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Biology Articles » Evolutionary Biology » SENI Biometric Analysis on the extinct Scincidae species: Macroscincus coctei (underlined)

SENI Biometric Analysis on the extinct Scincidae species: Macroscincus coctei (underlined)

Brian L. Schnirel

Leeway Corucia Research Center (LCRC)

Courtesy: Polyphemos (2004)

 

Introduction:

It has been determined that through mitochrondrial DNA research that Macroscincus coctei has been linked to the Mabuya genus and may both belong to the same clade. Evidence suggests that due to rafting episodes, Mabuya species occupied the Cape Verde archipelago from West Africa. By the Pleistocene, Macroscincus coctei had occupied the northwestern group of islands and in a case of parallelism, Mabuya villianti occupied the southern group of Cape Verde islands (Carrenza et al.,2001). Both were large Scincids of a somewhat herbivorous nature (based on dentition). The Cape Verde Islands were denuded some five hundred years ago with importation of domestic animals. Working with an extant living relative, Mabuya striata sparsa, many common features were noted. On this work submitted both Macroscincus coctei and Mabuya striata sparsa had a SENI value of .13 ; indicating a similar low canopy arboreal niche.

 

Abstract:

Macroscincus coctei, a giant member of the Scincidae, became extinct before a proper study of it's lifestyle could be conducted. The few scientific studies of this species that were done were made after the ecosystem was vastly altered.

Using a designed biometric ratio, extant members of the Scincidae were tested. A systematic numerical linkage of a given species to a known ecological niche resulted. The technique was then utilized with Macroscincus coctei to determine it's ecological niche.

The SENI (Scincidae Ecological Niche Index) is a ratio based on anterior foot length at the junction of the ulna/radius-carpal bones to the longest digit divided by the snout to vent length {SVL} (B. Schnirel, 2003). It had been determined that a relationship seemed to exist between the length of certain body proportions such as the anterior foot length and type of environment common to a given Scincidae species. The more arboreal a skink species, the larger the proportion. The SENI method can be a useful in confirming the environmental niche, and possibly determining the trophic level of extinct skink species unavailable for direct study.

Species (extant) known Ecological Niche Seni
Scientific Name/Common Name

Chalcides chalcides Subterranean .01
North African Worm Skink ( Deep-Burrower)

Chalcides sepsoides Subterranean .02
North African Ribbon Skink (Shallow-Burrower)

Eumeces scheideri Fossorial .06
Berber Skink

Tiliqua gigas Fossorial .06
New Guinea Blue-Tongue Skink

Hemisphaeriodon gerrardi Semi-Arboreal .11
Pink-Tongue Skink

Kabuya striata sparsa Arboreal .13
Kalahari Black Tree Skink (Low-Canopy)

Corucia zebrata zebrata Arboreal .17
Common Monkey Skink (High-Canopy)

Macroscincus coctei .13
Cape Verde Giant skink

 

Discussion:

The SENI biometric ratio has given a good numerical perspective of the differences between Scincidae species in their lifestyle as well as appearance.

Since the initial development of the SENI biometric ratio in 2003 and the intial study of the species described in this paper, the Leeway Corucia Research Center has used this method extensively and it has given insight into our research with the extant species: Corucia zebrata. In addition to C/A biometric ratio studies and comparisons of SVL and LOA measurements, the SENI formula is one more tool for comparison of Corucia zebrata with Macroscincus coctei and other members of the Scincidae. Based on the .13 assessment for Macroscincus, It would appear that this species originally was a lower level arboreal species before the Cape Verde Archipelago was denuded. Hemisphaeriodon at .11 is a known semi-arboreal extant species. Corucia at .17 is a known high arboreal extant species.

Cape Verde Giant Skink
Macroscincus coctei
Bibron & Dumeril 1939

Literally on the other side of the world from the Solomon archipelago lies the Cape Verde archipelago. On these islands hailed a large member of the Scincidae, The Cape Verde Giant Skink: Macroscincus coctei - (also known as Bibron's Skink and Cocteau's Skink). The Cape Verde archipelago lies off the west coast of Africa; several hundred miles from Senegal and Mauritania. Hundreds of years ago, rich vegetation abounded but was denuded by introduced dogs, cats, sheep, and cattle. Uninvited introductions included rats and green monkeys. Extensive agriculture and demand for wood also destroyed the habitat and led to subsequent erosion. Macroscincus coctei was most likely found throughout the island chain but in recorded times this skink was found only on the two smallest islands in the fifteen island archipelago (Ilhe'u Branco-1.2 sq. miles and Ilhe'u Razo-2.7 sq. miles). A report by Jim Pether states that they existed on Ilhe'u Santa Luzia. Other evidence suggests (bones, etc.) that they were on Ilhe'u Sao Vincente and Ilhe'u Sao Anto. These islands are described as uninhabited, rocky outcrops with sparse vegetation consisting only of ten species of mallows and great quantities of sand dunes (due to erosion) on their southern tier.

The Cape Verde Giant Skink was a heavy built member of the Scincidae with powerful limbs and claws. The digits were long; suggesting a more arboreal existence. Macroscincus records a SENI value of .13 (Schnirel, 2002). This places this skink in the Low Canopy Arboreal Niche. This would be consistant with the original biofauna found on Cape Verde before interference by Homo sapiens. The SENI Biometric ratio can be a valuable paleontological tool to determine the ecological niche of extinct members of the Scincidae lost to direct living observation. Three color morphs of grey, yellow and intermediate have been described. There was no banding but the body had dark stippled blotches and freckles with a yellow green- grey standard background. The underside was largely devoid of freckles with a solid color somewhat lighter than the back. The tail was less than half the length of the body (SVL)-.402 of the LOA. Corucia has a longer tail in comparison to the SVL. In size, Macroscincus had an adult SVL from 283-286 mm in males and 253.5-255 mm in females. LOA in adult males was 473.6-478.6 mm and in adult females: 424.2-426.7mm. In comparison, Corucia zebrata has an average longer tail length of .539 LOA (males range .53-.55, females range .53-.56). In adult Northern Solomon males, the average SVL is 320mm and 660 LOA. Adult Northern Solomon females, the average is 330mm SVL and 670mm LOA. Common Solomon adult males range about 230-270mm SVL and 520-580mm LOA. Common Solomon adult females have a SVL range of 260-280mm and 560-605mm LOA. Andreone and Guarino (10/03) using LAGS (lines of arrested growth) measured an age of sixteen years for a male Macroscincus and twelve years for a female. A juvenile measured four years. Their study indicated by the LAGS that males reached a maximum adult size quicker than females. Male Macroscincus coctei has been described as having a larger head and longer hindlegs than the female. Andreone/Gavetti described the tail as being prehensile but Pether however, wrote that the tails were capable of caudal autonomy and it was shown in individuals-particularly males. Bartleia describes older individual males having thick, hanging dewlaps-unusual in the skink world and would indicate this was to drive off rival males from the defending territory. The lower eyelid was described as having a transparent window (Bartelia). It is unknown for certain if Macroscincus coctei was crepuscular ( Pether describes Macroscincus to be crepuscular like Corucia) but if so, could utilize the transparent lower window while sleeping on a lower canopy rest spot with it's eyes closed. The reason for only the lower lid being clear could be an evolutionary necessitative development to avoid predation by a native predator long vanished. The predator apparently approached from below. If Macroscincus coctei was diurnal, a clear lower eyelid when sleeping at night would not be as functional since at night depth perception decreases and shadows fade. Bartelia also mentions the dorsal scales are small and keeled in 100+ rows at the midsection. The osteodermal covering is mentioned as being less developed than in other skinks. Andreone/Gavetti describe a maximum scale at midbody of 114 for both male and female and 116 for a single juvenile. The teeth were pleurodontid and pterygoid. Bartelia mentions the teeth as being compressed and serrated like the genus Tiliqua and Ergernia. The head was more streamlined than Corucia zebrata. The head particularly the jaws were thicker in male Macroscincus compared to females.

Macroscincus coctei was first noted by Jose Dasilva Feijo in 1784. Several specimens were filed away/forgotten in a museum in Lisbon, Portugal. In 1809, one of the specimens was transferred to a museum in Paris, France. In 1832, Charles Darwin visited Cape Verde and was dismayed at the sparseness and lack of biodiversity due to human interference. In 1833, the viable population crashed when a group of starving convicts were marooned on Ilhe'u Branco. Use of Macroscincus as food and as a medicinal paste for fat content led to a rapid decline. In 1839, Macroscincus was finally described by Dumeril and Bibron as being of the genus Euprepes and named the species coctei after Cocteau, anoted scientist. Erroneously, they believed the newly described skink hailed from the west coast of Africa. In 1873, Dubocage became aware of a giant oceanic skink from Cape Verde. He arranged the shipment of three individuals; one of which was a youngster. In study, he determined that they were unique enough to be put in a genus of their own- Macroscincus (Some scientists have speculated affinities of Macroscincus to Corucia and Tiliqua.). He is noted as being the first person to maintain Macroscincus in captivity. Two died shortly after arrival. The last (not noted if adult or young) lasted on a vegetarian diet for four years. In 1891, a Turinese reptile acquisitioner by the name of Mario Giancinto Peracca took forty living Macroscincus back to Italy. Unfortunately, they all perished and were lost for many years. Twenty six of these individuals (eleven males and fifteen females) were found and are now housed at the Museo Regionale Di Scienze Naturali Di Torino. Peracca indicated seven eggs were laid over fifteen days in pure, white coloration and were 1 1/2 inches in diameter. Dr. Andreone reported Macroscincus eggs are housed at the Museo Regionali Di Torino. This is notable as on preserved specimens belly-button slits indicate Viviparous Matrotrophy was utilized in reproduction. Perhaps Macroscincus coctei utilized both methods. It is not without precident. In the January 2003 issue of Reptiles magazine, Bill Love mentions the Sheen Skink (eugongylus albofasciolatus) from the Solomon islands using both forms of reproduction. Not only the species but a single Sheen female can switch from Viviparism to Oviparism and vica versa. Several Museums supposedly had eggs and individual Macroscincus specimens by the turn of the century. In 1898, Leonardo Fea visited the Cape Verde Islands and was one of the last scientists to be able to work with live Macroscincus in their natural habitat. By the beginning of the twentieth century, live Macroscincus were appearing in Europe. Many were acquired by zoos. Pether reported a London animal dealer on July 22, 1891 listed Macroscincus coctei at 2 Pounds each and offered these to the London Museum. German hobbyists in general took an active interest in this species before WW I. Individuals would become tame and generally would eat vegetation and fruit. One individual was noted as eating a bird. Regrettably, no captive breeding populations became established. Macroscincus, like the Tuatara, lost ground on the larger islands until being primarily restricted to Ilhe'u Branco and Ilhe'u Razo. Soil erosion due to lost vegetation and lingering, very oppressive draught were the non-human factors leading to the decline. Area fisherman would collect Macroscincus as food from these islands. By 1940, this hardy, adaptable skink could hold out no longer and Macroscincus coctei was declared extinct. Day reported that despite being told he was four decades too late, Hans Hermann Schleich searched both Ilhe'u Razo and Ilhe'u Branco for Macroscincus without success in 1979. However, in 1985, UN System Earthwatch reported one living Macroscincus seen on Ilhe'u Branco. 1985 was the year for extinct species to supposedly return from the dead. Also in that year, a Thylacine (Marsupial tiger/wolf, a species through Parallelism occuping the same niche as Placental dogs and cats) was seen in Western Australia. Australian Thylacines were thought extinct over 1000 years. On Tasmania, free from the pressures of the introduced Dingo to the Australian mainland, Thylacines lasted into the twentieth century. However, being a large predator, The species fell into disfavor with farmers and the government. A bounty was placed on Thylacines with the result of complete extermination in a very short time. The last Thylacine died in captivity in a zoo in 1930. Absurdly, the Tasmanian government halted the bounty and gave complete protection to the Thylacine several years after being declared extinct. In 1998 (On he 100th anniversary of Dr. Fea's Cape Verde expedition), Dr. Franco Andreone investigated the entire Cape Verde Archipelago without finding any trace of living Macroscincus. Jim Pether also noted this in 1995. Pether undertook a trip to Cape Verde and found no living Macroscincus coctei but managed to still find bones of this species. Also in 1995, the Genus name of Macroscincus was switched to be included in the Genus Gonglyus (Interesting, considering that a species of Eugongylus was just discussed on the subject of dual forms of reproduction. If not direct relation, a close affinity of Macroscincus to this genus gives even greater credence to the possibility of some occurrences of Viviparism.) by Frank/Remus. In 1998, Andreone placed the species back in the separate Genus Macroscincus.

Probably due to the sparseness of the environment, Macroscincus was an opportunistic feeder. It is most likely that the Cape verde Giant Skink evolved from a carnivorous ancestry to a herbivorous diet consistent with the original biofauna of the Cape Verde Archipelago. After the devastation by man and his introduced animals 500 years ago, Macroscincus coctei probably switched to an omnivorous diet or more accurately, an on/off/on herbivore-carnivore-herbivore coinciding with the spring Leach Petrel breeding season. At other times, according to David Day, Macroscincus fed on Mallows (About the only game left in town) and their seeds. David Day noted that Macroscincus coctei would routinely enter the burrows and devour both the eggs and birds present. This explains the German captive Macroscincus devouring a bird. The available abundant source of avian nourishment was probably in good timing Macroscincus coctei's own breeding season. Developing eggs in the female is taxing enough but if the females were Vivparous by Matrotrophy, there would be even more of a drain of the females body reserves - especially if a single youngster was produced the length of time and size of the neonate of Corucia zebrata. More likely, Viviparism would have resulted in the birth of several, smaller youngsters.

It had been reported (Carranza S., Arnold E.N., Mateo J.A., Lopez-Jurado L.F. - 2001) that the ancestors of Macroscincus coctei arrived possibly by a rafting episode from the West African mainland in the Late Miocene or Early Pliocene period. Mitochondrial DNA sequences have indicated a close affinity and possible linkage to the same clade between Macroscincus coctei and the Mabuya genus. Although not a genetic link, SENI data gives both Macroscincus coctei and Mabuya striata sparsa (The Kalahari Black Tree Skink) a value of .13 which links the two species to the same ecological niche- low canopy arboreal (B. Schnirel, 2003). Evidence suggests that the Mayuba genus occupied the Northeastern islands of the Cape Verde Archipelage first, evolving into the various Mabuya species. The ancestor of Mayuba vaillanti and Mayuba delalanti may have originated on the Island of Boavista. Subsequent decendants of this clade rafted to the islands of Ilheh'u Santiago or Ilheh'u Fogo. Later evolution in the Pliocene gives evidence of latter clade species of Mayuba fogoensis-Mayuba strangeri colonizing the islands of Ilheh'u Branco, Ilheh'u Razo (Two islands documented to be occupied later by Macroscincus coctei), Ilheh'u Sao Vincente, and Ilheh'u Santa Luzia by way of Ilheh'u Sao Nicolau. Subsequent migration led to the colonization of Ilheh'u Santo Antao. The evidence suggests these rafting episodes to the Northeastern islands was protracted due to the Northest Trade Winds and Canary Current although the Carranza et al. study also suggests the islands may have not have fully developed to the point of being hospitable for Scincidae occupation. The Southwestern islands were rapidly occupied after the speciation of Mabuya vaillanti and Mabuya delalanti. It is not known for certain why the Southwestern Islands were so rapidly occupied at a later time. It had been suggested in the Carranza et al. study that pre-Pleistocene volcanism may have kept skinks off the islands or completely obliterated all traces of earlier species that occupied them. Mabuya vaillanti evolved into a large Scincidae with herbivorous tendencies in the Southeastern islands; a parallism to Macroscincus coctei which evolved in the Northeastern islands.

It is, and will remain unfortunately forever unknown if Macroscincus coctei had a Circulus relationship. If a large single neonate was not produced after a long gestation, a Circulus relationship may have not had to evolve to protect the single large genetic investment. As such, a more loose association of some sort may have been the rule. The Male dewlap may have been used as in other lizards- i.e. Anoles. A territory may have been established by the male with females coming and going randomly. Any female wandering in the male's territory would be subject to submission and mating if the conditions were right. After mating, no lasting relationship was extant.

It is indeed remarkable that Macroscincus coctei lasted as long as it did. For hundreds of years, the vegetation and land scape as noted had been eradicated. Many indigenous species had vanished long before. The art of survival of Macroscincus coctei (underlined) was more surprising given the fact that the species remained on two islands diminutive in size and with great hunting pressure on them. Fortunately, a SENI value of .13 apparently was low enough to adjust from a lower Arboreal herbivorous niche to a ground-level / near saxicolous existence in the conditions of squalor. A trophic level switch was also more possible from herbivory given the lower SENI value compared to Corucia zebrata - a high canopy herbivore (SENI value .17). The Pink-Tongue skink which is a Semi-Arboreal carnivore, has a SENI value of .11. That Macroscincus coctei lasted as long as it did is a testiment to the hardiness of this lizard.

References:

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Austin, C.C; 1995 Molecular and morphological evolution in south Pacific lizards. Herpetologica: pp.291-300.

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de Vosjoli Phillippe; Notes on three species of New Caledonian Fast, Frank; 1995. geckos of the Genus Rhactodactylus. The Vivarium, Volume 6-Number 6, Escondido, California, U.S.A. pp. 26-29, 53-54.

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Schnirel, Brian L.; 2004. SENI biometric analysis on the extinct Scincidae species: Macroscincus coctei. Polyphemos, Volume 1, Issue 2, May, Florence, South Carolina, U.S.A. pp. 12-22.

Contributed by Brian-LCRC.
Accepted on October 12, 2007.


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