estimation of the earliest flea node being younger than the estimated Middle Jurassic split of Monotremata and Theria (Bininda-Emonds et al., 2007;dos Reis et al., 2012;Meredith et al., 2011;O'Leary et al., 2013). ...
... The platypus (Ornithorhynchidae) morphotype extends at least back to the Paleocene (Monotrematum, Pascual et al., 1992), while fossil echidnas (Tachyglossidae) date to no older than the Middle Miocene. This disparity raises the uncertainty of whether echidnas have a very long ghost lineage or are instead derived from platypuslike ancestors (Musser, 2003). Recent analysis of both morphological and molecular data ) strongly supports the latter hypothesis, and illuminates the selection of calibration bounds for Monotremata. ...
... Discussion. In light of sparse fossil records and 'platypus' morphology being ancestral among crown monotremes (see Gregory, 1947;Musser, 2003;Phillips et al., 2009), molecular timetrees calibrated independently of Monotremata have been particularly important for estimating monotreme crown divergence. Modern relaxed-clock molecular dating estimates concur on a Tertiary divergence between the platypus and echidnas, with most estimates falling between 21-48 Ma (e.g., Janke et al., 2002;Hugall et al., 2007;Warren et al., 2008). ...
With the introduction of relaxed-clock molecular dating methods, the role of fossil calibration has expanded from providing a timescale, to also informing the models for molecular rate variation across the phylogeny. Here I suggest fossil calibration bounds for four mammal clades, Monotremata (platypus and echidnas), Macropodoidea (kangaroos and potoroos), Caviomorpha-Phiomorpha (South American and African hystricognath rodents), and Chiroptera (bats). In each case I consider sources of uncertainty in the fossil record and provide a molecular dating analysis to examine how the suggested calibration priors are further informed by other mammal fossil calibrations and molecular data.
... T he fossil record and extant distribution of monotremes is almost restricted to Australasia, with the single exception of a fossil ornithorhynchid from the earliest Cenozoic in Patagonia 1 . In this context, occurrence of a monotreme in Patagonia was interpreted as the result of a single dispersal from Australia to South America, before or during the Late Cretaceous or early Paleocene [2][3][4][5][6] . ...
Monotremata is a clade of egg-lying mammals, represented by the living platypus and echidnas, which is endemic to Australia, and adjacent islands. Occurrence of basal monotremes in the Early Cretaceous of Australia has led to the consensus that this clade originated on that continent, arriving later to South America. Here we report on the discovery of a Late Cretaceous monotreme from southern Argentina, demonstrating that monotremes were present in circumpolar regions by the end of the Mesozoic, and that their distinctive anatomical features were probably present in these ancient forms as well.
... Молочные железы у утконоса и ехидны есть, но сосок в них отсутствует, и молоко просто вытекает в особые бороздки на коже, с которых его и слизывает детеныш. Такое строение молочной железы принято считать самым примитивным среди современных млекопитающих -учитывая исторический возраст «современных» утконосов и ехидн, составляющий как минимум несколько миллионов лет [2]. Считается, что молочная железа стала результатом ряда последовательных изменений кожных желез, которые и сегодня можно встретить у представителей животного мира, не относящихся к млекопитающим [3]. ...
The paper provides review of the scientific literature dedicated to the evolutionary aspects of breastfeeding in the animal kingdom. Differences in breast milk composition amongst different mammals along with changes in breast milk composition during evolution provided. Special attention is paid to oligosaccharides — unique components of the breast milk of Homo sapiens .
... Качконосові -значно давніша від єхиднових родина, яка жила ще в мезозої. Довговічність однопрохідних надзвичайна: цей підклас ссавців, можливо, існує 200 мільйонів років (Musser, 2003). Отже, тут першозвірів розглядаємо як представлених одним рядом і дво ма сучасними родинами, які поширені в межах Австралійської зоогеографічної області. ...
... Качконосові -значно давніша від єхиднових родина, яка жила ще в мезозої. Довговічність однопрохідних надзвичайна: цей підклас ссавців, можливо, існує 200 мільйонів років (Musser, 2003). Отже, тут першозвірів розглядаємо як представлених одним рядом і дво ма сучасними родинами, які поширені в межах Австралійської зоогеографічної області. ...
The present research is devoted to the review of mammal families of the world and to the basics of creation of Ukrainian family vernacular names. This necessity is actualized by the expansion of the range of objects that draw special attention in diversitology in connection with the development of museum ex positions, education, educational literature, monitoring programs of alien species and their invasions and expansions, etc. The specifics of formation of typified and unified names for families in the Ukrainian lan guage and the clarity of Ukrainian vernacular names according to the scientific names of corresponding taxa of mammals of the world fauna are considered. All such features are reviewed regarding to the whole set of the modern mammal fauna, including family names initially offered to extinct groups and families in which typical genera are extinct. The basis for the study of the mammal taxonomy was the review of the "Mammal Species of the World" (2005, edited by D. Wilson and D. Reeder) with a number of reconsidered details from other authors, including T. Vaughan with colleagues (2011), S. Kisia (2016), and R. Novak (2018). A list of 16 additions is presented regarding the names of families (one more addition deals with order range) both accepted or (rarely) rejected after the publication of mentioned review of 2005. The generalization of data on typical morphemes in taxonomic names of different ranks and recommendations regarding the formation of vernacular names are made. Similarly to the accepted provisions of the ICZN (International Code of Zoological Nomenclature) concerning scientific names of families presented in Latin or Latinized forms from other languages, the basis for the family name is the name of the type genus of family formatted by the wordforming suffixes "ov/ev" in the form of "ovi" or "evi" (for example, the name "vyvirkovi" for the family Sciuridae with the type genus Sciurus, the "inievi" for the Iniidae family with the type genus Inia). Formants "achi", "yni" and others (for example, "myshachi", "myshyni") are rejected as unproductive for the formation of group names. A list of mammal families of the world (totally 160) and their type genera and type species is arranged. New names are proposed for taxa, which did not have Ukrainian equivalents to valid scientific names (totally 33). The etymology of scientific and vernacular names for type genera of mammal families of the world is collected.
... The 20 LF species or taxa are as follows (common names, scientific names are found in Table 1): aardvark [20], platypus [21,22], opossum [23,24], elephant shrew [25], giant panda [26], koala [23,27], Philippine tarsier [28], pelican [29], New Zealand wren [30,31], speckled mousebird [32], red-legged seriema [33], tinamou [34], hoatzin [35][36][37], crocodilians [38], arowana [39], spotted gar [40], and coelacanth [12,41]. The 24 R species or taxa are as follows (common names, scientific names are found in Table 1): bats [42][43][44], dolphins and whales [45,46], lemurs [47][48][49], medium ground finch [50,51], great tit [51], Carolina anole [52][53][54][55], black rockcod [56][57][58], and three cichlid species [59][60][61][62]. ...
Adaptive radiation and evolutionary stasis are characterized by very different evolution rates. The main aim of this study was to investigate if any genes have a special role to a high or low evolution rate. The availability of animal genomes permitted comparison of gene content of genomes of 24 vertebrate species that evolved through adaptive radiation (representing high evolutionary rate) and of 20 vertebrate species that are considered as living fossils (representing a slow evolutionary rate or evolutionary stasis). Mammals, birds, reptiles, and bony fishes were included in the analysis. Pathway analysis was performed for genes found to be specific in adaptive radiation or evolutionary stasis respectively. Pathway analysis revealed that DNA repair and cellular response to DNA damage are important (false discovery rate = 8.35 × 10−5; 7.15 × 10−6, respectively) for species evolved through adaptive radiation. This was confirmed by further genetic in silico analysis (p = 5.30 × 10−3). Nucleotide excision repair and base excision repair were the most significant pathways. Additionally, the number of DNA repair genes was found to be linearly related to the genome size and the protein number (proteome) of the 44 animals analyzed (p < 1.00 × 10−4), this being compatible with Drake’s rule. This is the first study where radiated and living fossil species have been genetically compared. Evidence has been found that cancer-related genes have a special role in radiated species. Linear association of the number of DNA repair genes with the species genome size has also been revealed. These comparative genetics results can support the idea of punctuated equilibrium evolution.
... Other mammals are represented by extremely rare, but beautifully preserved craniodental remains. Two taxa are known: Kollikodon ritchei is an australosphenidian and was recovered as the sister taxon to Monotremata (Flannery et al., 1995;Musser, 2003Musser, , 2006Pian et al., 2016; Fig. 13A). Steropodon galmani (Fig. 13B) is accepted as a true monotreme on the line to Ornithorhynchidae (Archer et al., 1985;Musser, 2006;Phillips et al., 2009;Pian et al., 2016). ...
The mid-Cretaceous Griman Creek Formation (GCF), which crops out near the town of Lightning Ridge in the Surat Basin of north-central New South Wales, Australia, is noteworthy for its opalised vertebrate fauna. The fossil assemblage comprises remains of aspidorhynchid teleosts, lamniform chondrichthyans, dipnoans, chelid and possible meiolaniform turtles, leptocleidid-like and possible elasmosaurid plesiosaurians, anhanguerian pterosaurs, titanosauriform sauropods, megaraptoran theropods, ankylosaurians, several forms of non-iguanodontian and iguanodontian ornithopods, crocodylomorphs, enantiornithine birds, and stem and true monotremes, making it one of the most diverse mid-Cretaceous terrestrial vertebrate faunas in Australia. A detailed stratigraphic survey of twenty subterranean opal mines provides new information on the geology, age and palaeoenvironment of the main fossil-bearing beds. Vertebrate remains derive from the ‘Finch Clay facies’ laterally-extensive but discontinuous lenses of claystone that likely accumulated relatively rapidly in near-coastal but freshwater embayments (i.e. lagoonal conditions), and probably represent a single, roughly contemporaneous fauna. U-Pb age dating of detrital zircons extracted from a distinct layer of volcanogenic claystone immediately overlying one of the opalised fossil-bearing layers yields a maximum depositional age of 100.2–96.6 Ma. These new dates confirm an early to mid-Cenomanian age for the fauna, rather than Albian, as has been reported previously. The GCF at Lightning Ridge is therefore equivalent to the middle part of the Winton Formation (Queensland) and several million years older than the sauropod-dominated fauna at Winton.
... Interestingly, the presence of an alanine at position 164 of cTnI is conserved across mammals, with a single notable exception: Ornithorhynchus anatinus (platypus), which instead harbors a proline at this position (13). Phylogenetically, the egg-laying mammals branched off from their viviparous counterparts close to 200 million years ago to give rise to the modern order Monotremata (22). The only five extant monotremes are the platypus and four species of echidna. ...
The heterotrimeric cardiac troponin complex is a key regulator of contraction and plays an essential role in conferring Ca2+ sensitivity to the sarcomere. During ischemic injury, rapidly accumulating protons acidify the myoplasm, resulting in markedly reduced Ca2+ sensitivity of the sarcomere. Unlike the adult heart, sarcomeric Ca2+ sensitivity in fetal cardiac tissue is comparatively pH insensitive. Replacement of the adult cardiac troponin I (cTnI) isoform with the fetal troponin I (ssTnI) isoform renders adult cardiac contractile machinery relatively insensitive to acidification. Alignment and functional studies have determined histidine 132 of ssTnI to be the predominant source of this pH insensitivity. Substitution of histidine at the cognate position 164 in cTnI confers the same pH insensitivity to adult cardiac myocytes. An alanine at position 164 of cTnI is conserved in all mammals, with the exception of the platypus, which expresses a proline. Prolines are biophysically unique because of their innate conformational rigidity and helix-disrupting function. To provide deeper structure-function insight into the role of the TnC-TnI interface in determining contractility, we employed a live-cell approach alongside molecular dynamics simulations to ascertain the chemo-mechanical implications of the disrupted helix 4 of cTnI where position 164 exists. This important motif belongs to the critical switch region of cTnI. Substitution of a proline at position 164 of cTnI in adult rat cardiac myocytes causes increased contractility independent of alterations in the Ca2+ transient. Free-energy perturbation calculations of cTnC-Ca2+ binding indicate no difference in cTnC-Ca2+ affinity. Rather, we propose the enhanced contractility is derived from new salt bridge interactions between cTnI helix 4 and cTnC helix A, which are critical in determining pH sensitivity and contractility. Molecular dynamics simulations demonstrate that cTnI A164P structurally phenocopies ssTnI under baseline but not acidotic conditions. These findings highlight the evolutionarily directed role of the TnI-cTnC interface in determining cardiac contractility.
... Interestingly, the divergence times we and Gongora et al. (2012) have estimated predate the earliest fossil evidence for platypus (Musser, 1998(Musser, , 2013, although we are conscious that our absolute estimates do depend on the generation time and mutation rate. This finding does not necessarily contradict fossil evidence but suggest that the modern platypus extends back to the Early to Middle Pliocene. ...
The platypus is an egg-laying mammal which, alongside the echidna, occupies a unique place in the mammalian
phylogenetic tree. Despite widespread interest in its unusual biology, little is known about its population struc-
ture or recent evolutionary history. To provide new insights into the dispersal and demographic history of this
iconic species, we sequenced the genomes of 57 platypuses from across the whole species range in eastern mainland
Australia and Tasmania. Using a highly-improved reference genome, we called over 6.7M SNPs, providing an
informative genetic data set for population analyses. Our results show very strong population structure in the
platypus, with our sampling locations corresponding to discrete groupings between which there is no evidence for
recent gene flow. Genome-wide data allowed us to establish that 28 of the 57 sampled individuals had at least a
third-degree relative amongst other samples from the same river, often taken at di↵erent times. Taking advantage
of a sampled family quartet, we estimated the de novo mutation rate in the platypus at 7.0⇥10
... Interestingly, the divergence times we and Gongora et al. (2012) have estimated predate the earliest fossil evidence for platypus (Musser, 1998(Musser, , 2013, although we are conscious that our absolute estimates do depend on the generation time and mutation rate. This finding does not necessarily contradict fossil evidence but suggest that the modern platypus extends back to the Early to Middle Pliocene. ...
The platypus is an egg-laying mammal which, alongside the echidna, occupies a unique place in the mammalian phylogenetic tree. Despite widespread interest in its unusual biology, little is known about its population structure or recent evolutionary history. To provide new insights into the dispersal and demographic history of this iconic species, we sequenced the genomes of 57 platypuses from across the whole species range in eastern mainland Australia and Tasmania. Using a highly-improved reference genome, we called over 6.7M SNPs, providing an informative genetic data set for population analyses. Our results show very strong population structure in the platypus, with our sampling locations corresponding to discrete groupings between which there is no evidence for recent gene flow. Genome-wide data allowed us to establish that 28 of the 57 sampled individuals had at least a third-degree relative amongst other samples from the same river, often taken at di↵erent times. Taking advantage of a sampled family quartet, we estimated the de novo mutation rate in the platypus at 7.0⇥10 9 /bp/generation (95% CI 4.1⇥10 9-1.2⇥10 8 /bp/generation). We estimated e↵ective population sizes of ancestral populations and haplotype sharing between current groupings, and found evidence for bottlenecks and long-term population decline in multiple regions, and early divergence between populations in different regions. This study demonstrates the power of whole-genome sequencing for studying natural populations of an evolutionarily important species.
... Molecular studies based on the sequenced genome of the platypus corroborate the long held interpretation that the monotremes diverged prior to the metatherian/eutherian split, consistent with proposed fossil-based phylogenies (Warren et al., 2008). Unfortunately, there are almost no reported hindlimb specimens of any extinct monotreme (including probable early monotreme fossils found in South America; Musser, 2003), with the exception of the Pleistocene Zaglossus (echidna) from Australia and New Guinea (which may be the same as the extant species of that name). Unfortunately, although fossil Zaglossus hindlimb elements exist, including an articulated knee, neither presence nor absence of the patella has been reported (Murray, 1984). ...
The patella is a sesamoid bone located in the major extensor tendon of the knee joint, in the hindlimb of many tetrapods. Although numerous aspects of knee morphology are ancient and conserved among most tetrapods, the evolutionary occurrence of an ossified patella is highly variable. Among extant (crown clade) groups it is found in most birds, most lizards, the monotreme mammals and almost all placental mammals, but it is absent in most marsupial mammals as well as many reptiles. Here, we integrate data from the literature and first-hand studies of fossil and recent skeletal remains to reconstruct the evolution of the mammalian patella. We infer that bony patellae most likely evolved between four and six times in crown group Mammalia: in monotremes, in the extinct multituberculates, in one or more stem-mammal genera outside of therian or eutherian mammals and up to three times in therian mammals. Furthermore, an ossified patella was lost several times in mammals, not including those with absent hindlimbs: once or more in marsupials (with some re-acquisition) and at least once in bats. Our inferences about patellar evolution in mammals are reciprocally informed by the existence of several human genetic conditions in which the patella is either absent or severely reduced. Clearly, development of the patella is under close genomic control, although its responsiveness to its mechanical environment is also important (and perhaps variable among taxa). Where a bony patella is present it plays an important role in hindlimb function, especially in resisting gravity by providing an enhanced lever system for the knee joint. Yet the evolutionary origins, persistence and modifications of a patella in diverse groups with widely varying habits and habitats—from digging to running to aquatic, small or large body sizes, bipeds or quadrupeds—remain complex and perplexing, impeding a conclusive synthesis of form, function, development and genetics across mammalian evolution. This meta-analysis takes an initial step toward such a synthesis by collating available data and elucidating areas of promising future inquiry.
... Monotremes (i.e., the platypus and the short and long beaked echidnas) are an early-divergent clade of crown Mammalia that are different from extant therians (i.e., marsupials and placentals) in many anatomical structures and functions, such as interclavicular bones, epipubic bones, cloaca and laying shelled eggs (Archer et al., 1985;Rowe, 1988;Zeller, 1999;Luo et al., 2001;Musser, 2003;Mikoleit, 2004;Augee et al., 2006;Grant, 2007;Rowe et al. 2008, Phillips et al., 2009Ashwell, 2013;O'Meara and Thompson, 2014). In addition, several inner ear features distinguish monotremes from therians (Pritchard, 1881;Denker, 1901;Gray, 1908;Zeller, 1989;Jørgensen and Locket, 1995). ...
The monophyletic clade Monotremata branches early from the rest of the mammalian crown group in the Jurassic and members of this clade retain many ancestral mammalian traits. Thus, accurate and detailed anatomical descriptions of this group can offer unique insight into the early evolutionary history of Mammalia. In this study, we examine the inner ear anatomy of two extant monotremes, Ornithorhynchus anatinus and Tachyglossus aculeatus, with the primary goals of elucidating the ancestral mammalian ear morphology and resolving inconsistencies found within previous descriptive literature. We use histological serial sections and high-resolution microcomputed tomography (µCT) for correlating soft tissue features of the vestibule and cochlea to the osseous labyrinth endocast. We found that in both monotremes the scala tympani coils to a lesser degree than scala vestibuli and scala media, although all three scalae show an apical coil inside the osseous cochlear tube. The helicotrema (conduit between scala tympani and scala vestibuli) is in subapical position, and the cochlear and lagenar ganglia and their associated nerve fibers are not enclosed by bone. In comparison, in extant therian mammals (i.e., marsupials and placentals) the helicotrema is located at the apex of the osseous cochlear canal, the three scalae coil to the same degree and the cochlear ganglion is enclosed by the primary bony lamina. Whether the lagenar ganglion is lost in therian mammals or integrated into the cochlear ganglion is still debated. The presence of a sensory lagenar macula at the apex of the membranous cochlear duct, innervated by a separate lagenar nerve and ganglion is a plesiomorphic condition of amniotes that monotremes share. A separate osseous lagenar canaliculus for the lagenar nerve, and the coiling of the distended lagenar sac at the end of the cochlear duct are autapomorphies of monotremes. Based on our findings we hypothesize that the ancestral inner ear of stem mammaliaforms is characterized by a straight or slightly curved osseous cochlear canal, a lagenar macula, lagenar nerve fibers separated from a larger bundle of cochlear nerve fibers, the presence of an organ of Corti and an intra-otic cochlear ganglion suspended by membranous connective tissue. Among the major Mesozoic clades of crown mammals, cladotherians and gondwanatherians most likely acquired a fully functioning organ of Corti but lost the sensory lagenar macula, like extant therians. However, Mesozoic spalacotherioids, multituberculates and eutriconodonts likely retained the mammaliaform condition. J. Morphol., 2016.
... Monotremes are represented today by three genera (Ornithorynchus, Tachyglossus, and Zaglossus) each with specialized skeletal morphology. Their poor fossil record includes material from Australia and South America (Pascual et al., 1992;Musser & Archer, 1998;Musser, 2003). Accordingly, the bone histology of monotremes has been scarcely studied. ...
The interest in mammalian palaeohistology has increased dramatically in the last two decades. Starting in 1849 via descriptive approaches, it has been demonstrated that bone tissue and vascularisation types correlate with several biological variables such as ontogenetic stage, growth rate, and ecology. Mammalian bone displays a large variety of bone tissues and vascularisation patterns reaching from lamellar or parallel-fibred to fibrolamellar or woven-fibred bone, depending on taxon and individual age. Here we systematically review the knowledge and methods on mammalian bone and palaeohistology and discuss potential future research fields and techniques. We present new data on the bone microstructure of two extant marsupial species and of several extinct continental and island placental mammals. Three juvenile specimens of the dwarf island hippopotamid Hippopotamus minor from the Late Pleistocene of Cyprus show reticular to plexiform fibrolamellar bone. The island murid Mikrotia magna from the Late Miocene of Gargano, Italy displays parallel-fibred primary bone with reticular vascularisation being pervaded by irregular secondary osteons in the central part of the cortex. Leithia sp., the dormouse from the Pleistocene of Sicily, is characterised by a primary bone cortex consisting of lamellar bone and low vascularisation. The bone cortex of the fossil continental lagomorph Prolagus oeningensis and three fossil species of insular Prolagus displays parallel-fibred primary bone and reticular, radial as well as longitudinal vascularisation. Typical for large mammals, secondary bone in the giant rhinocerotoid Paraceratherium sp. from the Miocene of Turkey is represented by dense Haversian bone. The skeletochronological features of Sinomegaceros yabei, a large-sized deer from the Pleistocene of Japan closely related to Megaloceros, indicate a high growth rate. These examples and the critical summary of existing data show how bone microstructure can reveal essential information on life history evolution. The bone tissue and the skeletochronological data of the sampled island species show that there is no universal modification of bone tissue and life history specific to insular species.
... Monotremes are represented today by three genera (Ornithorynchus, Tachyglossus, and Zaglossus) each with specialized skeletal morphology. Their poor fossil record includes material from Australia and South America (Pascual et al., 1992;Musser & Archer, 1998;Musser, 2003). Accordingly, the bone histology of monotremes has been scarcely studied. ...
The interest in mammalian palaeohistology has increased dramatically in the last two decades. Starting in 1849 via descriptive approaches, it has been demonstrated that bone tissue and vascularisation types correlate with several biological variables such as ontogenetic stage, growth rate, and ecology. Mammalian bone displays a large variety of bone tissues and vascularisation patterns reaching from lamellar or parallel-fibred to fibrolamellar or woven-fibred bone, depending on taxon and individual age. Here we systematically review the knowledge and methods on mammalian bone and palaeohistology and discuss potential future research fields and techniques. We present new data on the bone microstructure of two extant marsupial species and of several extinct continental and island placental mammals. Three juvenile specimens of the dwarf island hippopotamid Hippopotamus minor from the Late Pleistocene of Cyprus show reticular to plexiform fibrolamellar bone. The island murid Mikrotia magna from the Late Miocene of Gargano, Italy displays parallel-fibred primary bone with reticular vascularisation being pervaded by irregular secondary osteons in the central part of the cortex. Leithia sp., the dormouse from the Pleistocene of Sicily, is characterised by a primary bone cortex consisting of lamellar bone and low vascularisation. The bone cortex of the fossil continental lagomorph Prolagus oeningensis and three fossil species of insular Prolagus displays parallel-fibred primary bone and reticular, radial as well as longitudinal vascularisation. Typical for large mammals, secondary bone in the giant rhinocerotoid Paraceratherium sp. from the Miocene of Turkey is represented by dense Haversian bone. The skeletochronological features of Sinomegaceros yabei, a large-sized deer from the Pleistocene of Japan closely related to Megaloceros, indicate a high growth rate. These examples and the critical summary of existing data show how bone microstructure can reveal essential information on life history evolution. The bone tissue and the skeletochronological data of the sampled island species show that there is no universal modification of bone tissue and life history specific to insular species.
... The platypus and echidnas are the only remaining members of mammalian subclass Prototheria, a group that once contained a diverse range of animals that are now extinct (Musser 2003). The living monotremes are sometimes referred to as "primitive" mammals. ...
The platypus
is a monotreme, an egg-laying mammal, found only in Australia. Males are venomous. During the breeding season they are able to deliver venom through spurs located on their hind legs. Venom delivery is believed to provide individuals with an advantage over conspecifics throughout the breeding season. This paper reviews the current literature on platypus venom, focusing primarily on recent advances which have been made since the sequencing of the platypus genome and venom gland transcriptome. It first provides an overview of the genes and molecules involved in venom production and focuses on how these molecules explain the symptoms of envenomation: allodynia, hyperalgesia, swelling and changes to blood pressure. The paper concludes by providing insights into how these venom peptides could be developed into novel therapeutics for human use.
... The platypus and echidnas are the only remaining members of mammalian subclass Prototheria, a group that once contained a diverse range of animals that are now extinct (Musser 2003). The living monotremes are sometimes referred to as "primitive" mammals. ...
The platypus
is a monotreme, an egg-laying mammal, found only in Australia. Males are venomous. During the breeding season they are able to deliver venom through spurs located on their hind legs. Venom delivery is believed to provide individuals with an advantage over conspecifics throughout the breeding season. This paper reviews the current literature on platypus venom, focusing primarily on recent advances which have been made since the sequencing of the platypus genome and venom gland transcriptome. It first provides an overview of the genes and molecules involved in venom production and focuses on how these molecules explain the symptoms of envenomation: allodynia, hyperalgesia, swelling and changes to blood pressure. The paper concludes by providing insights into how these venom peptides could be developed into novel therapeutics for human use.
... Monotremes are represented today by three genera (Ornithorynchus, Tachyglossus, and Zaglossus) each with specialized skeletal morphology. Their poor fossil record includes material from Australia and South America (Pascual et al., 1992;Musser & Archer, 1998;Musser, 2003). Accordingly, the bone histology of monotremes has been scarcely studied. ...
The interest in mammalian palaeohistology has increased dramatically in the last two decades. Starting in 1849 via descriptive approaches, it has been demonstrated that bone tissue and vascularisation types correlate with several biological variables such as ontogenetic stage, growth rate, and ecology. Mammalian bone displays a large variety of bone tissues and vascularisation patterns reaching from lamellar or parallel-fibred to fibrolamellar or woven-fibred bone, depending on taxon and individual age. Here we systematically review the knowledge and methods on cynodont and mammalian bone microstructure as well as palaeohistology and discuss potential future research fields and techniques. We present new data on the bone microstructure of two extant marsupial species and of several extinct continental and island placental mammals. Extant marsupials display mainly parallel-fibred primary bone with radial and oblique but mainly longitudinal vascular canals. Three juvenile specimens of the dwarf island hippopotamid Hippopotamus minor from the Late Pleistocene of Cyprus show reticular to plexiform fibrolamellar bone. The island murid Mikrotia magna from the Late Miocene of Gargano, Italy displays parallel-fibred primary bone with reticular vascularisation and strong remodelling in the middle part of the cortex. Leithia sp., the dormouse from the Pleistocene of Sicily, is characterised by a primary bone cortex consisting of lamellar bone and a high amount of compact coarse cancellous bone. The bone cortex of the fossil continental lagomorph Prolagus oeningensis and three fossil species of insular Prolagus displays mainly parallel-fibred primary bone and reticular, radial as well as longitudinal vascularisation. Typical for large mammals, secondary bone in the giant rhinocerotoid Paraceratherium sp. from the Late Oligocene of Turkey is represented by dense Haversian bone. The skeletochronological features of Sinomegaceros yabei, a large-sized deer from the Pleistocene of Japan closely related to Megaloceros, indicate a high growth rate. These examples and the synthesis of existing data show the potential of bone microstructure to reveal essential information on life history evolution. The bone tissue and the skeletochronological data of the sampled island species suggest the presence of various modes of bone histological modification and mammalian life history evolution on islands to depend on factors of island evolution such as island size, distance from mainland, climate, phylogeny, and time of evolution.
... Monotremes are represented today by three genera (Ornithorynchus, Tachyglossus, and Zaglossus) each with specialized skeletal morphology. Their poor fossil record includes material from Australia and South America (Pascual et al., 1992;Musser & Archer, 1998;Musser, 2003). Accordingly, the bone histology of monotremes has been scarcely studied. ...
The interest in mammalian palaeohistology has increased dramatically in the last two decades. Starting in 1849 via descriptive approaches, it has been demonstrated that bone tissue and vascularisation types correlate with several biological variables such as ontogenetic stage, growth rate, and ecology. Mammalian bone displays a large variety of bone tissues and vascularisation patterns reaching from lamellar or parallel-fibred to fibrolamellar or woven-fibred bone, depending on taxon and individual age. Here we systematically review the knowledge and methods on cynodont and mammalian bone microstructure as well as palaeohistology and discuss potential future research fields and techniques. We present new data on the bone microstructure of two extant marsupial species and of several extinct continental and island placental mammals. Extant marsupials display mainly parallel-fibred primary bone with radial and oblique but mainly longitudinal vascular canals. Three juvenile specimens of the dwarf island hippopotamid Hippopotamus minor from the Late Pleistocene of Cyprus show reticular to plexiform fibrolamellar bone. The island murid Mikrotia magna from the Late Miocene of Gargano, Italy displays parallel-fibred primary bone with reticular vascularisation and strong remodelling in the middle part of the cortex. Leithia sp., the dormouse from the Pleistocene of Sicily, is characterised by a primary bone cortex consisting of lamellar bone and a high amount of compact coarse cancellous bone. The bone cortex of the fossil continental lagomorph Prolagus oeningensis and three fossil species of insular Prolagus displays mainly parallel-fibred primary bone and reticular, radial as well as longitudinal vascularisation. Typical for large mammals, secondary bone in the giant rhinocerotoid Paraceratherium sp. from the Late Oligocene of Turkey is represented by dense Haversian bone. The skeletochronological features of Sinomegaceros yabei, a large-sized deer from the Pleistocene of Japan closely related to Megaloceros, indicate a high growth rate. These examples and the synthesis of existing data show the potential of bone microstructure to reveal essential information on life history evolution. The bone tissue and the skeletochronological data of the sampled island species suggest the presence of various modes of bone histological modification and mammalian life history evolution on islands to depend on factors of island evolution such as island size, distance from mainland, climate, phylogeny, and time of evolution.
... The expected fossil record of armadillo foraging pit fossils is thus limited to the Cenozoic. Rodents, echidnas, and Varanus sp., other noted producers of large, terrestrial, conical foraging pits, are likewise restricted to the Cenozoic (Huchon et al., 2000;Musser, 2003;Conrad et al., 2012). Vertebrate foraging by excavating pits in soils and sediments is not necessarily restricted to these taxa, however. ...
The nine-banded armadillo (Dasypus novemcinctus) is a well known burrower, but individuals spend the majority of their time above ground foraging for soil organisms by repeatedly digging pits through the soil surface. Little ichnological attention has been given to these foraging pits even though their great prevalence within the geographic range of extant armadillos implies that they might have a trace fossil record in paleosols extending back to at least the Paleocene. This research describes the forag-ing pits constructed by D. novemcinctus with implications for recognition and interpre-tation of similar conical trace fossils. Field observations yielded an association between one large-diameter (41 cm wide) dwelling burrow, three relatively short, straight shelter burrows (up to 19 cm wide and 38 cm long), and abundant variously sized foraging pits (up to 18 cm wide and 14.5 cm deep). Plaster casts of foraging pits showed that most were asymmetrical, vertically oriented, downward-tapering elliptical cones (width>depth), with smooth to coarsely dimpled walls and common elongate, parallel grooves, isolated curved grooves, and distinct paired grooves, resulting from scratching with the elongated middle two digits of the forelimb. Digital models of plaster casts are used to quantify several aspects, including a new property, conicality. Rela-tive compactness and volume exploited indicate that surface pits are more efficient for soil foraging than subterranean burrows. Recognition of fossil armadillo foraging pits would enable paleoenvironmental and paleoclimatic interpretations analogous to the habitats and ranges of extant armadillos. Conical trace fossils in the Upper Jurassic Morrison Formation are potential examples of ancient vertebrate foraging pits, although they are not attributable to armadillos because of their age.
... Extant long-beaked echidnas comprise three species (Zaglossus bruijnii, Zaglossus bartoni and Zaglossus attenboroughi) living only in New Guinea (Flannery and Groves, 1998), whereas the short-beaked echidna, Tachyglossus aculeatus, is found in both Australia and New Guinea. The monotremes diverged from the line leading to eutherian mammals at least 125 and possibly as much as 240 million years ago (Musser, 2003;Murphy et al., 2004) (Fig. 1). Apart from their unique significance for mammalian evolution, the nervous systems of modern Tachyglossidae are of interest for several reasons. ...
In 2020, the Australasian palaeontological association Australasian Palaeontologists (AAP) joined the Australian government-supported Australian National Species List (auNSL) initiative to compile the first Australian Fossil National Species List (auFNSL) for the region. The goal is to assemble comprehensive systematic data on all vertebrate, invertebrate and plant fossil taxa described to date, and to present the information both within a continuously updated open-access online framework, and as a series of primary reference articles in AAP’s flagship journal Alcheringa. This paper spearheads these auFNSL Alcheringa publications with an annotated checklist of Australian Mesozoic tetrapods. Complete synonymy, type material, source locality, geological age and bibliographical information are provided for 111 species formally named as of 2022. In addition, chronostratigraphically arranged inventories of all documented Australian Mesozoic tetrapod fossil occurrences are presented with illustrations of significant, exceptionally preserved and/or diagnostic specimens. The most diverse order-level clades include temnospondyl amphibians (34 species), saurischian (13 species) and ornithischian (12 species) dinosaurs (excluding ichnotaxa), and plesiosaurian marine reptiles (11 species). However, numerous other groups collectively span the earliest Triassic (earliest Induan) to Late Cretaceous (late Maastrichtian) and incorporate antecedents of modern Australian lineages, such as chelonioid and chelid turtles and monotreme mammals. Although scarce in comparison to records from other continents, Australia’s Mesozoic tetrapod assemblages are globally important because they constitute higher-palaeolatitude faunas that evince terrestrial and marine ecosystem evolution near the ancient South Pole. The pace of research on these assemblages has also accelerated substantially over the last 20 years, and serves to promote fossil geoheritage as an asset for scientific, cultural and economic development. The auFNSL augments the accessibility and utility of these palaeontological resources and provides a foundation for ongoing exploration into Australia’s unique natural history.
Advances in dating and systematics have prompted a revision of monotreme evolution to refine the timing of adaptative trends affecting body size and craniodental morphology. The oldest known monotreme, Teinolophos trusleri, is restricted to uppermost Barremian deposits of the Strzelecki Group in Victoria, Australia. Its body mass is estimated at ∼40 g, making it the smallest known monotreme. Teinolophos trusleri likely possessed an electro-sensitive and/or mechano-sensitive ‘bill’ or ‘beak’, which we suggest evolved for insectivory in seasonally dark Early Cretaceous polar forests. During the early Albian–mid-Cenomanian, monotremes diversified in Australia and evolved body masses greater than 4 kg, becoming amongst the largest Mesozoic mammals. A gap of 35 million years subsequently separates the youngest Mesozoic monotremes from the oldest Cenozoic monotreme, Monotrematum sudamericanum, which is a Paleocene stem ornithorhynchid from southern South America. We also hypothesize that tachyglossids originated in Melanesia, perhaps on the emergent Vogelkop landmass, and then dispersed to Australia during the Pliocene-Pleistocene. Finally, we present a classification of Monotremata to include five families—Teinolophidae fam. nov., Kollikodontidae, Steropodontidae, Ornithorhynchidae, and Tachyglossidae. We also propose a new genus, Murrayglossus gen. nov. for a gigantic Pleistocene echidna from southwestern Western Australia.
http://zoobank.org/urn:lsid:zoobank.org:pub:E39E2644-DADD-49F4-B2B7-47A25C072B07
Timothy F. Flannery [tim.flannery@textpublishing.com.au], Kristofer M. Helgen [Kris.Helgen@Australian.Museum], Australian Museum, 1 William St Sydney 2000, Australia; Thomas H. Rich [trich@museum.vic.gov.au], Tim Ziegler [tziegler@museum.vic.gov.au], Museums Victoria, PO Box 666, Melbourne, Victoria 3001, Australia; Patricia Vickers-Rich [pat.rich@monash.edu; prich@swin.edu.au], School of Earth, Atmosphere and Environment, Monash University, Victoria 3800, Australia; Swinburne University of Science and Technology, Department of Chemistry and Biotechnology, Hawthorn, Victoria 3122, Australia; Elizabeth Grace Veatch [elizabeth.veatch@gmail.com], National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA.
The South American fossil record of Mesozoic mammals and close relatives is one of the best for Gondwana. Early mammals and relatives are found in about a dozen localities in Argentina, Brazil, Bolivia, Chile, and presumably Peru, including a broad sample of non-mammaliaform cynodonts of the Triassic age. Mesozoic mammals span from the latest Early Jurassic to the latest Cretaceous, furthermore some of those archaic lineages unexpectedly survived the end of the Cretaceous period, remaining as minority elements in the Paleocene–Miocene faunal associations. The fossiliferous localities bearing these fossils are presented in this chapter, highlighting the geological setting, age, and their faunal associations.
As presently understood Australosphenida is a clade of Gondwanan taxa, including an array of Jurassic and Cretaceous extinct forms and the extant monotremes as the sole survivors. Mesozoic Australosphenida show plesiomorphic features in the lower jaw and derived tribosphenic, or tribosphenic-like, dentition, possibly acquired independently from boreal tribosphenic taxa, namely, therians and their immediate relatives. However, non-monotreme australosphenidans are known by rare and incomplete material making alternative hypotheses of dental homologies viable. Fossil and extant monotremes are hard to relate to Mesozoic non-monotreme australosphenidans, but a few dental and mandibular characters support them as members of the group. South American australosphenidans are the oldest currently known undisputed mammals, highlighting the early acquisition of complex tribosphenic dentitions and the importance of the fossil record from southern continents in the history of early mammals.
Living monotremes (the platypus and echidnas) are highly specialised egg‐laying mammals found only in Australia and New Guinea. However, their fossil history extends back to the Mesozoic Era. The past distribution of platypuses included Antarctica and southern South America, and their history extends back to the Mesozoic. Monotremes are, therefore, the oldest living mammalian group known. Platypuses are semi‐aquatic, feeding on benthic invertebrates in rivers, streams and lakes of eastern Australia. Echidnas are spine‐covered, terrestrial insectivores. There is just a single species of living platypus (Ornithorhynchus anatinus), but four living species of echidna: the short‐beaked echidna (Tachyglossus aculeatus) from Australia and New Guinea, and three species of long‐beaked echidna (genus Zaglossus), all of which live only in New Guinea. All monotreme species face challenges from climate change, development and human pressure. The platypus and long‐beaked echidnas are especially vulnerable, and there is much concern for their future.
Key Concepts
• Monotremes are mammals that lay eggs, like the earliest mammals, instead of bearing live young like all other living mammals.
• Living monotremes are found only in Australia and New Guinea, but platypuses were once distributed across southern Gondwana to the southern tip of South America.
• Many anatomical features in monotremes have an ancient heritage, such as the retention of certain skull bones and additional bones in the shoulder girdle.
• Both living monotreme types – platypuses and echidnas – are highly specialised for particular niches.
• Monotremes have a ‘sixth sense’ that helps them find cryptic prey: uniquely sensitive beaks or bills with both touch receptors and electroreceptors.
• Platypuses are extremely well adapted for life in water, with a wide bill, streamlined bodies, webbed feet and thick, waterproof fur.
• Echidnas are toothless, spine‐covered ant and termite specialists with long tubular beaks.
• There are two types of echidnas, the short‐beaked echidna from Australia and New Guinea and three very rare long‐beaked echidna species known only from New Guinea.
• Although the fossil record for monotremes is over 100 million years old, they are now threatened by climate change, hunting and development pressures, and their ongoing survival is not assured.
(in Japanese)
The topic of macroevolution of mammals has recently been disputed by paleontologists and molecular biologists, specifically in regards to the dispersal timing of crown Placentalia (crown Eutheria) and placental orders around the Cretaceous/Paleogene (K/Pg) boundary (ca. 66 Ma). Except Monotremata, there is no positive fossil evidence that Marsupialia (crown Metatheria) and Placentalia existed in the Mesozoic. Current fossil records from Cenozoic localities indicate that the oldest species included in the placental orders appeared at the beginning of the Paleocene (ca. 60–50 Ma). This strongly supports the explosive divergence model, which claims that crown placentals evolved immediately after the K/Pg boundary. However, this hypothesis is criticized primarily because the interval of diversification after the K/Pg boundary is too short in terms of molecular evolution of mammals. A plausible model that agrees with both paleontological and molecular phylogenetic studies explains that major crown clades of placentals (e.g., Xenarthra and Laurasiatheria) originated in the Late Cretaceous and then ordinal groups dispersed in the early Paleocene.
Monotremes are egg-laying mammals and include the modern platypus and the short- and long-beaked echidnas. The monotremes occupy a unique place in mammalian brain evolution and diverged in evolutionary history from all other mammals as much as 115 million years, but they should not be seen as evolutionary relics, nor as models of the archaic mammalian brain. The nervous systems of extant monotremes exhibit specializations such as electroreception that are just as remarkable as those found among the eutherians, and the monotreme brain is as far removed from the ancestral mammal brain as any other modern mammal.
To superficial inspection, the mammalian cerebellum appears to be a stereotypical structure that varies little in morphology across mammals. In the present study, the volumes of components of the corpus cerebelli, foliation of the cerebellar cortex and the volumes of the pontine and deep cerebellar nuclei have been measured and compared in three species of monotreme, 90 species of marsupial and 57 species of eutherian mammal. In all three mammalian groups, the volume of the corpus cerebelli scales isometrically with brain volume, and pontine nuclear volume also scales isometrically with cerebellar volume. The ratio of hemisphere to vermal cerebellar cortex is comparable in all mammals at small cerebellar volume, but elaboration of cerebellar hemispheres is largely confined to large cerebella of eutherian mammals. At small cerebellar volumes, diprotodontid metatherians have proportionally large cerebellar hemispheres compared to non-diprotodontid metatherians, and metatherian cerebella in general have a high volume of central white matter for a given cerebellar cortex volume compared to eutherians. The degree of foliation of the cerebellum scales similarly in therian mammals, but is relatively low in the monotremes for the volume of their corpus cerebelli. Among metatherians, cerebellar foliation is stronger among diprotodontid as compared to non-diprotodontids. Although the cerebellum has a similar structure in all mammals, there are subtle differences in structure between different mammal groups with possible functional implications.
The platypus (Ornithorhynchus anatinus) is one of the world's most evolutionarily distinct mammals, one of five extant species of egg-laying mammals, and the only living species within the family Ornithorhynchidae. Modern platypuses are endemic to eastern mainland Australia, Tasmania, and adjacent King Island, with a small introduced population on Kangaroo Island, South Australia, and are widely distributed in permanent river systems from tropical to alpine environments. Accumulating knowledge and technological advancements have provided insights into many aspects of its evolutionary history and biology but have also raised concern about significant knowledge gaps surrounding distribution, population sizes, and trends. The platypus' distribution coincides with many of Australia's major threatening processes, including highly regulated and disrupted rivers, intensive habitat destruction, and fragmentation, and they were extensively hunted for their fur until the early 20th century. Emerging evidence of local population declines and extinctions identifies that ecological thresholds have been crossed in some populations and, if threats are not addressed, the species will continue to decline. In 2016, the IUCN Red Listing for the platypus was elevated to "Near Threatened," but the platypus remains unlisted on threatened species schedules of any Australian state, apart from South Australia, or nationally. In this synthesis, we review the evolutionary history, genetics, biology, and ecology of this extraordinary mammal and highlight prevailing threats. We also outline future research directions and challenges that need to be met to help conserve the species.
Monotremes are egg-laying mammals and include the modern platypus and the short- and long-beaked echidnas. The monotremes occupy a unique place in mammalian brain evolution and diverged in evolutionary history from all other mammals as much as 115 million years, but they should not be seen as evolutionary relics, nor as models of the archaic mammalian brain. The nervous systems of extant monotremes exhibit specializations such as electroreception that are just as remarkable as those found among the eutherians, and the monotreme brain is as far removed from the ancestral mammal brain as any other modern mammal.
The patella is a sesamoid bone located in the major extensor tendon of the knee joint, in the hindlimb of many tetrapods. Although numerous aspects of knee morphology are ancient and conserved among most tetrapods, the evolutionary occurrence of the patella is highly variable. Among extant (crown clade) groups it is found in most birds, most lizards, the monotreme mammals and almost all placental mammals, but it is absent in most marsupial mammals as well as many reptiles. Here we integrate data from the literature and first-hand studies of fossil and recent skeletal remains to reconstruct the evolution of the mammalian patella. We infer that patellae most likely evolved between four to six times in crown group Mammalia: in monotremes, in the extinct multituberculates, in one or more stem-mammal genera outside of therian or eutherian mammals, and up to three times in therian mammals. Furthermore, a patella was lost several times in mammals, not including those with absent hindlimbs: once or more in marsupials (with some re-acquisition), and at least once in bats. Our inferences about patellar evolution in mammals are reciprocally informed by the existence of several human genetic conditions in which the patella is either absent or severely reduced. Clearly, development of the patella is under close genomic control, although its responsiveness to its mechanical environment is also important (and perhaps variable among taxa). Where a patella is present it plays an important role in hindlimb function; especially in resisting gravity by providing an enhanced lever system for the knee joint. Yet the evolutionary origins, persistence and modifications of a patella in diverse groups with widely varying habits and habitats -- from digging to running to aquatic, small or large body sizes, bipeds or quadrupeds -- remain complex and perplexing, impeding a conclusive synthesis of form, function, development and genetics across mammalian evolution. This meta-analysis takes an initial step toward such a synthesis by collating available data and elucidating areas of promising future inquiry.
The patella is a sesamoid bone located in the major extensor tendon of the knee joint, in the hindlimb of many tetrapods. Although numerous aspects of knee morphology are ancient and conserved among most tetrapods, the evolutionary occurrence of the patella is highly variable. Among extant (crown clade) groups it is found in most birds, most lizards, the monotreme mammals and almost all placental mammals, but it is absent in most marsupial mammals as well as many reptiles. Here we integrate data from the literature and first-hand studies of fossil and recent skeletal remains to reconstruct the evolution of the mammalian patella. We infer that patellae most likely evolved between four to six times in crown group Mammalia: in monotremes, in the extinct multituberculates, in one or more stem-mammal genera outside of therian or eutherian mammals, and up to three times in therian mammals. Furthermore, a patella was lost several times in mammals, not including those with absent hindlimbs: once or more in marsupials (with some re-acquisition), and at least once in bats. Our inferences about patellar evolution in mammals are reciprocally informed by the existence of several human genetic conditions in which the patella is either absent or severely reduced. Clearly, development of the patella is under close genomic control, although its responsiveness to its mechanical environment is also important (and perhaps variable among taxa). Where a patella is present it plays an important role in hindlimb function; especially in resisting gravity by providing an enhanced lever system for the knee joint. Yet the evolutionary origins, persistence and modifications of a patella in diverse groups with widely varying habits and habitats -- from digging to running to aquatic, small or large body sizes, bipeds or quadrupeds -- remain complex and perplexing, impeding a conclusive synthesis of form, function, development and genetics across mammalian evolution. This meta-analysis takes an initial step toward such a synthesis by collating available data and elucidating areas of promising future inquiry.
Hornworts are the least species-rich bryophyte group, with around 200–250 species worldwide. Despite their low species numbers, hornworts represent a key group for understanding the evolution of plant form because the best–sampled current phylogenies place them as sister to the tracheophytes. Despite their low taxonomic diversity, the group has not been monographed worldwide. There are few well-documented hornwort floras for temperate or tropical areas. Moreover, no species level phylogenies or population studies are available for hornworts. Here we aim at filling some important gaps in hornwort biology and biodiversity. We provide estimates of hornwort species richness worldwide, identifying centers of diversity. We also present two examples of the impact of recent work in elucidating the composition and circumscription of the genera Megaceros and Nothoceros. Important areas for further research are highlighted, particularly at taxonomic, ultrastructural, phylogenetic and genomic levels.
The first South American monotreme is described from early Paleocene (Tiupampian) sediments in Patagonia, Argentina. Monotrematum sudamericanum n. gen. & n. sp., represented
by a single upper second molar, ís the first monotreme known from outside the Australian regíon and the first early Terliary monotreme known. It represents a temporal position midway between the early Cretaceous Steropodon galmani and the Oligo-Miocene species of Obdurodon. It corroborates the geological distinction of the Patagonian Terrane, which shares unique aspects of its earliest Cainozoic biota with at least the Australian part of eastern Gondwana. It also demonstrates, in its Obdurodon-like morphology, a remarkable conservatism of mammalian molar morphology spanning at least 110 million years. Overall, M. sudamericanum appeal to be more plesiomorphic than the modem platypus and the species of
Obdurodon. Its relationships to S. galníani are difficult to determinate because S. galmani is only known from a lower jaw fragment with M1-3. It is regarded to be one of three basic platypus lineages within what may be, because of the uncertain relationshjps of tachyglossids to
other monotremes, a paraphyletic Ornithorhynchidae.
We describe an additional fragmentary upper molar and the first lower molar known of Monotrematum sudamericanum, the oldest Cenozoic (Paleocene) monotreme. Comparisons suggest that the monotreme evolution passed through a stage in which their molars were "pseudo-triangulate", without a true trigonid, and that the monotreme pseudo-triangulate pattern did not arise through rotation of the primary molar cusps. Monotreme lower molars lack a talonid, and consequently there is no basin with facets produced by the wearing action of a "protocone"; a cristid obliqua connecting the "talonid" to the "trigonid" is also absent. We hypothesize that acquisition of the molar pattern seen in Steropodon galmani (Early Cretaceous, Albian) followed a process similar to that already postulated for docodonts (Docodon in Laurasia, Reigitherium in the South American sector of Gondwana) and, probably, in the gondwanathere Ferugliotherium.
The Middle Jurassic mammal Shuotherium has lower molars that possess a trigonid and talonid, but are unique in having the talonid situated in front of the trigonid, rather than behind it, as in molars of usual tribosphenic pattern. Shuotherium dongi Chow and Rich, 1982 was based on a dentary bearing seven teeth, originally interpreted as three premolars and four molars. Based on comparison with other groups of early mammals, we reinterpret the premolar-molar boundary in the holotype of S. dongi, and propose a dental formula of four (or more) premolars and three molars. The ultimate lower premolar (previously identified as the first molar) has a completely developed trigonid and no talonid or pseudo-talonid. We hypothesize that the mesial cingulid on molars of Australosphenida is a highly plausible structural antecedent to the pseudo-talonid of Shuotherium. This and other shared, derived features support a relationship of Shuotherium and Australosphenida as sister-taxa. We hypothesize that the common ancestor of Shuotherium + Australosphenida had a global distribution no younger than early Middle Jurassic, and that the respective clades diverged prior to full separation of Gondwanan and Laurasian landmasses.
In this chapter, we (1) describe and illustrate the anatomy of a complete skull, posterior half of a dentary, and cheektooth dentition of a Miocene ornithorhynchid, Obdurodon dicksoni from Riversleigh, Queensland, Australia; (2) use this new information to reevaluate understanding of the anatomy of the living Ornithorhynchus anatinus; (3) revise previous understanding about the monotreme dentition; and (4) reconsider monotreme relationships. The skull differs from that of Or. anatinus in many features but demonstrates that by the Miocene much of the pattern evident in Or. anatinus had already been attained. However, in its more primitive state, the Miocene taxon reveals details of morphology unclear in the living taxon such as the undoubted presence of an enormous septomaxilla at the front of the skull. Contrary to recent suggestions, there is no evidence of postdentary bones in the mandible. On balance, Obdurodon could have been ancestral to Ornithorhynchus. The dentition of Ob. dicksoni is more plesiomorphic than that of Or. anatinus, but the tooth formula agrees in general with the ontogenetic pattern established for the living Platypus. Molar morphology is highly autapomorphic and mimics, with half as many teeth, the serial pattern of four tribosphenid molars. The evidence regarding monotreme relationships is reviewed. Although it is contradictory, on balance it does not support a close relationship between monotremes and any group of tribosphenid mammals. On the one hand, although the contention of Kielan-Jaworowska et al. (1987) that monotremes are descendants of pre-tribosphenid eupantotheres such as peramurids (or vincelestids as discussed here) is possible, there are as many similarities to molars of South American mesungulatid dryolestoids (Archer et al., 1979). Although similarities to these particular late Cretaceous dryolestoids are probably convergent (aspects of the mesungulatid pattern probably being secondarily monotreme-like), the dentition of the early Cretaceous monotreme S. galmani is at least superficially annectant between that of dryolestoids and Oligo-Miocene ornithorhynchids of the genus Obdurodon. As suggested by Bonaparte (1990), monotremes could be a specialized part of an endemic southern eupantothere if not dryolestoid radiation. The evidence, not wholly negative, thus tends to emphasize the sharp separation from all other mammals seen throughout the whole organization of Ornithorhynchus. For what it is worth, it tends to remove the group from any central position in therian phylogeny, to emphasize the rather widespread opinion that Ornithorhynchus is not merely a more primitive therian, but something quite distinct (Simpson 1929, p. 14).
Archer. M. et a\..1999. The evolutionary history and diversity of Australian mammals. Australian Mammalogy 2l: 1-45. Palaeodiversity and relationships of all groups of Australian mammals are reviewed. The fossil record spanning this time is of variable quality. 'Dark Ages'about which nothing is known in terms of Australian mammal evolution include the late Triassic to late Jurassic, late Cretaceous to late Paleocene and middle Eocene to middle Oligocene. Very little is known about the early Cretaceous and late Miocene. The late Oligocene to middle Miocene record documents the highest levels of biodiversity known for the continent, comparabie to that which characterises the lowland rainforests of Borneo and Brazil. Order Monotremata spans at least the last 110 million years and includes four families. The enigmatic Ausktribosphenos from I 15 million-year-old sediments in Victoria may ..piesent an archaic monotreme, specialised peramurid or previously undocumented order of mammals but is unlikely to represent a placental as suggested in the initial description. Order Microbiotheria is represented in the early Eocene (-55 mya) by two genera similar in morphology to early Eocene taxa from Argentina. Order Peramelemorphia spans the early Eocine to Holocene and includes at least five families. Order Dasyuromorphia spans at least the late Oligocene to Holocene and includes at least three families. Other dasyuromorphian-like marsupials are indeterminate in terms of family-level affinities. Order Notoryctemorphia spans the early Miocene to Holocene rvith one family. Order Yalkaparidontia spans the late Oligocene to middle Miocene with one genus. Order Diprotodontia spans the late Oligocene to Holocene, represented throughout by three *ujot groups: Phalangerida (eight families), Vombatomorphia (seven families) and Macropodoidea (at least three families). A possible placental condylarth (Tingamarua) has been iecorded from the early Eocene. An archaeonycteridid bat (Australonycteris) is known from the early Eocene. Among bats, the late Oligocene to middle Miocene is dominated by rhinolophoids, many of which have European, Asian and African affinities. Mystacinids, megadermatids, hipposiderids and molossids are rvell-represented in the Oligocene to Miocene deposits. Vespertilionids are uncommon in the Oligocene to Miocene but become more diverse in the Pliocene to Holocene. Emballonurids and rhinolophids appear for the first time in the Plio-Pleistocene. Pteropodids are unknown prior to the Holocene. Murids span the early Pliocene to Holocene. In the oldest assemblage at Riversleigh. one undescribed lineage resembles archaic forms otherwise only known from the fossil records of Africa and Eurasia. tschool of Biotogicat Science, (tniversity ofNew South llales, Sydney 2052; 2Centre for Research into the Evolution of Australia's Terrestrial Ecosystems, Australian Museum, 6-8 College St, Sydney, NSII 2000; tschool of nuatural Resource sciences, .oueensland
The morphology of the single preserved molar of the holotype of the Australian Early Creta-ceous (Aptian) mammal Teinolophos trusleri shows that it is a monotreme and probably a steropodontid, rather than a 'eupantothere' as originally proposed. The structure of the rear of the jaw of T. trusleri supports the molecular evidence that previously formed the sole basis for recognising the Steropodontidae as a distinct family. When the holotype of Teinolophos trusleri was first described from the Early Cretaceous (Aptian) Strzelecki Group of southern Victoria, Australia (Rich et al. 1999), it was regarded as a member of the Order Eupantotheria Kermack & Mussett, 1958 (= Legion Cladotheria McKenna, 1975 -Infralegion Tribosphenida McKenna, 1975) of uncertain family. This interpretation was based in large part on the inferred structure of the penultimate lower molar, the only tooth preserved on the se-verely crushed holotype. The crown of that tooth was largely obscured by a hard matrix. As a conse-quence of that, a critical misidentification of the cusp in the posterolingual region of the tooth as the metaconid rather than the hypoconulid was made. It was this erroneous interpretation and the conse-quent corollaries that the trigonid was anteroposteriorly expanded and the talonid unbasined that led Rich et al. (1999) to intepret the specimen as a 'eupantothere'. In September 1999, Mr. Charles Schaff of Harvard University successfully cleared the obscuring matrix from crown of the tooth (Fig. 1). Upon his doing so, it became immediately obvious that this tooth, although much smaller, bore a remarkable resemblance to the m2'in the somewhat younger Early Cretaceous (Albian) monotreme Steropodon galmani Archer, Flannery, Ritchie, & Molnar 1985 from Lightning Ridge, New South Wales, Australia. There is also a significant resemblance to two species of the Cainozoic ornithorhynchid monotreme Obdurodon: Obdurodon insignis Wood-burne & Tedford, 1975 from South Australia and Obdurodon dicksoni Archer, Jenkins, Hand, Murray, & Godthelp, 1992 from Queensland. To date, no specimen has been described or figured of the lower dentition of the Paleocene Argentine ornithorhynchid Monotrematum sudamericanum Pascual, Archer, Jaureguizar, Prado, Godthelp, & Hand, 1992. Abbreviations.
Field work recently completed in the Lake Eyre Basin, South Australia, has resulted in the development of a land mammal (marsupial) biostratigraphy of the Etadunna Formation. Whereas traditional interpretations of the age of this sequence suggest it is about 15 m.y. old, new information indicates that the Etadunna likely is 24–26 m.y. old. In either case, it appears possible to document a four-fold fossil mammal zonation of this rock unit at lakes Palankarinna, Kanunka, Pitikanta, and Ngapakaldi, in a composite section of strata that spans at least 30 m. Magnetostratigraphic data for the same succession are generally consistent with the correlation of the Etadunna Formation sites at Lake Palankarinna with of those at lakes Kanunka, Pitikanta, and Ngapakaldi to the north, as based on paleontological information. The magnetic polarity zonation of these Etadunna Formation strata is consistent with a correlation to the world magnetic polarity time scale at about 24–26 m.y. This is the first fine-scale zonation based on fossil land mammals for strata of late Oligocene age in Australia. The combined mammal and magnetic data show promise of developing the Etadunna Formation as a reference standard for land mammal correlations within Australia and the relation of these to land mammal zonations beyond the Australian continent.
This paper reviews present understanding of the evolution of the ornithorhynchids. An ancient family within the mammalian order Monotremata. Ornithorhynchidae today is represented only by the living platypus Ornithorhynchus analinus but has a history that probably predates the Tertiary and a past distribution that spanned at least three continents. Analysis of the palaeontological record has focused on the distinctive ornithorhynchid dentition, which in species of Monotrematum and Obdurodon was probably functional throughout life. The retention of functional dentition in concert with the great age of Ornithorhynchidae gives the platypus family a much larger role in analysis of the biogeographic and phylogenetic history of the monotremes than is given to the more specialised, edentate tachyglossids, or echidnas. A complete ornithorhynchid skull, recovered from Miocene deposits at Riversleigh in north-western Queensland, has allowed comparison between the cranium of a generally more plesiomorphic platypus and that of the living Or. anatinus, a study that answers some of the morphological questions posed by this enigmatic group while raising others. This review concludes with a discussion of the biogeography and palaeoecology of the family.
The comparative description of multituberculate crania has provided a solid morphological data base for the character analysis, which reveals that a majority of multituberculate cranial features are merely mammalian plesiomorphies. A few specializations do exist and appear to be either peculiar to all multituberculates or evolved within the group. These include inflated vestibular apparatus in taeniolabidoids, reduced post-orbital process and jugal, large premaxilla, nasal and jugular foramen, and exclusion of palatine from orbit, Previously proposed synapomorphies to relate multituberculates as a sister taxon to either monotremes or Recent therians may simply be homoplasies, that is, independent acquisition of three-boned middle ear and independent loss of septomaxilla. Therefore, multituberculates appear to have been a separate lineage in early mammalian radiation either prior to emergence of the latest common ancestor of Recent mammals or before any other mammals even evolved.
In all living groups of mammals, prolonged protection of the developing young is a characteristic strategy of reproduction. Lactation, however, is the only uniquely mammalian characteristic, and ail three groups have characteristic adaptations for achieving the transfer of energy from mother to young first via the uterus and placenta, and subsequently via the milk.
The distribution of thirty-eight basicranial characters is considered among monotremes, marsupials, placentals, and the following extinct taxa—Tritheledontidae, Tritylodontidae, Sinoconodon, Morganucodontidae, Haldanodon, Triconodontidae, Multituberculata, and Vincelestes.
The anatomies of four well-preserved, fossilised tachyglossid skulls from Naracoorte, South Australia are described and compared with that of a fossilised skull from north-western Tasmania, with those of 13 extant Long-beaked Echidnas, Zaglossus bruijnii, from New Guinea, and with those of II Short-beaked Echidnas, Tachyglossus aculeatus. The difference in structure and proportions of the rostrums, palates and craniums of the fossil forms from those of Z. bruijnii and T. aculeatus are so great that it is concluded that the former should be placed in a new genus; the name Megalibgwilia is proposed. From the conformation of the rostrum and palate it is suggested that the principal prey of Megalibgwilia was large insects such as scarab and moth larvae, not oligochaete worms as is the case with Z. bruijnii.
Recent work in Late Cretaceous beds of the Los Alamitos Formation, Campanian sensu lato, of northeastern Patagonia led to the discovery of an assemblage of 14 species of non-tribosphenic mammals. Eight new genera and species are here described. Five genera are referred to Symmetrodonta, two to Dryolestoidea, and one to ?Paratheria. Los Alamitos fauna demonstrates strong compositional differences from other Late Cretaceous assemblages of mammals. A long period of isolation between Gondwana and Laurasia is most likely responsible for such distinct faunal differences. The dryolestoid and symmetrodont adaptive radiation recorded at the Los Alamitos Formation is interpreted as a possible result of the absence of tribosphenic mammals. It is suggested that the Australian monotremes may be a local product of the dryolestoid radiation. Gondwanatheria may be ancestral to the Xenarthra. The Cretaceous mammals of South America and Australia suggest long-term isolation of Gondwana and Laurasia, perhaps from the Late Jurassic until the Late Cretaceous. Such separation may have resulted in the dominance of tribosphenic mammals in Laurasia, and derived non-tribosphenic mammals in South America (and possibly in Gondwana in general). -from Author
The comparative description of multituberculate crania has provided a solid morphological data base for the character analysis, which reveals that a majority of multituberculate cranial features are merely mammalian plesiomorphies. A few specializations do exist and appear to be either peculiar to all multituberculates or evolved within the group. These include inflated vestibular apparatus in taeniolabidoids, reduced postorbital process and jugal, large premaxilla, nasal and jugular foramen, and exclusion of palatine from orbit. Previously proposed synapomorphies to relate multituberculates as a sister taxon to either monotremes or Recent therians may simply be homoplasies, that is, independent acquisition of three-boned middle ear and independent loss of septomaxilla. Therefore, multituberculates appear to have been a separate lineage in early mammalian radiation either prior to emergence of the latest common ancestor of Recent mammals or before any other mammals even evolved. “The result of this increased knowledge is to strengthen the growing conviction toward which all the recent accretions of data on the multituberculates have contributed, that these animals were not the ancestors of or closely related to monotremes, marsupials, or placentals, that any phyletic connection between them and the later three groups must have been far back toward the origin of the Mammalia, possibly even before that artificially delimited event, and that taxonomically this means that the Multituberculata form a separate subclass, Allotheria.” (Simpson, 1937, p. 761)
In all living groups of mammals, prolonged protection of the developing young is a characteristic strategy of reproduction. Lactation, however, is the only uniquely mammalian characteristic, and all three groups have characteristic adaptations for achieving the transfer of energy from mother to young first via the uterus and placenta, and subsequently via the milk. In mammals the simple oviduct of lower vertebrates has differentiated into the uterus and vagina. There is a tendency toward fusion of the posterior end of the paired oviducts. The vagina remains paired in monotremes and marsupials, but is a single fused tube in all eutherians; the uterus may be paired, partly fused, or completely fused as in humans. This fusion occurs independently in unrelated mammalian families as a correlate of reduction in litter size. The relative position of the ureters and the genital ducts is the character that most clearly separates the major groups of living mammals. The ureters of monotremes open into the urogenital sinus opposite the urethral openings of the bladder. In therians, the ureters migrate from a dorsal position adjacent to the Wolffian duct to a direct connection to the bladder, but the ureters pass medially between the genital duct in marsupials, not laterally as in eutherians. The conclusion must be that the original selection for the migration of the urinary ducts to the bladder in therian mammals was for an excretory and not a reproductive function, though the subsequent consequences for the development of the reproductive tract were profound. This is a true dichotomy, and allows for no intermediate stage. When the reproductive processes of the three major groups of mammals are compared, many features emerge as synapomorphies. Examples are the Graafian follicles, functional corpora lutea, bilaminar blastocysts, uterine secretion, yolk sac placentae, mammary glands, and lactation. Although monotremes retain some plesiomorphic characters (e.g, egg laying), which show an early divergence from the stock leading to therians, comparisons between marsupials and eutherians suggest a dichotomy in development from a common ancestral group not a derivation of one from the other. Most of the apomorphic therian characters of marsupial reproduction are associated with the greater emphasis on lactation rather than gestation. There appears to be a major dichotomy in the control of sexual differentiation in therian mammals. In eutherians, the sexual development of the male and female reproductive tracts has been assumed to be solely the result of the presence or absence of hormones secreted by the fetal testis, but in marsupials, several sexually dimorphic characters (the scrotum, mammary anlagen, gubernaculum, and processus vaginalis) are under direct genetic control. It now appears that certain sexual dimorphisms are also under direct genetic control in eutherians. Tyndale-Biscoe and Renfree (1987) suggested that the basic mode of mammalian reproduction evolved simultaneously with the origin of mammals in the Triassic, but remained almost unchanged until the late Mesozoic because it was the most appropriate mode for small nocturnal insectivorous mammals. Tyndale-Biscoe and Renfree (1987) have further suggested that the present-day differences appear to have evolved during the adaptive radiation of the therian mammals in response to the metabolic requirement of increasing body size and the constraints imposed as these mammals moved into new ecological niches. Recent comparative studies detailed here on the anatomy and physiology of marsupials support these ideas.
The distribution of thirty-eight basicranial characters is considered among monotremes, marsupials, placentals, and the following extinct taxa—Tritheledontidae, Tritylodontidae, Sinoconodon, Morganucodontidae, Haldanodon, Triconodontidae, Multituberculata, and Vincelestes. PAUP analysis of the ensuing data matrix supports the following conclusions: 1. Marsupialia and Placentalia form a clade supported by an anterior lamina of the petrosal that is greatly reduced or absent, a cavum epiptericum floored primarily by the alisphenoid, major basicranial drainage via the postglenoid foramen, and a squamosal contributing broadly to the cranial wall.
Periodically it is worthwhile to assess our knowledge and understanding of mammalian phylogeny and one of its expressions, classification. This short paper is yet another attempt to do so, taking into account the results of recently published paleontological research and drawing heavily on work in progress by many researchers in many fields and in various parts of the world. Concepts of mammalian phylogeny and classification have changed markedly during the last few years. A good many of the ideas expressed here are frankly speculative, but they are presented anyway in order to determine how well they will stand scrutiny, especially by nonpaleontologists. A few years ago I prepared a paper with a similar aim (McKenna, 1969), but that paper is now outdated. In the present offering I attempt to update certain aspects of my previous review by taking into account research published since 1969, as well as work being incorporated into a new classification of the Mammalia now being prepared which wall deal with all taxonomic levels down to the subgeneric level in essentially the same style as Simpson’s (1945) classification.
On the basis of a unique specialization of the braincase the four nontherian orders of mammals—the living Monotremata and the extinct Tricono-donta, Docodonta, and Multituberculata—are united into a single subclass, Prototheria. The Triconodonta and Docodonta are closely related and are grouped together in the infraclass Eotheria. The Monotremata and Multituberculata are only remotely allied to all other mammals and are each placed in a separate infraclass—Ornithodelphia for the monotremes and Allotheria for the Multituberculates. A classification of prototherian mammals to family is presented.
The foramen for the mandibular division of the trigeminal nerve opens between the periotic and alisphenoid bones in all known therapsid reptiles (including ictidosaurs and tritylodonts) but perforates the alisphenoid bone in some Late Cretaceous and most Cenozoic mammals. Contrary statements in the literature notwithstanding, the position of this foramen in young monotremes is the same as in therapsid reptiles; in adult monotremes, the bones of the braincase are fused together, obscuring this relationship. In morganucodonts, triconodonts, and multituberculates, the position of the foramen with respect to these bones is ambiguous, because the braincase is evidently fused in the known specimens. The skulls of symmetrodonts, haramyids, and docodonts are unknown. The term "quasi-mammal" is proposed as an informal designation for the above near-mammalian but non-therian groups (ictidosaurs, monotremes, etc.) which are of uncertain relationships but may be most fruitfully studied as therapsid reptiles. A definition of the Class Mammalia is proposed which would exclude quasi-mammals.
The amino acid sequences of the α-lactalbumins of the echidna, Tachyglossus aculeatus, and the platypus, Ornithorhynchus anatinus, were compared with each other and with those of 13 eutherian and 3 marsupial species. Phylogenetic parsimony analyses, in which selected mammalian lysozymes were used as outgroups, yielded trees whose consensus indicated that the two monotremes are sister taxa to marsupials and eutherians and that the latter two clades are each other's closest relatives. The data do not support the notion of a Marsupionta (monotreme–marsupial) clade. Pairwise comparison between the α-lactalbumins yielded maximum-likelihood distances from which divergence dates were estimated on the basis of three calibration points. The distance data support the view that the echidna and platypus lineages diverged from their last common ancestor at least 50 to 57 Ma (million years ago) and that monotremes diverged from marsupials and eutherian mammals about 163 to 186 Ma.
In Rowe (1988), 158 characters of the skull and postcranial skeleton distributed among Placentalia, Marsupialia, Monotremata, Multituberculata, Morganucodontidae, Tritylodontidae, and Exaeretodon were analyzed with PAUP. Mammalia, defined by Rowe as comprising the most recent common ancestor of living monotremes, marsupials, and placentals, was distinguished from its nearest extinct relatives by 37 osteological synapomorphies, including 24 characters of the cranium and dentition. Within Mammalia, Multituberculata was identified as the sister taxon of Marsupialia plus Placentalia.The 91 craniodental characters employed by Rowe (1988) are reevaluated here and placed in one of five categories: characters needing no alteration (11); characters with a derived state occurring in an outgroup not considered by Rowe (8); characters for which the distribution given by Rowe is altered (16); characters for which the description given by Rowe is modified (30); and characters that are excluded from further analysis (26). The distributions of the characters in the first four categories are scored among the seven taxa considered by Rowe (1988) plus Cynognathus, Diademodon, Probainognathus, Tritheledontidae, Sinoconodon, Dinnetherium, Kuehneotherium, Haramiyidae, and Vincelestes. The ensuing taxon/character matrix for all (or subsets of) these 16 taxa are analyzed with several PAUP runs. The major difference between the most parsimonious trees produced here and by Rowe is the reversed position of Monotremata and Multituberculata—i.e., in this report Multituberculata is the first outgroup to Mammalia sensu Rowe. Moreover, the boundary between Mammalia and it nearest extinct relatives is not very distinct, because only five unequivocal craniodental synapomorphies of Mammalia are identified.
A systematic revision of monotremes of the genus Zaglossus has revealed unexpected morphological diversity. Statistical and non-metric analysis indicate that three species can be recognised: Zaglossus bruijnii (Peters and Doria, 1876), which inhabits the Vogelkop, Fak Fak and possibly the Charles Louis Mountains regions; Zaglossus bartoni Thomas, 1907a, which occurs on the central cordillera between the Paniai Lakes and the Nanneau Range, as well as the Huon Peninsula; and Zaglossus attenboroughi n. sp. from the Cyclops Mountains. Four distinct subspecies of Z. bartoni can be discerned. The three subspecies inhabiting the central cordillera increase in size from east to west: Z. b. smeenki n. ssp. of the Nanneau Range being the smallest, the nominotypical form intermediate in size, and Z. b. diamondi n. sep. the largest. Zaglossus b. clunius inhabits the Huon Peninsula.
The record of the Antarctic marine fauna during the Paleogene indicates the occurrence of taxa in high latitude regions (>60°) before these same taxa are known in midto low latitudes. It has been hypothesized that high latitude regions serve both as 'holding tanks' for taxa and as regions in which novel adaptations leading to new lineages within a taxon can arise. These features of high latitude regions appear to have had a major impact on the origin of the Australian marsupial fauna. The australidelphian marsupial clade (all Australian marsupials plus South American microbiotheriids) and the ameridelphian marsupial clade (all South American marsupials except microbiotheriids) diverged in the Late Cretaceous. The South American marsupial radiation occurred in mid- to low latitude regions during the Late Cretaceous to early Paleocene. The Australian marsupial radiation probably did not occur until the medial or late Eocene. If accurate, this represents a time differential of 20 to 25 Ma between the two marsupial radiations. The heterochroneity of the marsupial radiations results from the fact that during the Late Cretaceous to Eocene, Australia resided in a high latitude region, the cool temperate Weddellian Biogeographical Province. The radiation of Australian marsupials only reaches a level of taxonomic diversity comparable to that in South America after the continent drifted northward into lower latitudes and habitat diversity increased. This is deduced from changes in floral diversity and the projected timing of the diprotodontian divergences based on DNA hybridization data.
This paper is a study of the structure of the braincase in two closely related Mesozoic mammals: Triconodon mordax and Trioracodon ferox. They belong to the order Triconodonta, subfamily Triconodontinae, and are from the English Upper Jurassic (Purbeck). One specimen of each species was available showing cranial structure, both from the collection in the British Museum. By chemical methods, both petrosals and the sphenoid of the specimen of Triconodon and both petrosals of the specimen of Trioracodon were prepared. The material shows that the Triconodonta had a braincase of an essentially reptilian pattern. There was a persistent cavum epiptericum lying outside the ossified lateral wall (formed by the petrosal) of the braincase. The alisphenoid, forming the lateral boundary of the cavum epiptericum, formed no part of the braincase wall in this region. This was also true of the Rhaetic Morganucodon, and may have been true of all pre-Cretaceous mammals. In basic construction the braincase of these mammals differs from that of an advanced therapsid only in the narrower cavum epiptericum in the former. This difference is due to the relatively larger size of the brain in the mammal. To convert a braincase constructed in this way into that of a modern mammal either the alisphenoid would have to be lost-leading to the condition found in the monotremes-or the lateral wall of the neurocranum would have to fail to ossify-thus incorporating the cavum epiptericum in the cranial cavity in the manner typical of marsupials and placentals. Although on these grounds alone the monotreme stock need not have separated from that which gave rise to the marsupials and placentals until early in the Cretaceous, other considerations suggest that the last common ancestor lived in Triassic times at the reptilian grade of organization. There seems, however, less reason than formerly to consider Morganucodon an ancestral monotreme. Finally, a reconsideration of all the evidence shows that there was no acceleration of evolutionary rates at the time the Mammalia came into existence.