Biology subjects

Lanzetti, A.

Publications and source records attributed to Lanzetti, A..

4 recordsLinked to original sources

bioRxiv2023

The three-dimensionally articulated oral apparatus of a Devonian heterostracan sheds light on feeding in Palaeozoic jawless fishes

Attempts to explain the origin and diversification of vertebrates have commonly invoked the evolution of feeding ecology, contrasting the passive suspension feeding of invertebrate chordates and larval lampreys with active predation in living jawed vertebrates. Of the extinct jawless vertebrates that phylogenetically intercalate these living groups, the feeding apparatus is preserved only in the early diverging stem-gnathostome heterostracans and its anatomy remains poorly understood. Here we use X-ray microtomography to characterise the feeding apparatus of the pteraspid heterostracan Rhinopteraspis dunensis (Roemer, 1855). We show that the apparatus is composed of thirteen plates arranged approximately bilaterally, the majority of which articulate from the postoral plate. Our reconstruction of the apparatus shows that the oral plates would have been capable of movement within the dorso-ventral plane, but their degree of movement was limited. The functional morphology of the apparatus in Rhinopteraspis precludes all proposed interpretations of feeding except for suspension/deposit feeding and we interpret the apparatus as having served primarily to moderate the oral gape. This is consistent with evidence that at least some early jawless gnathostomes were suspension feeders and runs contrary to macroecological scenarios that envisage early vertebrate evolution as characterised by a directional trend towards increasingly active food acquisition.

paleontology↗

bioRxiv2022

Testing heterochrony: Connecting skull shape ontogeny and evolution of feeding adaptations in baleen whales

Ontogeny plays a key role in the evolution of organisms, as changes during the complex processes of development can allow for new traits to arise. Identifying changes in ontogenetic allometry - the relationship between skull shape and size during growth - can reveal the processes underlying major evolutionary transformations. Baleen whales (Mysticeti, Cetacea) underwent major morphological changes in transitioning from their ancestral raptorial feeding mode to the three specialised filter feeding modes observed in extant taxa. Heterochronic processes have been implicated in the evolution of these feeding modes, and their associated specialised cranial morphologies, but their role has never been tested with quantitative data. Here, we quantified skull shapes ontogeny and reconstructed ancestral allometric trajectories using 3D geometric morphometrics and phylogenetic comparative methods on sample representing modern mysticetes diversity. Our results demonstrate that Mysticeti, while having a common developmental trajectory, present distinct cranial shapes from early in their ontogeny corresponding to their different feeding ecologies. Size is the main driver of shape disparity across mysticetes. Disparate heterochronic processes are evident in the evolution of the group: skim feeders present accelerated growth relative to the ancestral nodes, while Balaenopteridae have overall slower growth, or paedomorphosis. The grey whale is the only taxon with a relatively faster rate of growth in this group, which might be connected to its unique benthic feeding strategy. Reconstructed ancestral allometries and related skull shapes indicate that extinct taxa used less specialized filter feeding modes, a finding broadly in line with the available fossil evidence.

evolutionary biology↗

bioRxiv2022

The ontogeny of asymmetry in echolocating whales

Extreme asymmetry of the skull is one of the most distinctive traits that characterizes toothed whales (Odontoceti, Cetacea). The origin and function of cranial asymmetry are connected to the evolution of echolocation, the ability to use high frequency sounds to navigate the surrounding environment. Although this novel phenotype must arise through changes in cranial development, the ontogeny of cetacean asymmetry has never been investigated. Here we use three-dimensional geometric morphometric to quantify the changes in degree of asymmetry and skull shape during prenatal and postnatal ontogeny for five genera spanning odontocete diversity (oceanic dolphins, porpoises, and beluga). Asymmetry in early ontogeny starts low and tracks phylogenetic relatedness of taxa. Distantly-related taxa that share aspects of their ecology overwrite these initial differences via heterochronic shifts, ultimately converging on comparable high levels of skull asymmetry. Porpoises maintain low levels of asymmetry into maturity and present a decelerated rate of growth, likely retained from the ancestral condition. Ancestral state reconstruction of allometric trajectories demonstrates that both paedomorphism and peramorphism contribute to cranial shape diversity across odontocetes. This study provides a striking example of how divergent developmental pathways can produce convergent ecological adaptations, even for some of the most unusual phenotypes exhibited among vertebrates.

evolutionary biology↗

bioRxiv2022

Anatomical, ontogenetic, and genomic homologies guide reconstructions of the teeth-to-baleen transition in mysticete whales

The transition in Mysticeti (Cetacea) from capture of individual prey using teeth to bulk filtering batches of small prey using baleen ranks among the most dramatic evolutionary transformations in mammalian history. We review phylogenetic work on the homology of mysticete feeding structures from anatomical, ontogenetic, and genomic perspectives. Six characters with key functional significance for filter-feeding behavior are mapped to cladograms based on 11 morphological datasets to reconstruct evolutionary change across the teeth-to-baleen transition. This comparative summary within a common parsimony framework reveals extensive conflicts among independent systematic efforts but also broad support for the newly named clade Kinetomenta (Aetiocetidae + Chaeomysticeti). Complementary anatomical studies using CTscans and ontogenetic series hint at commonalities between the developmental programs for teeth and baleen, lending further support for a transitional chimaeric feeder scenario that best explains current knowledge on the transition to filter feeding. For some extant mysticetes, the ontogenetic sequence in fetal specimens recapitulates the inferred evolutionary transformation: from teeth, to teeth and baleen, to just baleen. Phylogenetic mapping of inactivating mutations reveals mutational decay of dental genes related to enamel formation before the emergence of crown Mysticeti, while baleen genes that were repurposed or newly derived during the evolutionary elaboration of baleen currently are poorly characterized. Review and meta-analysis of available data suggest that the teeth-to-baleen transition in Mysticeti ranks among the best characterized macroevolutionary shifts due to the diversity of data from the genome, the fossil record, comparative anatomy, and ontogeny that directly bears on this remarkable evolutionary transformation.

evolutionary biology↗