Florida Museum of Natural History

Abstracts of AES Scientific Papers

American Elasmobranch Society 1999 Annual Meeting
State College, Pennsylvania
ABSTRACTS - Part 2: Gash through Lund
*Gash, Thomas A., MacKenzie, Duncan S., Manire, Charles A.

(TAG, DSM) Departmant of Biology, Texas A&M University, College Station, TX 77843; (CAM) Center for Shark Research, Mote Marine Laboratory, Mote Marine Laboratory, Center for Shark Research, Sarasota, FL 34236

Seasonal changes in thyroid hormones in the bonnethead shark Sphyrna tiburo.

Studies among vertebrates suggest that thyroid hormones may influence, or be influenced by, the reproductive cycle. Whereas the reproductive cycle in bonnethead shark populations along the southwest coast of Florida has been described, the relationship of thyroid function to reproduction has not been characterized in this species. To determine if thyroid hormone production is activated during periods of spermatogenesis, vitellogenesis, and gestation, circulating thyroxine (T) and 3,5,3,-triiodothyronine (T) were measured in serum samples collected during discrete phases of reproduction in two southwest Florida populations. Results showed that both these populations exhibited a bimodal annual cycle in serum T levels ranging from mean levels of 2 to 12 ng/ml, with peaks during the spring and again in the fall. In contrast, T levels were not detectable. Seasonal changes in T levels did not differ between mature and immature sharks, between males and females, or between the two populations sampled. These results suggest that seasonal changes in circulating T are not directly related to reproductive condition, but may correlate instead with temperature-related feeding or migration.

*Gelsleichter, Jim, Musick, John A.

(JG) Center for Shark Research, Mote Marine Laboratory, Sarasota, FL 34236; (JAM) Virginia Institute of Marine Science, The College of William and Mary, VA 23062

The production of seasonal increments in the vertebral cartilage of the clearnose skate,  Raja eglanteria : Changes in cartilage growth or mineralization?

Seasonal increments present in the vertebral cartilage of most elasmobranchs are commonly used to determine age and growth rate in these fishes. However, the physiological process(es) that gives rise to these structural phenomena are poorly understood. The goal of this study was to determine if increments present in the vertebrae of the clearnose skate,  Raja eglanteria  were a consequence of seasonal changes in cartilage growth or mineralization. Changes in the appositional growth of vertebral cartilage were examined by histologic and histochemical observations. Patterns of vertebral mineralization were investigated by energy-dispersive spectrophotometry (EDS). Visible differences in matrix synthesis and cellular activity of vertebral cartilage were apparent, and indicated that growth of the vertebral margin was greatest during late spring to early fall. However, there appeared to be no changes in cartilage mineralization associated with season. In fact, concentrations of calcium and phosphorus appeared to be relatively stable throughout the entire vertebral cartilage. Additional observations using scanning electron microscopy, coupled with these studies, demonstrate that seasonal vertebral increments are directly related to changes in cartilage growth, and that differences in mineral concentration appear secondary to regional cell concentrations. 

González-García, Jeanette

Instituto de Ecología, A.C., Xalapa, Veracruz 91000 México

Phylogenetic relationships among the hammerhead sharks (Chondrichthyes: Carcharhiniformes: Sphyrnidae)

The hammerhead sharks are poorly know species that inhabits coastal and all oceanic waters. The unusual lateral expansion of the head or cephalofoil, is the diagnostic feature of the family. Previous phylogenetic analysis of morphology between these sharks ordered taxa according to the absolute degree of cephalofoil lateral expansion (small cephalofoil = ancestral taxa; exaggerated cephalofoil= derived taxa), this hypothesis suggests directional selection for the lateral expansion character. Phylogenetic analysis of the DNA data provided support for to claim that hammerheads constitute a monophyletic group, but that the evolution of cephalofoil was contrary to the generaly accepted hypothesis. For this reason this study research the sphyrnids interspecific relationships based on based about morphology and morphometry chondrocranium characters. The description of ontogenetic and morphological variation among species propose an hypothesis to explain the presence and different cephalofoil shapes in the hammerhead sharks. The technique of phylogeny reconstruction (cladistic method) was carried out by the maximum parsimony method (PAUP 3.1.1). The results shows phylogenetic evidence for to eliminatee the division hierarchy of genus  Eusphyra  and subgenus of  Sphyrna . The variation among specimens of the same specie is discussed from morphometric view, because certain modifications in shape of the head of sphyrnids can to provide ontogenetic transformational series. 

*Gonzalez-García, Jeanette , Villavicencio-Garayzar, Carlos, Balart-Páez, Eduardo

(JG) Instituto de Ecología, A.C., Xalapa, Veracruz 91000 México; (CV) Km. 2.5 Carretera al Sur, La Paz, Universidad Autónoma de Baja California Sur, La Paz, Baja California Sur 23000 Mexico; (EB) Carretera a San Juan de la Costa ìEl Comitanî, A.P. 128, Centro de Investigaciones Biológicas del Noroeste, La Paz, Baja California Sur 23000 México

Morphological and osteological features in the embryonic development of  Rhinobatos productus  (Girard, 1854) (Chondrichthyes:Rajiformes:Rhinobatidae)

Embryonic development of the guitarfish  Rhinobatos productus  is described in detail based on a complete series of embryos from 5.6 to 200 mm TL (total length). A total of 494 specimens were collected from Almejas bay in the west coast of Baja California and others two fisheries centers in the middle region of the Gulf of California. The development of  Rhinobatos productus  is defined by a suite of morphological characters in addition to total length including the size and shape of paired and unpaired fins, the disc wide and cephalic characters. Particular attention is given to features of the branchial arches and external branchial filaments. Apparently the embryos utilize histotrophic nutrition in the early development.

Embryological development of  Rhinobatos productus  is similar to that described previously for elasmobranchs taxa. These include sharks such as the spiny dogfish,  Squalus acanthias, and other rhinobatids closely related including R. horkelii, R. hynnicephalus  and R. halavi . The external features of these specimens, in comparison with other chondrichthyans embryos, are proposed to stablish the embryonic development of Rhinobatidae. This study provides information on  Rhinobatos productus  embryonic development, determines the morphological, morphometric and osteological changes in the embryonic development and shows the relationships between corporal proportions and growth during the development of this specie.

*Grogan, Eileen D., Lund, Richard

(EDG) Biology Department, Saint Joseph's University, Philadelphia, PA 19131; (RL) Department of Biology, Adelphi University, Garden City, NY 11530

Re-examination of  Helodus simplex  and the relationships of Carboniferous Euchondrocephalans.

Cranial morphological analyses of Paleozoic Chondrichthyes suggests division of the Class into two discrete units, elasmobranchs and euchondrocephalans (paraselachians + holocephalimorphs). The previous interpretations of the skull of Helodus have been the subject of much debate and are inconsistent with the data for all known Paleozoic chondrichthyan cranial types. Our re-interpretation of Helodus' cranium is presented. The dorsally flaring orbitonasalis identified by Moy-Thomas is shown to be internal, not superficial. Further, the ethmoidal region is completely roofed over, in a manner consistent with all other euchondrocephalans. The shape and dimensions of the cranium approximate that of iniopterygians. These analyses result in a logical placement of Helodus within the euchondrocephalans, at or near the base of the Holocephalimorpha. 

*Grogan, Eileen D., Yucha, David T.

Saint Joseph's University, Philadelphia, PA 19131

Endoskeletal Mineralization in  Squalus : types, development, and evolutionary implications.

Research on the structure and composition of  Squalus acanthias  calcified cartilage demonstrates the existence of at least three modes of endoskeletal mineralization; tesserate cap, tesserate body, and notochordal areolar. Globular (spheritic) and prismatic forms of calcification have been confirmed as the same type of mineralization and merely represent different developmental stages. Areolar mineralization, by comparison, is radically different in structure, development and chemical composition. It does not involve hyaline cartilage, but arises through direct mineralization of a centrum comprised of circumferentially arranged fibroblastic cells. Select morphological and chemical characteristics of areolar mineralizations reveal greater similarities to bone than to the calcified cartilage of terrestrial vertebrates. This, and the differential staining of the tesserae cap compared to that of the body, indicate that selachian calcified cartilage exhibits features of both endochondral and intramembranous bone. Such data suggests reconsideration of the popular paradigms for mineralized tissue development and the phylogenetic relationship of selachian calcified cartilage to the mineralized tissues of the higher vertebrate classes. 

*Haenni, Eric G., Wourms, John P., Manire, Charles A., Hueter, Robert E.

(EGH, JPW) Department of Biological Sciences, Clemson University, Clemson, SC 29634; (CAM, REH) Mote Marine Laboratory, Sarasota, FL 34236

Embryological development of the cephalofoil in the bonnethead shark,  Sphyrna tiburo .

Selected embryological stages of the bonnethead shark,  Sphyrna tiburo, were examined to analyze the development of a unique morphological modification of the head that is characteristic of the sphyrnid sharks. Lateral expansion of the head, accompanied by flattening along the dorsal-ventral axis of the expansions, produces a morphological modification known as a cephalofoil. Specimens, representative of stages from early embryogenesis through parturition, were examined using macrophotography, light microscopy and electron microscopy. Measurements were made of the width of the entire cephalofoil, the length of the right and left lateral extensions, and the total fork length of each embryo. Changes in chondrocranium morphology, elongation of the optic nerve, expansion of the olfactory sacs, and general neural development were also characterized. Based on our observations, the morphogenetic events that produce the unique bonnethead cephalofoil are initiated early in embryonic development. Thus, the major morphological modifications of the head are established relatively early in development, whereas the middle and late phases of development involve growth of the cephalofoil relative to growth of the body. 

*Heist, Edward J., Gold, John R.

(EJH) Department of Zoology, Southern Illinois University Carbondale, Carbondale, IL 62901; (JRG) Center for Biosystematics and Biodiversity, Texas A&M University, College Station, TX 23062

DNA Microsatellite abundance, allelic diversity, and cross-species amplification in three sharks.

Subgenomic DNA libraries were prepared and screened for di-, tri-, and tetranucleotide repeat motifs in three sharks: sandbar shark  Carcharhinus plumbeus, blacktip shark  C. limbatus  and shortfin mako  Isurus oxyrinchus . DNA sequences from positive clones were used to identify and characterize microsatellite repeat motifs. PCR primers were developed and used to amplify loci and screen for allelic diversity within and among putative populations of each species. Amplification of loci in species other than those from which the loci were identified was attempted with some success. Compared to similar studies in other vertebrate taxa, microsatellite loci are relatively scarce in sandbar and blacktip sharks and only slightly more frequent in shortfin mako. Low frequencies of microsatellites occurs in the presence of large genome sizes, ranging from 5.9 to 8.5 picograms DNA per diploid nucleus as determined from flow cytometry and from published reports. Many loci averaged fewer than ten uninterrupted repeats per microsatellite motif. There is a positive correlation between the number of uninterrupted repeats per microsatellite motif and allelic diversity in microsatellite loci in sharks. 

*Henningsen, Alan D., Trant, John M., Place, Allen R.

(ADH) The National Aquarium in Baltimore, Biological Programs, Baltimore, MD 21202; (JMT, ARP) Univ. of Maryland Biotechnology Institute, Center of Marine Biotechnology, University of Maryland, Baltimore, MD 21202

Preliminary results on the size of proteins and protein concentration in histotroph from three species of batoids.

Myliobatoid rays reproduce via aplacental viviparity. Uterine milk ,or histotroph, produced by uterine villi (trophonemata) is the sole source of embryonic nutrition once the yolk supply is exhausted through parturition. Previous studies have documented that protein is a major component of histotroph. To determine protein size and concentration, we collected histotroph from three species of myliobatoid rays: the southern stingray,  Dasyatis americana, the cownose ray  Rhinoptera bonasus, and the yellow ray  Urolophus jamaicensis . Preliminary results on the size and concentration of proteins in histotroph were obtained in all three species. Histotroph and serum collected from a gravid southern stingray on day 54 of a 138 day gestation were analyzed via gel filtration, SDS-PAGE, and protein assay. The predominant protein was ~55-61 KDa from both histotroph and serum. Fractions collected off the gel filtration column yielded a protein concentration of 39.1 mg/ml in the histotroph. SDS-PAGE of histotroph from all three species indicated the relative sizes of the predominant protein to be ~55-61, 64.6, and 53.5-64 KDa for the southern, yellow, and cownose ray, respectively. The protein concentrations in the histotroph from the three species were 20.6, 1.2, and 80.0 mg/ml, for the southern, yellow, and cownose ray, respectively. 

*Heupel, Michelle R., Bennett, Michael B.

(MRH) Mote Marine Laboratory, Center for Shark Research, Sarasota, FL 34236; (MBB) Dept. of Anatomical Sciences, University of Queensland, St. Lucia, Queensland 4072 Australia

Aspects of the life history of epaulette sharks,  Hemiscyllium ocellatum  on Heron Island Reef, Great Barrier Reef, Australia

The population of  Hemiscyllium ocellatum  on Heron Island Reef, Great Barrier Reef, Australia was examined over a three year period. The abundance of  H. ocellatum  on a 0.25 km2 site on the reef flat was examined by conducting a tag-recapture study. A total of 494 sharks were tagged during 11 sampling trips from July 1994 to August 1997. The interval between initial release and recapture of sharks ranged from 1 - 725 days. The overall recapture rate was 22% with an estimated 3% tag loss. Recaptured sharks appeared to move randomly within the study site, and distances between initial release site and recapture site ranged from 0 - 329 m. There was no obvious site attachment. Estimates of animal abundance using the Jolly-Seber method gave a range of 93 - 1359 sharks during the study period. The Peterson and Fisher-Ford methods provided ranges of 320 - 3298 and 200 - 2190 respectively. Catch per unit effort and captive observations showed  H. ocellatum  were most active at dusk/dawn hours and during night low tides. Activity patterns coincided with prey activity periods. Sharks were found to consume polychaete worms and crustaceans. 

*Heupel, Michelle R., Manire, Charles A., Simpfendorfer, Colin A., Bennett, Michael B.

(MRH, CAM) Mote Marine Laboratory, Center for Shark Research, Sarasota, FL 34236; (CAS) Fisheries Western Australia, North Beach, Western Australia 6020 Australia; (MBB) Department of Anatomical Sciences, University of Queensland, St. Lucia, Queensland 4072 Australia

Spinal deformities in elasmobranchs

Three shark species from Australian waters, and two species from North American waters, were found with skeletal deformities. Three epaulette sharks,  Hemiscyllium ocellatum, one gummy shark,  Mustelus antarcticus, one whiskery shark,  Furgaleus macki, one bull shark,  Carcharhinus leucas  and two bonnethead sharks,  Sphyrna tiburo  were all found with similar spinal curvatures. Spinal curves consisted of large scoliotic (lateral spinal curvature), lordotic (axial spinal curvature) and kyphotic (humpback curve) bends of the vertebral column. Possible causes of these deformities are currently unknown, but may include asymmetrical stresses to the vertebral column, parasites, arthritis, injury, disease, localized tumors or malnutrition. However, all species show similar curvatures along the vertebral column, suggesting the cause of the deformity is uniform across multiple families and geographic areas. 

*Hilkemann, Brenda A., Stanhope, Michael J., Shivji, Mahmood S.

(BAH, MSS) Oceanographic Center, Nova Southeastern University, Dania, FL 33004; (MJS) Biology and Biochemistry, The Queen's University, Belfast, Northern Ireland BT9 7BL UK

Comparative structure and evolution of mitochondrial genome control region in sharks

The control region is the main non-coding region of vertebrate mitochondrial (mt) DNA, and contains the major regulatory elements controlling replication and transcription of this genome. In many vertebrates, the control region appears to be the fastest evolving locus in the mt genome, and portions of this locus are often used in population and phylogenetics studies. The control region has most extensively been studied in mammals, where it is partitioned into three domains: the two peripheral, highly variable domains I and III, and a central conserved domain II. To better understand the organization and evolutionary dynamics of this locus in vertebrates, we have performed a comparative analysis of control regions from divergent sharks with the mammalian control region. Our analysis reveals an overall similarity in the structure of the control region between sharks and mammals, and identifies several shared conserved elements (TAS, CSBs1-3). Like mammals, variability in shark control regions occurs mainly in peripheral domains I and III, with the central domain II exhibiting significant conservation among species. Domain II from sixteen globally distributed blue sharks reveals no sequence variation. The overall similarity in control region structure between sharks and mammals suggests strong functional constraints control evolution of this locus in vertebrates. 

Hubbell, Gordon L.

Jaws International, Key Biscayne, FL 33149

Comparing the dentition of the extant white shark with the fossil megatooth shark,  Carcharocles megalodon 

Descriptions of fossil species of sharks are often based upon comparisons with living species. Since the cartilaginous skeletons of sharks do not fossilize well, our deductions are often limited to the examination of fossil shark teeth. This is especially true for Tertiary sharks where whole or partially preserved specimens are very few. It is difficult to identify the more recent fossil sharks and to establish relationships to other species, both living and extinct. Although fossil shark teeth are the most commonly collected fossil in the world, naturally associated sets of teeth, i.e. a group of teeth from one individual, are a very rare find. These naturally associated sets are essential for understanding the evolution of a species or family of sharks. A careful examination of a naturally associated set of 95  Carcharocles megalodon  teeth found in Central Florida shows distinct differences between  C. megalodon  and the recent  Carcharodon carcharias  and suggests that the two species are only distantly related. 

Jones, Lisa M.

Pascagoula Facility, National Marine Fisheries Service, Pascagoula, MS 39568

Probable range extensions for several species of sharks from NMFS bottom longline survey data.

This study examined shark catch data from NMFS-SEFSC bottom longline surveys conducted between 1973 and 1997 for geographical, depth, temperature and salinity distributions by species of sharks captured. Analyses of geographical distribution using SURFER plots revealed probable range extensions for 11 species of sharks, including the night shark Carcharhinus signatus , the bignose shark Carcharhinus altimus , the sharpnose sevengill shark Heptranchias perlo , the bigeye sixgill shark Hexanchus vitulus , the spiny dogfish  Squalus acanthias , and 6 additional species of dogfish. Analyses of distribution by depth indicated probable range extensions for 6 species of benthic sharks: the Caribbean reef shark Carcharhinus perezi, the bignose shark Carcharhinus altimus , the nurse shark Ginglymostoma cirratum, the Cuban dogfish Squalus cubensis, the smooth dogfish Mustelus canis, and the Florida smooth-hound Mustelus norrisi. Temperature range extensions were indicated for the silky shark Carcharhinus falciformis, and the night shark Carcharhinus signatus. In addition, useful information on depth, temperature, and salinity distributions were found for species for which little or no information of this type has been published. 

*Jones, Lisa M., Grace, Mark A.

SEFSC; Mississippi Laboratories; Pascagoula Facility, National Marine Fisheries Service, Pascagoula, MS 39568

Shark nursery areas in the major bay systems of Texas.

The Texas parks and Wildlife Department conducted gill net surveys in major Texas bay systems from 1975 - 1995. Data collected includes indentification to lowest possible taxon, length, date, location, water temperature, and salinity. Included in the catch from these surveys are a number of shark species. By using available published information on age and growth for these species, the sharks captured can be separted into age classes and this database used to identify probable shark nursery areas. The environmental data gives an indication of preferred temperature and salinity regimes and the temporal distribition for each species. Included in the species that appear to be using these bays as pupping or nursery areas are: the bull shark Carcharhinus leucas, the blacktip shark Carcharhinus limbatus, the finetooth shark Carcharhinus isodon, the spinner shark Carcharhinus brevipinna, the Atlantic sharpnose shark Rhizoprionodon terraenovae, the bonnethead shark Sphyrna tibure, the scalloped hammerhead Sphyrna lewini, and 8 other shark species. The results of this study indicate that databases of this type can be useful as a step in the identification of shark nursery areas and characterization of essential habitat. 

Keeney, Devon B.

Biology Department, University of Massachusetts Dartmouth, North Dartmouth, MA 02747

The cestode faunas of some skates from the Bering Sea

The cestode faunas of six species of deep-water skates belonging to the genera  Bathyraja  and  Rhinoraja  from the Bering Sea were identified and observations were made on the enteric distribution of the parasites. Nine cestode species were encountered, several of which are new. All except one cestode species represent new host and locality records. A relatively low degree of host specificity was observed among the parasites in this study and evidence is given to suggest that this may be the result of similarities in mucosal morphology reflecting the systematic relatedness of the hosts. Zoogeographic records indicate a bipolar distribution among  Phyllobothrium,  Onchobothrium  and possibly  Echeneibothrium  in species of  Bathyraja  when compared to Antarctic hosts.  Echeneibothrium  and  Phyllobothrium  species closely resemble those reported from  Raja naevus  in the North Atlantic and occur in hosts with similar mucosal morphologies.  Echeneibothrium  species had wide distributions within the spiral valves but cestodes were consistently absent from the posterior regions. The enteric distribution of the worms appears related to villus length in the spiral valve mucosa. The distribution of juveniles and adults of  Onchobothrium  changed significantly along the antero-posterior axis within the spiral valves of  B. parmifera 

*Koester, David M., Spirito, Carl P.

(DMK) Department of Anatomy, University of New England, Biddeford, ME 04005; (CPS) Department of Physiology, University of New England, Biddeford, ME 04005

Punting: pelvic fin locomotion in  Raja erinacea 

The pelvic fins of the little skate  Raja erinacea  resemble most other skates in that an external notch or concavity in the lateral border partially separates each fin into anterior and posterior lobes. Dissections reveal that skeletal elements and musculature of the anterior lobe are highly modified and comprise a functionally distinct appendage (walking finger or crus) with three flexible joints. Anecdotal reports have suggested that the anterior portion of the fin might assist in locomotion especially along the bottom. Video recordings of skate movements in the field and in captivity clearly show that locomotion along the bottom is frequently carried out exclusively by the crural portion of the pelvic fin. Each cycle consists of two phases: a thrust generating phase which involves the synchronous action of the crura pushing off the bottom and a gliding phase during which time the crura are re-positioned for the next cycle. This mode of locomotion is referred to as punting (Long, J.H. personal communication; Martinez, et. al., 1998). Analysis of punting cycles and a brief anatomical description of the pelvic fin will be presented. This is the first time punting has been described for any species of fish. 

*López, Andrés, Naylor, Gavin, Ryburn, Julie A., Fedrigo, Olivier

Zoology and Genetics, Iowa State University, Ames, IA 50011

Lamniform phylogeny based on DNA sequence comparisons.

Representatives of each of the 14 described species of Lamniform sharks were sequenced for the mitochondrial genes NADH-2, NADH-4 and Cytochrome B, and the recombination activating single copy nuclear gene, rag1. The sequences were used in phylogenetic analyses with parsimony and likelihood optimality criteria. Spectral analyses were carried out to contrast signals derived from the different genes and to determine the relative amount of support for different nodes on the cladogram. The hypothesis of lamniform inter-relationships supported by the molecular data is discussed in the context of previous, morphology-based hypotheses, particularly those of Compagno (1990) and Maisey (1985). 

Loefer, Joshua K.

Grice Marine Laboratory, University of Charleston, SC, Charleston, SC 29412

Life History of the Atlantic sharpnose shark,  Rhizoprionodon terraenovae, in the South Atlantic Bight

The life history of the Atlantic sharpnose shark ( Rhizoprionodon terraenovae ), is well documented in the Gulf of Mexico, yet there are no published age and growth data available on this species in the South Atlantic Bight. A total of 1013 specimens were collected from Virginia to northern Florida during the first 22 months of a 24 month sampling schedule. Frontally sectioned vertebral centra were used to age each specimen, and the periodicity of circuli deposition was validated through marginal increment analysis. Atlantic sharpnose shark reached a maximum size of 813 mm precaudal length (PCL, or 1045 mm TL) at age ten. Sexual maturity (100%) was reached at age three and size 601 mm PCL (801 mm TL) for females, and age three and size 617 mm PCL (827 mm TL) for males. Mean back-calculated lengths at age ranged from 401 mm PCL (543 mm TL) at age one to 754 mm PCL (993 mm TL) at age ten. Back-calculated lengths from the last annulus for each age group yielded the following von Bertalanffy growth equation: L = 773.5(1 - e-0.323(t - (-1.276) ). The 95% confidence intervals for Linf, K and t0, respectively, were: 768.0-779.3, 0.331-0.334 and -1.340 to -1.215. 

*Lund, Richard, Leliävre , Hervé, Grogan, Eileen D.

(RL) Department of Biology, Adelphi University, Garden City, NY 11530; (HL) Musèum National d'Histoire Naturelle, Laboratoire de Palèontologie, Paris, 75005 France; (EDG) St. Joseph's University, Philadelphia, PA 19131

Endoskeletal mineralization of several Paleozoic Chondrichthyes: some observations

Histological studies of the endoskeletons of several Paleozoic chondrichthyans reveal a greater variety of types of mineralization than previously reported. The primitive vertebrate condition consists of perichondral bone alone. A successor condition, as observed in actinopterygians, reveals an underlayer of either sphaeritic calcified cartilage, trabecular bone, or both in the same fish. Sphaeritic calcification is the most primitive of the non-perichondral mineralization types. Modern prismatic calcified cartilage, as observed in Euselachii, lacks a gross perichondral cap component. Variations upon the successor condition are noted for Cladodont sharks, a petalodont, and an iniopterygian. Holocephalimorpha have several different styles of mineralization that are phylogenetically and regionally specific, but generally display acellular tesserae. Some mandibles exhibit fibrous mineralization. Other chondrichthyans of uncertain affinity display three-dimensional trabecular, tesserate mineralization. Aside from the growth of osteonal bone spines and clasper sheaths of perichondral bone, tile-like (tesserate) mineralization is common to some growth stage of all observed specimens but the types of mineralization observed within and among the tesserae are variable among the Paleozoic Chondrichthyes.