Biology and Management of Dogfish Sharks

2009 ◽  
Keyword(s):  
Deep Water ◽  
Fossil Record ◽  
Skeletal Remains ◽  
Phylogenetic Hypothesis ◽  
Population Crisis ◽  
Root Face ◽  
Hypothetical Ancestor ◽  
Careful Management ◽  
Fin Spines

Abstract.—Squaliform sharks constitute a monophyletic group of predominantly deep-water neoselachians. Their fossil record mainly consists of isolated teeth; complete skeletons or skeletal remains are very rare. The quality of the fossil record of squaliform sharks is analyzed using a phylogenetic hypothesis based on a supertree to establish the timing of cladogenetic events, those related to descent from a common ancestor, and gaps in the fossil record. The supertree is the most inclusive estimate of squaliform interrelationships that has been proposed to date and contains 23 fossil and extant members of all major groups. In addition, the simple completeness metric is used to examine the quality of the fossil record of squaliforms as an independent measure. Although different (48% and 61%, respectively), both measures indicate that the fossil record of squaliforms is very incomplete considering that most living and extinct squaliforms are deep-water sharks and corresponding sediments are very scarce. Gaps in the fossil record range from 5 to 100 million years. The most basal and stratigraphically oldest group within Squaliformes consists of <em>Squalus </em>and †<em>Protosqualus</em><sup>1</sup><em>. </em>The phylogenetic hypothesis indicates a gap in the fossil record of <em>Squalus </em>spp. of about 25–30 million years. Our results show a postJurassic origination of squaliforms in the shallow waters of the northern Tethyal margin. The hypothetical ancestor of squaliforms is characterized by two dorsal fin spines and absence of dignathic heterodonty (the morphology of upper and lower teeth differs significantly). Lower teeth are characterized by a slightly oblique basal root face and overlapping upper teeth. Although disappearance and appearance of organisms is a fact of life, the very long geologic range and success of <em>Squalus </em>highlights the need for very careful management of its current population crisis, which is due to causes that never occurred before in Earth’s history–the anthropogenetic impact.

REVISITING THE QUALITY OF CALIFORNIA'S FOSSIL RECORD

2020 ◽  
Author(s):  
Austin J.W. Hendy ◽  
◽  
Shawn Wiedrick
Keyword(s):  
Fossil Record

The Fossil Record of the Pancrustacea

2020 ◽  
pp. 21-52 ◽  
Author(s):  
Thomas A. Hegna ◽  
Javier Luque ◽  
Joanna M. Wolfe
Keyword(s):  
Fossil Record ◽  
Hydrothermal Vents ◽  
Molecular Phylogenetics ◽  
Imaging Techniques ◽  
Extant Species ◽  
Evolutionary Studies ◽  
Molecular Phylogenetic ◽  
Terrestrial Habitats ◽  
Molecular Phylogenetic Data

Fossils are critically important for evolutionary studies as they provide the link between geological ages and the phylogeny of life. The Pancrustacea are an incredibly diverse clade, representing over 800,000 described extant species, encompassing a variety of familiar and unfamiliar forms, such as ostracods, tongue worms, crabs, lobsters, shrimps, copepods, barnacles, branchiopods, remipedes, and insects. Having colonized nearly every environment on Earth, from hydrothermal vents to terrestrial habitats, they have a diverse fossil record dating back to the Cambrian (540–485 Ma). The quality of the fossil record of each clade is variable and related to their lifestyle (e.g., free-living versus parasitic, benthic versus pelagic) and the degree of mineralization of their cuticle. We review the systematics, morphology, preservation, and paleoecology of pancrustacean fossils; each major clade is discussed in turn, and, where possible, fossil systematics are compared with more recent data from molecular phylogenetics. We show that the three epic clades of the Pancrustacea—Allotriocarida, Multicrustacea, and Oligostraca—all have Cambrian roots, but the diversification of those clades did not take place until the Middle and Late Paleozoic. We also address the potential affinities of three “problematic” clades: euthycarcinoids, thylacocephalans, and cyclids. We conclude by assessing the future of pancrustacean paleobiology, discussing new morphological imaging techniques and further integration with growing molecular phylogenetic data.

Second-Order Sequence Stratigraphic Controls on the Quality of the Fossil Record at an Active Margin: New Zealand Eocene to Recent Shelf Molluscs

Palaios ◽  
2006 ◽  
Vol 21 (1) ◽  
pp. 86-105 ◽  
Author(s):  
J. S. CRAMPTON ◽  
M. FOOTE ◽  
A. G. BEU ◽  
R. A. COOPER ◽  
I. MATCHAM ◽  
...  
Keyword(s):  
New Zealand ◽  
Fossil Record ◽  
Second Order ◽  
Active Margin ◽  
Sequence Stratigraphic ◽  
Order Sequence

scholarly journals Sporadic sampling, not climatic forcing, drives observed early hominin diversity

2018 ◽  
Vol 115 (19) ◽  
pp. 4891-4896 ◽  
Author(s):  
Simon J. Maxwell ◽  
Philip J. Hopley ◽  
Paul Upchurch ◽  
Christophe Soligo
Keyword(s):  
Fossil Record ◽  
Detailed Examination ◽  
Hominin Evolution ◽  
Rock Exposure ◽  
Early Hominin ◽  
Positive Correlations ◽  
Taxic Diversity ◽  
Diversity Estimates

The role of climate change in the origin and diversification of early hominins is hotly debated. Most accounts of early hominin evolution link observed fluctuations in species diversity to directional shifts in climate or periods of intense climatic instability. None of these hypotheses, however, have tested whether observed diversity patterns are distorted by variation in the quality of the hominin fossil record. Here, we present a detailed examination of early hominin diversity dynamics, including both taxic and phylogenetically corrected diversity estimates. Unlike past studies, we compare these estimates to sampling metrics for rock availability (hominin-, primate-, and mammal-bearing formations) and collection effort, to assess the geological and anthropogenic controls on the sampling of the early hominin fossil record. Taxic diversity, primate-bearing formations, and collection effort show strong positive correlations, demonstrating that observed patterns of early hominin taxic diversity can be explained by temporal heterogeneity in fossil sampling rather than genuine evolutionary processes. Peak taxic diversity at 1.9 million years ago (Ma) is a sampling artifact, reflecting merely maximal rock availability and collection effort. In contrast, phylogenetic diversity estimates imply peak diversity at 2.4 Ma and show little relation to sampling metrics. We find that apparent relationships between early hominin diversity and indicators of climatic instability are, in fact, driven largely by variation in suitable rock exposure and collection effort. Our results suggest that significant improvements in the quality of the fossil record are required before the role of climate in hominin evolution can be reliably determined.

scholarly journals The early elasmobranch Phoebodus : phylogenetic relationships, ecomorphology and a new time-scale for shark evolution

2019 ◽  
Vol 286 (1912) ◽  
pp. 20191336 ◽  
Author(s):  
Linda Frey ◽  
Michael Coates ◽  
Michał Ginter ◽  
Vachik Hairapetian ◽  
Martin Rücklin ◽  
...  
Keyword(s):  
Phylogenetic Analysis ◽  
Time Scale ◽  
Body Shape ◽  
Skeletal Remains ◽  
Late Devonian ◽  
Crown Group ◽  
Anatomical Knowledge ◽  
Close Relationship ◽  
Stem Lineage ◽  
Fin Spines

Anatomical knowledge of early chondrichthyans and estimates of their phylogeny are improving, but many taxa are still known only from microremains. The nearly cosmopolitan and regionally abundant Devonian genus Phoebodus has long been known solely from isolated teeth and fin spines. Here, we report the first skeletal remains of Phoebodus from the Famennian (Late Devonian) of the Maïder region of Morocco, revealing an anguilliform body, specialized braincase, hyoid arch, elongate jaws and rostrum, complementing its characteristic dentition and ctenacanth fin spines preceding both dorsal fins. Several of these features corroborate a likely close relationship with the Carboniferous species Thrinacodus gracia , and phylogenetic analysis places both taxa securely as members of the elasmobranch stem lineage. Identified as such, phoebodont teeth provide a plausible marker for range extension of the elasmobranchs into the Middle Devonian, thus providing a new minimum date for the origin of the chondrichthyan crown-group. Among pre-Carboniferous jawed vertebrates, the anguilliform body shape of Phoebodus is unprecedented, and its specialized anatomy is, in several respects, most easily compared with the modern frilled shark Chlamydoselachus . These results add greatly to the morphological, and by implication ecological, disparity of the earliest elasmobranchs.

On the ancestry of woodrats

2019 ◽  
Vol 100 (5) ◽  
pp. 1564-1582 ◽  
Author(s):  
Robert A Martin ◽  
Richard J Zakrzewski
Keyword(s):  
New Species ◽  
Fossil Record ◽  
Coniferous Forests ◽  
Phylogenetic Hypothesis ◽  
Western Mexico ◽  
Lower Elevation ◽  
Two New Species ◽  
Fourth Root ◽  
Extinct Genus ◽  
Coniferous Ecosystems

Abstract We evaluated the fossil record of extinct and extant woodrats, and generated a comprehensive phylogenetic hypothesis of woodrat origins and relationships based on these data. The galushamyinin cricetines are redefined and reclassified as a subtribe of the Neotomini, including Repomys, Miotomodon, Galushamys, Nelsonia, and a new extinct genus with two new species. The geographic distribution of Nelsonia, restricted to montane coniferous forests of western Mexico, suggests that this subtribe was mostly confined to western coniferous ecosystems or similar ecosystems at lower elevation during glacial advances. A second subtribe of the Neotomini includes a new archaic genus and species, Neotoma, Hodomys, and Xenomys. Lindsaymys, a possible neotominin from the late Clarendonian (late Miocene) of California, demonstrates an occlusal morphology consistent with ancestry for the Neotomini, but the presence of a fourth root on M1 is problematic and may preclude the known populations from filling that role. Molars identified as Neotoma sp. from the Hemphillian (latest Miocene or early Pliocene) Rancho el Ocote assemblage of Guanajuato, Mexico, may represent the earliest Xenomys. Extant Neotoma species with a bilobed m3 appear to have originated subsequent to about 2.0 Ma, whereas Hodomys alleni and Xenomys nelsoni likely originated earlier from one or more extinct ancestors with an S-shaped m3.

scholarly journals A mid-Cretaceous enantiornithine foot and tail feather preserved in Burmese amber

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Lida Xing ◽  
Ryan C. McKellar ◽  
Jingmai K. O’Connor ◽  
Kecheng Niu ◽  
Huijuan Mai
Keyword(s):  
Fossil Record ◽  
Skin Surface ◽  
Skeletal Remains ◽  
Tail Feather ◽  
Burmese Amber ◽  
Morphological Disparity

Abstract Since the first skeletal remains of avians preserved in amber were described in 2016, new avian remains trapped in Cretaceous-age Burmese amber continue to be uncovered, revealing a diversity of skeletal and feather morphologies observed nowhere else in the Mesozoic fossil record. Here we describe a foot with digital proportions unlike any previously described enantiornithine or Mesozoic bird. No bones are preserved in the new specimen but the outline of the foot is recorded in a detailed skin surface, which is surrounded by feather inclusions including a partial rachis-dominated feather. Pedal proportions and plumage support identification as an enantiornithine, but unlike previous discoveries the toes are stout with transversely elongated digital pads, and the outer toe appears strongly thickened relative to the inner two digits. The new specimen increases the known diversity and morphological disparity among the Enantiornithes, hinting at a wider range of habitats and behaviours. It also suggests that the Burmese amber avifauna was distinct from other Mesozoic assemblages, with amber entrapment including representatives from unusual small forms.

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