Publication Date:
2021-06-24
Description:
The Neocoleoidea, sister group to the Belemnoidea, includes all living cephalopod species except nautilids, as well as their immediate ancestors. Several hypotheses have been published about the morphology of ancestral neocoleoids. Ancestral states are easily infe1red from fossils for some characters, such as 10 arms and the presence of an ink sac in basal coleoids or the presence of fins in ancient octopods. Many inferences are less strongly supported, though, and open to debate. We examine this problem using three cladograms resulting from analyses of morphology and DNA sequences (both mitochondrial and nuclear) from samples representing the full diversity of extant coleoids. Character states at three ancestral nodes (neocoleoid, octopodiform, and decapodiform) are reconstructed for 51 morphological characters using cladistic parsimony. Strong or moderate agreement among the three trees was found for almost 3/4 of the character-at-node reconstructions. The level of agreement among the trees varied among nodes, with strongest agreement found at the ancestral octopodiform node. However, some of these reconstructions seem unlikely to be co1rect. Changes in subclade resolution can exert varying effects on inferences about basal nodes. Because several subclades within the neocoleoids are not yet adequately resolved, we cannot be very confident in reconstructions of ancestral character states based solely on parsimony and we propose a provisional suite of character-state reconstructions including other sources of inference in addition to parsimony.
Type:
Article
,
PeerReviewed
Format:
text
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