Prorotodactylus
Encyclopedia
Prorotodactylus is an dinosauromorph ichnogenus known from fossilized footprints
found in Poland
and France
. It may have been made by a dinosauromorph that was a precursor to the dinosaur
s, possibly closely related to Lagerpeton
. Fossils of Prorotodactylus date back to the early Olenekian
stage of the Early Triassic
, making it the oldest known dinosauromorph. Its presence during this time extends the range of the dinosaur stem lineage to the start of the Early Triassic, soon after the Permian-Triassic extinction event
. Prorotodactylus is the only ichnogenus within the ichnofamily Prorotodactylidae. Two ichnospecies are known, the type
P. mirus and P. lutevensis.
in reference to unusual features in forefoot imprints. A second ichnospecies, P. lutevensis, was erected along with the type. P. lutevensis is from the Middle Triassic
of France and was first described in 1984 as Rhynchosauroides lutevensis. It was reassigned on the basis of many similarities with P. mirus.
P. mirus tracks have been found in many localities. The holotype
specimen, a set of left forefoot and hind foot imprints, are from the Wióry locality near the town of Ostrowiec Świętokrzyski
. The footprints were located in the Labyrinthodontidae Beds of the Middle Buntsandstein
, or Bunter sandstone. Recent studies of the biostratigraphy
and magnetostratigraphy
of the area have shown that the Wióry site is Early Spathian (Early to Late Olenekian) in age. More tracks have been found from Wióry since the initial description of P. mirus, and have shown that P. mirus was a rare component of the ichnofauna.
P. mirus is also known from the Stryczowice locality, which has a much more diverse assemblage of ichnofossils than Wióry. Like in Wióry, Prorotodactylus tracks are rare in Stryczowice.
, are clawed. Digits II-IV are angled skightly away from digit I, with digit IV being the longest. Digit V is smaller than the other four and is placed farther back on the foot, occurring only occasionally in footprints. The fifth digit of the forefoot, or manus, is separate from the rest of the digits, placed behind digits I-IV and angled outward. Digit III is the longest, with digits II and I being progressively smaller.
The fifth digits of both the manus and pes aren't rotated in Prorotodactylus like they are in the related ichnogenus Rotodactylus. The shape of the manus differentiates Prorotodactylus from members of the family Rhynchosauridae, which have also been found in Early Triassic Polish strata. The manus of Prorotodactylus is similar in shape to the pes of members of the ichnofamily Chirotheridae
.
Prorotodactylus tracks were probably made by a small dinosauromorph. The ichnogenus possesses several distinctively archosaurian features, such as narrow trackways and a pace angulation of 130°. The pace angulation, or the angle made between two successive footprints, shows that Prorotodactylus had an erect stance rather than a sprawling one. Dinosauromorph characteristics include digitigrade
prints (in which only the digits touch the ground), bunched metatarsals, a reduction of the first and fifth digits, and the posterior deflection of the fifth digit. Prorotodactylus prints share several characteristics with the dinosauromorph genus Lagerpeton from Argentina
, indicating that the print maker was closely related to Lagerpeton. The three central digits of the foot are parallel, a feature otherwise only seen in Lagerpeton. Digit IV is the longest digit in the foot of both Prorotodactylus and Lagerpeton. In both animals, there is a progressive decrease in size from digits IV to II, with digit III angled relative to the midline.
The bunched metatarsals in Prorotodactylus are a synapomorphy
of the clade
Avemetatarsalia
. The metatarsal pads, preserved only in deeply imprinted footprints, are united in a single unit. This makes the foot act as a single unit rather than a collection of splayed digits. In ichnotaxa similar in appearance to Prorotodactylus, the digits are not parallel to one another and the posterior margin of the metatarsal pads is curved, making the digits splay.
, occurs later in the Triassic and is fully bipedal. The transition to bipedality probably occurred between Prorotodactylus and Sphingopus. During this transition, body size also increased, as Sphingopus tracks are larger than those of Prorotodactylus.
The different shapes of the manus and pes of Prorotodactylus may show different forms of specialization. The forelimbs, which were reduced, may have been used for hunting, grasping, or manipulating. The bunched metatarsals of the hind feet may have enabled the metatarsals to act as a lever, along with the stylopodium, or upper leg, and the zeugopodium, or lower leg. This would have enabled facultative bipedalism in Prorotodactylus, and a wholly bipedal gait in later dinosauromorphs. Pace angulation is relatively high in Prorotodactylus, and increased as bipedalism becomes obligate in later dinosauromorphs.
Ichnite
An ichnite is a fossilised footprint. This is a type of trace fossil. Over the years, many ichnites have been found, around the world, giving important clues about the behaviour of the animals that made them...
found in Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
and France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. It may have been made by a dinosauromorph that was a precursor to the dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, possibly closely related to Lagerpeton
Lagerpeton
Lagerpeton is a genus of basal dinosauromorph from the Ladinian . Lagerpeton is known from several specimens of hindlimbs, hips, vertebrae, and feet. It was about 0.7 metres long and was found in the Chañares Formation of Argentina. It has unique feet, with an unusually long fourth toe...
. Fossils of Prorotodactylus date back to the early Olenekian
Olenekian
In the geologic timescale, the Olenekian is an age in the Early Triassic epoch or a stage in the Lower Triassic series. It spans the time between 249.7 ± 0.7 Ma and 245 ± 0.7 Ma . The Olenekian follows the Induan and is followed by the Anisian.The Olenekian saw the deposition of a large part of the...
stage of the Early Triassic
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
, making it the oldest known dinosauromorph. Its presence during this time extends the range of the dinosaur stem lineage to the start of the Early Triassic, soon after the Permian-Triassic extinction event
Permian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...
. Prorotodactylus is the only ichnogenus within the ichnofamily Prorotodactylidae. Two ichnospecies are known, the type
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
P. mirus and P. lutevensis.
Specimens
Prorotodactylus mirus, the type ichnospecies, has been found in the Holy Cross Mountains in Poland. It was named in 2000, with the specific name meaning "strange" in LatinLatin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
in reference to unusual features in forefoot imprints. A second ichnospecies, P. lutevensis, was erected along with the type. P. lutevensis is from the Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
of France and was first described in 1984 as Rhynchosauroides lutevensis. It was reassigned on the basis of many similarities with P. mirus.
P. mirus tracks have been found in many localities. The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen, a set of left forefoot and hind foot imprints, are from the Wióry locality near the town of Ostrowiec Świętokrzyski
Ostrowiec Swietokrzyski
Ostrowiec Świętokrzyski is a town in south-central Poland with 74,211 inhabitants .Main industry is metallurgy. Ostrowiec is the capital city of Ostrowiec Świętokrzyski County, part of Świętokrzyskie Voivodeship , previously it belonged to Kielce Voivodeship .- History:The oldest testimonies of...
. The footprints were located in the Labyrinthodontidae Beds of the Middle Buntsandstein
Buntsandstein
The Buntsandstein or Bunter sandstone is a lithostratigraphic and allostratigraphic unit in the subsurface of large parts of west and central Europe...
, or Bunter sandstone. Recent studies of the biostratigraphy
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. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period...
and magnetostratigraphy
Magnetostratigraphy
Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their characteristic remanent magnetization , that is, the...
of the area have shown that the Wióry site is Early Spathian (Early to Late Olenekian) in age. More tracks have been found from Wióry since the initial description of P. mirus, and have shown that P. mirus was a rare component of the ichnofauna.
P. mirus is also known from the Stryczowice locality, which has a much more diverse assemblage of ichnofossils than Wióry. Like in Wióry, Prorotodactylus tracks are rare in Stryczowice.
Description
Prorotodactylus tracks were made by a small quadrupedal animal. The tracks are long-striding, showing that the hind feet often overstepped the forefeet, or were placed on the lame line. The first four digits of the hind foot, or pesPes (zoology)
The pes is the zoological term for the distal portion of the hind limb of tetrapod animals. It is the part of the pentadactyl limb that includes the metatarsals and digits . During evolution, it has taken many forms and served a variety of functions...
, are clawed. Digits II-IV are angled skightly away from digit I, with digit IV being the longest. Digit V is smaller than the other four and is placed farther back on the foot, occurring only occasionally in footprints. The fifth digit of the forefoot, or manus, is separate from the rest of the digits, placed behind digits I-IV and angled outward. Digit III is the longest, with digits II and I being progressively smaller.
The fifth digits of both the manus and pes aren't rotated in Prorotodactylus like they are in the related ichnogenus Rotodactylus. The shape of the manus differentiates Prorotodactylus from members of the family Rhynchosauridae, which have also been found in Early Triassic Polish strata. The manus of Prorotodactylus is similar in shape to the pes of members of the ichnofamily Chirotheridae
Chirotherium
Chirotherium, also known as Cheirotherium , is the name of a Triassic archosaur known only from fossil imprints of its tracks...
.
Prorotodactylus tracks were probably made by a small dinosauromorph. The ichnogenus possesses several distinctively archosaurian features, such as narrow trackways and a pace angulation of 130°. The pace angulation, or the angle made between two successive footprints, shows that Prorotodactylus had an erect stance rather than a sprawling one. Dinosauromorph characteristics include digitigrade
Digitigrade
A digitigrade is an animal that stands or walks on its digits, or toes. Digitigrades include walking birds , cats, dogs, and many other mammals, but not plantigrades or unguligrades...
prints (in which only the digits touch the ground), bunched metatarsals, a reduction of the first and fifth digits, and the posterior deflection of the fifth digit. Prorotodactylus prints share several characteristics with the dinosauromorph genus Lagerpeton from Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
, indicating that the print maker was closely related to Lagerpeton. The three central digits of the foot are parallel, a feature otherwise only seen in Lagerpeton. Digit IV is the longest digit in the foot of both Prorotodactylus and Lagerpeton. In both animals, there is a progressive decrease in size from digits IV to II, with digit III angled relative to the midline.
The bunched metatarsals in Prorotodactylus are a synapomorphy
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
of the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Avemetatarsalia
Avemetatarsalia
Avemetatarsalia is a clade name established by British palaeontologist Michael Benton in 1999 for all crown group archosaurs that are closer to birds than to crocodiles. It includes a similarly defined subgroup, Ornithodira...
. The metatarsal pads, preserved only in deeply imprinted footprints, are united in a single unit. This makes the foot act as a single unit rather than a collection of splayed digits. In ichnotaxa similar in appearance to Prorotodactylus, the digits are not parallel to one another and the posterior margin of the metatarsal pads is curved, making the digits splay.
Paleobiology
Trackways indicate that the maker of Prorotodactylus footprints was quadrupedal. However, the overstep of the hind feet beyond the front feet indicates that the forelimbs were reduced, a characteristic of bipedal animals. Another Polish dinosauromorph ichnogenus, SphingopusSphingopus
Sphingopus is an ichnogenus of dinosauriform footprints found in sediments dating to 250 and 228 Ma. The exact species which created Sphingopus tracks have not been identified.-Specimens:Sphingopus type footprints are known from two locations...
, occurs later in the Triassic and is fully bipedal. The transition to bipedality probably occurred between Prorotodactylus and Sphingopus. During this transition, body size also increased, as Sphingopus tracks are larger than those of Prorotodactylus.
The different shapes of the manus and pes of Prorotodactylus may show different forms of specialization. The forelimbs, which were reduced, may have been used for hunting, grasping, or manipulating. The bunched metatarsals of the hind feet may have enabled the metatarsals to act as a lever, along with the stylopodium, or upper leg, and the zeugopodium, or lower leg. This would have enabled facultative bipedalism in Prorotodactylus, and a wholly bipedal gait in later dinosauromorphs. Pace angulation is relatively high in Prorotodactylus, and increased as bipedalism becomes obligate in later dinosauromorphs.