''Caeruleum'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus of

lamprey Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...

from the

Lower Cretaceous Lower may refer to: * ''Lower'' (album), 2025 album by Benjamin Booker * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) * Lower Wick Gloucestershire, England See also * Nizhny {{Disambiguation ...

Jiufotang Formation The Jiufotang Formation () is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see Jehol Biota). It is a member of the Jehol group. T ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. The genus contains two species, ''C. miraculum'' and ''C. gracilis'', known from various specimens including complete and partial bodies.

Discovery and naming

The first described ''Caeruleum'' fossil material was discovered in sediments of the

near Naizi (or Naitou) Mountain in Weichang County of

Chengde Chengde, formerly known as Jehol and Rehe, is a prefecture-level city in Hebei province, situated about northeast of Beijing. It is best known as the site of the Mountain Resort, a vast imperial garden and palace formerly used by the Qing e ...

City,

Hebei Province Hebei is a Provinces of China, province in North China. It is China's List of Chinese administrative divisions by population, sixth-most populous province, with a population of over 75 million people. Shijiazhuang is the capital city. It bor ...

, China. Various lamprey specimens were found in this formation. In 2023, Weijia Huang described ''Caeruleum miraculum'' as a new genus and species of lamprey based on several fossil remains. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen, BMM 3770, consists of a complete animal preserved on a slab and counterslab. Several additional specimens of various levels of completion were also assigned to ''Caeruleum'' as

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype (biology), isotype ...

s. These include BMM 3771 (an incomplete specimen with a complete tail), BMM 3772 (the posterior end of an animal with a mutilated tail), BMM 3776 (the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

end with a complete head), and BMM 3775, 3777, and 778 (nearly complete specimens missing the posterior ends). The generic name, "''Caeruleum''", implements the blue color caeruleum. The specific name, "''miraculum''", is derived from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

"mirabilis", meaning "wonderful", in reference to the nature of the fossil specimens. The full

binomial name In taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, altho ...

references the Blue Miracle Museum Science Research Studio in

Guangzhou Guangzhou, Chinese postal romanization, previously romanized as Canton or Kwangchow, is the Capital city, capital and largest city of Guangdong Provinces of China, province in South China, southern China. Located on the Pearl River about nor ...

(

Guangdong Province ) means "wide" or "vast", and has been associated with the region since the creation of Guang Prefecture in AD 226. The name "''Guang''" ultimately came from Guangxin ( zh, labels=no, first=t, t= , s=广信), an outpost established in Han dynasty ...

), China, where the specimens are housed. In 2024, Huang and colleagues named a second species of the genus ''Caeruleum'', ''Caeruleum gracilis'', also from Naizi Mountain outcrops. ''C. gracilis'' is only known the holotype specimen, BMM 3990, a partial individual missing the end of the tail. The specific name, "''gracilis''", is derived from a Latin word meaning "slender", in reference to the body shape of the species in comparison to ''C. miraculum''. ''Caeruleum'' is the sixth named genus of fossil lamprey, after '' Mayomyzon'', '' Pipiscius'', '' Hardistiella'', '' Mesomyzon'', and ''

Priscomyzon ''Priscomyzon riniensis'' is an extinct lamprey that lived some 360 million years ago during the Famennian (Late Devonian) in a marine or estuarine environment in South Africa. This small agnathan is anatomically similar to the Mazon Creek lam ...

''. After '' Mesomyzon'', ''Caeruleum'' is also the second Cretaceous fossil lamprey genus named from China. A short time after the initial description of ''Caeruleum'', Xu, Janvier & Zhang (2023) named the new genus '' Yanliaomyzon'', containing the two species ''Y. occisor'' and ''Y. ingensdentes'', from the Middle–

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

Tiaojishan Formation The Tiaojishan Formation is a geological formation in Hebei and Liaoning, People's Republic of China, dating to the middle-late Jurassic period (Bathonian-Oxfordian (stage), Oxfordian stages). It is known for its Lagerstätte, exceptionally preser ...

of China.

Description

The ''Caeruleum'' specimens exhibit significant variation in size; ''C. miraculum'' specimens range from in length. This is significantly larger than most other fossil lampreys and is comparable to some

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

species. Contrastingly, the ''C. gracilis'' holotype is even smaller, with a preserved length of and an estimated total length of or longer. Like modern lampreys, ''Caeruleum'' had seven gill pouches. In ''C. miraculum'', the anterior

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

originates after the last gill pouch, while in ''C. gracilis'', the dorsal fin is smaller, beginning after the second gill pouch and extending only past the last. In comparison, the Cretaceous ''Mesomyzon'' from the

Yixian Formation The Yixian Formation (; formerly Romanization of Chinese, transcribed as Yihsien Formation or Yixiang Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the Barremian stage of the Early Cretaceous. I ...

ranged from long, with the dorsal fin beginning after the fourth gill pouch. Mesomyzon mengae NMNS

Paleoenvironment

The fossil material of both ''Caeruleum'' species was discovered in layers of the

, which dates to the

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

age (122.1±0.3 Ma) of the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

period. Huang et al. (2024) suggested that ''Caeruleum'' inhabited a

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

freshwater environment. Well-preserved fossils of many other animals, including non-avian dinosaurs, early birds, pterosaurs, mammals, turtles, lizards, and fish, have also been found in the Jiufotang Formation.

References

{{Taxonbar, from=Q123475605 † Early Cretaceous fish of Asia Mesozoic jawless fish Fossil taxa described in 2023 Fish described in 2023