Jaw Length Research Articles

Effects of egg size, food supply and spawning time on early life history success of haddock Melanogrammus aeglefinus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 285:169-180 (2005) - doi:10.3354/meps285169 Effects of egg size, food supply and spawning time on early life history success of haddock Melanogrammus aeglefinus R. M. Rideout1,2,3,*, E. A. Trippel1, M. K. Litvak2 1Biological Station, Fisheries and Oceans Canada, 531 Brandy Cove Road, St. Andrews, New Brunswick E5B 2L9, Canada 2Department of Biology and Centre for Coastal Studies and Aquaculture, University of New Brunswick Saint John, New Brunswick E2L 4L5, Canada 3Present address: Fisheries Conservation Group, Marine Institute of Memorial University of Newfoundland, PO Box 4920, St. John’s, Newfoundland A1C 5R3, Canada *Email: rick.rideout@mi.mun.ca ABSTRACT: Eggs and larvae produced by pairs of spawning haddock Melanogrammus aeglefinus were monitored between 2001 and 2003 to determine the effects of spawning time, egg size and food supply on early life history success. Females usually released eggs at 3 d intervals. All females exhibited a continuous decrease in egg diameter and dry weight with consecutive batches, but the decrease in size did not influence fertilization or hatching success. Larval size (standard length and dry weight), yolk area, eye diameter, myotome height, and finfold area were all positively related to egg size and therefore decreased between early- and late-season larvae produced by the same spawning pairs. Differences in larval morphology persisted for at least the first 5 d after hatching. Jaws were not developed at hatching (5°C), but jaw length did show a strong positive relationship with egg size at 5 d post-hatch (dph). The ability of newly hatched larvae to withstand periods of starvation was directly related to initial egg size. Under high prey abundance (5000 l-1) larval survival to 20 dph was highly variable (1.8 to 50.7%) with no differences in survivorship or specific growth rate (0.818 to 0.936% d-1 in standard length) for larvae from early-, middle- and late-season egg batches. With low prey density (1000 l-1) survival of larvae from late-season egg batches was significantly lower (0.4%) than those from early egg batches (1.8%). No differences in larval specific growth rate existed between early and late batches, but growth rate was reduced in both cases with low food abundance (0.683 to 0.690 d-1 in standard length). Results suggest that smaller larvae produced late in the spawning season have reduced feeding capabilities and may experience lower survivorship in the ocean than larger, early-season larvae. KEY WORDS: Haddock · Spawning time · Egg size · Larvae · Prey density · Early life history success · Recruitment Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 285. Online publication date: January 19, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Possible evidence of a venom apparatus in a Middle Jurassic Sphenodontian from the Huizachal red beds of Tamaulipas, México

ABSTRACT A new sphenodontid is described from the Middle Jurassic red beds in Huizachal Canyon, Tamaulipas, northern Mexico. The new taxon is characterized by the presence of two fang-like acrodont teeth at the anterior end of the lower jaw similar to those of the upper Jurassic sphenodontian Theretairus antiquus from the Morrison Formation. However, the new sphenodontian has a single well established groove on the anteromedial surface of each fang, here interpreted as a venom conducting groove convergent with those of opisthoglyphous colubrids and helodermatid lizards. The presence of a complex venom apparatus is supported by the reduction of the postcoronoid portion of the lower jaw to only 30% of the total jaw length and the anterior displacement of the jaw articulation by an unusual, medially inflected condyle. The shortening of the postcoronoid portion of the jaw reduces the estimated jaw moment-arm, trading bite strength for speed; simultaneously the mouth gape is increased by an additional 100% compared to other sphenodontians. Both modifications are necessary in an akinetic skull to facilitate venom injection to the victims. The phylogenetic relationships of the new sphenodontian are uncertain although the presence of propalinal jaw action and caniniform teeth suggests close relationship with Theretairus, Cynosphenodon, and Sphenodon. The transformation series leading to the presence of one or two caniniform teeth can be reconstructed either as an independent origin for both conditions or as an ordered transformation from one to two caniniform teeth. The new sphenodontian adds to the growing list of unusual forms and corroborates the view that Rhynchocephalia were once a very diverse group.

Reproductive Ecology of Pterapogon kauderni, an Endemic Apogonid from Indonesia with Direct Development

Pterapogon kauderni does not have secondary sexual dimorphism, and has an equal sex ratio (50.8% males : 49.2% females). Females first mature at a length of about 34 mm. Data from both laboratory-bred and wild-collected eggs and embryos are not consistent with the presence of differential reproductive allocation in this species. Analysis from clutches brooded by wild-collected males shows a significant intra-clutch and among-clutch variation in egg size. Mean individual egg size (diameter, volume, or weight) is not correlated with the size (standard length, head length, or lower jaw length) of the males brooding those eggs. P. kauderni has a lunar reproductive cycle, with a major spawning peak during full moon and a smaller peak during the last quarter. Similarly, it has a major juvenile release (settlement) peak at full moon, with a minor peak at new moon. However, one population, which is located in a site with distinct environmental conditions and which was sampled a year earlier, shows a different reproductive pattern, last quarter being the phase where most of spawn and release events take place.

Chromosomal aberrancy and the level of fluctuating asymmetry in black-striped mouse (Apodemus agrarius): effects of disturbed environment.

Analysis of chromosomal aberrations in bone marrow cells and determination of the level of fluctuating asymmetry (FA) for eight bilateral cranial traits were used to estimate effects of disturbed environment on natural populations of small mammals. During the spring and fall of 1994-2000 (except in 1999) black-striped mice (Apodemus agrarius) were collected from a polluted industrial area (Pancevo) and from an unpolluted reference site (Cer) in Serbia and Montenegro. Mice from the polluted area had significantly higher mean number of aberrant cells per individual than those in the reference site (p<0.01). Both sexes had the greater number of lesions in the polluted site than in the reference one. Also, there were no significant differences between sexes, neither within the same site/season nor between sites/seasons. Chi-square analysis of the difference between lesions per individual and aberrant cells per individual among sites showed that no site deviated from the expected difference (p=1.000). Developmental stability, assessed as FA, was reduced in the polluted area for two traits (width of lower jaw and length of the diastema lower jaw). Juvenile animals from the polluted area had significantly higher levels of FA compared to those from the reference site for three traits (length of the foramina incisiva, distance between incisor and the third upper molar, and length of the upper molars row). Juvenile animals from the polluted area had significantly higher levels of FA for three traits (length of the foramina incisiva, length of the lower molars row and width of lower jaw) compared to adult ones. In the polluted area seasonal differences were detected for two traits (length of the foramina incisiva and length of the upper molars row). Finally, Apodemus agrarius may be an important species for environmental quality evaluation studies based on an assay using a combination of end-points.

Paternal effects on haddock early life history traits

Paternal effects on haddock Melanogrammus aeglefinus early life history traits were examined by crossing eggs and sperm in a nested design and analysing the progeny at 0, 5 and 10 days post‐hatch (dph). The proportion of the variance in early life history traits that was due to paternity was significant for hatching success, larval standard length, myotome height, jaw length and yolk size, but not eye diameter or yolk utilization efficiency. Some morphological traits were influenced more by paternity than maternity. The findings suggest that the importance of males in the early life history success of marine fishes be reconsidered.

Age-related foetal sex ratio bias in Iberian red deer ( Cervus elaphus hispanicus ): are male calves too expensive for growing mothers?

Several theories predict offspring biases towards males or females with increasing reproductive resources of the mother to maximize reproductive returns by offspring, or as a result of prohibitive cost of the most expensive sex for young mothers or those in poor condition. This study examines foetus sex of 221 harvested hinds in a food-supplemented game estate for 10 years, according to hind age class (yearlings, subadults or adults), precise age, body mass and condition, and jaw length. A logistic model showed that hinds had a greater probability of bearing a male foetus with increasing age class, but not with any other variable. The greatest bias was found in yearling hinds. After controlling for age class and mass, jaw length was smaller in pregnant compared to non-pregnant yearlings and subadults, which suggests a trade-off between reproduction and growth. The bias towards females in yearlings increased as gestation proceeded, which suggests that the bias might be a result of selective abortion of male foetuses. Although results do not exclude an investment in males to increase number of grand-offspring, they suggest that young hinds may produce daughters as a trade-off between low energetic-cost offspring and their need to grow.

Paraheminodus kochiensis Kamohara, 1957 (Teleostei: Peristediidae), a junior synonym of Paraheminodus murrayi (G�nther, 1880), with a comparison of Paraheminodus murrayi and Paraheminodus laticephalus (Kamohara, 1952)

Paraheminodus kochiensis Kamohara, 1957 (family Peristediidae), has been regarded by most workers as a junior synonym of P. murrayi (GUnther, 1880), but sufficient argument for combining the two species has not been made. A detailed comparison of the type and non-type material of P. kochiensis and P. murrayi revealed no significant differences between the two; thus, their synonymy is hereby confirmed. Paraheminodus murrayi and P. laticephalus (Kamohara, 1952) are clearly distinguished by the morphology of the upper jaw teeth, length of the upper jaw, and by the number of barbels.

Lycenchelys melanostomias Toyoshima, 1983, a senior synonym of L. brevimaxillaris Toyoshima, 1985 (Teleostei: Zoarcidae)

The holotype of Lycenchelys melanostomias Toyoshima, 1983, the original description of L. brevimaxillaris Toyoshima, 1985, and 54 Lycenchelys specimens from the Okhotsk Sea and the Pacific off northern Japan were compared. Lycenchelys brevimaxillaris was distinguished from L. melanostomias in having 4 postorbital pores, pale-colored stomach, and smaller mouth in the original description (vs. 5 postorbital pores, dark stomach, and larger mouth in L. melanostomias). However, L. melanostomias has 4 or 5 postorbital pores, as recently pointed out. The coloration of the stomach of the L. melanostomias holotype and the new material is pale. Meristic counts and proportional measurements of the new material include those of the type specimens of both species. The length of upper jaw exhibits sexual dimorphism in L. melanostomias larger than ca. 170 mm TL: upper jaw reaching near posterior margin of pupil in males vs. near middle of eye in females. The L. brevimaxillaris holotype (female) agrees well with female L. melanostomias in this character. These facts indicate that L. melanostomias is a senior synonym of L. brevimaxillaris.

Diet divergence, jaw size and scale counts in two neighbouring populations of tiger snakes (Notechis scutatus)

AbstractLarge snakes usually possess a higher number of scales to cover their larger bodies and their larger heads. It has been suggested that a diet based on large prey items also favours the development of scale number because the skin would be more extensible and would enable easier swallowing of voluminous prey. A recent study, however, suggested that although body size positively influences scale count in snakes, diet is probably unimportant (Shine, 2002). We took advantage of a natural experiment that separated two neighbouring and genetically indistinguishable populations of tiger snakes in the vicinity of Perth, Western Australia. In one population, situated on a small coastal Island (Carnac Island), snakes feed primarily on seagull chicks (large prey). In the second population, located on the mainland (Herdsman Lake), snakes feed mostly on frogs (small prey). Carnac Island snakes possess more scales (labial and mid-body rows) and larger relative jaw lengths compared with Herdsman Lake snakes. Although preliminary, these data suggest that tiger snakes, whose many populations show contrasted feeding habits, are suitable models to test the "dietary habits / scale count" hypothesis.

Body size plasticity and local variation of relative head and body size sexual dimorphism in garter snakes (Thamnophis sirtalis)

AbstractFor snakes, prey size and sex are two possible determinants of head and body size. In garter snakes Thamnophis sirtalis, females are generally longer and have greater body weights than males, and also have larger relative head sizes, which may facilitate foraging success. The selective pressures that account for sexual size dimorphism in garter snakes have not been unequivocally demonstrated. In this study, the body (length and mass) and head (head length, head width, jaw length, inter‐ocular distance) sizes of garter snakes inhabiting two nearby but ecologically dissimilar sites with different types of available prey were compared. Overall, the adult female snakes were larger and had greater relative head sizes than males. Males from the two sites did not differ significantly in body or head sizes. However, the mean body length and mass of females from a site where vertebrates are included in the diet were greater than that of females feeding almost exclusively on earthworms. There were also significant site differences in all four head measurements in females, although the direction of the difference varied by site. Diet‐induced morphological plasticity is well documented and was evident in this study, although the relative roles of genotype, ontogeny, and competing selective forces in the expression of such plasticity can only be ascertained through future experimental studies.

Evolutionary trends and the origin of the mammalian lower jaw

The single bony element forming the lower jaw of living mammals, the dentary, has been interpreted as representing the culmination of a long and gradual evolutionary trend. Numerous fossil nonmammalian synapsids (“mammal-like reptiles”) show varying degrees of enlargement of the dentary and concomitant reduction in the postdentary bones. To quantitatively reexamine patterns of morphological change in the evolution of the mammalian lower jaw, measurement and discrete character data were collected from 322 fossil synapsid mandibles spanning Late Carboniferous through Jurassic time. Measurements confirm that the relative contribution of the dentary increased in theriodont (advanced therapsid) evolution with regard to both stratigraphic and phylogenetic position. However, dentary enlargement and postdentary reduction failed to typify all therapsid subclades. Qualitative characters of the mandible were used to quantify morphological similarity with regard to the early mammal Morganucodon . Analyses contrasting stratigraphic and phylogenetic position with mammalian similarity indicate that mandibular evolution was primarily conservative, with only anomodont therapsids evolving substantial morphological novelty. Scaling analyses comparing the area of the dentary and postdentary regions to jaw length uniformly show isometry or slight positive allometry, although cynodont therapsids have a smaller postdentary region than any other therapsid subgroup. These results suggest that body size decreases cannot fully explain the reduction of the postdentary bones. Finally, step size bias was tested as a mechanism for explaining long-term trends. Qualitative data reveal no significant difference in the magnitude of character changes occurring in mammalian and nonmammalian directions.

Acromegalic features in growth hormone (GH)-deficient patients after long-term GH therapy.

Craniofacial, hand, foot and somatic growth depend on normal GH secretion. Acromegalic features have been described in children with GH insensitivity after IGF-I treatment. We observed patients with acromegalic features such as increase of foot size, nose and jaw enlargement among our cases with GH deficiency, treated with standard recombinant (rh)GH doses. The aim of our study was to analyse the possible factors involved in the development of acromegalic features in these patients. We evaluated 21 patients, 17 with combined pituitary hormone deficiency and four with isolated GH deficiency treated with rhGH (0.05-0.15 U/kg/day, sc, at night) for 2-12 years who achieved final height. IGF-I and IGFBP-3 were measured before and every 6 months during therapy and bone age was evaluated yearly. At the end of therapy, patients' hand and foot sizes and height were measured and plotted on nomograms for hand according to height and age, and foot size according to height. Lateral radiographs of the face were performed to obtain the linear measurement of the lower jaw length. Foot size was greater than 97th percentile in 8/21 patients and lower jaw length was greater than +2SD in 4/21 patients. Patients were classified in two groups: group 1 (with foot size greater than 97th percentile and/or lower jaw length greater than +2SD) consisted of 11 patients (six females); nine had combined pituitary hormone deficiency (six associated to hypogonadotrophic hypogonadism) and three had isolated GH deficiency; group 2 (with foot size smaller than 97th percentile and lower jaw length less than +2SD) consisted of 10 patients (seven boys); nine had combined pituitary hormone deficiency (six associated to hypogonadotrophic hypogonadism) and one with isolated GH deficiency. During treatment, IGF-I levels ranged from < or = 3 to +2SD and IGFBP-3 levels ranged from -3 to +2SD, in both groups. We observed no statistically significant differences between the two groups regarding chronological age, bone age, height at the beginning and at the end of therapy, pubertal development, duration of rhGH treatment and IGF-I and IGFBP-3 levels (P > 0.05). Foot size percentile exceeded final height percentile in 11/21 patients (seven girls). Long-term rhGH treatment with standard doses might be associated with acromegalic features (increased foot size and lower jaw measurements) in patients with GH deficiency who achieved final height, especially in girls. Neither the clinical nor the hormonal parameters, IGF-I and IGFBP-3 levels, were useful to predict the development of these features. Further studies are necessary to analyse the frequency of this side-effect and how to prevent it.

Migratory costs and contemporary evolution of reproductive allocation in male chinook salmon.

Energetically demanding migrations may impact the resources available for reproductive trait development and activity, and hence favour evolution of new investment strategies for remaining resources. We conducted a large-scale experiment to evaluate the proximate cost of migration on male reproductive investment in chinook salmon (Oncorhynchus tshawytscha) and contemporary evolution of reproductive allocation. Experimentally induced differences in migratory costs (17 km inland and 17 m elevation vs. 100 km and 430 m) influenced dorsal hump size and upper jaw length, two traits influencing male mating success that are developed during migration. Longer migration also reduced tissue energy reserves available for competition and length of breeding life. Corresponding shifts in the balance between natural and sexual selection appear to have been responsible for heritable population divergence in secondary sexual trait investment, in approximately 26 generations, following colonization of spawning sites with different migratory demands.

Trichiurus nickolensis , a new hairtail from Australia belonging to the Trichiurus russelli complex (Perciformes: Trichiuridae)

A new hairtail, Trichiurus nickolensis, is described on the basis of ten specimens collected off northwestern Australia, off the Northern Territory, and in the Gulf of Carpentaria, Queensland. The new species strongly resembles T. brevis Wang and You in Wang et al., 1992, off Hainan Island, South China Sea, and T. russelli Dutt and Thankam, 1966, off the Waltair Coast, Andhra Pradesh, India, in having the highest point of the supraoccipital crest situated directly above the posterior margin of the eye and a relatively short caudal peduncle. Trichiurus nickolensis differs from those two species in being strongly pigmented on the anterior section of the dorsal fin membrane (vs. slightly pigmented), and having a dorsal head margin that appears concave in lateral view, rises gently from snout tip to above middle of orbit, and then extends more steeply to dorsal fin origin (vs. rising gently from tip of snout to dorsal fin origin). The new species also has a greater number of dorsal fin rays (III, 138–143 vs. III, 127–132 and III, 127–131 in T. brevis and T. russelli, respectively) and total vertebrae (160–166 vs. 147–155 and 149–153), and shorter preanal length (mean 30% TL vs. 33% TL and 35% TL), head length (11% TL vs. 12% TL and 13% TL) and upper jaw length (4% TL vs. 5% TL and 5% TL).

The ontogeny of bite‐force performance in American alligator (Alligator mississippiensis)

American alligators Alligator mississippiensis undergo major transformations in morphology and ecology during development. These include several thousand‐fold changes in body mass, modified snout and dental proportions, and shifts in diet from small, delicate foodstuffs to the inclusion of increasingly larger, more robust prey. How these changes in anatomical form contribute to actual physical performance and niche use is largely unknown. In the present study, bite‐force measurements for 41 specimens of A. mississipiensis, were made throughout ontogeny (hatchling–older adults) using a series of precision force transducers. How this performance indicator scaled with respect to cranial and whole‐body measurements was determined. Bite‐force production throughout development was contrasted with ontogenetic changes in trophic ecology. The influences of this performance measure on these changes were then analysed. The results showed a 800‐fold range (12–9452 N) of bite forces with values positively correlating with increases in body size. Scaling of biting forces through ontogeny showed positive allometry with respect to body mass, head length, jaw length, snout–vent length and total length. These patterns may be attributable to allometric growth of individual skeletal elements (and associated musculature), and/or progressive fusion and ossification of skull and jawbones during development. The overall pattern of force increase throughout ontogeny did not vary in association with major shifts in diet. Notably, the bite‐force values for adult A. mississippiensis are the highest measured for any living animal and represent the first measures for a large crocodilian. Additionally, these data provide the first documentation of how bite force changes during ontogeny in a reptile. By bridging the rich morphological and ecological databases for these animals, this study opens the door to a comprehensive understanding of feeding in A. mississippiensis. Furthermore, it provides groundwork for standardized comparative studies of feeding among crocodilian, reptilian, or other gnathostome vertebrates.

Relative feeding specialization may depress ontogenetic, seasonal, and sexual variations in diet: the endemic lizard Cnemidophorus littoralis (Teiidae).

We investigated the feeding habits of the teiid lizard Cnemidophorus littoralis in the markedly seasonal habitat of Restinga da Barra de Maricá (22 degrees 57'S, 43 degrees 50'W), Rio de Janeiro State, Brazil, to evaluate to what extent its diet is ontogenetically, sexually, and/or seasonally conservative. Lizard stomach contents were analyzed, identified, counted, estimated for volume (in mm3), and grouped in four classes (active, sedentary, and clumped preys, and plant material). The relative contribution of each food class to the total prey volume consumed by adult males and females and juveniles was compared in three ways: between juveniles and adults, sexes, and seasons (wet and dry). Sexual dimorphism in head size was tested by comparing head width and jaw length using analysis of covariance (ANCOVA). Isopterans were the most important prey item, occurring in 93% of the lizard stomachs examined and corresponding to 96.4% of total prey content and 69.7% of total prey volume. They occurred in high frequencies in the stomachs of C. littoralis throughout all study months. We found no sexual, ontogenetic, or seasonal differences in C. littoralis diet although the sexes differed significantly in head width. We concluded that isopterans are the main item in the diet of C. littoralis in Restinga da Barra de Maricá, both for juveniles and adults. The lack of seasonal, sexual, or ontogenetic variation in its diet results from the massive consumption of these insects. Isopterans are small, occur in clumps, and are available year-round, and thus are an advantageous food item for the active forager C. littoralis. We also found sexual dimorphism in the head size of C. littoralis: males have wider heads than females. This dimorphism, however, does not seem to be related with the diet of the species, and is probably a result of sexual selection.

Directional selection has shaped the oral jaws of Lake Malawi cichlid fishes.

East African cichlid fishes represent one of the most striking examples of rapid and convergent evolutionary radiation among vertebrates. Models of ecological speciation would suggest that functional divergence in feeding morphology has contributed to the origin and maintenance of cichlid species diversity. However, definitive evidence for the action of natural selection has been missing. Here we use quantitative genetics to identify regions of the cichlid genome responsible for functionally important shape differences in the oral jaw apparatus. The consistent direction of effects for individual quantitative trait loci suggest that cichlid jaws and teeth evolved in response to strong, divergent selection. Moreover, several chromosomal regions contain a disproportionate number of quantitative trait loci, indicating a prominent role for pleiotropy or genetic linkage in the divergence of this character complex. Of particular interest are genomic intervals with concerted effects on both the length and height of the lower jaw. Coordinated changes in this area of the oral jaw apparatus are predicted to have direct consequences for the speed and strength of jaw movement. Taken together, our results imply that the rapid and replicative nature of cichlid trophic evolution is the result of directional selection on chromosomal packages that encode functionally linked aspects of the craniofacial skeleton.

Surgery of the lateral nasal wall and ethmoid: effects on sinonasal growth: An experimental study in rabbits

Objective: To assess the impact of lateral nasal wall surgery on sinonasal growth Methods: Twenty young New Zealand White rabbits, 6 weeks of age, were included in this experimental study. Surgery was performed on two groups of ten animals each (series I and II). Entrance to the left nasal cavity is achieved through the nasal dorsum via mobilization and rotation of the left nasal bone. Series I: partial resection of the lateral nasal wall (including the ostium to the maxillary sinus) on the left side. Series II: partial resection of the lateral nasal wall and anterior ethmoid. Follow-up period was 20 weeks. Twenty rabbits served as controls. Results: In series I, all skulls have grown normally. In series II the nasal dorsum has also developed symmetrically. Snout length and growth of upper jaw are normal; there is no malocclusion. Three skulls show a slight deviation of the nasal dorsum (two to the left, one to the right). Morphometric measurements of 20 points on the skulls show no significant difference between the control group and the experimental series I and II. Conclusion: This experimental study demonstrates that visually controlled partial resection of the bony sinonasal wall, with or without resection of the anterior ethmoid does not affect later development of nose and upper jaw on condition that eventually underlying cartilage is preserved. Contradictory results from other experimental studies, previously published and concerning negative effects of sinus surgery, might be attributed to surgical traumatization of intranasal cartilage structures, in particular, the upper lateral cartilages.

Ontogeny of feeding function in the gray short-tailed opossumMonodelphis domestica: empirical support for the constrained model of jaw biomechanics

The constrained model of masticatory function enables specific predictions of bite force potentials in skulls of differing craniodental configurations. In this study, empirical support for the constrained model is provided using maximum voluntary bite force data along Region I and II of the jaws of gray short-tailed opossums Monodelphis domestica. Then, growth series of M. domestica are used to assess how bite force potential changes with growth by evaluating craniodental changes using longitudinal sets of dorsoventral radiographs and by assessing maximal bite force potential at the Region I-II boundary of the jaw in juveniles (aged 70-80 days) and adults. Our findings show that, while juveniles and adults alike enclose at least three molariform teeth within Region II (the area of highest bite force potential along the jaw), age-dependent elongation of the masticatory muscle resultant lever arm and narrowing of the palate relative to jaw length especially enhance the mechanical advantage of the adductor muscle resultant in adults. While maximal bite forces at the Region I-II boundary are absolutely greater in adults, these bite forces scale isometrically with body mass, which suggests that mass-specific forces exerted by jaw adductor muscles of larger (adult) opossums are disproportionately smaller than those exerted by smaller (juvenile) opossums.

Origins and escalation of herbivory in fishes: a functional perspective

One of the central goals in paleoecology is to understand the nature and consequences of biotic interactions. In marine systems, it has been argued that one of the major steps in the escalation of biotic interactions was marked by the origins of grazing fishes in the Cenozoic. Here I investigate the origins of herbivory and grazing in marine fishes using analyses of functional morphospace. Closing and opening lever ratios and relative length of the lower jaw are used to construct a plot of functional morphospace, a quantitative description of the potential feeding modes of fishes. Four fish faunas were examined, spanning the Mesozoic and Cenozoic (Triassic, Jurassic, Eocene and Recent). All three fossil faunas are from conservation Lagerstätten in the central Tethys, in the vicinity of coral reefs or coral-bearing hardgrounds. Changes in functional morphospace occupation reveal a marked shift in the Cenozoic, with the appearance of fishes with relatively small forceful jaws. In Recent faunas, this functional morphospace is occupied almost exclusively by grazing herbivores. This taxon-independent morphological signal of herbivory was lacking in the Mesozoic faunas, was first recorded in the Eocene, and persisted throughout the Cenozoic. This suggests that the Cenozoic did indeed witness the appearance and proliferation of herbivory and grazing by marine fishes. The arrival of these piscine herbivores had the potential to fundamentally alter the dynamics of benthic marine communities.