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Bones and Fish Evolution
Bones and Fish Evolution

"Following the violent moves of tectonic plates about 1.5 billion (1.5 × 109) years ago, huge amounts of minerals, including CaCO3, were washed into the oceans. This created the possibility for its inhabitants of developing hard body parts, such as shells or spines. At first, this helped unicellular organisms to cope with excessive amounts of minerals and to prevent over-crusting. It also led to the sharp increase in the diversity of multicellular organisms (and their fossils!) a little more than 0.5 billion years ago, known as the “Cambrian explosion” (Schopf 1994, Kawasaki et al. 2004). Furthermore, the appearance of a rigid outside skeleton extended the effective length of limbs, thus permitting more rapid locomotion in many organisms. The appearance of mineralized body parts is seen by many scientists as one of the forces that generally increased the pace of animal evolution (Kumar and Hedges 1998, Kutschera and Niklas 2004)."

"The earliest skeleton in the vertebrate lineage was a non-collagen-based unmineralized cartilaginous endoskeleton. It was associated mostly with the pharynx, in taxa such as lancelets, lampreys, and hagfish . After the evolution of collagen II from earlier simple collagens, a collagen-based cartilage could form. In contrast to animals with completely non-collagenous skeletons, some of the primitive chondrichthyans (such as sharks) were able to form skeletal parts though the process of endochondral ossification; however, due to the lack of fossil record s, the exact time of origin and the extent to which this mechanism was used is unclear (Hall 2005 and references therein)."

"In addition to delivering bone as an organ, endochondral ossification provided a structural support for vertebrate limb development. However, there is still debate and uncertainty concerning the transition from fish fins to vertebrate limbs. Did limbs first develop in aquatic animals, thus predisposing them to walk on land? Did digits appear in the water, or do they represent an adaptation to terrestrial environments? What was the original number of digits? The pair of limbs that came first, and also many details about their embryonic development are awaiting more definite answers (Hell 2005, and references therein). A recent study suggested that it is mostly the loss of the actinodin gene family (this family encodes proteins making up the rigid fibers of fins) which might explain how fish evolved into four-limbed vertebrates (Zhang et al. 2010). These authors' genetic experiments on zebrafish showed that it was probably a loss of only a small number of genes that acted as a creative force in evolution, accounting for the huge evolutionary transition from fins to limbs.

With the advent of terrestrial vertebrates, skeletal function expanded in new directions. Although bone was still a reservoir of calcium and phosphorus, and acted as a shield for vulnerable body parts, it also began to serve as a site of blood cell production, and allowed movement and mechanical support."
- Where did bone come from? An overview of its evolution; Darja Obradovic Wagner and Per Aspenberg
Acta Orthop. 2011 Aug; 82(4): 393–398. Published online 2011 Sep 2. doi: 10.3109/17453674.2011.588861

http://www.senckenberg.de/files/content/forschung/publikationen/vertebratezoology/vz62-2/02_vertebrate_zoology_62-2_costa_161-180.pdf

The caudal skeleton of extant and fossil cyprinodontiform fishes (Teleostei: Atherinomorpha): comparative morphology and delimitation of phylogenetic characters

The caudal skeleton of teleost fishes of the order Cyprinodontiformes is described and compared on the basis of 394 extant and eight fossil species, supporting delimitation of 21 phylogenetic characters, of which 13 are firstly reported. The Cyprinodontiformes are unambiguously diagnosed by the presence of a single, blade-like epural, and by principal caudal-fin rays continuous on upper and lower hypural plates. Monophyly of the suborder Cyprinodontoidei is supported by the widened neural and hemal spines of the preural centrum 3 and presence of a spine-like process on the stegural, and monophyly of the Aplocheiloidei by the absence of radial caudal cartilages. A keel-shaped lateral process on the compound centrum supports monophyly of the Nothobranchiidae. Some characters of the caudal skeleton in combination to other osteological features indicate the cyprinodontiform fossil genus †Prolebias to be a paraphyletic assemblage; †P. aymardi, †P. delphinensis and †P. stenoura, the type species of the genus, all from the Lower Oligocene of Europe, possibly are closely related to recent valenciids; †“P.” meridionalis from the Upper Oligocene of France is an incertae sedis cyprinodontid; and, †“P”. cephalotes, †“P”. egeranus and †“P”. malzi from the Upper Oligocene-Lower Miocene of Europe are closely related to poeciliids, probably closely related to the recent African genus Pantanodon due to they sharing unique derived features of pelvic fin, branchial arches and jaws.


Phylogenetic reorganization of Cyprinodontiform fishes

"Within the Cyprinodontiforms, fusion of the hypural plates into a so-called hypural fan (following the terminology of Rosen, 1964) occurs within several monophyletic groups of genera (e.g., fig. 2F). There is just one epural which mirrors in shape and position the autogenous parhypural. There are no separate ural centra. The hypochordal musculature is also absent (Rosen, 1964). This formation of a symmetrical caudal fin in unique among teleost fishes." (Emph. mine - RJS)


Evolution's Mirror in a Fish's Spines

"Kingsley and his colleagues found such an animal in the threespine stickleback fish. These small fish typically live in the ocean but breed in coastal streams. After the last ice age ended some 11,000 years ago, populations of sticklebacks rapidly colonized newly formed freshwater streams and lakes - through a process known as adaptive radiation.

The many stickleback populations underwent disparate and parallel evolutionary changes, among them partial or complete loss of their pelvic spines. These spines are thought to protect the fish from being devoured by predators. As Kingsley points out, however, pelvic spines may be a disadvantage if the fish live in environments that have very low calcium levels available for building the skeletal structures, or in locations with many large predatory insects that hunt sticklebacks by grabbing hold of the spines. “Although vastly different morphologies have evolved in different stickleback populations, they have evolved recently enough that you can still take those different populations, cross them and actually let the genetics of the trait guide you to the underlying events that have controlled the process,” said Kingsley."


Development of the caudal-fin skeleton reveals multiple convergent fusions within Atherinomorpha

Abstract

Background
The caudal fin of teleosts is a highly diverse morphological structure and a valuable source of information for comparative analyses. Within the Atherinomorpha a high variation of conditions of the caudal-fin skeleton can be found. These range from complex but basal configurations to simple yet derived configurations. When comparing atherinomorph taxa, it is often difficult to decide on the homology of skeletal elements if only considering adult specimens. However, observing the development of caudal-fin skeletons allows one to evaluate complex structures, reveal homologies and developmental patterns, and even reconstruct the grundplan of the examined taxa.

Results
We studied the development of the caudal-fin skeleton in different atheriniform, beloniform and cyprinodontiform species using cleared and stained specimens. Subsequently we compared the development to find similarities and differences in terms of 1) which structures are formed and 2) which structures fuse during ontogeny. For many structures, i.e., the parhypural, the epural(s), the haemal and neural spines of the preural centra and the uroneural, there were either no or only minor differences visible between the three taxa. However, the development of the hypurals revealed a high variation of fusions within different taxa that partly occurred independently in atheriniforms, beloniforms and cyprinodontiforms. Moreover, comparing the development of the ural centra exposed two ways of formation of the compound centrum: 1) in atheriniforms and the beloniforms Oryzias and Hyporhamphus limbatus two ural centra develop and fuse during ontogeny while 2) in cyprinodontiforms and Exocoetidae (Beloniformes) only a single ural centrum is formed during ontogeny.

Conclusions
We were able to reconstruct the grundplan of the developmental pattern of the caudal-fin skeleton of the Atheriniformes, Beloniformes and Cyprinodontiformes as well as their last common ancestors. We found two developmental modes of the compound centrum within the Atherinomorpha, i.e., the fusion of two developing ural centra in atheriniforms and beloniforms and the development of only one ural centrum in cyprinodontiforms. Further differences and similarities for the examined taxa are discussed, resulting in the hypothesis that the caudal-fin development of a last common ancestor to all atherinomorphs is very much similar to that of extant atheriniforms.


https://www.scielo.br/j/ni/a/qTGmfmg3dM3MK758jKgd8xy/?format=pdf&lang=en

Towards a complete classification of the Neotropical thorny catfishes (Siluriformes: Doradidae)

Mark Henry Sabaj and Mariangeles Arce H.

We propose a revised classification of Doradidae based on phylogenetic analyses of sequence data for one nuclear (rag1) and two mitochondrial (co1, 16s) genes, and corroborated by caudal-fin morphology. The molecular dataset comprises 174 doradid specimens representing all 31 valid genera, 83 of the 96 valid extant species and 17 species-level taxa that remain undescribed or nominally unassigned. Parsimony and Bayesian analyses of molecular data support six major lineages of doradids assigned here to three nominal subfamilies (Astrodoradinae, Doradinae, Wertheimerinae) and three new ones (Acanthodoradinae, Agamyxinae, Rhinodoradinae). The maximum parsimony topology of Doradidae was sensitive to ingroup density and outgroup age. With the exceptions of Astrodoradinae and Doradinae, each subfamily is diagnosed by caudal-fin characteristics. The highest degree of fusion among skeletal elements supporting the caudal fin is observed in Acanthodoradinae and Aspredinidae, lineages that are sister to the remaining doradids and aspredinoids (i.e., Auchenipteridae + Doradidae), respectively. Fusion among caudal-fin elements tends to be higher in taxa with rounded, truncate or emarginate tails and such taxa typically occupy shallow, lentic habitats with ample structure. Caudal-fin elements are more separated in taxa with moderately to deeply forked tails that occupy lotic habitats in medium to large river channels




Costa2015: The caudal skeleton of extant and fossil cyprinodontiform fishes (Teleostei: Atherinomorpha): comparative morphology and delimitation of phylogenetic characters
http://www.senckenberg.de/files/content/forschung/publikationen/vertebratezoology/vz62-2/02_vertebrate_zoology_62-2_costa_161-180.pdf


Parenti 1991: Phylogenetic reorganization of Cyprinodontiform fishes
http://info.killi.palo-alto.ca.us/ref/taxonomy/Parenti/1981/parenti_1981_AMNH.pdf


hhmi2004: Evolution's Mirror in a Fish's Spines
http://www.hhmi.org/news/evolutions-mirror-fishs-spines


2021 Thieme: Development of the caudal-fin skeleton reveals multiple convergent fusions within Atherinomorpha
https://frontiersinzoology.biomedcentral.com/articles/10.1186/s12983-021-00408-x


2021 Sabaj: Towards a complete classification of the Neotropical thorny catfishes (Siluriformes: Doradidae)
https://www.scielo.br/j/ni/a/qTGmfmg3dM3MK758jKgd8xy/?format=pdf&lang=en








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