Ascendonanus

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Ascendonanus
Temporal range: Early Permian, ~290  Ma
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Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Synapsida
Family:
† Varanopidae
Genus:
†Ascendonanus

Spindler et al., 2018
Type species
†Ascendonanus nestleri
Spindler et al., 2018

Ascendonanus (meaning "climbing dwarf") is an extinct genus of varanopid amniote from the Early Permian of Germany. [1] It is one of the earliest specialized arboreal (tree-living) tetrapods currently known and outwardly resembled a small lizard. The animal was about 40 cm long, with strongly curved claws, short limbs, a slender, elongated trunk, and a long tail. It would have preyed on insects and other small arthropods. [1] [2]

Contents

The taxonomic position of varanopids is currently debated between synapsids (related to mammals, the most widely accepted idea) and diapsids (related to reptiles). The fossils of Ascendonanus are of special scientific importance because they include remains of skin, scales, scutes, bony ossicles, and soft-tissue body outlines, which could indicate that some of the oldest relatives of mammals had a scaly "reptilian-type" appearance.

The related small varanopid Eoscansor , recently described from New Mexico, was also adapted to climbing, very likely in trees, but dates from 15 million years earlier during the Pennsylvanian subperiod of the Carboniferous, indicating that climbing varanopids have a longer history and were likely widespread. [3]

Ascendonanus was named and described in 2018 from remains of five individuals that were discovered in the Chemnitz petrified forest, an Early Permian tropical fossil forest preserved under the city of Chemnitz, Germany. A Pompeii-like pyroclastic volcanic eruption 291 million years ago [4] buried the forest and created the Zeisigwald Tuff Horizon in the uppermost Leukersdorf Formation (late Sakmarian/early Artinskian transition stage), preserving some of the animals that lived there in exceptional detail in a bottom layer of volcanic ash. [1]

The type species name Ascendonanus nestleri honors Knut Nestler, a long-time local supporter (deceased) of the Chemnitz Museum of Natural History (Museum für Naturkunde Chemnitz (MNC)), where the specimens of Ascendonanus are stored. [1]

Description

Ascendonanus was about 40 cm long, although the end of the tail is missing in all specimens and the full body length in life is not currently known. It is the smallest known member of the clade Varanopidae, a group of early synapsids that generally resembled the unrelated monitor lizards. Features that identify Ascendonanus as a "pelycosaur" grade synapsid and a member of the Varanopidae include a single lateral temporal opening (fenestra) in the skull, a ridge on the underside of the centra of the vertebrae, and enlarged blades on the ilium of the pelvis. [1]

Specimens

The five recovered fossils of Ascendonanus are strongly compacted and were split open as flattened counterslabs that revealed articulated partial or near complete skeletons with remains of soft tissue and some internal features. The bone material itself, however, often was not clearly preserved, making interpretation of some details more difficult. The specimens were CT scanned to reveal additional information. Based on the ossification of different bones, all individuals appear to be fully grown despite some differences in size. [1]

The specimen designated MNC-TA0924 was made the diagnostic holotype of Ascendonanus nestleri because it provides the clearest details of the skull. The most remarkable specimen (MNC-TA1045) preserves the clear body outline of nearly the entire animal on counterslabs, showing the thickness in life of the limbs and the neck, and the full covering of scales. [5] [1] [6]

Skull

Skull of Ascendonanus reconstructed in lateral view Ascendonanus skull reconstruction.svg
Skull of Ascendonanus reconstructed in lateral view

Because of compaction over time, it is not known if the skull is relatively flat or if it has a taller profile. The tip of the snout is not well preserved in any specimens. The orbits are very large but the sclerotic rings to support the eyeball are not ossified. Some specimens preserve dozens of tiny round dermal bones or ossicles that were embedded in the skin of the upper eyelid. Such eyelid ossicles are currently not known in any other amniotes, but have been found in some dissorophid temnospondyl amphibians, a non-amniote tetrapod group that is not closely related to synapsids. The eyelid ossicles in Ascendonanus may have evolved independently or may be an ancient feature retained from the earliest tetrapods. Such eyelid ossicles are distinct from the rod-like dermal bones, called palpebral bones, that evolved above the eye socket in a number of later non-synapsid groups, including some ornithischian dinosaurs. The pointed teeth are slender, without flattened cross-sections, serrations, or a cutting edge, and are moderately recurved in the upper jaw and straighter in the lower jaw. [1]

Skeleton

Ascendonanus differs notably from other varanopids in its elongated trunk section, with 34 to 37 presacral vertebrae compared to 26 in most synapsids. It has a dense set of thin belly ribs or gastralia along the underside. The full length of its tail is not known based on current fossils, but it was longer than in other described varanopids and would have helped with balance in climbing, similar to some tree-living lizards with very long tails. It is unknown whether the distal part of the tail was prehensile. [1]

Limbs

The forelimbs are almost as long as the hindlimbs, but both pairs of legs are very short compared to the length of the trunk. The elements of the feet are enlarged, with elongated and slender digits. Distinct from other varanopids, the claws on Ascendonanus have a very strong curvature. The curved claws and the size and shape of the feet, including a longer fourth digit on the manus and on the pes, indicate Ascendonanus would have been a "clinging" climber rather than a "grasping" climber. [1] [7]

Skin and scales

The specimens show a regular scale pattern over their bodies, similar to living squamates and archosaurs, suggesting dry, scaly skin was present in the earliest amniotes before the split into synapsids and sauropsids (reptiles) during the Carboniferous Period. Some synapsid groups later developed bare, glandular skin, eventually with hair and whiskers that became characteristics of mammals. Unlike some varanopids (such as Archaeovenator and Microvaranops ), Ascendonanus does not have dorsal osteoderms on its upper trunk section along the back. However, the middle part of the tail has a covering of small scutes that continues to where the end of the tail is missing in all current specimens. The body outlines preserved show that Ascendonanus had a plump neck and muscular thighs (although the femur bone itself is relatively thin) on its short hindlimbs, while the trunk and the forelimbs are relatively slender. [1]

Discovery

Hilbersdorf scientific excavation

All of the current fossils of Ascendonanus were discovered during a test dig by the Chemnitz Museum of Natural History in the Hilbersdorf district of Chemnitz between April 2008 to October 2011. [6] The site was limited to a pit 24 m by 18 m, down to a depth of at least 5 m, and was the first systematic scientific excavation of the Chemnitz fossil forest ever conducted in the city. The museum began a second, more extensive, and ongoing, dig in the Sonnenberg district in 2014. In addition to finding fossils of trees and plants at the Hilbersdorf site, the team recovered remains of vertebrates (synapsids, temnospondyl, aistopods) and arthropods (scorpions, Arthropleura , spiders), some later identified as species new to science. [1]

Taphonomy

Stratigraphic diagram in German of a fossil site in Chemnitz, showing the successive layers of volcanic ash and debris. All of the Ascendonanus specimens were found in the Level 5 (S 5) fine, wet ash fall layer at the start of eruptions, directly on top of the forest soil layers in the lower third of the sequence. A violent pyroclastic flow then covered the ash layer, making up most of the deposit. Stratigraphic log fossil site Frankenberger Str Chemnitz Dunlop et al (2016) DE.png
Stratigraphic diagram in German of a fossil site in Chemnitz, showing the successive layers of volcanic ash and debris. All of the Ascendonanus specimens were found in the Level 5 (S 5) fine, wet ash fall layer at the start of eruptions, directly on top of the forest soil layers in the lower third of the sequence. A violent pyroclastic flow then covered the ash layer, making up most of the deposit.

During an early phase of the volcanic eruption, rising rhyolitic magma came into contact with groundwater, exploding molten rock into tiny fragments mixed with steam, resulting in falls of wet, relatively cool, fine volcanic ash particles. [4] An initial ash layer covered the ground and knocked leaves off trees, but left the trunks standing. [6]

All of the Acendonanus specimens were found close to the base of upright fossil trees from which the animals evidently had fallen to the ground onto the first ash fall, either after being dislodged by a volcanic blast [6] or, more likely, after being overcome by breathing ash particles or toxic gases, or possibly by lethal temperatures. [1] A second fall of wet ash quickly buried the Ascendonanus individuals and the other animals that were on or under the forest floor up to about 53 cm deep, preventing decay and preserving bodies largely intact (but compacted over time), with detailed impressions or traces of soft tissues. The fossil plant material in the wet ash layer shows no evidence of charring, indicating that the temperature of the ash fall was below 280°C. [1]

Later, more violent phases of the eruption covered the wet ash layer in much deeper deposits of coarser hot pyroclastic material that make up most of the Zeisigwald Tuff Horizon (total depth up to 4 m). [4] The upper trunks and branches of embedded upright trees were snapped off above about 1 m to 3 m from the ground. [6]

Related Research Articles

<span class="mw-page-title-main">Synapsid</span> Clade of tetrapods

Synapsids are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptiles and birds. The group includes mammals and every animal more closely related to mammals than to sauropsids. Unlike other amniotes, synapsids have a single temporal fenestra, an opening low in the skull roof behind each eye orbit, leaving a bony arch beneath each; this accounts for their name. The distinctive temporal fenestra developed about 318 million years ago during the Late Carboniferous period, when synapsids and sauropsids diverged, but was subsequently merged with the orbit in early mammals.

<i>Dimetrodon</i> Genus of carnivorous synapsids from the Permian

Dimetrodon is a genus of non-mammalian synapsid that lived during the Cisuralian age of the Early Permian period, around 295–272 million years ago. It is a member of the family Sphenacodontidae. With most species measuring 1.7–4.6 m (5.6–15.1 ft) long and weighing 28–250 kg (62–551 lb), the most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It was an obligate quadruped and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the Southwestern United States, the majority of these coming from a geological deposit called the Red Beds of Texas and Oklahoma. More recently, its fossils have also been found in Germany and over a dozen species have been named since the genus was first erected in 1878.

<span class="mw-page-title-main">Pelycosaur</span> Informal grouping composed of basal or primitive Late Paleozoic synapsids

Pelycosaur is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile had been used, and pelycosaur was considered an order, but this is now thought to be incorrect, and seen as outdated.

<span class="mw-page-title-main">Eupelycosauria</span> Clade of synapsids

Eupelycosauria is a large clade of animals characterized by the unique shape of their skull, encompassing all mammals and their closest extinct relatives. They first appeared 308 million years ago during the Early Pennsylvanian epoch, with the fossils of Echinerpeton and perhaps an even earlier genus, Protoclepsydrops, representing just one of the many stages in the evolution of mammals, in contrast to their earlier amniote ancestors.

<span class="mw-page-title-main">Caseasauria</span> Extinct clade of synapsids

Caseasauria is one of the two main clades of early synapsids, the other being the Eupelycosauria. Caseasaurs are currently known only from the Late Carboniferous and the Permian, and include two superficially different families, the small insectivorous or carnivorous Eothyrididae, and the large, herbivorous Caseidae. These two groups share a number of specialised features associated with the morphology of the snout and external naris.

Varanopidae is an extinct family of amniotes that resembled monitor lizards and may have filled a similar niche, hence the name. Typically, they are considered synapsids that evolved from an Archaeothyris-like synapsid in the Late Carboniferous. However, some recent studies have recovered them being taxonomically closer to diapsid reptiles. A varanopid from the latest Middle Permian Pristerognathus Assemblage Zone is the youngest known varanopid and the last member of the "pelycosaur" group of synapsids.

<i>Mycterosaurus</i> Extinct genus of tetrapods

Mycterosaurus is an extinct genus of synapsids belonging to the family Varanopidae. It is classified in the varanopid subfamily Mycterosaurinae. Mycterosaurus is the most primitive member of its family, existing from 290.1 to 272.5 MYA, known to Texas and Oklahoma. It lacks some features that its advanced relatives have.

<i>Varanodon</i> Extinct genus of tetrapods

Varanodon is an extinct genus of amniotes from the family Varanopidae. It has been found in the Chickasha Formation of Oklahoma, which dates to the Roadian stage of the Middle Permian. The largest varanopid known at the time of its description, with a skull length of 17.5 centimetres (6.9 in), it was closely related to and lived alongside its much larger relative Watongia. The two may represent growth stages of a single animal.

<i>Aerosaurus</i> Extinct genus of tetrapod

Aerosaurus is an extinct genus within Varanopidae, a family of non-mammalian synapsids. It lived between 252-299 million years ago during the Early Permian in North America. The name comes from Latin aes (aeris) “copper” and Greek sauros “lizard,” for El Cobre Canyon in northern New Mexico, where the type fossil was found and the site of former copper mines. Aerosaurus was a small to medium-bodied carnivorous synapsid characterized by its recurved teeth, triangular lateral temporal fenestra, and extended teeth row. Two species are recognized: A. greenleeorum (1937) and A. wellesi (1981).

Elliotsmithia is a small varanopid synapsid found from the late Middle Permian of South Africa. It is the sole basal synapsid "pelycosaur" known from the supercontinent Gondwana and only two specimens have been yielded to date. Its species name longiceps is derived from Latin, meaning "long head". Both known Elliotsmithia fossils were recovered from Abrahamskraal Formation rocks—within the boundaries of the Tapinocephalus Assemblage Zone—of the lower Beaufort Group. It was named for the late Sir Grafton Elliot Smith in 1937.

<i>Mesenosaurus</i> Extinct genus of synapsids

Mesenosaurus is an extinct genus of amniote. It belongs to the family Varanopidae. This genus includes two species: the type species Mesenosaurus romeri from the middle Permian Mezen River Basin of northern Russia, and Mesenosaurus efremovi from the early Permian (Artinskian) Richards Spur locality. M. romeri’s stratigraphic range is the middle to late Guadalupian while M. efremovi’s stratigraphic range is the Cisuralian.

<i>Ianthodon</i> Extinct genus of synapsids

Ianthodon is an extinct genus of basal haptodontiform synapsids from the Late Carboniferous about 304 million years ago. The taxon was discovered and named by Kissel & Reisz in 2004. The only species in the taxon, Ianthodon schultzei, was found by separating it from a block that also contained the remains of Petrolacosaurus and Haptodus. The evolutionary significance of the taxon wasn't realized until a publication in 2015. The fossil of this organism was discovered in Garnett, Kansas.

<i>Heleosaurus</i> Extinct genus of tetrapods

Heleosaurus scholtzi is an extinct species of basal synapsids, known as pelycosaurs, in the family of Varanopidae during the middle Permian. At first H. scholtzi was mistakenly classified as a diapsid. Members of this family were carnivorous and had dermal armor, and somewhat resembled monitor lizards. This family was the most geologically long lived, widespread, and diverse group of early amniotes. To date only two fossils have been found in the rocks of South Africa. One of these fossils is an aggregation of five individuals.

<i>Callibrachion</i>

Callibrachion is an extinct genus of caseid synapsids that lived in east-central France during the Lower Permian (Asselian). The holotype and only known specimen (MNHN.F.AUT490) is represented by an almost complete postcranial skeleton associated with skull fragments discovered at the end of the 19th century in the Permian Autun basin in Saône-et-Loire department, in the Bourgogne-Franche-Comté region. It belongs to an immature individual measuring less than 1.50 m in length. Callibrachion was long considered a junior synonym of the genus Haptodus and classified among the sphenacodontid pelycosaurs. In 2015, a new study found that Callibrachion was a different animal from Haptodus and that it was a caseasaur rather than a sphenacodontid. This was confirmed in 2016 by a cladistic analysis which recovered Callibrachion as a basal caseid. Callibrachion's sharp teeth and unenlarged ribcage indicate that this animal was likely faunivorous.

<i>Orovenator</i>

Orovenator is an extinct genus of diapsid from Lower Permian deposits of Oklahoma, United States. It is known from two partial skulls from the Richards Spur locality in Oklahoma. The holotype OMNH 74606 consists of a partial skull preserving snout and mandible, and the referred specimen, OMNH 74607, a partial skull preserving the skull roof, vertebrae and palatal elements. It was first named by Robert R. Reisz, Sean P. Modesto and Diane M. Scott in 2011 and the type species is Orovenator mayorum. The generic name means "mountain", oro, in Greek in reference to the Richards Spur locality, which was mountainous during the Permian period and "hunter", venator, in Latin. The specific name honours Bill and Julie May. Orovenator is the oldest and most basal neodiapsid to date.

<span class="mw-page-title-main">Chemnitz petrified forest</span>

The Chemnitz petrified forest is a petrified forest in Chemnitz, Germany.

Microvaranops is a Middle Permian synapsid of the family Varanopidae from the Abrahamskraal Formation of South Africa. It includes one species, Microvaranops parentis, which was probably arboreal. A slab containing five specimens of Microvaranops indicates that it gathered or lived in groups.

Dendromaia is an extinct genus of varanopid from the Carboniferous of Nova Scotia. It contains a single species, Dendromaia unamakiensis. Dendromaia is the oldest known varanopid, likely the oldest known synapsid, and the only member of the family Varanopidae to be discovered in Nova Scotia. Known from a large partial skeleton preserved with its tail wrapped around a much smaller partial skeleton, Dendromaia may also represent the oldest known occurrence of parental care in the fossil record. While the larger skeleton possessed certain mycterosaurine-like features, the smaller skeleton resembled basal varanopids such as Archaeovenator and Pyozia, creating uncertainty over whether characteristics at the base of Varanopidae have legitimate phylogenetic significance or instead reflect the immaturity of basal varanopid specimens.

<i>Cabarzia</i> Extinct genus of lizard-like animals

Cabarzia is an extinct genus of varanopid from the Early Permian of Germany. It contains only a single species, Cabarzia trostheidei, which is based on a well-preserved skeleton found in red beds of the Goldlauter Formation. Cabarzia shared many similarities with Mesenosaurus romeri, although it did retain some differences, such as more curved claws, a wide ulnare, and muscle scars on its sacral ribs. With long, slender hindlimbs, a narrow body, an elongated tail, and short, thick forelimbs, Cabarzia was likely capable of running bipedally to escape from predators, a behavior shared by some modern lizards. It is the oldest animal known to have adaptations for bipedal locomotion, predating Eudibamus, a bipedal bolosaurid parareptile from the slightly younger Tambach Formation.

Anningia is an extinct genus in Varanopidae, a family of monitor lizard-like amniotes. It contains a single species, Anningia megalops.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Frederik Spindler; Ralf Werneburg; Joerg W. Schneider; Ludwig Luthardt; Volker Annacker; Ronny Rößler (2018). "First arboreal 'pelycosaurs' (Synapsida: Varanopidae) from the early Permian Chemnitz Fossil Lagerstätte, SE Germany, with a review of varanopid phylogeny". PalZ. 92 (2): 315–364. doi:10.1007/s12542-018-0405-9. S2CID   133846070.
  2. ↑ Ascendonanus nestleri • First Arboreal 'Pelycosaurs' (Synapsida: Varanopidae) from the early Permian Chemnitz Fossil Lagerstätte, SE Germany http://novataxa.blogspot.com/2018/03/ascendonanus.html
  3. ↑ Lucas, Spencer G.; Rinehart, Larry F.; Celeskey, Matthew; Berman, David S. (2022). "A SCANSORIAL VARANOPID EUPELYCOSAUR FROM THE PENNSYLVANIAN OF NEW MEXICO". Annals of Carnegie Museum. 87 (3): 167–205. doi:10.2992/007.087.0301. S2CID   250015681.
  4. 1 2 3 Ludwig Luthardt; Mandy Hofmann; Ulf Linnemann; Axel Gerdes; Linda Marko; Ronny Rößler (2018). "A new U-Pb zircon age and a volcanogenic model for the early Permian Chemnitz Fossil Forest". International Journal of Earth Sciences. 107 (7): 2465–2489. Bibcode:2018IJEaS.107.2465L. doi:10.1007/s00531-018-1608-8. S2CID   133884490.
  5. ↑ Photo of Ascendonanus specimen TA1045 in Chemnitz Museum of Natural History. https://sachsen.museum-digital.de/index.php?t=objekt&oges=8453
  6. 1 2 3 4 5 Ronny Rößler; Thorid Zierold; Zhuo Feng; Ralph Kretzschmar; Mathias Merbitz; Volker Annacker; Jörg W. Schneider (2012). "A Snapshot of an Early Permian Ecosystem Preserved by Explosive Volcanism: New Results from the Petrified Forest of Chemnitz, Germany". PALAIOS. 27 (11): 315–364. doi:10.2110/palo.2011.p11-112r. S2CID   140661360.
  7. ↑ Jörg Fröbisch; Robert R. Reisz (2009). "The Late Permian herbivore Suminia and the early evolution of arboreality in terrestrial vertebrate ecosystems". Proceedings of the Royal Society B. 276 (1673): 3611–3618. doi:10.1098/rspb.2009.0911. PMC   2817304 . PMID   19640883.
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