Fieldwork snapshots: prospecting dredging spoils along Charleston Harbor

Amidst the panic of end-of-semester grading, exam writing and proctoring, and preparations for heading to California and Montana for the holidays, Sarah and I managed to have a day free to head out to a dredge spoil site out on Charleston harbor with our friend Ashby Gale. Ashby runs a fossil collecting tour guide business (Charleston Fossil Adventures), and has recently bought a boat that can help get out to some places a bit too far - or too rough/risky - for kayaking. Ashby and his clients have put together a pretty spectacular collection of dolphin periotics from our waterways, and these trips are a great way to add a few more - and a good opportunity to find the occasional trophy tooth. This particular day in December was one of the coldest - there was frost on our grass when I woke up and it was 43F (about 6C for our foreign readers) at the boat landing at 8am, meaning I was fairly apprehensive about getting wet or falling in the drink; the high would only be in the mid 50s (~12-13C) so drying off would be unlikely.

Captain Ashby bringing us in! This is actually Ashby's second boat, a somewhat larger Carolina skiff than the one he had before, and he had not yet installed his depth finder, so we were using the old fashioned 'stick a paddle in the water to estimate how deep it is' method. And we, as in me. Recall the frigid temperatures. Ashby was nervous about getting the propeller blades in the sand (which he had done with his first boat on the very first outing he invited me along on) or running the hull aground, as the larger, heavier boat would be more unlikely to be freed if stuck in the mud. We coasted in, and when the paddle indicated about 2' depth, Ashby told me to stop, and we coasted in for a few more seconds before he instructed me to hop off the front. I couldn't see the bottom - our water here is notoriously murky, with 18" visibility (meaning that if you see the bottom, it's shallow enough for your boots to keep you dry). Being another eagle scout I had my full faith in Ashby and jumped - into water two inches deeper than my boots! Frigid saltwater filled both up. Some choice words I won't repeat then filled the vicinity. Since I was already soaked and cold, I dropped off my bag and carried Sarah to shore so she would at least stay dry. On shore, I took off both boots and dumped out a half gallon of water each. My feet never quite went numb and my socks never quite dried out, but the fluid that was in there eventually, after about two hours, finally warmed up.

Within five minutes of getting ashore, I found this nice medium-sized tympanic bulla from a dolphin - probably an Oligocene waipatiid dolphin - with some brown siltstone matrix embedded within the tympanic cavity. If matrix inside this cavity becomes phosphatized, this is basically the only way you'll find a dolphin bulla with the outer lip attached.

Ashby quickly found this very nice dolphin periotic after paddling himself in - these periotics have a mixture of features found in eurhinodelphinid and waipatiid dolphins and are challenging to place. There's at least one soon-to-be published dolphin from the lower Miocene of Europe with similar periotics that may represent a new family. Regardless, the immediate discovery of a bulla and complete periotic helped me relax somewhat and realize that at least my freezing feet were not in vain and we would end up with at least a couple of nice earbones.

Sarah found this unusually complete and unscavenged longnose gar (Lepistoseus osseus) - who knows how it ended up here! The harbor is completely saltwater - apparently they can tolerate some salinity, but I generally don't hear about them much in the harbor; I imagine this individual died inland in a swamp or at least brackish water drainage and drifted out with the tide.

Our dredge spoils here in the lowcountry are generated from harbor excavations meant to deepen and/or maintain required depths for shipping lanes. This does two things: 1) dumps fossil-bearing sand and gravel above water onto dredge spoils and 2) occasionally incises into fossiliferous bedrock. Fossils from modern sediments were eroded out and reworked sometime, likely in the Holocene (but are all pre-Holocene). Owing to the abundant fossils in our subsurface, there's just a ton of shark teeth wherever dredging occurs. Here are a couple of sand tiger teeth (Odontaspididae).

About an hour in I found my first periotic of the day, this little beauty - which at first I thought rather looked like Papahu, a dolphin my Otago doctoral colleague Gabriel Aguirre-Fernandez described in 2014, but after brushing it off and looking it over, it rather looks like the more gracile periotic Ashby found earlier in the morning.

Here's the other side:

There really is a variety of neat stuff out there, including teeth of the considerably more rare megatoothed shark, Parotodus. Most of the teeth of Parotodus are P. benedeni, though elsewhere in Charleston an older unnamed species bearing lateral cusplets and resembling the Paleocene-Eocene species Otodus obliquus can be found. This is a small P. benedeni. Many folks go diving for meg teeth, but these ones are a bit more prized because they are considerably more rare.

A horseshoe crab cephalothorax plate, with a nice little erosional scour around it.

We find tons and tons of phosphatized steinkerns throughout the lowcountry, some of which are identifiable. In this case, we've got a cone snail steinkern. Cone snails, or cone shells (Conidae), are more common and diverse at tropical latitudes - and are famous for being absurdly venomous.

Here's a partial Carcharocles tooth one of us found - we've generally not had much luck with enormous teeth out here. This one's about 3 inches long (~7 cm).

A very nice little periotic I found in our third or fourth hour out there - one of about a dozen or so lowcountry specimens I believe are close to Eoplatanista italica from the lower Miocene of Italy.

A nice little Carcharocles megalodon tooth found by Sarah.

Nearly at the end of the day I found this ~3.5" (8 cm) busted up Carcharocles tooth that had escaped detection - possibly the last rain had just exposed it, though there were no shortage of bootprints in the vicinity.

I realize you've probably already seen this image a few times on other posts, but we really did have a pretty good day out there when it comes to earbones. The big partial one in the middle was found by Ashby in the last 30 minutes, and is a partial periotic of Ankylorhiza - and a great match for "Genus Y" proper, an unnamed species represented by the big skeleton over at Charleston Museum.

Bobby's guide to whale & dolphin earbones 2: identifying toothed whale periotics

Read Part 1 here for an introduction to whale and dolphin earbones (recommended before diving right in).

This is perhaps the part that most readers are looking for – how to identify different dolphin periotic bones. For each family of cetaceans, I’ll briefly list the approximate size reported as complete periotic length (not specific measurements, this is from memory), some of the main attributes, along with any unique features of the family or higher level features within Odontoceti, similar periotic morphs they can be confused with, age, known distribution, and established localities (e.g. localities, including rock unit, where these are confirmed to have been found or are reliably known from).

This guide is not exhaustive, nor is it perfect: identifying isolated periotics has long been called a 'black art' even by seasoned whaleontologists. The attributes listed below should not be interpreted by professionals as synapomorphies - they are generalizations, which can help someone identify many isolated periotics to the family level. Some families are very obvious, but others range quite a bit in anatomy, overlapping with other families - this is particularly a problem within the Delphinoidea. Regardless, I have almost certainly glossed over some important details and missed some things - so if you want to help me improve this, let me know what I've screwed up! Also, I will likely expand this in the future. The specimens in this post are mostly in collections of the Mace Brown Museum of Natural History; genus-level identifications (upper right) for some of these should be taken with a grain of salt. All photographs are by me, unless otherwise stated.

Though many features and conditions vary considerably and have evolved and lost again and again, some major groups are united by some periotic features. Archaic dolphins generally have long anterior and posterior processes and some remnant of the suprameatal fossa, which is large and deep in basilosaurid whales. Many archaic dolphins, as well as platanistoids, have a small spur lateral to the posterior process called the articular process - in Platanista (Ganges river dolphin) it is long and hooked, and generally needs to be broken in order for the periotic to be removed from the skull. The anterior bullar facet is primitively shallow in the earliest dolphins, but deeply concave in many long-snouted early to middle Miocene dolphins (Eurhinodelphinidae, Eoplatanistidae), and the facet is lost entirely in Delphinoidea. Delphinoids also tend to have a proportionally huge pars cochlearis.

As with all other fossils, periotic bones have some degree of natural variation. Above are some photos of periotics of Parapontoporia sternbergi, reasonably interpreted by L.G. Barnes (1985) as a single species from the San Diego Formation of southern California (Pliocene). You'll notice that much of the variation is in the length and inflation of the anterior process and the particular shape of the posterior bullar facet. The cochlear morphology - especially ventrally - seems to vary the least, which according to my Ph.D. adviser Ewan Fordyce, is likely because it ossifies the earliest and is associated with the middle ear sinus. The dorsal side varies considerably as this continues to ossify during growth, so the shape and size of the body and the configuration of foramina and crests within the meatus, and the shape and size of the meatus itself, also can change during growth. What this means is that no two periotics of the same species will ever be identical, and I guarantee you will go mad picking out differences between specimens only to find out they represent different edges of the anatomical envelope of variation or juveniles v. adults. As a result, it's better to look for shared similarities and when possible, match a particular periotic morph to periotics found associated with a skull, though this is certainly more typically the realm of activities of a whaleontologist rather than an amateur collector as many such specimens needed for such comparisons are in museum collections. Image from Barnes (1985).

 

And, just for reference, here is the complete labeled figure of the periotic of a bottlenose dolphin (Tursiops truncatus) from Mead and Fordyce (2009).

Ashley Formation, Oligocene, Summerville, South Carolina, USA, CCNHM collections.

Xenorophidae

Size: Small (~2.5-4 cm)

Attributes: Anterior process short and typically ‘hatchet’ shaped or rectangular in medial view, with bladelike tip in ventral view; pars cochlearis large, boxy; low superior process present, along with a suprameatal fossa (a deep, small, circular pit in some), short posterior bullar facet, long, triangular lateral tuberosity. Anterior process bears shallow anterior bullar facet and often is hatchet shaped or rectangular in medial view. A small to medium articular process may be present anterolateral to the posterior process.

Confused with: Difficult to confuse these with other odontocetes, perhaps agorophiid periotics.

Typically found genera: Albertocetus, Echovenator, Xenorophus

Age: Oligocene

Distribution: South Carolina (mostly), some specimens from North Carolina

Established Localities: Ashley and Chandler Bridge formations, Charleston, South Carolina.

Abundance: Uncommon in Charleston, South Carolina.

Pysht Formation, Oligocene, Olympic Peninsula, Washington, USA, CCNHM collections.

Simocetidae

Size: Small (~2.5-4 cm)

Attributes: Long subrectangular anterior process with bladelike anterior tip (in medial view), broad shallow suprameatal fossa with low, rounded superior process lateral to it, triangular and bladelike lateral tuberosity, dorsoventrally shallow pars cochlearis frequently with anteromedial bony spurs giving it a subrectangular shape, transversely narrow and dorsomedially facing internal acoustic meatus, low articular process, ventrally deflected posterior process with flat to sinuous smooth to grooved and leaf-shaped posterior bullar facet.

Confused with: Perhaps Xenorophidae and Waipatiidae.

Typically found genera: none are ‘typically’ found, but some named simocetid-grade dolphins from the Pacific Northwest include Simocetus and Olympicetus.

Age: Oligocene

Distribution: North Pacific.

Established Localities: Alsea Formation, Oregon; Pysht Formation, Washington.

Abundance: Rare, but Olympicetus is locally common in the Pysht Formation.

Chandler Bridge Formation, Oligocene, Summerville, South Carolina, USA, CCNHM collections.

Agorophiidae

Size: Medium to large (3-5cm).

Attributes: Elongate periotics with long anterior and posterior processes, anterior process lozenge-shaped with blunt apex, and shallow anterior bullar facet; trough-like suprameatal fossa, small, hemispherical pars cochlearis, long and tapering posterior bullar facet with deep grooves at very end but otherwise flat. Periotics of Ankylorhiza are large with dorsally expanded and slightly flattened anterior process that is triangular and somewhat ventrally deflected in medial view; posterior bullar facet is proportionally smaller.

Confused with: Waipatiidae, Squalodontidae. Squalodontids possess a large tubercle on the medial side of the anterior process and a posterior bullar facet that is ‘folded over’ into two facets, rather than the flat facet in Agorophiidae. Periotics of the giant dolphin Ankylorhiza in particular can be confused with Squalodon.

Typically found genera: Agorophius, Ankylorhiza

Age: Oligocene.

Distribution: North Atlantic and Paratethys (eastern Europe).

Established Localities: Ashley and Chandler Bridge Formations of South Carolina.

Abundance: Locally common in Charleston, South Carolina.

Chandler Bridge Formation, Oligocene, Summerville, South Carolina, USA, CCNHM collections.

Waipatiidae

Size: medium (~3-4 cm)

Attributes: Periotics with long, cylindrical anterior processes (with shallow to moderately deep anterior bullar facet) that are generally not bent medially or ventrally with triangular shape in medial view, small hemispherical pars cochlearis, bump-like lateral tuberosity, a suprameatal fossa developed as a sulcus or furrow, and medium to long posterior processes that can be ventrally deflected. A small articular process may be present anterolateral to the posterior process. Often has U or C-shaped parabullary sulcus on lateral side of anterior process.

Confused with: Squalodontidae, Agorophiidae. Very similar to the latter, differs from former in smaller size and by (typically) lacking a tubercle on medial side of anterior process.

Typically found genera: Waipatia, Ediscetus, Otekaikea; many unnamed taxa from Charleston, SC

Age: Oligocene, earliest Miocene.

Distribution: New Zealand, North Atlantic, Mediterranean, Paratethys?

Established Localities: Oligocene Kokoamu Greensand and Otekaike Limestone of New Zealand, with some likely (but unpublished) waipatiids from the Ashley and Chandler Bridge formations of South Carolina.

Abundance: Common in Charleston, South Carolina, and Oligocene of New Zealand.

Pungo River Limestone, Miocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Squalodontidae

Size: Medium to large (3.5-5 cm).

Attributes: Long, robust anterior process with shallow anterior bullar facet and process with a triangular apex in medial view; massive body lacking suprameatal fossa or superior ridge, and lateral surface transversely expanded, often with oblique striations, proportionally small and hemispherical pars cochlearis, internal acoustic meatus usually transversely narrow, large tubercle present on medial side of anterior process, and posterior bullar facet folded over into two surfaces at approximately a 90 degree angle; hinge of posterior bullar facet transitions into posteriorly elongate apex of posterior process. A small articular process may be present anterolateral to the posterior process.

Confused with: Waipatiidae, Agorophiidae.

Typically found genera: Eosqualodon, Squalodon

Age: latest Oligocene?, mostly early to middle Miocene.

Distribution: Worldwide.

Established Localities: Calvert Formation, Maryland/Virginia; Pungo River Limestone, North Carolina; Belluno Sandstone, Italy.

Abundance: Uncommon. 

?Yorktown Formation or Pungo River Limestone, Mio-Pliocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Physeteridae

Size: Medium to Large (3-5+ cm)

Attributes: Proportionally small, ventrally curving anterior process; proportionally enormous pars cochlearis; internal acoustic meatus is frequently narrow, keyhole-shaped and transversely oriented rather than oblique or anteroposteriorly; massive, hemispherical lateral tuberosity; meatus lacks transverse crest; body of periotic dorsoventrally deep and frequently bears triangular peak (dorsal and posterior margins forming a corner); large accessory ossicle frequently fused to anterior process.

 Confused with: Kogiidae, perhaps Ziphiidae.

Typically found genera: Aulophyseter, Orycterocetus.

Age: early Miocene to Pliocene (recent).

Distribution: Worldwide.

Established Localities: Calvert Formation, Maryland/Virginia; Sharktooth Hill, California.

Abundance: Rare.

Both from Yorktown Formation, Pliocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Kogiidae

Size: Small to Large (2-4.5 cm)

Attributes: Anteromedially directed anterior process with rectangular outline in ventral and medial view, anterior process often bilobate with sulcus dividing it into dorsal and ventral partitions; accessory ossicle often fused in place; transversely oriented internal acoustic meatus like Physeteridae, crista transversa occasionally elevated; pars cochlearis small and somewhat anteroposteriorly compressed with fenestra rotundum; small lateral tuberosity; large to enormous posterior bullar facet with flat posterior bullar facet that is posteriorly flattened and bladelike in posterior view; body of periotic swollen and smooth posteriorly.

Confused with: Physeteridae.

Typically found genera: None; most kogiid periotics found isolated have not been identified to the genus level.

Age: late Miocene to Pliocene (recent).

Distribution: Worldwide.

Established Localities: Yorktown Formation, Lee Creek Mine, North Carolina, USA; Bone Valley Formation, Florida.

Abundance: uncommon.

?Yorktown Formation, ?Pliocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

 

?Pungo River Limestone, ?Miocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Ziphiidae

Size: Medium to Large (2.5-5+ cm)

Attributes: Short transversely inflated anterior process with blunt apex, separated from pars cochlearis by deep, dorsally facing anterior incisure; shallow to deep anterior bullar facet; large pars cochlearis and body together form proportionally enormous smoothly convex subspherical to ovoid shape; oval internal acoustic meatus with deeply recessed transverse crest; pars cochlearis markedly deeper than anterior process in medial view; small posterior process with equidimensional and smooth posterior bullar facet, typically curving or deflected ventrally.

Confused with: perhaps Physeteridae.

Typically found genera:  Mesoplodon.

Age: middle Miocene to Pliocene (recent).

Distribution: Worldwide.

Established Localities: Yorktown Formation, Lee Creek Mine.

Abundance: Rare.

Unknown stratum, ?Miocene, Charleston lowcountry, South Carolina, USA, CCNHM collections.

Eoplatanistidae

Size: Small, 2-3 cm.

Attributes: Small overall size with proportionally large and hemispherical pars cochlearis, absurdly small anterior process, and ‘peaked’ body with acute angle formed between body and posterior process in medial view, ventrally deflected and proportionally small posterior bullar facet. Only a single genus is assigned to Eoplatanistidae, Eoplatanista, and its periotics are quite distinctive. Body lacks suprameatal fossa and superior ridge.

Confused with: Eurhinodelphinidae. Eurhinodelphinid periotics differ mostly by having a wider angle formed by the dorsal and posterior margins in medial view and by having a much larger and longer anterior process.

Typically found genera: Eoplatanista

Age: Early Miocene.

Distribution: Mediterranean, Western North Atlantic?

Established Localities: Belluno Sandstones of Italy.

Abundance: Locally uncommon in Charleston, South Carolina (only).

Pungo River Limestone, Miocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Eurhinodelphinidae

Size: Small to medium (2.5-4 cm)

Attributes: Long, narrow, cylindrical anterior process (straight in ventral view) bearing distinctly concave, elongate and oval to rectangular anterior bullar facet, proportionally small and hemispherical pars cochlearis, and relatively small, short, leaf-shaped posterior bullar facet that is directed ventrally; body lacks suprameatal fossa and superior ridge. Hemispherical lateral tuberosity. A distinctive U or V-shaped sulcus (parabullary sulcus) is present on the ventrolateral surface of the anterior process.

Confused with: Eoplatanistidae.

Typically found genera: Eurhinodelphis, Schizodelphis, Xiphiacetus

Age: Early to middle Miocene, possibly late Oligocene.

Distribution: Worldwide.

Established Localities: Calvert and Choptank formations, Maryland and Virginia; Pungo River Limestone, North Carolina; early to middle Miocene strata of Belgium; Chilcatay Formation, Peru; Belluno Sandstone, Italy.

Abundance: Common on Atlantic coast; rare in North Pacific.

Pungo River Limestone, Miocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Squalodelphinidae

Size: Medium (3-4 cm)

Attributes: Long cylindrical and straight to medially bent anterior process, often with a medial tubercle, proportionally small and rectangular pars cochlearis with large and dorsomedially facing aperture for the cochlear aqueduct, small body with triangular gap between posterior process and lateral tuberosity, small square to trapezoidal and roughly equidimensional (short) posterior bullar facet.

Confused with: Pomatodelphine platanistoids.

Typically found genera: Notocetus, Phocageneus, Medocinia

Age: Early to middle Miocene, possibly late Oligocene.

Distribution: Worldwide.

Established Localities: Calvert and Choptank formations, Maryland and Virginia; Pungo River Limestone, North Carolina; Chilcatay Formation, Peru; Gaiman Formation, Argentina; Belluno Sandstone, Italy.

Abundance: Common to uncommon in North Atlantic; rare on Pacific coast.

Round Mountain Silt, Miocene, Sharktooth Hill, California, USA. Image from Kimura and Barnes (2016).

Allodelphinidae

Size: medium (3-4 cm)

Attributes: Large, inflated anterior process; large hemispherical pars cochlearis; small, tear-drop shaped internal acoustic meatus with raised rim; dorsal side of periotic with remnant suprameatal fossa developed as long sulcus; lateral surface of periotic transversely expanded (like Squalodontidae) at level of posterior pars cochlearis; highly reduced posterior process with posteroventrally facing, convex, smooth, and small posterior bullar facet.

Note: these features characterize Zarhinocetus, the only allodelphinid likely to be discovered by collectors. Ninjadelphis has a long posterior process, Allodelphis is similar to this, but these taxa are unlikely to be encountered as they are known by singleton specimens.

Confused with: Squalodelphinidae, Platanistidae

Typically found genera: Zarhinocetus

Age: early to late Miocene

Distribution: North Pacific

Established Localities: Sharktooth Hill Bonebed, California; Monterey Formation, California; Santa Margarita Sandstone, California.

Abundance: rare.

Bone Valley Formation, Miocene, Florida, USA. Image from Case (1934).

Pomatodelphinae (subfamily of Platanistidae)

Size: Medium to Large (3-5 cm)

Attributes: Long, highly inflated cylindrical and straight to medially bent anterior process, large and deep anterior bullar facet, hemispherical to rectangular pars cochlearis with endocranial opening of facial canal shifted lateral rather than anterior to vestibulocochlear opening (resulting in an internal acoustic meatus that has a nearly transverse rather than anteroposterior long axis), large articular rim, small, triangular to trapezoidal posterior bullar facet.

Confused with: Squalodelphinidae. Differs based on more grossly inflated anterior process and more acutely triangular gap between posterior process.

Typically found genera: Pomatodelphis, Zarhachis

Age: middle to late Miocene.

Distribution: North Atlantic.

Established Localities: Calvert Formation, Maryland and Virginia; Bone Valley Formation, Florida.

Abundance: Common. 

Yorktown Formation, Pliocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Pontoporiidae

Size: Very Small (1.5-2 cm).

Attributes: Compact, small periotics with tiny anterior process and small, oval to square posterior bullar facet and proportionally enormous hemispherical pars cochlearis.

Confused with: Some Delphinidae, perhaps Phocoenidae.

Typically found genera: Pontoporia, Auroracetus

Age: Middle Miocene to Pliocene.

Distribution: North and South Atlantic.

Established Localities: Yorktown Formation, North Carolina; St. Marys Formation, Maryland/Virginia; Bone Valley Formation, Florida; Pliocene deposits, Belgium/Netherlands.

Abundance: Rare.

San Diego Formation, Pliocene, San Diego, California, USA, UCMP collections.

Lipotidae

Size: Medium (2.5-3.5 cm).

Attributes: Massive anterior process, triangular in ventral view, and bearing tubercle medially; proportionally large hemispherical pars cochlearis, small posteror process with tiny, deeply concave posterior bullar facet; body dorsoventrally deep, together with pars cochlearis forming trapezoidal shape; deep, large aperture for the vestibular aqueduct. Sword-like “styloid” process projecting from tip of anterior process (almost always broken in loose periotics). Ventral surface of anterior process deeply concave in lateral view; anterior bullar facet present.

Confused with: None, owing to location, but similar to some Kentriodontidae; differs from kentriodontids, and Delphinoidea, in possessing anterior bullar facet.

Typically found genera: Parapontoporia

Age: Late Miocene to Pliocene

Distribution: North Pacific

Established Localities: Purisima, San Diego, San Mateo, and Capistrano formations of California, and Almejas Formation of Baja California, Mexico.

Abundance: Common in California deposits. Most common odontocete in Purisima Formation at Santa Cruz.

Pungo River Limestone, Miocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Kentriodontidae

Size: Small to large (1.5-5+ cm)

Attributes: Inflated anterior process typically with blunt apex and lacking anterior bullar facet; proportionally small and hemispherical pars cochlearis; lateral surface smooth and convex, lacking suprameatal fossa or groove; long posterior bullar facet concave, short to long. Generally differentiated from Delphinidae by longer anterior/posterior processes and proportionally smaller pars cochlearis; very difficult to differentiate from extinct genera Phocoenidae. Diverse family and diverse periotics, identifying to genus level frequently easier than to family, given that Kentriodontidae is probably paraphyletic or even polyphyletic.

Confused with: Delphinidae, Phocoenidae

Typically found genera: Delphinodon, Kentriodon, Liolithax, Hadrodelphis, Nannolithax; many additional named taxa

Age: late early Miocene to early late Miocene

Distribution: Worldwide

Established Localities: Calvert through St. Mary’s formations, Calvert Cliffs and beyond, Maryland/Virginia; Pungo River Limestone, Lee Creek Mine, North Carolina; Temblor Formation, Sharktooth Hill, California; Santa Margarita Sandstone, Santa Cruz, California; Astoria Formation, Oregon/Washington.

Abundance: Uncommon to common.

 

All from Yorktown Formation, Pliocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Delphinidae

Size: Small to very large (2-5+ cm)

Attributes: Proportionally small and blunt anterior process lacking anterior bullar facet; proportionally large to enormous circular (and frequently dorsoventrally shallow) pars cochlearis, sometimes with posteromedial bulge; smoothly convex and featureless dorsal surface of body lacking suprameatal fossa or groove, but occasionally possessing longitudinal ridge adjacent to dorsolaterally facing facet; internal acoustic meatus typically teardrop-shaped with anterolateral fissure for hiatus fallopii, and crista transversa deeply recessed into meatus;  posterior process short with equidimensional, concave posterior bullar facets with deep (and lateral to posterolaterally directed) grooves/ridges for posterior process of bulla; posterior process with apex positioned laterally.

Confused with: Kentriodontidae, Monodontidae, Phocoenidae.

Typically found genera: Delphinus, Tursiops, Stenella, Globicephala, Pseudorca

Age: late Miocene through Pliocene (recent).

Distribution: Worldwide.

Established Localities: San Diego and San Mateo Formations, San Diego County, California; Yorktown Formation, Lee Creek Mine, North Carolina; Pliocene strata of Belgium & Netherlands; Plio-Pleistocene Red and Coralline Crag of UK; Pliocene of Australia/NZ.

Abundance: Rare to uncommon in North Pacific; common in North Atlantic.

Yorktown Formation, Pliocene, Lee Creek Mine, North Carolina, USA, CCNHM collections.

Monodontidae

Size: Medium to large (3-5 cm)

Attributes: Short, reduced, and blunt anterior process; proportionally enormous and anteriorly thrusted pars cochlearis; dorsoventrally thick body of periotic (elevated far dorsal to meatus) with transversely convex dorsolateral margin; in dorsal view, body of periotic widens posteriorly; large and transversely elongated internal acoustic meatus with high crista transversa; flat, ventrally facing small-medium sized leaf-shaped posterior bullar facet with anteroposteriorly (not posterolaterally) directed (and deep) ridges; entire periotic has triangular posterior margin as both the lateral and posterodorsal edges converge toward the posteriorly positioned apex of the posterior bullar facet.

Note: this is chiefly based on the beluga, Delphinapterus, and fossil monodontid periotics that seem similar to Delphinapterus; the narwhal, Monodon, possesses a much more delphinid-like periotic, and such examples are not yet known from the fossil record.

Confused with: Delphinidae, Albireonidae

Typically found genera: Delphinapterus, Bohaskaia, Denebola

Age: Late Miocene through Pliocene (recent)

Distribution: North Pacific and North Atlantic.

Established Localities: Almejas Formation, Baja California, Mexico; San Diego Formation, San Diego, California; Yorktown Formation, Lee Creek Mine, North Carolina.

Abundance: Rare in North Pacific; uncommon in North Atlantic.

Almejas Formation, Miocene, Isla Cedros, Baja California, Mexico. Image from Murakami and Koda (2013).

Albireonidae

Size: Medium (3-4 cm)

Attributes: Large, somewhat long and inflated/blunt anterior process, proportionally large, inflated, and hemispherical to subrectangular pars cochlearis (not anteriorly thrusted), large fenestra rotunda with a large nodule/expanse of bone posteromedial, often a posteromedial eminence on pars cochlearis; pars cochlearis (unlike Monodontidae) and body dorsoventrally deep (similar to Monodontidae); posterior process dorsoventrally quite deep (unlike Phocoenidae), deeper than Monodontidae; long, leaf-shaped posterior bullar facet.

Confused with: Phocoenidae, Monodontidae, Kentriodontidae

Typically found genera: Albireo

Age: late Miocene to Pliocene

Distribution: North Pacific

Established Localities: Almejas Formation, Baja California, Mexico.

Abundance: Very rare. Locally uncommon in Purisima Formation at Santa Cruz, but unpublished.

Unknown stratum, Pliocene/Pleistocene?, Folly Beach, South Carolina, USA, CCNHM collections.

Purisima Formation, Pliocene, Santa Cruz, California, USA, UCMP collections.

Phocoenidae

Size: Small to medium (2-3 cm).

Attributes: Extant genera: Dorsoventrally narrow anterior process; low pars cochlearis; small, anteroposteriorly elongate posterior process that in medial view tapers posteriorly into a triangular point, similar to Monodontidae. Extinct forms approach the morphology of kentriodontids and delphinids and can be difficult to differentiate; tend to have proportionally large and anteriorly thrusted pars cochlearis, small posterior bullar facet. Identification to particular published genera is typically easier for extinct forms than identification to family. All phocoenids lack an anterior bullar facet, and all periotics smaller than Albireonidae. Tend to have longer anterior process and proportionally smaller pars cochlearis than Delphinidae.

Note: Phocoenids typically occur in strata that are younger entirely than kentriodontids, and tend to be rare where delphinids are common, such as the Atlantic coast Pliocene. Phocoenids are anomalously diverse in North Pacific and eastern South Pacific marine mammal assemblages.

Confused with: Albireonidae

Typically found genera: mostly unnamed, Piscolithax, ?Haborophocoena, ?Numataphocoena

Age: late Miocene to Pliocene

Distribution: North and South Pacific, North Atlantic (rare)

Established Localities: Numerous late Miocene and Pliocene localities in California (Purisima, Capistrano, San Diego, San Mateo formations), Almejas Formation of Baja California, Mexico; late Miocene-Pliocene localities in Japan; Pisco Formation of Peru

Abundance: Common in late Neogene Pacific localities; rare in Atlantic.

 

Others - Miscellaneous unusual periotics

 I've added these mostly for folks to keep an eye out - these are unusual periotics from unusual dolphins that may or may not be found. Since they are unlikely to be found, I'll keep the commentary to a minimum.

 

Yaquinacetus meadi is a squaloziphiid dolphin from the earliest Miocene Nye Mudstone of Oregon. Squaloziphiids are a completely extinct family of longirostrine dolphins with homodont teeth known only from early Miocene rocks of the Pacific Northwest; Squaloziphius emlongi was reported from the coeval Clallam Formation of Washington. Late occurring squaloziphiids might be expected further south or potentially in the North Atlantic. In the Pacific Northwest all known specimens are from concretions. Image from Lambert et al. 2019.

Inticetus vertizi is a strange longirostrine "platanistoid" dolphin with archaeocete-like teeth from the late early Miocene Chilcatay Formation of Peru. Similar teeth in the tooth-taxon Phococetus are known from the late early Miocene of France as well as the Lee Creek Mine of North Carolina, and Phococetus is likely an inticetid. Though the teeth are extremely rare - four or five known altogether from the North Atlantic, including one in a private collection - periotics might be found. They roughly resemble squalodontid, waipatiid, and some aspects of eurhinodelphinid periotics. Image from Lambert et al. 2018.