Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs

Background

Tooth replacement rate can be calculated in extinct animals by counting incremental lines of deposition in tooth dentin. Calculating this rate in several taxa allows for the study of the evolution of tooth replacement rate. Sauropod dinosaurs, the largest terrestrial animals that ever evolved, exhibited a diversity of tooth sizes and shapes, but little is known about their tooth replacement rates.

Methodology/Principal Findings

We present tooth replacement rate, formation time, crown volume, total dentition volume, and enamel thickness for two coexisting but distantly related and morphologically disparate sauropod dinosaurs Camarasaurus and Diplodocus. Individual tooth formation time was determined by counting daily incremental lines in dentin. Tooth replacement rate is calculated as the difference between the number of days recorded in successive replacement teeth. Each tooth family in Camarasaurus has a maximum of three replacement teeth, whereas each Diplodocus tooth family has up to five. Tooth formation times are about 1.7 times longer in Camarasaurus than in Diplodocus (315 vs. 185 days). Average tooth replacement rate in Camarasaurus is about one tooth every 62 days versus about one tooth every 35 days in Diplodocus. Despite slower tooth replacement rates in Camarasaurus, the volumetric rate of Camarasaurus tooth replacement is 10 times faster than in Diplodocus because of its substantially greater tooth volumes. A novel method to estimate replacement rate was developed and applied to several other sauropodomorphs that we were not able to thin section.

Conclusions/Significance

Differences in tooth replacement rate among sauropodomorphs likely reflect disparate feeding strategies and/or food choices, which would have facilitated the coexistence of these gigantic herbivores in one ecosystem. Early neosauropods are characterized by high tooth replacement rates (despite their large tooth size), and derived titanosaurs and diplodocoids independently evolved the highest known tooth replacement rates among archosaurs.     

Growth rates and body condition factors of Alligator mississippiensis in coastal Louisiana wetlands: A comparison of wild and farm-released juveniles

• 1.1. Growth rates and body condition factors for native wild and captive-raised juvenile alligators (Alligator mississippiensis) that had been released to the wild were studied using tag-recapture methods for 274 alligators over a 4-year period. Alligators were grouped by sex, size class, source (farm-released vs native wild) and as to whether they had overwintered or not.
• 2.2. In most groups, the farm-released alligators grew significantly better than wild alligators matched for sex and size; in the remaining groups the post-release alligators grew as well as their counterparts, though not better.
• 3.3. Overwintering tended to slow growth rates in both groups, but farm-released alligators still demonstrated superior growth over native wild alligators even after overwintering.
• 4.4. Males tended to grow faster than females, though this trend was not always significantly greater. In no matched group did females grow faster than males.
• 5.5. Growth rates diminished with increasing size in native wild alligators (smaller alligators grew faster), but growth rates of farm-released alligators remained accelerated even at the larger size classes.
• 6.6. Growth curves were constructed using known recapture data with three growth models (von Bertlanffy, Gompertz and logistic); the calculated maximum attainable length and growth parameters were significantly larger (P < 0.01) for farm-released alligators than wild using all three models.
• 7.7. Body condition factors were not different in captive-raised post-released alligators than native wild alligators.

     

Thermal acclimation,mitochondrial capacities and organ metabolic profiles in a reptile (<Emphasis Type="Italic">Alligator mississippiensis</Emphasis>)

Reptiles thermoregulate behaviourally, but change their preferred temperature and the optimal temperature for performance seasonally. We evaluated whether the digestive and locomotor systems of the alligator show parallel metabolic adjustments during thermal acclimation. To this end, we allowed juvenile alligators to grow under thermal conditions typical of winter and summer, providing them with seasonally appropriate basking opportunities. Although mean body temperatures of alligators in these groups differed by approximately 10°C, their growth and final anatomic status was equivalent. While hepatic mitochondria isolated from cold-acclimated alligators had higher oxidative capacities at 30°C than those from warm-acclimated alligators, the capacities did not differ at 20°C. Cold acclimation decreased maximal oxidative capacities of muscle mitochondria. For mitochondria from both organs and acclimation groups, palmitate increased oligomycin-inhibited respiration. GDP addition reduced palmitate-uncoupled rates more in liver mitochondria from warm- than cold-acclimated alligators. In muscle mitochondria, carboxyatractyloside significantly reduced palmitate-uncoupled rates. This effect was not changed by thermal acclimation. The aerobic capacity of liver, skeletal muscle and duodenum, as estimated by activities of cytochrome c oxidase (COX), increased with cold acclimation. At acclimation temperatures, the activities of COX and citrate synthase (CS) in these organs were equivalent. By measuring COX and CS in isolated mitochondria and tissue extracts, we estimated that cold acclimation did not change the mitochondrial content in liver, but increased that of muscle. The thermal compensation of growth rates and of the aerobic capacity of the locomotor and digestive systems suggests that alligators optimised metabolic processes for the seasonally altered, preferred body temperature. The precision of this compensatory response exceeds that typically shown by aquatic ectotherms whose body temperatures are at the mercy of their habitat.     

Febrile response to infection in the American alligator (Alligator mississippiensis)

Temperature probes were inserted into the stomachs of juvenile American alligators (Alligator mississippiensis) maintained outdoors at ambient fluctuating temperatures. Internal body temperatures (T_b) were measured every 15 min for two days, and then the alligators were injected with bacterial lipopolysaccharide (LPS), pyrogen-free saline, or left untreated. Alligators injected intraperitoneally with LPS exhibited maximum T_bs 2.6 ± 1.1 °C and 3.5 ± 1.2 °C higher than untreated control animals on days one and two after treatment, respectively. T_bs for these animals fell to within control ranges by day three postinjection. Similarly, mean preferred body temperatures (MPBTs) were significantly higher for LPS-injected alligators on days one (4.2 ± 1.8 °C) and two (3.5 ± 1.6 °C) after treatment. Intraperitoneal injection of heat-killed Aeromonas hydrophila, a gram-negative bacterium known to infect crocodilians, resulted in a fever while injection of Staphylococcus aureus (gram positive) did not elicit a febrile response. Injection of LPS in alligators maintained indoors in a constant temperature environment resulted in no increase in internal T_b. These results indicate that alligators did not exhibit a febrile response in the absence of a thermal gradient, and suggest that febrile responses observed are probably behavioral in nature.     

The appearance pattern of tooth germs in the round crucian carp,Carassius auratus grandoculis

Cyprinid fishes generally replace their teeth alternately and cephalad. The larvae ofCarassius auratus grandoculis also replace their teeth alternately and cephalad, in a pattern of 4-2-3-1-. However, adults ofCarassius species replace their teeth from anterior to posterior, in a pattern of 1-2-3-4-1-. So I analyzed the appearance pattern of tooth germs in larvae and juveniles inCarassius auratus grandoculis. At stage 5 of the post-larval period, developmental difference is made between both sides. In the pharyngeal dentition on one side developing poorly, the anterior tooth on the fifth replacement wave, tooth₄[An2] appeared later than the central teeth on following replacement wave, tooth₅[Pol]. Moreover, the anterior tooth on the seventh replacement wave, tooth₆[An2], appeared later than the central teeth on the following replacement wave, tooth₇[Pol], on both sides. The reverse of tooth germ appearance between anterior teeth and central teeth makes a change of replacement pattern from 4-2-3-1-4- to 1-2-3-4-1-. The change of replacement pattern is caused by the confusion of tooth germs of anterior teeth on both sides.Mylopharyngodon piceus andCyprinus carpio make a change of replacement patterns in the early juvenile period, too. This change of replacement pattern may be a specialized character among the subfamily Cyprininae.     

Structure, attachment, replacement and growth of teeth in bluefish, Pomatomus saltatrix (), a teleost with deeply socketed teeth

Tooth replacement poses many questions about development, pattern formation, tooth attachment mechanisms, functional morphology and the evolution of vertebrate dentitions. Although most vertebrate species have polyphyodont dentitions, detailed knowledge of tooth structure and replacement is poor for most groups, particularly actinopterygians. We examined the oral dentition of the bluefish, Pomatomus saltatrix, a pelagic and coastal marine predator, using a sample of 50 individuals. The oral teeth are located on the dentary and premaxillary bones, and we scored each tooth locus in the dentary and premaxillary bones using a four-part functional classification: absent (A), incoming (I), functional (F=fully ankylosed) or eroding (E). The homodont oral teeth of Pomatomus are sharp, deeply socketed and firmly ankylosed to the bone of attachment. Replacement is intraosseus and occurs in alternate tooth loci with long waves of replacement passing from rear to front. The much higher percentage of functional as opposed to eroding teeth suggests that replacement rates are low but that individual teeth are quickly lost once erosion begins. Tooth number increases ontogenetically, ranging from 15–31 dentary teeth and 15–39 premaxillary teeth in the sample studied. Teeth increase in size with every replacement cycle. Remodeling of the attachment bone occurs continuously to accommodate growth. New tooth germs originate from a discontinuous dental lamina and migrate from the lingual (dentary) or labial (premaxillary) epithelium through pores in the bone of attachment into the resorption spaces beneath the existing teeth. Pomatomus shares unique aspects of tooth replacement with barracudas and other scombroids and this supports the interpretation that Pomatomus is more closely related to scombroids than to carangoids.     

Tooth replacement patterns in young Caiman sclerops

Although there are many reports of tooth replacement patterns in lower vertebrates, few show the range of pattern to be found in a number of similar aged specimens of one species. Fifteen specimens of Caiman sclerops, head length 4–5 cms, were examined by a radiographic technique and their tooth replacement patterns analysed. Whole head radiography and dissected head radiographs were compared and the resulting tooth replacement waves were found to be comparable. Wave replacement (sensu Edmund, '60) in odd and even tooth positions in the tooth row was observed in all the specimens examined. Whereas most waves passed in a cephalad direction, wave reversal (caudad) was also observed, particularly in the anterior parts of the jaws. In some specimens simple alternation in tooth replacement was observed, particularly in the mid-portion of each quadrant. The smooth, age-related change-over from cephalad to caudad demonstrated by Edmund ('62) in captive Alligator mississippiensis was not observed in wild specimens of Caiman sclerops.     

Characteristics of American alligator bites on people in Florida

Human–American alligator (Alligator mississippiensis) conflict in Florida, USA, has increased since the early 1970s, along with the recovery of the American alligator population. To better understand factors contributing to the risk of people being bitten by free-ranging alligators in Florida, we evaluated the trend of alligator bites during 1971–2014 and examined characteristics associated with bites on people documented during 1948–2014. We classified 372 bites as either unprovoked or unintentionally provoked and used these in further analyses. Major injuries to victims occurred in 247 bite incidents. The estimated annual number of bites resulting in major injury to the victim increased from 3.5 to 7.0 during 1971–2014. The number of bites per Florida resident did not show a significant trend during 1971–2014. No significant change occurred in the frequency of fatal attacks during 1971–2014. Monthly frequency of bites was positively correlated with both mean maximum and mean minimum air temperatures but was not significantly correlated with testosterone concentration in adult male alligators, suggesting that bites are more likely related to feeding rates associated with seasonal fluctuations in ambient temperature than to aggression by male alligators during the breeding season. A high percentage of bites (41.8%) occurred in unnamed water bodies, which were generally small or man-made. Most (93.7%) victims were Florida residents, and 58.7% resided close to the incident site. Victims were predominantly male (81.4%), and adults were more frequently victims than were adolescents or children. Most victims (93.9%) were in the water or near the shore when bitten. Victims were more likely to sustain major injuries if the bite occurred in deeper water. Male alligators were more frequently (76.9%) responsible for bites. We found only 1 instance in which a bite was associated with defense of eggs or young by an adult female alligator. Evidence of people feeding alligators before the bite was documented in 34.7% of bite incidents. Twenty-two fatalities were attributed to alligator attacks, but we could not discern a pattern in the ages of victims. Alligators responsible for severe or fatal bites were predominantly in good condition with few deformities or injuries. Most alligator bites in Florida appeared to be attempts at feeding, although 36.8% of incidents entailed a single bite followed by immediate release, suggesting that alligators were unsure about their prey or were biting in defense. The risk of alligator bites can be reduced by educating people likely to interact with alligators and by selectively removing problem alligators in human residential areas and water bodies used regularly by people for swimming, wading, and shoreline activities. © 2019 The Wildlife Society.     

Isolation of faecal coliform bacteria from the American alligator (Alligator mississippiensis)

Aims: To determine whether American alligators (Alligator mississippiensis) are an unrecognized poikilothermic source of faecal coliform and/or potential pathogenic bacteria in South Carolina’s coastal waters. Methods and Results: Bacteria from the cloaca of American alligators, as well as bacteria from surface water samples from their aquatic habitat, were isolated and identified. The predominant enteric bacteria identified from alligator samples using biochemical tests included Aeromonas hydrophila, Citrobacter braakii, Edwardsiella tarda, Escherichia coli, Enterobacter cloacae, Plesiomonas shigelloides and putative Salmonella, and these were similar to bacteria isolated from the surface waters in which the alligators inhabited. Based on most‐probable‐number enumeration estimates from captive alligator faeces, faecal coliform bacteria numbered 8·0 × 10⁹ g^?1 (wet weight) of alligator faecal material, a much higher concentration than many other documented endothermic animal sources. Conclusions: A prevalence of enteric bacteria, both faecal coliforms and potential pathogens, was observed in American alligators. The high faecal coliform bacterial density of alligator faeces may suggest that alligators are a potential source of bacterial contamination in South Carolina coastal waters. Significance and Impact of the Study: These findings help to increase our understanding of faecal coliform and potential pathogenic bacteria from poikilothermic reptilian sources, as there is the potential for these sources to raise bacterial water quality levels above regulatory thresholds.     

Tooth replacement in the red-backed salamander, Plethodon cinereus

The developmental cycle of the teeth in Plethodon cinereus is analyzed on morphological grounds using alizarin preparations. All the stages in development do not occupy the same proportion of the life cycle time. Functional teeth and germs at an early stage in development occupy a large proportion of the life cycle time, whereas the processes of tooth shedding and ankylosis occur very quickly. The time during which any locus does not bear a functional tooth, and is therefore a non-functional locus, is reduced to a minimum. P. cinereus has a basic pattern of tooth replacement which is consistent with Zahnreihen which are 2.0 tooth spaces apart. Variations in the replacement pattern are common and these are produced by relatively small fluctuations in the spacing of the Zahnreihen around the ?mean? of 2.0. Localized disturbances which produce breaks in the replacement pattern and cause waves to cross also occur. These may be due to the failure of tooth germs to develop, the fusion of tooth germs, or may be the result of the inherent variability in a complex biological system. This variability causes individual tooth germs to develop too slowly or too quickly and hence assume an ?abnormal”? position thus causing breaks in the replacement pattern. Tooth replacement may be controlled by an intra-local mechanism(s) rather than by stimuli which travel along the jaw.     

Estimating Survival for Elusive Juvenile Pond-Breeding Salamanders

Juvenile vital rates have important effects on population dynamics for many species, but this demographic is often difficult to locate and track. As such, we frequently lack reliable estimates of juvenile survival, which are necessary for accurately assessing population stability and potential management approaches to conserve biodiversity. We estimated survival rates for elusive juveniles of 3 species, the ringed salamander (Ambystoma annulatum), spotted salamander (A. maculatum), and small-mouthed salamander (A. texanum), using 2 approaches. First, we conducted an 11-month (2016–2017) mark-recapture study within semi-natural enclosures and used Bayesian Cormack-Jolly-Seber models to estimate survival and recapture probabilities. Second, we inferred the expected annual juvenile survival rate given published vital rates for pre-metamorphic and adult ambystomatids assuming stable population growth. For all 3 species, juvenile survival probabilities were constant across recapture occasions, whereas recapture probability estimates were time-dependent. Further, survival and recapture probabilities among study species were similar. Post-study sampling revealed that the initial study period median estimate of annual survival probability (0.39) underestimated the number of salamanders known alive at 11 months. We therefore appended approximately 1 year of opportunistic data, which produced a median annual survival probability of 0.50, encompassing salamanders that we knew to have been alive. Calculation from literature values suggested a mean annual terrestrial juvenile ambystomatid survival probability of 0.49. Similar results among our approaches indicated that juvenile survival estimates for the study species were robust and likely comparable to rates in nature. These estimates can now be confidently applied to research, monitoring, and management efforts for the study species and ecologically similar taxa. Our findings indicated that similarly robust vital rate estimates for subsets of ecologically and phylogenetically similar species can provide reasonable surrogate demographic information that can be used to reveal key factors influencing population viability for data-deficient species. © 2020 The Wildlife Society.     

The effects of turbidity and vegetation on the risk of juvenile salmonids, Oncorhynchus spp., to predation by adult cutthroat trout, O. clarkii

Synopsis During their seaward migration, juvenile salmonids encounter structural and visual cover which varies between and within watersheds. In this study, the effects of two types of cover (turbidity and artificial vegetation) on the predation mortality of juvenile salmonids exposed to fish piscivores was investigated in outdoor concrete ponds. During experiments, adult coastal cutthroat trout, Oncorhynchus clarkii clarkii, were allowed to feed on juvenile salmonid prey — chinook salmon, O. tshawytscha, chum salmon, O. keta, sockeye salmon, O. nerka, and cutthroat trout — in separate trials. Daily instantaneous per capita predation rate was determined for each turbidity and vegetation treatment, within each trial. Mean predation rates varied between 1% and 76% daily. In the presence of cover, mean daily predation rates were 10–75% lower than those in controls (no vegetation and clear water), depending on prey species. Predation rates were significantly lower in the presence of vegetation cover and did not covary with prey size or species. The effects of turbidity were generally not significant and were not additive with the effects of vegetation. However, turbidity appeared to significantly reduce the effectiveness of vegetation as cover for juvenile chinook and sockeye salmon. We suggest that these two forms of cover do not affect risk of predation by fish piscivores to juvenile salmonids via the same mechanism.     

Tooth replacement and growth in the young green iguana,Iguana iguana

A study using eight rapidly growing young green iguanas (Iguana iguana; initial mean weight 68.0 ± 3.8 gm) examined the changes in the wave replacement of teeth, the increased size of the teeth, and the posterior migration of tooth positions over a period of 16 weeks. The teeth increase in width as the lizards grow. The tooth positions shifted posteriorly, providing adequate space for the larger replacement teeth. These observations suggest that the wave replacement of teeth allows for growth of the dentition in length and height adequate to maintain tooth size in proportion to the overall size of the individual.     

Impact of tooth replacement strategies on the nutritional status of partially-dentate elders

doi: 10.1111/j.1741‐2358.2011.00579.x
Impact of tooth replacement strategies on the nutritional status of partially‐dentate elders Objective: To investigate the impact of tooth replacement on the nutritional status of partially dentate older patients, and, to compare two different tooth replacement strategies; conventional treatment using removable partial dentures and functionally orientated treatment based on the shortened dental arch. Background: Amongst older patients, diet plays a key role in disease prevention, as poor diets have been linked to numerous illnesses. Poor oral health and loss of teeth can have very significant negative effects on dietary intake and nutritional status for elderly patients. There is evidence that good oral health generally, has positive effects on the nutritional intake of older adults. Materials and methods: A randomised, controlled clinical trial was designed to investigate the impact of tooth replacement on the nutritional status of partially dentate elders. Forty‐four patients aged over 65 years completed the trial, with 21 allocated to conventional treatment and 23 allocated to functionally orientated treatment. Nutritional status was accessed at baseline and after treatment using the Mini Nutritional Assessment (MNA) and a range of haematological markers. Results: At baseline, relationships were observed between the number of occluding tooth contacts and some measures of nutritional status. As the number of contacts increased, MNA scores (R = 0.16), in addition to vitamin B12 (R = 0.21), serum folate (R = 0.32) and total lymphocyte count (R = 0.35), also increased. After treatment intervention, the only measure of nutritional status that showed a statistically significant improvement for both treatment groups was MNA score (p = 0.03). No significant between group differences were observed from analysis of the haematological data. Conclusion: In this study, prosthodontic rehabilitation with both conventional treatment and functionally orientated treatment resulted in an improvement in MNA score. Haematological markers did not illustrate a clear picture of improvement in nutritional status for either treatment group.     

Evaluation of Effects of Harvest on Alligator Populations in Louisiana

Biologists with the Louisiana Department of Wildlife and Fisheries, Louisiana, USA, have managed statewide annual harvest of alligators (Alligator mississippiensis) for 35 years (1981–present). We collected and analyzed harvest data for Louisiana alligators to determine the effects of harvest on the population structure, focusing on the larger size classes (≥274 cm) of this slow-growing species. Linear regression analyses revealed that body size-class structure, based on overall average size and the percentage of animals harvested in the larger size classes was relatively stable. Annual aerial alligator nest counts indicated a continual growth of the population, and over time harvested alligators maintained a constant average size. Analyses of population size (based on number of nests and population modeling) indicated that the current annual harvest represents approximately 3% of the population. Linear regression analysis showed that annual hunter success declined only slightly during the study period, and the scheduling of the hunt season after the hatch period and recommended hunting in areas not frequented by breeding females provides economic opportunities for hunters to participate in a sustainable harvest that preserves the larger size classes of alligators in the population. Strict enforcement of existing laws was a key factor responsible for the success of this harvest program. Comparison of alligator population size and number of harvest-related citations indicated that illegal harvest did not have a negative effect on population size, and linear regression analyses revealed that the rate of increase in citations was lower than the increase in populations over the study period. The results of this harvest program indicated that alligators can be hunted in a sustainable manner if hunting is conducted after the hatch period and occurs in areas that primarily exclude the harvest of adult females, and strict law enforcement curbs illegal activities that negatively affect populations. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

Morphology of the tooth of the American alligator (Alligator mississippiensis): The fine structure and elemental analysis of the cementum

The fine structure and the concentration of trace elements in the cementum layer in functional teeth of subadult alligators (ca. 120 cm to 160 cm total length) was studied by using scanning electron microscopy (SEM), microradiography, and electron microprobe analysis (EMPA). The cementum layer was hypertrophic and consisted of two layers: the fibrous layer and the calcified layer. The two layers undergo developmental changes as a result of resorption and replacement. During the tooth replacement in the American alligator, trace elements decreased at the base of the dentine layer; the resorption of the alveolar bone occurred simultaneously at the tooth socket. We concluded that the resorption of the cementum in the alligator provided a useful indication of the mechanism of tooth replacement in crocodilian.     

Preliminary investigation of variations in tooth replacement in adult Necturus maculosus

Although there are a number of studies on tooth replacement patterns in lower vertebrates, most do not indicate whether this process is continuous throughout the year or is affected by either breeding or seasonal cycles. We have surveyed the replacement patterns found in living and specifically killed Necturus maculosus (Amphibia: Proteidae) to determine the nature of their variation throughout the year prior to investigating possible controlling mechanisms of the formation and eruption of amphibian teeth. Some animals (34), kept in a large outside tank, were killed at monthly intervals and their tooth-bearing bones radiographed using a modification of the technique previously described (Miller and Radnor, '70). Other animals (9), kept at 4°C, were anesthetized with tricaine methanesulphonate (M.S. 222), and wax impressions taken with beading (carding) wax of the functioning teeth at regular intervals. Animals examined in the late spring and summer (25) showed no signs of active tooth replacement. Small replacement teeth visible beneath each functioning tooth enlarged only slightly throughout the summer. In early and late fall some functioning teeth were lost and replacement teeth grew and erupted to replace them. Replacement patterns were very irregular and classical alternate form rarely seen. In a number of animals the replacement series was formed from every third tooth. Animals kept constantly at 4°C showed no replacement phenomena. Patterns varied between the different bones of the jaws and did not support the Zahnreihe concept of Edmund ('60).     

Relationship between body condition of American alligators and water depth in the Everglades, Florida

Feeding opportunities of American alligators (Alligator mississippiensis) in freshwater wetlands in south Florida are closely linked to hydrologic conditions. In the Everglades, seasonally and annually fluctuating surface water levels affect populations of aquatic organisms that alligators consume. Since prey becomes more concentrated when water depth decreases, we hypothesized an inverse relationship between body condition and water depth in the Everglades. On average, condition of adult alligators in the dry season was significantly higher than in the wet season, but this was not the case for juveniles/subadults. The correlation between body condition and measured water depth at capture locations was weak; however, there was a significant negative correlation between the condition and predicted water depth prior to capture for all animals except for spring juveniles/subadults which had a weak positive condition–water depth relationship. Overall, a relatively strong inverse correlation occurred at 10–49 days prior to the capture day, suggesting that current body condition of alligators may depend on feeding opportunities during that period. Fitted regression of body condition on water depth (mean depth of 10 days when condition-water depth correlation was greatest) resulted in a significantly negative slope, except for spring adult females and spring juveniles/subadults for which slopes were not significantly different from zero. Our results imply that water management practices may be critical for alligators in the Everglades since water depth can affect animal condition in a relatively short period of time.     

Prozostrodon brasiliensis,a probainognathian cynodont from the Late Triassic of Brazil: second record and improvements on its dental anatomy

Probainognathian cynodonts are conspicuous elements of the Assemblage Zones of the Triassic Santa Maria Supersequence in southern Brazil. Within this group, the derived clade Prozostrodontia, in which the crown group Mammalia is included, is taxonomic diverse in the Hyperodapedon and Riograndia AZs. We describe here the second known specimen (CAPPA/UFSM 0123) of Prozostrodon brasiliensis, until now only represented by its holotype. CAPPA/UFSM 0123 includes a right dentary with dentition. As in the holotype of P. brasiliensis, it has four lower incisors, pc4 with conspicuous cusp a, and small cusps b, c, and d, pc5-pc6 of ‘triconodont’ type with cusps a > c > b > d, with continuous lingual cingulum bearing up to six small discrete cusps, length of the lower tooth row more than half the length of the dentary, and relatively deep horizontal ramus of the dentary. The new specimen is about 25% smaller than the holotype and there is not a diastema between the canine and postcanine teeth, indicating its juvenile condition. Based on both known specimens of P. brasiliensis, a discussion on tooth replacement is presented, showing that the adult individual has more postcanine tooth morphotypes than the juvenile one.     

Pathogen-induced systemic resistance in Ipomoea purpurea

Infection of Ipomoea purpurea by anthracnose, the disease caused by the fungal pathogen Colletotrichum dematium, increases resistance to subsequent infections on previously uninfected leaves. Fungal isolates varied in their levels of virulence but not in the extent to which they induced resistance. Induced resistance was equally effective against all isolates tested. Plant lines varied in the baseline level of resistance expressed in newly emerging leaves. In some lines, new leaves were poorly defended but developed resistance with maturity, even in the absence of infection. In those lines, induced resistance could not prevent anthracnose damage to young leaves, and this damage reduced plant fitness by increasing juvenile mortality and decreasing juvenile growth rates. In contrast, anthracnose damage to well-defended older leaves had no effect on juvenile growth rates. In at least one line, new leaves were well-defended, regardless of disease experience. This line did not experience reduced growth from anthracnose infection of either young or mature leaves, suggesting that lines with higher baseline levels of resistance are more fit than those dependent upon induced resistance. These results suggest that induced resistance cannot substitute for baseline local resistance in this I. purpurea population.