This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
It’s time to crack on with the Tet Zoo guide to the crocodiles of the world (part I here, part II here, part III here). I haven’t been able to do much on the blog lately due to technical work on pterosaurs, cats and the whole sexual selection project.
Anyway - - in the previous article in this series we looked at the Saltwater crocodile Crocodylus porosus (aka Estuarine crocodile, Indopacific crocodile or Saltie), a species of southern Asia and northern Australasia often considered close to (or part of) an 'Indopacific assemblage' of crocodile species. As we saw in that last article, molecular studies indicate that the Saltwater croc is close to the Mugger C. palustris and/or Siamese croc C. siamensis, and maybe not so close to other Australasian species or to the crocodiles of the Philippines. In this article, we look at two of the ‘remaining’ species in the Indopacifc assemblage.
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The New Guinea crocodile C. novaeguineae is a poorly known, medium-sized crocodile species, said to reach a maximum length of 4 m, though 5 m is claimed by some (Wermuth & Fuchs 1978) [portrait above by Wilfried Berns of www.Tierdoku.com; adjacent image by Vlad Dinets, from here]. Its snout is medium in length compared to that of other crocodiles (being about twice as long as it is wide at the base). Distinctive features include longitudinal ridges anterior to each eye and the presence of small, granular scales between the four largest osteoderms on the dorsal surface of the neck. In contrast to the Saltwater crocodile, a transverse row of large cervical scutes is present close to the rear border of the head (Ross & Mayer 1983).
The New Guinea croc was only recognised as a distinct taxonomic entity in 1928. Prior to this, examples were assumed to be immature Saltwater crocs, and even after 1928 doubt remained as to its distinction. It's mostly a freshwater animal of rivers, lakes and swamps; there are records of individuals from brackish and coastal waters, but it seems that it mostly avoids habitats frequented by the larger and more powerful Saltwater crocodile. Scant data from ecology and diet has led some authors to suggest that the New Guinea and Saltwater crocodiles may avoid competition through niche differentiation, with the former mostly eating fish and birds while the latter takes larger prey (Trutnau & Sommerlad 2006). [Photo below by Midori.]
The existence of two morphologically distinct and genetically separate C. novaeguineae populations – one in the north of the island and one in the south – is well known, and people have been saying for decades that this division will eventually result in the naming of distinct subspecies. They differ in patterns of scalation and skull form, with the southern animals having a relatively longer premaxillary region and two or more additional post-occipital scutes when compared to northern ones (Hall 1989). Southern animals also produce smaller egg clutches (on average), have larger hatchlings, and breed in the wet season instead of the dry season (Hall 1989).
It used to be said that the New Guinea crocodile also occurred on the Aru Islands (130 km west of New Guinea), but apparently this is incorrect and based on mistaken accounts of juvenile Saltwater crocodiles. The New Guinea crocodile has, however, been introduced to the Palau Islands in Micronesia (Steel 1989) [UPDATE: nope, this is erroneous. Please see comments].
Crocodiles on the Philippines
A very similar, closely related crocodile often regarded as the sister-species to the New Guinea crocodile (e.g., Meganathan et al. 2010, Man et al. 2011, Oaks 2011) is known from the Philippines. This is the Mindoro crocodile, Philippine crocodile or Philippine freshwater crocodile C. mindorensis, named as a new species in 1935 but later demoted by some authors to the rank of a C. novaeguineae subspecies. In keeping with most recent authors, I regard it as a distinct species.
Intriguingly, Oaks (2011) found C. mindorensis to be paraphyletic with respect to C. novaeguineae: that is, the New Guinea croc was recovered as a population within the Philippine crocodile. This may tell us something about the biogeographic history of these animals. Does this result mean that C. novaeguineae should be sunk into C. mindorensis? Actually, seeing as C. novaeguineae was named first (1928 vs 1935), this is the name that would get used, should the two be combined. The genetic distance between (1) the clade that includes C. mindorensis and the most C. mindorensis-like specimens of C. novaeguineae, and (2) the remainder of C. novaeguineae was still relatively great, suggesting a separation that occurred somewhere between 6.8 and 2.6 million years ago. Separate species status for these crocodiles should therefore be maintained (Oaks 2011)… though, as usual, we run into the usual problem of deciding just what a ‘species’ really is. Oaks (2011) even suggested that some crocodile populations on New Guinea should best be interpreted as C. mindorensis, meaning that both species occur on the island.
Anyway, the Philippine crocodile (as conventionally understood) is relatively small, mostly 1.5-2 m long in total but with some individuals perhaps reaching 3.5 m. Its dorsal osteoderm shield is more complete than that of C. novaeguineae, and the four large scutes of the cervical shield aren’t separated by small scales as they generally are in C. novaeguineae (Ross & Mayer 1983). It also has a proportionally shorter snout than C. novaeguineae and the top of its head is more distinctly textured, often giving individuals a more 'gnarly' look. It tends to be white ventrally and dull brown dorsally, often with transverse stripes.
Until very recently, the Philippine crocodile was present across most of the Philippine islands from north to south. It must have been extremely abundant as late as the 1930s, since in 1932 a single American hunter apparently killed over 12,000 individuals for their leather in a single six-month period (Trutnau & Sommerlad 2006). Due to this level of hunting, it seems to have disappeared from most islands and today remains present in small numbers on Luzon and Mindanao alone. The populations on Mindoro and Negros apparent became extinct in the 1990s. Its former presence in the Sulu archipelago (just to the west of Mindanao in the southern part of the Philippines) has been mentioned (Steel 1989).
In fact, persecution of this species has been so severe that only about 100 post-hatching individuals were thought to be present in the late 1990s, making it critically endangered. Captive breeding efforts during, and since, the 1990s resulted in the hatching of over 1000 babies, though problems of funding and disease transmission have meant that these conservation efforts were not quite the success story they should have been. Furthermore, reintroduction projects were hampered by uncertainty over the affinities of the animals concerned, since some individual acquired from private collections were suspected (and confirmed) of being C. mindorensis x C. porosus hybrids. In a 2010 PhD project devoted to this issue (Hinlo 2010), Ma. Rheyda Penetrante Hinlo was able to distinguish hybrid Philippine crocs from pure ones – unfortunately, some of the hybrids had already been released as part of a 2009 reintroduction effort (Hinlo suggested that these individuals should be captured and removed from the breeding population). On top of these problems, crocodiles on the Philippines still have an image problem, with many locals viewing them negatively and as a danger to livestock and people.
The surviving northern and southern C. mindorens populations are genetically distinct (about as distinct as are mainland and Madagascan populations of C. niloticus), but it probably isn’t advantageous to view them as separate populations when it comes to management (Hinlo 2010).
With the New Guinea and Philippine crocodile done, we’re left with a single member of the traditional Indopacific assemblage: the Australian Johnston’s crocodile, Freshwater crocodile or Freshie. That’s the species we’ll be looking at next.
For previous Tet Zoo articles on crocodiles, see...
Refs - -
Hall, P. 1989. Variation in geographic isolates of the New Guinea crocodile (Crocodylus novaeguinae Schmidt) compared with the similar, allopatric Philippine crocodile (C. mindorensis Schmidt). Copeia 1989, 71-80.
Hinlo, Ma. Rheyda Penetrante 2010. Population Genetics and Conservation of the Philippine Crocodile. Unpublished MSc thesis, Massey University, Manawatu, New Zealand.
Man, Z., Yishu, W., Peng, Y. & Wu, X. 2011. Crocodilian phylogeny inferred from twelve mitochondrial protein-coding genes, with new complete mitochondrial genomic sequences for Crocodylus acutus and Crocodylus novaeguineae. Molecular Phylogenetic and Evolution 60, 62-67.
Meganathan, P. R., Dubey, B., Batzer, M. A., Ray, D. A. & Haque, I. 2010. Molecular phylogenetic analyses of genus Crocodylus (Eusuchia, Crocodylia, Crocodylidae) and the taxonomic position of Crocodylus porosus. Molecular Phylogenetics and Evolution 57, 393-402.
Oaks JR (2011). A time-calibrated species tree of Crocodylia reveals a recent radiation of the true crocodiles. Evolution; international journal of organic evolution, 65 (11), 3285-97 PMID: 22023592
Ross, F. D. & Mayer, G. C. 1983. On the dorsal armor of the Crocodilia. In Rhodin, A. G. J. & Miyata, K. (eds) Advances in Herpetology and Evolutionary Biology. Museum of Comparative Zoology (Cambridge, Mass.), pp. 306-331.
Steel, R. 1989. Crocodiles. Christopher Helm, London.
Trutnau, L. & Sommerlad, R. 2006. Crocodilians: Their Natural History and Captive Husbandry. Edition Chimaira, Frankfurt.
Wermuth, H. & Fuchs, K. 1978. Bestmmen von krokodilen und ihrer Häute. New York, Gustav Fischer.