Convergence on dental simplification in the evolution of whales

Paleobiology ◽  
2018 ◽  
Vol 44 (3) ◽  
pp. 434-443 ◽  
Author(s):  
Carlos Mauricio Peredo ◽  
Julio S. Peredo ◽  
Nicholas D. Pyenson
Keyword(s):  
Fossil Record ◽  
Evolutionary History ◽  
Feeding Strategy ◽  
Filter Feeding ◽  
Enabling Factors ◽  
Dental Complexity ◽  
Insight Into

AbstractThe fossil record of mammal dentition provides crucial insight into key ecological and functional transitions throughout mammalian evolutionary history. For cetaceans, both extant clades differ markedly from their stem ancestors; neither retains the differentiated dentition or the tribosphenic molars characteristic of Mammalia. We used quantitative measures of dental complexity across fossil and living cetaceans to identify a trend toward dental simplicity through the Neogene. Both extant cetacean clades depart from the ancestral mammalian condition and concurrently converge upon a reduced and simplified dentition; modern mysticetes all have become entirely edentulous (at birth), and living odontocetes possess teeth as single-rooted, conical pegs. These two parallel trends accompany major shifts in feeding strategy (i.e., filter feeding in mysticetes and echolocation in odontocetes), suggesting that these evolutionary innovations for prey acquisition are enabling factors for the loss of prey processing and subsequent convergence on dental simplification.

A fossil record of land plant origins from charophyte algae

Science ◽  
2021 ◽  
Vol 373 (6556) ◽  
pp. 792-796 ◽  
Author(s):  
Paul K. Strother ◽  
Clinton Foster
Keyword(s):  
Fossil Record ◽  
Evolutionary History ◽  
Phylogenetic Signal ◽  
Land Plant ◽  
Fossil Plants ◽  
Fossil Plant ◽  
Molecular Phylogenetic ◽  
History Of ◽  
Time Gap ◽  
Evolutionary Continuity

Molecular time trees indicating that embryophytes originated around 500 million years ago (Ma) during the Cambrian are at odds with the record of fossil plants, which first appear in the mid-Silurian almost 80 million years later. This time gap has been attributed to a missing fossil plant record, but that attribution belies the case for fossil spores. Here, we describe a Tremadocian (Early Ordovician, about 480 Ma) assemblage with elements of both Cambrian and younger embryophyte spores that provides a new level of evolutionary continuity between embryophytes and their algal ancestors. This finding suggests that the molecular phylogenetic signal retains a latent evolutionary history of the acquisition of the embryophytic developmental genome, a history that perhaps began during Ediacaran-Cambrian time but was not completed until the mid-Silurian (about 430 Ma).

scholarly journals Experimental degradation of helicoidal photonic nanostructures in scarab beetles (Coleoptera: Scarabaeidae): implications for the identification of circularly polarizing cuticle in the fossil record

2018 ◽  
Vol 15 (148) ◽  
pp. 20180560 ◽  
Author(s):  
Giliane P. Odin ◽  
Maria E. McNamara ◽  
Hans Arwin ◽  
Kenneth Järrendahl
Keyword(s):  
Uric Acid ◽  
Fossil Record ◽  
Evolutionary History ◽  
Polarized Light ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Alkaline Conditions ◽  
History Of ◽  
Diagenetic History ◽  
Scarab Beetles

Scarab beetles (Coleoptera: Scarabaeidae) can exhibit striking colours produced by pigments and/or nanostructures. The latter include helicoidal (Bouligand) structures that can generate circularly polarized light. These have a cryptic evolutionary history in part because fossil examples are unknown. This suggests either a real biological signal, i.e. that Bouligand structures did not evolve until recently, or a taphonomic signal, i.e. that conditions during the fossilization process were not conducive to their preservation. We address this issue by experimentally degrading circularly polarizing cuticle of modern scarab beetles to test the relative roles of decay, maturation and taxonomy in controlling preservation. The results reveal that Bouligand structures have the potential to survive fossilization, but preservation is controlled by taxonomy and the diagenetic history of specimens. Further, cuticle of specific genus ( Chrysina ) is particularly decay-prone in alkaline conditions; this may relate to the presence of certain compounds, e.g. uric acid, in the cuticle of these taxa.

Postembryonic development of Dalmanitina, and the evolution of facial suture fusion in Phacopina

Paleobiology ◽  
2018 ◽  
Vol 44 (4) ◽  
pp. 638-659
Author(s):  
Harriet B. Drage ◽  
Lukáš Laibl ◽  
Petr Budil
Keyword(s):  
Fossil Record ◽  
Postembryonic Development ◽  
Large Sample Size ◽  
Upper Ordovician ◽  
Geological Time ◽  
Fusion Event ◽  
Large Sample ◽  
Prague Basin ◽  
Suture Fusion ◽  
Insight Into

AbstractA large sample of postembryonic specimens of Dalmanitina proaeva elfrida and D. socialis from the Upper Ordovician (Sandbian to Katian) Prague Basin allows for the first reasonably complete ontogenetic sequence of Dalmanitoidea (Phacopina). The material provides an abundance of morphological information, including well-preserved marginal spines in protaspides and meraspides, and hypostome external surfaces throughout. The development of D. proaeva elfrida is unusual due to variability in timing of the first trunk articulation. This broadens our developmental understanding of Phacopina, a diverse group of phacopid trilobites, and also allows us to study the evolution of their specializations in exoskeletal molting behavior. Adult phacopines, unlike most other trilobites, had fused facial sutures. This means that rather than molting through the sutural gape mode, characterized by opening of the facial sutures and separation of the librigenae, they disarticulated the entire cephalon in Salter’s mode of molting. For other phacopine clades (Phacopoidea) the transition to Salter’s mode occurs during the meraspid period or at the onset of holaspis, and its developmental timing is intraspecifically fixed. However, owing to the large sample size, we can see that facial suture fusion likely occurred later in Dalmanitina, usually during the holaspid period, and was intraspecifically variable with holaspides of varying sizes showing unfused sutures. Further, D. proaeva elfrida specimens showed an initial librigenal–rostral plate fusion event, where the librigenae began as separate entities but appear fused with the rostral plate as one structure (the “lower cephalic unit”) from M1, and are discarded as such during molting. Dalmanitoidea is considered to represent the first phacopine divergence, occurring earliest in the fossil record. This material therefore provides insight into how linked morphologies and behaviors evolved, potentially suggesting the timing of facial suture fusion in Phacopina moved earlier during development and became more intraspecifically fixed over geological time.

scholarly journals Early fossil record of Euarthropoda and the Cambrian Explosion

2018 ◽  
Vol 115 (21) ◽  
pp. 5323-5331 ◽  
Author(s):  
Allison C. Daley ◽  
Jonathan B. Antcliffe ◽  
Harriet B. Drage ◽  
Stephen Pates
Keyword(s):  
Fossil Record ◽  
Trace Fossils ◽  
Cambrian Explosion ◽  
Burgess Shale ◽  
Crown Group ◽  
Total Group ◽  
Stem Lineage ◽  
Coherent Picture ◽  
Insight Into ◽  
Phosphate Deposits

Euarthropoda is one of the best-preserved fossil animal groups and has been the most diverse animal phylum for over 500 million years. Fossil Konservat-Lagerstätten, such as Burgess Shale-type deposits (BSTs), show the evolution of the euarthropod stem lineage during the Cambrian from 518 million years ago (Ma). The stem lineage includes nonbiomineralized groups, such as Radiodonta (e.g., Anomalocaris) that provide insight into the step-by-step construction of euarthropod morphology, including the exoskeleton, biramous limbs, segmentation, and cephalic structures. Trilobites are crown group euarthropods that appear in the fossil record at 521 Ma, before the stem lineage fossils, implying a ghost lineage that needs to be constrained. These constraints come from the trace fossil record, which show the first evidence for total group Euarthropoda (e.g., Cruziana, Rusophycus) at around 537 Ma. A deep Precambrian root to the euarthropod evolutionary lineage is disproven by a comparison of Ediacaran and Cambrian lagerstätten. BSTs from the latest Ediacaran Period (e.g., Miaohe biota, 550 Ma) are abundantly fossiliferous with algae but completely lack animals, which are also missing from other Ediacaran windows, such as phosphate deposits (e.g., Doushantuo, 560 Ma). This constrains the appearance of the euarthropod stem lineage to no older than 550 Ma. While each of the major types of fossil evidence (BSTs, trace fossils, and biomineralized preservation) have their limitations and are incomplete in different ways, when taken together they allow a coherent picture to emerge of the origin and subsequent radiation of total group Euarthropoda during the Cambrian.

scholarly journals Unusually variable paleocommunity composition in the oldest metazoan fossil assemblages

Paleobiology ◽  
2019 ◽  
Vol 45 (02) ◽  
pp. 235-245 ◽  
Author(s):  
Seth Finnegan ◽  
James G. Gehling ◽  
Mary L. Droser
Keyword(s):  
Fossil Record ◽  
Benthic Communities ◽  
Benthic Assemblages ◽  
Β Diversity ◽  
Marine Habitats ◽  
Fossil Assemblages ◽  
Early Metazoan ◽  
Insight Into ◽  
Faunal Variability ◽  
Ecological Differences

AbstractRecent excavations of Ediacaran assemblages have revealed striking bed-to-bed variation in diversity–abundance structure, offering potential insight into the ecology and taphonomy of these poorly understood early Metazoan ecosystems. Here we compare faunal variability in Ediacaran assemblages to that of younger benthic assemblages, both fossil and modern. We decompose the diversity of local assemblages into within-collection (α) and among-collection (β) components and show that β diversity in Ediacaran assemblages is unusually high relative to younger assemblages. Average between-bed ecological dissimilarities in the Phanerozoic fossil record are comparable to within-habitat dissimilarities typically observed over meter to kilometer scales in modern benthic marine habitats, but dissimilarities in Ediacaran assemblages are comparable to those typically observed over 10–100 km scales in modern habitats. We suggest that the unusually variable diversity–abundance structure of Ediacaran assemblages is due both to their preservation as near snapshots of benthic communities and to original ecological differences, in particular the paucity of motile taxa and the near lack of predation and infaunalization.

Reefs as the Centralizing Theme in an Undergraduate Invertebrate Paleontology Course

2012 ◽  
Vol 12 ◽  
pp. 21-42
Author(s):  
Constance M. Soja
Keyword(s):  
Fossil Record ◽  
Evolutionary History ◽  
Marine Invertebrate ◽  
Scientific Information ◽  
Field Trip ◽  
Mass Extinctions ◽  
Paleontological Data ◽  
San Salvador ◽  
Invertebrate Paleontology ◽  
The Impact

This course is designed so that topics in invertebrate paleontology are discussed in the context of reefs and their change through time. The goal is to help undergraduate students connect modern conservation issues with an enlightened appreciation of the fossil record. Using reefs as the centralizing theme of the course allows key concepts (invertebrate taxonomy and systematics, form and function, evolution, etc.) to be emphasized while exploring the importance of biogenic buildups—and communities that inhabited ecosystems adjacent to those “engines of evolution”—from the past to the present. Students who satisfactorily complete the course achieve seven main learning objectives: They 1) are intimately familiar with the fossil record of marine invertebrate life; 2) understand the evolutionary history of reefs and the ecological roles played by key reef-building invertebrates through time; 3) are able to engage in discussions about paleontological data published in the primary literature; 4) are knowledgeable about the value of paleontological evidence for shedding insights into the decline of ancient and living reefs; 5) gain experience working collaboratively and thinking outside-of-the-box to explore solutions to societal problems linked with the degradation of modern coral reefs; 6) improve scientific writing; and 7) develop a personal style for communicating scientific information to the general public. During classroom discussions, laboratories, a field trip, and museum visit, students explore the anatomy, ecology, evolutionary history, and life-sustaining ecosystem services of shelly animals and associated marine organisms that coexisted in reefs and adjacent habitats past and present. Evolutionary events, including the Cambrian “explosion,” mass extinctions, and gaps in reef existence, are linked to dramatic physical (tectonic) and climatic changes that occurred in Earth's past. Emphasizing evidence for the impact of global change on ancient reef communities alerts students to the value of paleontological data for predicting how modern reefs—and invertebrates living in interconnected marine ecosystems—will respond as the Sixth Extinction gains traction. That topic is the focus of an optional extended study (nine-day field trip offered in alternate years during spring break) of modern and Pleistocene reefs on San Salvador Island, Bahamas.

The first potential fossil record of a dibamid reptile (Squamata: Dibamidae): a new taxon from the early Oligocene of Central Mongolia

2019 ◽  
Vol 187 (3) ◽  
pp. 782-799 ◽  
Author(s):  
Andrej Čerňanský
Keyword(s):  
Fossil Record ◽  
Evolutionary History ◽  
Phylogenetic Analyses ◽  
New Taxon ◽  
Unique Combination ◽  
Central Mongolia ◽  
Squamate Reptiles ◽  
The Past ◽  
Early Oligocene ◽  
Fossil Material

Abstract Dibamid reptiles have a known current distribution on two continents (Asia and North America). Although this clade represents an early-diverging group in the Squamata and thus should have a long evolutionary history, no fossil record of these peculiar burrowing squamate reptiles has been documented so far. The fossil material described here comes from the early Oligocene of the Valley of Lakes in Central Mongolia. This material consists of jaws and is placed in the clade Dibamidae on the basis of its morphology, which is further confirmed by phylogenetic analyses. In spite of the fragmentary nature of this material, it thus forms the first, but putative, fossil evidence of this clade. If correctly interpreted, this material demonstrates the occurrence of Dibamidae in East Asia in the Palaeogene, indicating its distribution in higher latitudes than today. The preserved elements possess a unique combination of character states, and a new taxon name is therefore erected: Hoeckosaurus mongoliensis sp. nov. The dentary of Hoeckosaurus exhibits some characters of the two extant dibamid taxa. However, the open Meckel’s groove, together with other characters, show that this group was morphologically much more diverse in the past.

scholarly journals A comparative atlas of the skull osteology of European lizards (Reptilia: Squamata)

2019 ◽  
Vol 187 (3) ◽  
pp. 829-928 ◽  
Author(s):  
Andrea Villa ◽  
Massimo Delfino
Keyword(s):  
Fossil Record ◽  
Evolutionary History ◽  
European Species ◽  
History Of ◽  
Diagnostic Key ◽  
Single Bone ◽  
Fossil Lizards ◽  
Bone Remains ◽  
Comparative Osteology ◽  
Broad Scale

Abstract The fossil record provides evidence of a long evolutionary history of European lizards. Since fossil lizards are regularly represented by bone remains, the knowledge of the origins of extant taxa and their distribution in time and space is hindered by the fact that their comparative osteology is not yet completely and adequately known. In spite of a rising interest in this topic since the end of the 20th century, a gap in our knowledge is still evident. We here report the first broad-scale comparative osteological analysis of the skulls of extant European lizards, highlighting significant differences that can be used in identification. This comparative study, including as many European species as possible, leads to the creation of a detailed diagnostic key for each single bone. Also, our data significantly improve the recognizability of extant European non-snake squamates, with 54% of the current diversity to be recognized based on the new results contra the previously estimated 31%. This recognizability is expected to further increase in the future, with new studies focusing on species that are either missing or poorly represented here, or applying promising advanced methodologies.

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