Dendromaia

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Dendromaia
Temporal range: Late Moscovian, 309–306  Ma
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Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Family:† Varanopidae
Genus:† Dendromaia
Maddin, Mann, & Hebert, 2019
Type species
†Dendromaia unamakiensis
Maddin, Mann, & Hebert, 2019

Dendromaia is an extinct genus of varanopid from the Carboniferous of Nova Scotia. It contains a single species, Dendromaia unamakiensis. [1] Dendromaia is the oldest known varanopid, the only member of which 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. [1]

Contents

Discovery

Dendromaia unamakiensis is known from a slab and counterslab containing two skeletons. The specimen, NSM017GF020.001, was discovered in a petrified lycopod stump at Point Aconi on Cape Breton Island in Nova Scotia. This site is part of the Sydney Mines Formation, which is dated to the late Moscovian stage of the Carboniferous period, 309-306 million years ago. [2] "Dendromaia" roughly translates to "the mother in the tree", [3] according to its discovery in a stump and proposed parental care. The specific name references Unama'kik, the Mi'kmaq name for Cape Breton Island. The genus and species were described by Hillary Maddin, Arjan Mann, and Brian Hebert in 2019. [1] Hebert had discovered the specimen in 2017. [3] [4]

The two skeletons had different sizes and preserved different areas, with the larger skeleton (designated the holotype) incorporating a large portion of the rear half of the body and the smaller skeleton (designated the paratype) including a skull and only fragments of the postcranium, 1/4th the size of the larger one. These skeletons were inferred to represent two individuals of a single new taxon based on their similar overlapping anatomy, apparent varanopid ancestry, close association, and the fact that there are no other varanopids known from Nova Scotia. [1]

Description

The 6 preserved dorsal vertebrae of the larger skeleton were among the most characteristic bones in the animal. They shared several traits with Mycterosaurus , such as tall rectangular neural spines with slight depressions at their base. However, the rib facets at the tip of the transverse processes were not vertical, but instead oriented diagonally. Like other non-varanodontine varanopids, the lower edge of each centrum had a rounded keel. 10 incomplete caudal vertebrae preserved on the counterpart were elongated and had low neural spines. Holocephalous (single-headed) ribs and Heleosaurus -like gastralia were also present, though osteoderms were seemingly absent. The plate-like bones composing the pelvis were not fused to each other, and Dendromaia had a large pubic foramen like that of Heleosaurus. The femur was lightly-built and twisted, similar to mycterosaurines. The rest of the leg and foot was present but incomplete. [1] The larger specimen may have been 20 to 30 centimeters (7.9-12 inches) long from the tip of the snout to the base of the tail, and its full tail length is unknown but likely elongated. [4] [5]

The small skeleton's poorly-preserved skull was triangular and pointed like those of Archaeovenator , Pyozia , and Heleosaurus. It had thin, curved teeth on the maxilla (without a canine region) and smaller teeth on the palate, which also possessed a varanopid-like pterygoid and cultriform process. Isolated hyoid bones were also identifiable. Like the larger skeleton, the small skeleton's vertebrae had a rounded keel on their underside. It also possessed several limb bone fragments, including a twisted humerus. [1]

Classification

Dendromaia is the oldest member of a family of amniotes known as varanopids. Varanopids are traditionally considered early synapsids (part of the lineage of amniotes leading to mammals), although some studies alternatively propose that they are diapsid reptiles related to Orovenator . [6] [7] The describers of Dendromaia prefer a position for varanopids among synapsids, citing both biological characteristics (parental care) and arguing that traits which link varanopids to diapsids may be based on oversampling of juvenile specimens at the base of Varanopidae. [1] Recent studies from the early 2020s also support their traditional placement as synapsids on the basis of high degree of bone labyrinth ossification, maxillary canal morphology and phylogenetic analyses. [8] [9] [10]

To investigate the position of Dendromaia among other varanopids, the describers adapted a phylogenetic analysis matrix previously utilized by Brocklehurst & Fröbisch (2018). [11] The resulting strict consensus tree (average result of most parsimonious trees) of the parsimony analysis placed Dendromaia in a polytomy near the base of Varanopidae, along with Pyozia and a clade which forks into Varanodontinae and Mycterosaurinae. The Bayesian analysis recovers a similar result, albeit with the polytomy resolved, placing Dendromaia as the sister taxon to Pyozia. [1] The following cladogram is based on the results of the Bayesian analysis in Maddin, Mann, & Hebert (2019): [1]

Varanopidae

Paleobiology

The delicate preservation of the skeletons indicated that they likely died and were quickly buried at the same place and time. They were positioned with the smaller skeleton encircled by the tail of the larger skeleton. These taphonomic qualities led the paleontologists who described them to propose that the two skeletons were denning together under the roots of a lycopod tree, with the smaller skeleton likely representing the offspring of the larger skeleton. This may be the oldest fossil evidence of parental care, predating the previously oldest evidence, an aggregation of varanopids from the Permian of South Africa which may represent their own species ( Microvaranops parentis ) [12] or specimens of Heleosaurus scholtzi . [1] On the other hand, it remains a possibility that the two skeletons were not close relatives, and instead simply sheltered from a storm in the same stump. [3] The anatomy of the juvenile Dendromaia skeleton is remarkably similar to that of basal varanopids such as Archaeovenator and Pyozia , indicating that these genera may be based on juvenile specimens of larger varanopids. Likewise, certain characteristics (such as reduced dentition and limb development) found to link basal varanopids with diapsids may be a consequence of juvenile specimen sampling, rather than valid phylogenetic signals. [1]

Related Research Articles

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

Synapsida is one of the two major clades of vertebrate animals in the group Amniota, the other being the Sauropsida. The synapsids were the dominant land animals in the late Paleozoic and early Mesozoic, but the only group that survived into the Cenozoic are mammals. 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.

<span class="mw-page-title-main">Amniote</span> Clade of tetrapods including reptiles, birds and mammals

Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial and semiaquatic vertebrates. Amniotes evolved from amphibian ancestors during the Carboniferous period and further diverged into two groups, namely the sauropsids and synapsids. They are distinguished from the other living tetrapod clade — the non-amniote lissamphibians — by the development of three extraembryonic membranes, thicker and keratinized skin, and costal respiration. Additional unique features are the presence of adrenocortical and chromaffin tissues as a discrete pair of glands near their kidneys, which are more complex, the presence of an astragalus for better extremity range of motion, and the complete loss of metamorphosis, gill and skin breathing, and any lateral line system.

<span class="mw-page-title-main">Sauropsida</span> Taxonomic clade

Sauropsida is a clade of amniotes, broadly equivalent to the class Reptilia, though typically used in a broader sense to also include extinct stem-group relatives of modern reptiles and birds. The most popular definition states that Sauropsida is the sibling taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early synapsids have historically been referred to as "mammal-like reptiles", all synapsids are more closely related to mammals than to any modern reptile. Sauropsids, on the other hand, include all amniotes more closely related to modern reptiles than to mammals. This includes Aves (birds), which are recognized as a subgroup of archosaurian reptiles despite originally being named as a separate class in Linnaean taxonomy.

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

Dimetrodon is an extinct genus of non-mammalian synapsid belonging to the family Sphenacodontidae that lived during the Cisuralian age of the Early Permian period, around 295–272 million years ago. 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.

<i>Hylonomus</i> Extinct genus of reptiles

Hylonomus is an extinct genus of reptile that lived 318 million years ago during the Bashkirian stage of the Late Carboniferous. It is the earliest known crown group amniote and the oldest known unquestionable reptile, with the only known species being Hylonomus lyelli. Despite being amongst the oldest known reptiles, it is not the most primitive member of the group, being a eureptile more derived than either parareptiles or captorhinids.

<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. Although some studies from the late 2010s have recovered them being taxonomically closer to diapsid reptiles, recent studies from the early 2020s support their traditional placement as synapsids on the basis of high degree of bone labyrinth ossification, maxillary canal morphology and phylogenetic analyses. 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 amniotes 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.

<span class="mw-page-title-main">Parareptilia</span> Extinct subclass of reptiles (306–201Ma ago)

Parareptilia ("near-reptiles") is an extinct subclass or clade of basal sauropsids/reptiles, typically considered the sister taxon to Eureptilia. Parareptiles first arose near the end of the Carboniferous period and achieved their highest diversity during the Permian period. Several ecological innovations were first accomplished by parareptiles among reptiles. These include the first reptiles to return to marine ecosystems (mesosaurs), the first bipedal reptiles, the first reptiles with advanced hearing systems, and the first large herbivorous reptiles. The only parareptiles to survive into the Triassic period were the procolophonoids, a group of small generalists, omnivores, and herbivores. The largest family of procolophonoids, the procolophonids, rediversified in the Triassic, but subsequently declined and became extinct by the end of the period.

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

Archaeovenator is an extinct genus of Late Carboniferous varanopid synapsids known from Greenwood County, Kansas of the United States. It was first named by Robert R. Reisz and David W. Dilkes in 2003 and the type species is Archaeovenator hamiltonensis. Archaeovenator hamiltonensis is known from the holotype KUVP 12483, a three-dimensionally preserved, nearly complete and articulated skeleton, including the skull, with limbs and girdles slightly separated from postcranial skeleton. It was collected in the Hamilton Quarry, from the Calhouns Shale Formation of the Shawnee Group, dating to the Virgilian stage of the Late Pennsylvanian Series, about 300 million years ago. The generic name is derived from the Latin Archaeo and venator, meaning "ancient hunter". The specific name is named after its finding place Hamilton Quarry. Archaeovenator is one of the oldest known varanopid, though Dendromaia is known from older rocks.

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

Asaphestera is an extinct genus of a synapsid described on the basis of fossils from the Carboniferous of the Joggins locality in Nova Scotia, Canada. It was originally described as an undetermined lepospondyl and subsequently classified as a microsaur within the family Tuditanidae. A study published in May 2020 found that specimens referred to Asaphestera represented several unrelated species. Steen (1934)'s original species name Asaphestera platyris was retained for a skull which has been re-evaluated as the earliest known synapsid.

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

Echinerpeton is an extinct genus of synapsid, including the single species Echinerpeton intermedium from the Late Carboniferous of Nova Scotia, Canada. The name means 'spiny lizard' (Greek). Along with its contemporary Archaeothyris, Echinerpeton is the oldest known synapsid, having lived around 308 million years ago. It is known from six small, fragmentary fossils, which were found in an outcrop of the Morien Group near the town of Florence. The most complete specimen preserves articulated vertebrae with high neural spines, indicating that Echinerpeton was a sail-backed synapsid like the better known Dimetrodon, Sphenacodon, and Edaphosaurus. However, the relationship of Echinerpeton to these other forms is unclear, and its phylogenetic placement among basal synapsids remains uncertain.

<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.

<span class="mw-page-title-main">Evolution of reptiles</span> Origin and diversification of reptiles through geologic time

Reptiles arose about 320 million years ago during the Carboniferous period. Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic metabolisms. So defined, the group is paraphyletic, excluding endothermic animals like birds that are descended from early traditionally-defined reptiles. A definition in accordance with phylogenetic nomenclature, which rejects paraphyletic groups, includes birds while excluding mammals and their synapsid ancestors. So defined, Reptilia is identical to Sauropsida.

<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">Younginidae</span> Extinct family of reptiles

Younginidae is an extinct family of diapsid reptiles from the Late Permian and Early Triassic. In a phylogenetic context, younginids are near the base of the clade Neodiapsida. Younginidae includes the species Youngina capensis from the Late Permian of South Africa and Thadeosaurus colcanapi from the Late Permian and Early Triassic of Madagascar. Heleosuchus griesbachi from the Late Permian of South Africa may also be a member of the family.

Ascendonanus is an extinct genus of varanopid amniote from the Early Permian of Germany. 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.

<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.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 Maddin, Hillary C.; Mann, Arjan; Hebert, Brian (23 December 2019). "Varanopid from the Carboniferous of Nova Scotia reveals evidence of parental care in amniotes". Nature Ecology & Evolution. 4 (1): 50–56. doi:10.1038/s41559-019-1030-z. ISSN   2397-334X. PMID   31900446. S2CID   209672554.
  2. ↑ Allen, Jonathan P.; Fielding, Christopher R.; Gibling, Martin R.; Rygel, Michael C. (2013). "Recognizing products of palaeoclimate fluctuation in the fluvial stratigraphic record: An example from the Pennsylvanian to Lower Permian of Cape Breton Island, Nova Scotia". Sedimentology. 61 (5): 1332–1381. doi:10.1111/j.1365-3091.2013.12102.x. ISSN   1365-3091.
  3. 1 2 3 Wu, Katherine J. (23 December 2019). "Lizard-Like Fossil May Represent 306-Million-Year-Old Evidence of Animal Parenting". Smithsonian Magazine.
  4. 1 2 Davis, Nicola (2019-12-23). "300m-year-old fossil is early sign of creatures caring for their young". The Guardian. ISSN   0261-3077.
  5. ↑ Choi, Charles Q. (2019-12-23). "Oldest Fossil Evidence of Animal Parenting Found in Canada". Inside Science.
  6. ↑ Ford, David P.; Benson, Roger B. J. (2019). "A redescription of Orovenator mayorum (Sauropsida, Diapsida) using high-resolution μCT, and the consequences for early amniote phylogeny". Papers in Palaeontology. 5 (2): 197–239. doi: 10.1002/spp2.1236 . ISSN   2056-2802. S2CID   92485505.
  7. ↑ Ford, David P.; Benson, Roger B. J. (23 December 2019). "The phylogeny of early amniotes and the affinities of Parareptilia and Varanopidae". Nature Ecology & Evolution. 4 (1): 57–65. doi:10.1038/s41559-019-1047-3. ISSN   2397-334X. PMID   31900445. S2CID   209673326.
  8. ↑ Bazzana, K. D.; Evans, D. C.; Bevitt, J. J.; Reisz, R. R. (2021). "Neurosensory anatomy of Varanopidae and its implications for early synapsid evolution". Journal of Anatomy. 240 (5): 833–849. doi:10.1111/joa.13593. PMC   9005680 . PMID   34775594. S2CID   244116303.
  9. ↑ Benoit, J.; Ford, D. P.; Miyamae, J. A.; Ruf, I. (2021). "Can maxillary canal morphology inform varanopid phylogenetic affinities?". Acta Palaeontologica Polonica. 66 (2): 389–393. doi: 10.4202/app.00816.2020 . S2CID   237333701.
  10. ↑ Simões, T.; Kammerer, C. (August 2022). "Successive climate crises in the deep past drove the early evolution and radiation of reptiles". Science Advances. 08 (33): eabq1898. Bibcode:2022SciA....8.1898S. doi: 10.1126/sciadv.abq1898 . PMC   9390993 . PMID   35984885. S2CID   251694019.
  11. ↑ Brocklehurst, Neil; Fröbisch, Jörg (2018-09-03). "A reexamination of Milosaurus mccordi, and the evolution of large body size in Carboniferous synapsids". Journal of Vertebrate Paleontology. 38 (5): e1508026. doi:10.1080/02724634.2018.1508026. ISSN   0272-4634. S2CID   91487577.
  12. ↑ Spindler, Frederik; Werneburg, Ralf; Schneider, Joerg W.; Luthardt, Ludwig; Annacker, Volker; Rößler, Ronny (2018-06-01). "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. ISSN   1867-6812. S2CID   133846070.
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