Imaginative AI reconstruction of a Protemnodon.
Illustration by Superinnovators x AI
Science works because scientists, unlike religious fundamentalists, don't have fixed dogmas and doctrines they must adhere to and so are free to re-examine the evidence, reassess their conclusions and change their minds.
Unlike creationists, scientists are free to question, reassess and rethink without fear of a terrible fate awaiting them for having the temerity to question the cult dogma, or the social stigma, ostracism and in some cases threats of physical violence, that would be heaped upon a fundamentalist who questioned the basic tenets of the cult.
So, scientists are free from the sophophobia that charcterises creationism and which the cult leaders go to great lengths to inflict on their followers, and, unlike with creationism, the standing of a scientists who changes his or her mind with good reason goes up, while the social standing in creationist circles of a creationists who shows intellectual integrity and changes his or her mind will actually go down, in the prevailing anti-intellectual culture of the creationist cult!
What information do you have on the extinct marsupials, Protemnodon, and how modern kangaroos are related to them? Protemnodon is an extinct genus of marsupials that belonged to the family Macropodidae, which also includes modern kangaroos and wallabies. These prehistoric creatures roamed Australia during the Pleistocene epoch, around 2 million to 10,000 years ago. Here are some key points about Protemnodon and their relation to modern kangaroos:An example of scientists changing their collective minds was published recently in the Journal of Mammalian Evolution, in a prize-winning paper by Billie Jones & Professor Christine M. Janis of Bristol University, Bristol, UK. And it's more bad news for creationists.
Characteristics of Protemnodon
- Size and Build: Protemnodon species varied in size, but many were larger and more robust than contemporary kangaroos. They had powerful limbs adapted for browsing rather than the high-speed hopping seen in modern kangaroos.
- Diet: Unlike modern kangaroos, which are predominantly grazers feeding on grasses, Protemnodon species were primarily browsers. They likely fed on leaves, shrubs, and other vegetation found in the forests and woodlands they inhabited.
- Habitat: Protemnodon lived in a variety of environments across Australia, including forests and open woodlands. Their robust build suggests they were well-adapted to navigating dense vegetation.
Evolutionary Relationships
- Common Ancestry: Protemnodon and modern kangaroos share a common ancestor within the Macropodidae family. The evolutionary split between the ancestors of Protemnodon and those of modern kangaroos occurred millions of years ago.
- Adaptations: Modern kangaroos (genus Macropus) evolved several distinct adaptations that differentiate them from their extinct relatives, including specialized teeth and digestive systems for grazing on tough grasses, as well as the iconic hopping locomotion.
- Extinction: The reasons for the extinction of Protemnodon are not fully understood but may include climate changes, habitat loss, and human activities such as hunting.
Fossil Record and Research
- Fossils: Fossils of Protemnodon have been found in various sites across Australia. These fossils provide valuable insights into the diversity, morphology, and ecological roles of these ancient marsupials.
- Research: Ongoing paleontological research continues to uncover new information about Protemnodon and their relationship to other macropodids. This research helps to build a more comprehensive picture of Australia's prehistoric ecosystems and the evolutionary history of marsupials.
In summary, Protemnodon was an important genus of prehistoric marsupials that shared a common ancestry with modern kangaroos. While they possessed different physical and ecological traits compared to their contemporary relatives, their study provides crucial insights into the evolutionary pathways that led to the diverse array of macropodids seen today.
As well as illustrating the intellectual integrity of science compared to the intellectual bankruptcy of creationism, it concerns the long-extinct giant relatives of kangaroos of Australia, the Protemnodons. These lived in the 2,500,000 years before creationism's mythical 'Creation Week', with its small, flat, dome-covered planet with nothing in it that didn't live in the immediate vicinity of Canaanite Hills, where and when the Bronze Age authors of the myths lived - polar bears, penguins, elephants, kangaroos and koalas, and other people and cultures from distant continents and climates.
In particular the reassessment of the evidence strongly suggests that these giant kangaroos walked on all fours rather than hopping like modern kangaroos and wallabies, as was previously thought. The reason for this new thinking is that the ankle bones of the Protemnodons were too weak to support the stresses of hopping and the forelimbs are adapted for weight-bearing, unlike those of modern kangaroos and wallabies.
The research is the subject of a University of Bristol news release:
Ancient large kangaroo moved mainly on four legs, according to new research
A type of extinct kangaroo that lived during the Pleistocene around two and a half million to ten thousand years ago, known as the ‘giant wallaby’, was a poor hopper, a study by scientists at the University of Bristol have found.
Several large key species of kangaroo, all bigger than modern kangaroos and known as Protemnodon, were previously assumed to have hopped, despite their size. However, findings published today in the Journal of Mammalian Evolution, show that they were mainly quadrupedal and likely used four legs to move around most of the time.
There had been some speculation in a graduate thesis from the University of Uppsala that it might have been more quadrupedal in its habits compared to living kangaroos. This new paper draws on a couple of previous quantitative studies that looked at the anatomy of the humerus (upper arm bone) in a diversity of mammals, and concluded that Protemnodon habitually put more weight on its forelimbs than kangaroos today.
Billie Jones, Lead author
Palaeobiology Group, School of Earth Sciences, University of Bristol, Bristol.
Previous research has shown that the ankle bones of Protemnodon were unsuited to withstand the stresses of hopping.
The team showed that the limb proportions of Protemnodon were quite unlike that of any living kangaroos, especially the short feet, backing up the proposal that it was mainly quadrupedal, rather than a dedicated hopper like living large kangaroos.
This new paper is a quantitative study of limb proportions, plus a more qualitative discussion of some other aspects of the anatomy, in an attempt to confirm the locomotion of this extinct animal.
This provides further evidence that the taxonomic diversity of large kangaroos in the Pleistocene of Australia was matched by a locomotor diversity. Supervisor Professor Christine Janis of Bristol’s School of Earth Sciences had already shown that extinct sthenurines - a separate subfamily of kangaroos - were bipedal striders rather than hoppers. This locomotor diversity suggests a greater variety of habitats in the Australian Pleistocene than previously considered, with the continent not as arid as it is currently.
Billie Jones won both the David Dineley Prize and the Curry Prize for this thesis.A study of the limb bones, and the bone proportions to each other, show that the so-called extinct ‘giant wallaby’, Protemnodon, was likely a poor hopper at best, and probably moved mostly quadrupedally, perhaps bounding on all fours like tree-kangaroos do on the ground.
Professor Christine M. Janis, co-author
Palaeobiology Group, School of Earth Sciences, University of Bristol, Bristol, UK.
Paper:‘Hop, Walk or Bound? Limb Proportions in Kangaroos and the Probable Locomotion of the extinct genus Protemnodon’ by Billie Jones and Christine Marie Janis in Journal of Mammalian Evolution.
Technical details are provided in the scientists open access paper:
AbstractCreationists who try to fool people with the claim that scientists are only ever allowed to publish papers that agree with the consensus will need to ignore the evidence that this paper won the lead author two prizes, even though it disputed the current idea that these extinct relatives of kangaroos hopped like their later relatives.
Kangaroos (Macropodoidea) display a diversity of locomotor modes, from bounding quadrupedally to hopping bipedally; but hopping has a body mass limit, which was exceeded by a number of extinct taxa. In the Pleistocene, a variety of “giant” kangaroos existed, both within the extinct subfamily Sthenurinae and the extant subfamily Macropodinae (both within the family Macropodidae). Sthenurines have been previously considered to have a type of locomotion (bipedal striding) different from extant kangaroos, but the primary locomotor mode of the large species of the extinct “giant” macropodine genus Protemnodon, closely related to extant large kangaroos, has undergone little question and has been assumed to be hopping. Here, the association between limb proportions and locomotor mode across Macropodoidea is assessed by examination of functional limb indices. We show that large (> 100 kg) Protemnodon species are unlike any other known macropodoids; their position in this functional morphospace, along with previously published evidence on humeral morphology, supports a prior hypothesis of a primarily quadrupedal mode of locomotion, likely some sort of bounding.
Introduction
The conventional view of a kangaroo (superfamily Macropodoidea) is of a relatively large animal that locomotes via hopping (also referred to as bipedal saltation or ricochetal locomotion). Indeed, the “poster child” of kangaroos is the Red Kangaroo (Osphranter rufus) or the Eastern Grey Kangaroo (Macropus giganteus): however, members of Macropodoidea encompass a range of sizes and locomotor modes. Today, kangaroos (macropodoids or kangaroos in the broad sense) range from body masses of 500 g (Hypsiprymnodon moschatus, the Musky Rat-Kangaroo) to > 70 kg (O. rufus) (Kear et al. 2008). We consider an extinct “giant” kangaroo to be one of larger body mass than extant large kangaroos (i.e., > 100 kg).
With the exception of H. moschatus, all extant kangaroos use hopping as a fast gait. For slow gaits, kangaroos either employ a quadrupedal bound, or some, mostly larger species (in the genera Macropus, Onychogalea, Osphranter, and Wallabia), employ a “pentapedal walk” where the tail is used as a fifth limb in supporting the body (Dawson et al. 2015). Some species have abandoned hopping almost entirely to become primarily quadrupedal; for example, tree-kangaroos (Dendrolagus spp.) hop intermittently when on the ground but more frequently bound or use a four-footed walk, the latter gait being used most often along tree branches (Windsor and Dagg 1971). Secondary reliance on quadrupedal locomotion has arisen multiple times within Macropodoidea. Potoroids (rat-kangaroos; Potoroidae) use their forelimbs to dig for food, and so can be termed “semi-fossorial”, and some potoroids (species of Potorous and Bettongia) have been observed to climb (Seebeck and Rose 1989). Figure 1 shows a phylogeny of macropodoids including their mode of locomotion.
Today the most efficient kangaroos in terms of energy consumption are the largest species (i.e., greatest body masses) (Osphranter rufus, Macropus giganteus and M. fuliginosus); during hopping locomotion, their oxygen consumption at speeds over 3.9 m/s does not increase with speed, a stark difference to the linear increase in oxygen consumption with speed for similar sized quadrupedal mammals (Baudinette et al. 1992). Nevertheless, even the largest kangaroos, extant or extinct, are small in comparison with quadrupeds of similar ecology (i.e., ungulate placental mammals). Biomechanical modeling has thrown light on the size limits for hopping. Optimum body mass for hopping has been estimated to be ~50 kg, the average body mass for today’s largest kangaroos (Bennett and Taylor 1995). As kangaroos increase in body mass, they experience unusually high skeletal and tendon stresses (McGowan et al. 2008.1); this ultimately limits locomotor ability, with a body mass limit to hopping estimated at 160 kg (Snelling et al. 2017). In the Pleistocene, a variety of “giant” kangaroos existed that attained masses considerably above this limit, reaching up to 230 kg (Helgen et al. 2006) and calling into question their ability to hop.Fig. 1.
Simplified phylogeny of macropodoids, modified from Llamas et al. (2015.1), with the position of the Balbaridae from Den Boer et al. (2019), and the term Macropodia from Westerman et al. (2022). See text for explanations of locomotor categories. Dagger symbol (†) indicates an extinct taxon. Sources for silhouettes: Hypsiprymnodon moschatus, Bettongia lesueur, Setonix brachyurus and Trichosurus vulpecula from phylopic.org (Credits: Carly Monks [B. lesueur], T. Michael Keesey [others], S. brachyurus photo taken by Sean Mack; images available for reuse under the Attribution-ShareAlike 3.0 Unported license https://creativecommons.org/licenses/by-sa/3.0/). All other silhouettes created by BJ using Inkscape v. 1.3.2 (Smith 2020). Osphranter rufus was created from a composite of images in the public domain; Sthenurus stirlingi was modified from Regal in Janis et al. (2014), with permission from Brian Regal; Dendrolagus goodfellowi was created from a photo taken by BJ of an animal in the Bristol Zoological Gardens; Protemnodon anak was created from a photo taken by CMJ of the mounted specimen in the South Australian Museum. The genera grouped together here of Macropus, Osphranter and Notamacropus, previously all included within Macropus, are known as the “Macropus complex” (Celik et al. 2019.1); their interrelationships remain in debate.Figure created in Adobe Illustrator by Science Graphic Design (www.sciencegraphicdesign.com)
Recent studies have found that the diversity of locomotor modes within Macropodoidea was likely far greater in the past than it is in the present day. The extinct sthenurines (Macropodidae: Sthenurinae) demonstrate anatomical evidence for a bipedal striding type of locomotion unlike any extant kangaroo (Janis et al. 2014), a notion supported by trackway data (Camens and Worthy 2019.2). Sthenurine forelimbs were likely not primarily weight-bearing at any gait (Wells and Tedford 1995.1; Janis et al. 2014, 2020.1; Jones et al. 2022.1), and their rigid lumbar region would also make spinal flexion for quadrupedal locomotion difficult (Wells and Tedford 1995.1). Wagstaffe et al. (2022.2) found that the resistance to bending stresses are different in the foot bones of similarly sized sthenurines and macropodines, supporting the hypothesis of different modes of locomotion in the two subfamilies.
Several extinct macropodid taxa are hypothesized to have been at least semi-arboreal if not fully so. These include species in the Balbaridae (Oligocene to Miocene stem macropodoids; Den Boer et al. 2019); Bohra, a Pleistocene stem dendrolagine much larger than extant dendrolagines (tree-kangaroos) (Warburton and Prideaux 2010); and a late-diverging Pleistocene macropodin, Congruus kitcheni, likely related to Protemnodon (see Fig. 1) that was around the size of an extant grey kangaroo (Warburton and Prideaux 2021).
Of particular interest here are species in the genus Protemnodon, a close relative of the Macropus group of taxa in the Macropus species complex (i.e., Macropus, Osphranter and Notamacropus) (Llamas et al. 2015.1). Although the genus originally was comprised of a miscellany of many different extinct and extant macropods, it is now limited to the smaller New Guinea species (Pr. otibandus, Pr. snewini at ~50 kg; Flannery 1994; plus the related Nombe nombe; Kerr and Prideaux 2022.3) and larger Australian species (Pr. roechus at ~160 kg; Pr. anak at ~131 kg; Pr. brehus at ~110 kg; Helgen et al. 2006) (see Kerr et al. 2024 for some additional species). Note that the species Pr. roechus and Pr. brehus have recently been determined to be nomina dubia (Kerr et al. 2024). The individuals of Pr. roechus and Pr. brehus described by Helgen et al. (2006) are included in the new species Pr. mamkurra (Kerr et al. 2024) and Pr. viator (Kerr et al. 2024), respectively. The individual of Pr. viator we consider here was originally classified as Pr. brehus; this is the same individual described in other publications (Janis et al. 2020.1, 2023; Jones et al. 2022.1;Wagstaffe et al. 2022.2; Janis et al. 2023).
The locomotor mode of Protemnodon has remained somewhat a mystery, though in recent years more evidence has begun to come to light (see also Kerr et al. 2024). The largest species of Protemnodon approached the body mass limit to hopping (160 kg). With extremely short feet and long, robust arms, their body plan appears unsuited to hopping; nevertheless, it has long been assumed that the larger species of Protemnodon were consistent hoppers like their Macropus relatives, although the smaller New Guinea species that have short tibiae have been considered as quadrupedal (Kear et al. 2008). It has been suggested that the anatomy of the large species of Protemnodon may also reflect more reliance on quadrupedal locomotion (Den Boer 2018). Janis et al. (2020.1) and Jones et al. (2022.1) found that the proximal and distal humeral morphology of Protemnodon indicates that a significantly greater proportion of the body weight was borne on the forelimbs than in extant hopping macropodids, supporting this hypothesis of committed quadrupedality.
Here we present a study of relative limb proportions within Macropodoidea. Relative limb proportions and limb indices have been widely employed as functional indicators of locomotor mode in extant and extinct mammals, although to date among large mammals only placentals have been considered (e.g., Van Valkenburgh 1987; Shockey et al. 2007; Croft and Anderson 2008.2; Samuels and Van Valkenburgh 2008.3; Meachen-Samuels and Van Valkenburgh 2009; Meachen-Samuels 2012; Samuels et al. 2013; Dunn 2018.1). The use of limb indices (i.e., proportions of one limb, or portion of a limb, relative to another) has relative pros and cons over the use of individual linear measurements (see discussion in Dunn 2018.1). Limb indices are considered to be a correlate of the mechanical advantage of the primary locomotor muscles (Samuels and Van Valkenburgh 2008.3). Limb indices also eliminate the effects of size but not allometry (Chen and Wilson 2015.2). One disadvantage is that the data should be collected from a single individual, at least for any given index, which may be difficult given the fragmentary nature of fossils (see discussion below). If an extinct macropodid employed a mode of locomotion divergent from extant taxa, the relative proportions of its limbs will likely reflect this. Thus, the divergent types of locomotion proposed above for sthenurines and large species of Protemnodon are expected to be apparent in their limb proportions.
This study will enable a better understanding of macropodoid biodiversity and ecomorphology, especially the locomotor diversity of Pleistocene forms. A potential locomotor mode for large species of Protemnodon is presented, given the evidence found here and in previous studies (Den Boer 2018; Janis et al. 2020.1; Jones et al. 2022.1).
It's probably difficult for creationists to understand how scientific disputes are resolved amicably by a dispassionate assessment of the evidence, with none of the resort to threats, intimidation and violence that characterise evidence-free theological disagreements.
They will also need to ignore that fact that the researchers show not the slightest doubt that these and living megapodes share a common ancestor from which they have evolved to suit a changing environment as Australia's climate became more arid and forest gave way to bush, grassland and desert.
What Makes You So Special? From The Big Bang To You
How did you come to be here, now? This books takes you from the Big Bang to the evolution of modern humans and the history of human cultures, showing that science is an adventure of discovery and a source of limitless wonder, giving us richer and more rewarding appreciation of the phenomenal privilege of merely being alive and able to begin to understand it all.
Available in Hardcover, Paperback or ebook for Kindle
Ten Reasons To Lose Faith: And Why You Are Better Off Without It
This book explains why faith is a fallacy and serves no useful purpose other than providing an excuse for pretending to know things that are unknown. It also explains how losing faith liberates former sufferers from fear, delusion and the control of others, freeing them to see the world in a different light, to recognise the injustices that religions cause and to accept people for who they are, not which group they happened to be born in. A society based on atheist, Humanist principles would be a less divided, more inclusive, more peaceful society and one more appreciative of the one opportunity that life gives us to enjoy and wonder at the world we live in.
Available in Hardcover, Paperback or ebook for Kindle
No comments:
Post a Comment
Obscene, threatening or obnoxious messages, preaching, abuse and spam will be removed, as will anything by known Internet trolls and stalkers, by known sock-puppet accounts and anything not connected with the post,
A claim made without evidence can be dismissed without evidence. Remember: your opinion is not an established fact unless corroborated.