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Crocodylus moreletiiMorelet’s Crocodile

By Brigid-Catherine Hurley

Geographic Range

Morelet's crocodiles are found on the eastern coastal plain of Mexico, across most of the Yucatan peninsula, and throughout Belize and northern Guatemala. Their range also overlaps that of the American crocodile, but the relationships between the two are unknown. Some Morelet's crocodiles have escaped from captive breeding areas in Mexico outside their normal range. (Britton, 2002)

Habitat

Morelet's crocodiles live primarily in freshwater areas such as swamps and marshes and can also be found in forested riparian habitats. Recently, C. moreletii has even been found residing in coastal brackish water. Juveniles prefer denser cover for protection, and adults tend to aestivate in burrows during the dry season. (Britton, 2002)

Physical Description

The primary distinguishing feature of Crocodylus moreletii is the snout, which is uncharacteristically blunt for a crocodile. The snout has nostrils centered at its end. The eyes are situated behind the snout and ears behind the eyes. The location of all the sensory receptors are on the same plane (the top of the head) which allows them to be completely submerged in water and still have the ability to hear, see, and smell. Their eyes, which are silvery-brown, have special eyelids with nictitating membranes covering them, allowing for vision underwater. Morelet's crocodiles generally have 66 to 68 teeth, with the distinguishing purely Crocodylus characteristic of having them in perfect alignment. Their appearance and color is similar to the American crocodile, but Morelet's crocodiles tend to be a darker grayish-brown. Adults have dark bands and spots before the tail, while juveniles are a brighter yellow with black banding. Morelet's crocodiles lack bony plates (ventral osteoderums) beneath the skin. They have powerful legs with clawed webbed feet, and large tails that allow them to swim with powerful thrusts. They are medium-sized crocodiles, averaging 3 m and attaining a maximum of 4.7 m. ("Morelet's Crocodile Video", 2003; Britton, 2002)

  • Sexual Dimorphism
  • male larger
  • Range mass
    38.5 to 58.1 kg
    84.80 to 127.97 lb
  • Average mass
    51 kg
    112.33 lb
  • Range length
    2.2 to 4.7 m
    7.22 to 15.42 ft
  • Average length
    3.0 m
    9.84 ft

Development

When born, juveniles generally weigh about 31.9 grams. Morelet's crocodiles have three main life stages, classified through their length: juveniles < 100 cm, sub adults 100-150 cm, and adults >150 cm. Not much information is known about the specific life cycle of this crocodile. As in all crocodilians, however, sex is determined by the incubation temperature of the eggs. (Britton, 2002; Liesegang and Baumgartner, 2002)

  • Development - Life Cycle
  • temperature sex determination

Reproduction

Not much information is known about particular mating habits between males and females, although they appear to follow some of the same mating habits (such as being polygynous) of the American crocodile (Crocodylus acutus). Probably large males dominate the other males in their area, and females prefer to mate with the dominant males. (Britton, 2002)

Oviposition for crocodiles living on the Yucatan primarily takes place in Chiapas between April and June. Crocodylus moreletii is unique because it is the only crocodile known to be exclusively mound nesting, laying between 20 and 40 eggs in nests that are approximately 3 m wide by 1 m high. Some nests have been found containing more than one female's eggs.

At hatching time, two to three months after laying the eggs, female Morelet's crocodiles have been known to carry eggs to water areas and crack them open. Reproductive rates are generally high among C. moreletii because of the relatively early maturation of the females. Not much information is available about the specific behavior of juveniles or the fertilization process. Research is currently being conducted in these areas. (Platt and Thorbjarnason, November 2000)

  • Breeding interval
    Morelet's crocodiles breed once a year directly before the rainy season.
  • Breeding season
    Oviposition takes place between April and June. The incubation period lasts 2 to 3 months.
  • Range number of offspring
    20 to 40
  • Range age at sexual or reproductive maturity (female)
    7 to 8 years
  • Average age at sexual or reproductive maturity (female)
    7 years
  • Range age at sexual or reproductive maturity (male)
    7 to 8 years
  • Average age at sexual or reproductive maturity (male)
    7 years

Female Morelet's crocodiles guard their nests until the eggs are ready to hatch. Studies among captive Crocodylus moreletii show females will respond to newborn vocalizations and open the nests. Males and females will also fiercely defend hatchlings against larger juveniles or other predators. Not much information is known about further interaction between juveniles and parents. (Britton, 2002; Platt and Thorbjarnason, November 2000)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • protecting
      • male
      • female
  • pre-independence
    • protecting
      • male
      • female

Lifespan/Longevity

Because they are both rare and difficult to study, not much is known about specific life cycles. Morelet's crocodiles that are bred in captivity appear to have a slightly longer lifespan (up to 80 years) than those that live in the wild (50 to 65 years). Females appear to live slightly longer than males. (Stafford and Meyer, 2000)

  • Range lifespan
    Status: captivity
    80 (high) years
  • Typical lifespan
    Status: wild
    50 to 65 years
  • Average lifespan
    Status: wild
    60 years
  • Typical lifespan
    Status: captivity
    55 to 70 years
  • Average lifespan
    Status: captivity
    65 years

Behavior

Research is currently being conducted into C. moreletii social behavior because not much information is available. These crocodiles appear to share similar qualities with the American crocodile, such as habitat selection and feeding behaviors. Typically, Morelet's crocodiles can be spotted in wetlands submerged below the surface with just the top of their heads visible. Crocodylus moreletii is active primarily at night, when it accomplishes its hunting and mating. It spends the daylight hours basking lazily in the sun, although very alert and aware of what is happening around it. (Britton, 2002)

  • Range territory size
    16.45 to 18 km^2
  • Average territory size
    17.15 km^2

Communication and Perception

Juveniles communicate through vocalization (known as barking) when born, though not much information is known about specific social communication. They tend to follow the basic patterns of all Crocodylus, which are the most vocal of all reptiles; their calls tend to differ depending on age, sex and situation. They may share the similar habit of the American crocodile, whose young are not as vocal as other species, which may be a response to high hunting pressures, resulting in a rapid adaptation for survival.

Scales covering most of the head and parts of the body are equipped with integumentary sense organs (ISO's) that perform a number of tasks, such as detecting pressure, salinity, and vibrations. (Britton, 2002; Stafford and Meyer, 2000)

Food Habits

Morelet's crocodiles vary in diet according to their age and size. Juveniles eat small invertebrates and fish. Sub adults feed on aquatic snails, fish, small birds, and mammals. Adults feed on larger prey, including birds, fish, lizards, turtles, and domestic animals such as dogs. They can also become cannibalistic in times of low food, eating newborns. Crocodylus moreletii is generally shy around humans, but larger ones may attack if provoked. ("Morelet's Crocodile Video", 2003; Britton, 2002; Rainwater, et al., 2002)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • fish
  • carrion
  • insects
  • mollusks
  • aquatic crustaceans

Predation

While Morelet's crocodiles tend to be dominant predators in their communities, their eggs and young often fall prey to older juveniles, larger mammals, snakes, wading birds, and gulls. A key protection from predators is their tough hide and their loud vocal cries. Larger individuals are potentially preyed upon by humans and jaguars. (Britton, 2002)

Ecosystem Roles

While not much information is known about the specific impact of the Morelet's crocodiles on their ecosystem, they do share many similar traits with the American crocodile, such as the role of primary carnivore in the ecosystem, thus affecting nutrient dispersal and ecosystem dynamics. (Richardson, 2003)

Economic Importance for Humans: Positive

Unlike most other species of crocodilian, Morelet's crocodiles have no bony plates (called osteoderms) in their skin. This makes the skin more valuable as leather, and has motivated over-hunting.

Also, studies of the levels of mercury within the eggs of Morelet's crocodiles in Belize has also led to clues about biological contamination there. (Britton, 2002; Rainwater, et al., 2002)

  • Positive Impacts
  • body parts are source of valuable material
  • research and education

Economic Importance for Humans: Negative

Although generally shy, as with any crocodile, C. moreletii has been known to bite humans if provoked. (Matthews, 1995)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

Due to their valuable hide, Morelet's crocodiles were hunted almost to extinction through the years 1940 to 1950. Under the Mexican Wildlife Protection Act, hunting them became illegal and their numbers have steadily risen, although illegal poaching and habitat loss continue to threaten the animal. To counteract this, Mexico has begun breeding Morelet's crocodiles in captivity. However, some individuals have escaped to form feral populations outside of their regular breeding zones, creating a problem for the populations of American crocodile, which must compete with this newly-invasive species. (Matthews, 1995; Platt and Thorbjarnason, November 2000)

Now primary focus remains in the development of sustainable use programs, such as commercial farming. More general knowledge about the species is required first, however. Status in the south of Belize is unknown; reports suggest the species is widely distributed in the Mexican states of Tabasco, Chiapas, Yucatan and Quintana Roo, and their situation in the interior of Guatemala is unknown. There remains little information on both specific numbers and general behavior patterns needed to judge their actual status throughout most of its range. (Britton, 2002; Platt and Thorbjarnason, November 2000)

Morelet's crocodiles are listed as Endangered under the U.S. Endangered Species Act, and are included in Appendix I of the CITES Treaty. The IUCN rates the species as "Lower Risk", but this rating would revert to Threatened or Endangered if ongoing conservation efforts were ended.

Other Comments

Texas Tech currently maintains extensive research in Belize studying the genetics of different populations and the impact of various pesticides and heavy metal contamination throughout this species. Other research institutions include the Lamanai Research Center in Belize and researcher Howard Hunt of the Atlanta Zoo in Cox Lagoon, Belize. (Britton, 2002)

Contributors

George Hammond (editor), Animal Diversity Web.

Allison Poor (editor), University of Michigan-Ann Arbor.

Brigid-Catherine Hurley (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

polygynous

having more than one female as a mate at one time

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

threatened

The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Belize Biodiversity Information System-Morelet's Crocodile. Belize: Wildlife Conservation Society. 01/19/98. Accessed (Date Unknown) at http://fwie.fw.vt.edu/wcs/030970.HTM.

Belize Zoo. 2003. "Morelet's Crocodile Video" (On-line video). Accessed March 18, 2003 at http://www.belizezoo.org/zoo/zoo/herps/cro/cro1.html.

Britton, A. 2002. "Crocodilian Species-Morelet's Crocodile (Crocodylis Moreletii)" (On-line ). Crocodilian Species List. Accessed 03/18/03 at http://www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/csl.html.

Liesegang, D. A., D. K. Baumgartner. 2002. "Rickets in juvenile Morelet's Crocodile" (On-line ). Accessed 03/18/03 at http://www.research-projects.unizh.ch/vet/unit51100/area217/p2373.htm.

Matthews, D. 1995. "Four Faces of Mexico; in the Yucatan, a wild and seldom visited wetland". Washtington Post, 01908286: E01.

Platt, S. G., J. B. Thorbjarnason. November 2000. Population Status and Conservation of Morelet's Crocodile. Biological Conservation, 96/1: 21-29.

Rainwater, T., B. Adair, S. Platt, T. Anderson, G. Cobb. 2002. Mercury in Morelet's Crocodile Eggs from Northern Belize. Archives of Environmental Contamination and Toxicology, 10.1007/s00244-001-0020-7: 319-324.

Richardson, D. C. J. 2003. "The American Crocodile" (On-line ). Accessed 04/09/03 at http://www.env.duke.edu/wetland/american.htm.

Stafford, P. J., J. R. Meyer. 2000. A Guide to the Reptiles of Belize. London: Natural History Museum of London.

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