Cretaceous Ichthyosaurs: Dwindling Diversity, or the Empire Strikes Back?

Zammit, Maria

doi:10.3390/geosciences2020011

Cited by 24 publications

(17 citation statements)

References 40 publications

(81 reference statements)

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“…If a species was considered a nomen dubium , it was excluded, except in cases where taxonomic validity was debated, for example the Cretaceous genus Platypterygius . Here, for completeness, we chose to retain species whose status is debated (Zammit ) as the study is based on individual specimens, and records of stratigraphic age, geographical location and overall size are unaffected.…”

Section: Methodsmentioning

confidence: 99%

The fossil record of ichthyosaurs, completeness metrics and sampling biases

et al. 2015

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Ichthyosaurs were highly successful marine reptiles with an abundant and well-studied fossil record. However, their occurrences through geological time and space are sporadic, and it is important to understand whether times of apparent species richness and rarity are real or the result of sampling bias. Here, we explore the skeletal completeness of 351 dated and identified ichthyosaur specimens, belonging to all 102 species, the first time that such a study has been carried out on vertebrates from the marine realm. No correlations were found between time series of different skeletal metrics and ichthyosaur diversity. There is a significant geographical variation in completeness, with the well-studied northern hemisphere producing fossils of much higher quality than the southern hemisphere. Medium-sized ichthyosaurs are significantly more complete than small or large taxa: the incompleteness of small specimens was expected, but it was a surprise that larger specimens were also relatively incomplete. Completeness varies greatly between facies, with fine-grained, siliciclastic sediments preserving the most complete specimens. These findings may explain why the ichthyosaur diversity record is low at times, corresponding to facies of poor preservation potential, such as in the Early Cretaceous. Unexpectedly, we find a strong negative correlation between skeletal completeness and sea level, meaning the most complete specimens occurred at times of global low sea level, and vice versa. Completeness metrics, however, do not replicate the sampling signal and have limited use as a global-scale sampling proxy.

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Section: Methodsmentioning

confidence: 99%

The fossil record of ichthyosaurs, completeness metrics and sampling biases

et al. 2015

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“…The marine reptile, Platypterygius, is one of the most geographically widely distributed and stratigraphically long-lived Cretaceous ichthyosaur genera, as it has been reported from the Hauterivian to Barremian of South America, Aptian to Albian of Australia and Albian to Cenomanian of Europe, Russia and North America (e.g., Zammit, 2012;Figs. 5 and 6).…”

Section: Palaeobiogeographic Considerationsmentioning

confidence: 99%

Cretaceous vertebrate fauna of the Cauvery Basin, southern India: Palaeodiversity and palaeobiogeographic implications

Verma

2015

Palaeogeography, Palaeoclimatology, Palaeoecology

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“…Nearly all ichthyosaur lineages from the Late Jurassic onwards belong to Ophthalmosauridae. Whereas the ophthalmosaurid subclade Platypterygiinae diversified during the Late Jurassic (Kimmeridgian), only three ophthalmosaurine taxa survived into the Cretaceous with the majority going extinct in the latest Jurassic, and the last known occurrences from the Aptian-Albian of Europe (Zammit, 2012;Arkhangelsky & Zverkov, 2014;Roberts et al, 2014). However, this pattern is obscured by the paucity of earliest Cretaceous ichthyosaur specimens (Fischer et al, 2012;Green & Lomax, 2014;Fig.…”

Section: (D) Ichthyopterygiansmentioning

confidence: 99%

“…The staggered Late Jurassic decline in thalattosuchians, along with semi-aquatic crocodylomorphs, is likely to have been related to the closing off of shallow marine basins during a global sea-level regression (Hallam, 1988(Hallam, , 1992(Hallam, , 2001Miller et al, 2005;Pierce et al, 2009). It might be that among marine tetrapods, those fully adapted to a free-swimming lifestyle (such as ichthyosaurs) were more resistant to regional sea-level changes occurring over the J/K boundary by exploiting new dispersal pathways (Zammit, 2012;Stinnesbeck et al, 2014;Zverkov et al, 2015), and therefore did not experience elevated extinction rates.…”

Section: (B) Marine Patternsmentioning

confidence: 99%

Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover

Mannion¹,

Upchurch²,

Sutton³

et al. 2018

Preprint

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The Late Jurassic to Early Cretaceous interval represents a time of environmental upheaval and cataclysmic events, combined with disruptions to terrestrial and marine ecosystems. Historically, the Jurassic/Cretaceous (J/K) boundary was classified as one of eight mass extinctions. However, more recent research has largely overturned this view, revealing a much more complex pattern of biotic and abiotic dynamics than has previously been appreciated. Here, we present a synthesis of our current knowledge of Late Jurassic-Early Cretaceous events, focusing particularly on events closest to the J/K boundary. We find evidence for a combination of short-term catastrophic events, large-scale tectonic processes and environmental perturbations, and major clade interactions that led to a seemingly dramatic faunal and ecological turnover in both the marine and terrestrial realms. This is coupled with a great reduction in global biodiversity which might in part be explained by poor sampling. Very few groups appear to have been entirely resilient to this J/K boundary 'event', which hints at a 'cascade model' of ecosystem changes driving faunal dynamics. Within terrestrial ecosystems, larger, more-specialised organisms, such as saurischian dinosaurs, appear to have suffered the most. Medium-sized tetanuran theropods declined, and were replaced by larger-bodied groups, and basal eusauropods were replaced by neosauropod faunas. The ascent of paravian theropods is emphasised by escalated competition with contemporary pterosaur groups, culminating in the explosive radiation of birds, although the timing of this is obfuscated by biases in sampling. Smaller, more ecologically diverse terrestrial non-archosaurs, such as lissamphibians and mammaliaforms, were comparatively resilient to extinctions, instead documenting the origination of many extant groups around the J/K boundary. In the marine realm, extinctions were focused on low-latitude, shallow marine shelf-dwelling faunas, corresponding to a significant eustatic sea-level fall in the latest Jurassic. More mobile and ecologically plastic marine groups, such as ichthyosaurs, survived the boundary relatively unscathed. High rates of extinction and turnover in other macropredaceous marine groups, including plesiosaurs, are accompanied by the origin of most major lineages of extant sharks. Groups which occupied both marine and terrestrial ecosystems, including crocodylomorphs, document a selective extinction in shallow marine forms, whereas turtles appear to have diversified. These patterns suggest that different extinction selectivity and ecological processes were operating between marine and terrestrial ecosystems, which were ultimately important in determining the fates of many key groups, as well as the origins of many major extant lineages. We identify a series of potential abiotic candidates for driving these patterns, including multiple bolide impacts, several episodes of flood basalt eruptions, dramatic climate change, and major disruptions to oceanic systems. The J/K t...

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Cretaceous Ichthyosaurs: Dwindling Diversity, or the Empire Strikes Back?

Cited by 24 publications

References 40 publications

The fossil record of ichthyosaurs, completeness metrics and sampling biases

The fossil record of ichthyosaurs, completeness metrics and sampling biases

Cretaceous vertebrate fauna of the Cauvery Basin, southern India: Palaeodiversity and palaeobiogeographic implications

Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover

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