Vertebrate Extinctions Research Articles

Major Conservation Policy Issues for Biodiversity in Oceania

Oceania is a diverse region encompassing Australia, Melanesia, Micronesia, New Zealand, and Polynesia, and it contains six of the world's 39 hotspots of diversity. It has a poor record for extinctions, particularly for birds on islands and mammals. Major causes include habitat loss and degradation, invasive species, and overexploitation. We identified six major threatening processes (habitat loss and degradation, invasive species, climate change, overexploitation, pollution, and disease) based on a comprehensive review of the literature and for each developed a set of conservation policies. Many policies reflect the urgent need to deal with the effects of burgeoning human populations (expected to increase significantly in the region) on biodiversity. There is considerable difference in resources for conservation, including people and available scientific information, which are heavily biased toward more developed countries in Oceania. Most scientific publications analyzed for four threats (habitat loss, invasive species, overexploitation, and pollution) are from developed countries: 88.6% of Web of Science publications were from Australia (53.7%), New Zealand (24.3%), and Hawaiian Islands (10.5%). Many island states have limited resources or expertise. Even countries that do (e.g., Australia, New Zealand) have ongoing and emerging significant challenges, particularly with the interactive effects of climate change. Oceania will require the implementation of effective policies for conservation if the region's poor record on extinctions is not to continue.

The Forgotten Megafauna

An expanded megafauna concept elucidates how extinctions of the largest vertebrates in any ecosystem have similar effects.

The terrestrial Permian-Triassic boundary event bed is a nonevent

Research Article| March 01, 2009 The terrestrial Permian-Triassic boundary event bed is a nonevent Robert A. Gastaldo; Robert A. Gastaldo 11Department of Geology, Colby College, Waterville, Maine 04901, USA Search for other works by this author on: GSW Google Scholar Johann Neveling; Johann Neveling 22Council for Geosciences, Private Bag x112, Silverton, Pretoria 0001, South Africa Search for other works by this author on: GSW Google Scholar C. Kittinger Clark; C. Kittinger Clark 11Department of Geology, Colby College, Waterville, Maine 04901, USA Search for other works by this author on: GSW Google Scholar Sophia S. Newbury Sophia S. Newbury 11Department of Geology, Colby College, Waterville, Maine 04901, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Robert A. Gastaldo 11Department of Geology, Colby College, Waterville, Maine 04901, USA Johann Neveling 22Council for Geosciences, Private Bag x112, Silverton, Pretoria 0001, South Africa C. Kittinger Clark 11Department of Geology, Colby College, Waterville, Maine 04901, USA Sophia S. Newbury 11Department of Geology, Colby College, Waterville, Maine 04901, USA Publisher: Geological Society of America Received: 13 Jun 2008 Revision Received: 15 Oct 2008 Accepted: 16 Oct 2008 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2009 Geological Society of America Geology (2009) 37 (3): 199–202. https://doi.org/10.1130/G25255A.1 Article history Received: 13 Jun 2008 Revision Received: 15 Oct 2008 Accepted: 16 Oct 2008 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Robert A. Gastaldo, Johann Neveling, C. Kittinger Clark, Sophia S. Newbury; The terrestrial Permian-Triassic boundary event bed is a nonevent. Geology 2009;; 37 (3): 199–202. doi: https://doi.org/10.1130/G25255A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A unique isochronous interval in the Karoo Basin, South Africa, previously has been interpreted to postdate vertebrate extinction at the Permian-Triassic boundary in the Bethulie area, Lootsberg Pass, and elsewhere. It is demonstrated that the laminated beds, or laminites, in the Bethulie region are stratigraphically indistinct. The heterolithic interval exposed on the Heldenmoed farm is ~8 m below the Bethel farm section, <1 km away. At Lootsberg Pass, the laminated interval is below the Permian-Triassic boundary as defined by vertebrate biostratigraphy, rather than overlying it. Hence, this interval, critical to models of end-Permian mass extinction, is neither isochronous across the basin nor unique. Rather, the lithofacies represents avulsion channel-fill deposits within aggradational landscapes. South African models for the response of terrestrial ecosystems to the perturbation in the marine realm require critical reevaluation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Chronology and causes of the extinction of the Lava Mouse, Malpaisomys insularis (Rodentia: Muridae) from the Canary Islands

Understanding late Holocene extinctions on islands requires accurate chronologies for all relevant events, including multiple colonisations by humans and the introduction of alien species. The most widely held hypothesis on the causes of Holocene island vertebrate extinctions incorporates human impacts, although climatic-related hypotheses cannot be excluded. Both hypotheses have been suggested to account for the extinction of the endemic Lava Mouse, Malpaisomys insularis from the Canary Islands. Here we present the first accelerator mass spectrometer (AMS) 14C ages from collagen of M. insularis bones from ancient owl pellets collected at Fuerteventura (Canary Islands, eastern Atlantic Ocean). These new dates contribute to an understanding of the extinction of this species. We are able to exclude climatic causes, predation by invasive species, and competition with the house mouse, Mus musculus. The arrival of Europeans in the Canary Islands correlates with the extinction of Malpaisomys. The introduction of rats, Rattus spp., together with their parasites and diseases, emerges as the most reasonable hypothesis explaining the extinction of M. insularis.

Holocene underkill

In this issue of PNAS, Jones et al. (1) address an issue that has been with us, in one way or another, for some 200 years. Around the year 1800, French paleontologist Georges Cuvier established the reality of vertebrate extinction by using animals so large that their future discovery on the hoof was highly unlikely (2). Included on the list were some now known to have been late Pleistocene in age, including mammoth and mastodon. As time went on, the list of extinct American and Eurasian mammals of this age grew hand in hand with our understanding of the geological deposits in which the fossils were embedded. As this happened, it became harder and harder to understand why all of these extinctions had occurred.

Springs and wire plants: anachronistic defences against Madagascar's extinct elephant birds

The extinction of large vertebrates in the last few millennia has left a legacy of evolutionary anachronisms. Among these are plant structural defences that persist long after the extinction of the browsers. A peculiar, and controversial, example is a suite of traits common in divaricate (wide-angled branching) plants from New Zealand. Divaricate architecture has been interpreted as an adaptive response to cold climates or an anachronistic defence against the extinct moas. Madagascar, a larger tropical island, also had a fauna of large flightless birds, the elephant birds. If these extinct ratites selected for similar plant defences, we expected to find convergent features between New Zealand and Malagasy plants, despite their very different climates. We searched the southern thickets of Madagascar for plants with putative anti-ratite defences and scored candidate species for a number of traits common to many New Zealand divaricates. We found many Malagasy species in 25 families and 36 genera shared the same suite of traits, the 'wire plant' syndrome, as divaricates in New Zealand that resist ratite browsing. Neither ecologically, nor phylogenetically, matched species from South Africa shared these traits. Malagasy wire plants differ from many New Zealand divaricates in lacking the distinctive concentration of leaves in the interior of shrubs. We suggest that New Zealand divaricates have a unique amalgam of traits that acted as defences and also confer tolerance to cold. We conclude that many woody species in the thickets of southern Madagascar share, with New Zealand, anachronistic structural defences against large extinct bird browsers.

Geochemical and mineralogical investigation of the Permian–Triassic boundary in the continental realm of the southern Karoo Basin, South Africa

Mineralogical and geochemical studies of the non-marine Permian–Triassic (P–Tr) boundary across two stratigraphically well-constrained sections (Commando Drift Dam and Wapadsberg, Eastern Cape Province) in the southern Karoo Basin, South Africa, have been undertaken to provide further input on the cause of this mass extinction event, and so has a sedimentological and geochemical evaluation of a third P–Tr boundary section at Injusiti (Kwazulu-Natal) in the eastern Karoo Basin, South Africa. The Commando Drift Dam section has been constrained by previous palaeontological and palaeomagnetic work, with a palaeomagnetic reversal positioned 5.3 m above the palaeontological P–Tr boundary. The Wapadsberg section has been constrained palaeontologically. All these P–Tr sections studied here mostly comprise mudstones, together with siltstones, sandstones, and in the southern Karoo Basin, carbonate nodular horizons. A change in colour of the mudstones from green-grey to red-brown takes place at the palaeontologically defined boundary. Variations in the major and trace element abundance profiles are usually limited to the carbonate nodular horizons, besides the overall effects of weathering. Bulk carbon isotopic studies of the Commando Drift Dam section revealed a negative δ 13C bulk excursion (background values of −15 to −20‰, with total extent of excursion to −24.9‰) 2 cm below the palaeontological boundary, followed by a gradual recovery and then another decrease in values leading towards the palaeomagnetic boundary. Above this boundary recovery to less negative δ 13C bulk values (ca. −18‰) occurs. The organic carbon record from the Commando Drift Dam (southern Karoo Basin) and Injusiti (eastern Karoo Basin) oscillates between −26.1 and −28.9‰, which is comparable to previous studies of different sections in the southern Karoo Basin. The magnitude of both the bulk and organic carbon isotopic variation can be interpreted to indicate a number of inputs (due to the fluctuating values) of organic carbon. The carbon isotope data for carbonates in the Injusiti section are different from the results on carbonates from other studies, but more work to expand this dataset is necessary. The palynological studies on the Commando Drift Dam section reveal the presence of a low diversity flora composed principally of bryophytes, lycophytes, and gymnosperms. These forms, including several Late Permian key-species, are traces of the surviving plants enduring after the major extinction-pulse. The presence of fungal palynomorphs and dearth of pollen/spores related to photosynthetic plants some metres above the palaeontological P–Tr boundary demonstrate similarities to the pattern of floral extinction at the Cretaceous–Palaeogene (K–Pg) boundary. The timing of vertebrate extinctions in the Karoo Basin has so far not been determined, but the 252.5 Ma age for a single zircon crystal from Commando Drift Dam dated here gives a maximum constraint on the age of the event bed, which is in agreement with the accepted age of the boundary. No evidence for impact-produced microdeformation features were found in quartz grains from either the Wapadsberg or Commando Drift Dam sections. Also, siderophile element data (including platinum group element (PGE) concentrations) do not support the possible presence of a meteoritic component at the boundary. Thus, a link between impact and P–Tr extinction is not indicated by the results of this study.

Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event?

We present new data and a synthesis of cyclostratigraphic, lithostratigraphic, biostratigraphic, and published magnetostratigraphic and basalt geochemical data from eastern North America and Morocco in an attempt to clarify the temporal relationship between the Triassic–Jurassic mass extinction (∼ 202 Ma) and Earth's largest sequence of continental flood basalts, the Central Atlantic magmatic province (CAMP). Newly discovered zones of reverse polarity within CAMP flow sequences of Morocco have been hypothesized by Marzoli et al. [Marzoli, A., Bertrand, H., Knight, K.B., Cirilli, S., Buratti, N., Vérati, C., Nomade, S., Renne, P.R., Youbi, N., Martini, R., Allenbach, K., Neuwerth, R., Rapaille, C., Zaninetti, L., Bellieni, G., 2004. Synchrony of the Central Atlantic magmatic province and the Triassic–Jurassic boundary climatic and biotic crisis. Geology 32, 973–976.] and Knight et al. [Knight, K.B., Nomade, S., Renne, P.R., Marzoli, A., Betrand, H., Youbi, N., 2004. The Central Atlantic Magmatic Province at the Triassic–Jurassic boundary: paleomagnetic and 40Ar/ 30Ar evidence from Morocco for brief, episodic volcanism. Earth and Planetary Science Letters 228, 143–160.] as correlates of a very short, uppermost Triassic age reverse chron in the Newark basin, thus suggesting that much of the Moroccan CAMP was synchronous with or predates the Triassic–Jurassic boundary. Here, however, we explain these apparent reverse polarity zones as possible correlatives of poorly sampled lower Jurassic basalt flow sequences and overlying strata in eastern North America and lower Jurassic reverse polarity sequences recognized by others in the Paris basin. A revised Milankovitch cyclostratigraphy based on new core and field data constrains the duration of eastern North America basaltic flows to ∼ 610 ky after the Triassic–Jurassic palynological turnover event. Palynological data indicates correlation of the initial carbon isotopic excursion of Hesselbo et al. [Hesselbo, S.P., Robinson, S.A., Surlyk, F., Piasecki, S., 2002. Terrestrial and marine extinction at the Triassic–Jurassic boundary synchronized with major carbon-cycle perturbation: a link to initiation of massive volcanism. Geology 30, 251–254.] at St. Audrie's Bay to the palynological turnover event and vertebrate extinction level in eastern North America, suggesting a revised magnetostratigraphic correlation and robust carbon isotopic tests of the Marzoli–Knight hypothesis. We conclude that as yet there are no compelling data showing that any of the CAMP predated or was synchronous with the Triassic–Jurassic extinction event.

Extinction of endemic vertebrates on islands: The case of the giant rat Canariomys bravoi (Mammalia, Rodentia) on Tenerife (Canary Islands, Spain)

Fossil bone collagen 14C dating and δ 13C and δ 15N isotopic measurements of the rodent Canariomys bravoi from Tenerife (Canary Islands, Spain) were used to test two different hypotheses about the causes of extinctions of endemic vertebrates on islands, climate versus humans. For the Tenerife giant rat, we show that it survived the climatic change that occurred between the Middle and Late Holocene, but not the settlement of humans on the island. To cite this article: H. Bocherens et al., C. R. Palevol 5 (2006) .

The recovery of terrestrial vertebrate diversity in the South African Karoo Basin after the end-Permian extinction

The southern half of the main Karoo Basin in South Africa contains an almost continuous stratigraphic record of terrestrial sedimentation through the Permo-Triassic boundary (PTB). Detailed logging of multiple sections through the boundary sequence has defined the end-Permian mass extinction event using vertebrate fossils as well as a synchronous change in fluvial style reflecting a rapid aridification of climate. Field data demonstrates a 69% mass extinction of Late Permian terrestrial vertebrates lasting some 300 kyr terminating at the PTB, followed by a lesser extinction event (31%) approximately 160 kyr later involving four survivor taxa that crossed the PTB. The Early Triassic recovery fauna comprises proterosuchian archosauromorphs ( Proterosuchus), small amphibians ( Micropholis, Lydekkerina), small procolophonoids ( ‘Owenetta’ kitchingorum, Procolophon), medium-sized dicynodonts ( Lystrosaurus) and small insectivorous cynodonts ( Progalesaurus, Galesaurus, Thrinaxodon). Taphonomic bias towards preferential preservation of drought accumulations in the Early Triassic has probably over-emphasized the abundance and diversity of semi aquatic and burrowing animals. To cite this article: R. Smith, J. Botha, C. R. Palevol 4 (2005) .

The carbon and sulfur cycles and atmospheric oxygen from middle Permian to middle Triassic

The results of a theoretical isotope mass balance model are presented for the time dependence of burial and weathering-plus-degassing fluxes within the combined long-term carbon and sulfur cycles. Averaged data for oceanic δ 13C and δ 34S were entered for every million years from 270 to 240 Ma (middle Permian to middle Triassic) to study general trends across the Permian-Triassic boundary. Results show a drop in the rate of global organic matter burial during the late Permian and a predominance of low values during the early-to-middle Triassic. This overall decrease with time is ascribed mainly to epochs of conversion of high biomass forests to low biomass herbaceous vegetation resulting in a decrease in the production of terrestrially derived organic debris. Additional contributions to lessened terrestrial carbon burial were increased aridity and a drop in sea level during the late Permian which led to smaller areas of low-lying coastal wetlands suitable for coal and peat deposition. Mirroring the drop in organic matter deposition was an increase in the burial of sedimentary pyrite, and a dramatic increase in the calculated global mean ratio of pyrite-S to organic-C. High S/C values resulted from an increase of deposition in marine euxinic basins combined with a decrease in the burial of low-pyrite associated terrestrial organic matter. The prediction of increased oceanic anoxia during the late Permian and early Triassic agrees with independent studies of the composition of sedimentary rocks. Weathering plus burial fluxes for organic carbon and pyrite sulfur were used to calculate changes in atmospheric oxygen. The striking result is a continuous drop in O 2 concentration from ∼30% to ∼13% over a twenty million year period. This drop was brought about mainly by a decrease in the burial of terrestrially derived organic matter. but with a possible contribution from the weathering of older organic matter on land. It must have exerted a considerable influence on animal evolution because of the role of O 2 in respiration. Some examples are the extinction of many vertebrates, loss of giant insects and amphibians, and the restriction of animals to low elevations. It is concluded that the extinction of plants may have contributed to the extinction of animals.

Polar dinosaurs and the question of dinosaur extinction: a brief review

Abstract Although the physiology of dinosaurs is still a matter of controversy, there is no doubt that some of them were able to live in environments that were too cold for ectothermic reptiles, as shown by discoveries of Jurassic and Cretaceous polar vertebrate assemblages which contain dinosaurs but lack turtles and crocodiles. This adaptation of dinosaurs to cool climates invalidates hypotheses according to which dinosaur extinction at the end of the Cretaceous was a result of long-term climatic cooling. The pattern seen at the K/T boundary, with the disappearance of dinosaurs and the survival of ectothermic reptiles, is completely different from that seen in Arctic regions during the Late Cretaceous, where ectotherms disappeared, while dinosaurs subsisted, during cooler periods. The idea of an intense and enduring cold spell at the K/T boundary, caused by the Chicxulub impact, is extremely unlikely in view of the pattern of vertebrate extinction (survival of endotherms, extinction of dinosaurs). Models of environmental events following the impact must take this palaeontological constraint into consideration.

Polar dinosaurs and the question of dinosaur extinction: a brief review

Although the physiology of dinosaurs is still a matter of controversy, there is no doubt that some of them were able to live in environments that were too cold for ectothermic reptiles, as shown by discoveries of Jurassic and Cretaceous polar vertebrate assemblages which contain dinosaurs but lack turtles and crocodiles. This adaptation of dinosaurs to cool climates invalidates hypotheses according to which dinosaur extinction at the end of the Cretaceous was a result of long-term climatic cooling. The pattern seen at the K/T boundary, with the disappearance of dinosaurs and the survival of ectothermic reptiles, is completely different from that seen in Arctic regions during the Late Cretaceous, where ectotherms disappeared, while dinosaurs subsisted, during cooler periods. The idea of an intense and enduring cold spell at the K/T boundary, caused by the Chicxulub impact, is extremely unlikely in view of the pattern of vertebrate extinction (survival of endotherms, extinction of dinosaurs). Models of environmental events following the impact must take this palaeontological constraint into consideration.

Late Quaternary vegetation change and the extinction of Black-flanked Rock-wallaby ( Petrogale lateralis) at Tunnel Cave, southwestern Australia

Quaternary vertebrate extinctions attract wide interest because of the role ascribed to humans as agents of extinction, through either over-hunting or altering habitat. This paper examines faunal and floral records from the archaeological site at Tunnel Cave, Leeuwin–Naturaliste Region, southwestern Australia, which are relevant to the Mid-Holocene local extinction of Black-flanked Rock-wallaby ( Petrogale lateralis). Possible factors causing the population decline include inter-species competition, over-hunting by humans or other predators, or vegetation habitat change caused by climate change or changes in human firing practices. Identification of macroscopic charcoal excavated at Tunnel Cave shows that changes in canopy trees began from 10,000 BP, consistent with post-glacial rainfall increases, and probably causing the encroachment of closed habitats and loss of grazing areas. These changes are consistent with other faunal shifts at Tunnel Cave and with faunal and identified charcoal records from the nearby Devil's Lair deposit. There is little evidence for changes in competitor or predator behaviour, although increasing geographic isolation of Petrogale habitats possibly exacerbated predator impacts. The timing of human occupations at Tunnel Cave in relation to vegetation change suggests that human firing was a minor influence on forest composition or structure. Petrogale's Mid-Holocene disappearance from the region is therefore attributable to climatically driven encroachment of closed habitat.

Vertebrate extinction across Permian-Triassic boundary in Karoo Basin, South Africa: Reply

Research Article| September 01, 2004 Vertebrate extinction across Permian-Triassic boundary in Karoo Basin, South Africa: Reply G.J. Retallack G.J. Retallack 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2004) 116 (9-10): 1295–1296. https://doi.org/10.1130/B25614.1 Article history received: 30 Mar 2004 accepted: 30 Mar 2004 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation G.J. Retallack; Vertebrate extinction across Permian-Triassic boundary in Karoo Basin, South Africa: Reply. GSA Bulletin 2004;; 116 (9-10): 1295–1296. doi: https://doi.org/10.1130/B25614.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Our hypothesis of terminal-Permian vertebrate mass extinction by pulmonary edema (Retallack et al., 2003) rested on observations of victims (1) and survivors (2) of mass murder, and a plausible lethal weapon (3), as follows: (1) mass mortality of vertebrates at the Permian-Triassic boundary; (2) improved respiratory capacity of earliest-Triassic survivors (development of secondary bony palate, shortened internal nares, high dorsal vertebral spines, thickened ribs, barrel chests, shortened limbs, reduced lumbar ribs); and (3) evidence of dramatically lowered earliest Triassic atmospheric oxygen levels (berthierine in paleosols, lowered stomatal index of seed ferns from increased carbon dioxide, declining carbon isotope... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Vertebrate extinction across Permian-Triassic boundary in Karoo Basin, South Africa: Discussion

The Permian-Triassic boundary was a time of lowered atmospheric oxygen and raised carbon dioxide pressure and massive vertebrate extinction. The levels of oxygen (12 vol%) and carbon dioxide (∼2000 ppmV) are typically tolerated by modern vertebrates and are not abnormal enough to have contributed significantly to the extinction.

Causes of extinction of vertebrates during the Holocene of mainland Australia: arrival of the dingo, or human impact?

The arrival of the dingo in mainland Australia is believed to have caused the extinction of three native vertebrates: the thylacine, the Tasmanian devil and the Tasmanian native hen. The dingo is implicated in these extinctions because, while these three species disappeared during the late Holocene of mainland Aus tralia in the presence of the dingo, they persisted in Tasmania in its absence. Moreover, the dingo might plausibly have competed with the thylacine and devil, and preyed on the native hen. However, another variable is similarly correlated with these extinctions: there is evidence for an increase in the human population on the mainland that gathered pace about 4000 years ago and was associated with innovations in hunting technology and more intensive use of resources. These changes may have combined to put increased hunting pressure on large vertebrates, and to reduce population size of many species that were hunted by people on the mainland. We suggest that these changes, which were quite dramatic on mainland Australia but were muted or absent in Tasmania, could have led to the mainland extinctions of the thylacine, devil and hen.

Fungal abundance spike and the Permian–Triassic boundary in the Karoo Supergroup (South Africa)

The most severe mass extinction of marine species and terrestrial vertebrates and plants is associated with the Permian–Triassic boundary (∼251 Ma). The extinction interval is also marked by the disappearance of most Late Permian gymnosperm palynomorphs at a layer containing solely the abundant remains of fungi. This ‘fungal spike’ apparently represents widespread devastation of arboreous vegetation. Stratigraphic and palynological study of the Carlton Heights section in the southern Karoo Basin of South Africa revealed a 1-m-thick fungal spike zone that occurs simultaneously with the last appearance of typically Late Permian gymnosperm pollen. The plant extinction and fungal spike zone are found above the last occurrence of Late Permian mammal-like reptiles of the Dicynodont Zone at other Karoo sections. Using the fungal event as a time line in marine and non-marine sections allows placement of the marine extinctions and the extinction of terrestrial plants and reptiles within a brief crisis interval of less than about 40 000 years at the end of the Permian.

Vertebrate extinction across Permian–Triassic boundary in Karoo Basin, South Africa

Distinct assemblages of paleosols above and below the Permian–Triassic boundary in the Karoo Basin of South Africa are evidence for reorganization of ecosystems following this greatest of all mass extinctions. The Permian–Triassic boundary is recognized from the last appearance of Dicynodon and from a series of negative excursions in the isotopic composition of carbon within therapsid tusks, pedogenic carbonate nodules, and organic matter. The boundary is also marked by laminated beds with very weakly developed paleosols, a change from purple (10R) to brownish red (2.5YR) paleosols, and a thin (10-cm) claystone breccia of reworked soil clasts. Paleoclimatic changes include a shift from arid and highly seasonal paleoclimate inferred from diffuse and shallow calcareous nodules in Permian paleosols to semiarid and less seasonal paleoclimate inferred from deep and well-focused calcic horizons in Triassic paleosols. An earliest Triassic shift to warmer and wetter paleoclimate is also indicated by increased chemical weathering, abundance of lycopsids, and diversity of labyrinthodonts. Permian paleosols have root traces comparable to those of open shrubland and riparian woodland, whereas Triassic paleosols have root traces and profile forms like soils of open woodland. This is a significant paleoenvironmental change, but not as dramatic a change as would be expected from the devastating extinctions of 88% of fossil vertebrate genera. Latest Permian therapsid reptiles were diverse and ecologically specialized. In contrast, the principal earliest Triassic therapsid, Lystrosaurus , was a burrower with no specific habitat preference. Its short internal nares, barrel chest, and high neural spines would have given it greater aerobic scope than preexisting therapsids and may have been an advantage under conditions of hypercapnia and hypoxia. These adaptations and associated ecosystem changes are compatible with widespread vertebrate mortality by acidosis and pulmonary edema in a post-apocalyptic greenhouse created by the voluminous release of methane from shallow marine and permafrost clathrates.

The Economics of Controlling a Stochastic Biological Invasion

The invasion of ecological systems by nonindigenous species is now recognized as a growing global problem that imposes significant economic and ecological damages. In the United States alone, the total costs of nonindigenous species have been estimated to be at least $137 billion per year (Pimentel et al.). Approximately one-fourth of the value of the country’s agricultural output is lost to nonindigenous plant pests or to the costs of controlling them (Simberloff). The economic damages from a single invasive species can be enormous. The costs of controlling the zebra mussel (Dreissena polymorpha) in the Great Lakes were estimated to reach $5 billion in 2001 (U.S. Geological Survey (USGS)) while the Russian wheat aphid (Diuraphis noxia) caused an estimated $600 million (1991$) in crop damages between 1987 and 1989 (Office of Technology Assessment (OTA)). Invasive species also cause significant ecological harm. They can alter ecosystem processes, act as vectors of disease, and reduce biodiversity (Vitousek et al.). Worldwide, out of 256 vertebrate extinctions with an identifiable cause, 109 are known to be due to biological invaders. In comparison, seventy such extinctions are known to be caused by human exploitation (Cox). The potential for a single invasive species to cause irreparable ecological damage is manifest in the extinction of twelve of Guam’s native bird species following the invasion of the island by the brown tree snake, Boiga irregularis, in the mid-twentieth century (Savidge).