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Fonseca PHM, Martinelli AG, Gill PG, Rayfield EJ, Schultz CL, Kerber L, Ribeiro AM, Francischini H, Soares MB. New evidence from high-resolution computed microtomography of Triassic stem-mammal skulls from South America enhances discussions on turbinates before the origin of Mammaliaformes. Sci Rep 2024; 14:13817. [PMID: 38879680 PMCID: PMC11180108 DOI: 10.1038/s41598-024-64434-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Accepted: 06/10/2024] [Indexed: 06/19/2024] Open
Abstract
The nasal cavity of living mammals is a unique structural complex among tetrapods, acquired along a series of major morphological transformations that occurred mainly during the Mesozoic Era, within the Synapsida clade. Particularly, non-mammaliaform cynodonts document several morphological changes in the skull, during the Triassic Period, that represent the first steps of the mammalian bauplan. We here explore the nasal cavity of five cynodont taxa, namely Thrinaxodon, Chiniquodon, Prozostrodon, Riograndia, and Brasilodon, in order to discuss the main changes within this skull region. We did not identify ossified turbinals in the nasal cavity of these taxa and if present, as non-ossified structures, they would not necessarily be associated with temperature control or the development of endothermy. We do, however, notice a complexification of the cartilage anchoring structures that divide the nasal cavity and separate it from the brain region in these forerunners of mammals.
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Affiliation(s)
- Pedro H M Fonseca
- Programa de Pós-Graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Bairro Agronomia, Porto Alegre, Rio Grande do Sul, 91501-970, Brazil.
| | - Agustín G Martinelli
- CONICET-Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Av. Ángel Gallardo 470, C1405DJR, Buenos Aires, CABA, Argentina.
- Núcleo Milenio EVOTEM-Evolutionary Transitions of Early Mammals-ANID, Santiago, Chile.
| | - Pamela G Gill
- Palaeobiology Research Group, School of Earth Sciences, University of Bristol, Life Sciences Building, Bristol, BS8 1TQ, UK.
- Science Department, Natural History Museum, Cromwell Road, London, SW7 5HD, UK.
| | - Emily J Rayfield
- Palaeobiology Research Group, School of Earth Sciences, University of Bristol, Life Sciences Building, Bristol, BS8 1TQ, UK.
| | - Cesar L Schultz
- Programa de Pós-Graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Bairro Agronomia, Porto Alegre, Rio Grande do Sul, 91501-970, Brazil
| | - Leonardo Kerber
- Centro de Apoio à Pesquisa Paleontológica, Universidade Federal de Santa Maria, São João do Polêsine, Brazil
| | - Ana Maria Ribeiro
- Programa de Pós-Graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Bairro Agronomia, Porto Alegre, Rio Grande do Sul, 91501-970, Brazil
- Museu de Ciências Naturais/SEMA, Porto Algre, RS, Brazil
| | - Heitor Francischini
- Programa de Pós-Graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Bairro Agronomia, Porto Alegre, Rio Grande do Sul, 91501-970, Brazil
| | - Marina B Soares
- Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista s/n, São Cristovão, Rio de Janeiro, RJ, 20940-040, Brazil.
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Laaß M, Kaestner A. Nasal turbinates of the dicynodont Kawingasaurus fossilis and the possible impact of the fossorial habitat on the evolution of endothermy. J Morphol 2023; 284:e21621. [PMID: 37585231 DOI: 10.1002/jmor.21621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2022] [Revised: 06/28/2023] [Accepted: 06/29/2023] [Indexed: 08/17/2023]
Abstract
The nasal region of the fossorial anomodont Kawingasaurus fossilis was virtually reconstructed from neutron-computed tomographic data and compared with the terrestrial species Pristerodon mackayi and other nonmammalian synapsids. The tomography of the Kawingasaurus skull reveals a pattern of maxillo-, naso-, fronto- and ethmoturbinal ridges that strongly resemble the mammalian condition. On both sides of the nasal cavity, remains of scrolled maxilloturbinals were preserved that were still partially articulated with maxilloturbinal ridges. Furthermore, possible remains of the lamina semicircularis as well as fronto- or ethmoturbinals were found. In Kawingasaurus, the maxilloturbinal ridges were longer and stronger than in Pristerodon. Except for the nasoturbinal ridges, no other ridges in the olfactory region and no remains of turbinates were recognized. This supports the hypothesis that naso-, fronto-, ethmo- and maxilloturbinals were a plesiomorphic feature of synapsids, but due to their cartilaginous nature in most taxa were, in almost all cases, not preserved. The well-developed maxilloturbinals in Kawingasaurus were probably an adaptation to hypoxia-induced hyperventilation in the fossorial habitat, maintaining the high oxygen demands of Kawingasaurus' large brain. The surface area of the respiratory turbinates in Kawingasaurus falls into the mammalian range, which suggests that they functioned as a countercurrent exchange system for thermoregulation and conditioning of the respiratory airflow. Our results suggest that the environmental conditions of the fossorial habitat led to specific sensory adaptations, accompanied by a pulse in brain evolution and of endothermy in cistecephalids, ~50 million years before the origin of endothermy in the mammalian stem line. This supports the Nocturnal Bottleneck Theory, in that we found evidence for a similar evolutionary scenario in cistecephalids as proposed for early mammals.
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Affiliation(s)
- Michael Laaß
- Fakultät für Geowissenschaften, Geotechnik und Bergbau, TU Bergakademie Freiberg, Freiberg, Germany
- FRM II and Physics E21, Technische Universität München, Garching, Germany
| | - Anders Kaestner
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, Villigen PSI, Switzerland
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At the root of the mammalian mind: The sensory organs, brain and behavior of pre-mammalian synapsids. PROGRESS IN BRAIN RESEARCH 2023; 275:25-72. [PMID: 36841570 DOI: 10.1016/bs.pbr.2022.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
All modern mammals are descendants of the paraphyletic non-mammaliaform Synapsida, colloquially referred to as the "mammal-like reptiles." It has long been assumed that these mammalian ancestors were essentially reptile-like in their morphology, biology, and behavior, i.e., they had a small brain, displayed simple behavior, and their sensory organs were unrefined compared to those of modern mammals. Recent works have, however, revealed that neurological, sensory, and behavioral traits previously considered typically mammalian, such as whiskers, enhanced olfaction, nocturnality, parental care, and complex social interactions evolved before the origin of Mammaliaformes, among the early-diverging "mammal-like reptiles." In contrast, an enlarged brain did not evolve immediately after the origin of mammaliaforms. As such, in terms of paleoneurology, the last "mammal-like reptiles" were not significantly different from the earliest mammaliaforms. The abundant data and literature published in the last 10 years no longer supports the "three pulses" scenario of synapsid brain evolution proposed by Rowe and colleagues in 2011, but supports the new "outside-in" model of Rodrigues and colleagues proposed in 2018, instead. As Mesozoic reptiles were becoming the dominant taxa within terrestrial ecosystems, synapsids gradually adapted to smaller body sizes and nocturnality. This resulted in a sensory revolution in synapsids as olfaction, audition, and somatosensation compensated for the loss of visual cues. This altered sensory input is aligned with changes in the brain, the most significant of which was an increase in relative brain size.
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Grigg G, Nowack J, Bicudo JEPW, Bal NC, Woodward HN, Seymour RS. Whole-body endothermy: ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians. Biol Rev Camb Philos Soc 2021; 97:766-801. [PMID: 34894040 PMCID: PMC9300183 DOI: 10.1111/brv.12822] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Revised: 11/25/2021] [Accepted: 11/29/2021] [Indexed: 12/31/2022]
Abstract
The whole‐body (tachymetabolic) endothermy seen in modern birds and mammals is long held to have evolved independently in each group, a reasonable assumption when it was believed that its earliest appearances in birds and mammals arose many millions of years apart. That assumption is consistent with current acceptance that the non‐shivering thermogenesis (NST) component of regulatory body heat originates differently in each group: from skeletal muscle in birds and from brown adipose tissue (BAT) in mammals. However, BAT is absent in monotremes, marsupials, and many eutherians, all whole‐body endotherms. Indeed, recent research implies that BAT‐driven NST originated more recently and that the biochemical processes driving muscle NST in birds, many modern mammals and the ancestors of both may be similar, deriving from controlled ‘slippage’ of Ca2+ from the sarcoplasmic reticulum Ca2+‐ATPase (SERCA) in skeletal muscle, similar to a process seen in some fishes. This similarity prompted our realisation that the capacity for whole‐body endothermy could even have pre‐dated the divergence of Amniota into Synapsida and Sauropsida, leading us to hypothesise the homology of whole‐body endothermy in birds and mammals, in contrast to the current assumption of their independent (convergent) evolution. To explore the extent of similarity between muscle NST in mammals and birds we undertook a detailed review of these processes and their control in each group. We found considerable but not complete similarity between them: in extant mammals the ‘slippage’ is controlled by the protein sarcolipin (SLN), in birds the SLN is slightly different structurally and its role in NST is not yet proved. However, considering the multi‐millions of years since the separation of synapsids and diapsids, we consider that the similarity between NST production in birds and mammals is consistent with their whole‐body endothermy being homologous. If so, we should expect to find evidence for it much earlier and more widespread among extinct amniotes than is currently recognised. Accordingly, we conducted an extensive survey of the palaeontological literature using established proxies. Fossil bone histology reveals evidence of sustained rapid growth rates indicating tachymetabolism. Large body size and erect stature indicate high systemic arterial blood pressures and four‐chambered hearts, characteristic of tachymetabolism. Large nutrient foramina in long bones are indicative of high bone perfusion for rapid somatic growth and for repair of microfractures caused by intense locomotion. Obligate bipedality appeared early and only in whole‐body endotherms. Isotopic profiles of fossil material indicate endothermic levels of body temperature. These proxies led us to compelling evidence for the widespread occurrence of whole‐body endothermy among numerous extinct synapsids and sauropsids, and very early in each clade's family tree. These results are consistent with and support our hypothesis that tachymetabolic endothermy is plesiomorphic in Amniota. A hypothetical structure for the heart of the earliest endothermic amniotes is proposed. We conclude that there is strong evidence for whole‐body endothermy being ancient and widespread among amniotes and that the similarity of biochemical processes driving muscle NST in extant birds and mammals strengthens the case for its plesiomorphy.
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Affiliation(s)
- Gordon Grigg
- School of Biological Sciences, University of Queensland, Brisbane, QLD, 4072, Australia
| | - Julia Nowack
- School of Biological and Environmental Sciences, Liverpool John Moores University, James Parsons Building, Byrom Street, Liverpool, L3 3AF, U.K
| | | | | | - Holly N Woodward
- Oklahoma State University Center for Health Sciences, Tulsa, OK, 74107, U.S.A
| | - Roger S Seymour
- School of Biological Sciences, University of Adelaide, Adelaide, SA, 5005, Australia
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