Shell abnormalities in scaphitid ammonites

The kinds incidence of shell abnormalities were investigated in over 2000 adult Late Cretaceous scaphitid ammonites. Most are species of Hoploscaphites Discoscaphites from the Maastrichtian Fox Hills Formation; for comparison, four older species of Scaphites were also studied. Four kinds of abnormalities vary in their incidence among the Fox Hills taxa but display no general trends. (1) Morton's syndrome, shell asymmetry unrelated to external injury, occurs in 3 to 6% of the Fox Hills scaphites. (2) Suture wander. veering-off of the ventral lobe of the suture from the midline of the venter, occurs in most Fox Hills taxa with an incidence ranging from 1 to 11%. (3) Stretch pathology, an attenuation of the shell on the posterior part of the adult body chamber, is confined to Hoploscaphifes nicolleti. (4) Externally inflicted injury, indicated by repaired damage on mature shells, has an average incidence of 10% in Fox Hills scaphites except in the stratigraphically youngest H. nebrascensis H. cheyennewis which approach 25 40% respectively. Good correlation between percent injuries adult size ornamentation is obtained only in Discoscaphifes; all morphs of the co-occurring Hoploscaphites display nearly the same incidence of injuries regardless of their morphologic variation. The stratigraphically youngest H. nebrascensis becomes larger more nodose simultaneously sustains more injuries. However, its dimorph H. cheyennensis remains morphologically unchanged although its incidence of injuries quadruples. These injury data, in themselves, do not support the hypothesis that predators were contributing more heavily to the mortality of Maastrichtian ammonites precipitated their extinction.     

Survival and repair of surgical and natural shell damage in the articulate brachiopod Terebratulina retusa (Linnaeus)

Living specimens of Terebratulina retusa from the Firth of Lorn, Scotland, were surgically damaged by drilling 2 mm diameter holes or narrow slits one cm long in the anterior portion of one valve, by bevelling the anterior margin of both valves, or by amputation of the anterior third of one valve. These injuries to the shell and mantle simulated the type of repaired shell damage seen in Paleozoic species, i.e., scalloped, divoted, cleft, and embayed valves. Less than ten percent of the 200 damaged specimens survived until the 25th week after surgery. Specimens of T. retusa showed the ability to repair drill holes, slits, and bevelled anterior shell regions, but not the most severe damage, i.e., amputations of the anterior third of one valve. Shell‐repair was initiated in the fourth week after surgery by the development of a membrane across the wound. The development of caeca in the new shell layer secreted to plug the drill holes became apparent by the eighth week. The punctate pattern was complete in the new, translucent shell material of bevelled and drilled specimens by the 25th week following surgery. Failure of any specimens to survive amputation of the anterior portion of a valve for more than seven weeks after surgery, and the absence of initiation of the repair process, suggests that terebratulids do not have the tolerance for, nor the ability to repair, the severe injuries (embayed valves) which were sustained and mended by extinct strophomenids.     

Broken pieces: can variable ecological interactions be deduced from the remains of crab attacks on bivalve shells?

Shell fragmentation patterns that result from attacks by durophagous predators on hard‐shelled marine invertebrates are a rich source of indirect evidence that have proved useful in interpreting predation pressure in the fossil record and recent ecology. The behaviour and effectiveness of predators are known to be variable with respect to prey size. It is less well understood if variable predator–prey interactions are reflected in shell fragmentation patterns. Therefore, we conducted experimental trials to test the behavioural response of a living crab, Carcinus maenas, during successful predatory attacks on the blue mussel Mytilus edulis on two prey size categories. Further, we examined resultant shell fragments to determine whether specific attack behaviours by C. maenas could be successfully deduced from remaining mussel shells. In contrast to previous studies, we observed no significant differences in attack behaviour by the predators attributable to prey size. In most experimental predation events, crabs employed an ad hoc combination of five mechanisms of predation previously described for this species. We identified seven categories of shell breakage in predated mussels, but none of these were unambiguously correlated with specific attack behaviour. Combined attack behaviours may produce shell breakage patterns that have previously been assumed to be attributable to a single behaviour. While specific patterns of shell breakage are clearly attributable to durophagy, the results of this study provide important insights into the limitations of indirect evidence to interpret ecological interactions.     

Causes of damage to brachiopods from the Middle Pennsylvanian Naco Formation, central Arizona

The Kohl Ranch locality in the Naco Formation of central Arizona has yielded an abundant and diverse fauna including eight genera of brachiopods and four of sharks including Cochliodus. The most abundant brachiopod, Composita subtilita , was analyzed for predation damage and of 935 specimens 503 (53.7%) were found to show the type of unrepaired crushing previously attributed to shark predation. Reconstruction of the jaw of Cochliodus , however, suggests that it may have been a selective feeder similar to the modern Heterodontus and unlikely therefore to have left so many damaged but uningested specimens. Evidence from specimens collected in situ suggests that the damage mostly occurred post-mortem due to the compaction of the sediments and was not due to the sharks who would have comminuted any prey items taken.     

The relationship between geographic area and the latitudinal gradient in species richness in New World birds

One hypothesis for the latitudinal gradient in species richness observed in most animal taxa is that the richness of a region is determined by its geographic area. However, the relationship between geographic area and species richness across regions is generally weak. It has been suggested that this is because species from the tropics spill out of this region of high richness, artificially inflating the richness of other regions. This generates the interesting prediction that the area and richness of extra-tropical regions should be more strongly correlated if tropical species are excluded. We test this prediction using the avifauna of the New World. We find that there is indeed a relationship between the land area and species richness of a region once tropical species are excluded. This relationship is independent of the latitude and productivity of regions. Both latitude and productivity can explain variance in richness unexplained by land area. There is no relationship between land area and species richness if tropical species are not excluded from the analysis, suggesting that tropical species do indeed mask the relationship between richness and area. We conclude that our results generally support the geographic area hypothesis, although tests of its other predictions and on other land masses are required.