''Solitudo'' is an extinct genus of

tortoise Tortoises () are reptiles of the family Testudinidae of the order Testudines (Latin: ''tortoise''). Like other turtles, tortoises have a turtle shell, shell to protect from predation and other threats. The shell in tortoises is generally hard, ...

that was found during the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

on the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...

islands of

Menorca Menorca or Minorca (from la, Insula Minor, , smaller island, later ''Minorica'') is one of the Balearic Islands located in the Mediterranean Sea belonging to Spain. Its name derives from its size, contrasting it with nearby Majorca. Its capi ...

Malta Malta ( , , ), officially the Republic of Malta ( mt, Repubblika ta' Malta ), is an island country in the Mediterranean Sea. It consists of an archipelago, between Italy and Libya, and is often considered a part of Southern Europe. It lies ...

and

Sicily (man) it, Siciliana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Ethnicity , demographics1_footnotes = , demographi ...

. The genus includes three described species, ''Solitudo robusta'', ''Solitudo gymnesica'' and ''Solitudo sicula'' as well as a likely fourth, undescribed species from

Monte Pellegrino Mount Pellegrino is a hill facing east on the bay of Palermo, Sicily, southern Italy, located north of the city. It is 606 metres (1,970 ft) high with panorama views of the city, its surrounding mountains and the Tyrrhenian Sea. In his b ...

in Sicily. ''Solitudo sicula'', the youngest of the species, died out approximately 12.5 thousand years BP. The largest species, ''Solitudo gymnesica'', has been estimated to have reached a carapace length of .

History

The oldest discoveries of fossil turtles now included under ''Solitudo'' were made in the 19th century, with Leith-Adams describing remains from Zebbug Cave (

) as ''Testudo robusta''. In 1914 ''Testudo gymnesica'' was described based on Pliocene material found on

. Younger material was later discovered in the Zubbio di Cozzo San Pietro cave in northern

Sicily (man) it, Siciliana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Ethnicity , demographics1_footnotes = , demographi ...

. These remains, which include a

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

phalanx The phalanx ( grc, φάλαγξ; plural phalanxes or phalanges, , ) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar pole weapons. The term is particularly use ...

, pubis and an

ischium The ischium () form ...

, were found in what is thought to be a prehistoric funeral site, however repeated human or animal activity changed the stratigraphy of the site. Due to this the turtle remains, although suspected to have belonged to a single individual, were dispersed across the site. Additionally, these finds have been found to be unrelated to the human activity at the site, having been deposited there independently of the human remains. These remains were described in 2022 by Valenti and colleagues, who found sufficient anatomical evidence to establish a new genus they dubbed ''Solitudo'', with ''"Testudo" robusta'' serving as the type species. The remains from Sicily were used to erect a new species, ''Solitudo sicula'' and ''Solitudo gymnesica'' became a new name for ''"Testudo" gymnesica'' from Menorca. The name ''Solitudo'' derives from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

word for loneliness or solitude, which reflects the isolation of islands where members of this genus have been found. The name ending with "tudo" furthermore serves as an allusion to the genus '' Testudo'' with which the genus shares characteristics with. The species name of the youngest member, ''Solitudo sicula'', is the female form of the Latin word for "Sicilian".

Description

The different species of ''Solitudo'' differ from the tortoises of the ''Testudo'' genus mostly in the anatomy of the

trochanter A trochanter is a tubercle of the femur near its joint with the hip bone. In humans and most mammals, the trochanters serve as important muscle attachment sites. Humans are known to have three trochanters, though the anatomic "normal" includes ...

s. In ''Testudo'', the trochanters are fused at the proximal end of the bone through the presence of a rounded ridge which is absent in ''Solitudo'', leaving the trochanters only incompletely fused. The femur is generally slender and its head narrower than the width between the two trochanters. Additionally, the femoral head is oriented in a 25-45° angle when viewed from above, while other genera of tortoise have femoral heads with more anteroposterior orientation. ''Solitudo sicula'' is distinguished by the other species of the genus by having trochanters that are at the same height as the femoral head, additionally, the femoral head is also more elliptical than in more derived ''Solitudo species''. The entire femur of ''S. sicula'' measures long, which is notably larger than that of the biggest extant tortoise of Europe, the

Marginated tortoise The marginated tortoise (''Testudo marginata'') is a species of tortoise in the family Testudinidae. The species is endemic to Greece, Italy, and the Balkans in Southern Europe. It is the largest European tortoise. The marginated tortoise is ...

. Assuming similar proportions, this would mean that ''Solitudo sicula'' may have reached a straight carapace length of . Larger sizes have been estimated for the older species. ''Solitudo robusta'' may have reached a carapace length of up to , while some estimates suggest that ''Solitudo gymnesica'' could have reached a carapace length of .

Phylogeny

Although repeated attempts at extracting genetic material were conducted, no methods yielded DNA which rendered molecular phylogenetic analysis impossible. Due to this restriction, the relationship between ''Solitudo'' and other circum-Mediterranean tortoises was established on the basis of femur morphology, which is well known in the relevant taxa. Morphological analysis concluded that among the tortoises found around the Mediterranean, three separate femur morphotypes could be found. The "Testudinini morphotype", which is generally slender with a more narrow and oblique head, the "‘Geochelonini morphotype" which was found to be more robust and with a less oblique head and the "Insular morphotype" which typically shows a non-oblique head, slender diaphysis and trochanters that unlike in the other groups are not fully joined at the proximal end of the bone. The clade that contains all ''Solitudo'' species is based on a single synapomorphy, the incompletely fused trochanter, supported by the geographical proximity. The ''Solitudo sicula'' is recovered in a basal position within the genus, its femur still retaining some similarities to the "Testudinini morphotype". Besides the three named species of ''Solitudo'', a fourth, unnamed taxon from

was also found to fall within the "Insular morphotype", sharing the unfused trochanter that defines the clade. The idea that this specific morphotype is the result of the tortoise's insular habitat is dismissed on account of other insular species retaining their ancestral morphology, such as the Galápagos tortoise and Gran Canaria giant tortoise. The exact relationship between ''Solitudo'' and the other tortoises surrounding the Mediterranean remains unknown until better material, in particular fossils of the head and shell, is found.

Paleobiology

Remains of ''Solitudo'' are exclusively known from Mediterranean islands. The type species, ''Solitudo robusta'', was found on the island of Malta and has been dated to the Middle Pleistocene. ''Solitudo gymnesica'' is known from Pliocene Menorca and ''Solitudo sicula'' from Sicily. Dating the pubis of ''Solitudo sicula'' revealed that the animal lived approximately 12.5 ± 0.5 thousand years BP. ''Solitudo sicula'' would have shared its home island with the extant Hermann's Tortoise, which has been continuously present on Sicily since at least the Middle Pleistocene. There are also remains of unnamed giant tortoises found on Sicily, they were however not contemporary with ''Solitudo'' and instead correlate with the Middle Pleistocene.

References

{{Taxonbar, from=Q113545461 Testudinidae Pleistocene turtles Pleistocene genus extinctions Pliocene turtles Pliocene reptiles of Europe Prehistoric turtle genera Fossil taxa described in 2022 Extinct turtles