Succinipatopsis is an extinct genus of animal from Eocene-aged Baltic amber. This animal is known from a single fossil that preserves a body with 10 pairs of stubby , with a hole between the third pair. Due to its poor preservation, the placement of Succinipatopsis is contested, as there are multiple interpretations of its anatomy. Some researchers consider it an (velvet worm) that lost its when fossilized. Others reject this affinity due to differences between its cuticle and its apparent lack of onychophoran-specific traits.
Discovery and naming
Succinipatopsis was first mentioned in a 1996 paper by George Poinar Jr.,
who formally described it four years later.
was found in
Eocene-aged
Baltic amber which dates to roughly 40 million years ago. Its location or even
country of origin is unknown.
Succinipatopsis is known from a single fossil that is deposited at the Poinar Amber Collection of Oregon State University in Corvallis, Oregon. The etymology of the animal's species or genus name was not provided in its description.
Description
The
Succinipatopsis holotype is encased in
amber and had at least 10
, with the rest being cut off. Visually, the animal was poorly preserved. Its body is covered with a fine deposit and surrounded by small cracks in the amber matrix. This made examining its external appearance difficult, and it is unclear whether
Succinipatopsis had annulations (rings of dermal papillae) along its trunk or
. While some cracks looked like spines jutting out from the body, these were probably artifacts of preservation as their placement is irregular.
The holotype had a purplish-black
In the original description, the fossil was interpreted as the anterior (front) part of the animal, for two reasons. First, the underside had a roughly triangular opening between the third pair of visible appendages. This was interpreted as a mouth, as modern velvet worms have a mouth between their second and third segments. Second, in living velvet worms, the anus is located at either the very end of the body or between the last pair of . Using the framework above, the first pair of appendages were interpreted as antennae. The second pair of appendages were shorter than the antennae but longer than the rest. Because of their position on the animal, these were interpreted as slime papillae. The remaining appendages were interpreted as legs known as lobopods. These lobopods were described as simple and lacked the distinct foot, claw, and spinous pads typical of modern velvet worms. Based on a length-to-width comparison with extant , Succinipatopsis is estimated to have 18–20 pairs of legs. The animal was also said to have large epidermal cells without protrusions.
Classification
Original classification
When first described by Poinar,
Succinipatopsis was classified using a now-outdated definition of
Onychophora that included various
Paleozoic .
This classification is now obsolete, as modern
phylogenies label this grouping "total-group Onychophora" which lacks many of the traditional members
or do not recover it at all.
In its original description, Succinipatopsis was placed in a variety of newly created Taxon. The first of these was a class named Udeonychophora that contained terrestrial onychophorans with a ventral (bottom-facing) mouth. The class was divided into two new orders, Euonychophora and Ontonychophora. Succinipatopsis was placed in Ontonychophora, a group defined by their simple lobopods (no annulations of dermal papillae), variability in having claws, and the lack of a specialized terminal foot. Ontonychophora also included Helenodora (put in the new family Helenodoridae) and the co-described Tertiapatus. Ontonychophora was further subdivided into the superfamily Tertiapatoidea, defined by a lack of claws and spinous cushions. This clade included Succinipatopsis and Tertiapatus, both placed in their own Monotypic taxon families (Succinipatopsidae and Tertiapatidae).
Later critiques
Grimaldi et al. (2002)
Soon after its original description,
Succinipatopsiss
anatomy and classification came into question. In a 2002 paper, Grimaldi et al. contended the animal's placement in a new family and order, and stated that the vast majority of
Baltic amber fossils came from modern families, and despite being older, a fossil it described (
Cretoperipatus) belonged to the modern family
Peripatidae. Because of this, they argued that
Succinipatopsis belonging to an extinct
clade was highly improbable, especially since it existed so recently.
The paper also claimed that Succinipatopsiss lack of feet or claws was probably an artifact of preservation. are known to retract their feet, and most specimens preserved in ethanol have their feet retracted with only the claws protruding. Based on these points, the paper synonymized Udeonychophora and Ontonychophora with Euonychophora, lumping Succinipatopsis, Tertiapatus, and Helenodora with the extant onychophorans.
Garwood et al. (2016)
Disputes about
Succinipatopsis 's classification reemerged more than a decade later in 2016. In a study by Garwood et al. describing
Antennipatus, the authors questioned if
Succinipatopsis was an onychophoran in the first place. To justify this, the paper cited how the animal had fine projections on its skin which differed from the onychophoran cuticle and lacked any traits specific to the group.
Grimaldi et al. (2016)
Later in the same year, Grimaldi et al. disagreed with Garwood and instead considered
Succinipatopsis an onychophoran. This paper focused on
Cretoperipatus and the insights gained from redescribing it. While studying new fossils, the authors noticed that claws often detached from the animal's foot and could disperse throughout the
amber, sometimes very far away. Because of how frequent this was, the authors reasoned that
Succinipatopsis may have had claws, but that these were either trimmed away or left unnoticed. Ultimately, the study concluded that this animal should be reclassified in the future.
Paleoenvironment
Succinipatopsis was found in Baltic amber, a
tree resin produced by vast
of closely related trees, maybe even a single species. Based on the amber's absorption spectra, it was likely produced by conifers in the family
Sciadopityaceae, the only extant member being the
Koyamaki (
Sciadopitys verticillata).
Additionally, due to being redeposited in younger
rock layers, the exact age of Baltic amber is controversial. The amber is generally agreed to be from the
Eocene and is conservatively estimated to be between 35 and 55 million years old. However, some authors argue for narrower ranges of between 40 and 47 or between 35 and 43 million years old.
lived along a wide variety of
including numerous
,
as well as rarer groups such as
and
.
While arthropods make up the majority of inclusions, the animal also lived with vertebrates such as the
lizard Succinilacerta succinea.
