''Eichstaettisaurus'' (meaning "Eichstätt lizard") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia altho ...

s from the

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

and

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 145& ...

of Germany, Spain, and Italy. With a flattened head, forward-oriented and partially symmetrical feet, and tall claws, ''Eichstaettisaurus'' bore many adaptations to a climbing lifestyle approaching those of

gecko Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates throughout the world. They range from . Geckos a ...

es. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...

, ''E. schroederi'', is among the oldest and most complete members of the

Squamata Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species, ...

, being known by one specimen originating from the

Tithonian In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by ...

-aged Solnhofen Limestone of Germany. A second species, ''E. gouldi'', was described from another skeleton found in the

Matese The Matese ( Italian: Monti del Matese or Massiccio del Matese) is a chain of mountains in southern Apennines, southern Italy. Geography The Matese mountains straddle two regions (Molise and Campania) and four provinces (Campobasso, Isernia, B ...

Mountains of Italy. Despite being very similar to ''E. schroederi'', it lived much later, during the

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

stage. Fossils of both species show exceptional preservation due to deposition in low-oxygen marine environments. Initially named as a species of the genus '' Ardeosaurus'' by Ferdinand Broili in 1938, ''E. schroederi'' has had a convoluted taxonomic history. It was initially recognized as a relative of night lizards until research in the 1960s identified it and ''Ardeosaurus'' as geckoes. However, phylogenetic analyses conducted in the 1990s suggested that it was closer to the ancestor of all

squamates Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species, it ...

. Various conflicting positions were found until the advent of analyses incorporating more species and better data, which resolved ''E. schroederi'' as a close relative of geckoes in the

Gekkonomorpha Gekkonomorpha is a clade of lizards that includes geckos and their closest relatives. Although it was first named in 1900, Gekkonomorpha was not widely used as a formal taxon until it was given a phylogenetic definition in the 1990s. Under this d ...

. However, the position of ''Ardeosaurus'' in relation to ''E. schroederi'' remains uncertain: one species, ''A. digitatellus'', has been recovered as its close relative in some analyses, but the other species ''A. brevipes'' has been found to be more distantly related.

Discovery and naming

''E. schroederi''

In 1938, Ferdinand Broili described an exquisitely-preserved specimen of lizard, preserved top-side-up, from

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

-aged rock deposits in the municipality of Wintershof,

Eichstätt Eichstätt () is a town in the federal state of Bavaria, Germany, and capital of the district of Eichstätt. It is located on the Altmühl river and has a population of around 13,000. Eichstätt is also the seat of the Roman Catholic Diocese ...

, Germany. The specimen came into the possession of the Bavarian State Collection of Paleontology and Historical Geology (BSPG), where it was prepared by L. Haimerl. It consists of a nearly-complete skeleton, albeit with a crushed skull, a tail missing the tail after the fifth vertebra (probably the result of

amputation Amputation is the removal of a limb by trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is carried out on indi ...

and replacement by

cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck ...

, and several vertebrae preserved only as impressions (but their presence could still be verified by the associated ribs). A

counterslab A compression fossil is a fossil preserved in sedimentary rock that has undergone physical compression. While it is uncommon to find animals preserved as good compression fossils, it is very common to find plants preserved this way. The reason f ...

to the specimen also exists. Today, the rock deposits are known to belong to the Altmühltal Formation, and the specimen and its counterslab are stored under the accession numbers BSPG 1937 I 1a and 1b. Although he was unable to examine it first-hand, Broili noted from

Christian Erich Hermann von Meyer Christian Erich Hermann von Meyer (3 September 1801 – 2 April 1869), known as Hermann von Meyer, was a German palaeontologist. He was awarded the 1858 Wollaston medal by the Geological Society of London. Life He was born at Frankfurt am ...

's description of the

type specimen In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...

of '' Ardeosaurus brevipes'' that it bore similarities to this specimen, but also that they had important differences in snout and

frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, ...

shape, as well as vertebral counts. However, he hesitated to create a new genus due to the preservational state of the skull. Thus, he assigned it to the genus ''Ardeosaurus'' with reservations as a new species, ''A.? schröderi'', named after his colleague J. Schröder. (The current specific name is ''schroederi'': by Article 32.5.2.1 of the

International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the I ...

, umlauts in German names published before 1985 must be deleted and be replaced with an "e" inserted as the next letter.)

Robert Hoffstetter Robert Julien Hoffstetter (11 June 1908 in Fargniers – 29 December 1999 in Gennevilliers) was a French taxonomist and herpetologist who was influential in categorizing reptiles Reptiles, as most commonly defined are the animals in the clas ...

formally recognized the distinction between ''A.? schroederi'' and ''A. brevipes'' in 1953, and established a new generic name, ''Broilisaurus''. However, Oskar Kuhn had already named a

stegocephalia Stegocephali (often spelled Stegocephalia) is a group containing all four-limbed vertebrates. It is equivalent to a broad definition of Tetrapoda: under this broad definition, the term "tetrapod" applies to any animal descended from the first ve ...

n amphibian with the same name in 1938; thus, in 1958, he established another generic name for the species, ''Eichstättisaurus''. (Again, due to the ICZN, the current generic name is ''Eichstaettisaurus''.) In 1963, Marguerite Cocude-Michel opined that ''E. schroederi'' really represented the same species as ''Homoeosaurus digitatellus'', which had previously been named as a non-type species of '' Homoeosaurus'' in 1914 by N.M. Grier. Thus, she created the new combination ''Eichstaettisaurus digitatellus''. Contrary to Cocude-Michel, Hoffstetter identified ''digitatellus'' as a member of ''Ardeosaurus'' separate from ''Eichstaettisaurus'' in 1964. Even though Cocude-Michel was aware of Hoffstetter's paper, in 1965 she reiterated her argument and made no attempt to address Hoffstetter. Hoffstetter responded in 1966, calling Cocude-Michel's synonymy "unbearable". He noted that it would entail the revision of the diagnostic characteristics of ''Eichstatettisaurus'' to a point where it would be practically indistinguishable from ''Ardeosaurus'', which would contradict her family-level separation of the two. Subsequent literature has retained ''Eichstaettisaurus schroederi'' and ''Ardeosaurus digitatellus'' as separate, although they received little attention until Tiago Simões and colleagues published a redescription of both in 2017.

''E. gouldi''

For many years, ''Eichstaettisaurus'' was known from the single specimen of ''E. schroederi'' until

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

-aged remains were found elsewhere in Europe. In 2000, Susan Evans and colleagues described a small lizard specimen in the

Berriasian In the geological timescale, the Berriasian is an age/stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ag ...

–

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretace ...

aged locality of Montsec in

Catalonia Catalonia (; ca, Catalunya ; Aranese Occitan: ''Catalonha'' ; es, Cataluña ) is an autonomous community of Spain, designated as a '' nationality'' by its Statute of Autonomy. Most of the territory (except the Val d'Aran) lies on the no ...

, Spain. Despite its poor preservation, the specimen was clearly distinct from the more common lizard in the locality, '' Meyasaurus''; Evans and colleagues suggested that it held affinities to ''Eichstaettisaurus''. In 2004, Evans and colleagues reported even younger remains of ''Eichstaettisaurus'', which originated from the

-aged

Pietraroja Plattenkalk The Pietraroia Plattenkalk is a Cretaceous geologic formation located in the Italian municipality of Pietraroja,Pietraroia, which is located in the

Mountains of southern Italy. A specimen catalogued as MPN 19457 formed the type specimen of a new species, ''E. gouldi'', which they named after the late biologist

Stephen Jay Gould Stephen Jay Gould (; September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. He was one of the most influential and widely read authors of popular science of his generation. Goul ...

; it is a skeleton preserved bottom-side-up, which includes the skull and parts of the vertebral column and limbs. A second specimen consists of a disarticulated skull, which is preserved as part of the gut contents of an indeterminate

rhynchocephalia Rhynchocephalia (; ) is an order of lizard-like reptiles that includes only one living species, the tuatara (''Sphenodon punctatus'') of New Zealand. Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a diverse gr ...

n catalogued as MPN A01/82. Both specimens are stored in the Museum of Palaeontology at the

University of Naples The University of Naples Federico II ( it, Università degli Studi di Napoli Federico II) is a public university in Naples, Italy. Founded in 1224, it is the oldest public non-sectarian university in the world, and is now organized into 26 depar ...

(MPN).

Description

''Eichstaettisaurus'' was a relatively small animal. ''E. schroederi'' had a snout-vent length (measured from the tip of the snout to the opening of the

cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, ...

) of , while ''E. gouldi'' had a snout-vent length of .

Skull

''Eichstaettisaurus'' can be identified by flattened skulls with short, blunt, and rounded snouts. ''E. schroederi'' had large nostrils. The tooth-bearing bones of the snout, the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

and the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...

, were likely connected by a band of

soft tissue Soft tissue is all the tissue in the body that is not hardened by the processes of ossification or calcification such as bones and teeth. Soft tissue connects, surrounds or supports internal organs and bones, and includes muscle, tendons, ...

in ''E. schroederi''. The premaxilla had 6 or 7 teeth in ''E. gouldi'', but the number in ''E. schroederi'' is unknown; the maxilla had approximately 22 teeth in ''E. schroederi'', and at least 30 in ''E. gouldi''. The teeth of both species were small, narrow, conical, and single- cusped; they had a pleurodont implantation, meaning that they were fused to the inner side of the jawbone. Like ''Ardeosaurus'', both species lacked the

lacrimal bone The lacrimal bone is a small and fragile bone of the facial skeleton; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders. Several bony landmarks of ...

, usually a part of the eye socket. Also in the eye socket, the postfrontal and postorbital bones were separate unlike ''Ardeosaurus'', and the rearward projection of the latter bones were relatively wide. In ''E. schroederi'', the contact between these bones was further forward than most lizards. The squamosal bones were slender and projected downwards to meet the quadrate bones, as in most lizards; unlike the

Iguania Iguania is an infraorder of squamate reptiles that includes iguanas, chameleons, agamids, and New World lizards like anoles and phrynosomatids. Using morphological features as a guide to evolutionary relationships, the Iguania are believed ...

and Teiidae, however, they lacked upward projections. Living geckoes lack the postorbital and squamosal bones, and they also have relatively shorter

jugal bone The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Ana ...

s than ''Eichstaettisaurus''. On the

palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separ ...

of ''E. schroederi'', the ectopterygoid bones overlapped the

pterygoid bone The pterygoid is a paired bone forming part of the palate of many vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and ...

s at their rear. Unlike ''A. brevipes'', ''E. schroederi'' lacked bone ornamentation and

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amp ...

s on the

skull roof The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In compar ...

. In both species, the frontal bones were fused and narrower between the eye sockets than they were at the front. The downward projections on the frontals known as subolfactory processes were well-developed in both species, but met at the midline only in ''E. schroederi''. The

suture Suture, literally meaning "seam", may refer to: Arts, entertainment, and media * ''Suture'' (album), a 2000 album by American Industrial rock band Chemlab * ''Suture'' (film), a 1993 film directed by Scott McGehee and David Siegel * Suture (ban ...

between the frontal and

parietal bone The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is n ...

s was convex in ''E. schroederi'' and concave in ''E. gouldi'', unlike ''Ardeosaurus'' where it was straight. ''E. gouldi'' and most other lizards have fused parietal bones, but they were paired and unfused in ''E. schroederi''. The parietals of both species lacked rearward projections and nuchal fossae. In ''E. schroederi'', the outer edges of the parietals curved inwards, and the rearward projections known as the supratemporal processes were short, widely separated, and bore depressions. Also in ''E. schroederi'', a pair of crests were present on the

supraoccipital bone The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cere ...

of the braincase, which were likely imprinted by the semicircular canals due to the skull's reduced

ossification Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in ...

Vertebrae and ribs

Compared to most iguanian,

gekkota Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates throughout the world. They range from . Geckos ar ...

n, and scincomorphan lizards, which generally have 24–26

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

e in front of the

sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part o ...

(or hip), ''E. schroederi'' had 31, including 7 neck vertebrae and approximately 24 back vertebrae. ''E. gouldi'' had 6–7 neck vertebrae, and an unknown number of back vertebrae. In ''E. gouldi'', the second ( axis) and third neck vertebrae were connected to the next by elements known as intercentra. In ''E. schroederi'', most of the neck vertebrae lacked

cervical rib A cervical rib in humans is an extra rib which arises from the seventh cervical vertebra. Their presence is a congenital abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2% to 0.5% (1 in 200 to 500) of the ...

s, save for the last two. The upward-projecting

neural spines The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

on the back vertebrae were small, and the last few back vertebrae lacked

rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...

s in the vein of lumbar vertebrae.

Zygosphene-zygantrum articulation The zygosphene-zygantrum articulation is an accessory joint between vertebrae found in several lepidosauromorph reptiles. This pivot joint consists of a forward-facing, wedge-shaped process called the zygosphene, that fits in a depression on the r ...

s are present on the back vertebrae of both species. The ribs were single-headed and had circular articulating surfaces. In ''E. gouldi'', the

centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees. The chain has three different ...

(main bodies) of the tail vertebrae were broad, cylindrical, amphicoelous (concave on both ends), and bore strongly developed

transverse processes The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

Limbs and limb girdles

''Eichstaettisaurus'' had a well-developed

acromion In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade). Together with the coracoid process it extends laterally over the shoulder joint. The ...

process, or the attachment for the

clavicle The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the r ...

, on the

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...

(shoulder blade). The clavicles of ''E. schroederi'' did not curve forward, unlike most members of the Autarchoglossa, and also lacked rearward projections. As in ''Ardeosaurus'', both species of ''Eichstaettisaurus'' had relatively stout forelimbs. In ''E. schroederi'', the olecranon process of the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

was well-developed. In ''E. gouldi'', the

carpal bones The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, t ...

were likely not fully ossified. The five-digited hand of ''E. schroederi'' bore 2, 3, 4, 5, and 3

phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...

(finger bones) on each digit; the second-to-last phalanges from the tips were relatively long. ''E. gouldi'' appears to have had 4 phalanges on the fourth digit, and its claws were short, deep, and sharp, with well-developed flexor

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection ...

s. In the

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

of ''E. schroederi'', the expansion of the pubes into the fused pubic apron was relatively narrow; the pubes also lacked the forward projections known as the

pubic tubercle The pubic tubercle is a prominent tubercle on the superior ramus of the pubis bone of the pelvis. Structure The pubic tubercle is a prominent forward-projecting tubercle on the upper border of the medial portion of the superior ramus of the ...

s. The

ischia Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures approximately east to ...

were enlarged and contacted each other extensively, and the rear expansion of the blade of the ilium was long. Both ''Eichstaettisaurus'' species had stout hindlimbs similar in length to the forelimbs. The

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 ...

had a straight shaft, unlike most other lizards where it is sigmoidal. In the foot, the first

metatarsal bone The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...

was slightly shorter than the second to fourth metatarsal bones. Unusually, the fifth metatarsal bone was much shorter and hooked. In ''E. schroederi'', the foot was five-digited like the hands, with 2, 3, 4, 5, and 4 phalanges on each digit, and the second-last phalanges and claws were similar. ''E. schroederi'' shared two features of the foot claws with the living

Tokay gecko The tokay gecko (''Gekko gecko'') is a nocturnal arboreal gecko in the genus ''Gekko'', the true geckos. It is native to Asia and some Pacific Islands. Subspecies Two subspecies are currently recognized. *''G. g. gecko'' ( Linnaeus, 1758): t ...

: the claws had expanded bottom ends; and the articulations between phalanges were simple concave-convex joints, instead of bicondylar (i.e. based on two rounded projections on the ends of the phalanges), unlike most other lizards.

Classification

The

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...

history of ''Eichstaettisaurus'' has been tumultuous like that of ''Ardeosaurus'', which has been a consequence of both incomplete data and its primitive form. von Meyer did not provide a placement for ''Ardeosaurus'' when he named the genus;

Richard Lydekker Richard Lydekker (; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history. Biography Richard Lydekker was born at Tavistock Square in London. His father was Gerard Wolfe Lydekker ...

and

Karl Alfred von Zittel Karl Alfred Ritter von Zittel (25 September 1839 – 5 January 1904) was a German palaeontologist best known for his ''Handbuch der Palaeontologie'' (1876–1880). Biography Karl Alfred von Zittel was born in Bahlingen in the Grand Duchy o ...

placed it and ''Homoeosaurus'' in the Rhynchocephalia, Baron Franz Nopcsa placed ''Ardeosaurus'' as a close relative of the

skink Skinks are lizards belonging to the family Scincidae, a family in the infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genera, the family Scincidae is one of the most diverse families of lizards. ...

s, and

Charles Camp Charles Lewis Camp (March 12, 1893 Jamestown, North Dakota – August 14, 1975 San Jose, California) was a palaeontologist and zoologist, working from the University of California, Berkeley. He took part in excavations at the 'Placerias Quarry', in ...

placed it close to the Gekkonidae. Based on the well-developed rims of the eye sockets and supratemporal fenestrae on the skull in the type specimen of ''E. schroederi'', Broili concurred with Nopcsa's conclusion in 1938. Within the Scincomorpha, he noted that the amphicoelous vertebrae of ''Ardeosaurus'' (including ''E. schroederi'') best resembled that of the Xantusiidae (night lizards), as most other skinks have procoelous (convex on the rear surface) vertebrae. Upon separating ''schroederi'' into the genus ''Broilisaurus'', Hoffstetter retained it within the Xantusiidae in 1953, but he noticed that its skull curiously resembled those of geckoes. Since xantusiids and geckoes were then placed on the two major recognized branches of lizards, Autarchoglossa and Ascalabota, Hoffstetter speculated that it was close to the ancestral stock of lizards. Upon renaming it to ''Eichstaettisaurus'', Kuhn established the family Eichstaettisauridae, still in the Xantusiidae. In 1961 and then 1963, Cocude-Michel concurred with Camp that Ardeosauridae and Eichstaettisauridae were actually geckoes and not xantusiids, based on major differences in the postcranial skeleton, and placed both in the

. Hoffstetter accepted this identification in 1966, as did Richard Estes in 1983. However, phylogenetic analyses conducted by Victor Reynoso in 1996 (not published), Evans and Luis Javier Barbadillo in 1998 and 1999, and Evans and Daniel Chure in 1998 suggested that both ''Eichstaettisaurus'' and ''Ardeosaurus'' were much more basal (early-diverging)

. Along with ''

Bavarisaurus ''Bavarisaurus'' ('Bavarian lizard') is an extinct genus of basal squamate found in the Solnhofen limestone near Bavaria, Germany.Scandensia'', and '' Hoyalacerta'', the two were found to fall outside the

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...

of Squamata. This would make them stem-squamates, i.e. not descendants of the common ancestor of all living squamates. However, in the 1999 analysis, Evans and Barbadillo acknowledged that the position of ''Eichstaettisaurus'' was unstable due to missing data (only 44% of the characteristics used in their analysis could be coded for it), and one of their

phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

s placed it as the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to Scleroglossa among crown squamates. Evans and colleagues found ''E. gouldi'' to be the sister group of ''E. schroederi'' in 2004, and recovered a similar position for both. Subsequent phylogenetic analyses from Evans and colleagues found a variety of conflicting positions for ''Eichstaettisaurus'' and ''Ardeosaurus''. In 2005, Evans and Yuan Wang conducted two analyses, one based on a 1998 analysis by Michael Lee and the other based on Evans and Chure's 1998 analysis, but they added '' Dalinghosaurus'', '' Dorsetisaurus'', and ''

Parviraptor ''Parviraptor'' is a genus of stem-snake (clade Ophidia) containing one species, ''Parviraptor estesi'', from the Late Jurassic (Tithonian) or Early Cretaceous (Berriasian) Purbeck Limestone Formation of Dorset, England. A second species, ''Par ...

'' to both. One found ''Eichstaettisaurus'' as the sister group of a group containing Xantusiidae, Gekkonidae,

Pygopodidae Pygopodidae, commonly known as legless lizards, snake-lizards, or flap-footed lizards, is a family of squamates with reduced or absent limbs, and are a type of gecko. At least 35 species are placed in two subfamilies and eight genera. They hav ...

, and

Amphisbaenia Amphisbaenia (called amphisbaenians or worm lizards) is a group of usually legless squamates, comprising over 200 extant species. Amphisbaenians are characterized by their long bodies, the reduction or loss of the limbs, and rudimentary eyes. As ...

, with ''Ardeosaurus'' being close to

Lacertidae The Lacertidae are the family of the wall lizards, true lizards, or sometimes simply lacertas, which are native to Afro-Eurasia. It is a diverse family with at least 300 species in 39 genera. They represent the dominant group of reptiles found i ...

and Teiioidea; the other united ''Eichstaettisaurus'' with ''Dalinghosaurus'' and the Xenosauridae in the Anguimorpha, with ''Ardeosaurus'' as the sister group of Iguania. After Evans, Wang, and Chun Li added '' Yabeinosaurus'' to the same analyses, one found ''Eichstaettisaurus'', ''Ardeosaurus'', ''Yabeinosaurus'', and ''Parviraptor'' to form the sister group to the Scleroglossa, while the other recovered ''Ardeosaurus'' as a stem-squamate and ''Eichstaettisaurus'', ''Hoyalacerta'', ''Parviraptor'', and ''Scandensia'' to form a group among Scleroglossa. A 2006 phylogenetic analysis by Jack Conrad and Mark Norell likewise found ''Eichstaettisaurus'' as close to the Scleroglossa. In 2008, Conrad published a large phylogenetic analysis of squamates including 222

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

and 363 characteristics, which attempted to address the problem of incomplete taxon sampling (i.e. an insufficient number of included taxa) causing phylogenetic instability. To include ''Eichstaettisaurus'', he combined data from ''E. schroederi'' and ''E. gouldi''. He found that both ''Eichstaettisaurus'' and ''Ardeosaurus'', along with ''Bavarisaurus'', were part of the stem group of Scleroglossa. Along with the crown group of Scleroglossa, they comprised the Scincogekkonomorpha. Arnau Bolet and Evans conducted two analyses based on Conrad's analysis, for the 2010 and 2012 descriptions of '' Pedrerasaurus'' and '' Jucaraseps'', and recovered similar positions for ''Eichstaettisaurus''. However, the former contained a

polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...

since the relationship between Iguania, ''Pedrerasaurus'', a group containing ''Ardeosaurus'', ''Yabeinosaurus'', and '' Sakurasaurus'', and all other squamates could not be resolved.

Jacques Gauthier Jacques Armand Gauthier (born June 7, 1948 in New York City) is an American vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology. Life and career Gauthier is the so ...

and colleagues published another large phylogenetic analysis in 2012, containing 192 taxa and 976 characteristics. Like Conrad, they also combined data from ''E. schroederi'' and ''E. gouldi''. They recovered a more derived position for ''Eichstaettisaurus'' as part of the stem group of Gekkota, along with the unnamed specimen AMNH FR 21444; in particular, they noted that its limb proportions strongly resembled gekkotans. After adding ''Ardeosaurus digitatellus'' and re-coding ''Eichstaettisaurus'' to only include data from ''E. schroederi'', Simões and colleagues found ''E. schroederi'' in a similar position, albeit in a polytomy with ''A. digitatellus'' and AMNH FR 21444. They identified a number of gekkotan traits: the paired parietals; the closed Meckelian groove on the lower jaw; the small, conical maxillary teeth; the short, blunt snout and flattened skull; the ectopterygoids overlapping the pterygoids; the two pterygoids and

palatine bone In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxillae, they comprise the hard palate. (''Palate'' is derived from the Latin ...

s being widely separated; the wide

dividing the pterygoids and palatines from each other; and the lumbar-like vertebrae. In 2018, Mateusz Tałanda added ''Ardeosaurus brevipes'' to Gauthier and colleagues' analysis (but did not include the revisions of Simões and colleagues). He found ''Eichstaettisaurus'' in the same location alongside '' Norellius'', but also recovered ''A. brevipes'' as a scincomorph closely related to skinks (in contrast to the stem-gekkotan position of ''A. digitatellus''). Despite their different phylogenetic positions, Tałanda observed that the two species only differ by the widths of their parietals. He speculated that incomplete data due to the poor preservation of ''A. digitatellus'' could have influenced these results, and thus he retained it in the genus ''Ardeosaurus''. Another analysis conducted by Simões, Tałanda, and colleagues in 2018, this time using the revised data of Simões and colleagues, found a similar position for ''E. schroederi'' but a more basal one for ''A. brevipes'' in the Autarchoglossa. In 2019, Vladimir Alifanov considered both ''Eichstaettisaurus'' and ''Ardeosaurus'' as scincomorphs closely related to ''

Carusia ''Carusia'' is an extinct genus of lizards from the Late Cretaceous of Mongolia. It is a close relative of the family Xenosauridae, which includes living knob-scaled lizards. Fossils of the type and only species ''Carusia intermedia'' come from ...

'' but not to Xenosauridae, but did not perform a phylogenetic analysis. Below,

s from the two major phylogenetic analyses including ''Eichstaettisaurus'' are shown: one based on that of Conrad (Bolet & Evans, 2012, with relationships within Scleroglossa from Conrad, 2008), and one based on that of Gauthier and colleagues (Simões and colleagues, 2018). Topology A: Bolet & Evans (2012) with Scleroglossa from Conrad (2008) Topology B: Simões ''et al.'' (2018)

Paleobiology

Modern geckoes are unusual among lizards in that the digits of their limbs are relatively symmetrical in length, and are splayed in a broad arc; by contrast, the digits in other lizards are usually nearly parallel to each other, especially on the feet. The pattern seen in geckoes facilitates gripping while the body is in various orientations, since it spreads out the adhesive

seta In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. ...

e (bristles) on their toepads while allowing the first and last digits to oppose each other. ''Eichstaettisaurus schroederi'' exhibited two characteristics that contributed to foot symmetry: its first metatarsal was long relative to its third metatarsal (with the third metatarsal only being 1.41 times as long as the first, as opposed to 2 times in a typical lizard), and its fourth metatarsal was relatively short. In 2017, Simões and colleagues observed that ''E. schroederi'' had stronger foot symmetry than ''Ardeosaurus digitatellus'', and they inferred that the feet of both were likely directed further forwards than other lizards. This was also supported by the lack of bicondylar articulations in the phalanges, which are an adaptation for outwards-facing feet that resists displacement in the horizontal plane while enabling flexion in the vertical plane. Simões and colleagues also identified several other characteristics in ''E. schroederi'', which suggest that the scansorial (climbing-based) lifestyles of modern geckoes arose earlier than previously appreciated. Its tall claws and elongate second-from-tip phalanges on the digits are both traits that have been strongly correlated with scansorial lifestyles in lizards. In particular, the tall claws may have provided longer lever arms for the flexor tendons that retracts them, thus improving their gripping strength. Meanwhile, its relatively short limbs and flattened body may have improved climbing performance by lowering its centre of gravity, as has been suggested for the Tokay gecko, but this feature may not be correlated with scansorial lifestyles. Finally, its limbs of similar lengths may have improved grip as in the sharp-snouted rock lizard; the significance of this trait may be diminished given the adhesive toepads of geckoes, and the lack of correlation between limb length ratio and scansoriality in the

. In 2004, Evans and colleagues had also discussed the lifestyle of ''E. gouldi'' in light of its bodily proportions. They pointed to a previous study on how variation between proportions among species of snow skinks ('' Carinascincus'') was correlated with habitat usage: short torsos and long hindlimbs were correlated with rock climbing (in large species) and tree climbing (in small species), while long torsos and shorter hindlimbs were correlated with ground dwelling. Evans and colleagues found that ''E. gouldi'' was closest to the ground-dwelling species, which have slow running speeds and are relatively poor climbers, in its proportions. Nevertheless, they recognized that the flat bodies and tall claws of ''E. gouldi'' were adapted for clinging to rough surfaces. They proposed a hybrid lifestyle for ''E. gouldi'': a slow-moving ground lizard with some capacity for climbing on rocks and hiding in crevices from predators like rhynchocephalians.

Paleoecology

''E. schroederi''

The rock units at Wintershof that produced the only known specimen of ''E. schroederi'' are part of the Solnhofen limestones of southern Germany, which are well known for their exceptionally preserved fossils. Historically, the

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers ( strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

of the Solnhofen limestones has been the subject of considerable confusion, with the variety of environments and depositional patterns contributing to the confusion. They are now understood to consist of several

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

s in the Weißjura Group: in the strictest sense, they consist of the Altmühltal Formation to the northwest of

Ingolstadt Ingolstadt (, Austro-Bavarian: ) is an independent city on the Danube in Upper Bavaria with 139,553 inhabitants (as of June 30, 2022). Around half a million people live in the metropolitan area. Ingolstadt is the second largest city in Upper Ba ...

(including localities around Eichstätt), and the Painten Formation to the northeast of Ingolstadt. Within the Altmühltal Formation, the Wintershof quarry is part of the Upper Eichstätt Member, which in terms of

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefis ...

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of ...

lies in the '' Euvirgalithacoceras eigeltingense''-β horizon between the '' Lithacoceras riedense'' and '' Hybonoticeras hybonotum'' subzones. The deposits of the Altmühltal Formation, which have been dated to the lower

stage of the

period, consist of

plattenkalk Plattenkalk is a very finely grained limestone chemically precipitated in a stratified water column under conditions where bioturbation does not occur. The reasons for the quiet depositional environment and the processes of sediment accumulation v ...

(very finely-grained

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...

-based muds such as

micrite Micrite is a limestone constituent formed of calcareous particles ranging in diameter up to four μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( Amer ...

) forming even, thin layers measuring about thick that generally lack evidence of

bioturbation Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a ...

(disturbance by living organisms). During the Tithonian, the plattenkalk of the Altmühltal Formation was deposited in

oceanic basin In hydrology, an oceanic basin (or ocean basin) is anywhere on Earth that is covered by seawater. Geologically, ocean basins are large  geologic basins that are below sea level. Most commonly the ocean is divided into basins fol ...

s (called "wannen") within a warm, shallow sea surrounding an

archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or sometimes a sea containing a small number of scattered islands. Examples of archipelagos include: the Indonesian Arch ...

. These basins, which may have been

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into '' coastal lagoons'' (or ''barrier lagoons ...

s, had a palaeolatitude of approximately 34° N, and were located at the northern margin of the

Tethys Ocean The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...

. Fossils of bottom-dwelling animals like brittle stars and

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...

are virtually absent, which suggests that conditions at the sea floor were inhospitable to life; this may have been caused by one of several factors including

hypersalinity A hypersaline lake is a landlocked body of water that contains significant concentrations of sodium chloride, brines, and other salts, with saline levels surpassing that of ocean water (3.5%, i.e. ). Specific microbial species can thrive in ...

, oxygen depletion, or the accumulation of toxic

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...

. These conditions were responsible for the exceptional preservation of fossils like that of ''E. schroederi'', which would have been predominantly transported from the surrounding land during heavy rainfall and storms. On land, the absence of

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...

s and the dominance of dry-adapted

conifer Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ext ...

s suggest that the climate was

semi-arid A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi- ...

Archaeopteryx lithographica (Eichstätter Specimen)

Both ''Ardeosaurus brevipes'' and ''A. digitatellus'' were discovered at Wintershof with ''E. schroederi'', along with ''Homoeosaurus maximiliani'' and the rhynchocephalian '' Pleurosaurus goldfussi''. Also known from Wintershof are the

pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...

'' Rhamphorhynchus muensteri'', the

crocodyliform Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseu ...

'' Alligatorellus bavaricus'', and various aquatic animals: the fish '' Anaethalion angustus'', '' Ascalabos voithii'', '' Aspidorhynchus acutirostris'', '' Belonostomus spyraenoides'', '' Caturus giganteus'', '' Gyrodus circularis'', '' Macrosemius rostratus'', '' Palaeomacrosemius thiollieri'', '' Propterus elongatus'', and '' Zandtfuro tischlingeri''; the angelshark '' Pseudorhina alifera''; the squid-like coleoids '' Acanthoteuthis problematica'', '' Belemnotheutis mayri'', and '' Plesioteuthis prisca''; the

crinoid Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which are ...

'' Saccocoma tenella'', which is very common in Solnhofen deposits; the shrimp '' Dusa reschi''; and the

horseshoe crab Horseshoe crabs are marine and brackish water arthropods of the family Limulidae and the only living members of the order Xiphosura. Despite their name, they are not true crabs or crustaceans: they are chelicerates, most closely related to ar ...

Mesolimulus walchi ''Mesolimulus'' is an extinct genus of horseshoe crab. The best known examples are found in Solnhofen limestone near Solnhofen, Bavaria, Germany. Originally assigned to the living genus ''Limulus'', they are related to and look virtually identi ...

''. Nearby quarries have produced the Eichstätt specimen of the avialan

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

'' Archaeopteryx lithographica'', and the pterosaurs '' Aerodactylus scolopaciceps'', '' Germanodactylus cristatus'', and possibly ''

Cycnorhamphus ''Cycnorhamphus'' (meaning "swan beak") is a genus of gallodactylid ctenochasmatoid pterosaur from the Late Jurassic period of France and Germany, about 152 million years ago. It is probably synonymous with the genus ''Gallodactylus''. History ...

''.

''E. gouldi''

The Pietraroia locality, from where ''E. gouldi'' specimens are known, is formed by a plattenkalk outcrop at the top of a rock slope (the "Civita di Pietraroia") located at the eastern margin of the Matese Mountains. These mountains did not start to form until the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

, with the majority of the

tectonic uplift Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal th ...

that brought them to their current elevation having occurred between 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 ...

. At the locality, there are two distinct plattenkalk beds; the lower bed is coarser-grained and is largely devoid of fossils, while the upper bed is muddier and is the source of most fossils. The two beds are separated by lagoonal limestones. The plattenkalk is formed by layers of packstone and grainstone measuring thick, which alternate with layers of

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.' ...

, wackestone, and

marl Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. Marl makes up the lower part ...

; the upper bed is also characterized by the presence of

sponge spicules Spicules are structural elements found in most sponges. The meshing of many spicules serves as the sponge's skeleton and thus it provides structural support and potentially defense against predators. Sponge spicules are made of calcium carbon ...

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...

bitumen Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...

, and

coprolite A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is ...

s. On the basis of

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

ns, the Pietaroia locality has been dated to the

epoch of the Early Cretaceous. During this time, the plattenkalk of Pietraroia would have been laid down in a shallow water

carbonate platform A carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonic calcareous deposits. Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms (usually m ...

close to a small island. The depositional environment was originally thought to have been a lagoon, but it has been re-interpreted as an east-flowing underwater channel that was gradually filled during the Aptian, based on patterns in the arrangement of fossils, the water currents, and the transportation of sediments. The lack of bioturbation likewise points to an anoxic environment, possibly related to a global oceanic anoxic event. Some fossils are well preserved while others were nearly destroyed, suggesting that they originated from various locations, with terrestrial animals like ''E. gouldi'' being brought into the channel by freshwater flows. The climate would have been

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

subtropical The subtropical zones or subtropics are geographical and climate zones to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from to approximately 35° north a ...

In addition to ''E. gouldi'' and the rhynchocephalian MPN A01/82, other

lepidosaurs The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 specie ...

from Pietraroia include the lizards '' Chometokadmon fitzingeri'' and '' Costasaurus rusconi'', and the rhynchocephalian '' Derasmosaurus pietraroiae'' as well as a third unnamed juvenile specimen. The most well known fossil from Pietraroia is that of the

compsognathid Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other d ...

dinosaur '' Scipionyx samniticus'', which preserves soft tissues including internal organs. Other reptiles include two crocodyliform specimens belonging to '' Pietraroiasuchus ormezzanoi'', and the albanerpetontid amphibian ''

Celtedens megacephalus ''Celtedens'' is an extinct genus of albanerpetontid amphibian from the Early Cretaceous of England, Spain, Sweden and Italy, and the Late Jurassic of Portugal. Taxonomy * †''Celtedens ibericus'' McGowan and Evans 1995 La Huérguina Forma ...

''. Many fish are known from Pietraroia, with the most common being a pycnodontid formerly identified as '' Coelodus costae'' but now known as '' Gregoriopycnodus bassanii''. Others include '' Anaethalion robustus'', ''Belonostomus crassirostris'', '' Caeus leopoldi'', '' Cavinichthys pietrarojae'', '' Chirocentrites coroninii'', relatives of ''

Diplomystus brevissimus ''Diplomystus'' is an extinct genus of freshwater clupeomorph fish distantly related to modern-day extant herrings, alewives, and sardines. The genus was first named and described by Edward Drinker Cope in 1877. There are seven species of ...

'' and '' Elopopsis fenzii'', '' Hemieloposis gibbus'', '' Ionoscopus petrarojae'', '' Italophiopsis derasmoi'', a species of '' Lepidotes'', '' Notagogus pentlandi'', '' Pleuropholis decastroi'', '' Propterus scacchii'', and '' Sauropsidium laevissimum''. Cartilaginous fish included the angelshark ''

Phorcynis ''Phorcynis'' is an extinct genus of cartilaginous fish. The scales of Phorcynis have elongated crowns with a narrow median keel and short lateral folds and the teeth are asymmetrical, similar to those of ''Orectolobus ''Orectolobus'' is a ...

'' and the

ray Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (gr ...

'' Rhinobatus obtusatus''. Invertebrates included rudists,

bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the a ...

s of the genus ''

Nerinea †''Nerinea'' is an extinct genus of fossil sea snails, marine gastropod molluscs in the clade Heterobranchia. Fossil record This genus is present from the Jurassic to the Cretaceous periods. Fossils are known from various localities of Eur ...

'', shrimp, and starfish.

References

{{Taxonbar, from=Q48965453 Jurassic lizards Cretaceous lizards Tithonian first appearances Albian genus extinctions Jurassic reptiles of Europe Early Cretaceous reptiles of Europe Jurassic Germany Fossils of Germany Cretaceous Italy Fossils of Italy Fossil taxa described in 1958