Abstracts of AES Scientific Papers
American Elasmobranch Society 1999 Annual Meeting
ABSTRACTS - Part 2: Gash through Lund
State College, Pennsylvania
*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 (T4 )
and 3,5,3,-triiodothyronine (T3 ) 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 T4 levels ranging from mean
levels of 2 to 12 ng/ml, with peaks during the spring and again in the fall. In
contrast, T3 levels were not detectable. Seasonal changes in T4
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 T4 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.
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
*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
Morphological and osteological features in
the embryonic development of Rhinobatos productus (Girard,
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,
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
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
*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
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
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.
*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
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
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: Lt =
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,
(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.