MURRAY, C. M., RUSSO, P., ZORRILLA, A. & McMAHAN, C. D. (2019)
Divergent Morphology among Populations of the New Guinea Crocodile, Crocodylus novaeguineae (Schmidt, 1928): Diagnosis of An Independent Lineage and Description of A New Species.
Copeia. 107(3): 517-523.
Abstract:
The New Guinea Crocodile (Crocodylus novaeguineae) is a freshwater species of crocodilian endemic to the island of New Guinea in northern Oceania. The species inhabits both the country of Papua New Guinea in the east and Indonesian West Papua. Crocodylus novaeguineae occurs on both the northern and southern side of the Central Highlands, which span east to west dividing the entire island into northern and southern halves. Like most crocodilians, C. novaeguineae inhabits various grassy and forested swamps in lowland freshwater areas and has maintained both cultural and economic significance in the region for centuries. Neill (1971) and, more recently, Hall (1989) have suggested that Crocodylus novaeguineae on the northern side of the Central Highlands (“NCN”) and those on the southern side (“SCN”) are on independent evolutionary trajectories and should be taxonomically recognized. Hall (1989) attempted to affirm the suspicions of Neill and presented compelling morphological and ecological data to do so. Morphologically, the northern and southern hypothesized lineages differed in proportional premaxillary (PXS) to maxillary (MXS) length (NCN: MXS > PXS; SCN: PXS > MXS) and patterns of cervical squamation (NCN: >4 post-occipital scutes with lateral contiguity between them, anteromedial nuchal scute separation absent; SCN: 4 post-occipital scutes with lateral discontinuity between them, anteromedial nuchal scute separation present). Ecologically, C. novaeguineae south of the Central Highlands nest in the wet season, in synchrony with sympatric Crocodylus porosus, whereas north of the Central Highlands, nesting occurs in the dry season. Additionally, variation in reproductive strategy (clutch size and egg size ratios) was diagnosed between NCN and SCN; however, reproductive strategy is highly plastic, even intraspecifically, among crocodilians. Thus, these character states are not robustly interpretable as diagnostic. Phylogenetic approaches using molecular data were later tested and interpreted in the unpublished thesis of Gratten (2003) in which NCN and SCN were considered distinct operational taxonomic units in light of Hall (1989). A Bayesian analysis of relationships of Indo-Pacific Crocodylus using mtDNA curiously recovered a paraphyletic C. novaeguineae, rendered so by the purported Borneo Crocodile C. raninus, described from a skull and two preserved juveniles with no known extant population (Muller and Schlegel, 1844). NCN was recovered as more closely related to C. raninus than to SCN. This finding was attributed to either extremely recent divergence in NCN or misidentification of a dispersed or introduced NCN to Borneo from which the molecular sample was taken. Oaks (2011) recovered a paraphyletic C. novaeguineae; however, all samples of this species were from captive animals and identification of some samples appeared problematic. Thus, our analyses and comparisons herein only include populations of C. novaeguineae due to the lack of biologically reasonable comparisons. Crocodylus novaeguineae is the only freshwater crocodilian in the region besides the putative C. raninus. Little material with robust locality data exists in collections for this species, and in the absence of more specimens and diverse datasets we are unable to make additional comparisons. An improved analysis of morphological variation among populations of C. novaeguineae is warranted, given the ecological and molecular patterns that have slowly emerged. Here, we use multivariate geometric morphometric approaches to gain clarity on the differentiation of populations north and south of the Central Highlands by assessing cranial shape variation across the distribution. We aim to identify diagnostic characters for populations on independent evolutionary trajectories and test whether cranial shape variation corresponds to the hypothesized lineages (a clade north of the central highlands and one south). We predicted that specimens from drainages on the northern side would more closely resemble each other than specimens from drainages on the southern side of the highlands and that shape-based diagnostic characters would be revealed.
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