Skeletal variation in extant species enables systematic identification of New Zealand’s large, subfossil diplodactylids

Abstract

New Zealand’s diplodactylid geckos exhibit high species-level diversity, largely independent of discernible osteological changes. Consequently, systematic affinities of isolated skeletal elements (fossils) are primarily determined by comparisons of size, particularly in the identification of Hoplodactylus duvaucelii, New Zealand’s largest extant gecko species. Here, three-dimensional geometric morphometrics of maxillae (a common fossilized element) was used to determine whether consistent shape and size differences exist between genera, and if cryptic extinctions have occurred in subfossil ‘Hoplodactylus cf. duvaucelii’. Sampling included 13 diplodactylid species from five genera, and 11 Holocene subfossil ‘H. cf. duvaucelii’ individuals. We found phylogenetic history was the most important predictor of maxilla morphology among extant diplodactylid genera. Size comparisons could only differentiate Hoplodactylus from other genera, with the remaining genera exhibiting variable degrees of overlap. Six subfossils were positively identified as H. duvaucelii, confirming their proposed Holocene distribution throughout New Zealand. Conversely, five subfossils showed no clear affinities with any modern diplodactylid genera, implying either increased morphological diversity in mainland ‘H. cf. duvaucelii’ or the presence of at least one extinct, large, broad-toed diplodactylid species.

Morphometric analyses of the vertebrae of Ambystoma (Tschudi, 1838) and the implications for identification of fossil salamanders

“…Morphometric approaches are often utilized in fossil identifications when morphological differences are small or otherwise not easily described qualitatively and have been applied across many groups of organisms (e.g., Marramà & Kriwet, 2017; Moroz et al, 2021; Scarsbrook et al, 2021). Although morphometrics can help researchers easily visualize morphological differences, the value of using morphometrics for fossil identifications can be variable, as we have shown here.…”

“…One approach that has not been used to study osteological variation in the vertebrae of Ambystoma is geometric morphometrics. Geometric morphometrics employs landmarks to quantify shape differences, and it has been used by biologists to differentiate species (e.g., Scarsbrook et al, 2021), characterize sexual dimorphism (e.g., Bonnan et al, 2008), relate form to function (e.g., Gray et al, 2019), and study morphological variation through time (e.g., Moroz et al, 2021). Geometric morphometrics allows us to consider aspects of vertebrae that are not captured through linear measurements alone and quantifies many of the qualitative descriptions of features that previous researchers made.…”

The Contribution of Kurī (Polynesian Dog) to the Ecological Impacts of the Human Settlement of Aotearoa New Zealand

“…Given the presence of reptiles in the stomach contents of introduced mammalian predators like stoats (McAulay et al, 2020), it is probable that kurī could have also preyed on skinks, geckos, frogs and tuatara (Figure 3)there are records from the nineteenth century of dogs killing escaped captive tuatara (Cree, 2014). At least one species of giant skink (Worthy, 1991) and three frogs are known to have gone extinct prior to European colonisation, with several species only surviving on offshore islands (e.g., Scarsbrook et al, 2021). Indeed, tuatara were effectively extinct on the mainland before European arrival and now only survive on islands without kiore and dogs (Cree, 2014).…”

“…The top predators in the pre-human ecosystem were also birds including Haast's eagle (Aquila moorei) and Eyles' harrier (Circus eylesi; Tennyson and Martinson, 2007). Within reptiles, there were at least 110 species of Eugongylinae skinks and Diplodactylid geckos, seven Leiopelmatid frogs and one tuatara (Sphenodon punctatus) (Easton et al, 2017;Gemmell et al, 2020;Scarsbrook et al, 2021).…”

The potential contribution of kurī (Polynesian dog) to the ecological impacts of the human settlement of Aotearoa New Zealand

“…Finsch's, blue-billed, musk and pink-eared ducks, and poūwa swan), as well as extant terrestrial birds including takahē, kākāpō and kiwi (Worthy and Holdaway, 2002). Within reptiles, there were at least 110 species of Eugongylinae skinks and Diplodactylid geckos, seven Leiopelmatid frogs and one tuatara (Sphenodon punctatus) (Easton et al, 2017;Gemmell et al, 2020;Scarsbrook et al, 2021).…”