Chelonoidis Fossil Record and Extinction History

The Chelonoidis fossil record stretches back to the Pleistocene epoch, with the first known fossils dating to around 2.5 million years ago.

These early fossils were found on the Galapagos Islands, where Chelonoidis species would go on to thrive and eventually become extinct.

The largest species of Chelonoidis, the Chelonoidis niger, is known from fossil evidence to have grown up to 300 kilograms in weight.

Fossil records show that Chelonoidis species were once widespread across the Galapagos Islands, but their populations declined significantly in the centuries following human arrival.

Related reading: Giant Tortoise in the Galapagos Islands

The taxonomy of Chelonoidis is a complex and evolving field. A 2006 genetic analysis suggested that Chelonoidis was closely related to hingeback tortoises, but this was later found to be incorrect.

Chelonoidis ancestors floated across the Atlantic from Africa to South America in the Oligocene, a feat made possible by their ability to float with their heads up and survive up to six months without food or water.

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The genus Chelonoidis is masculine under the rules of the ICZN, and adjectival species names must agree in gender. This means that species names within the genus are masculine.

A 2021 study found that the extent of divergence among the species in the Galápagos and Bahamian Chelonoidis radiations may have been overestimated, and supported subsuming many of the species in both complexes to being subspecies of two parent species.

Some species of Chelonoidis, such as those from Hispaniola, were specialists adapted to dry, open habitats and had a major role in shaping them. These tortoises were restricted to refugia habitats up until their extinction.

The names of several species in the genus have often been misspelled, beginning in the 1980s when Chelonoidis was elevated to genus and mistakenly treated as feminine. This error was recognized and fixed in 2017.

Chelonoidis has a rich history, with many fossil species discovered over the years. One of the most notable is the †C. lutzae, also known as Lutz's giant tortoise, which lived during the Late Pleistocene era in Argentina.

Some other fossil species include the †C. marcanoi, found in the Dominican Republic, though its holotype fossil makes it difficult to distinguish between species. The †C. pucara is another example, discovered in the Buenos Aires province of Argentina during the Late Pleistocene era. Finally, there's the †C. sombrerensis, also known as the Sombrero giant tortoise, found in Anguilla during the same time period.

Here are some of the fossil species mentioned in the article:

Late Quaternary fossils of the Chelonoidis genus are a fascinating topic. The Sombrero giant tortoise, †C. sombrerensis, was a species found in the Late Pleistocene of Sombrero, Anguilla.

One of the most interesting facts about this species is that it was a giant tortoise. The Lutz's giant tortoise, †C. lutzae, was another Quaternary fossil species found in Argentina.

Here are some Quaternary fossil species of the Chelonoidis genus:

The Floreana Galápagos tortoise extinction is a tragic tale of human impact on the environment.

By the 1700s, whalers and tortoise hunters stopped on Floreana Island, where they exploited the tortoises for food and took them from the island.

Human settlement occurred on Floreana by at least 1807, when an Irish sailor was abandoned on the island.

The introduction of non-native species, such as goats, donkeys, cattle, pigs, rats, and dogs, permanently altered the Galápagos environments, including Floreana Island.

These introduced animals led to direct predation of tortoises and hatchlings, competition for resources, and foraging areas.

The presence of invasive plants, like thickets of impenetrable vegetation, created barriers for tortoise mobility and impacted their habitats.

Invasive plants also provided new food types for tortoise consumption, with over 40% of tortoise foraging including non-native plants by the 2009-2013 study on Santa Cruz.

The 1833 tortoise on Floreana would have experienced both human exploitation and landscape manipulation, which would explain the difference in isotopic values between this specimen and the other four tortoises.

The Floreana Island tortoise went extinct during the 1850s, likely due to the same combination of processes that caused the isotopic signature visible in the 1833 specimen.

Charles Darwin regretted not collecting more tortoises or keeping their skeletal remains after they were consumed on the Beagle, realizing the potential of using individuals from different islands for his theory of evolution.

The Galápagos tortoise's diet can be understood through stable isotope analysis of their skeletal remains, which can provide insights into their ecological niches and feeding behaviors.

During the nineteenth to twentieth centuries, human exploitation of Galápagos tortoises led to significant population declines and extinctions, making it difficult to study certain populations.

The 1905 to 1906 California Academy of Sciences expedition collected tortoise specimens from Española Island that are now being studied for their stable isotope dietary ecology.

Only through continued and exhaustive investigation of tortoise skeletal collections will it be possible to reconstruct additional island-specific records and understand the full extent of anthropogenic impacts on Galápagos tortoise populations.

The genetic analysis of Chelonoidis reveals a fascinating story of diversity and distinctiveness.

MtDNA diversity is higher in the Reserva population, with 21 haplotypes recognized among 70 control region sequences, compared to only 7 haplotypes among 54 sequences from the Cerro Fatal population.

The mtDNA haplotype network shows two distinct haplogroups, one containing the 21 haplotypes from Reserva and the other consisting of 7 haplotypes, including 4 unique to Cerro Fatal.

This suggests a distinct demographic history for the Cerro Fatal population.

Microsatellite genotypic diversity is also lower in Cerro Fatal than La Reserva, echoing the mtDNA data and indicating independent demographic histories.

The Cerro Fatal population is characterized by significantly different allele frequencies at 12 microsatellite loci and has three private alleles.

The genetic analysis of the Galapagos tortoises from Cerro Fatal and Reserva populations has revealed some fascinating insights.

Cerro Fatal and Reserva populations exhibit distinct genetic characteristics that set them apart from one another and from other Galapagos tortoise species.

The mtDNA haplotype network showed two distinct haplogroups, one containing the 21 haplotypes from Reserva and the other consisting of seven haplotypes, four of which were unique to Cerro Fatal.

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The Cerro Fatal population has a much lower level of microsatellite diversity compared to Reserva, indicating independent demographic histories.

Bayesian clustering of genotypic data revealed that Cerro Fatal and Reserva populations constitute genetically distinct clusters relative to each other and to all other named Galapagos tortoise species.

The Cerro Fatal population is characterized by significantly different allele frequencies at the 12 microsatellite loci and has three private alleles compared to Reserva.

A set of polymorphisms in the mitochondrial control region sequence is unique to the Cerro Fatal taxon, separating them from C. porteri and C. chathamensis.

The genetic divergence between Cerro Fatal and Reserva is much higher than corresponding values between each of these populations and named species from different islands.

The Cerro Fatal population is genetically distinct from Reserva and C. chathamensis, its sister taxon from San Cristóbal Island, as evidenced by 18 and six diagnostic mtDNA sites, respectively.

The isotope mixing model is a powerful tool used to estimate the proportion of C3 and C4 plants in the diets of Galápagos tortoises.

This model uses a Bayesian Monte Carlo fitted model, which takes into account consumer (tortoise), sources (plants), and trophic enrichment factors.

A dataset of non-corrected stable isotopes from Galápagos tortoises served as the consumer data for the model.

Plant δC and δN values were extracted from a study by Gibbs et al. on three islands - Pinta, Santa Fe, and Española.

These plant values were then averaged to create source input values for the model, grouping them into C3 and C4 plant categories.

Tortoise trophic enrichment factors were obtained from turtle controlled feeding studies.

Museum collections can provide valuable insights into the history of human-tortoise interaction in the Galápagos. Unfortunately, some subspecies of tortoises were already extinct by the time scientists started studying them, leaving a lack of living tortoises or skeletal material for research.

The California Academy of Sciences expedition in 1905-1906 collected tortoise specimens that are still being studied today. These specimens can help researchers understand the dietary ecology and impact of human activities on tortoise populations.

Natural history museums worldwide may hold additional specimens from earlier expeditions, waiting to be analyzed and providing a more comprehensive picture of Galápagos tortoise history.

Natural history collections have played a crucial role in understanding Galápagos tortoises, but their history is also marked by human exploitation that led to several subspecies becoming extinct.

Charles Darwin regretted not collecting more tortoises or keeping their skeletal remains after they were consumed on the Beagle.

The California Academy of Sciences expedition in 1905-1906 collected tortoise specimens that are now used in research, highlighting the potential of natural history museum collections.

These collections can provide valuable insights into the dietary ecology and anthropogenic impacts on Galápagos tortoises, but only if they are thoroughly investigated.

Floreana Island tortoises, for example, have a record of stable isotope dietary ecology, but more research is needed to reconstruct island-specific records.

Natural history museum collections can hold secrets to the past, like the Española Island tortoises that remain hidden within museum collections worldwide, waiting to be analyzed.

Museum specimens from Galápagos tortoises have been used to study their genetics, with DNA extractions performed in physically isolated laboratories to prevent contamination.

Approximately 700 bp of the mtDNA control region and 12 microsatellite loci were amplified from these museum specimens using previously published primers and protocols.

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The holotype for the new species Chelonoidis donfaustoi was identified from a museum specimen, specifically the skull from the University of Wisconsin Zoological Collection (UWZS).

This skull, designated as UWZS 32700, was chosen as the holotype because it clearly represents the new species from Cerro Fatal in Santa Cruz Island.

The International Code of Zoological Nomenclature (Article 17) states that the availability of a name is not affected even if the original description or name-bearing type specimen(s) relates to more than one taxon.

The C. porteri holotype, which was originally thought to be the holotype for the new species, was found to be a hybrid individual between two lineages, but its name is still valid according to the code.

The skull from UWZS 32700 was selected as the holotype for Chelonoidis sp. nov. because it strongly assigns to the Reserva lineage and is likely to have been the result of a remote introgression event followed by multiple mating events involving only Reserva tortoises.

Here is a list of the key characteristics of the Chelonoidis donfaustoi holotype:

* CharacteristicsDescriptionBasicranial length and maximum widthNearly equalQuadratojugal contactBroadly contacts the jugal anteriorly and narrowly contacts the postorbital dorsallyMaxilla edgeRoughSquamosal visibilityOnly narrowly visible dorsal to the quadrateParietal extensionNearly as far dorsally as the pre-frontal extends posteriorly

The skull from UWZS 32700 provides a clear description of the new species, Chelonoidis donfaustoi, and will serve as a reference point for future studies.

The Cerro Azul Giant Tortoise is a species of Galapagos Giant Tortoise that's found on the island of Fernandina. It's one of the largest terrestrial reptiles, with a body length of up to 1.2-1.8 m (4-6 ft).

These tortoises have a variety of carapace shapes, including the round "domed" type and the flatter "saddleback" type with a high anterior opening. The saddleback carapace type is found on small, dry islands with low elevation and sparse resources.

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In the wild, Cerro Azul Giant Tortoises can go months without food or water, generating water internally by metabolizing stored fat. They drink large amounts of water if available.

Here's a comparison of the clutch sizes of different species of Galapagos Giant Tortoises:

Domed carapace types, including the Cerro Azul Giant Tortoise, are found on larger, wetter islands with higher elevation areas, more resources, and more diversity of habitats.