The extraordinary osteology and functional morphology of the limbs in Palorchestidae, a family of strange extinct marsupial giants

Richards, Hazel L.; Wells, Rod; Evans, Alistair R.; Fitzgerald, Erich M. G.; Adams, Justin W.

doi:10.1371/journal.pone.0221824

Cited by 22 publications

(31 citation statements)

References 51 publications

(54 reference statements)

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“…In this study, we set out to quantitatively test previous functional interpretations of the bizarre forelimb anatomy of Palorchestes, using 3D ROM mapping of elbow mobility with a comparative dataset of extant and extinct mammals. This multiaxial approach has confirmed that even when degrees of freedom available are maximised, Palorchestes has remarkably low elbow mobility compared to other mammals, although this joint may not have been quite as 'fixed' as previously thought (Flannery & Archer, 1985;Richards et al, 2019). Our results highlight that even 'hinge' joints such as the elbow, which have traditionally been assumed to be uniaxial in their movements, can in fact show complex multiaxial rotations in maximal osteological ROM.…”

Section: Discussionsupporting

confidence: 76%

“…We suggest this forelimb anatomy may have been used either in scratch digging or, perhaps more likely, bipedal browsing-a functional niche unrepresented among living mammals (Coombs, 1983). This may partly explain the lack of functional similarities recovered in our results, and makes sense given their koala-like claw morphology (Richards et al, 2019). This compromise in locomotor efficiency in favour of other forelimb uses was evidently successful for a time-Palorchestes azael is the most common and widely distributed palorchestid, recovered in Middle to Late Pleistocene deposits right across the eastern half of the Australian continent (Davis & Archer, 1997)-until their existence was cut short by the extinctions that decimated Australia's megafauna some 40,000 years ago (Hocknull et al, 2020).…”

Section: Palorchestes Posture Locomotion and Forelimb Usementioning

confidence: 78%

“…Palorchestes, but we speculate such traces may be highly distinctive, reflecting this wide forelimb posture coupled with a comparatively narrow-gauge hindlimb (Richards et al, 2019).…”

Section: Palorchestes Posture Locomotion and Forelimb Usementioning

confidence: 83%

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Low elbow mobility indicates unique forelimb posture and function in a giant extinct marsupial

et al. 2021

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Joint mobility is a key factor in determining the functional capacity of tetrapod limbs, and is important in palaeobiological reconstructions of extinct animals. Recent advances have been made in quantifying osteological joint mobility using virtual computational methods; however, these approaches generally focus on the proximal limb joints and have seldom been applied to fossil mammals. Palorchestes azael is an enigmatic, extinct ~1000 kg marsupial with no close living relatives, whose functional ecology within Australian Pleistocene environments is poorly understood. Most intriguing is its flattened elbow morphology, which has long been assumed to indicate very low mobility at this important joint. Here, we tested elbow mobility via virtual range of motion (ROM) mapping and helical axis analysis, to quantitatively explore the limits of Palorchestes' elbow movement and compare this with their living and extinct relatives, as well as extant mammals that may represent functional analogues. We find that Palorchestes had the lowest elbow mobility among mammals sampled, even when afforded joint translations in addition to rotational degrees of freedom. This indicates that Palorchestes was limited to crouched forelimb postures, something highly unusual for mammals of this size. Coupled flexion and abduction created a skewed primary axis of movement at the elbow, suggesting an abducted forelimb posture and humeral rotation gait that is not found among marsupials and unlike that seen in any large mammals alive today. This work introduces new quantitative methods and demonstrates the utility of comparative ROM mapping approaches, highlighting that Palorchestes' forelimb function was unlike its contemporaneous relatives and appears to lack clear functional analogues among living mammals.

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Section: Discussionsupporting

confidence: 76%

Section: Palorchestes Posture Locomotion and Forelimb Usementioning

confidence: 78%

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Low elbow mobility indicates unique forelimb posture and function in a giant extinct marsupial

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“…– or identify anatomical novelties – such as apomorphically robust/gracile limbs possibly associated with particular ecologies (e.g. Richards et al ., 2019). Emphatically, the results of mass estimation should never be presented as a point estimate.…”

Section: Resultsmentioning

confidence: 99%

The accuracy and precision of body mass estimation in non‐avian dinosaurs

Campione

Evans

2020

Biological Reviews

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Inferring the body mass of fossil taxa, such as non‐avian dinosaurs, provides a powerful tool for interpreting physiological and ecological properties, as well as the ability to study these traits through deep time and within a macroevolutionary context. As a result, over the past 100 years a number of studies advanced methods for estimating mass in dinosaurs and other extinct taxa. These methods can be categorized into two major approaches: volumetric‐density (VD) and extant‐scaling (ES). The former receives the most attention in non‐avian dinosaurs and advanced appreciably over the last century: from initial physical scale models to three‐dimensional (3D) virtual techniques that utilize scanned data obtained from entire skeletons. The ES approach is most commonly applied to extinct members of crown clades but some equations are proposed and utilized in non‐avian dinosaurs. Because both approaches share a common goal, they are often viewed in opposition to one another. However, current palaeobiological research problems are often approach specific and, therefore, the decision to utilize a VD or ES approach is largely question dependent. In general, biomechanical and physiological studies benefit from the full‐body reconstruction provided through a VD approach, whereas large‐scale evolutionary and ecological studies require the extensive data sets afforded by an ES approach. This study summarizes both approaches to body mass estimation in stem‐group taxa, specifically non‐avian dinosaurs, and provides a comparative quantitative framework to reciprocally illuminate and corroborate VD and ES approaches. The results indicate that mass estimates are largely consistent between approaches: 73% of VD reconstructions occur within the expected 95% prediction intervals of the ES relationship. However, almost three quarters of outliers occur below the lower 95% prediction interval, indicating that VD mass estimates are, on average, lower than would be expected given their stylopodial circumferences. Inconsistencies (high residual and per cent prediction deviation values) are recovered to a varying degree among all major dinosaurian clades along with an overall tendency for larger deviations between approaches among small‐bodied taxa. Nonetheless, our results indicate a strong corroboration between recent iterations of the VD approach based on 3D specimen scans suggesting that our current understanding of size in dinosaurs, and hence its biological correlates, has improved over time. We advance that VD and ES approaches have fundamentally (metrically) different advantages and, hence, the comparative framework used and advocated here combines the accuracy afforded by ES with the precision provided by VD and permits the rapid identification of discrepancies with the potential to open new areas of discussion.

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“…Given data availability, we settled on a total of 21 species (13 extinct; 8 extant) from five different functional/taxonomic groups: ( i ) 5 vombatiform herbivores: Diprotodon optatum (2786 kg; extinct) ( Wroe et al, 2004 ), Palorchestes azael (1000 kg; extinct) ( Richards et al, 2019 ), Zygomaturus trilobus (500 kg; extinct) ( Johnson, 2006 ), Phascolonus gigas (200 kg; extinct) ( Johnson, 2006 ), and Vombatus ursinus (common wombat; 25 kg; extant) ( McIlroy, 1996 ; Saran et al, 2011 ); ( ii ) 7 macropodiform herbivores: Procoptodon goliah (250 kg; extinct) ( Johnson and Prideaux, 2004 ), Sthenurus stirlingi (150 kg; extinct) ( Johnson and Prideaux, 2004 ), Protemnodon anak (130 kg; extinct) ( Johnson, 2006 ), Simosthenurus occidentalis (120 kg; extinct) ( Johnson, 2006 ), Metasthenurus newtonae (55 kg; extinct) ( Johnson, 2006 ), Osphranter rufus (red kangaroo; 25 kg; extant) ( McIlroy, 2008 ), and Notamacropus rufogriseus (red-necked wallaby; 14 kg; extant) ( Strahan, 1991 ); ( iii ) 3 omnivorous (but primarily plant-eating) large birds: Genyornis newtoni (200 kg; extinct) ( Johnson, 2006 ), Dromaius novaehollandiae (emu; 55 kg; extant) ( Sales, 2007 ), and Alectura lathami (brush turkey; 2.2 kg; extant) ( Jones et al, 1995 ); ( iv ) 4 carnivores: Thylacoleo carnifex (marsupial ‘lion’; 110 kg; extinct) ( Johnson, 2006 ), Thylacinus cynocephalus (marsupial ‘tiger’; 20 kg; extinct) ( Jones and Stoddart, 1998 ), Sarcophilus harrisii (devil; 6.1 kg; extinct in mainland Australia, but extant in Tasmania — see below) ( Guiler, 1978 ), and Dasyurus maculatus (spotted-tail quoll; 2.0 kg; extant) ( Belcher et al, 2008 ); and ( v ) 2 monotreme invertivores: Megalibgwilia ramsayi (11 kg; extinct) ( Johnson, 2006 ), and Tachyglossus aculeatus (short-beaked echidna; 4.0 kg; extant) ( Nicol and Andersen, 2007 ).…”

Section: Choice Of Species and Body Mass Distributionmentioning

confidence: 99%

Relative demographic susceptibility does not explain the extinction chronology of Sahul’s megafauna

Bradshaw

Johnson

Llewelyn

et al. 2021

eLife

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The causes of Sahul's megafauna extinctions remain uncertain, although several interacting factors were likely responsible. To examine the relative support for hypotheses regarding plausible ecological mechanisms underlying these extinctions, we constructed the first stochastic, age-structured models for 13 extinct megafauna species from five functional/taxonomic groups, as well as eight extant species within these groups for comparison. Perturbing specific demographic rates individually, we tested which species were more demographically susceptible to extinction, and then compared these relative sensitivities to the fossil-derived extinction chronology. Our models show that the macropodiformes were the least demographically susceptible to extinction, followed by carnivores, monotremes, vombatiform herbivores, and large birds. Five of the eight extant species were as or more susceptible than the extinct species. There was no clear relationship between extinction susceptibility and the extinction chronology for any perturbation scenario, while body mass and generation length explained much of the variation in relative risk. Our results reveal that the actual mechanisms leading to the observed extinction chronology were unlikely related to variation in demographic susceptibility per se, but were possibly driven instead by finer-scale variation in climate change and/or human prey choice and relative hunting success.

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The extraordinary osteology and functional morphology of the limbs in Palorchestidae, a family of strange extinct marsupial giants

Cited by 22 publications

References 51 publications

Low elbow mobility indicates unique forelimb posture and function in a giant extinct marsupial

Low elbow mobility indicates unique forelimb posture and function in a giant extinct marsupial

The accuracy and precision of body mass estimation in non‐avian dinosaurs

Relative demographic susceptibility does not explain the extinction chronology of Sahul’s megafauna

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