Basal Bone Research Articles

Midpalatal cortex osteotomy assisted rapid maxillary expansion for correction of maxillary transverse deficiency in young adults

Objective: To evaluate the application of midpalatal cortex osteotomy assisted rapid maxillary expansion for correction of maxillary transverse deficiency in young adults. Methods: Fourteen young adult patients with maxillary transverse deficiency were treated with midpalatal cortex osteotomy assisted rapid maxillary expansion. Lateral cephalogram and cone beam CT (CBCT) were taken before and 3 months after treatment. The width of basal bone, arch of maxilla and the torque of anchorage teeth were compared before and after treatment. Results: The width of dental arch of maxilla was increased from 40.54±5.26 mm before treatment to 46.83±5.83 mm after treatment (P<0.05) and the width of basal bone was increased from 64.86±4.16 mm to 67.60±4.66 mm (P<0.05) at the plane of the maxillary first molars. Accordingly, the width of dental arch of maxilla was increased from 31.92±2.55 mm to 38.65±3.14 mm (P<0.05) and the width of basal bone was increased from 43.33±3.70 mm to 45.78±4.57 mm (P<0.05) at the plane of first premolar. And the torque of maxillary anchorage teeth were increased (P<0.05). Conclusion: Midpalatal cortex osteotomy assisted rapid maxillary expansion is an effective micro-invasive method in expansion of basal bone and arch of maxilla for young adult patients with maxillary transverse deficiency.

Possibilities and limits of orthodontico-surgical treatments in case of macrodontia

Tooth-arch discrepancy is a disproportion between dental volume and bone base. Extraction therapy can be a solution in case of excessive tooth volume and insufficient basal bone length. Techniques including bone distraction popularized by Ilizarov in the fifties allow the increase of the basal arch length in the maxilla as well as in the mandible. We will describe the procedure of this dental arch length augmentation since the reflection about the therapeutic plan until the sufficient arch length is obtained and describe the indications of this orthodontic and surgical treatment in case of dental crowding, buccal and labial inclination and functional problems. Distraction is an interesting technique to be considered for the management of macrodontia that allows to get enough basal bone lenght to reach the therapeutic goal.

Alveolar bone height and thickness assessed by CBCT

Abstract Objectives To seek information regarding the relationship between the quantity of alveolar bone and the angle and sagittal position of the incisors. This was to be further determined in relation to the basal bones and facial pattern with the aim of establishing a predictive model based on the study of a lateral cephalogram. Methods The distance from the cemento-enamel junction to the labial alveolar crest and the bone thickness half-way along the root of the most prominent upper and lower incisor were measured in a sample of 100 cone beam computed tomography (CBCT) scans of patients aged between 15 and 34 years. Lateral cephalograms of the patients were extracted from the scans and used to measure the buccolingual angle and antero-posterior position of the incisors in addition to the facial pattern of each patient. Results A correlation was found between bone thickness around the upper incisor and the variables of the incisal angle and its sagittal position. The inclination of the lower incisor (IMPA) was related to cortical bone thickness. The cemento-enamel junction to alveolar crest measurement (bone height) was related to the antero-posterior position of the lower incisor in men. The facial pattern was unrelated to any of the variables. Conclusions The angle and sagittal position of the upper and lower incisors were associated with alveolar bone thickness in men. Only the antero-posterior position of the lower incisor was related to its alveolar bone height. In women, only the angle of the lower incisor was associated with bone thickness.

Skeletal and dentoalveolar changes after miniscrew-assisted rapid palatal expansion in young adults: A cone-beam computed tomography study.

ObjectiveThe aim of this study was to evaluate the skeletal and dentoalveolar changes after miniscrew-assisted rapid palatal expansion (MARPE) in young adults by cone-beam computed tomography (CBCT).MethodsThis retrospective study included 14 patients (mean age, 20.1 years; range, 16–26 years) with maxillary transverse deficiency treated with MARPE. Skeletal and dentoalveolar changes were evaluated using CBCT images acquired before and after expansion. Statistical analyses were performed using paired t-test or Wilcoxon signed-rank test according to normality of the data.ResultsThe midpalatal suture was separated, and the maxilla exhibited statistically significant lateral movement (p < 0.05) after MARPE. Some of the landmarks had shifted forwards or upwards by a clinically irrelevant distance of less than 1 mm. The amount of expansion decreased in the superior direction, with values of 5.5, 3.2, 2.0, and 0.8 mm at the crown, cementoenamel junction, maxillary basal bone, and zygomatic arch levels, respectively (p < 0.05). The buccal bone thickness and height of the alveolar crest had decreased by 0.6–1.1 mm and 1.7–2.2 mm, respectively, with the premolars and molars exhibiting buccal tipping of 1.1°–2.9°.ConclusionsOur results indicate that MARPE is an effective method for the correction of maxillary transverse deficiency without surgery in young adults.

Stability of dental, alveolar, and skeletal changes after miniscrew-assisted rapid palatal expansion.

ObjectiveMiniscrew-assisted rapid palatal expansion (MARPE) is a means for expanding the basal bone without surgical intervention in young adults. Here, we assessed the differences in dental, alveolar, and skeletal measurements taken before (T0), immediately after (T1), and 1 year after (T2) MARPE.MethodsTwenty-four patients (mean age, 21.6 years) who had undergone MARPE and cone-beam computed tomography at T0, T1, and T2 were included. Changes in the following parameters were compared using paired t-tests: intercusp, interapex, alveolar, nasal floor, and nasal cavity widths; inclination of the first molar (M1) and its alveolus; and thickness and height of the alveolar bone. A linear mixed-effects model was used to determine variables that affected periodontal changes in the M1.ResultsMARPE produced significant increases in most measurements during T0–T2, despite relapse of some measurements during T1–T2. The alveolar thickness decreased on the buccal side, but increased on the palatal side. The alveolar crest level at the first premolar moved apically. Changes in the thickness and height of the alveolar bone were affected by the corresponding initial values.ConclusionsMARPE can be used as an effective tool for correcting maxillomandibular transverse discrepancy, showing stable outcomes 1 year after expansion.

Residents' journal review

Residents' journal review

BRAF-V600E expression correlates with ameloblastoma aggressiveness.

The aim of this study was to investigate whether the expression of BRAF-V600E determines an aggressive clinical and molecular presentation of ameloblastoma. Ninety-three cases of solid ameloblastomas were arranged in a 1.0-mm tissue microarray (TMA) block. Immunohistochemistry against a large panel of cytokeratins (CK), epidermal growth factor receptor (EGFR), parathyroid hormone-related peptide (PTHrP), syndecan-1, Ki67, p53 and BRAF-V600E were performed. Clinicopathological parameters, including sex, age, tumour size, tumour duration, tumour location, treatment, recurrences, radiographic pattern, vestibular/lingual and basal cortical plates disruption and follow-up data, were obtained from patients' medical records. Immunoexpression of BRAF-V600E was investigated in 73 cases that remained available in TMA sections. Our results indicated that 46.6% (34 cases) demonstrated cytoplasm positivity (six weak and 28 strong positivity). BRAF-V600E expression was associated significantly with the expression of CK8 (P = 0.00077), CK16 (P = 0.05), PTHrP (P = 0.0082) and p53 (P = 0.0087). Additionally, a significant association was seen with the presence of recurrences (P = 0.0008), multilocular radiographic appearance (P = 0.044) and disruption of basal bone cortical (P = 0.05). Univariate analysis showed that BRAF-positive cases (P = 0.001), EGFR-negative/weak positive cases (P = 0.03) and multilocular tumours (P = 0.04) had a significantly lower disease-free survival rate, but these parameters were not considered independent prognostic factors in the multivariate analysis (P > 0.05). Our findings suggest an association of BRAF-V600E with parameters of a more aggressive behaviour of ameloblastoma, supporting the future use of BRAF inhibitors for targeted therapy of this neoplasm.

Elegestolepis and its kin, the earliest monodontode chondrichthyans

ABSTRACTChondrichthyan-like scales with simple, single-odontode crowns, reminiscent of those of euselachians, have been reported from Silurian strata in a number of previous studies. These specimens comprise the genera Elegestolepis (from Siberia, Mongolia, and Tuva) and Kannathalepis (from the Canadian Arctic) and have been considered to exhibit contrasting patterns of ontogenetic development. A study of elegestolepid microremains from the Chargat Formation of Mongolia (Llandovery–lower Wenlock) and the Baital Formation of Tuva (Wenlock–Ludlow) has been undertaken using scanning electron microscopy and micro-computed tomography to examine scale canal system and hard tissue structure. These investigations revealed scales at different stages of development, whose morphogenesis is characterized by growth (elongation) of the crown odontode and formation of neck canals. This ontogenetic pattern (Elegestolepis-type morphogenesis) is also recognized in Kannathalepis and the Lower Devonian species Ellesmereia schultzei and forms the basis for the unification of these taxa into a new chondrichthyan order Elegestolepidida, ordo nov. Similarities in crown vascularization (branching pulp, single neck canal) shared by Elegestolepis, Ellesmereia, and Deltalepis, gen. nov. (D. magna, sp. nov., and D. parva, sp. nov., erected herein for Mongolian specimens), require the erection of the family Elegestolepididae, fam. nov., that is distinguished from the monogeneric Kannathalepididae (non-branching pulp, multiple neck canals). Elegestolepid scales exhibit characteristics (neck canal formation and lack of enamel and basal bone osteons) consistent with those of the chondrichthyan dermal skeleton. This establishes Elegestolepidida as the stratigraphically oldest chondrichthyan taxon to develop monodontode scales, which, in contrast to the ‘placoid’ scales of euselachians, are growing structures.http://zoobank.org/urn:lsid:zoobank.org:pub:46F95C47-6926-4F3DB96D-9890527BA8DECitation for this article: Andreev, P. S., M. I. Coates, V. Karatajūtė-Talimaa, R. M. Shelton, P. R. Cooper, and I. J. Sansom. 2016. Elegestolepis and its kin, the earliest monodontode chondrichthyans. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1245664.

Retrospective study of maxillary sinus dimensions and pneumatization in adult patients with ananterior open bite.

The aim of this study was to evaluate differences in the maxillary sinus floor levels between adults with an anterior open bite and those without. This retrospective study included 30 subjects: 15 adults with an anterior open bite (mean age, 21.5±4.3years) and 15 control subjects with normal occlusion (mean age, 21.7±3.1years). Cone-beam computed tomography and lateral cephalograms were analyzed before treatment. The open-bite group exhibited a significantly greater maxillary posterior alveolar height (P<0.05). The craniocaudal heights of the maxillary sinus in the region between the first and secondmolars and between the second premolar and first molar were significantly greater in the open bite group (40.5 and 39.0mm, respectively) than in the control group (36.7 and 34.7mm, respectively; P<0.05 for both). The basal bone heights in the regions between the first and secondmolars, the second premolar and first molar, and the first and second premolars were significantly smaller in the open-bite group than in the control group (P<0.001 for all). Vertical pneumatization of the maxillary sinus floor in the region between the first and secondmolars and between the second premolar and first molar is greater in adults with an anterior open bite than in those without, whereas basal bone height in the maxillary posterior region is lower in the open-bite patients.

Longitudinal Evaluation of Bone Mineral Density and Bone Metabolism Markers in Patients with Indolent Systemic Mastocytosis Without Osteoporosis

Systemic Mastocytosis has been long identified as a potential cause of osteoporosis; nevertheless, data regarding longitudinal variation of bone mineral density (BMD) in patients with indolent systemic mastocytosis (ISM) are missing . We studied BMD variation at lumbar spine and proximal hip after 30-month (±6months) follow-up in a large cohort of patients (83) with ISM without osteoporosis, supplementated with vitamin D and/or calcium when needed. We also analyzed the correlation between variation of BMD, basal serum tryptase levels and bone turnover markers (BTM). Sixty-four percent of our population was male; mean age was 52.1 (±11.5) years. Vitamin D insufficiency (serum levels of 25-OH-vitamin D, 25OHD, lower than 75nmol/L) was found in more than 70% of patients. After a follow-up of 30±6months with only vitamin D (5000-7500IU weekly of oral cholecalciferol) or calcium (500mg/die) supplementation when needed, we observed 2.1% increase in BMD at lumbar spine, with no significant changes at hip. At the end of follow-up, almost 60% of patients showed 25OHD serum levels still lower than recommended, despite vitamin D supplementation. Reduction in BMD after follow-up significantly correlated with high C-telopeptide of type I collagen serum levels at the time of diagnosis. In patients with ISM without osteoporosis, a routinary BMD evaluation within a time <2years is not justified, except in the presence of elevated BTM. In these patients, vitamin D supplementation is frequently needed.

New Technique for Mandibular Symphyseal Distraction by a Double-Level Anchorage and Fixation System: Advantages and Results.

A surgical technique to widen the mandible is the mandibular midline distraction: the most common indications for mandibular midline distraction are severe mandibular anterior crowding, severe mandibular transverse deficiency, uni- or bilateral crossbite, impacted anterior teeth with inadequate space, and tipped teeth. Commonly used distraction devices can be divided into 2 systems: bone-borne distraction system appliance, dental-borne distraction systems. Each system has peculiar advantages, disadvantages, and different indications. To combine advantages of both systems we developed a new technique adopting an immediate basal bone widening with fixation after osteotomy and a dental borne rigid lingual system for distraction. The aim of this work is to show a new technique for symphysis mandibular distraction based on a double-level anchorage and fixation system on clinical patients showing final results and advantages. Two patients affected by dento-alveolar and basal bone maxillary and mandibular transversal collapse even in association with other skeletal malocclusion were selected. Patients were clinically and radiographically studied and analyzed at different times before and after surgery. Dental and basal bone measurements were performed clinically and radiographically. The results were optimal with perfect dental arches alignment followed by closing of the open bites with multiple-segmented surgery in a second surgical time. No misalignment of the 2 mandibular halves was noticed during the distraction procedure. Dental-bone discrepancies correction is mandatory before orthodontic treatment alignment. Transversal jaw expansion can be achieved safely and stably by distraction of both maxillae for the combination of osteogenesis and histogenesis with augmentation of both bone and soft tissue. Bone-borne distraction will result in more stable results; dental-borne devices will result in more simple and aesthetically rewarding procedures. Hybrid techniques usually show mixed results depending on the characteristics of the device. For this reason we developed a combination of both the aforementioned systems which is not a hybrid system but the combination of an immediate expansion of the symphysis and fixation by 1 miniplate with only 2 screws acting like hinges during distraction, combined with a lingual distraction system at the alveolar bone level. Bone-borne distraction systems result in more efficient basal bone mandibular widening with increased stability for dental results. For dental-borne appliance the advantages consist in no second surgery need for their removal, no transmucosal hardware emergence and better aesthetic, especially when lingual devices were used. Our technique combines advantages of both procedures.

Articulation temporomandibulaire (ATM) : hypercondylie et condylectomie

The mandibular condyle is a special structure. Its embryology and physiology provide to the TMJ a particular behavior that explains the occurrence of specific diseases. Condyle hyperplasia is one of these disorders. It can be explained by a dysregulation of the prechondroblast cell layer within the cartilage cap providing an increase in volume first of the condyle, then of the ramus and finally of the entire affected hemiface. Mandible deformation affects the basal bone, leading to dento-alveolar deformations related to compensation attempts. Controversies, condylectomy is performed by many surgeons. This procedure allows for the correction of some of the dento-alveolar compensations. In some cases, an additional orthognathic surgery will be required to achieve a perfect result.

Microvertebrates from multiple bone beds in the Rhaetian of the M4–M5 motorway junction, South Gloucestershire, U.K.

The Rhaetian (latest Triassic) is best known for its basal bone bed, but there are numerous other bone-rich horizons in the succession. Boreholes taken around the M4–M5 motorway junction in SW England provide measured sections with multiple Rhaetian bone beds. The microvertebrate samples in the various bone beds differ through time in their composition and in average specimen size. The onset of the Rhaetian transgression accumulated organic debris to form a fossiliferous layer high in biodiversity at the base of the Westbury Formation. The bone bed at the top of the Westbury Formation represents a community with lower biodiversity. The bone beds differ in their faunas: chondrichthyan teeth are dominant in the basal bone bed, but actinopterygians dominate the higher bone bed. These differences could be taphonomic, but are more likely evidence for ecological-evolutionary changes. Further, a change from larger to smaller specimen sizes up-sequence allows rejection of an earlier idea that the successive bone beds represented multiple reworkings of older bone beds.

De novo bone formation underneath the sinus membrane supported by a bone patch: a pilot experiment in rabbit sinus model.

The objectives of this study were to evaluate bone regeneration beneath a newly devised bone substitute combined with collagen membrane (called a bone patch) lying over a concomitantly placed mini-implant following sinus floor elevation and verify its usefulness as a carrier system for recombinant human bone morphogenetic protein-2 (rhBMP-2) in rabbits. The sinus floor elevation procedure was performed bilaterally in five rabbits. Either a plain bone patch (control group) or an rhBMP-2-loaded patch (experimental group) was randomly placed beneath the elevated sinus membrane (SM) of both sinuses, where the mini-implants were concomitantly placed. Micro-computed tomographic and histologic analyses were performed at 4weeks post-surgery. In micro-computed tomography, the median values of the total augmented volume and the mineralized bone volume were significantly higher in the experimental group than in the control group (161 vs. 122mm3 [P<0.01] and 48 vs. 42mm3 [P<0.05], respectively). Histometric analysis revealed the same outcomes, with new bone areas of 6.41 and 2.97mm2 in the experimental and control groups, respectively (P<0.001), and bone-to-implant contact ratios of 22.6% and 5.2%, respectively (P<0.001). The newly devised bone patch in this study can support the elevated SM and facilitate bone regeneration from the basal bone with a reduced amount of biomaterial. The addition of rhBMP-2 may shorten the healing time for multidirectional bone regeneration toward the implant.

Physiological and pathophysiological bone turnover - role of the immune system.

Osteoporosis develops when the rate of osteoclastic bone breakdown (resorption) exceeds that of osteoblastic bone formation, which leads to loss of BMD and deterioration of bone structure and strength. Osteoporosis increases the risk of fragility fractures, a cause of substantial morbidity and mortality, especially in elderly patients. This imbalance between bone formation and bone resorption is brought about by natural ageing processes, but is frequently exacerbated by a number of pathological conditions. Of importance to the aetiology of osteoporosis are findings over the past two decades attesting to a deep integration of the skeletal system with the immune system (the immuno-skeletal interface (ISI)). Although protective of the skeleton under physiological conditions, the ISI might contribute to bone destruction in a growing number of pathophysiological states. Although numerous research groups have investigated how the immune system affects basal and pathological osteoclastic bone resorption, recent findings suggest that the reach of the adaptive immune response extends to the regulation of osteoblastic bone formation. This Review examines the evolution of the field of osteoimmunology and how advances in our understanding of the ISI might lead to novel approaches to prevent and treat bone loss, and avert fractures.

The systematics of the Mongolepidida (Chondrichthyes) and the Ordovician origins of the clade.

The Mongolepidida is an Order of putative early chondrichthyan fish, originally erected to unite taxa from the Lower Silurian of Mongolia. The present study reassesses mongolepid systematics through the examination of the developmental, histological and morphological characteristics of scale-based specimens from the Upper Ordovician Harding Sandstone (Colorado, USA) and the Upper Llandovery–Lower Wenlock Yimugantawu (Tarim Basin, China), Xiushan (Guizhou Province, China) and Chargat (north-western Mongolia) Formations. The inclusion of the Mongolepidida within the Class Chondrichthyes is supported on the basis of a suite of scale attributes (areal odontode deposition, linear odontocomplex structure and lack of enamel, cancellous bone and hard-tissue resorption) shared with traditionally recognized chondrichthyans (euchondrichthyans, e.g., ctenacanthiforms). The mongolepid dermal skeleton exhibits a rare type of atubular dentine (lamellin) that is regarded as one of the diagnostic features of the Order within crown gnathostomes. The previously erected Mongolepididae and Shiqianolepidae families are revised, differentiated by scale-base histology and expanded to include the genera Rongolepisand Xinjiangichthys, respectively. A newly described mongolepid species (Solinalepis levis gen. et sp. nov.) from the Ordovician of North America is treated as family incertae sedis, as it possesses a type of basal bone tissue (acellular and vascular) that has yet to be documented in other mongolepids. This study extends the stratigraphic and palaeogeographic range of Mongolepidida and adds further evidence for an early diversification of the Chondrichthyes in the Ordovician Period, 50 million years prior to the first recorded appearance of euchondrichthyan teeth in the Lower Devonian.

The Rhaetian (Late Triassic) vertebrates of Hampstead Farm Quarry, Gloucestershire, UK

The Rhaetian marine transgression, which occurred across Europe in the latest Triassic, 205.5Ma, famously deposited one or more bone beds. Attention has generally focused on the basal bone bed alone, but here we explore this bed, and a stratigraphically higher bone bed at the top of the Westbury Formation, and compare the faunas. The Rhaetian at Hampstead Farm Quarry, Chipping Sodbury, Gloucestershire, UK, has produced more than 26,000 identifiable microvertebrate remains, including teeth and scales of chondrichthyan and osteichthyan fishes, as well as vertebrae of sharks, bony fishes, ichthyosaurs, and plesiosaurs. The higher bone bed (‘bed 9’) contains more small specimens than the basal bone bed, and they are also less abraded, suggesting less transport. Both bone beds yield largely the same taxa, but Rhomphaiodon minor and rare Vallisia coppi and Sargodon tomicus are found only in the basal bone bed. Duffinselache is reported only from units above the basal bone bed, but low in the Westbury Formation, and durophagous teeth only from two horizons. Four out of nine chondrichthyan species are common to both bone beds, whereas Rhomphaiodon minor and Ceratodus are absent, and hybodonts in general are rarer, in bed 9. Bed 9 is the richer source of marine reptile remains, including ichthyosaur teeth, jaw fragments, vertebrae, rare plesiosaur teeth and vertebrae, and a few Pachystropheus vertebrae and limb bones. Whereas the basal bone bed represents considerable transport and possible storm bed deposition associated with the onset of the Rhaetian Transgression, bed 9 was deposited under a lower energy regime.

Relationship Between Biotype and Bone Morphology in the Lower Anterior Mandible: An Observational Study.

Different clinical parameters have been advocated as potential predictors of alveolar and basal jawbone morphology. The aim of this study is to describe, by tomographic means, alveolar and basal osseous dimensions of the anterior mandible in healthy individuals and evaluate potential correlations with biotype, along with other clinical parameters. One hundred consecutive healthy patients needing surgery in the posterior mandible were enrolled in this observational study (group 1 = 50 patients with thin biotype; group 2 = 50 patients with thick biotype). Data were collected for: 1) Little irregularity index for anterior crowding; 2) molar and canine class relationship; 3) previous orthodontic treatment; 4) gingival recession; and 5) band of keratinized gingiva for each of the six anterior mandibular teeth (#22 through #27). At the most mid-buccal computerized tomography slice of each tooth, other parameters were measured, including: 1) distance from the cemento-enamel junction to the bone crest; 2) tooth torque (TT); 3) labial cortical bone thickness (BT) for alveolar and basal bone; and 4) BT 5 and 10 mm apical to the tooth apex. Data were statistically analyzed, and significance was set at P ≤0.05. Mean thickness of alveolar bone ranged from 6.66 to 4.51 mm (standard deviation [SD] = 1.46 for tooth #27; SD = 1.01 for tooth #25) whereas mean thickness of basal bone ranged from 8.9 to 8.2 mm (SD = 2.06 for tooth #22; SD = 2.06 for tooth #26). Mean thickness of bone at 5 mm from apex ranged from 11.94 to 10.47 mm (SD = 2.96 for tooth #25; SD = 2.22 for tooth #22), whereas mean thickness of bone at 10 mm from apex ranged from 13.75 to 11.08 mm (SD = 2.79 for tooth #25; SD = 2.53 for tooth #27). No statistically significant differences were detected among biotypes, whereas: 1) TT, 2) age, and 3) smoking habit were often predictors of reduction in BT in a multiple linear regression model. Male sex was often a predictor of positive changes in BT, and previous orthodontic therapy was a protective factor against developing bone loss >5 mm. Although some differences were detected among biotypes, data indicate that biotype does not play a fundamental role in influencing alveolar BT, whereas other variables (i.e., TT, sex, age, and smoking habit) do influence alveolar BT. Further studies are needed to better understand the extent of influence of each clinical variable.

The Rhaetian vertebrates of Chipping Sodbury, South Gloucestershire, UK, a comparative study

Microvertebrates are common in the basal bone bed of the Westbury Formation of England, documenting a fauna dominated by fishes that existed at the time of the Rhaetian Transgression, some 206Myr ago. Two sites near Chipping Sodbury, south Gloucestershire, Barnhill Quarry and Chipping Sodbury railway cutting, show differing faunas. Top predators are the large bony fish Severnichthys and the shark Hybodus cloacinus, which preyed on smaller sharks such as Lissodus and Rhomphaiodon. These fishes in turn may have fed on a mixed diet of other fishes and invertebrates, and Lissodus was a shell crusher. Comparisons of these faunas with others described recently from the Bristol region, and from Devon, indicate remarkable faunal similarities in the Rhaetian basal Westbury Formation bone bed over a wide area, based on a variety of ecological statistics that document species diversities and relative abundances. Only the fauna from the Chipping Sodbury railway cutting differs significantly.

The Cenomanian short snout enchodontid fishes (Aulopifomes, Enchodontidae) from Sierra Madre Formation, Chiapas, southeastern Mexico

In this paper the short snout Cenomanian enchodontids from the El Chango quarry, Chiapas, southeastern Mexico, are reviewed. Unicachichthys multidentata nov. gen. and sp. is named and identified as a new member of the Enchodontidae because it has the predorsal scute series that is the distinctive character of such family. This new genus resembles other short snout enchodontids, as Enchodus and Eurypholis; however, Unicachichthys differs from these and other members of the family because it shows characters ever observed, including a multitoothed dermopalatine, the presence of a basal sclerotic bone, and the serrations in the posterior edge of the preopercle vertical limb. The inclusion of Unicachichthys in two phylogenetic analyses, based on studies previously performed, suggests that this is a primitive representative of the family Enchodontidae. Additionally specimens of two different species of Enchodus from the El Chango quarry are also described; these specimens are so scarce and fragmentary that it is not possible to determine their specific taxonomic identity. The record of these Mexican fossils enrich the knowledge about the diversity of Cenomanian enchodontids in the North American domain of the Tethys Sea, which now contains new taxa that should be considered in future efforts to recognize the phylogenetic and biogeographic processes experienced by this fish group.