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Journal of Paleontology 92(1):40–48
comparable to Peytoia, but whether observed differences between the subquadrate central opening in Hurdia and the irregular central opening in Anomalocaris are biological or taphonomic artifacts will require further study.
Feeding mechanisms.—Morphological variations shown by radiodontan oral cones, which are exemplified by the new morphotype here, may reflect different feeding mechanisms (Daley and Bergström, 2012). However, in the absence of preserved frontal appendages, the feeding mechanism of the Guanshan oral cone cannot be unequivocally determined. A comprehensive understanding of radiodontan feeding mechanisms requires an integrative consideration of both frontal appendages and oral cones. Future studies could investigate whether the morphological variations shown by oral cones, including differences in plate configurations, presence or absence of furrowed folds, scale-like nodes, and extra inner teeth, are correlated with specific feeding behaviors such as macrophagous predation or filter feeding. Both new fossil discoveries (e.g., Daley and Bergström, 2012) and biomecha- nical modelling (e.g., Hagadorn, 2009, 2010) would play important roles in these investigations.
Evolutionary implications.—The unique combination of features in the Guanshan oral cone represents an intermediate morphotype between the oral cones of Anomalocaris and Peytoia/Hurdia. Recent phylogenetic studies have revealed two main radiodontan lineages (Cong et al., 2014; Vinther et al., 2014; Van Roy et al., 2015), Anomalocarididae+ Amplectobeluidae, including Anomalocaris, Amplectobelua Hou et al., 1995 and Lyrarapax Cong et al., 2014, and Hurdiidae, comprising Hurdia, Peytoia,and Aegirocassis Van Roy et al., 2015. Anatomical differences between Anomalocaris- type and Peytoia/Hurdia–type oral cones may thus represent a characteristic distinction between the two major radiodontan lineages. However, it remains unclear which oral cone type represents the primitive radiodontan condition. Because the Guanshan oral cone combines features from
both radiodontan lineages, its phylogenetic position would aid our understanding the evolution of oral cones. However, the current framework of radiodontan phylogeny is largely based on frontal appendage morphology, and only a few characters, which include plate configuration, furrowed folds, and scale- like nodes, can be meaningfully coded for the four types of oral cones we know (Table 1). In this case, lack of knowledge of the frontal appendages, in addition to the unique combination of character states in the Guanshan oral cone, makes it difficult to resolve its phylogenetic position from character state data. Recent attempts to resolve the phylogeny of radiodontans from limited character data have led to conflicting results.
For example, the sister grouping of Peytoia and Anomalocaris resolved by a data set featured by ecdysozoan oral structures (Smith and Caron, 2015, fig. 4) is contradicted with a Peytoia+ Hurdia grouping in analyses based on comprehensive radiodontan characters including frontal appendages and oral cones (Cong et al., 2014; Vinther et al., 2014; Van Roy et al., 2015). Moreover, comparable character states in outgroup taxa such as scale-like nodes are inconsistent and are currently unhelpful in resolving character polarity. Without new anato- mical or taxonomic data, a data set–based analysis remains unreliable in resolving the evolution of radiodontan oral cones. Without a data set–based phylogeny, evolution of radio-
dontan oral cones can still be inferred by considering all possible scenarios in a phylogenetic framework. This becomes a question of determining the root in an unrooted three-taxon network made up of Anomalocaris, Peytoia +Hurdia, and the Guanshan oral cone (Fig. 3.5). Thus, three alternative evolutionary scenarios of radiodontan oral cones corresponding to three possible positions of the Guanshan oral cone can be recon- structed (A, B, C in Fig. 3.5; Table 2). Given the uncertain plesiomorphic character states, the possible character changes involved would include the increase or decrease in numbers of large and small plates and the gain or loss of furrowed folds and scale-like nodes (Table 2). Unfortunately, counting character state changes in each scenario only reaches an unresolved situation with the same steps (Table 2). Therefore, despite the possible morphological transformations being known, the exact evolutionary scenario of radiodontan oral cones cannot be determined with the limited data available at present. Incorpo- rating additional fossil evidence such as the frontal appendages associated with the Guanshan oral cone and new oral cones of other radiodontans would resolve this issue. As discussed, it is likely that the new oral cone belongs to one established radiodontan species in the Guanshan Lagerstätte, Anomalocaris kunmingensis or Paranomalocaris multisegmentalis (Wang et al., 2013) assigned to Amplectobeluidae and Anomalocarididae, respectively (Cong et al., 2014; Vinther et al., 2014; Van Roy et al., 2015), and is not a third hitherto unknown radiodontan. If this is the case, evolutionary scenario A (A in Fig. 3.5; Table 2) would be favored, where the Peytoia-type oral cone with a ‘tetraradial’ configuration is the plesiomorphic morphotype, and the Anomalocaris-type oral cone with a ‘triradial’ configuration and differentiated small plates is a derived feature of the clade Anomalocarididae+Amplectobeluidae. In conclusion, with a unique combination of Peytoia/
Hurdia–type plate configuration and Anomalocaris-type plate structures, the new radiodontan oral cone from the Guanshan Lagerstätte augments our knowledge of the fossil record and morphological disparity of radiodontan oral cones and enlightens their potentially diverse feeding mechanisms and
Table 2. Character state changes in different evolutionary scenarios corresponding to alternative phylogenetic positions of the Guanshan oral cone. Plesiomorphic states are followed by steps taken for each character in parentheses.
Position of Guanshan oral cone
A: Anomalocarididae + Amplectobeluidae B: Hurdiidae
C: Basal lineage
Large plates Small plates 4 (1)
3 or 4 (1) 28 or more (1) 4 (1)
28 (1) 28 (1)
Plesiomorphic character states Furrowed folds
Present or absent (1) Present or absent (1) Present (1) Present (1)
Present (1) Present (1)
Scale-like nodes Total steps 4
4 4
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