The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata
Abstract Background Segmental composition and homologies of the head of stem-group Euarthropoda have been the foci of recent studies on arthropod origins. An emerging hypothesis suggests that upper-stem group euarthropods possessed a three-segmented head/brain, including an ocular segment (protocere...
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| Format: | Article |
| Language: | English |
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BMC
2017-08-01
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| Series: | BMC Evolutionary Biology |
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| Online Access: | http://link.springer.com/article/10.1186/s12862-017-1049-1 |
| _version_ | 1818606220568690688 |
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| author | Peiyun Cong Allison C. Daley Gregory D. Edgecombe Xianguang Hou |
| author_facet | Peiyun Cong Allison C. Daley Gregory D. Edgecombe Xianguang Hou |
| author_sort | Peiyun Cong |
| collection | DOAJ |
| description | Abstract Background Segmental composition and homologies of the head of stem-group Euarthropoda have been the foci of recent studies on arthropod origins. An emerging hypothesis suggests that upper-stem group euarthropods possessed a three-segmented head/brain, including an ocular segment (protocerebrum) followed by the deutocerebrum with associated antennae/raptorial limbs and the tritocerebrum, while in the lower stem, head structures of Radiodonta are wholly associated with the protocerebrum and its preceding part. However, this hypothesis is incompletely tested because detailed knowledge on the head components of radiodontans is patchy, and informative articulated specimens are lacking for many taxa. Amplectobelua symbrachiata is the most common radiodontan species in the Chengjiang biota (ca. 520 Ma), normally known as isolated frontal appendages. Here we present detailed descriptions of new articulated specimens that elucidate the morphology and function of its head structures, and discuss their implications for hypotheses about euarthropod cephalic organisation. Results In addition to a central oval head shield, A. symbrachiata also bears a pair of P-elements connected by an elongated rod. The mouth consists of sets of smooth and tuberculate plates, in contrast to the typical radial oral cones of other radiodontans. Previously identified ‘palm-like teeth’ are located external to the mouth in the posterior head region, and are interpreted as segmental gnathobase-like structures (GLSs) associated with at least three reduced transitional flaps in a one (pair)-to-one (pair) pattern, consistent with an appendicular nature. Comparisons with other panarthropods show that GLSs are morphologically similar to the mandibles and other gnathobasic mouthparts of euarthropods, as well as to the jaws of onychophorans, indicating their functional integration into the feeding activities of A. symbrachiata. Conclusions The functional head of A. symbrachiata must include the reduced transitional segments (and their associated structures), which have been identified in several other radiodontans. This functional view supports the idea that the integration of segments (and associated appendages) into the head region, probably driven by feeding, occurred along the euarthropod stem-lineage. However, the number of reduced transitional segments varies between different groups and it remains uncertain whether GLSs represent proximal or distal parts of appendages. Our study is the first description of appendicular structures other than the frontal appendages in the functional head region of radiodontans, revealing novel feeding structures in the morphological transition from the lower- to the upper- stem-group of Euarthropoda. |
| first_indexed | 2024-12-16T14:07:24Z |
| format | Article |
| id | doaj.art-f5f1866659644716b5b50819a416a270 |
| institution | Directory Open Access Journal |
| issn | 1471-2148 |
| language | English |
| last_indexed | 2024-12-16T14:07:24Z |
| publishDate | 2017-08-01 |
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| spelling | doaj.art-f5f1866659644716b5b50819a416a2702022-12-21T22:28:53ZengBMCBMC Evolutionary Biology1471-21482017-08-0117112310.1186/s12862-017-1049-1The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiataPeiyun Cong0Allison C. Daley1Gregory D. Edgecombe2Xianguang Hou3Yunnan Key Laboratory for Palaeobiology, Yunnan UniversityInstitute of Earth Sciences, University of LausanneDepartment of Earth Sciences, The Natural History MuseumYunnan Key Laboratory for Palaeobiology, Yunnan UniversityAbstract Background Segmental composition and homologies of the head of stem-group Euarthropoda have been the foci of recent studies on arthropod origins. An emerging hypothesis suggests that upper-stem group euarthropods possessed a three-segmented head/brain, including an ocular segment (protocerebrum) followed by the deutocerebrum with associated antennae/raptorial limbs and the tritocerebrum, while in the lower stem, head structures of Radiodonta are wholly associated with the protocerebrum and its preceding part. However, this hypothesis is incompletely tested because detailed knowledge on the head components of radiodontans is patchy, and informative articulated specimens are lacking for many taxa. Amplectobelua symbrachiata is the most common radiodontan species in the Chengjiang biota (ca. 520 Ma), normally known as isolated frontal appendages. Here we present detailed descriptions of new articulated specimens that elucidate the morphology and function of its head structures, and discuss their implications for hypotheses about euarthropod cephalic organisation. Results In addition to a central oval head shield, A. symbrachiata also bears a pair of P-elements connected by an elongated rod. The mouth consists of sets of smooth and tuberculate plates, in contrast to the typical radial oral cones of other radiodontans. Previously identified ‘palm-like teeth’ are located external to the mouth in the posterior head region, and are interpreted as segmental gnathobase-like structures (GLSs) associated with at least three reduced transitional flaps in a one (pair)-to-one (pair) pattern, consistent with an appendicular nature. Comparisons with other panarthropods show that GLSs are morphologically similar to the mandibles and other gnathobasic mouthparts of euarthropods, as well as to the jaws of onychophorans, indicating their functional integration into the feeding activities of A. symbrachiata. Conclusions The functional head of A. symbrachiata must include the reduced transitional segments (and their associated structures), which have been identified in several other radiodontans. This functional view supports the idea that the integration of segments (and associated appendages) into the head region, probably driven by feeding, occurred along the euarthropod stem-lineage. However, the number of reduced transitional segments varies between different groups and it remains uncertain whether GLSs represent proximal or distal parts of appendages. Our study is the first description of appendicular structures other than the frontal appendages in the functional head region of radiodontans, revealing novel feeding structures in the morphological transition from the lower- to the upper- stem-group of Euarthropoda.http://link.springer.com/article/10.1186/s12862-017-1049-1RadiodontaAmplectobeluaFeeding structuresFunctional headChengjiang |
| spellingShingle | Peiyun Cong Allison C. Daley Gregory D. Edgecombe Xianguang Hou The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata BMC Evolutionary Biology Radiodonta Amplectobelua Feeding structures Functional head Chengjiang |
| title | The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata |
| title_full | The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata |
| title_fullStr | The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata |
| title_full_unstemmed | The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata |
| title_short | The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata |
| title_sort | functional head of the cambrian radiodontan stem group euarthropoda amplectobelua symbrachiata |
| topic | Radiodonta Amplectobelua Feeding structures Functional head Chengjiang |
| url | http://link.springer.com/article/10.1186/s12862-017-1049-1 |
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