Alan G. Beu

Completeness of the fossil record: Estimating losses due to small body size

Size bias in the fossil record limits its use for interpreting patterns of past biodiversity and ecological change. Using comparative size frequency distributions of exceptionally good regional records of New Zealand Holocene and Cenozoic Mollusca in museum archive collections, we derive first-order estimates of the magnitude of the bias against small body size and the effect of this bias on completeness of the fossil record. Our database of 3907 fossil species represents an original living pool of 9086 species, from which ∼36% have been removed by size culling, 27% from the smallest size class (<5 mm). In contrast, non-size-related losses compose only 21% of the total. In soft rocks, the loss of small taxa can be reduced by nearly 50% through the employment of exhaustive collection and preparation techniques.

On the bidirectional relationship between geographic range and taxonomic duration

Abstract Geographic range and taxonomic duration are known to be positively correlated in a number of biologic groups; this is usually attributed to the influence of range upon duration rather than the other way about. Here we analyze two distinct components of this correlation within species and genera of marine invertebrates and microfossils by partitioning the total duration into two parts: the time it takes a taxon to attain its maximum geographic range, and the time a taxon persists after attaining its peak range. We find that the longer it takes a taxon to attain its maximum geographic range, the wider is that range. We also find that the broader the maximum range, the greater is the duration after this maximum is attained. These two correlations are equally strong on average. There is thus a reciprocal relationship between duration and geographic range, and there is no compelling evidence that range generally determines duration more or less than duration determines range.

Late Holocene uplift of beach ridges at Turakirae Head, south Wellington coast, New Zealand

Abstract Holocene terraces at Turakirae Head on the south coast of the North Island, New Zealand, record four recent earthquakes from simultaneous rupture of the Wairarapa Fault and flexure of the Rimutaka Anticline. The lowest tread and riser is the modern marine platform and storm beach that began forming when the area was raised during the Mw 8.2 Wairarapa earthquake of AD 1855 January. The remaining chronology is established by radiocarbon dating, in situ 10Be surface‐exposure dating, and slip‐predictable uplift estimation. Prior to AD 1855, uplifts occurred at 110–430 BC (max. 9.1 m), 2164–3468 BC (6.8 m), and 4660–4970 BC (7.3 m). Earlier uplift of unknown magnitude occurred at c. 7000 BC but went unrecorded because of rapidly rising sea level. Sea level was still rising when the two oldest surviving beach ridges were raised. Uplift at Turakirae Head in AD 1855 varied from 1.5 m at the Wainuiomata River to 6.4 m at the crest of the Rimutaka Anticline. Older beaches also are tilted, with the amount of tilt increasing with age. Coastal uplift at the anticline crest has averaged 3.32 ± 0.17 mm/yr over the past 9000 yr, and has changed little over the past 0.5 m.y. Uplift fits a slip‐predictable model of earthquake occurrence, and is log‐normally distributed with a mean of 7.3 ± 0.7 m. The most frequently occurring uplift is 7.1 ± 0.9 m. Uplift in AD 1855 was not significantly smaller than mean or mode, suggesting that the Turakirae Head sequence records four great earthquakes of at least similar magnitude to that of AD 1855. The mean earthquake recurrence interval is 2194 ± 117 yr; the modal interval is 2122 ± 193 yr. At the crest of the anticline, the coastal platform was cut entirely during the postglacial rise of sea level until shortly before 4660–4970 BC. Away from the crest, however, it may have been partially cut during low sea level of the penultimate glaciation. The open‐ocean radiocarbon reservoir correction (δR) for 10 14C dates of coastal marine shells that died in AD 1855 at Turakirae Head is 3 ± 14cal. yrBP(andnot‐31 ± 13 cal. yr BP, the currently accepted δR for central New Zealand coastal waters).

The ark was full! Constant to declining Cenozoic shallow marine biodiversity on an isolated midlatitude continent

Abstract In recent years several authors have questioned the reality of a widely accepted and apparently large increase in marine biodiversity through the Cenozoic. Here we use collection-level occurrence data from the rich and uniquely well documented New Zealand (NZ) shelfal marine mollusc fauna to test this question at a regional scale. Because the NZ data were generated by a small number of workers and have been databased over many decades, we have been able to either avoid or quantify many of the biases inherent in analyses of past biodiversity. In particular, our major conclusions are robust to several potential taphonomic and systematic biases and methodological uncertainties, namely non-uniform loss of aragonitic faunas, biostratigraphic range errors, taxonomic errors, choice of time bins, choice of analytical protocols, and taxonomic rank of analysis. The number of taxa sampled increases through the Cenozoic. Once diversity estimates are standardized for sampling biases, however, we see no evidence for an increase in marine mollusc diversity in the NZ region through the middle and late Cenozoic. Instead, diversity has been approximately constant for much of the past 40 Myr and, at the species and genus levels, has declined over the past ∼5 Myr. Assuming that the result for NZ shelfal molluscs is representative of other taxonomic groups and other temperate faunal provinces, then this suggests that the postulated global increase in diversity is either an artifact of sampling bias or analytical methods, resulted from increasing provinciality, or was driven by large increases in diversity in tropical regions. We see no evidence for a species-area effect on diversity. Likewise, we are unable to demonstrate a relationship between marine temperature and diversity, although this question should be re-examined once refined shallow marine temperature estimates become available.

Pleistocene coastal terraces of Kaikoura Peninsula and the Marlborough coast, South Island, New Zealand

Abstract Pleistocene marine terraces along the Marlborough coast, South Island, New Zealand, have been re‐examined with detailed stratigraphic observations, accurate height data, and amino acid and thermo‐luminescence (TL) geochronology. Marine terraces range in age from c. 220 ka (oxygen isotope stage 7) to c. 60 ka (oxygen isotope stage 3), in the area from Cape Campbell to Conway River. At Kaikoura Peninsula, five marine terraces are preserved. The marine fauna, loess stratigraphy, and amino acid dating of Tawera spissa, from the Kaikoura I (highest) terrace and from the highest terrace at Haumuri Bluffs (Tarapuhi Terrace), indicate a correlation to oxygen isotope substage 5c, with an age of 100 ka. North of the Clarence River, marine terraces (including the Parikawa Formation) are correlated to oxygen isotope substage 5e of the last interglacial. TL dating of loess supports this interpretation. The Winterholme Formation terrace at Kekerengu is reinterpreted as a last glaciation fluvioglacial terrace g...

Second-Order Sequence Stratigraphic Controls on the Quality of the Fossil Record at an Active Margin: New Zealand Eocene to Recent Shelf Molluscs

Abstract New Zealand has the most complete Cenozoic molluscan fossil record in the Southern Hemisphere. In order to understand the true marine faunal history of the region, it is necessary first to identify apparent biodiversity changes that result simply from variations in the quality of the fossil record. The present study uses a range of methods to quantify both long-term, secular changes and short-term patterns of variation in sampling probability for New Zealand Cenozoic shelf molluscs. Overall, about one-third of all once-living Cenozoic species have been sampled, and average per-stage sampling probabilities are between 20% and 50%. Increase in per-stage sampling probability through time reflects the increase in outcrop area and ease of fossil recovery from older to younger stages. Short-term patterns of variation apparently are related to second-order sequence stratigraphic controls of preservation potential. Once the effects of stage duration are eliminated, patterns of stage-to-stage sampling probability reflect enhanced preservation in mid-cycle positions and, perhaps to a lesser extent, secondary post-depositional loss of stratigraphic record above and below sequence boundaries. Although this result mirrors patterns observed in Europe, it is possible that enhanced preservation mid-cycle is relatively more important at active margins, such as New Zealand, whereas secondary loss of record at the sequence boundary is more important at passive margins. Finally, it is worth noting that different methods and data compilations yield rather consistent estimates of short-term variation in sampling probability, lending confidence to the methods and suggesting that the patterns identified are likely to reflect true underlying features of the New Zealand marine fossil record.

Vertical tectonic movement in northeastern Marlborough: Stratigraphic, radiocarbon, and paleoecological data from Holocene estuaries

Abstract Height and age information from Holocene estuarine deposits along the northeastern Marlborough coast provide a database to evaluate coastal vertical tectonics. These data are related to the postglacial marine transgression and coastal geomorphic features formed since the culmination of sea‐level rise. Four tectonic domains are recognised. The Wairau domain is characterised by subsidence at rates over 4 mm/yr. About 60% of this subsidence is tectonic and may be related to Marlborough Sounds subsidence, and 40% is a result of compaction. The Vernon Fault at the south side of the lower Wairau plain separates the Wairau domain from the high‐standing Vernon domain. The Awatere Fault marks the southern boundary between the Vernon domain and the Grassmere domain, which extends from the Awatere River valley to Mussel Point. Slight uplift (c. 1 m in 6500 yr) characterises the Grassmere domain, based on data obtained from Blind River, Lake Grassmere, and, to a lesser extent, from Awatere River fluvial terr...

Biotic influences on species duration: interactions between traits in marine molluscs

Abstract We analyze relationships among a range of ecological and biological traits—geographic range size, body size, life mode, larval type, and feeding type—in order to identify those traits that are associated significantly with species duration in New Zealand Cenozoic marine molluscs, during a time of background extinction. Using log-linear modeling, we find that bivalves have only a small number of simple, two-way associations between the studied traits and duration. In contrast, gastropods display more complex interactions involving three-way associations between traits, a pattern that suggests greater macroecological complexity of gastropods. This is not an artifact caused by the larger number of gastropods than bivalves in our data set. We used stratified randomized resampling of families to test for associations between traits that might result from shared inheritance rather than ecological trait interactions; we found no evidence of phylogenetic effects in any associations examined. The relationships revealed by our study should serve to constrain the range of possible biological mechanisms that underlie these relationships. As previously observed, two-way associations are present between large geographic range and increased duration, and between large geographic range and large body size, in both bivalves and gastropods. In gastropods, planktotrophic larval type is associated with large range size through a three-way interaction that also involves duration; there is no direct association of larval type and geographic range. Gastropods also display two-way associations between duration and life mode, and duration and feeding type. We note that in gastropods, an infaunal life mode is associated with large range size, whereas in bivalves infaunality is associated with reduced range size.

Notes on the taphonomy and paleoecology of New Zealand tertiary spatangoida

Abstract The distribution of spatangoid echinoids and molluscs in New Zealand Tertiary formations is anomalous; formations relatively rich in spatangoids are poor in molluscs and vice versa. The absence of Mollusca from spatangoid-rich formations is attributed to diagenetic dissolution of aragonitic shells while the stabilisation of spatangoid magnesium calcite is attributed to incongruent dissolution. Irregular bevelled perforations in some spatangoid tests are attributed to predation by tonnacean gastropods such as Echinopboria and large Austrosassia. New Zealand Tertiary spatangoids are of little use as depth indicators as those genera still living have large depth ranges.

Pliocene‐Quaternary sedimentation and Alpine Fault related tectonics in the lower Cascade valley, South Westland, New Zealand

Abstract Study of Pliocene and Quaternary sediments west of the Alpine Fault in the Cascade valley, South Westland, New Zealand, has allowed determination of Alpine Fault displacement rate and coastal uplift rate over the last 3.5 m.y. Exposures of the Pliocene Halfway Formation (latest Opoitian‐Waipipian) are composed of marine sand and conglomerate deposited in c. 200–1000 m water depth. Beds are gently dipping and weakly deformed, with the direction of principal shortening oriented at a high angle to the Alpine Fault and plunging gently northwest (c. 107340°). Fiordland‐derived clasts indicate a minimum of 95–100 km of lateral offset on the Alpine Fault since deposition of Halfway Formation. Paleogeographic evidence suggests that first‐order features of the drainage were similar in Pliocene time to those of the present day. Quaternary moraines and fluvioglacial sediments are subdivided on the basis of composition and morphology into five groups: Cl (oldest) to C5 (youngest). The Cl deposits have a prov...