Serial block-face scanning electron microscopy of the tail tip of post-metamorphic amphioxus finds novel myomeres with odd shapes and unusually prominent sclerocoels.

Serial block-face scanning electron microscopy of the tail tip of post-metamorphic amphioxus (Branchiostoma floridae) revealed some terminal myomeres never been seen before with other techniques. The morphology of these myomeres differed markedly from the chevron shapes of their more anterior counterparts. Histologically, these odd-shaped myomeres ranged from empty vesicles bordered by undifferentiated cells to ventral sacs composed of well-developed myotome, dermatome, and sclerotome. Strikingly, several of these ventral sacs gave rise to a nipple-like dorsal projection composed either entirely of sclerotome or a mixture of sclerotome and myotome. Considered as a whole, from posterior to anterior, these odd-shaped posterior myomeres suggested that their more substantial ventral part may represent the ventral limb of a chevron, while the delicate projection represents a nascent dorsal limb. This scenario contrasts with formation of chevron-shaped myomeres along most of the antero-posterior axis. Although typical chevron formation in amphioxus is surprisingly poorly studied, it seems to be attained by a dorso-ventral extension of the myomere accompanied by the assumption of a V-shape; this is similar to what happens (at least superficially) in developing fishes. Another unusual feature of the odd-shaped posterior myomeres of amphioxus is their especially distended sclerocoels. One possible function for these might be to protect the posterior end of the central nervous system from trauma when the animals burrow into the substratum.

[Phenotyping the sheep tail - Presentation of characterization methods in the context of breeding for short-tailedness]. / Phänotypisierung des Schafschwanzes ­ Darstellung von Methoden zur Charakterisierung im Rahmen der Zucht auf Kurzschwänzigkeit.

OBJECTIVE: In order to establish targeted breeding for short-tailedness, a suitable method must initially be found that allows phenotyping of the sheep tail beyond tail length. In this study, in addition to assessing body measurements, more advanced studies such as ultrasonography and radiology were performed on the caudal spine of sheep for the first time. The objective of this work was to analyze the physiological variation of tail lengths and vertebrae within a merino sheep population. It also aimed to validate the use of sonographic gray scale analysis and perfusion measurement on the sheep tail. MATERIAL AND METHOD: Tail length and circumference in centimeters were measured in 256 Merino lambs on the first or second day of life. At 14 weeks of age the caudal spine of these animals was examined radiographically. Sonographic gray scale analysis and measurement of the perfusion velocity of the caudal artery mediana were also performed in a portion of the animals. RESULTS: The tested method of measurement showed a standard error of 0,08 cm and a coefficient of variation of 0,23% for tail length and 0,78% for tail circumference. The animals had a mean tail length of 22,5±2,32 cm and a mean tail circumference of 6,53±0,49 cm. The mean caudal vertebrae count for this population was 20,4±1,6. The use of a mobile radiographic unit is well suited for imaging the caudal spine in sheep. It was demonstrated that the caudal median artery could be imaged for measurement of perfusion velocity (cm/s), and sonographic gray-scale analysis also showed good feasibility. The mean gray scale value is 19,74±4,5 and the modal value for the most commonly found gray scale pixels is 191,53±120,2. The mean perfusion velocity for the caudal artery mediana is 5,83±3,04 cm/s. CONCLUSION: The results show that the methods presented are well suited for further characterization of the ovine tail. For the first time, gray values for the tail tissue and the perfusion velocity of the caudal artery mediana were determined.

Epidemiological study of congenital malformations of the vertebral column in French bulldogs, English bulldogs and pugs.

BACKGROUND: Congenital vertebral body malformations (CVBMs) have retrospectively been investigated in British and American canine populations. This study prospectively evaluates occurrence, localization, type and characteristic of CVBM along the entire vertebral column in a cohort of French Bulldogs, English Bulldogs and Pug dogs from Germany. METHODS: Prospective clinical and radiological screenings for CVBM were performed in brachycephalic dogs presented for reasons unrelated to neurological problems. Neurological and orthopaedic examinations as well as radiographs in two orthogonal planes of the entire vertebral column including the tail were performed in all dogs. Cobb angle and vertebral step were determined. Associations between CVBM, tail malformation, neurological deficits and occurrence of concurrent orthopaedic diseases were investigated. RESULTS: A total of 707 VBMs were identified in the whole vertebral column of 169 of 265 brachycephalic dogs. The most common types of CVBMs were ventral wedge shape (48%), dorsal wedge shape (14%) and shortened vertebral body (14%). A new type of malformation was investigated: dorsal wedge shape vertebrae. There was significant association between severe tail malformations with CVBM. Neurological deficits were significantly associated with ventrolateral wedge shape, dorso lateral hemivertebrae, Cobb angle > 30% and vertebral step ≥1.75 mm. Orthopaedic conditions were not significantly associated with CVBM. CONCLUSION: Kyphotic Cobb angle and vertebral step are radiological findings associated with neurological deficits. We propose severe tail malformation as an easy and accurate selection factor for determining breeding dogs.

A Murine Tail Lymphedema Model.

Lymphedema is extremity swelling caused by lymphatic dysfunction. The affected limb enlarges because of accumulation of fluid, adipose, and fibrosis. There is no cure for this disease. A mouse tail model that uses a focal full thickness skin excision near the base of the tail, resulting in tail swelling, has been used to study lymphedema. However, this model may result in vascular comprise and consequent tail necrosis and early tail swelling resolution, limiting its clinical translatability. The chronic murine tail lymphedema model induces sustained lymphedema over 15 weeks and a reliable perfusion to the tail. Enhancements of the traditional murine tail lymphedema model include 1) precise full thickness excision and lymphatic clipping using a surgical microscope, 2) confirmation of post-operative arterial and venous perfusion using high resolution laser speckle, and 3) functional assessment using indocyanine green near infrared laser lymphangiography. We also use tissue nanotransfection technology (TNT) for novel non-viral, transcutaneous, focal delivery of genetic cargo to the mouse tail vasculature.

Canine DVL2 variant contributes to brachycephalic phenotype and caudal vertebral anomalies.

A frameshift deletion variant in the Wnt pathway gene dishevelled 2 (DVL2) is associated with a truncated, kinked tail ("screw tail") in English Bulldogs, French Bulldogs and Boston Terriers. These breeds are also characterized by distinctive morphological traits, including a wide head, flat face and short-limbed dwarfism, which are characteristic of Robinow syndrome in humans, caused by defects in genes such as DVL1 and DVL3. Based on these phenotypic and genetic similarities, it has previously been hypothesized that the canine DVL2 variant results in a syndromic phenotype called the Robinow-like syndrome. In our study, we investigated the distribution of the DVL2 variant in 1954 dogs from 15 breeds, identifying breeds with allele variation and enabling the dissection of the genotype-phenotype correlation for the first time. With CT examinations in American Staffordshire Terriers, we confirmed that the DVL2 allele is associated with caudal vertebral malformations and a brachycephalic phenotype. We also hypothesize that the variant may be linked to additional health conditions, including brachycephalic obstructive airway syndrome and congenital heart defects. Altogether, our study strengthens the role of DVL2 as one of the contributors to the "bulldog type" morphology and features on the spectrum of human Robinow syndrome.

An attempt at estrus detection in cattle by continuous measurements of ventral tail base surface temperature with supervised machine learning.

We aimed to determine the effectiveness of estrus detection based on continuous measurements of the ventral tail base surface temperature (ST) with supervised machine learning in cattle. ST data were obtained through 51 estrus cycles on 11 female cattle (six Holsteins and five Japanese Blacks) using the tail-attached sensor. Three estrus detection models were constructed with the training data (n = 17) using machine learning techniques (random forest, artificial neural network, and support vector machine) based on 13 features extracted from sensing data (indicative of estrus-associated ST changes). Estrus detection abilities of the three models on test data (n = 34) were not statistically different among models in terms of sensitivity and precision (range 50.0% to 58.8% and 60.6% to 73.1%, respectively). The relatively poor performance of the models might indicate the difficulty of separating estrus-associated ST changes from estrus-independent fluctuations in ST.

A feasibility study for noninvasive measurement of shear wave speed in live zebrafish.

Zebrafish are being increasingly used as animal models for human diseases such as cardiomyopathy and neuroblastoma. Owing to a nearly fully sequenced genome and efficient genetics/chemical genetics, zebrafish open new research opportunities for human diseases research. The purpose of this study was to develop zebrafish ultrasound vibro-elastography (ZUVE) for measuring the shear wave speed of zebrafish. An adult female zebrafish was anesthetized for three minutes for the ZUVE testing. A 0.1 s gentle harmonic vibration was generated on the tail using a sphere tip indenter with 3 mm diameter. Shear wave propagation in the zebrafish was measured using a high frequency 18 MHz ultrasound probe. Shear wave speeds were measured at 300, 400, and 500 Hz. Shear wave speeds were, respectively, 3.13 ± 1.20 (m/s) for 300 Hz, 4.28 ± 1.36 (m/s) for 400 Hz, and 5.07 ± 1.45 (m/s) for 500 Hz for zebrafish 1 in a region of interest (ROI) which covered the central body. The shear wave speed dispersions were similar for four zebrafish and shear wave speeds ranged between 2.5 (m/s) and 5 (m/s) from 300 Hz to 500 Hz. The experimental setup and testing for a zebrafish lasted less than three minutes. All tested zebrafish were alive after testing. ZUVE is safe, fast, and noninvasive, making the testing of elastic properties of zebrafish feasible.

Fast diffraction-enhanced imaging using continuous sample rotation and analyzer crystal scanning.

Diffraction-enhanced imaging (DEI) has high sensitivity and a wide dynamic range of density and thus can be used for fine imaging of biological and organic samples that include large differences in density. A fast DEI method composed of continuous fast sample rotations and slow analyzer crystal scanning was developed to shorten the measurement period. Fine sectional images of a biological sample were successfully obtained within a half measurement period of the conventional step-scanning method while keeping the same exposure time. In addition, a fine three-dimensional image of a rat tail was obtained with a 375 s measurement period.

Effect of Collagen Peptide, Alone and in Combination with Calcium Citrate, on Bone Loss in Tail-Suspended Rats.

Oral administration of bovine collagen peptide (CP) combined with calcium citrate (CC) has been found to inhibit bone loss in ovariectomized rats. However, the protective effects of CP and CP-CC against bone loss have not been investigated in a tail-suspension simulated microgravity (SMG) rat model. Adult Sprague-Dawley rats (n = 40) were randomly divided into five groups (n = 8): a control group with normal gravity, a SMG control group, and three SMG groups that underwent once-daily gastric gavage with CP (750 mg/kg body weight), CC (75 mg/kg body weight) or CP-CC (750 and 75 mg/kg body weight, respectively) for 28 days. After sacrifice, the femurs were analyzed by dual-energy X-ray absorptiometry, three-point bending mechanical tests, microcomputed tomography, and serum bone metabolic markers. Neither CP nor CP-CC treatment significantly inhibited bone loss in SMG rats, as assessed by dual-energy X-ray absorptiometry and three-point bending mechanical tests. However, both CP and CP-CC treatment were associated with partial prevention of the hind limb unloading-induced deterioration of bone microarchitecture, as demonstrated by improvements in trabecular number and trabecular separation. CP-CC treatment increased serum osteocalcin levels. Dietary supplementation with CP or CP-CC may represent an adjunct strategy to reduce the risk of fracture in astronauts.

EVALUATION OF THE BONE MINERAL DENSITY OF ASIAN ELEPHANTS (ELEPHAS MAXIMUS) VIA DUAL-ENERGY X-RAY IMAGING OF TAILS.

Musculoskeletal problems are one of the top five causes of disease in elephants. However, recent blood chemistry analysis is the only routine protocol for bone mineral status evaluation, with no assessment method currently available for the direct measurement of elephant bone mineral density (BMD). This work applied the the dual-energy X-ray technique (DXA) technique for bone density assessment. The elephant's tail was chosen for the analysis to avoid the radiation harm. Twelve live Asian elephants (Elephas maximus) comprising eight males and four females with ages in the range of 4-77 yr were investigated. The BMD was calculated based on radiographic images acquired using the DXA technique carried out at 40 kVp 2 mAs and 50 kVp 2 mAs. Blood serum analysis of total calcium (Ca), phosphorus (Phos) and alkaline phosphatase (ALP) content was conducted in parallel with the physical examination to correlate age and BMD. Analyses produced an overall mean BMD value in the range of 0.54-1.39 g/cm2, with that of the males higher than that of the females. The BMD was found to be negatively correlated with age, Ca, and Phos, but not with ALP. In summary, the BMD analysis of an elephant's tail might be used with blood serum Ca and Phos to predict the overall bone mineral status of the animal.

Measurement of tissue optical properties in the context of tissue optical clearing.

Nowadays, dynamically developing optical (photonic) technologies play an ever-increasing role in medicine. Their adequate and effective implementation in diagnostics, surgery, and therapy needs reliable data on optical properties of human tissues, including skin. This paper presents an overview of recent results on the measurements and control of tissue optical properties. The issues reported comprise a brief review of optical properties of biological tissues and efficacy of optical clearing (OC) method in application to monitoring of diabetic complications and visualization of blood vessels and microcirculation using a number of optical imaging technologies, including spectroscopic, optical coherence tomography, and polarization- and speckle-based ones. Molecular modeling of immersion OC of skin and specific technique of OC of adipose tissue by its heating and photodynamic treatment are also discussed.

Ultrasonographic anatomy of reproductive female leopard geckos (Eublepharis macularius).

Captive leopard geckos (Eublepharis macularius) often present to the exotic clinic for gastrointestinal impactions, follicular stasis, or dystocia. To our knowledge, normal ultrasonographic anatomy of these lizards has not been described. The objectives of this prospective, anatomic, analytical study were to develop ultrasound techniques for this species and to describe the normal sonographic anatomy of the head, coelomic cavity, and tail. Eleven, healthy, female leopard geckos were included. A linear array 13-18 MHz transducer was used. Geckos were sedated and restrained in dorsal recumbency for coelomic structure examination and in ventral recumbency for head and tail examinations. Sagittal and transverse images were acquired and authors recorded qualitative and quantitative ultrasonographic characteristics of anatomic structures. The ventral surface of the lungs, liver, gallbladder, caudal vena cava, portal vein, ventral abdominal vein, aorta, ovarian follicles, fat bodies, tail, and brain were visualized in 10 of 11 individuals. In one individual, molt precluded ultrasonographic examination. The heart, kidneys, urinary bladder, spleen, and pancreas were not visualized. The digestive tract was observed in 10 individuals but was too small to be measured. Findings from the current study could be used as a reference for future studies of leopard geckos.

Tail reduction process during human embryonic development.

Although the human tail is completely absent at birth, the embryonic tail is formed just as in other tailed amniotes. Since all morphological variations are created from variations in developmental processes, elucidation of the tail reduction process during embryonic development may be necessary to clarify the human evolutionary process. The tail has also been of great interest to the medical community. The congenital anomaly referred to as 'human tail', i.e. the occurrence of a tail-like structure, has been reported and was thought to represent a vestige of the embryonic tail; however, this hypothesis has not been verified. Accordingly, in this study, we aimed to establish a new method to visualize all somites in an embryo. We used sagittal-sectioned embryos from Carnegie Stage (CS) 13 to CS23. All samples were obtained from the Congenital Anomaly Research Center, Kyoto University, Japan. Combining photomicroscopy and three-dimensional reconstruction, we clearly visualized and labeled all somites. We found that the number of somites peaked at CS16 and dramatically decreased by approximately five somites. Tail reduction with a decrease in somites has also been observed in other short-tailed amniotes; thus, this result suggested the possibility that there is a common mechanism for morphogenesis of short tails in amniote species. Additionally, our findings provided important insights into the cause of the congenital anomaly known as 'human tail'.

A True Human Tail in a Neonate: Case report and literature review.

A true human tail is a benign vestigial caudal cutaneous structure composed of adipose, connective tissue, muscle, vessels, nerves and mechanoreceptors. A true human tail can be distinguished from a pseudotail as the latter is commonly associated with underlying spinal dysraphism, which requires specialised management. True human tails are very rare, with fewer than 40 cases reported to date. We report a healthy one-day-old male newborn who was referred to the Bharath Hospital, Kottayam, Kerala, India, in 2014 with a cutaneous appendage arising from the lumbosacral region. Magnetic resonance imaging of the spine ruled out spinal dysraphism. The appendage was removed by simple surgical excision. Clinicians should emphasise use of 'true tail' and 'pseudotail' as specific disparate terms as the clinical, radiological and histological findings of these conditions differ significantly, along with management strategies and outcomes.

Cell Therapy Using Bone Marrow-Derived Stem Cell Overexpressing BMP-7 for Degenerative Discs in a Rat Tail Disc Model.

Degenerative discs can cause low back pain. Cell-based transplantation or growth factors therapy have been suggested as a strategy to stimulate disc regeneration. Bone marrow-derived mesenchymal stem cells (BMDMSC) containing bone morphogenetic protein-7 (BMP-7) gene were constructed. We evaluated the effectiveness of these BMP-7 overexpressing cells on degenerative discs in rat tails. In vitro and in vivo studies were designed. In the first stage, the rats were divided into two group according to discs punctured by different needle gauges (18 gauge and 22 gauge). In the second stage, the ideal size of needle was used to induce rat tail disc degeneration. These animals are divided into three groups according to timing of treatment (zero-week, two-week, four-week). Each group was divided into three treating subgroups: control group, BMDMSC group, and Baculo-BMP-7-BMDMSC group. Each rat undergoes radiography examination every two weeks. After eight weeks, the discs were histologically examined with hematoxylin and eosin stain and Alcian blue stain. The 18-gauge group exhibited significant decrease in disc height index (%) than 22-gauge group at eight weeks at both Co6-7 (58.1% ± 2.8% vs. 63.7% ± 1.0%, p = 0.020) and Co8-9 discs (62.7% ± 2.8% vs. 62.8% ± 1.5%, p = 0.010). Baculo-BMP-7-BMDMSCs group showed significant difference in disc height index compared to the BMDMSCs group at both Co6-7 (93.7% ± 1.5% vs. 84.8% ± 1.0%, p = 0.011) and Co8-9 (86.0% ± 2.1% vs. 81.8% ± 1.7%, p = 0.012). In Baculo-BMP-7-BMDMSCs group, the zero-week treatment subgroup showed significant better in disc height index compared to two-week treatment group (p = 0.044), and four-week treatment group (p = 0.011). The zero-week treatment subgroup in Baculo-BMP-7-BMDMSCs group also had significant lower histology score than two-week treatment (4.3 vs. 5.7, p = 0.045) and four-week treatment (4.3 vs. 6.0, p = 0.031). In conclusion, Baculo-BMP-7-BMDMSC can slow down the progression of disc degeneration, but could not provide evidence of regeneration. Early treatment might obtain more distinct results.

A rat tail temporary static compression model reproduces different stages of intervertebral disc degeneration with decreased notochordal cell phenotype.

The intervertebral disc nucleus pulposus (NP) has two phenotypically distinct cell types-notochordal cells (NCs) and non-notochordal chondrocyte-like cells. In human discs, NCs are lost during adolescence, which is also when discs begin to show degenerative signs. However, little evidence exists regarding the link between NC disappearance and the pathogenesis of disc degeneration. To clarify this, a rat tail disc degeneration model induced by static compression at 1.3 MPa for 0, 1, or 7 days was designed and assessed for up to 56 postoperative days. Radiography, MRI, and histomorphology showed degenerative disc findings in response to the compression period. Immunofluorescence displayed that the number of DAPI-positive NP cells decreased with compression; particularly, the decrease was notable in larger, vacuolated, cytokeratin-8- and galectin-3-co-positive cells, identified as NCs. The proportion of TUNEL-positive cells, which predominantly comprised non-NCs, increased with compression. Quantitative PCR demonstrated isolated mRNA up-regulation of ADAMTS-5 in the 1-day loaded group and MMP-3 in the 7-day loaded group. Aggrecan-1 and collagen type 2α-1 mRNA levels were down-regulated in both groups. This rat tail temporary static compression model, which exhibits decreased NC phenotype, increased apoptotic cell death, and imbalanced catabolic and anabolic gene expression, reproduces different stages of intervertebral disc degeneration.

Chondrocyte-specific inhibition of ß-catenin signaling leads to dysplasia of the caudal vertebrae in mice.

STUDY DESIGN: To inhibit ß-catenin specifically signaling in chondrocytes Col2-ICAT transgenic mice were generated. Anomalies in caudal vertebrae were detected during embryonic and postnatal stages of Col2-ICAT transgenic mice. OBJECTIVE: To determine the role of canonical ß-catenin signaling in caudal vertebral development. SUMMARY OF BACKGROUND DATA: ß-catenin signaling plays a critical role in skeletal development. Col2-ICAT transgenic mice were generated to selectively block ß-catenin signaling by overexpression of the ICAT gene in chondrocytes. METHODS: Tails of E16.5 transgenic embryos and adult Col2-ICAT transgenic mice and their wild-type littermates were collected and analyzed. Skeletal preparation, 3-dimensional micro-computed tomographic and histological analyses were performed to evaluate changes in the structure of caudal vertebrae. Bromodeoxyuridine labeling was performed to evaluate changes in chondrocyte proliferation in caudal vertebrae. RESULTS: Skeletal preparation and 3-dimensional micro-computed tomographic analyses revealed bone deformation and angulated deformities in tail tissue in Col2-ICAT transgenic mice. Histological studies revealed abnormal bone development and dysplastic caudal vertebrae in Col2-ICAT transgenic mice. Inhibition of ß-catenin signaling in cartilage resulted in vertebral dysplasia leading to aberrant resegmenting process. Thus, 2 poorly developed sclerotomes failed to fuse to form a complete vertebrae. BrdU labeling revealed a decreased chondrocyte proliferation in both cartilageous templates of transgenic embryos and the growth plate of adult Col2-ICAT transgenic mice. CONCLUSION: Wnt/ß-catenin signaling plays an important role in vertebral development. Inhibition of ß-catenin signaling in chondrocytes results in caudal vertebra deformity in mice, which may occur as early as in the stage of sclerotome formation. LEVEL OF EVIDENCE: N/A.

Emergence of the advancing neuromechanical phase in a resistive force dominated medium.

Undulatory locomotion, a gait in which thrust is produced in the opposite direction of a traveling wave of body bending, is a common mode of propulsion used by animals in fluids, on land, and even within sand. As such, it has been an excellent system for discovery of neuromechanical principles of movement. In nearly all animals studied, the wave of muscle activation progresses faster than the wave of body bending, leading to an advancing phase of activation relative to the curvature toward the tail. This is referred to as "neuromechanical phase lags" (NPL). Several multiparameter neuromechanical models have reproduced this phenomenon, but due to model complexity, the origin of the NPL has proved difficult to identify. Here, we use perhaps the simplest model of undulatory swimming to predict the NPL accurately during sand-swimming by the sandfish lizard, with no fitting parameters. The sinusoidal wave used in sandfish locomotion, the friction-dominated and noninertial granular resistive force environment, and the simplicity of the model allow detailed analysis, and reveal the fundamental mechanism responsible for the phenomenon: the combination of synchronized torques from distant points on the body and local traveling torques. This general mechanism should help explain the NPL in organisms in other environments; we therefore propose that sand-swimming could be an excellent system with which to generate and test other neuromechanical models of movement quantitatively. Such a system can also provide guidance for the design and control of robotic undulatory locomotors in complex environments.

Highly deformable bones: unusual deformation mechanisms of seahorse armor.

Multifunctional materials and devices found in nature serve as inspiration for advanced synthetic materials, structures and robotics. Here, we elucidate the architecture and unusual deformation mechanisms of seahorse tails that provide prehension as well as protection against predators. The seahorse tail is composed of subdermal bony plates arranged in articulating ring-like segments that overlap for controlled ventral bending and twisting. The bony plates are highly deformable materials designed to slide past one another and buckle when compressed. This complex plate and segment motion, along with the unique hardness distribution and structural hierarchy of each plate, provide seahorses with joint flexibility while shielding them against impact and crushing. Mimicking seahorse armor may lead to novel bio-inspired technologies, such as flexible armor, fracture-resistant structures or prehensile robotics.

Anatomy and evolution of heterocercal tail in lamniform sharks.

Lamniformes is a small shark group consisting of 15 extant species with remarkably diverse lifestyles and a wide range in heterocercal tail morphology. The caudal fin morphology must be related to their lifestyle because the tail is a main locomotive structure in sharks, but such relationships have remained largely uninvestigated. Here, the morphology-lifestyle relationship in lamniforms is examined through phylogenetic mapping. This study suggests that, within Lamniformes, caudal fins with a more horizontally directed curvature of the vertebral column are plesiomorphic, whereas those with a large dorsally directed curvature of the vertebral column are apomorphic. It also shows that caudal fins with posteriorly directed hypochordal rays are plesiomorphic, and that those with ventrally directed hypochordal rays are apomorphic within Lamniformes. Four basic caudal fin types are recognized in lamniforms on the basis of these skeletal variables in which one corollary is that the evolution of external morphology of caudal fin does not necessarily correspond to the evolution of its skeletal anatomy. This study also demonstrates that specific lifestyles seen in different lamniforms are indeed correlative with different caudal fin types in which a less asymmetrical heterocercal tail is a derived feature in lamniforms that evolved for fast swimming to capture fast swimming prey.