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Brocklehurst N. The decline and fall of the mammalian stem. PeerJ 2024; 12:e17004. [PMID: 38436024 PMCID: PMC10906263 DOI: 10.7717/peerj.17004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Accepted: 02/05/2024] [Indexed: 03/05/2024] Open
Abstract
The mammalian crown originated during the Mesozoic and subsequently radiated into the substantial array of forms now extant. However, for about 100 million years before the crown's origin, a diverse array of stem mammalian lineages dominated terrestrial ecosystems. Several of these stem lineages overlapped temporally and geographically with the crown mammals during the Mesozoic, but by the end of the Cretaceous crown mammals make up the overwhelming majority of the fossil record. The progress of this transition between ecosystems dominated by stem mammals and those dominated by crown mammals is not entirely clear, in part due to a distinct separation of analyses and datasets. Analyses of macroevolutionary patterns tend to focus on either the Mammaliaformes or the non-mammalian cynodonts, with little overlap in the datasets, preventing direct comparison of the diversification trends. Here I analyse species richness and biogeography of Synapsida as a whole during the Mesozoic, allowing comparison of the patterns in the mammalian crown and stem within a single framework. The analysis reveals the decline of the stem mammals occurred in two discrete phases. The first phase occurred between the Triassic and Middle Jurassic, during which the stem mammals were more restricted in their geographic range than the crown mammals, although within localities their species richness remained at levels seen previously. The second phase was a decline in species richness, which occurred during the Lower Cretaceous. The results show the decline of stem mammals, including tritylodontids and several mammaliaform groups, was not tied to a specific event, nor a gradual decline, but was instead a multiphase transition.
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Affiliation(s)
- Neil Brocklehurst
- Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom
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Brocklehurst N, Panciroli E, Benevento GL, Benson RBJ. Mammaliaform extinctions as a driver of the morphological radiation of Cenozoic mammals. Curr Biol 2021; 31:2955-2963.e4. [PMID: 34004143 DOI: 10.1016/j.cub.2021.04.044] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Revised: 12/04/2020] [Accepted: 04/19/2021] [Indexed: 11/17/2022]
Abstract
Adaptive radiations are hypothesized as a generating mechanism for much of the morphological diversity of extant species.1-7 The Cenozoic radiation of placental mammals, the foundational example of this concept,8,9 gave rise to much of the morphological disparity of extant mammals, and is generally attributed to relaxed evolutionary constraints following the extinction of non-avian dinosaurs.10-13 However, study of this and other radiations has focused on variation in evolutionary rates,4,5,7,14 leaving the extent to which relaxation of constraints enabled the origin of novel phenotypes less well characterized.15-17 We evaluate constraints on morphological evolution among mammaliaforms (mammals and their closest relatives) using a new method that quantifies the capacity of evolutionary change to generate phenotypic novelty. We find that Mesozoic crown-group therians, which include the ancestors of placental mammals, were significantly more constrained than other mammaliaforms. Relaxation of these constraints occurred in the mid-Paleocene, post-dating the extinction of non-avian dinosaurs at the K/Pg boundary, instead coinciding with important environmental shifts and with declining ecomorphological diversity in non-theriimorph mammaliaforms. This relaxation occurred even in small-bodied Cenozoic mammals weighing <100 g, which are unlikely to have competed with dinosaurs. Instead, our findings support a more complex model whereby Mesozoic crown therian evolution was in part constrained by co-occurrence with disparate mammaliaforms, as well as by the presence of dinosaurs, within-lineage incumbency effects, and environmental factors. Our results demonstrate that variation in evolutionary constraints can occur independently of variation in evolutionary rate, and that both make important contributions to the understanding of adaptive radiations.
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Affiliation(s)
- Neil Brocklehurst
- Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK.
| | - Elsa Panciroli
- Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK; Oxford University Museum of Natural History, Parks Road, Oxford OX1 3PW, UK
| | - Gemma Louise Benevento
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Roger B J Benson
- Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
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Chimento NR, Agnolin FL, Tsuihiji T, Manabe M, Novas FE. New record of a Mesozoic gondwanatherian mammaliaform from Southern Patagonia. Naturwissenschaften 2020; 107:49. [PMID: 33211174 DOI: 10.1007/s00114-020-01705-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Revised: 08/13/2020] [Accepted: 10/28/2020] [Indexed: 11/26/2022]
Abstract
Gondwanatheria is an enigmatic mammaliaform clade distributed in the Cretaceous and Paleogene of South America, Africa, Madagascar, India and Antarctica. The Mesozoic record in South America is restricted to the Latest Cretaceous of Río Negro and Chubut provinces, Argentina and Magallanes Region of southern Chile. The aim of the present contribution is to describe a new specimen of gondwanatherian mammaliaforms from beds belonging to the Maastrichtian Chorrillo Formation, cropping out 30 km SW of El Calafate, Santa Cruz Province, Argentina. It is represented by a single molariform referable to the species Magallanodon baikashkenke with which it shares a unique combination of characters. Analysis of the unique combination of characters exhibited by Magallanodon shed doubts on the monophyly of Ferugliotheriidae and suggest that South American taxa may be closely related to each other. The wide geographical distribution and occurrence of gondwanatherians on geological units of diverse origins suggest that they were capable of facing disparate environmental conditions.
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Affiliation(s)
- Nicolás R Chimento
- Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" - CONICET, Av. Ángel Gallardo 470, Buenos Aires, 1405DJR, Argentina.
| | - Federico L Agnolin
- Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" - CONICET, Av. Ángel Gallardo 470, Buenos Aires, 1405DJR, Argentina
- Fundación de Historia Natural "Félix de Azara", Departamento de Ciencias Naturales y Antropología, Universidad Maimónides, Hidalgo 775, 1405BDB, Buenos Aires, Argentina
| | - Takanobu Tsuihiji
- National Museum of Nature & Science, 4-1-1 Amakubo, Tsukuba, 305-0005, Japan
| | - Makoto Manabe
- National Museum of Nature & Science, 4-1-1 Amakubo, Tsukuba, 305-0005, Japan
| | - Fernando E Novas
- Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" - CONICET, Av. Ángel Gallardo 470, Buenos Aires, 1405DJR, Argentina
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Abstract
Improved understanding of tick phylogeny has allowed testing of some biogeographical patterns. On the basis of both literature data and a meta-analysis of available sequence data, there is strong support for a Gondwanan origin of Ixodidae, and probably Ixodida. A particularly strong pattern is observed for the genus Amblyomma, which appears to have originated in Antarctica/southern South America, with subsequent dispersal to Australia. The endemic Australian lineages of Ixodidae (no other continent has such a pattern) appear to result from separate dispersal events, probably from Antarctica. Minimum ages for a number of divergences are determined as part of an updated temporal framework for tick evolution. Alternative hypotheses for tick evolution, such as a very old Pangean group, a Northern hemisphere origin, or an Australian origin, fit less well with observed phylogeographic patterns.
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Affiliation(s)
- Lorenza Beati
- Institute for Coastal Plain Science and US National Tick Collection, Georgia Southern University, Statesboro, Georgia 30460, USA;
| | - Hans Klompen
- Department of Evolution, Ecology, and Organismal Biology and Museum of Biological Diversity, The Ohio State University, Columbus, Ohio 43212, USA
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Beck RMD. The Skull of Epidolops ameghinoi from the Early Eocene Itaboraí Fauna, Southeastern Brazil, and the Affinities of the Extinct Marsupialiform Order Polydolopimorphia. J MAMM EVOL 2016; 24:373-414. [PMID: 29187780 PMCID: PMC5684316 DOI: 10.1007/s10914-016-9357-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The skull of the polydolopimorphian marsupialiform Epidolops ameghinoi is described in detail for the first time, based on a single well-preserved cranium and associated left and right dentaries plus additional craniodental fragments, all from the early Eocene (53–50 million year old) Itaboraí fauna in southeastern Brazil. Notable craniodental features of E. ameghinoi include absence of a masseteric process, very small maxillopalatine fenestrae, a prominent pterygoid fossa enclosed laterally by a prominent ectopterygoid crest, an absent or tiny transverse canal foramen, a simple, planar glenoid fossa, and a postglenoid foramen that is immediately posterior to the postglenoid process. Most strikingly, the floor of the hypotympanic sinus was apparently unossified, a feature found in several stem marsupials but absent in all known crown marsupials. “Type II” marsupialiform petrosals previously described from Itaboraí plausibly belong to E. ameghinoi; in published phylogenetic analyses, these petrosals fell outside (crown-clade) Marsupialia. “IMG VII” tarsals previously referred to E. ameghinoi do not share obvious synapomorphies with any crown marsupial clade, nor do they resemble those of the only other putative polydolopimorphians represented by tarsal remains, namely the argyrolagids. Most studies have placed Polydolopimorphia within Marsupialia, related to either Paucituberculata, or to Microbiotheria and Diprotodontia. However, diprotodonty almost certainly evolved independently in polydolopimorphians, paucituberculatans and diprotodontians, and Epidolops does not share obvious synapomorphies with any marsupial order. Epidolops is dentally specialized, but several morphological features appear to be more plesiomorphic than any crown marsupial. It seems likely Epidolops that falls outside Marsupialia, as do morphologically similar forms such as Bonapartherium and polydolopids. Argyrolagids differ markedly in their known morphology from Epidolops but share some potential apomorphies with paucituberculatans. It is proposed that Polydolopimorphia as currently recognised is polyphyletic, and that argyrolagids (and possibly other taxa currently included in Argyrolagoidea, such as groeberiids and patagoniids) are members of Paucituberculata. This hypothesis is supported by Bayesian non-clock phylogenetic analyses of a total evidence matrix comprising DNA sequence data from five nuclear protein-coding genes, indels, retroposon insertions, and morphological characters: Epidolops falls outside Marsupialia, whereas argyrolagids form a clade with the paucituberculatans Caenolestes and Palaeothentes, regardless of whether the Type II petrosals and IMG VII tarsals are used to score characters for Epidolops or not. There is no clear evidence for the presence of crown marsupials at Itaboraí, and it is possible that the origin and early evolution of Marsupialia was restricted to the “Austral Kingdom” (southern South America, Antarctica, and Australia).
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Affiliation(s)
- Robin M. D. Beck
- School of Environment & Life Sciences, University of Salford, M5 4WT, Manchester, UK
- School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052 Australia
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Antoine PO, Salas-Gismondi R, Pujos F, Ganerød M, Marivaux L. Western Amazonia as a Hotspot of Mammalian Biodiversity Throughout the Cenozoic. J MAMM EVOL 2016. [DOI: 10.1007/s10914-016-9333-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Krause DW, Hoffmann S, Wible JR, Kirk EC, Schultz JA, von Koenigswald W, Groenke JR, Rossie JB, O’Connor PM, Seiffert ER, Dumont ER, Holloway WL, Rogers RR, Rahantarisoa LJ, Kemp AD, Andriamialison H. First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature 2014; 515:512-7. [DOI: 10.1038/nature13922] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Accepted: 10/07/2014] [Indexed: 11/10/2022]
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Paleogene Land Mammal Faunas of South America; a Response to Global Climatic Changes and Indigenous Floral Diversity. J MAMM EVOL 2013. [DOI: 10.1007/s10914-012-9222-1] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Carter AM, Mess AM. Conservation of placentation during the tertiary radiation of mammals in South America. J Morphol 2013; 274:557-69. [DOI: 10.1002/jmor.20120] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Revised: 11/19/2012] [Accepted: 11/30/2012] [Indexed: 11/10/2022]
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Rougier GW, Wible JR, Beck RMD, Apesteguía S. The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America. Proc Natl Acad Sci U S A 2012; 109:20053-8. [PMID: 23169652 PMCID: PMC3523863 DOI: 10.1073/pnas.1212997109] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The early Miocene mammal Necrolestes patagonensis from Patagonia, Argentina, was described in 1891 as the only known extinct placental "insectivore" from South America (SA). Since then, and despite the discovery of additional well-preserved material, the systematic status of Necrolestes has remained in flux, with earlier studies leaning toward placental affinities and more recent ones endorsing either therian or specifically metatherian relationships. We have further prepared the best-preserved specimens of Necrolestes and compared them with newly discovered nontribosphenic Mesozoic mammals from Argentina; based on this, we conclude that Necrolestes is related neither to marsupials nor placentals but is a late-surviving member of the recently recognized nontherian clade Meridiolestida, which is currently known only from SA. This conclusion is supported by a morphological phylogenetic analysis that includes a broad sampling of therian and nontherian taxa and that places Necrolestes within Meridiolestida. Thus, Necrolestes is a remnant of the highly endemic Mesozoic fauna of nontribosphenic mammals in SA and extends the known record of meridiolestidans by almost 45 million years. Together with other likely relictual mammals from earlier in the Cenozoic of SA and Antarctica, Necrolestes demonstrates the ecological diversity of mammals and the mosaic pattern of fauna replacement in SA during the Cenozoic. In contrast to northern continents, the Cenozoic faunal history of SA was characterized by a long period of interaction between endemic mammalian lineages of Mesozoic origin and metatherian and eutherian lineages that probably dispersed to SA during the latest Cretaceous or earliest Paleocene.
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Affiliation(s)
- Guillermo W Rougier
- Department of Anatomical Sciences and Neurobiology, University of Louisville, Louisville, KY 40202, USA.
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